WO2010048084A2

WO2010048084A2 - Electrode and power coupling scheme for uniform process in a large-area pecvd chamber

Info

Publication number: WO2010048084A2
Application number: PCT/US2009/061161
Authority: WO
Inventors: Jozef Kudela; Tsutomu Tanaka (Tom)
Original assignee: Applied Materials, Inc.
Priority date: 2008-10-24
Filing date: 2009-10-19
Publication date: 2010-04-29
Also published as: WO2010048084A3; TW201024455A

Abstract

Embodiments discussed herein generally include electrodes having parallel ferrite boundaries that suppress RF currents perpendicular to the ferrite boundary and absorb magnetic field components parallel to the boundary. The ferrites cause the standing wave to stretch outside the ferrites and shrink inside the ferrite. A plurality of power sources are coupled to the electrode. The phase of the VHF current delivered from the power sources may be modulated to move the standing wave that is perpendicular to the ferrites in a direction parallel to the ferrites. Thus, the VHF current on the uncovered electrode area will be a plane wave, quasi-uniform (in a direction perpendicular to the ferrites) propagating in the direction parallel to the ferrites.

Description

ELECTRODE AND POWER COUPLING SCHEME FOR UNIFORM PROCESS IN

A LARGE-AREA PECVD CHAMBER

BACKGROUND OF THE INVENTION Field of the Invention

[0001] Embodiments of the present invention generally relate to a plasma enhanced chemical vapor deposition (PECVD) apparatus.

Description of the Related Art

[0002] As demands for larger flat panel displays (FPDs) and solar panels for consumers (and consequently, demands for higher manufacturing cost-efficiency from the FPD and solar panel manufacturers), continues to increase, the size of PECVD chambers that are used for depositing thin films used for FPDs and solar panels increases. The chambers used in the deposition process are typically capacitively driven parallel-plate reactors using RF or VHF fields to ionize and dissociate processing gas between the plate electrodes. Due to finite reactor dimensions and boundary conditions on the electrodes, the excited fields inherently form standing waves. If the size of the electrodes becomes comparable with the excitation wavelengths, electromagnetic effects causing non-uniformities in plasma and deposited films becomes inevitable.

[0003] The standing waves and plasma non-uniformities have a strong influence on the thickness and properties of thin films deposited by PECVD reactors or on the process uniformity in plasma processing chambers in general. Non-uniform films may lead to the so-called "mura effects" on FPDs or to low-efficient cells in solar panels. In some cases, plasma non-uniformity may lead to non-functioning devices.

[0004] The standing wave effects and related plasma non-uniformities may be overcome to an extent by using shaped electrodes, lens electrodes, cavities behind resistive electrodes, lower frequencies, tuning the processing parameters such as chamber pressure, and combinations thereof. However, when the processing chamber size increases to reflect the demand for larger FPDs and solar panels, simply scaling up the aforementioned countermeasures to the standing wave effect and plasma non-uniformities may not be sufficient.

[0005] Therefore, there is a need for a plasma reactor designed to increase plasma uniformity and overcome standing wave effects.

SUMMARY OF THE INVENTION

[0006] Embodiments discussed herein generally include electrodes having parallel ferrite boundaries that suppress RF currents perpendicular to the ferrite boundary and absorb magnetic field components parallel to the boundary. The ferrites cause the standing wave to stretch outside the ferrites and shrink inside the ferrite. A plurality of power sources are coupled to the electrode. The phase of the RF or VHF current delivered from the power sources may be modulated to move the standing wave that is perpendicular to the ferrites in a direction parallel to the ferrites. Thus, the RF or VHF current on the uncovered electrode area will be a plane wave, quasi-uniform (in a direction perpendicular to the ferrites) propagating in the direction parallel to the ferrites.

[0007] In one embodiment, an apparatus may include a chamber body having a first wall with a slit valve opening therethrough, an electrode disposed in the chamber body, one or more ferrite pieces extending parallel to the slit valve opening, and a plurality of first VHF power sources coupled to the electrode at a plurality of locations.

[0008] In another embodiment, an apparatus may include an electrode, a first power source coupled to the electrode in a first plurality of locations along a first periphery of the electrode, and a second power source separate from the first power source and coupled to the electrode in a second plurality of locations along a second periphery of the electrode parallel to the first periphery. The apparatus may also include one or more first ferrite blocks extending along a third periphery of the electrode perpendicular to the first and second periphery and one or more second ferrite blocks extending along a fourth periphery of the electrode parallel to the third periphery. [0009] In another embodiment, a plasma enhanced chemical vapor deposition apparatus is disclosed. The apparatus may include a processing chamber body having a plurality of sidewalls, at least a first sidewall of the plurality of sidewalls having a slit valve opening therethrough. The apparatus may also include a susceptor disposed within the chamber body and a gas distribution showerhead disposed in the chamber body opposite the susceptor. The apparatus may also include a backing plate disposed in the chamber body adjacent the gas distribution showerhead. The backing plate may have a first side facing the gas distribution showerhead and a second side opposite the first side. The apparatus may also include one or more first ferrite blocks disposed along the second side of the backing plate along a first edge of the second side. The one or more first ferrite blocks may extend substantially parallel to the slit valve opening. The apparatus may also include a first power source coupled to the backing plate on the second side at a second edge perpendicular to the first edge and a second power source separate from the first power source coupled to the backing plate on the second side at a third edge parallel to the second edge.

[0010] In another embodiment, a method is disclosed. The method includes applying a first RF or VHF current to an electrode at one or more first locations. The electrode has a generally rectangular shape and one or more ferrite blocks extending along a substantial length of first and second parallel edges. The first RF or VHF current is applied at a first phase, and the first location is located at a third edge of the electrode perpendicular to the first and second edges. The method also includes applying a second RF or VHF current to the electrode at one or more second locations located at a fourth edge of the electrode parallel to the first edge. The second RF or VHF current is applied in a second phase different than the first phase. The phase of the second RF or VHF current relative to the first RF or VHF current can be varied over time.

[0011] In another embodiment, an apparatus is disclosed. The apparatus includes a chamber body having a slit valve opening through a first wall of the chamber body and a gas distribution showerhead disposed in the chamber body above the slit valve opening. The apparatus may also include a backing plate coupled to the chamber body and spaced form the gas distribution showerhead. The backing plate may have a substantially rectangular shape. A first side of the backing plate faces the gas distribution showerhead. The backing plate has a second side opposite the first side. The apparatus also may have a power source coupled to the backing plate at one or more locations and one or more first ferrite pieces extending along the second side of the backing plate.

[0012] In another embodiment, an apparatus may include a substantially rectangular shaped gas distribution showerhead, a backing plate coupled to the gas distribution showerhead, and one or more first ferrite blocks resting on the backing plate.

[0013] In another embodiment, a method may include applying an RF current to a backing plate of an apparatus. The apparatus may have a gas distribution showerhead coupled to the backing plate and one or more ferrite blocks resting on an edge of the backing plate. The RF current may be applied such that at least a portion of the RF current is suppressed in a direction perpendicular to the ferrite material. The method may also include introducing a processing gas through the gas distribution showerhead, igniting the processing gas into a plasma, and depositing material onto the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

[0014] So that the manner in which the above recited features of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to embodiments, some of which are illustrated in the appended drawings. It is to be noted, however, that the appended drawings illustrate only typical embodiments of this invention and are therefore not to be considered limiting of its scope, for the invention may admit to other equally effective embodiments.

