WO2001084624A2

WO2001084624A2 - Semiconductor lift pin for dechucking substrates

Info

Publication number: WO2001084624A2
Application number: PCT/US2001/013405
Authority: WO
Inventors: Peter K. Loewenhardt; Hiroji Hanawa; Raymond Gristi; Gerald Zheyao Yin; Yan Ye
Original assignee: Applied Materials, Inc.
Priority date: 2000-04-28
Filing date: 2001-04-25
Publication date: 2001-11-08
Also published as: WO2001084624A3

Abstract

A lift pin (95) capable of dechucking a substrate (15) on a support (65) comprises a body including a resistor (125). In one version the resistor comprises a body (126) comprising semiconducting material. The resistor (125) reduces the voltage caused by RF current while allowing residual electrostatic charge to be removed by flowing to a current sink (105).

Description

SEMICONDUCTOR LIFT PIN FOR DECHUCKING SUBSTRATES

BACKGROUND

The present invention relates to lift pins for dechucking a substrate held on a support in a process chamber.

In the manufacture of integrated circuits, a substrate is processed by process gas, for example a plasma, in a chamber. The substrate is typically supported in the chamber by a support, a portion of which may comprise a dielectric material covering an electrode. The electrode may be charged, for example with a DC voltage, to electrostatically hold the substrate. Lift pins may be used to lift and lower a substrate onto the support in the process chamber. Typically, a robotic arm transports the substrate into a process chamber where the substrate is deposited on lift pins that extend upwardly through the chuck. The lift pins are then lowered into a lower portion of the process chamber to deposit the substrate on the support. Thereafter, the robotic arm is withdrawn from the chamber. After processing of the substrate, the DC voltage applied to the chuck electrode is terminated to release the substrate, and the lift pins are raised upwardly through holes in the chuck to lift the substrate off the chuck by pushing up against the substrate. The robotic arm is then reinserted to withdraw the processed substrate from the chamber.

One problem with conventional lift pins arises when the lift pins attempt to lift the substrate off the chuck. Residual electrostatic charge in the substrate generates attractive electrostatic forces between the substrate and the chuck, that cause the substrate to adhere to the chuck, even when the voltage to the chuck is terminated. The upwardly pushing lift pins can damage or break the substrate. Lift pins are typically composed of electrically insulative material, which trap residual electrostatic charge in the substrate, causing the substrate to stick to the chuck as the lift pins are pushed against the substrate, resulting in damage or breakage of the substrate.

One solution is to use electrically grounded metal lift pins that allow the residual charge in the substrate to discharge through the lift pins. However, the metal pins may allow the high frequency RF energy used to sustain the plasma in the chamber, to propagate through the metal pins and into the lower portion of the chamber. This results in plasma formation in the lower portion of the chamber, causing erosion of the metal parts therein, and wasting the power used to generate the plasma. Also, the plasma heats up the lower portion of the process chamber, and causes deposits to form on the components therein.

Therefore, there is a need for a lift pin which allows discharging of residual electrostatic charge in a substrate. It is further desirable for the lift pins to reduce propagation of the RF energy into the lower portion of the process chamber.

SUMMARY

The present invention satisfies these needs. In one aspect of the invention a lift pin capable of dechucking a substrate on a support in a chamber comprises a body comprising semiconducting material.

In another aspect of the invention, a substrate processing chamber comprises a substrate support comprising an electrode, a dielectric at least partially covering the electrode, and a lift pin comprising a semiconducting material, a gas distributor, a gas energizer, and a gas exhaust, whereby a substrate received on the support may be processed by gas introduced through the gas distributor, energized by the gas energizer and exhausted by the gas exhaust and may thereafter be dechucked by the lift pin.

In another aspect of the invention, a method of dechucking a substrate in a chamber comprises providing a support in the chamber, the support comprising a lift pin comprising semiconducting material, supporting the substrate on the support, and moving the lift pin to contact the substrate.

