WO2002009198A1

WO2002009198A1 - Etching apparatus having a confinement and guide object for gas flow of plasma and method for using same

Info

Publication number: WO2002009198A1
Application number: PCT/US2001/041421
Authority: WO
Inventors: Jewon Lee; Mike Devre; Dave Johnson; Kenneth Mackenzie; Jay Sasserath
Original assignee: Unaxis Usa Inc.
Priority date: 2000-07-26
Filing date: 2001-07-26
Publication date: 2002-01-31
Also published as: WO2002009198A9; AU2001283503A1

Abstract

A method and apparatus for anisotropically plasma etching semiconductor materials is disclosed. The apparatus includes an etching chamber for plasma etching which includes therein a gas confinement apparatus and/or a gas flow modifier to focus the plasma gas onto the substrate to be etched and provide uniform etch rates, modulation of sidewall profile shapes or surface morphology during processing. The gas confinement apparatus and the gas flow modifier are formed of any suitable shape and may include openings therein to produce a balanced gas flow rate. The apparatus is especially useful for etching GaAs and InP substrates.

Description

Etching Apparatus having a Confinement and Guide Object for Gas Flow of Plasma and Method for Using Same

BACKGROUND OF THE INVENTION

1. FIELD OF THE INVENTION

The invention relates to a method and apparatus for anisotropically plasma etching

semiconductor materials whereby the gas flow to the substrate is improved.

2. DESCRIPTION OF THE FIELD

As the density of semiconductor devices increases, plasma etch processes are

increasingly utilized because such processes can be employed to etch films in situ and avoid

wet etch techniques. A typical plasma etch system includes a plasma processing chamber

and a workpiece holder to support the workpiece in the chamber. Inlet ports introduce a

reactant gas or gases into the chamber where electrodes are used to excite the gases into a

plasma state in the chamber. One or more of the electrodes may be excited by a direct

current (DC) voltage source or a radio frequency (RF) voltage source, often at frequencies

ranging between about 2 MHz and about 13.56 MHz to couple energy from the power

supply into the plasma. Typical methods for transferring the power into the gas include

direct coupling, capacitive coupling, and inductive coupling. Often, coupling includes a

combination of these methods. In addition, inductors (or coil arrangements) can be used in

a chamber arrangement to inductively couple power into the process chamber to excite gases introduced in the chamber into a plasma state. Plasma etch processes can be used to etch metals, semiconductors, inorganic

insulators and organic films using reactive gases. Typical reactive gases include fluorine-

containing gases, such as NF₃, SF₆, CHF₃, CF₄ or C₂F₆, sometimes in combination with O₂,

Ar, N₂, or He. These gases are useful in obtaining desired etch rates, selectivities and

uniformities, all of which must be precisely controlled. A mixture of chlorine and other

halogen gases is the most popular gas chemistry for etching of dielectrics, metals and

compound semiconductors such as, GaAs and InP. There has been a limitation to utilize

the gas flow with current hardware configuration in plasma process equipment. The

limitation is that significant volume of the gases inserted into a process chamber may be

pumped away without reacting with a sample due to inadequate confinement of the gas flow

onto the sample.

In order to obtain a substantially uniform etch across the substrate surface, it is

necessary to create and maintain a uniform plasma over the substrate and to monitor

changes in the plasma. For example, in an anisotropic etching technique, it is necessary to

achieve a laterally exact defined recess (trench via contact) in the substrate. These deeply- extending recesses must have parallel sidewalls.

The individual structures to be etched into the substrate are usually defined by

applying an etching mask(s) to the substrate by way of so-called masking layers, such as,

for example, a photoresist layer, which after exposure to UV light and subsequent developing, remains on the substrate, thereby protecting the underlying layer from the

etchant.

A typical process for etching a contact via is described in Arleo et al, U.S. Pat. No.

5,176,790, which discusses etching a dielectric in a plasma using a mixture of fluorine-

containing gases and nitrogen-containing gases. Dry etching of metals, such as aluminum and tungsten, can be performed either by reactive ion etching (RIE) or by plasma etching in

the presence of a halide gas, such as chlorine or bromine-containing gases for aluminum

etching and fluorine-containing gases for tungsten etching. In addition, dry etching of a

laminated film having a metal suicide layer and a polycrystalline silicon layer can be

performed using a mixed gas of SF₆ and O₂. Other gas combinations such as HBr, Cl₂ and O₂; NF₃, Cl₂ and O₂; Cl₂ and O₂; as well as other gases can also be used to perform dry

etching processes.

In U.S. Patent No. 5,501,893, an etching process is disclosed wherein a silicon

substrate first undergoes a plasma etching step which is followed by a second polymerizing

step wherein exposed areas are covered by a polymer layer which forms a temporary

etching stop. These two steps make up the process by alternately repeating the etching step

and the polymerizing step.