[0015] Figure 1A is a schematic cross sectional view of a PECVD apparatus according to one embodiment. [0016] Figure 1 B is a schematic cross sectional view of the PECVD apparatus of Figure 1 A having ferrites 132 disposed therein.

[0017] Figure 1 C is a schematic isometric view of the backing plate of Figure 1 B.

[0018] Figure 1 D is a schematic top view of an electrode having a single, substantially centered, RF feed location.

[0019] Figure 1 E is a schematic bottom view of the electrode of Figure 1 D.

[0020] Figure 2A is a schematic cross sectional view of a PECVD apparatus 200 according to one embodiment.

[0021] Figure 2B is a schematic cross sectional view of a Figure 2A with ferrites present.

[0022] Figure 3A is a schematic isometric top view of an electrode having a single, substantially centered RF feed location according to one embodiment.

[0023] Figure 3B is a schematic top view of an apparatus 320 according to one embodiment.

[0024] Figure 3C is a schematic isometric view of an apparatus 350 according to one embodiment.

[0025] Figure 3D is a schematic isometric view of the standing wave effect in the absence of ferrite boundaries.

[0026] Figure 3E is a schematic isometric view of the standing wave effect in the presence of ferrite boundaries.

[0027] Figure 4 is a graph showing the effects of a ferrite boundary on the standing wave profile.

[0028] Figure 5A shows a normalized electrode voltage distribution for a center fed RF feed. [0029] Figure 5B shows a normalized electrode voltage distribution for an RF feed displaced 0.5 meters from center.

[0030] Figures 5C and 5D show the effect of placing magnetic material or ferrites on the edges of the electrode.

[0031] Figure 6 shows the effects of utilizing multiple ferrite boundaries on plasma distribution.

[0032] Figure 7 is a schematic cross sectional view showing various locations for ferrites in a parallel plate apparatus.

[0033] To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. It is contemplated that elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation.

DETAILED DESCRIPTION

[0034] Embodiments discussed herein generally include electrodes having parallel ferrite boundaries that suppress RF currents perpendicular to the ferrite boundary and absorb magnetic field components parallel to the boundary. The ferrites cause the standing wave to stretch outside the ferrites and shrink inside the ferrite. A plurality of power sources are coupled to the electrode. The phase of the RF or VHF current delivered from the power sources may be modulated to move the standing wave that is perpendicular to the ferrites in a direction parallel to the ferrites. Thus, the RF or VHF current on the uncovered electrode area will be a plane wave, quasi-uniform (in a direction perpendicular to the ferrites) propagating in the direction parallel to the ferrites.

[0035] By positioning and orienting the ferrite elements in relation to the RF driven electrode, the RF feed position on the RF driven electrode, and/or features in the processing chamber the uniformity of the generated plasma can be altered to provide an improved plasma processing result. The ferrite elements may also be used to alter the RF standing wave patterns and generated field lines in various directions within the plasma processing chamber. In general, RF currents that are formed in a direction perpendicular to the boundary of the ferrite element are suppressed due to the preferential flow of the generated magnetic field through the ferrite element rather than through free-space, and the RF currents in a direction parallel to the ferrite boundary will be enhanced. While the term "ferrite element" and "ferrite material" are used herein, these terms are not intended to be limiting as to scope of invention described herein. In general, the ferrite elements can be formed from any material that can be used to provide a path through which the generated fields (e.g., magnetic fields), created by the flow of RF current within portions of the plasma processing chamber, will preferentially flow. In one example, the ferrite elements are formed from a ferromagnetic material.

[0036] Embodiments disclosed herein will be discussed with reference to a PECVD apparatus available from Applied Materials, Inc., Santa Clara, CA. It is to be understood that the embodiments discussed herein may have utility in other chambers including those sold by other manufacturers. The embodiments disclosed herein propose a solution for achievement of uniform plasma in the apparatus and/or uniform process conditions in large area RF or VHF capacitive plasma reactors. The solution includes enhancing RF or VHF current uniformity in one direction (for example, the x-axis of a rectangular electrode), and power coupling scheme that moves the non-uniform standing wave field pattern in the other direction (for example, the y-axis of the rectangular electrode) during the deposition process.

[0037] Figure 1A is a schematic cross sectional view of a plasma processing chamber, or PECVD apparatus 100, according to one embodiment. The apparatus 100 comprises a plurality of walls 102 and a bottom 104. In one embodiment, the walls 102 and the bottom 104 may comprise a conductive material, such as aluminum. Through one or more walls 102, a slit valve opening 106 may be present. The slit valve opening 106 permits a substrate 110 to enter and exit the apparatus 100.

[0038] The substrate 110 may be placed on a susceptor 108 when in the apparatus 100. The susceptor 108 may be raised and lowered on a shaft 112. In one embodiment, the shaft 112 and the susceptor 108 may comprise a conductive material, such as aluminum. The apparatus 100 may be evacuated by a vacuum pump 114. A valve 116 may be coupled between the chamber and the vacuum pump 114 to adjust the vacuum level of the apparatus 100.

[0039] Processing gas may be introduced into the apparatus 100 from a gas source 118 through a tube 122 that passes through the chamber lid 124. The tube 122 is coupled to the backing plate 126 to permit the processing gas to pass through the backing plate 126 and enter a plenum 148 between the backing plate 126 and the gas distribution showerhead 128. In one embodiment, the tube 122, the backing plate 126, and the gas distribution showerhead 128 may comprise a conductive material. In another embodiment, the tube 122, backing plate 126, and gas distribution showerhead 128 may comprise aluminum. The processing gas spreads out in the plenum 148 and then passes through gas passages 130 formed through the gas distribution showerhead 128 to the processing area 146.

[0040] A power source 120 is also coupled to the tube 122. In one embodiment, the power source 120 comprises an RF power source capable of generating RF currents at a frequency of about 13.56 MHz. In another embodiment, the RF power source 120 comprises a VHF power source capable of generating VHF currents, such as about 40 MHz or about 60 MHz. Depending upon the size of the RF power source, the frequency applied may be between about 0.4 MHz and about a few hundred MHz. In general, the power may be applied such that 1/8^th of the free space wavelength in vacuum at the applied frequency is comparable to the chamber diagonal. The chamber diagonal is the distance across a rectangular chamber from one corner to another corner diagonally opposite.

[0041] The current from the power source 120 flows along the outside surface of the tube 122 to the backing plate 126. RF current has a 'skin effect' in that the current does not penetrate all the way through a conductive body such as the tube 122 and the backing plate 126. RF current travels along the outside surface of a conductive object. The RF current then travels down a suspension 134 to the front face of the gas distribution showerhead 128. In one embodiment, the suspension 134 may comprise a conductive material, such as aluminum. The RF current flows along a path shown by arrows "A". Thus, the RF current travels along the back surface of the backing plate 126, the side surface of the backing plate 126, the outside surface of the suspension 134, and the bottom surface of the gas distribution showerhead 128.

