WO1999001888A1

WO1999001888A1 - Apparatus and method for uniform, low-damage anisotropic plasma processing

Info

Publication number: WO1999001888A1
Application number: PCT/US1998/014014
Authority: WO
Inventors: Kaihan Abidi Ashtiani; James Anthony Seirmarco
Original assignee: Tokyo Electron Arizona, Inc.
Priority date: 1997-07-02
Filing date: 1998-07-02
Publication date: 1999-01-14
Also published as: JP2001500322A; US6083363A

Abstract

An apparatus and method for processing the surface of a substrate with a plasma formed from a process gas comprises a processing chamber (10) defining a plasma source region (12) and a processing region (14) wherein electrical energy is coupled into the source region (12) to form and sustain a plasma therein, and an ion extraction mechanism (52) positioned between the source region (12) and processing region (14) for extracting ions (57) from the plasma and directing extracted ions (57) and neutral particles (72) into the processing region (14) to process a biased substrate (18) therein. A gas-dispersing element (24) in the processing space (149 disperses a process gas to intersect paths of the extracted ions (57) and to produce charge exchange collisions to create a large number of high-energy neutral particles (72) for processing the workpiece. A radiation-blocking apparatus (80) is positioned between the plasma source region (12) and processing region (14) proximate the ion extraction mechanism (52) and is operable for absorbing damaging radiation produced by the plasma to reduce radiation damage to the substrate (18).

Description

APPARATUS AND METHOD FOR UNIFORM, LOW-DAMAGE ANISOTROPIC PLASMA PROCESSING

FIELD OF THE INVENTION

The present invention relates to plasma processing for integrated

circuit (IC) fabrication, and more specifically, to a method and apparatus for

uniform, low-damage anisotropic processing of a substrate for the production

of VLSI and ULSI circuits.

BACKGROUND OF THE INVENTION

In the processing of semiconductor substrates, or wafers, into

integrated circuits (IC), gaseous plasmas are widely utilized. For example,

gaseous plasmas are used to process substrates via etching, deposition, or

other similar such procedures. One such plasma procedure which has found

increasing application in semiconductor processing, particularly in IC

fabrication such as ion implantation, sputter etching, and deposition, is a

procedure which utilizes a high-density plasma source for yielding fast

processing rates. High-density plasmas are desirable in the manufacturing of very large scale integrated "VLSI" and ultra large scale integrated "ULSI"

circuits, having diameters up to 300 mm.

For high-density plasma processing, the substrate is positioned in a

chamber on an electrically charged support base or electrode for biasing the

substrate. The chamber is vacuumed to a low pressure, such as 50 mTorr

or less. A process gas or work gas is then introduced into the chamber

opposite the biased substrate. RF energy is inductively coupled to the gas

for example, utilizing an induction coil coupled to an RF power supply. The

induction coil creates a time-varying magnetic field around itself at the

frequency of the applied RF energy, and the magnetic field in turn induces an

electric field in the chamber. The energy from the induced electric field

inside the chamber ionizes the process gas particles to form a gaseous

plasma (or glow discharge) which comprises, among other particles,

positively charged ions of the process gas. A negatively biased substrate

collects the positively charged ion particles from the plasma to process the

wafer, such as through etching or deposition. For example, the positively

charged plasma ions might be attracted to the negatively biased substrate

surface to bombard the surface and dislodge material particles from the

substrate to thereby sputter etch a material layer from the substrate surface.

Notwithstanding the increased popularity of high-density plasma

sources and their increased application to semiconductor processing, existing

high-density plasma apparatus and methods have several drawbacks. For

example, semiconductor wafers processed utilizing high-density plasmas are

particularly sensitive to ion damage associated with the high energy of the

ion particles bombarding the surface of the substrate. High-energy ions may implant into the surface of the substrate to an undesirable degree or may

create charge flow within the IC devices being processed on the substrate,

thus damaging those devices or changing their conductive characteristics.

Such ionic damage is exacerbated by the high density of the plasma.

Therefore, it is desirable to reduce the damage of the substrate attributable

to ionic bombardment and charging in high-density plasmas.

Another drawback of high-density plasmas is the large amount of

ultraviolet (UV) radiation which is generated by the plasma. UV rays of the

plasma strike the substrate and enter the oxide layers of the substrate to

create charges which may migrate into the gate regions of the IC devices.

Alternatively, the charges might actually be created in the gate regions of the

devices by the radiation. The created charges degrade the gate regions and

may change the electrical characteristics of the device. Furthermore, the

undesirable UV radiation may create charges which migrate to or are located

in the interfaces of the devices to create undesirable interfacial charge states

which also change the electrical characteristics of the device. Still further,

minority carrier action is changed by the damaging radiation which further

degrades the characteristics of the IC devices and the yield from the

processed substrate. Accordingly, it is desirable to reduce the effect of the

damaging UV radiation, and other radiation from the high-density plasma.