A great amount of effort has been paid to attempt to improve uniformity across the

wafer during plasma deposition and etching. It is understood to those of ordinary skill in this art that there are different mechanisms for each plasma process. For example, there are two popular plasma etching processes for III-V semiconductors, such as GaAs. The first is non-selective etching and the other is selective etching. Gases for GaAs non-

selective etching are typically based on Cl₂, BC1₃ and SiCl₄. Selective etching process, on

the other hand, requires the addition of a fluorine-based gas, such as, SF₆ or CF₄ together

with the chlorine gases. The radial distribution of etch rates for these two processes are the same. In both etching processes, the highest etch rate is usually found at the edge of the

wafer while the lowest etch rate is usually found at the center of the wafer. The etch

mechanism of the processes is generally understood to be reactant limited, which means

that distribution of neutral gas reactants can play a key role for etch rate uniformity.

GB 2,327,909 relates to anisotropically plasma etching a silicon wafer in a plasma

etching apparatus where the apparatus includes an aperture formed above the wafer. The

aperture is formed from a perforated diaphragm. A vertical cylindrical aluminum screen is

formed over the diaphragm.

U.S. Patent No. 5,891,348 discloses an apparatus for processing substrates which

includes a process chamber having a gas distributor, a support for supporting a substrate in

the process chamber, a plasma generator, and a focus ring. The focus ring has a wall

surrounding the substrate to contain the plasma on the substrate surface. The focus ring

also includes a channel, adjacent to, and extending continuously around the peripheral edge

of the substrate surface. The inlet of the channel has a allows a sufficient amount of process gas to flow into the channel in order to maintain substantially equal processing rates

at the center and peripheral edge of the substrate surface.

In U.S. Patent No. 5,474,649, a focus ring for surrounding a workpiece/surface

substrate during plasma processing is disclosed which includes a hollow annular assembly

comprised of electrically insulating material and having a texturized surface. According to

the patent, the texturized ring is preferably a cylindrical structure which is texturized by

surface abrasion, such as, bead blasting or chemical etching.

Rose et al., U.S. Patent No. 4,792,378 discloses a chemical vapor transport reactor

gas dispersion disk for counteracting vapor pressure gradients. According to the patent, the

gas dispersion disk provides a uniform deposition of material films on a semiconductor

slice. The gas dispersion disk has a number of apertures arranged to increase the aperture

area per unit of disk area when extending from the center of the disk to its outer peripheral

edge. The apparatus also includes an apertured annular ring for providing an outlet of the

gas vapors from the reactor chamber. Rose, U.S. Patent No. 4,820,371, discloses an

apertured ring discussed in 4,792,378. The annular ring is used in a plasma reaction

chamber and includes a central opening aperture for laterally retaining a semiconductor

slice in the chamber. The ring also includes a plurality of gas exhaust ports for providing a

back pressure within the chamber and for removing gases from the chamber.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to overcome the drawbacks of the

prior art and to provide an apparatus that can be used to effectively confine and guide gas

flows in the etching chamber to provide improved uniformity in a selective etching

processes without degrading the uniformity in a non-selective etching. The apparatus

according to the present invention can be used to confine and guide halogen gases such as,

for example, SF₆, Cl₂, BC1₃ NF₃, CHF₃, CF₄, C₂F₆ and HBr, and their mixtures in plasma

processing of semiconductor materials such as, for example, silicon, GaAs, InP, AlGaAs,

InGaP, AlInGaP, A1N, AlGaN, GaN, metals or dielectrics, to improve etch rates and

uniformity, and modulation of sidewall profile shapes or surface morphology during

processing. By using the apparatus according to the present invention, the present

inventors have discovered that it is possible to achieve over 5 μm/min of GaAs etch rate, an

improvement of more than 30 % of the rate obtained without using the apparatus of the present invention under similar process conditions and in a similar chamber.

According to one embodiment of the invention, an etching apparatus for etching a

substrate surface is provided wherein the etching apparatus includes a gas confinement

apparatus located inside the etching chamber to focus the etching gas uniformly over the

substrate. The method encompasses anisotropic plasma reactive ion etching wherein a desired plasma gas is input into the etching chamber, passed through the gas confinement apparatus

located inside the etching chamber and focused so that the etching gas uniformly contacts the

substrate. According to another embodiment of the invention, an etching apparatus for etching a

substrate surface is provided wherein the etching apparatus includes a gas flow modifier located inside the etching chamber to focus the etching gas uniformly over the substrate. The

method encompasses anisotropic plasma reactive ion etching wherein a desired plasma gas is

input into the etching chamber, passed through the gas flow modifier located inside the

etching chamber and focused so that the etching gas uniformly contacts the substrate.

According to yet another embodiment of the invention, an etching apparatus for

etching a substrate surface is provided wherein the etching apparatus includes both a gas

confinement apparatus and a gas flow modifier located inside the etching chamber to focus the

etching gas uniformly over the substrate. The method encompasses anisotropic plasma

reactive ion etching wherein a desired plasma gas is input into the etching chamber, passed

through the gas confinement apparatus and the gas flow modifier inside the etching chamber and focused so that the etching gas uniformly contacts the substrate.

Other objects, features and advantages of the invention will become apparent from

the following detailed description of the preferred embodiments of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an exemplary cross-sectional view of an etching apparatus according to the present invention. Figure 2 illustrates a perspective cross-sectional view of a gas confinement apparatus according to the present invention.

Figure 3 illustrates a perspective cross-sectional view of another gas confinement

apparatus according to the present invention.