[0042] In the embodiment shown in Figure 1A, the gas tube 122 is fed into the substantial center of the backing plate 126. Hence, the RF current supplied to the gas tube 122 is also fed to the backing plate 126 at the substantial center thereof. It is to be understood that, the RF current coupling location, could be moved to suit the needs of the user. For example, the RF current coupling location may be moved to compensate for the RF current return or for chamber asymmetry.

[0043] The RF current travels along an RF path from the source driving it and returning to the source driving it. The RF current flows down the outside of the gas tube 122 to the upper surface of the backing plate 126. The RF current then travels along the upper surface of the backing plate 126 and down the side of the backing plate 126 to the suspension 134 that couples the backing plate 126 to the gas distribution showerhead 128. From the suspension 134, the RF current then travels to the gas distribution showerhead 128 and along the surface of the gas distribution showerhead 128 that faces the substrate 110. The RF current then couples through the plasma that is generated during processing to the susceptor 108. The RF current then travels along the susceptor 108. The RF current seeks to return to the source driving it and therefore will seek the shortest path. In some cases, the RF current will flow along the shadow frame 138 (if the shadow frame is conductive) when it touches the susceptor 108 and the straps 142 coupling the shadow frame 138 to the walls 102 of the chamber. In other cases, the RF current travels down along the susceptor 108 to straps 150 that couple the susceptor 108 to the chamber bottom 104. The straps 150 shorten the RF return path because the RF current does not need to travel along the bottom of the susceptor 108 and down the shaft 112 to then begin a return along the bottom 104 of the chamber. The RF current flows along the walls 102 of the chamber and then the lid 124 and back to the power source 120. The longer the RF return path, the greater the likelihood of arcing or parasitic plasma igniting within the chamber in undesired locations. Arcing and parasitic plasma may sap energy from the deposition plasma and thus lead to nonuniform deposition conditions.

[0044] In the embodiment shown in Figure 1 B, ferrite 132 boundaries on the top of the backing plate 126 are present. Figure 1C is a close-up isometric view of the right edge of the backing plate 126 and ferrite 132 shown in Figure 1 B. In one embodiment, as shown in Figure 1C, the ferrites 132 are generally bar shaped and aligned along a side of the backing plate 126 that is parallel to the y-direction. It is to be understood that the ferrites 132 are not limited to bar shaped structures. For example, the ferrites 132 may be round shaped rods that span the length of the backing plate 126. Additionally, the ferrites 132 may comprise multiple pieces spaced apart where the spacing is less than the width of the ferrite 132. As will be discussed below in regards to Figure 4, the ferrites 132 also need not be at the edge of the backing plate 126 or directly in contact with the backing plate 126. The ferrites 132 can be proximate to the backing plate 126. The ferrite's 132 relative permeability, orientation and geometry will shape the fields created by the delivery of RF current to the backing plate 126 and gas distribution showerhead 128. By orienting the ferrites 132, the generated standing waves in the processing area 146 of the PECVD apparatus 100 will be altered. Referring to Figures 1 B and 1C, generated plane waves propagated in the y-direction will generally be quasi-uniform in the x-direction due to the preferential flow of the induced magnetic fields within the ferrites material aligned along the y-direction, while the waves propagating in the y- direction will be relatively unaffected by the bar shaped ferrites 132. Thus, the variation in fields will decrease in the x-direction between the two ferrites 132.

[0045] In one embodiment, the non-uniformity in the waves propagating in the y- direction is resolved by altering the standing wave pattern by controlling the phase delivered to two or more RF feeds that are spaced apart in the y-direction or by moving the substrate in the y-direction. Further control and/or improvement of the uniformity may be achieved by using multiple feeds with uneven power distribution and/or using multiple ferrite 132 boundaries on the backing plate 126. The design and power coupling may enhance the plasma uniformity in a direction parallel to the long axis of the ferrites 132 (e.g., y-direction). Therefore, any plasma uniformity issues created by the asymmetric shape of the PECVD apparatus 100, such as near the slit valve opening 106 may be alleviated by placing ferrites 132 parallel to the slit valve opening 106. In one embodiment, the ferrites 132 may be oriented perpendicular to the slit valve opening 106.

[0046] The standing wave effects and related plasma non-uniformities may be overcome to an extent by using shaped electrodes, lens electrodes, cavities behind resistive electrodes, multiple RF feeds or generators, multiple ports with phase modulation, lower frequencies, tuning the processing parameters such as chamber pressure, and combinations thereof in addition to the positioning and alignment of one or more ferrites 132.

[0047] For the embodiment shown in Figure 1B, the ferrites 132 extend along an edge of the backing plate 126 parallel to the slit valve opening 106. In one embodiment, the ferrites 132 may extend along an edge of the backing plate 126 perpendicular to the slit valve opening 106. The edges of the backing plate 126 extending perpendicular to the slit valve opening 106 do not have ferrites 132 extending thereon. The ends of the ferrites 132 do cover a short distance of the edge perpendicular to the slit valve opening 106, but its effect should be minimal. However, in some configurations it may be desirable to shape or align the ferrites 132 in other orientations. For example, bar shaped ferrites 132 may extend along the edge of the backing plate 126 perpendicular to the slit valve opening 106 instead of the edges parallel to the slit valve opening 106. Additionally, if desired, the ferrites 132 may be present on other edges. However, if ferrites 132 are present on other edges, it may be necessary to have some gaps therebetween to permit the RF current to travel down to the gas distribution showerhead 128. In other embodiments, the ferrites 132 may be configured in a circular, arc, or other desired shape to further reduce non-uniformities in the plasma formed in the processing area 146. The ferrites 132 are used to permit the applied current to follow a predetermined path such that the plasma is substantially uniform in a predetermined direction. [0048] Figure 1C is a schematic isometric view of the backing plate 126 of Figure 1 B that shows the RF current suppressed from passing along the backing plate 126 where the ferrites 132 are situated such that little or no RF current passes along the side parallel to the ferrite 132. On the other hand, on the side 152 perpendicular to the bar shaped ferrite 132, the RF current may pass freely down the side 152. The ferrite 132 may, however, reduce or prevent the RF current from traveling down the side in the area 154 directly underneath the ferrite 132.

[0049] It is to be understood that while the ferrites 132 have been shown as a single piece spanning the entire length of the backing plate 126, the ferrites 132 may comprise multiple pieces. The multiple pieces may each span the entire length or the multiple pieces may be coupled together to collectively span the entire length. Additionally, if desired, a ferrite 132 may be formed from multiple ferrite pieces that are spaced a distance apart. The ferrites 132 may be either parallel or perpendicular to the slit valve opening 106. Additionally, the ferrites 132 may be proximate to the backing plate 126. In one embodiment, the ferrites 132 may be in contact with the backing plate 126. The ferrites 132 may be cooled.

[0050] In the apparatus 100, there are four walls 102. Of those four walls 102, three of the walls 102 are substantially identical and look substantially identical to the RF current (in absence of the ferrites) when it travels thereon returning to the power source 120 as shown by arrows "B". The fourth wall 102, however, is different than the other walls 102 and looks different to the RF current as it returns to the power source 120. The fourth wall 102 has the slit valve opening 106 formed therethrough. The RF current travels a circuitous path along the wall 102 having the slit valve opening 106. The RF current actually travels around the slit valve opening 106. Thus, the RF current traveling along the wall 102 having the slit valve opening 106 has a longer inductive path to return to the power source 120 as compared to the three other walls 102.