As with most plasma applications, particularly plasma etching, it is

desirable to control the plasma to further control the etch and direct the etch

where it is required on the substrate. To that end, it is also desirable to

directionalize the etch produced from high-density plasmas for advanced

etching applications. Such directed or focused processing, referred to as anisotropic processing, is particularly applicable for narrow, high-aspect ratio

structures which need to be etched for subsequent deposition thereon. The

vertical characteristics of anisotropic etching allow deeper, cleaner etching

of narrow circuit structures. Therefore, anisotropic processing for the

manufacturing of VLSI and ULSI circuits is certainly a desirable feature for

high-density plasma processing.

Accordingly, it is an objective of the present invention to provide low-

damage processing of semiconductor materials for forming VLSI and ULSI

circuits.

Another objective of the present invention is to provide a uniform,

high-density plasma which may be utilized for high rate processing of VLSI

and ULSI circuits without subsequent damage of the devices therein.

It is another objective of the present invention to provide a high-

density, anisotropic plasma for directional etching of narrow, high aspect

ratio structures on a substrate.

It is still a further objective of the present invention to utilize a high-

density plasma source while reducing radiation damage of the devices on the

substrate being processed.

It is a further objective of the present invention to reduce the ion

damage of substrates processed utilizing high-density plasmas. SUMMARY OF THE INVENTION

The present invention addresses the above-discussed objectives and

provides low-damage processing of semiconductor materials utilizing a

uniform, high-density plasma. The present invention reduces radiation

damage of semiconductor devices and provides a high-density, anisotropic

plasma for directional etching of narrow, high-aspect ratio IC structures.

More specifically, the invention comprises a processing chamber

defining a plasma source region and a plasma processing region therein,

wherein the plasma processing region is located downstream of the source

region. The processing region includes a susceptor or other mounting

structure for supporting a workpiece or substrate within the processing

chamber. Process gas is introduced into the source region, and electrical

energy is coupled into the source region to form and sustain a plasma

therein. In a preferred embodiment of the invention, electrical energy is

inductively coupled into the source region utilizing a RF biased coil proximate

the source region and an adjacent dielectric window for passing the inductive

energy into the source region.

An ion extraction mechanism is positioned between the source region

and the processing region and is operable, when biased with electrical

energy, for extracting ions from the plasma in the source region and directing

high-energy extracted ions into the processing region for bombarding the

substrate for etching. The ion extraction mechanism, in one embodiment,

comprises a conductive plate, such as a stainless steel plate, having a

number of small apertures formed therein to allow for passage of plasma

species from the source region to the processing region. A DC power supply can be used to negatively bias the extraction plate. The apertures of the

plate are dimensioned to interfere minimally with the plasma particles so that

a suitable amount of the ions extracted from the source region are delivered

to the processing region to process the substrate. Alternatively, the ion

extraction mechanism may comprise a set of conductive wires, such as

stainless steel wires, cross-meshed to form a grid. In the embodiment, the

grid hole size of the ion extraction mechanism is sufficiently large so as not

to interfere substantially with the plasma to allow for free passage of plasma

species therethrough into the processing region. The grid can also be

negatively biased with a DC power supply. Preferably, the grid or plate is

generally planar and is positioned in between the source region and

processing region, generally parallel to the substrate being processed. The

substrate is DC or RF biased, or pulsed, for attracting the extracted ions. To

further focus, intensify, and direct the plasma, magnetic bucket structures

might be utilized around the source region.

In accordance with another aspect of the present invention, the

population of high-energy directed neutral species available for etching of the

substrate is increased. To that end, the invention further comprises a gas-

dispersing element positioned in the processing space downstream of the

plasma source region and downstream of the ion extraction mechanism. The

gas-dispersing element, such as a gas feed ring, disperses a process gas into

the processing region to intersect the paths of the high-energy extracted ions

which are traveling to the biased substrate. The charge-exchange collisions

between the introduced neutral process gas particles and the high-energy

ions in the processing region produce a population of directed neutral particles which are generally perpendicular to the substrate surface.

Therefore, the processing, such as etching, of the substrate is highly

directionalized or anisotropic. Thereby, the invention provides anisotropic

and directional etching which is particularly suitable for narrow, high-aspect

ratio IC structures.

In accordance with another aspect of the present invention, a radiation

blocking apparatus, and preferably a radiation blocking plate, is positioned

between the plasma source region and the processing region. In the

preferred embodiment, the radiation blocking plate is positioned generally

parallel to, and between, the ion extraction mechanism and the substrate

being processed. The radiation blocking plate has a plurality of apertures

formed therein for passing plasma from the source region and into the

processing region, while absorbing plasma radiation. The plate is formed of

a radiation absorbing material, such as quartz, and is operable for absorbing

radiation generated by the plasma, such as X radiation and UV radiation. By

reducing the exposure of the devices on the substrate to the plasma

radiation, damage to the devices being processed is reduced. The blocking

plate preferably interferes with the extracted plasma particles very minimally.