Figure 4 is a graph showing the effect of the presence of a gas confinement

apparatus in the etching chamber on the etch rate of the substrate.

Figure 5 is a scanning electron microscopy photo of a GaAs substrate etched

according to the present invention.

Figures 6A and 6B illustrate a gas flow modifier according to the present invention.

Figures 7A and 7B illustrate a second gas flow modifier according to the present

invention.

Figures 8A and 8B illustrate a third gas flow modifier according to the present

invention.

Figure 9 is a graph showing the radial distribution of etch depth with and without a

gas flow modifier.

Figure 10 illustrates a gas flow optimizer according to the present invention.

Figure 11 illustrates a second gas flow optimizer according to the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following detailed description, the preferred embodiments are described in

sufficient detail to enable those skilled in the art to practice the invention, and it is to be

understood that other embodiments may be utilized, and that changes may be made without

departing from the spirit and scope of the present invention.

As set forth above, there are different requirements for each plasma process. For

example, to etch III-V semiconductors, such as GaAs, there are two popular plasma

etching techniques. The first is non-selective etching and the other is selective etching.

Gases for GaAs non-selective etching are typically based on Cl₂, BC1₃ and SiCl₄ while a selective etching process, on the other hand, requires the addition of a fluorine-based gas,

such as, SF₆ or CF₄ together with other chlorine gases. The radial distribution of etch rates

for these two processes will likely be the same. In both etching processes, the highest etch

rate is usually found at the edge of the water and the lowest etch rate is usually found at the

center of the wafer. The etch mechanism of both processes typically is reactant-limited,

which means that distribution of neutral gas reactants can play a key role for etch rate

uniformity in selective etching of GaAs. The present invention provides improved

uniformity in both etching processes, i.e. selective and non-selective etching.

Reference is made to Fig. 1. This figure shows a cross sectional view of a exemplary processing apparatus 10 of the present invention for plasma etching a substrate

22. The apparatus 10 includes an enclosed etching chamber 18 having an exterior

peripheral wall 12. Plasma process gas which is used to etch the substrate 22 is introduced into the etching chamber 18 through an inlet 14. The plasma process gas 26 may be

introduced into the etching chamber 18 directly, by a "shower head" gas diffuser (not

shown) or by any method known in the art. The plasma gas 26 can be formed by inductive

coupling by using a coil (not shown) wrapped around the chamber 18, by capacitive

coupling using process electrodes (not shown) in the chamber 18, or by a combination

thereof. The plasma gas 26 may include fluorine-containing gases, such as NF₃, SF₆,

CHF₃, CF₄ or C₂F₆, sometimes in combination with O₂, Ar, N₂, or He, or Cl₂, BC1₃ and

SiCl₄, or SF₆ or CF₄ together with the chlorine gases. Preferably, the plasma gas is Cl₂,

BC1₃ and SiCl₄ for non-selective etching of the substrate 22 and SF₆ or CF₄ together with

Cl₂, BC1₃ and SiCl₄ for selective etching of the substrate 22. An outlet 16 is provided for

removing the plasma process gas 26 from the chamber 18.

The gas mixtures have a flow rate of from about 0 to 1000 seem, and preferably

from about 50 - 300 seem. The pressure of the process is from about 1 and 200 mT, and preferably from 10 to 100 mT at an output preferably between 0 and 5000W, a microwave,

ICP, TCP, helicon, ECR or other high density excitation source. The plasma gas 26 is

input at a gas flow of between 0 and 1000 seem and a processing pressure between 5 and

100 mT. The plasma generation for etching preferably takes place with an RF excitation or

other high density source at outputs between 0 and 5000W (up to about 2.45 GHz). A RF

(radio frequency) bias for ion acceleration may be applied to the substrate electrode. The

substrate bias is preferably between 0 and 500V, and can be achieved with a high-frequency

supply (13.56 MHz) at outputs between 0 and 500W. The etching may be performed for a time period in order to yield an etch depth of about 0.1 μm to about 500 μm. The absolute

depth of the etching is dependent upon the thickness of the substrate to be etched and the

amount of etching desired.

The substrate 22 is placed within etching chamber 18 on substrate support 20. The

substrate support 20 can be grounded or biased by connection to supply 24. The substrate

22 can be any semiconductor materials such as, for example, silicon, SOI, GaAs, InP,

AlGaAs, InGaP, AlInGaP, A1N, AlGaN, GaN, metals or dielectrics. Preferably, the

substrate is GaAs or InP.

A gas confinement apparatus 40 surrounding substrate 22 is placed in the etching

chamber 18. The gas confinement apparatus 40 can be designed as a structure attached to

the interior surface 17 of wall 12 as shown in Fig. 1, or as an integral portion of the

substrate support 20 (not shown).

The gas confinement apparatus 40 has an upper surface 42 and a lower surface 44

and further includes an opening 46 formed in the center for containing and directing the

flow of process gas or plasma 26 on the substrate 22. The wall 47 guides the flow of fresh reactive process gas 26 from the inlet 14 to the substrate 22. The gas confinement

apparatus is discussed in more detail below with reference to Figs. 2 and 3.