[0051] The longer the path the RF current has to travel to return to the RF power source 120 the larger the ohmic losses. Hence, the potential difference between the RF current flowing within the three substantially identical walls 102 back to the power source 120 is different than the RF current flowing within the wall 102 having the slit valve opening 106. The slit valve opening 106 may also cause a plasma to be formed therein, thus causing the generated plasma to be unevenly distributed in processing area 146. With an uneven plasma distribution, a non-uniform deposition of material onto the substrate 110 may occur.

[0052] The ferrites 132 may be used to counteract the effect of the slit valve opening 106. In the embodiment shown in Figure 1 B, the ferrite 132 extends parallel to the slit valve opening 106. The ferrites 132 suppress the RF current flowing along the edge of the backing plate 126 having ferrites 132 thereon and hence, the side of the gas distribution showerhead 128. The RF current, when returning to the source 120, seeks to take the shortest path possible. Hence, when returning to the source 120, the RF current will flow along the walls 102 perpendicular to the slit valve opening 106 (and hence, the ferrites 132) because the walls 102 perpendicular to the slit valve opening 106 (z-direction in Figure 1A-1C) (and hence, the ferrites 132) offer the shortest path to return to the source 120. Some RF current may, however, may return to the source 120 along the walls 102 parallel to the slit valve opening 106 (y-direction in Figure 1A-1C) (and hence, the ferrites 132), but the amount of RF current that flows along the walls 102 parallel to the slit valve opening 106 (and hence, the ferrites 132) is insignificant relative to the RF current returning to the source 120 along the walls 102 perpendicular to the slit valve opening 106 (and hence, the ferrites 132). Therefore, because little or no RF current returns to the source 120 along the walls 102 parallel to the slit valve opening 106 (and hence, the ferrites 132), the negative effect of the slit valve opening 106 may be substantially reduced, or in some cases, eliminated. Thus, the amount of current traveling along the slit valve opening path 106 is small enough that the plasma is not pulled toward the slit valve opening 106. If the plasma is pulled towards the slit valve opening 106, then the plasma is not uniformly spread across the processing area 146.

[0053] When the susceptor 108 raises the substrate 110 for processing, the susceptor 108 encounters a shadow frame 138 while moving to the processing position. The shadow frame 138 may prevent unwanted deposition from occurring on the areas of the susceptor 108 that are not covered by the substrate 110. The shadow frame 138 may rest on a ledge 140 prior to being displaced by the susceptor 108. The shadow frame 138 may also be a part of the RF return path. One or more straps 142 may be coupled to both the shadow frame 138 as well as the inside surface of the walls 102. The straps 142 -may. be coupled to the inside surface of the walls 102 with one or more fastening mechanisms 144. In one embodiment, the fastening mechanism 144 may comprise a screw. The RF or VHF current travels along the bottom electrode, the straps 142, the inside surface of the walls 102, the lid 124, and back to the power source 120 as shown by arrows "B" to complete the RF circuit.

[0054] By suppressing RF current with the ferrites spanning a length of the backing plate 126 parallel to the slit valve opening 106, the RF current in the direction of the slit valve opening (and opposite thereto) is controlled. However, because no ferrites 132 are oriented and/or aligned perpendicular to the slit valve opening 106 (or vice versa), the RF current that runs parallel to the slit valve opening 106 (or vice versa) between the ferrite boundaries is not controlled. Thus, the ferrites 132 remove one degree of uncertainty to control of the RF current. The control of the RF current in the direction parallel to the slit valve opening 106 (y- direction) aids in plasma uniformity and thus, deposition uniformity.

[0055] Not wishing to be bound by theory unless specifically set forth in the claims, it is believed that the ferrites cause the standing wave to stretch outside the ferrites and thus shrinking its affect in the regions found between the ferrites 132. Thus, as noted above, the RF current on the uncovered electrode area will be a quasi-uniform plane wave in a direction perpendicular to the ferrites, but will propagate in the direction parallel to the ferrites. The single RF feed location induces the same fields/currents on the gas distribution showerhead 128 as if two "mirror feeds" had been induced to the bottom of the showerhead at the edges of the gas distribution showerhead 128. The mirror feeds would be spaced by two electrode widths (2w), be same phased, and be prorated in amplitude. A standing wave would be formed on the gas distribution showerhead 128 with a maximum in the center. Thus, the single RF feed will induce a standing wave pattern that has a maximum in the center of the bottom surface of the gas distribution showerhead 128.

[0056] To deposit material on the substrate 110, processing gas is introduced from the gas source 118 through the backing plate 126 and into the plenum 148. Then, the processing gas passes through the gas passages 130 formed in the gas distribution showerhead 128 and into the processing area 146. The RF current flows along the tube 122, the back surface of the backing plate 126, the suspension 134, and the front surface of the showerhead 128. The RF fields then ignite the processing gas to form a plasma that causes the excited gas species found in the processing area 146 to deposit a desired material onto the substrate 110. Generally, the RF current propagates through the processing area 146 to the substrate 110 and along the shadow frame 138, the straps 142, the walls 102, and the lid 124 back to the power source 120. In one embodiment, the straps 142 may be present along the walls 102 perpendicular to the ferrites 132 but not present on the walls parallel to the ferrites 132. In another embodiment, the straps 142 may be coupled to all walls 102.

[0057] Figure 1 D is a schematic top view of an electrode 160 having a single, substantially centered, RF feed location "F". Figure 1 E is a schematic bottom view of the electrode 160 of Figure 1C. As seen in Figure 1 D, ferrites 162 span a length of a side of the electrode 160. The RF current is fed to the electrode at the substantial center thereof. The RF current travels out from the center in substantially all directions on the surface of the electrode 160 as shown by arrows "C". The RF current does not travel through the ferrites 162. Thus, the RF current that does not flow to the ferrite 162 continues to flow along its path. Due to the presences of the ferrites 162, substantially no current flows down to the bottom of the electrode 160 along the walls parallel to the ferrites 162.

[0058] As shown in Figure 1 E, the RF current that flows on the bottom surface is affected by the ferrites 162. Due to the ferrites 162 suppressing RF current from traveling along the sidewalls parallel to the ferrites 162, substantially the only RF current that travels down to the bottom surface of the electrode 160 will travel to the bottom surface along sidewalls perpendicular to the ferrites 162. Thus, the RF current that travels along the bottom surface of the electrode 160 will flow substantially parallel to the ferrites 162.

[0059] While the term ferrite has been used in the present application, it is to be understood that any ferromagnetic material may be used including non-oriented, amorphous ferromagnetic material. Additionally, magnets may be used. The permeability of the ferrites may be predetermined to suit the needs of the user.

[0060] Figure 2A is a schematic cross sectional view of a PECVD apparatus 200 according to another embodiment. The apparatus 200 comprises a plurality of walls 202 and a bottom 204. In one embodiment, the walls 202 and the bottom 204 may comprise a conductive material. In another embodiment, the walls 202 and bottom 204 may comprise aluminum. Through one or more walls 202, a slit valve opening 206 may be present. The slit valve opening 206 permits a substrate 210 to enter and exit the apparatus 200.