The present invention thus provides plasma processing utilizing a high-

density and directional plasma while reducing damage to the substrate or

workpiece attributable to high-energy ions and plasma radiation. The

directional or anisotropic processing of the present invention is particularly

useful for etching of narrow high-aspect ratio structures. The invention is

particularly suitable for sputter etching, but may also be utilized for reactive

etching and/or deposition. Further objectives of the present invention and its improvements over the prior art will become more readily apparent from the

detailed description hereinbelow.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute

a part of this specification, illustrate embodiments of the invention and,

together with a description of the invention given below, serve to explain

the principles of the invention.

Figure 1 is a schematic cross-sectional view of the reaction chamber

of the present invention.

Figures 2A and 2B are partial cross-sectional views of apparatus for

biasing an inductive coil used in one embodiment of the present invention.

Figure 3 is a cross-sectional view of a magnetic bucket for directing

the plasma from a source region to a processing region to process a

substrate in accordance with the principles of the invention.

Figure 4A is one embodiment of an ion extraction mechanism of the

present invention while 4B is an alternative embodiment of the plasma

extraction mechanism of the invention.

Figure 5 is a cross-sectional view of another invention embodiment. DETAILED DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates one embodiment of the inventive apparatus for

processing a semiconductor substrate utilizing a high-density plasma in

accordance with the principles of the present invention. The apparatus

includes a processing chamber 10 appropriately formed of a non-magnetic

material, such as aluminum, for producing a vacuum environment and containing a plasma therein to process a substrate. The processing chamber

1 0 defines a plasma source region 1 2 and a processing region 14, which is

downstream from the source region. Processing region 14 includes a

susceptor or other substrate support 1 6 for supporting a workpiece or

substrate 1 8, such as a semiconductor wafer. Susceptor 1 6 may be

stationary or rotating and should secure the substrate 1 8 thereon, such as

by physical clamping or a non-clamping device such as an electrostatic

chuck, both of which are known in the art. Substrate 18 is maintained in the

processing region 14 with an upper surface 20 generally facing source region

1 2. Susceptor 1 6 is preferably coupled to an RF power source 22 for biasing

substrate 1 8 for processing as discussed further hereinbelow.

For processing substrate 18, process gas or plasma gas, such as

Argon, is introduced into the source region 1 2 through an appropriate

mechanism, such as a gas feed ring 24, which encircles the source region

generally around an upper portion thereof. Feed ring 24 has a plurality of

passages (not shown) formed therearound for directing process gas into the

source region as indicated by arrows 25. Once plasma gas is introduced into

source region 1 2, electrical energy is coupled into the source region for

exciting the gas into a plasma discharge containing a plurality of positively

charged ions, free electrons, and other plasma species. In a preferred

embodiment of the invention, the electrical energy is preferably inductively

coupled into source region 1 2 by an RF-biased coil structure which has a

number of concentric loops forming a spiral or multiple spirals. There are

suitable examples of such RF coils illustrated and disclosed in U.S. Patent

No. 5,556,521 , and U.S. Patent Application Ser. No. 08/624,010, which is co-pending herewith, both patent and application being co-owned with the

present application, and both patent and application being incorporated

herein by reference in their entireties. Such inductively coupled plasmas

have a high density and are finding increasing application for fast rate

processing, which is desirable in the manufacturing of VLSI circuits and ULSI

circuits. The plasmas are generally very uniform and thus are suitable for

providing a uniform etch or deposition over the substrate surface being

processed.

Inductive coil 26 is biased by an RF power supply 28, which is

coupled to the coil through a match/tuner network 30. The RF power supply

28 may be operated in pulse or continuous mode and the match/tuner

network 30 provides for maximum power transfer from the power supply to

the coil 26. Frequency range of supply 28 can vary from 1 -1 3.56 MHZ,

although higher and lower frequencies may also be applicable. The plasma

density created as the result of the RF power will vary depending on the

frequency of the operation.

Inductive coil 26 may be a single spiral coil wherein a two lead (RF and

ground connection) network is utilized, as illustrated in Figures 1 and 2A,

with the RF connection coupled to an inward end 31 of the spiral (shown in

cross-section) and a ground connection to an outer end 33 of the spiral.

Alternatively, as illustrated in Figure 2B, the coil might include multiple

spirals, as illustrated in U.S. Patent Application Ser. No. 08/624,010, which

is biased by a three lead, symmetrically fed system (two RF and one ground

connection). Referring to Figure 2B, the RF power supply 28 and

match/tuner network 30 are coupled to inward ends 34a, 34b of the adjacent spirals 36a, 36b, and a ground connection is provided to a point on

a connecting leg 37 between the adjacent coils 36a, 36b. Alternatively, a

shaped coil might be utilized as disclosed in U.S. Patent No. 5,556,521 . In

any case, the coil 26 provides a high-density plasma in the source region 1 2

for processing a substrate.

For efficient transfer of inductive RF energy into source region 12, the

top portion of chamber 10 is terminated by a dielectric plate or window 40.

The dielectric window 40 is made of quartz or some other suitable dielectric

material which is transparent to RF fields from coil 26. The RF field from the

coil 26 propagates through the window 40 and into the source region 1 2 of

chamber 10. One particular dielectric window of the present invention might

be a shaped window as illustrated and disclosed in U.S. Patent No.