In another aspect of the invention, a method of processing a substrate in a chamber comprises providing a support in the chamber, the support comprising an electrostatic chuck and a lift pin comprising semiconducting material, generating an electrostatic chucking force to support the substrate on the support, providing energized process gas in the chamber, and moving the lift pin to contact the substrate to dechuck the support.

In another aspect of the invention, a method of fabricating a lift pin usable in a substrate support in a chamber comprises providing a body comprising semiconducting material and forming the body into the lift pin.

DRAWINGS

These features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings which illustrate exemplary features of the invention. However, it is to be understood that each of the features can be used in the invention in general, not merely in the context of the particular drawings, and the invention includes any combination of these features, where:

Figure 1 is a schematic sectional side view of a substrate processing apparatus according to the present invention;

Figure 2 is a schematic sectional side view of a lift pin according to the present invention;

Figure 3 is a schematic sectional side view of another version of a lift pin according to the present invention;

Figure 4 is a schematic sectional side view of another version of a lift pin according to the present invention; and

Figure 5 is a schematic sectional side view of another version of a lift pin according to the present invention. DESCRIPTION

The present invention relates to a lift pin for a support. The description represents illustrative embodiments of the invention and is not intended to limit the invention.

An exemplary apparatus 10 suitable for processing of a substrate 15, such as a semiconductor wafer, is shown in Figure 1 . The apparatus is particularly useful for energized gas processes, such as plasma processes, where RF currents are used to generate a plasma for processing the substrate. Examples of such plasma processes include plasma enhanced chemical vapor deposition, sputtering processes, ion implantation processes, and plasma etching or reactive ion etching processes.

The apparatus 10 generally comprises an enclosed process chamber 20 having an upper portion 22, a lower portion 24, and surrounded by walls 25. Process gas may be introduced into the chamber 20 through a gas distributor 30. The process gas may be energized by inductive coupling to form a plasma in the upper portion 22, using, for example, an inductor coil 35 wound around the chamber 20. Alternatively or in addition, energy may be capacitively coupled to the process gas by process electrodes 40a, 40b in the chamber 20. An exhaust 45 is provided for withdrawing spent process gas and process gas byproducts from the process chamber 20 and for generating a low pressure in the chamber 20.

The apparatus 10 may also include an electrostatic chuck 50 to hold the substrate 15 during processing of the substrate 15. A typical electrostatic chuck 50 comprises an electrostatic member 55 including one or more electrodes 60 at least partially covered by a dielectric material. The chuck 50 is secured .to a support 65 in the process chamber 20. An electrical connector 70 electrically connects the electrodes 60 in the chuck to a conventional electrostatic chuck power source 75 suitable for powering the chuck.

In energized gas processes, a substrate 15 is placed on the support 65 and the electrostatic chuck 50 is electrically biased with respect to the substrate 15 by the chuck power source 75. Process gas is introduced into the process chamber 20 via the gas distributor 30. A plasma can be inductively formed from the process gas by applying a high frequency RF source current to the inductor coil 35 using a plasma power source 80, and/or capacitively formed by applying a high frequency RF current to the process electrodes 40a, 40b using a bias power source 82. In one version, the electrode 60 in the electrostatic chuck 50 may be used as one of the process electrodes 40a. The RF frequencies used to inductively or capacitively form the plasma and attract the plasma to the substrate 15, are typically above 1 .5 MHz, and more typically from about 1 .8 MHz to about 60 MHz. In plasma processes, the voltage applied to the electrode 60 of the chuck 50 causes electrostatic charge to accumulate in the electrode, and the plasma in the chamber 20 provides electrically charged species having opposing polarity which accumulate in the substrate 15. The accumulated opposing electrostatic charge results in an attractive electrostatic force between the substrate 15 and the electrode 60 in the chuck 50, causing the substrate 15 to be electrostatically held to the chuck 50. Bipolar chucks having two electrodes (not shown) operate by electrically biasing the two electrodes with respect to one another to generate an electrostatic charge that holds the substrate 15 to the chuck 50. In alternative chamber versions (not shown), the capacitively generated plasma can also be enhanced by electron cyclotron resonance or magnetically enhanced by a magnetic field generator, such as a permanent magnet or an electromagnetic coil, which provide a magnetic field that may increase the density and uniformity of the plasma in the plasma zone. The magnetic field may also comprise a rotating magnetic field with the axis of the field rotating parallel to the plane of the substrate 15.