[0061] The substrate 210 may be placed on a susceptor 208 when in the apparatus 200. The susceptor 208 may be raised and lowered on a shaft 212. In one embodiment, the shaft 212 and the susceptor 208 may comprise a conductive material. In another embodiment, the shaft 212 and the susceptor 208 may comprise aluminum. The apparatus 200 may be evacuated by a vacuum pump 214. A valve 216 may be coupled between the chamber and the vacuum pump 214 to adjust the vacuum level of the apparatus 200.

[0062] Processing gas may be introduced into the apparatus 200 from a gas source 218 through a tube 222 that passes through the chamber lid 224. The tube 222 is coupled to the backing plate 226 to permit the processing gas to pass through the backing plate 226 and enter a plenum 248 between the backing plate 226 and the gas distribution showerhead 228. In one embodiment, the tube 222, the backing plate 226, and the gas distribution showerhead 228 may comprise a conductive material. In another embodiment, the tube 222, backing plate 226, and gas distribution showerhead 228 may comprise aluminum. The processing gas spreads out in the plenum 248 and then passes through gas passages 230 formed through the gas distribution showerhead 228 to the processing area 246. In general, the power may be applied such that 1/8^th of the wavelength at the applied frequency is comparable to the chamber diagonal. The chamber diagonal is the distance across a rectangular chamber from one corner to another corner diagonally opposite.

[0063] A plurality of power sources 220A, 220B are also coupled to the backing plate 226. In one embodiment, the power sources 220A, 220B comprise RF power sources capable of generating RF currents at a frequency of between about 13.56 MHz and about 100 MHz. In another embodiment, the power sources 220A, 220B comprise VHF power sources capable of generating VHF currents at a frequency of between about 40 MHz and about 60 MHz. In another embodiment, the power sources 220A, 220B comprise VHF power sources capable of generating VHF currents at a frequency of about 27 MHz. In another embodiment, the power sources 220A, 220B are capable of generating VHF currents of about 40 MHz and above. The power sources 220A, 220B may be phase modulated as will be discussed below.

[0064] The current from the power sources 220A, 220B flows along the outside surface of the backing plate 226. RF current and VHF current have a 'skin effect' in that the current does not penetrate all the way through a conductive body such as the backing plate 226. RF or VHF current travels along the outside surface of a conductive object and penetrates a predetermined distance into the conductive article. The amount that the RF or VHF current penetrates into the conductive article is a function of the frequency of the current and the material properties. The RF or VHF current then travels down a bracket 234 to the front face of the gas distribution showerhead 228. In one embodiment, the bracket 234 may comprise a conductive material. In another embodiment, the bracket 234 may comprise aluminum. The RF or VHF current flows along a path shown by arrows "C". Thus, the RF current travels along the back surface of the backing plate 226, the side surface of the backing plate 226 the outside surface of the bracket 234, and the bottom surface of the gas distribution showerhead 228. [0065] The RF or VHF current does not travel along the back surface of the gas distribution showerhead 228 that faces the backing plate 226. Additionally, the RF or VHF current does not travel along the front surface of the backing plate 226 that faces the gas distribution showerhead 228. Thus, the gas in the plenum 248 does not see the RF or VHF current and therefore does not ignite into a plasma in the plenum 248.

[0066] In the embodiment shown in Figure 2A, the gas tube 222 is fed into the substantial center of the backing plate 226. It is to be understood that the gas tube 222 could be moved to suit the needs of the user. Moving the gas tube 222 may not have a great affect on the gas distribution because the gas may substantially evenly distribute within the apparatus 200 due to the plenum 248. Hence, the gas flow uniformity into the processing area 246 may be controlled by the plenum 248 as opposed to the location where the gas tube 222 feeds gas into the plenum 248.

[0067] For RF or VHF current, on the other hand, the location where the current couples to the backing plate 226 makes a difference. In the embodiment shown in Figure 2A, two separate power sources 220A, 220B are shown connected to the backing plate 226. Each power source 202A, 220B is coupled to the backing plate 226 at multiple locations. However, it is to be understood that each power source 220A, 220B may be coupled to the backing plate 226 at one location. In one embodiment, the backing plate 226 may have a size of greater than about 60,000 square centimeters.

[0068] In the embodiment shown in Figure 2B, parallel ferrite 232 boundaries on the top of the backing plate 226 are present. The ferrites 232 may suppress RF and/or VHF currents perpendicular to the ferrite 232 boundary and will absorb the magnetic field component parallel to the boundary (i.e., the standing wave pattern in the direction perpendicular to the ferrite 232 boundary will be stretched outside the ferrites 232 and shrunk inside the ferrite 232). The ferrite's 232 relative permeability and geometry may determine what portion of the standing wave profile on the backing plate 226 will move into the ferrites 232. For the areas of the backing plate 226 not covered by ferrites 232, a plane wave with fields that are quasi-uniform in one direction (for example, the x direction) and propogating in the other, perpendicular direction (for example, the y-direction). The non-uniformity in the wave propogation direction will still exist, but may be resolved by moving the standing wave pattern in the perpendicular direction by using the multiple power sources 220A, 220B with phase and/or amplitude control and/or by moving the substrate. Further control and/or improvement of the uniformity may be achieved by using the multiple feeds with uneven power distribution and/or using multiple ferrite 232 boundaries on the backing plate 226. The design and power coupling may enhance the RF and/or VHF drive in the parallel direction (and/or suppress the perpendicular direction). Therefore, any uniformity issues caused by the slit valve opening 206 may be substantially reduced by placing ferrites 232 parallel to the slit valve opening 206.

[0069] For the embodiment shown in Figure 2B, the ferrites 232 extend along an edge of the backing plate 226 parallel to the slit valve opening 206. The edges of the backing plate 226 extending perpendicular to the slit valve opening 206 do not have ferrites 232 extending thereon. However, the ends of the ferrites 232 do cover a short distance of the edge perpendicular to the slit valve opening 206. It is to be understood that the ferrites 232 may be placed in other orientations. For example, the ferrites 232 may extend along the edge of the backing plate 226 perpendicular to the slit valve opening 206 instead of the edges parallel to the slit valve opening 206. Additionally, if desired, the ferrites 232 may be present on all edges. However, if ferrites 232 are present on all edges, it may be necessary to have some gaps therebetween to permit the RF or VHF current to travel down to the gas distribution showerhead 228.

[0070] In the apparatus 200, there are four walls 202. Of those four walls 202, three of the walls 202 are substantially identical and look substantially identical to the RF or VHF current (in absence of the ferrites 232) when it travels thereon returning to the power sources 220A, 220B as shown by arrows "D". The fourth wall 202, however, is different than the other walls 202 and looks different to the RF or VHF current as it returns to the power sources 220A, 220B. The fourth wall 202 has the slit valve opening 206 therethrough. The RF or VHF current travels a different path along the wall 202 having the slit valve opening 206. The RF or VHF current actually travels along the slit valve opening 206. Thus, the RF or VHF current traveling along the wall 202 having the slit valve opening 206 has a longer inductive path to return to the power sources 220A, 220B as compared to the three other walls 202.