The apparatus 10 may also contain a gas flow modifier 30. The gas flow modifier

30 may be incorporated into the apparatus 10 with or without gas confinement apparatus

40. For simplicity, these two elements are shown together inside etching chamber 18; however, it should be understood that either may be used alone or in combination with the

other. The gas flow modifier 30 can be designed as a free-standing ring structure resting

on the substrate support 20 (not shown), as an integral portion of the gas confinement

apparatus 40 as shown in Fig. 1, or as a fixed ring structure attached to the sidewall 17 or

interior bottom surface 21 of etching chamber 18. The gas flow modifier 30 has an outside

wall 38 and an inside wall 36. When the gas flow modifier is integrally attached to the gas

confinement apparatus 40, as illustrated in Fig. 1, the opening of the gas flow modifier is

preferably the same as the opening 46 in the gas confinement apparatus 40.

During processing of substrates in the etching chamber 18, the plasma gas 26 is

focused onto the substrate 22 by either one of, or both, the gas confinement apparatus 40

and/or the gas flow modifier 30. These elements allow the plasma 26 to be uniformly

distributed and focused onto the substrate 22.

Reference is now made to Figs. 2 and 3. Figure 2 shows a perspective cross-

sectional view of a gas confinement apparatus 40 according to the present invention. The

gas confinement apparatus 40 can be formed in any suitable shape. Accordingly, the gas

confinement apparatus 40 may be circular, square, rectangular or the like. The opening 46

can be of any suitable size to allow the plasma gases, neutrals and ions, 26 which are

generated by a plasma source to flow through the opening 46 in the gas confinement

apparatus 40 and arrive on the substrate 22. Preferably, the opening 46 is sized to surround

the substrate 22. The opening 46 may also be of any suitable shape, such as, for example,

circular, square, rectangular, triangular or the like. It should be understood that the opening is separate and distinct from the shape of the gas confinement apparatus 40. Thus, for example, for substrates having a diameter of 203.2 mm (8-inch), a suitable inner

diameter of the opening 46 is from about 200 mm to about 300 mm, and more preferably

from about 225 to about 275 mm. The thickness of the wall 47 is sufficiently thick to focus

the flow of the plasma gas 26 to the substrate 22. Thus, the thickness of the wall 47

depends upon the process conditions in the process chamber 18. A suitable thickness for a

150 to 300 mm (6 to 12 inch) diameter substrate is from about 1 to about 5 mm, preferably about 2 to about 3 mm.

Reference is now made to Fig. 3. This figure shows another embodiment of the gas

confinement apparatus 41 according to the present invention. The gas confinement

apparatus 41 may also be formed in any suitable shape. Accordingly, the gas confinement apparatus 41 may be circular, square, rectangular or the like. The opening 46 can be of

any suitable size and shape to allow the plasma gases, neutrals and ions, 26 which are

apparatus 41 and arrive on the substrate 22. Preferably, the opening 46 is sized to surround

the substrate 22. Thus, for example, the opening may be from about 200 mm to about 300

mm, and preferably from about 225 to about 275 mm. The thickness of the wall 47 is

sufficiently thick to focus the flow of the plasma gas 26 to the substrate 22. A suitable

thickness is from about 1 to about 5 mm, preferably from about 2 to about 3 mm. The gas

confinement apparatus 41 further includes openings 43 in the apparatus. The diameter of the openings 43 maybe from about 5 mm to about 30 mm, and preferably from about 10 to 15 mm. The number of the opening 43 can be about 5 to 30, and preferably about 10-15.

The openings 43 include inside walls 45 which pass completely through the thickness of the

gas confinement apparatus 41. While the openings 43 are depicted as being round, the

openings 43 may be present in any shape, size and density such that the gas confinement

apparatus 41 allows a balanced flow of the plasma gas 26 onto wafer 22. Furthermore,

openings 43 should be formed so that the flow of plasma gas 26 onto wafer 22 is uniform

and provides a high process rate. For example, the openings 43 may be formed such that

their density is greater nearer the outer perimeter of the gas confinement apparatus 41.

Likewise, the openings 43 may be formed such that their density is greater nearer the inner

perimeter of the gas confinement apparatus 41. Additionally, the openings 43 may be

formed such that there are circular shaped openings 43 near the outer perimeter of the gas

confinement apparatus 41 while square shaped openings 43 are formed near the inner

portion of the gas confinement apparatus 41.

Reference is now made to Fig. 4. This figure shows the gas etch rate of a GaAs substrate in an etching chamber under identical conditions except in the first instance there

was no gas confinement apparatus present in the chamber while in the second instance a gas

confinement apparatus was placed therein. As can be seen from the figure, the etch rate of

the substrate without the gas confinement apparatus was about 3.5 microns/minute while

when the gas confinement apparatus was present in the etching chamber, the GaAs substrate was etched at a rate of about 5 microns/minute. The process condition was low ICP power,

low RIE power. The process chemistry was chlorine-based. GaAs etch rate was 3.5 μm min. However, it is noted that GaAs etch rate of 5 μm/min could be achieved with a

confinement object at the fixed process condition. This indicates that the confinement

object effectively transfers the neutral gas flow , onto the GaAs wafer and provides an

enhanced etch rate. Accordingly to etch mechanism, the limiting factor of GaAs etch rate

is believed to be related to the number of gas reactants present on the GaAs subtrate. The

confinement object controlled and guided the path of gas flux on the GaAs and it

significantly improved the etch rate of the GaAs substrate.