The lower portion 24 of the process chamber 10 comprises a lift pin assembly 85 that may be used to lift and lower the substrate 15 onto the electrostatic chuck 50. In the version shown in Figure 1 , the lift pin assembly 85 comprises a support 90, such as, for example, a C-shaped ring, with a plurality of lift pins 95 mounted around the support 90. The lift pin assembly 85 may comprise a plurality of lift pins 95, such as for example three or four, which are mounted symmetrically on the support 90 so that the substrate 15 can be lifted off the chuck 50 by a uniformly applied pressure. The support 90 is attached to lift bellows 100 that can lift and lower the support 90, thereby lifting and lowering the lift pins 95 through the holes in the chuck 50, which in turn lift and lower the substrate 15 off the chuck 50. A lift pin 95 for dechucking a substrate 15 on a support 65 is shown in Figure 2. In one version, the lift pin 95 is able to dechuck a substrate 15 held to a chuck 50 by residual electrostatic charge, by passing the charge to a current sink 105. Generally, the lift pin 95 comprises a movable elongated member 1 10. Optionally, the member 1 10 may have a tip 1 15 suitable for lifting and lowering the substrate 15 off the chuck 50. When multiple lift pins are provided on the lift pin assembly 85, at least one lift pin 95 is capable of forming an electrically conductive path 120 between the substrate and the current sink 105. An RF voltage reducer 125, such as for example a resistor having a resistance of from about 1 MΩ to about 10 MΩ, is coupled in series along the electrically conductive path 120 of the elongated member 1 10. The resistor 125 allows substantially all the residual electrostatic charge in the substrate 15 to flow therethrough, substantially without allowing RF currents, used to form a plasma in the process chamber and to attract the plasma to the substrate, from flowing to the current sink 105. Thus, the undesirable RF propagation through the lift pins which can result in plasma formation in the lower portion of the chamber and cause deposits to form on the support components is substantially avoided, as discussed in U.S. Patent 5,900,062 which is incorporated herein by reference in its entirety.

To dechuck a substrate 15 held to an electrostatic chuck 50 by low frequency electrostatic residual charge, the lift pins 95 are raised and electrically contact the substrate 15. When a resistor 125 is used, the residual electrostatic charge in the substrate 15 discharges to the current sink 105, white the passage of voltage caused by the high frequency RF currents used to generate or attract the plasma to the substrate, is substantially reduced, thereby resulting in substantially no plasma formation in the lower portion of the chamber. The substrate 15 is lifted off the chuck after the residual electrostatic charge in the substrate 15. is substantially discharged. The lift pins 95 may be continuously raised in an upward direction while the residual electrostatic charge in the substrate 15 is discharging to the current sink 105 to speed process throughput. Thus, the residual charge in the substrate 15 may be discharged to the current sink 105 in a sufficiently short time that the substrate 15 is released from the chuck 50 without breaking, while the lift pins move in an upward direction. In one version, the lift pin 95 comprises an elongated member 1 10 comprising an electrically conductive upper portion 130, a central portion 135 comprising the resistor 125, and an electrically conductive lower portion 140 suitable for electrical connection to the current sink 105, as shown in Figure 2. The electrically conductive upper portion 130 and lower portion 140 are made from metals or other rigid conductive materials having low resistance to current flow. The upper portion 130 can also comprise a layer of a flexible material that prevents damage to the substrate 15 when the lift pins 95 are pushed upwardly against the substrate 15.