[0071] As the RF or VHF current travels back to the power sources 220A, 220B, the potential of the RF or VHF current decreases. Hence, the potential difference between the RF or VHF current flowing along the three substantially identical walls 202 back to the power sources 220A, 220B and the gas distribution showerhead 228 is different than the difference between the RF or VHF current flowing along the wall 202 having the slit valve opening 206 and the gas distribution showerhead 228, in absence of the ferrites 232. The slit valve opening 206 is a part of the RF return path and therefore leads to an asymmetry along the chamber walls. The asymmetric RF return path shifts the standing wave and thus, unevenly distributes the plasma within the apparatus 200. With an uneven plasma distribution, a uniform deposition of material onto the substrate 210 may not occur.

[0072] The ferrites 232 may be used to substantially reduce the effect of the slit valve opening 206. Ferrites 232 may be used to lengthen the RF return path along the wall opposite to the slit valve (i.e., the ferrites 232 would be placed, for example, above the electrode or backing plate opposite to the slit valve opening 206). The RF return path may be lengthened by using thicker ferrites 232 or stronger ferrites 232 opposite the slit valve opening 206. In the embodiment shown in Figure 2B, the ferrites 232 extend parallel to the slit valve opening 206. The ferrites 232 suppress the RF or VHF current flowing along the edge of the backing plate 226 having ferrites 232 thereon and hence, the side of the gas distribution showerhead 228. The RF or VHF current, when returning to the sources 220A, 220B, seeks to take the shortest path possible. Hence, when returning to the source 220A, 220B, the RF or VHF current will flow along the walls 202 perpendicular to the slit valve opening 206 (and hence, the ferrites 232) because the walls 202 perpendicular to the slit valve opening 206 (and hence, the ferrites 232) offer the shortest path to return to the sources 220A, 220B. Some RF or VHF current may, however, return to the sources 220A, 220B along the walls 202 parallel to the slit valve opening 206 (and hence, the ferrites 232), but the amount of RF or VHF current that flows along the walls 202 parallel to the slit valve opening 206 (and hence, the ferrites 232) is insignificant relative to the RF or VHF current returning to the sources 220A, 220B along the walls 202 perpendicular to the slit valve opening 206 (and hence, the ferrites 232). Therefore, because little or no RF or VHF current returns to the sources 220A, 220B along the walls 202 parallel to the slit valve opening 206 (and hence, the ferrites 232), the negative effect of the slit valve opening 206 may be substantially reduced, or in some cases, eliminated.

[0073] When the susceptor 208 raises the substrate 210 for processing, the susceptor 208 encounters a shadow frame 238 while moving to the processing position. The shadow frame 238 may prevent arcing between the susceptor 208 and the substrate coating top. The shadow frame 238 may rest on a ledge 240 prior to being displaced by the susceptor 208. The shadow frame 238 may also be a part of the RF or VHF return path. One or more straps 242 may be coupled to both the shadow frame 238 as well as the inside surface of the walls 202. The straps 242 may be coupled to the inside surface of the walls 202 with one or more fastening mechanisms 244. In one embodiment, the fastening mechanism 244 may comprise a screw. The RF or VHF current travels along the susceptor 208, the straps 254, the inside surface of the walls 202, the lid 224, and back to the power sources 220A, 220B as shown by arrows "D" to complete the RF or VHF circuit.

[0074] By suppressing RF or VHF current with the ferrites spanning a length of the backing plate 226 parallel to the slit valve opening 206, the RF or VHF current in the direction of the slit valve opening (and opposite thereto) is controlled. However, because no ferrites 232 are perpendicular to the slit valve opening 206 (or vice versa), the RF or VHF current that runs parallel to the slit valve opening 206 (or vice versa) is not controlled. Thus, the ferrites 232 remove one degree of uncertainty to control of the RF or VHF current. The control of the RF or VHF current in the direction parallel to the slit valve opening 206 aids in plasma uniformity and thus, deposition uniformity. [0075] To deposit material on the substrate 210, processing gas is introduced from the gas source 218 through the backing plate 226 and into the plenum 248. Then, the processing gas passes through the gas passages 230 formed in the gas distribution showerhead 228 and into the processing area 246. The RF or VHF current flows along the tube 222, the back surface of the backing plate 226, the bracket 234, and the front surface of the showerhead 228. The induced RF or VHF fields then ignite the processing gas into a plasma which deposits material onto the substrate 210. The RF or VHF current propagates through the plasma to the substrate 210 and along the shadow frame 238, the straps 242, the walls 202, and the lid 224 back to the power source 220A, 220B. In one embodiment, the straps 242 may be present along the walls 202 perpendicular to the ferrites 232 but not present on the walls parallel to the ferrites 232. In another embodiment, the straps 242 may be coupled to all walls 202.

[0076] It is to be understood that while the ferrites 232 have been discussed as being located behind the backing plate 226 on the atmosphere side of the chamber, the ferrites 232 may be placed in other locations as well. When the ferrites 232 are placed on the front surface of the gas distribution showerhead 228, the ferrites 232 may be enclosed in a cover such as a dielectric or ceramic cover to prevent the ferrites 232 from sputtering. Other potential locations for the ferrites 232 include under the susceptor 208, adjacent the backing plate 226, and adjacent the chamber walls 202 between the substrate 210 and the gas distribution showerhead 228. Additionally, while ferrites 232 have been described, it is to be understood that any ferromagnetic material, conducting or non-conducting, non-oriented, or ferromagnetic material, or oriented material such as magnets may be used.

[0077] Figure 3A is a schematic isometric top view of an electrode having a single, substantially centered RF feed location 304 according to one embodiment. Figure 3A shows ferrite boundaries along two sides of the electrode. The ferrite boundaries on the electrode edges move part of the standing wave profile into the ferrites (i.e., the standing wave pattern on the uncovered electrode area will be spread and thus, more uniform). The RF currents may be enhanced in the direction parallel to the ferrite boundary and suppressed in the direction perpendicular to the ferrite boundary. A plane wave like propogation between the ferrite boundaries (i.e., magnetic field components parallel to the ferrite boundaries move into the ferrites) may be present.

[0078] Figure 3B is a schematic top view of an apparatus 320 according to one embodiment. The apparatus includes an electrode 322 having ferrites 324 that span the length of two parallel sides of the electrode 322. The electrode 322 may be hypothetically divided in half at the center line 334 and separate power sources 326, 328 may be applied to each half 330, 332 of the electrode 322. The power sources 326, 328 may be coupled to the halves 330, 332 at locations spaced from the edges 336, 338 of the halves 330, 332. In one embodiment, the power sources 326, 328 may be coupled to the halves 330, 332 at the edges 336, 338. The RF or VHF current may be applied to the halves 330, 332 from the power sources 326, 328 such that the standing wave moves across the underside of the electrode 322. The ferrites 324 prevent or reduce the flow of the RF or VHF current in the "Y" direction, but permit the RF or VHF current to travel in the "X" direction. By modulating the power applied to the halves 330, 332, together with the ferrites 324 suppressing the RF or VHF current in the "Y" direction, the standing wave may be moved across the bottom face of the electrode 322. Alternatively, the substrate may be moved.