5,556,521 . Alternatively, other shaped windows, such as a flat window 40

as shown in Figure 1 , might be utilized.

A process or working gas (e.g., Argon, Neon, CF₄, C₂F₆, O₂, H₂, or a

combination thereof) is supplied to source region 12 via the gas feed ring 24.

The preferable inside diameter of the chamber might vary from approximately

4 inches to approximately 20 inches, depending upon the application and the

operating pressure that is desired. The processing region is generally larger

than the plasma region. A suitable vacuum pressure is created within

chamber 10 by a vacuum pump system 42 coupled to chamber 10 proximate

processing region. For high-density plasmas like that yielded by the present

invention, low pressures, often less than 20 mTorr, are desired. Accordingly,

vacuum pump system 42 is operable for yielding such low pressures in the chamber. To achieve a radially uniform plasma density profile in source region

12, a large diameter source region is desirable. However, as the source

region diameter is increased, its volume is increased, and therefore, more

power is needed to achieve a desired plasma density. In order to improve the

plasma confinement and increase its density in the source region, a magnetic

structure or magnetic bucket 44 may be utilized. The magnetic bucket 44

surrounds a portion of the outside of chamber 10 proximate plasma source

region 1 2. Since chamber 1 0 is non-magnetic, the magnetic bucket will

affect the plasma in source region 1 2. One suitable example of such a

magnetic bucket 44 is a magnetic multi-polar structure having vertically

aligned, elongated magnetic regions with the aligned regions being of

alternating polarities around the circumference of the bucket. Such a

structure, is more particularly disclosed in co-pending U.S. patent application

08/624,010. Utilizing such a magnetic multi-polar bucket, the residence time

of the electrons in the source region is increased, and their loss rate is

reduced. The reduced loss rate increases the plasma density near the

boundaries of coil 40 where the plasma density tends to be thinnest. The

increased plasma density at the boundaries yields better plasma uniformity

and better process uniformity.

An alternative embodiment of the magnetic bucket is illustrated in

Figure 3. Bucket 46 includes a set of circular conductor loops 48 surrounding

source region 1 2. Current is directed through the conductor loops 48 by an

energy source (not shown) and a magnetic field as indicated by field lines 50

is formed in the source region 1 2. The conductor loops 48 of bucket 46 are

biased such that the field lines magnetically confine the plasma and direct the ionized plasma species toward the downstream processing region 14. Bucket

46 improves the extraction of the plasma ions from the source region and

delivery into the processing region and generally enhances the ion extraction

of the invention as discussed in greater detail hereinbelow.

A magnetic bucket, or other magnetic structure, might also be utilized

proximate a portion of the chamber 10 downstream from the plasma source

region 1 2, such as proximate processing region 14. The bucket 45

influences the plasma in the processing region proximate substrate 1 8 to

provide for improved plasma uniformity and extraction of plasma ions.

Alternatively, the separate buckets proximate different portions of the

chamber might be combined into a unitary structure.

In accordance with the principles of the present invention, an ion

extraction mechanism 52 is utilized for extracting ions from the plasma in

source region 1 2 and delivering the ions to the processing region 1 4 to

process substrate 1 8. Referring to Figure 4, one embodiment of the

extraction mechanism of the invention comprises a conductive plate 54

having a plurality of apertures 55 formed therein for passing plasma from

source region 1 2 to processing region 14 through plate 54. Plate 43 is

preferably thin and has a thickness dimension of approximately 0.25-5 cm.

The diameter dimensions of the plate will depend upon the dimensions

of the source region 1 2 in the chamber 10. For example, a suitable diameter

for a circular plate might be the same as that of the chamber, although the

shape of plate 54 might be other than circular as illustrated.

The shape of the apertures 55 may be circular or can be of any other

suitable shape, such as square or polygonal. The conductive plate 54 is preferably coupled to a DC power supply 56, which can be operated in a

unipolar or bipolar mode for applying a net negative voltage to the plate. The

negatively biased plate 54 attracts the positively biased plasma ions 57 from

a plasma in source region 12 and propels the ions toward substrate surface

20 to process the surface. After passing through the plate, the ions have a

substantial amount of energy as they enter processing region 14 and possibly

impinge upon or bombard substrate surface 20. The ion extraction

mechanism, such as plate 54, is made of a conductive material which

preferably has a low sputtering yield to prevent excess sputter etching of it

during extraction of ions 57 from the plasma in source region 1 2. For

example, the plate 54 may be formed of stainless steel with a number of

small apertures 55 bored therein to allow for the passage of plasma species

to the processing region. Preferably, the sizes of the apertures 55 in the ion

extraction mechanism should be larger than a plasma Debye length, or a

diffusion length of the plasma, so that the extraction mechanism 52 does not

substantially interfere with the plasma and instead allows for free passage of

the plasma species therethrough. The size of the apertures will thus depend

upon the plasma density.