Additionally, Fig. 5 shows a scanning electron microscopy photo of GaAs via

etched with a gas confinement apparatus present in the etching chamber. As can be seen

from the figure, the gas confinement apparatus provides a GaAs etch via which has uniform

depth and smooth, vertical sidewalls. Another role of gas confinement object is to make

ions more directional to the substrate. For plasma etchmg, anisotropic etching is one

advantage over wet etching. Anisotropic etching is important for device processing since CD (critical dimension) loss must be optimized. For GaAs via etching, it is common to see

some undercutting of the sidewall after plasma etching due to insufficient sidewall

passivation. The results are more evident with deep feature etching (>6μm.) as it will make

subsequent metal contact on the via hole difficult. However, with a gas confinement

object, it is noticed that a vertical sidewall is achieved without undecutting the sidewall,

even after 70 μm etching of a 40 μm diameter via. The results prove that the gas

confinement object helps control gas flux and the direction of ions to achieve the desired

sidewall shape after etching. Reference is now made to Figs. 6 A and 6B. Figure 6 A shows a perspective cross-

sectional view of a gas flow modifier 30 according to the present invention. As set forth

above, the gas flow modifier 30 may be incorporated into the apparatus 10 with or without gas confinement apparatus 40. The gas flow modifier 30 can be designed as a free-standing

ring structure resting on the substrate support 20 (not shown), as an integral portion of the

gas confinement apparatus 40 as shown in Fig. 1, or as a fixed ring structure attached to the

sidewall 17 and/or the interior bottom surface 21 of etching chamber 18. The gas flow

modifier is positioned near the substrate 22 in order to improve the uniformity in selective

etching processes without degrading the uniformity in non-selective etching. The gas flow

modifier 30 has an outside wall 38 and an inside wall 36. When the gas flow modifier is

integrally attached to the gas confinement apparatus 40, as illustrated in Fig. 1, the opening

of the gas flow modifier is preferably the same as the opening 46 in the gas confinement

apparatus 40. The gas flow modifier 30 may be formed of a dielectric material, such as quartz, a ceramic, such as aluminum oxide or a conductor, such as a metal (for example

aluminum). If the gas flow modifier 30 is formed of a metal, then the gas flow modifier 30

can be grounded or biased in order to control ion direction in the plasma.

The gas flow modifier 30 can be formed in any suitable shape. For example, the

gas flow modifier 30 can be circular, square, rectangular or the like. The opening formed

in the gas flow modifier 30 can be of any suitable size to allow the plasma gases, neutrals

and ions, 26 which are generated by a plasma source to flow through the opening to the

substrate 22. Thus, for example, for substrates having a diameter of 203.2 mm (8-inch), a suitable inner diameter of the opening of the gas flow modifier 30 is from about 200 mm to

about 250 mm, and more preferably from about 205 to 225 mm. The thickness of the wall

of the gas flow modifier 30 is sufficiently thick to focus the flow of the plasma gas 26 to the

substrate 22 while maintaining structural stability of the device. Thus, the thickness of the

gas flow modifier 30 depends upon the process conditions in the process chamber 18 as

well as the location of the gas flow modifier in the chamber 18. A suitable thickness for a

150 to 300 mm (6 to 12 inch) diameter substrate is from about 2 to about 10 mm,

preferably about 3 to about 5 mm.

The gas flow modifier 30 has a height h which is sufficient to reduce the flow or

diffusive transport of stagnant reactive process gas species circulating in the process

chamber 18 to the substrate 22. The height h of the gas flow modifier 30 depends upon the

process conditions in the process chamber 18. Thus, for example, a suitable height h for a

150 to 300 mm (6 to 12 inch) diameter substrate processed using the process conditions

described herein is from about 10 to about 50 mm, preferably 15 to 25 mm, most

preferably about 20 mm.

Reference is now made to Fig. 6B. This figure shows a gas flow modifier 31

according to the present invention. The gas flow modifier 31 can also be formed in any

suitable shape and may be formed of the materials described above. For example, the gas

flow modifier 31 can be circular, square, rectangular or the like and may be formed of a

dielectric or a ceramic. A suitable inner diameter of the opening of the gas flow modifier

31 is from about 200 mm to about 250 mm, and more preferably from about 205 to 225 mm. The thickness of the wall of the gas flow modifier 31 is sufficiently thick to focus the

flow of the plasma gas 26 to the substrate 22 while maintaining structural stability of the

device. Thus, the thickness of the gas flow modifier 31 depends upon the process

conditions in the process chamber 18. A suitable thickness for a 150 to 300 mm (6 to 12

inch) diameter substrate is from about 2 to about 10 mm, preferably about 3 to about 7 mm.

Furthermore, the gas flow modifier 31 has a height h which is sufficient to reduce the flow

or diffusive transport of stagnant reactive process gas species circulating in the process

chamber 18 to the substrate 22. The height h of the gas flow modifier 31 depends upon the

described herein is from about 10 to about 50 mm, preferably 15 to 25 mm, most preferably about 20 mm.