In one version a central portion 135 of the lift pin 95 comprises a rigid electrically insulative shell sized to house the resistor 125. The insulative shell is mechanically connected to the upper portion 130 and the lower portion 140 so that the lift pin 95 can withstand a load when lifting the substrate 15 from the chuck 50. The insulative shell may be made from any electrically insulative polymer, such as polyimide, polyketone, polyetherketone, polysulfone, polycarbonate, polystyrene, nylon, polyvinylchloride, polypropylene, polyetherketones, polyethersulfone, polyethylene terephthalate, fluoroethylene propylene copolymers, silicone, and rubber. The insulative shell may be resistant to temperatures in excess of 50°C, or in excess of 100°C, or even in excess of 300°C, so that the lift pin 95 can be used for high temperature processes. Typically, the insulative shell has a resistivity ranging from about 10'³ Ω cm to 10²⁰ Ω cm. The thickness of the insulative shell is typically from about 1 mm to about 5 mm.

In one version, the resistor 125 comprises a resistor coupled in series with the electrically conductive path 120 defined by the lift pin 95. The resistor 125 has a resistance sufficiently elevated to reduce the voltage caused by the RF currents flowing therethrough by at least about 50%, and more preferably at least about 75%. The resistor 125 has a resistance sufficiently elevated that the resistor is capable of discharging residual electrostatic charge in the substrate while causing a drop in voltage of the RF currents used to generate the plasma or attract the plasma to the substrate, to a voltage level sufficiently low that the high frequency RF currents do not form a plasma in lower portions of the chamber. The resistance of the resistor 125 affects the length of time taken for discharge of the residual electrostatic charge in the substrate 15. This occurs because the resistor 125, substrate 15, and the chuck 50, form an RC circuit having a time constant R*C seconds, where C is capacitance in farads, and R is resistance in Ω. The time constant is the number of seconds required for the capacitor to reach about 63% of its full charge after a voltage is applied. Thus, depending on the capacitance of the substrate 15 and chuck 50, the value of the resistor is selected to obtain the desirable time constant as limited by the speed with which the lift pin 95 lifts the substrate 15 off the chuck 50. Typically, the electrostatically charged substrate 15 and chuck 50 form a capacitor having a capacitance of about 1 ,000 pF.

To determine a suitable resistance value for the resistor, the RC time constant equation is solved to determine the resistance value equal to the ratio of a desired time constant to the capacitance. Preferably, the resistance of the resistor at least about .5 MΩ, and more preferably from about 1 MΩ to about 100 MΩ, and most preferably from about 1 MΩ to about 10 MΩ, to achieve a 10 millisecond discharge period.

Selection of the type of resistor depends on the operating frequencies of the RF currents and the residual electrostatic charge in the substrate 15. Resistors change in their resistance value when subjected to RF alternating currents. The change in resistance with increasing frequency occurs because resistors have some inductance and capacitance in addition to the resistive component. The effect of frequency on resistance varies with the resistor construction. Wire-wound resistors typically exhibit an increase in their impedance with frequency. In composition resistors, capacitances are formed by the many conducting particles which are held in contact by a dielectric binder. Film resistors have the most stable RF performance, with their AC impedance remaining constant until about 100 Hz and decreasing at higher frequencies, and their decrease in DC resistance at higher frequencies decreasing for increasing resistances. Also, the smaller the diameter of the resistor, the better is its frequency response. Most RF resistors have a length to diameter ratio of 1 :4 to 10: 1 .

In another version,- such as the version shown in Figure 3, the resistor 125 comprises a body 126 comprising semiconducting material. The semiconducting material has a resistance selected so that the lift pin 95 can discharge residual electrostatic charge in the substrate 15 while reducing the amplitude of RF currents flowing therethrough to a level sufficiently low that the RF currents passed through do not form a plasma in the lower portions of the chamber 20. The path length and resistance of the semiconducting material is selected to operate as a resistor, as described above. For example, the semiconducting material may be sufficiently thick to provide an effective resistance to a current flowing therethrough of at least about .5 MΩ, and more preferably from about 1 MΩ to about 10 MΩ, and most preferably about 10 MΩ. In one version, the semiconducting material has a resistance that is sufficiently elevated to reduce the amplitude of the RF currents flowing therethrough by at least about 50%, and more preferably at least about 75%.