Figure 4B illustrates an alternative embodiment of the plasma

extraction mechanism 52. An extraction grid 58 is formed from a plurality

of cross-meshed stainless steel wires 59, which define a plurality of openings

60 therein for passing plasma from the source region through the grid and

into the processing region 14. The grid is preferably planar and the openings

60 will be dimensioned as discussed above. In yet another embodiment, a number of extraction plates can be used

in a parallel, stacked formation in such a manner that each plate is biased at

a different potential. For example, in a 3-plate extraction mechanism, the

first plate can be grounded, the second positively biased, and the third

negatively biased (see Figure 5).

Referring to Figure 5, the invention might utilize a plurality of elements,

such as a plurality of plates and grids, positioned in a stacked formation

between the source region 1 2 and processing region 14. For example,

elements 80, 82, and 84 may be positioned one over the other and generally

parallel to one another as shown in Figure 5. Furthermore, the elements may

be electrically biased differently from one another with at least two of the

elements having different potentials. For example, element 80 might be

grounded, element 82 might be positively biased, and element 84 might be

negatively biased.

in accordance with one aspect of the ion extraction mechanism 52 of

the present invention, the biased mechanism extracts ions from source region

1 2 and delivers them at high energy to the processing region 14 for

processing substrate 18. In addition, charge-exchange collisions between the

extracted ions and neutral particles of the processing gas in the processing

chamber produce a population of directed neutral particles which bombard

surface 20 of substrate 1 8, and in accordance with one aspect of the

invention, may be utilized to etch surface 20.

For further control of the energy level of the plasma process at surface

20, wafer support 1 6 is coupled to RF power supply 22 and applies a bias

to substrate 18 to control the plasma ion energy delivered thereto. RF power supply 22 is coupled to substrate support 1 6 through a match/tuner network

23 for efficient RF power coupling to the substrate. RF power supply 22 may

be pulsed or continuous, as desired, for use in the present invention.

Substrate 1 8 may also be coupled through support 1 6 to a unipolar or

multipolar DC biased power supply (not shown), in which case a match/tuner

network 23 might not be necessary. The RF power supply frequency can

take a value from well below the ion plasma frequency to well above the ion

plasma frequency, depending upon the application. The purpose of either a

DC or RF power supply is to induce a net negative voltage on the substrate

such that ion energies are controlled as they arrive to substrate surface 20.

The present invention is suitable for a number of different etching

processes, such as reactive etching or sputter etching, and may be utilized

to provide a low-damage and highly directional or anisotropic etch of

substrate surface 20. For reactive processing, such as a plasma-enhanced

reactive etching, an inert gas such as argon can be fed into the source region

1 2 to create a dense plasma therein. The ions of the plasma are then

extracted and a second reactant gas is introduced into the downstream

processing region. For doing so, processing chamber 10 includes another gas

feed system, which is a gas feed ring 70, for introducing the reactant gas.

The plasma provides energy to the reactive gas and reaction process on

surface 20 to etch the surface as is well known in the art.

Plasma processing chambers generally require routine cleaning and

maintenance at regular intervals. To that end, a removable sleeve 62, such

as a removable quartz sleeve, is inserted into source region 1 2 to surround

the region and protect the inner chamber walls from material which is dislodged from substrate 1 8, such as through sputter etching. Quartz sleeve

62 can be removed and cleaned or replaced at regular maintenance intervals

as desired.

In another aspect of the present invention, a sputter etching application

may be achieved by introducing an inert gas such as Argon into both the

source region and the processing region. The gas dispersing element, such

as feed ring 70, introduces or disperses the process gas into the processing

region 1 4 to intersect paths of the high-energy extracted ions 57. The

generally neutral process gas particles are indicated in Figure 1 by reference

numeral 72. In accordance with the principles of the present invention, a

charge exchange occurs between the high-energy ions 57 and the neutral

particles of the process gas 72, thus converting the high-energy ion particles

into high-energy, neutral particles for bombarding substrate 1 8, and

particularly surface 20, to etch the surface. The invention produces a large

number of high-energy, neutral gas species as the result of the charge

exchange collisions between the source plasma ions 57 and the downstream

neutral species 72 in accordance with the principles of the invention. The

etch provided by the high-energy neutral species created by the invention is

highly directional or anisotropic, and thus is suitable for advanced etching

applications wherein narrow, high aspect ratio structures need to be etched

with a directional etch. Furthermore, neutral species reduce the ionic damage

which occurs in the IC devices on surface 20. The low-damage, anisotropic

processing provided by the invention is particularly suited to VLSI and ULSI

processing wherein device sizes continue to decrease. While sputter etching may be achieved utilizing an inert process gas in both the source region and the processing region, a reactant gas in the processing region might be

similarly utilized for yielding a plasma enhanced reactive etching process for

achieving a directional or anisotropic reactive etching process on surface 20.