The gas flow modifier 31 further includes openings 37 in the wall of the gas flow

modifier 31. The openings 37 pass completely through the thickness of the gas flow

modifier 31. While the openings 37 are depicted as being circular, it should be understood

that the openings 37 may be present in any shape, size and density such that the gas flow

modifier 31 allows a balanced flow of the plasma gas 26 onto wafer 22. Furthermore,

openings 37 should be formed so that the flow of plasma gas 26 onto wafer 22 is uniform

their density is upper portion of the gas flow modifier 31. Likewise, the openings 37 may

be formed such that their density is greater nearer the middle of the gas flow modifier 31. Reference is now made to Figs. 7-8. Figure 7A illustrates a gas flow modifier 32

where the inner surface of the gas flow modifier forms an angle α with a vertical axis that

is perpendicular to the plane of the substrate 22, to form an inverted tapered conical surface

that smoothly directs the flow of plasma gas 26 to the substrate 22. Preferably, the angle α

is an acute angle. More preferably, the angle α is from about 10° to about 75°, more

preferably from about 15° to about 45°, and most preferably about 30°. Figure 7B

illustrates a gas flow modifier 33 where the inner surface of the gas flow modifier forms an

angle α with a vertical axis that is perpendicular to the plane of the substrate 22, to form an

inverted tapered conical surface that smoothly directs the flow of plasma gas 26 to the

substrate 22 in a converging pattern. The gas flow modifier 33 additionally includes openings 37 in the wall of the gas flow modifier 33 which pass completely through the wall

of the gas flow modifier 33. Again, while the openings 37 are depicted as being circular, it

should be understood that the openings 37 may be present in any shape, size and density

such that the gas flow modifier 33 allows a balanced flow of the plasma gas 26 onto wafer

22. Furthermore, openings 37 should be formed so that the flow of plasma gas 26 onto

wafer 22 is uniform and provides a high process rate.

Figure 8A illustrates a gas flow modifier 34 where the inner surface of the gas flow

modifier forms an angle β with a vertical axis that is perpendicular to the plane of the

substrate 22, to form a tapered conical surface that smoothly directs the flow of plasma gas

26 to the substrate 22 in a diverging pattern. Preferably, the angle β is an acute angle.

More preferably, the angle β is from about 10° to about 75°, more preferably from about 15° to about 45°, and most preferably about 30°. Figure 8B illustrates a gas flow modifier

35 where the inner surface of the gas flow modifier forms an angle β with a vertical axis

that is perpendicular to the plane of the substrate 22, to form a tapered conical surface that

smoothly directs the flow of plasma gas 26 to the substrate 22 in a diverging pattern. The

gas flow modifier 35 additionally includes openings 37 in the wall of the gas flow modifier

35 which pass completely through the wall of the gas flow modifier 35. While the openings

37 are depicted as being circular, it should be understood that the openings 37 may be

present in any shape, size and density such that the gas flow modifier 35 allows a balanced

₍flow of the plasma gas 26 onto wafer 22.

Reference is now made to Fig. 9. This figure shows the radial distribution of etch

depth with and without a gas flow modifier. As can be seen from the figure, when a GaAs

substrate is etched with a BC1₃/SF₆, 300W ICP source power, 15 WRIE chuck power, 5

mTorr chamber pressure without a gas flow modifier, the etching rate at the wafer edge is greater that the etching rate closer to the center of the substrate. In contrast, when a gas

flow modifier is added to the etching chamber, a more uniform etching across the wafer.

Thus, the presence of the gas flow modifier provides a uniform etch rate across the entire

wafer

Reference is now made to Figs. 10 and 11. Fig. 10 shows a gas flow optimizer 50

formed from a gas confinement apparatus 40 together with a gas flow modifier 31. The gas

confinement apparatus 40 is similar to those discussed above with reference to Fig. 2; however, as discussed above, the gas confinement apparatus 40 is square shaped. The gas flow modifier 31 is attached as an integral portion of the gas confinement apparatus 40.

The gas flow modifier 31 is integrated into the gas confinement apparatus 40 such that the

gas flow modifier 31 is located adjacent to and below the gas confinement apparatus 40 to form the gas flow optimizer 50. As discussed above, the opening in the gas flow modifier

31 is preferably the same as the opening 46 in the gas confinement apparatus 40.

Additionally, the gas flow modifier 31 and the gas flow confinement apparatus 40 have a

thickness, height and positioning within the chamber to improve the etch rate, uniformity,

and modulation of sidewall profile shapes or surface morphology of the substrate. As

illustrated in this figure, the gas flow modifier 31 includes openings 37 so that the flow of

plasma gas 26 onto wafer 22 is uniform and provides a high process rate.