[0079] Figure 3C is a schematic isometric view of an apparatus 350 according to one embodiment. As shown in Figure 3C, ferrites 352 span a length of an electrode 356 along an edge 360. The electrode 356 is positioned opposite the susceptor 358. A plurality of power sources 354A, 354B are shown coupled to the electrode 356, each coupled at a plurality of contact points 364, 366, 368, 370, 372, 374, 376, 378. One power source 354B is coupled to an edge 362 of the electrode 356. The other power source 354A is coupled at a plurality of contact points 364, 366, 368, 370 at an edge opposite to the edge 362. The power sources 354A, 354B may be driven out of phase with each including operating in a push-pull arrangement. For example, power source 354A will be driven in a first phase and the other power source 354B will be driven in a phase opposite to the first phase. Therefore, each power source 354B will act as the return path for the other power source 354A and vice versa. In one embodiment, the power sources 354A, 354B may operate in the same phase. In another embodiment, the power sources 354A, 354B may operate close to out of phase with each other. It is to be understood that while the power sources 354A, 354B have been shown coupled at the edges, the power sources 354A, 354B may be coupled at other locations as well that are spaced from the edges.

[0080] A non-uniform standing wave profile in the y-direction can be moved by means of time-varying asymmetric (in phase or amplitude or both) drive (i.e., two feeds on electrode sides (non-ferrite sides) or a feed on one side and variable capacitor on the other side. Thus, a time-averaged uniform field plasma may be formed. The profiles can be controlled/improved by using multiple contact points 364, 366, 368, 370, 372, 374, 376, 378 on each side with uneven power distribution, or by multiple ferrite boundaries. Anisotropy in the excited RF/VHF fields/currents on the electrodes may also help with the slit valve effect issue. The currents are driven in parallel to the slit valve (ferrite boundaries parallel with the slit valve). Additionally, due to multiple contact points 364, 366, 368, 370, 372, 374, 376, 378 the current delivered to the different contact points 364, 366, 368, 360, 362, 364, 366, 368 may be different.

[0081] The boundary condition is affected by the magnetic material. By shortening the magnetic component parallel to the edge, a high magnetic permeability material will force the magnetic field, and thus the wave front, to be perpendicular to the edges and help form plane waves. In other words, a high magnetic permeability may increase the electrical length to the side and effectively extend the electrode.

[0082] It is to be understood that while the ferrites 352 have been shown as a single piece spanning the entire length of the electrode 356, the ferrites 352 may comprise multiple pieces. The multiple pieces may each span the entire length or the multiple pieces may be coupled together to collectively span the entire length. Additionally, if desired, the multiple ferrite 352 pieces may be spaced apart. Additionally, the contact points 364, 366, 368, 370, 372, 374, 376, 378 may be moved laterally. The electrode 356 may be a scooped gas distribution showerhead having a concave bottom surface facing the susceptor 358. In one embodiment, the electrode 356 may comprise a gas distribution showerhead having a substantially planar surface facing the susceptor 358. The ferrites 352 may be spaced from the electrode 306.

[0083] The center high maximum of the standing wave, when viewed isometrically, will have a dome shape such as shown in Figure 3D. The RF current is flowing to the bottom surface of the electrode from all directions and thus, confluences at the center to create the dome shape shown in Figure 3D. The dome shape may be pulled off center due to the slit valve effect.

[0084] When ferrite boundaries are present, however, the standing wave maximum or peak spreads out in a direction perpendicular to the transversely oriented ferrite boundaries as compared to when no ferrites are present. Because the maximum or peak of the standing wave is substantially constant across substantially the entire distance between the ferrites, the plasma density may be substantially uniform across the electrode in the x-direction (showerhead in PECVD) as shown in Figure 3E. It is believed that the RF current flowing to the bottom surface of the electrode from the sides that did not have ferrites thereon will form the standing wave in the y-direction, as shown in Figure 3E. Thus, the RF current is flowing to the bottom surface of the electrode from only two sides. The ferrites have thus eliminated or substantially reduced the non-uniformity that would have been created by RF current flowing from the sides along which the ferrites are oriented (x- direction). By eliminating or reducing the RF current from the other two sides, the standing wave maximum is not compressed towards the center from the other two sides. In fact, little or no compression of the standing wave maximum towards the center occurs from the other two sides. Without the compression from the other two sides, the standing wave maximum or peak from the two sides having RF current flowing therefrom may be substantially uniformly spread across the width of the electrode. Hence, the standing wave profile shown in Figure 3E has a maximum or peak spanning the substantial width of the electrode. [0085] In comparing Figure 3D to Figure 3E, it can be seen that the standing wave of Figure 3D will have a dome shape with the highest point that may be in the substantial center of the electrode or even shifted to a side due to the slit valve effect. However, when ferrites are present, the standing wave in the y-direction may span across substantially the entire width of the electrode perpendicular to the ferrite material (x-direction). In the embodiment shown in Figure 3E, the ferrites are positioned in a direction perpendicular to the highest point of the standing wave (y- direction shown in Figure 3A). Therefore, the standing wave can be extended in the direction perpendicular to the ferrite material such that the plasma may be substantially uniformly distributed in the direction perpendicular to the ferrites.

[0086] Figure 4 is a graph showing the effects of a ferrite boundary on the standing wave profile. The ferrite boundaries on the electrode edges move part of the standing wave profile into the ferrites (i.e., the standing wave pattern on the uncovered electrode area will be spread and thus, more uniform) as shown in Figure 4 which compares the standing wave profile for an electrode with ferrites to an electrode without ferrites. As shown in Figure 4, the standing wave profile in the situation where ferrites are present results in a flatter profile as compared to the situation where no ferrites are present. By flattening out the standing wave profile, the plasma uniformity in the "X" direction may be substantially uniform. The RF or VHF currents may be enhanced in the direction parallel to the ferrite boundary and suppressed in the direction perpendicular to the ferrite boundary. A plane wave like propagation between the ferrite boundaries (i.e., magnetic field components parallel to the ferrite boundaries move into the ferrites) is created.

[0087] Figure 5A shows a normalized electrode voltage distribution for a center fed RF feed. As can be seen from Figure 5A, the electrode voltage is distributed substantially identical to both the left and right of center. Figure 5B shows a normalized electrode voltage distribution for an RF feed displaced 0.5 meters from center. Here, the electrode voltage is distributed differently to the left and right of center. Thus, by shifting the RF feed, the standing wave can also be shifted. [0088] Figures 5C and 5D show the effect of placing magnetic material or ferrites on the edges of the electrode. In both Figures 5C and 5D, the electrode is powered at opposite ends with a VHF frequency of 40 MHz. The VHF current is applied at five separate locations with the same phase. As shown in Figure 5C, when magnetic material or ferrites span the edge of sides perpendicular to the sides having the VHF power coupled thereto, the plasma generated is substantially uniform in the "X" direction. By phase modulating the VHF current applied to the electrode, the location where the plasma is most intense may be scanned the length of the electrode such that a substantially uniform plasma is present in not only the "X" direction but also the "Y" direction. By comparison, Figure 5D shows the same electrode and conditions, except that the magnetics or ferrites have been removed. As can be seen, the plasma is most intense in the middle and not uniform in either the "X" or "Y" direction. Even though the VHF current is launched from two opposite sides, the combined plasma field has a domed shaped pattern with the greatest concentration near the substantial center of the electrode. When the two power sources are phased, the dome moves from end to end, but not side to side. Thus, there is a plasma nonuniformity.

[0089] It is possible to deliver the VHF current from all sides and phasing in each direction, but such complexity is not necessary when using a ferrite system. The complexity is due to the plane waves that are launched from the power sources which make a linear wave front and makes the problem one dimension. Deflection from edges makes plane waves difficult and results in the domed wave front.