In accordance with another aspect of the present invention, harmful

radiation, such as UV radiation, is attenuated between the plasma source

region 12 and the processing region 14 for reducing the radiation damage to

devices on the substrate 1 8. As mentioned above, the radiation generated

by a plasma discharge or plasma glow can detrimentally affect the

construction and operation of IC devices on substrate 1 8, such as by causing

undesirable current flow in the devices, semiconductor junction leakage,

minority carrier lifetime degradation, and interfacial conductor states within

the interface of a device. Overall, the characteristics of the devices may be

detrimentally affected or permanently damaged due to such radiation.

Radiation damage is increased with the density of the plasma, and is thus a

particular problem with high-density plasmas of the kind discussed herein.

The invention comprises a radiation blocking apparatus 80 positioned

between the plasma source region 1 2 and the processing region 14. The

radiation blocking apparatus 80 is operable for absorbing radiation produced

by the plasma in the source region to reduce radiation damage to substrate

20. In one embodiment of the invention, the radiation blocking apparatus

comprises a planar plate having a plurality of apertures 82 formed therein for

passing plasma from the source region and into the processing region while

absorbing radiation from the plasma. In a preferred embodiment of the

invention, the planar plate is formed of a quartz material which has UV radiation blocking capabilities. The ion extraction mechanism 52 in the form of a plate or grid, as disclosed herein, also provides for some blockage of UV

radiation. The combination of the ion extraction mechanism and the radiation

blocking mechanism provides reduced radiation at substrate 20 and thus

reduces the damage to IC devices on the substrate. Preferably, the plate 80

is planar in shape and is positioned generally parallel to substrate surface 20

between source region 1 2 and processing region 14, generally below the ion

extraction mechanism 52. The plate 80 is preferably positioned close to ion

extraction mechanism 52 and preferably has a similar shape, such as a

circular shape, as the ion extraction mechanism plate shown in Figure 4A,

and will also generally have a similar diameter or other dimension for being

mounted in the chamber 10. The apertures 82 may take a plurality of

shapes, such as circular or square, and are large enough so as to provide

relatively unhindered passage of the plasma therethrough. In Figure 1 , the

apertures 82 of the radiation blocking plate are shown larger than the

apertures in the ion extracting mechanism only to illustrate the different

mechanisms. In fact, the blocking plate 80 and extraction mechanism 52

may have similarly shaped and dimensioned apertures.

The present invention thus provides a low-damage, anisotropic

processing apparatus and method for effectively using high-density plasmas.

The invention is particularly useful for VLSI and ULSI processing of substrates

having narrow, high-aspect ratio device features.

While the present invention has been illustrated by the description of

the embodiments thereof, and while the embodiments have been described

in considerable detail, it is not the intention of the applicant to restrict or in

any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art.

Therefore, the invention in its broader aspects is not limited to the specific

details representative apparatus and method, and illustrative examples shown

and described. Accordingly, departures may be made from such details

without departure from the spirit or scope of applicant's general inventive

concept.

What is claimed is:

Claims

1 . An apparatus for processing a surface of a substrate with a

plasma formed from a process gas, comprising:

a processing chamber defining therein a plasma source region and a

plasma processing region located downstream of the source region, the

processing region configured to contain a substrate to be processed;

an electrical energy source operably coupled to the chamber for

directing energy into the source region to form and sustain a plasma therein;

an ion extraction mechanism positioned between the source region

and the processing region, the ion extraction mechanism operable, when

biased with electrical energy, for extracting ions from the plasma in the

source region and directing high-energy extracted ions into the processing

region for processing a substrate therein;

a gas dispersing element positioned in the processing space

downstream of the plasma source region, the gas dispersing element operable

for dispersing a process gas into the processing region to intersect paths of

the high-energy extracted ions and produce a charge exchange between the

ions and particles of the process gas for creating high-energy neutral particles

for processing a substrate;

whereby a low-damage and directional processing of the substrate is

achieved.

2. The apparatus of claim 1 wherein the gas dispersing element is

operable for creating a pressure differential between the source region and

the processing region for increasing the rate of charge exchange between the

high-energy ions and the neutral particles and increasing the density of high-

energy neutral particles.

3. The apparatus of claim 1 wherein the ion extraction mechanism

comprises at least one conductive plate having a plurality of apertures formed

therein for passing the plasma from the source region, through the plate and

into the processing region.

4. The apparatus of claim 1 wherein the ion extraction mechanism

comprises at least one conductive grid defining a plurality of openings therein

for passing the plasma from the source region, through the grid and into the

processing region.

5. The apparatus of claim 1 wherein said extraction mechanism

further comprises at least one conductive element and an energy source

coupled to the element for biasing the element to attract ions from the

plasma.

6. The apparatus of claim 5 wherein the conductive element is

formed of stainless steel.

7. The apparatus of claim 1 further comprising a radiation blocking

apparatus positioned between the plasma source region and the processing

region, the radiation blocking apparatus operable for absorbing radiation

produced by the plasma in the source region to reduce the amount of

radiation falling on the substrate.

8. The apparatus of claim 7 wherein the radiation blocking

apparatus comprises a grid having a plurality of apertures formed therein for

passing plasma from the source region, through the radiation blocking grid

and into the processing region while absorbing radiation from the plasma.