Figure 11 shows a gas flow optimizer 51 formed from a gas confinement apparatus 41 together with a gas flow modifier 30. The gas confinement apparatus 41 is similar to

those discussed above with reference to Fig. 3; however, as discussed above, the gas

confinement apparatus 41 is square shaped. The gas flow modifier 30 is also attached as an

integral portion of the gas confinement apparatus 41. The gas flow modifier 30 is integrated into the gas confinement apparatus 41 such that the gas flow modifier 30 is

located adjacent to and below the gas confinement apparatus 41 to form the gas flow

optimizer 51. As discussed above, the opening in the gas flow modifier 30 is preferably the

same as the opening 46 in the gas confinement apparatus 41. Additionally, the gas flow

modifier 30 and the gas flow confinement apparatus 41 have a thickness, height and

positioning within the chamber to improve the etch rate, uniformity, and modulation of sidewall profile shapes or surface morphology of the substrate. As illustrated in this figure,

the gas confinement apparatus 41 includes openings 43 so that the flow of plasma gas 26

onto wafer 22 is uniform and provides a high process rate. While these figures illustrate

gas flow optimizers where either the gas confinement apparatus or gas flow modifier

portion of the gas flow optimizer includes openings, it should be understood that the

invention is not so limited. For example, either the gas confinement apparatus or gas flow

modifier portion of the gas flow optimizer, or both may have openings. Likewise, there

need not be any openings present in the gas flow optimizer. The person having ordinary

skill in the art understands whether and where the openings should be placed to provide a

uniform etch.

The apparatus and methods described herein are but some of many that could be

used within the scope of the present invention. Accordingly, the above description is only

illustrative of preferred embodiments which can achieve the features and advantages of the

present invention. It is not intended that the invention be limited to the embodiments

described in detail herein.

Claims

CLAIMSWhat is claimed is:

1. A method of etching a substrate in a plasma etching chamber,

comprising:

placing a substrate in the etching chamber;

introducing plasma gas in the plasma etching chamber, and maintaining the

plasma gas at process conditions suitable for etching said substrate; and

focusing said plasma gas onto said substrate by first passing said plasma gas

over a gas confinement member and subsequently passing said plasma gas over a gas

flow modifier, wherein said gas confinement member has a central opening for said

plasma gas to pass through and wherein said gas flow modifier has an outer wall and an inner wall wherein said inner wall defines a hollow aperture for said plasma gas

to flow onto said substrate.

2. The method according to claim 1, wherein said substrate is selected

from the group consisting of silicon, GaAs, InP, AlGaAs, InGaP, AlInGaP, A1N,

AlGaN, and GaN.

3. The method according to claim 1, wherein said substrate is GaAs.

4. The method according to claim 1, wherein said substrate is InP.

5. The method according to claim 1, wherein said plasma etching gas

includes Cl₂, BC1₃, SiCl₄ and mixtures thereof.

6. The method according to claim 1, wherein said plasma etching gas is

selected from the group consisting of Cl₂, BC1₃ and SiCl₄ in combination with SF₆

or CF₄.

7. The method according to claim 1, wherein said gas confinement

element further comprises openings in said element.

8. The method according to claim 7, wherein said openings have a

circular cross-section.

9. The method according to claim 1, wherein said gas flow modifier

further comprises openings in said walls.

10. The method according to claim 9, wherein said openings have a

circular cross-section.

11. The method according to claim 1, wherein said gas flow modifier has

a frusto-conical shape and said inner wall of said gas flow modifier is at an acute

angle with respect to the normal to the plane of the surface of the substrate.

12. The method according to claim 11, wherein said acute angle is from

about 15 to about 45 degrees.

13. The method according to claim 1, wherein said gas flow modifier has

a inverted conical shape and said inner wall of said gas flow modifier is at an acute

angle with respect to the normal to the plane of the surface of the substrate.

14. The method according to claim 13, wherein said acute angle is from

about 15 to about 45 degrees.

15. A method of etching a GaAs substrate in a plasma etching chamber,

comprising:

placing a GaAs substrate in the etching chamber; introducing plasma gas in the plasma etching chamber, and maintaining the

plasma gas at process conditions suitable for etching said GaAs substrate; and

focusing said plasma gas onto said GaAs substrate by first passing said

plasma gas over a gas confinement member and subsequently passing said plasma

gas over a gas flow modifier, wherein said gas confinement member has a central opening for said plasma gas to pass through and wherein said gas flow modifier has

an outer wall and an inner wall wherein said inner wall defines a hollow aperture for said plasma gas to further flow onto said GaAs substrate.

16. The method according to claim 15, wherein said plasma etching gas

includes Cl₂, BC1₃, SiCl₄, and mixtures thereof.

17. The method according to claim 15, wherein said plasma etching gas

includes Cl₂, BC1₃, SiCl₄, and mixtures thereof, in combination with SF₆ or CF₄.

18. The method according to claim 15, wherein said gas confinement

element further comprises openings in said element.

19. The method according to claim 18, wherein said openings have a

circular cross-section.

20. The method according to claim 15, wherein said gas flow modifier

further comprises openings in said walls.

21. The method according to claim 20, wherein said openings have a

circular cross-section.

22. The method according to claim 15, wherein said gas flow modifier

has a frusto-conical shape and said inner wall of said gas flow modifier is at an acute

angle with respect to the normal to the plane of the surface of the substrate.

23. The method according to claim 22, wherein said acute angle is from

about 15 to about 45 degrees.

24. The method according to claim 15, wherein said gas flow modifier

has a inverted conical shape and said inner wall of said gas flow modifier is at an acute angle with respect to the normal to the plane of the surface of the substrate.

25. The method according to claim 24, wherein said acute angle is from

about 15 to about 45 degrees.

