U.S. patent application number 10/024208 was filed with the patent office on 2003-04-17 for tunable multi-zone gas injection system.
Invention is credited to Benjamin, Neil, Cooperberg, David J., Ratto, Douglas, Singh, Harmeet, Vahedi, Vahid.
Application Number | 20030070620 10/024208 |
Document ID | / |
Family ID | 26698179 |
Filed Date | 2003-04-17 |
United States Patent
Application |
20030070620 |
Kind Code |
A1 |
Cooperberg, David J. ; et
al. |
April 17, 2003 |
Tunable multi-zone gas injection system
Abstract
A tunable multi-zone injection system for a plasma processing
system for plasma processing of substrates such as semiconductor
wafers. The system includes a plasma processing chamber, a
substrate support for supporting a substrate within the processing
chamber, a dielectric member having an interior surface facing the
substrate support, the dielectric member forming a wall of the
processing chamber, a gas injector fixed to part of or removably
mounted in an opening in the dielectric window, the gas injector
including a plurality of gas outlets supplying process gas at
adjustable flow rates to multiple zones of the chamber, and an RF
energy source such as a planar or non-planar spiral coil which
inductively couples RF energy through the dielectric member and
into the chamber to energize the process gas into a plasma state.
The injector can include an on-axis outlet supplying process gas at
a first flow rate to a central zone and off-axis outlets supplying
the same process gas at a second flow rate to an annular zone
surrounding the central zone. The arrangement permits modification
of gas delivery to meet the needs of a particular processing regime
by allowing independent adjustment of the gas flow to multiple
zones in the chamber. In addition, compared to consumable
showerhead arrangements, a removably mounted gas injector can be
replaced more easily and economically.
Inventors: |
Cooperberg, David J.; (Mount
Kisco, NY) ; Vahedi, Vahid; (Albany, CA) ;
Ratto, Douglas; (Santa Clara, CA) ; Singh,
Harmeet; (Berkeley, CA) ; Benjamin, Neil;
(East Palo Alto, CA) |
Correspondence
Address: |
Peter K. Skiff
BURNS, DOANE, SWECKER & MATHIS, L.L.P.
P.O. Box 1404
Alexandria
VA
22313-1404
US
|
Family ID: |
26698179 |
Appl. No.: |
10/024208 |
Filed: |
December 21, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60328796 |
Oct 15, 2001 |
|
|
|
Current U.S.
Class: |
118/723AN ;
156/345.48 |
Current CPC
Class: |
H01L 21/32136 20130101;
H01J 37/321 20130101; H01J 37/32715 20130101; H01L 21/31116
20130101; H01J 37/32449 20130101; H01J 2237/3323 20130101; H01J
2237/3344 20130101; C23C 16/45574 20130101; C23C 16/507 20130101;
H01J 37/3244 20130101; H01L 21/32137 20130101 |
Class at
Publication: |
118/723.0AN ;
156/345.48 |
International
Class: |
C23F 001/00; C23C
016/00 |
Claims
What is claimed is:
1. A plasma processing system comprising: a plasma processing
chamber; a vacuum pump connected to the processing chamber; a
substrate support on which a substrate is processed within the
processing chamber; a dielectric member having an interior surface
facing the substrate support, wherein the dielectric member forms a
wall of the processing chamber; a gas injector extending through
the dielectric member such that a distal end of the gas injector is
exposed within the processing chamber, the gas injector including a
plurality of gas outlets supplying process gas at flow rates that
are independently varied between at least some of the outlets into
the processing chamber; and an RF energy source which inductively
couples RF energy through the dielectric member and into the
chamber to energize the process gas into a plasma state to process
the substrate.
2. The system of claim 1, wherein the system is a high density
plasma chemical vapor deposition system or a high density plasma
etching system.
3. The system of claim 1, wherein the RF energy source comprises an
RF antenna and the gas injector injects the process gas toward a
primary plasma generation zone in the chamber.