9. The apparatus of claim 8 wherein the grid is formed of quartz.

10. The apparatus of claim 1 further comprising a magnetic bucket

surrounding a portion of the plasma source, the bucket operable for

magnetically influencing the plasma to produce a high density plasma.

1 1 . The apparatus of claim 1 further comprising a magnetic bucket

surrounding a portion of the plasma source, the bucket operable for

magnetically influencing the plasma to direct the plasma toward the ion

extraction apparatus.

12. The apparatus of claim 1 , further comprising a magnetic bucket

surrounding a portion of the plasma processing region.

1 3. The apparatus of claim 1 wherein the electrical energy source

comprises an RF biased spiral coil for coupling energy into the source region.

14. The apparatus of claim 1 wherein the ion extraction mechanism

comprises a plurality of conductive elements generally positioned in a stacked

formation for extracting ions.

1 5. The apparatus of claim 14, wherein at least two of said plurality

of stacked conductive elements are electrically biased at different potentials

from each other.

16. An apparatus for processing a surface of a substrate with a

plasma formed from a process gas, comprising:

a processing chamber defining therein a plasma source region and a

plasma processing region located downstream of the source region, the

processing region configured to contain a substrate to be processed;

an electrical energy source operably coupled to the chamber for

directing energy into the source region to form and sustain a plasma therein

which generates radiation;

a substrate support in the processing space for supporting a substrate,

the support operable for biasing the substrate to draw a portion of the plasma

thereto to process the substrate;

a radiation blocking apparatus positioned between the plasma source

region and the processing region, the radiation blocking apparatus operable

for absorbing radiation produced by the plasma in the source region to reduce

the damage to the substrate.

1 7. The apparatus of claim 1 6 wherein the radiation blocking

apparatus comprises a plate having a plurality of apertures formed therein for

passing plasma from the source region, through the radiation blocking plate

and into the processing region while absorbing radiation from the plasma.

1 8. The apparatus of claim 17 wherein the plate is formed of quartz.

1 9. The apparatus of claim 1 6 further comprising an ion extraction

mechanism positioned between the source region and the processing region,

the ion extraction mechanism operable, when biased with electrical energy,

for extracting ions from the plasma in the source region and directing high-

energy extracted ions into the processing region for bombarding a substrate

therein to etch the substrate.

20. The apparatus of claim 19 wherein the ion extraction mechanism

comprises at least one plate having a plurality of apertures formed therein for

passing the plasma from the source region, through the plate and into the

processing region.

21 . The apparatus of claim 1 9 wherein the ion extraction mechanism

comprises at least one grid defining a plurality of openings therein for passing

the plasma from the source region, through the grid and into the processing

region.

22. The apparatus of claim 1 9 further comprising a gas dispersing

element positioned in the processing space downstream of the plasma source

region, the gas dispersing element operable for dispersing a process gas into

the processing region to intersect paths of the high-energy extracted ions and

produce a charge exchange between the ions and particles of the process gas

for creating high-energy neutral particles for bombarding a substrate.

23. The apparatus of claim 1 6 further comprising a magnetic bucket

surrounding a portion of the plasma source for magnetically influencing the

plasma.

24. The apparatus of claim 1 6 further comprising a magnetic bucket

surrounding a portion of the plasma processing region of the chamber for

magnetically influencing the plasma.

25. The apparatus of claim 1 6 wherein the ion extraction mechanism

comprises a plurality of conductive elements generally positioned in a stacked

formation for extracting ions.

26. The apparatus of claim 25 wherein at least two of said plurality

of stacked conductive elements are electrically biased at different potentials

from each other.

27. A method for processing a surface of a substrate with a plasma

formed from a process gas, comprising:

positioning a substrate in a processing chamber having a plasma source

region and a plasma processing region located downstream of the source

region;

introducing process gas into the source region of the chamber and

directing energy into the source region to form and sustain a plasma therein;

extracting ions from the plasma in the source region and directing

high-energy extracted ions into the processing region for processing a

substrate therein;

dispersing gas into the processing space downstream of the plasma

source region so that the gas intersects paths of the high-energy extracted

ions and produces a charge exchange between the ions and particles of the

process gas for creating high-energy neutral particles for processing a

substrate;

whereby a low-damage and directional processing is achieved on the

substrate.

28. The method of claim 27 further comprising creating a pressure

differential between the source region and the processing region for

increasing the rate of charge exchange between the high-energy ions and the

neutral particles and increasing the density of high-energy neutral particles.

29. The method of claim 27 wherein the ion extracting step includes

positioning, between the source region and the processing region, at least

one biased plate having a plurality of apertures formed therein for passing the

plasma from the source region and into the processing region.

30. The method of claim 27 wherein the ion extracting step includes

positioning, between the source region and the processing region, at least

one biased grid defining a plurality of openings therein for passing the plasma

from the source region and into the processing region.

31 . The method of claim 27 further comprising positioning a

radiation blocking apparatus between the plasma source region and the

processing region for absorbing radiation produced by the plasma in the

source region to reduce the damage to the substrate.