Figures 4 and 5 show different versions of lift pins 95 comprising bodies 126 comprising semiconducting material. As shown in Figure 4, the lift pin 95 may comprise a solid body of semiconducting material making up the resistor 125. The version of Figure 4 is relatively easy to manufacture and possesses high strength. As shown in Figure 5, the body of semiconducting material may comprise a hollow section 150. The hollow section 150 allows for tailoring of resistance values and also allows for the installation of other electronic devices or features within the lift pin 95, if desired. In the versions shown in Figures 4 and 5, the lift pin 95 may be provided with an electrically conductive upper portion and/or an electrically conductive lower portion or the entire lift pin 95 may comprise semiconducting material. Alternatively, . spaced semiconducting portions can be connected by conducting portions. In another version, the resistor 125 comprises a combination of a conventional resistor in series or in parallel with a semiconducting material.

By "semiconducting material" it is meant a material whose electrical . conductivity is intermediate between that of a metal and an insulator. For example, the electrical conductivity of a semiconducting material may be from about 10³ to about 10^'9 ohm^"1 cm^"1. Suitable semiconducting^' materials include silicon carbide, titanium diboride, titanium oxide, aluminum nitride, silicon, germanium, tellurium and combinations thereof and any other material that can .be doped to form a semiconductor material. Conventional ceramic casting, molding, . and pressure-forming processes can be used, to fabricate a semiconductor structure shaped like the lift pin 95. For example, a semiconducting lift pin 95 can be fabricated by forming a slurry of silicon carbide and pouring the slurry into a mold corresponding to the desired shape of the lift pin 95. After drying the component, the silicon carbide lift pin 95 is fired to a temperature sufficiently elevated to sinter the silicon carbide to form a hard semiconductive silicon carbide lift pin 95. Conventional machining techniques can be used to shape, smooth, or machine holes in the lift pin 95 so that the lift pin can be attached to the support 90. Mixtures of ceramic insulative powders and conductive metal powders can also be used to provide the desired resistance for the semiconductor material.

In an exemplary version, the lift pin 95 comprises a solid body 126 comprising silicon carbide having a resistance of 1 to 10 mega ohms. Lift pins 95 comprising a solid semiconducting material remove the need for additional components, which can make the system more reliable.

The resistor 125 may also comprise a resistive-inductive circuit that includes a combination of an inductor and a resistor, coupled in series with the electrically conductive path 120. The inductance of the inductor, and the resistance of the resistor, are selected to provide a combination resistive-inductive circuit having the desired characteristics as described above. For example, the resistance of the resistor may be from about 100 kΩ to about 100 MΩ, and more preferably from about 10 MΩ to about 100 MΩ, and the inductance values for the inductor is from about 10 μ to about 1000 μH , and more preferably from about 100 μH to about 500 μH, to achieve a 10 millisecond discharge period.

While the present invention has been described in considerable detail with reference to certain preferred versions, many other versions should be apparent to those of ordinary skill in the art. For example, the support may be used in other substrate processing chambers. Therefore, the spirit and scope of the appended claims should not be limited to the description of the preferred versions contained herein.

Claims

What is claimed is:

1 . A lift pin capable of dechucking a substrate on a support in a chamber, the lift pin comprising: a body comprising semiconducting material.

2. A lift pin according to claim 1 wherein the semiconducting material is sufficiently thick to provide a resistance over the length of the lift pin of at least about 0.5 MΩ.

3. A lift pin according to claim 1 wherein the semiconducting material is sufficiently thick to provide a resistance over the length of the lift pin of from about 1 MΩ to about 10 MΩ.

4. A lift pin according to claim 1 wherein the semiconducting material is sufficiently doped to provide a resistance over the length of the lift pin of at least about 0.5 MΩ.