[0090] Figure 6 shows the effects of utilizing multiple ferrite boundaries on plasma distribution. In Figure 6, a 60 MHz VHF current was delivered to the electrode. The power was evenly distributed along the two opposite edges of the electrode. Ferrites spanned the length along the edges perpendicular to the edges where the power was delivered. Additionally, ferrites spanned the length along in the middle of the electrode to create additional ferrite boundaries. As shown in Figure 6, the ferrite boundaries create three separate zones. Each zone has substantially evenly distributed plasma in the "X" direction which can be moved in the "Y" direction by phase modulating the VHF current delivered to the electrode. [0091] Figure 7 is a simplified schematic cross sectional view illustrating various locations in which ferrites 710 can be positioned in relation to a processing area 746 within a parallel plate apparatus 700. The ferrites 710 may be placed on the back surface of the electrode 704 (i.e., backing plate/showerhead illustrated in Figure 1 B or 2B), on the surface of the electrode 704 facing the substrate 708, under the susceptor 706, or even on the walls 702. When the ferrites 710 are behind the electrode 704, the ferrites 710 may be in an atmospheric environment. However, when the ferrites 710 are positioned under the susceptor 706, on the electrode 704 facing the substrate 708, or on the walls 702, they may need to be covered by a cover 712 to isolate them from the vacuum environment. The cover 712 can be used to prevent the ferrites 710 from contaminating the processing environment due to attack caused by the radicals in the plasma, oxidation, corrosion, or by sputtering caused energetic species in the plasma. In one embodiment, the cover 712 may comprise an insulating material. The benefits to having the ferrites 710 on the atmospheric side of the electrode 704 include easy access to the ferrites 710, not exposed to reactive gas or high temperatures, and the need for less material because no cover is necessary. Additionally, the ferrites 710 may be between a backing plate and a showerhead in a PECVD system. The ferrites 710 may even be spaced from the electrode 704 for thermal purposes.

[0092] By utilizing ferrites strategically placed in a parallel plate reactor, better control of the RF or VHF current may occur. The ferrites may compensate for the standing wave effect and increase plasma uniformity. Due to an increased plasma uniformity, a more uniform and repeatable deposition may occur in the parallel plate reactor.

[0093] While the foregoing is directed to embodiments of the present invention, other and further embodiments of the invention may be devised without departing from the basic scope thereof, and the scope thereof is determined by the claims that follow.

Claims

Claims:

1. An apparatus, comprising: a chamber body having a first wall with a slit valve opening therethrough; an electrode disposed in the chamber body; one or more ferrite pieces extending parallel to the slit valve opening; and a plurality of first VHF power sources coupled to the electrode at a plurality of locations.

2. The apparatus of claim 1 , wherein a first VHF power source is coupled along an edge of the electrode perpendicular to the slit vale opening and a second power source separate from the first power source is coupled to the electrode at a plurality of locations opposite the first power source.

3. The apparatus of claim 1 , further comprising one or more second ferrite pieces extending parallel to the slit valve opening and separate from the one or more first ferrite pieces, wherein the one or more second ferrite pieces and the one or more first ferrite pieces are disposed in substantially the same plane on opposite sides of the electrode.

4. The apparatus of claim 1 , wherein the electrode is a gas distribution showerhead and the apparatus is a plasma enhanced chemical vapor deposition apparatus.

5. An apparatus, comprising: an electrode; a first power source coupled to the electrode in a first plurality of locations along a first periphery of the electrode; a second power source separate from the first power source and coupled to the electrode in a second plurality of locations along a second periphery of the electrode parallel to the first periphery; one or more first ferrite blocks extending along a third periphery of the electrode perpendicular to the first and second periphery; and one or more second ferrite blocks extending along a fourth periphery of the electrode parallel to the third periphery.

6. The apparatus of claim 5, wherein the electrode is a gas distribution showerhead and the apparatus is a plasma enhanced chemical vapor deposition apparatus.

7. A plasma enhanced chemical vapor deposition apparatus, comprising: a processing chamber body having a plurality of sidewalls, at least a first sidewall of the plurality of sidewalls having a slit valve opening therethrough; a susceptor disposed within the chamber body; a gas distribution showerhead disposed in the chamber body opposite the susceptor; a backing plate disposed in the chamber body adjacent the gas distribution showerhead, the backing plate having a first side facing the gas distribution showerhead and a second side opposite the first side; one or more first ferrite blocks disposed along the second side of the backing plate along a first edge of the second side, the one or more first ferrite blocks extend substantially parallel to the slit valve opening; a first power source coupled to the backing plate on the second side at a second edge perpendicular to the first edge; and a second power source separate from the first power source coupled to the backing plate on the second side at a third edge parallel to the second edge.

8. The apparatus of claim 7, further comprising one or more second ferrite blocks separate from the one or more first ferrite blocks, the one or more second ferrite blocks disposed along the second side of the backing plate along a fourth edge substantially parallel to the first edge, wherein the first edge is adjacent the first sidewall.

9. The apparatus of claim 7, wherein the first power source is coupled to the second edge at a plurality of locations, wherein the second power source is coupled to the fourth edge at a plurality of locations and wherein the first power source and the second power source are VHF power sources capable of operating at frequencies of about 40MHz or greater.

10. A method, comprising: applying a first RF or VHF current to an electrode at one or more first locations, the electrode having a generally rectangular shape and one or more ferrite blocks extending along a substantial length of first and second parallel edges, the first RF or VHF current applied at a first phase, and the first location located at a third edge of the electrode perpendicular to the first and second edges; and applying a second RF or VHF current to the electrode at one or more second locations located at a fourth edge of the electrode parallel to the first edge, the second RF or VHF current applied in a second phase opposite to the first phase.

11. The method of claim 10, wherein the first RF or VHF current is applied at a plurality of first locations and wherein the second RF or VHF current is applied at a plurality of second locations.

12. The method of claim 10, further comprising modulating the first RF or VHF current and the second RF or VHF current to move a standing wave generated by the first and second RF or VHF currents across the electrode, wherein the method is a plasma enhanced chemical vapor deposition method.

13. An apparatus, comprising: a chamber body having a slit valve opening through a first wall of the chamber body; a gas distribution showerhead disposed in the chamber body above the slit valve opening; a backing plate coupled to the chamber body and spaced from the gas distribution showerhead, the backing plate having a substantially rectangular shape, a first side facing the gas distribution showerhead, and a second side opposite the first side; a power source coupled to the backing plate at a substantial center thereof; and one or more first ferrite pieces extending along the second side of the backing plate.

14. An apparatus, comprising: a substantially rectangular shaped gas distribution showerhead; a backing plate coupled to the gas distribution showerhead; and one or more first ferrite blocks resting on the backing plate.

15. A method, comprising: applying an RF current to a backing plate of an apparatus, the apparatus having a gas distribution showerhead coupled to the backing plate and one or more ferrite blocks resting on an edge of the backing plate, the RF current applied such that at least a portion of a the RF current is suppressed in a direction perpendicular to the ferrite material; introducing a processing gas through the gas distribution showerhead; igniting the processing gas into a plasma; and depositing material onto the substrate.