32. The method of claim 31 wherein the radiation blocking apparatus

comprises a plate having a plurality of apertures formed therein for passing

plasma from the source region, through the radiation blocking plate and into

the processing region while absorbing radiation from the plasma.

33. The method of claim 32 wherein the radiation blocking grid is

formed of quartz.

34. The method of claim 27 further comprising magnetically

influencing the plasma with a magnetic bucket surrounding a portion of the

plasma source to produce a high density plasma.

35. The method of claim 27 further comprising magnetically

influencing the plasma with a magnetic bucket surrounding a portion of the

plasma source to direct the plasma toward the ion extraction apparatus.

36. The method of claim 27 further comprising directing energy into

the source region with an RF biased spiral coil.

37. The method of claim 27 further comprising magnetically

influencing the plasma with a magnetic bucket surrounding a portion of the

processing region.

38. The method of claim 27 further comprising extracting ions with

an extraction mechanism positioned between the source region and processing region.

39. The method of claim 38 wherein the extraction mechanism

comprises a plurality of conductive elements generally positioned in a stacked

formation.

40. The method of claim 39 further comprising biasing at least two

of said plurality of stacked conductive elements to have different potentials

from each other.

41 . Method for processing a surface of a substrate with a plasma

formed from a process gas, comprising:

positioning a substrate in a processing chamber having a plasma source

region and a plasma processing region located downstream of the source

region;

introducing process gas into the source region of the chamber and

directing energy into the source region to form and sustain a plasma therein;

biasing the substrate to draw a portion of the plasma thereto to

process the substrate;

positioning a radiation blocking apparatus between the plasma source

region and the processing region for absorbing radiation produced by the

plasma in the source region to reduce the damage to the substrate.

42. The method of claim 41 wherein the radiation blocking apparatus

comprises a plate having a plurality of apertures formed therein for passing

plasma from the source region, through the radiation blocking grid and into

the processing region while absorbing radiation from the plasma.

43. The method of claim 42 wherein the plate is formed of quartz.

44. The method of claim 41 further comprising extracting ions from

the plasma in the source region and directing high-energy extracted ions into

the processing region for bombarding a substrate therein to etch the

substrate.

45. The method of claim 44 further comprising positioning an ion

extraction mechanism between the source region and the processing region

and biasing the ion extraction mechanism with electrical energy for extracting

ions from the plasma in the source region and directing high-energy extracted

ions into the processing region.

46. The method of claim 45 wherein the ion extraction mechanism

comprises at least one plate having a plurality of apertures formed therein for

passing the plasma from the source region, through the plate and into the

processing region.

47. The method of claim 46 wherein the ion extraction mechanism

comprises at least one grid defining a plurality of openings therein for passing the plasma from the source region, through the grid and into the processing

region.

48. The method of claim 41 further comprising dispersing gas into

the processing space downstream of the plasma source region so that the

gas intersects paths of the high-energy extracted ions and produces a charge

exchange between the ions and particles of the process gas for creating high-

energy neutral particles for processing a substrate.

49. The method of claim 41 further comprising magnetically

influencing the plasma with a magnetic bucket surrounding a portion of at

least one of the plasma source region and the processing region to direct the

plasma to the substrate.

50. An apparatus for processing a surface of a substrate with a

plasma formed from a process gas, comprising:

a processing chamber defining therein a plasma source region and a

plasma processing region located downstream of the source region, the

processing region configured to contain a substrate to be processed;

an electrical energy source operably coupled to the chamber for

directing energy into the source region to form and sustain a plasma therein

which generates radiation;

an ion extraction mechanism positioned between the source region

and the processing region, the ion extraction mechanism operable, when

biased with electrical energy, for extracting ions from the plasma in the

source region and directing high-energy extracted ions into the processing

region for processing a substrate therein;

a gas dispersing element positioned in the processing space

downstream of the plasma source region, the gas dispersing element operable

for dispersing a process gas into the processing region to intersect paths of

the high-energy extracted ions and produce a charge exchange between the

for processing a substrate;

a radiation blocking apparatus positioned between the plasma source

region and the processing region, the radiation blocking apparatus operable

for absorbing radiation produced by the plasma in the source region to reduce

the damage to the substrate.

whereby low-damage and directional processing is achieved.

51 . The apparatus of claim 40 wherein the ion extraction mechanism

comprises at least one plate having a plurality of apertures formed therein for

passing the plasma from the source region, through the plate and into the

processing region.

52. The apparatus of claim 50 wherein the ion extraction

mechanism comprises at least one grid defining a plurality of openings therein

for passing the plasma from the source region, through the grid and into the

processing region.

53. The apparatus of claim 50 wherein the radiation blocking

apparatus comprises a plate having a plurality of apertures formed therein for

passing plasma from the source region, through the radiation blocking grid

and into the processing region while absorbing radiation from the plasma.

54. The apparatus of claim 53 wherein the plate is formed of quartz.

55. The apparatus of claim 50 wherein the ion extraction mechanism

comprises a plurality of conductive elements generally positioned in a stacked

formation.