5. A lift pin according to claim 1 further comprising a conductive upper portion and a conductive lower portion connected to the body.

6. A lift pin according to claim 1 wherein the semiconducting material comprises silicon carbide.

7. A lift pin according to claim 1 wherein the semiconducting material comprises titanium diboride.

8. A lift pin according to claim 1 wherein the body comprises a unitary piece of semiconducting material.

A lift pin according to claim 1 wherein the body is solid.

1 0. A lift pin according to claim 1 wherein the body is hollow.

1 1 . A substrate processing chamber comprising: a substrate support comprising an electrode, a dielectric at least partially covering the electrode, and a lift pin comprising a semiconducting material; a gas distributor; a gas energizer; and a gas exhaust, whereby a substrate received on the support may be processed by gas introduced through the gas distributor, energized by the gas energizer and exhausted by the gas exhaust and may thereafter be dechucked by the lift pin.

12. A substrate processing chamber according to claim 1 1 wherein the lift pin is adapted to provide an electrically conducting path between the substrate and a current sink.

1 3. A substrate processing chamber according to claim 1 1 wherein the semiconducting material is sufficiently thick to provide a resistance over the length of the lift pin of at least about 0.5 MΩ.

1 . A substrate processing chamber according to claim 1 1 wherein the semiconducting material is sufficiently thick to provide a resistance over the length of the lift pin of from about 1 MΩ to about 10 MΩ.

15. A substrate processing chamber according to claim 1 1 wherein the semiconducting material is sufficiently doped to provide a resistance over the length of the lift pin of at least about 0.5 MΩ.

16. A substrate processing chamber according to claim 1 1 wherein the semiconducting material comprises silicon carbide.

17. A substrate processing chamber according to claim 1 1 wherein the semiconducting material comprises titanium diboride.

18. A substrate processing chamber according to claim 1 1 wherein the lift pin is formed from a unitary piece of semiconducting material.

1 9. A method of dechucking a substrate in a chamber, the method comprising: providing a support in the chamber, the support comprising a lift pin comprising semiconducting material; supporting the substrate on the support; and moving the lift pin to contact the substrate.

20. A method according to claim 1 9 comprising supporting the substrate on the support by generating an electrostatic chucking force.

21 . A method according to claim 20 comprising flowing residual electrostatic charge from the substrate through the lift pin to a current sink.

22. A method according to claim 1 9 wherein the semiconducting material is sufficiently thick to provide a resistance over the length of the pin of at least about 0.5 MΩ.

23. A method according to claim 1 9 wherein the semiconducting material comprises silicon carbide.

24. A method according to claim 1 9 wherein the semiconducting material comprises titanium diboride.

25. A method of processing a substrate in a chamber, the method comprising: providing a support in the chamber, the support comprising an electrostatic chuck and a lift pin comprising semiconducting material; generating an electrostatic chucking force to support the substrate on the support; providing energized process gas in the chamber; and moving the lift pin to contact the substrate to dechuck the support.

26. A method according to claim 25 comprising flowing residual electrostatic charge from the substrate through the lift pin to a current sink.

27. A method according to claim 25 wherein the semiconducting material is sufficiently thick to provide a resistance over the length of the pin of at least about 0.5 MΩ.

28. A method according to claim 25 wherein the semiconducting material comprises silicon carbide.

29. A method according to claim 25 wherein the semiconducting material comprises titanium diboride.

30. A method of fabricating a lift pin usable in a substrate support in a chamber, the method comprising: providing a body comprising semiconducting material and forming the body into the lift pin.

31 . A method according to claim 30 wherein the body is formed from a unitary piece of semiconducting material.

32. A method according to claim 30 comprising forming an electrically conducting upper portion and an electrically conducting lower portion on the body.

33. A method according to claim 30 comprising providing sufficient semiconducting material to provide a resistance over the length of the lift pin of at least about 0.5 MΩ.

34. A method according to claim 30 comprising doping the semiconducting material sufficiently to provide a resistance over the length of the lift pin of at least about 0.5 MΩ.