26. The method according to claim 22, wherein said wherein said gas

flow modifier further comprises openings in said walls.

27. The method according to claim 24, wherein said wherein said gas

flow modifier further comprises openings in said walls.

28. An apparatus for etching a substrate in a plasma etching chamber,

comprising: an etching chamber having a gas input for inputting plasma etching gas;

a plasma generator; a support for supporting a substrate in said chamber;

a gas confinement member; and

a gas flow modifier, wherein said gas confinement member has a

predetermined thickness and has a central opening for plasma to pass through and

wherein said gas flow modifier has an outer wall and an inner wall wherein said

inner wall defines a hollow aperture for plasma gas to flow through, and wherein

said gas flow modifier is located above said support and said gas confinement

element is located above said gas flow modifier and below said gas input.

29. The apparatus according to claim 28, wherein said gas confinement

element further comprises openings in said element.

30. The apparatus according to claim 29, wherein said openings have a

circular cross-section.

31. The apparatus according to claim 29, wherein said openings have a

rectangular cross-section.

32. The apparatus according to claim 28, wherein said gas flow modifier

further comprises openings in said walls.

33. The apparatus according to claim 32, wherein said openings have a

circular cross-section.

34. The apparatus according to claim 32, wherein said openings have a

rectangular cross-section.

35. The apparatus according to claim 28, wherein said gas flow modifier has a frusto-conical shape and said inner wall of said gas flow modifier is at an acute

angle with respect to the normal to the plane of the surface of the substrate.

36. The apparatus according to claim 35, wherein said acute angle is from about 15 to about 45 degrees.

37. The apparatus according to claim 28, wherein said gas flow modifier

has a inverted conical shape and said inner wall of said gas flow modifier is at an

acute angle with respect to the normal to the plane of the surface of the substrate.

38. The apparatus according to claim 37, wherein said acute angle is

from about 15 to about 45 degrees.

39. The apparatus according to claim 35, wherein said gas flow modifier

further comprises openings in said walls.

40. The apparatus according to claim 39, wherein said openings have a

circular cross-section.

41. The apparatus according to claim 39, wherein said openings have a

rectangular cross-section.

42. The apparatus according to claim 37, wherein said gas flow modifier

further comprises openings in said walls.

43. The apparatus according to claim 42, wherein said openings have a

circular cross-section.

44. The apparatus according to claim 42, wherein said openings have a

rectangular cross-section.

45. An apparatus for etching a substrate in a plasma etching chamber, comprising:

an etching chamber having a gas input for inputting plasma etching gas;

a plasma generator; a support for supporting a substrate in said chamber; and

a gas flow modifier, wherein said gas flow modifier has an outer wall and an inner wall wherein said inner wall defines a hollow aperture for plasma gas to flow

through and said gas flow modifier has an inverted conical shape and said inner wall

of said gas flow modifier is at an acute angle with respect to the normal to the plane

of the surface of the substrate.

46. The apparatus according to claim 45, wherein said acute angle is

from about 15 to about 45 degrees.

47. The apparatus according to claim 45, wherein said gas flow modifier

further comprises openings in said walls.

48. The apparatus according to claim 47, wherein said openings have a

circular cross-section.

49. The apparatus according to claim 47, wherein said openings have a

rectangular cross-section.

50. A gas confining apparatus comprising: a gas confinement member; and a gas flow modifier, wherein said gas confinement member has a

wherein said gas flow modifier has an outer wall and an inner wall wherein said

said gas confinement element is formed above said gas flow modifier.

51. The gas confining apparatus according to claim 50, wherein said gas

confinement element further comprises openings in said element.

52. The gas confining apparatus according to claim 51, wherein said

openings have a circular cross-section.

53. The gas confining apparatus according to claim 51, wherein said

openings have a rectangular cross-section.

54. The gas confining apparatus according to claim 50, wherein said gas

flow modifier further comprises openings in said walls.

55. The gas confining apparatus according to claim 54, wherein said openings have a circular cross-section.

56. The gas confining apparatus according to claim 54, wherein said

openings have a rectangular cross-section.

57. The gas confining apparatus according to claim 50, wherein said gas

flow modifier has a frusto-conical shape and said inner wall of said gas flow

modifier is at an acute angle with respect to the normal to the plane of the surface of

said gas confinement member.

58. The gas confining apparatus according to claim 57, wherem said

acute angle is from about 15 to about 45 degrees.

59. The gas confining apparatus according to claim 50, wherein said gas

flow modifier has a inverted conical shape and said inner wall of said gas flow

said gas confinement member.

60. The gas confining apparatus according to claim 59, wherein said

acute angle is from about 15 to about 45 degrees.

61. The gas confining apparatus according to claim 57, wherein said gas flow modifier further comprises openings in said walls.

62. The gas confining apparatus according to claim 61, wherein said

openings have a circular cross-section.

63. The gas confining apparatus according to claim 61, wherein said

openings have a rectangular cross-section.

64. The gas confining apparatus according to claim 59, wherein said gas

flow modifier further comprises openings in said walls.

65. The gas confining apparatus according to claim 64, wherein said

openings have a circular cross-section.

66. The gas confining apparatus according to claim 64, wherein said

openings have a rectangular cross-section.