4. The system of claim 1, wherein the gas outlets include a single
on-axis outlet in an axial end surface of the gas injector and a
plurality of off-axis outlets in a side surface of the gas
injector, the on-axis outlet and the off-axis outlets being
supplied process gas from a single gas supply via first and second
gas lines, the gas lines including flow controllers which provide
adjustable gas flow to the on-axis outlet independently of the
off-axis outlets.
5. The system of claim 1, wherein the gas outlets include a center
gas outlet extending in an axial direction perpendicular to the
exposed surface of the substrate and a plurality of angled gas
outlets extending at an acute angle to the axial direction, the
center gas outlet receiving process gas supplied by a first gas
line and the angled gas outlets receiving process gas from a second
gas line, the first and second gas lines receiving process gas from
the same gas supply.
6. The system of claim 1, wherein the gas injector injects the
process gas at a subsonic, sonic, or supersonic velocity.
7. The system of claim 1, wherein the gas injector includes a
planar axial end face having an on-axis outlet therein and a
conical side surface having off-axis outlets therein, the on-axis
outlet receiving process gas from a central passage in the injector
and the off-axis outlets receiving process gas from an annular
passage surrounding the central passage.
8. The system of claim 1, wherein the gas injector is removably
mounted in the dielectric window and supplies the process gas into
a central region of the chamber.
9. The system of claim 1, wherein the gas injector includes at
least one on-axis outlet which injects process gas in an axial
direction perpendicular to a plane parallel to an exposed surface
of the substrate and off-axis gas outlets which inject process gas
at an acute angle relative to the plane parallel to the exposed
surface of the substrate.
10. The system of claim 1, wherein the gas injector is removably
mounted in the opening in the dielectric window and a vacuum seal
is provided between the gas injector and the dielectric window.
11. The system of claim 1, wherein the RF energy source comprises
an RF antenna in the form of a planar or non-planar spiral coil and
the gas injector injects the process gas toward a primary plasma
generation zone in the chamber.
12. The system of claim 1, wherein a single main gas supply is
split into multiple gas supply lines to feed the gas outlets.
13. The system of claim 1, wherein the ratio of gas flow through at
least some of the gas outlets is independently varied using
variable flow restriction devices.
14. The system of claim 1, wherein the ratio of gas flow through at
least some of the gas outlets is independently varied using a
network of valves and throttling elements.
15 The system of claim 1, wherein the gas injector is further
provided with an electrically conducting shield which minimizes
plasma ignition within gas passages located in the gas
injector.
16. A method of plasma processing a substrate comprising: placing a
substrate on a substrate support in a processing chamber, wherein
an interior surface of a dielectric member forming a wall of the
processing chamber faces the substrate support; supplying process
gas into the processing chamber from a gas injector extending
through the dielectric member such that a distal end of the gas
injector is exposed within the processing chamber, the gas injector
including a plurality of gas outlets supplying process gas into the
processing chamber; controlling the flow rate of the process gas to
at least one of the outlets independently of the flow rate of the
process gas to at least one other of the outlets; energizing the
process gas into a plasma state by inductively coupling RF energy
produced by the RF energy source through the dielectric member into
the processing chamber, the process gas being plasma phase reacted
with an exposed surface of the substrate.
17. The method of claim 16, wherein the RF energy source comprises
an RF antenna in the form of a planar or non-planar spiral coil and
the gas injector injects some of the process gas through an on-axis
outlet to a central zone in the chamber and through off-axis
outlets to an annular zone surrounding the central zone.
18. The method of claim 16, wherein at least some of the gas
outlets inject the process gas in a direction other than directly
towards the exposed surface of the substrate.
19. The method of claim 16, wherein the gas injector extends below
an inner surface of the dielectric window and the gas outlets
inject the process gas in a plurality of directions.
20. The method of claim 16, wherein the gas injector injects the
process gas at a subsonic, sonic, or supersonic velocity.
21. The method of claim 16, wherein individual substrates are
consecutively processed in the processing chamber by depositing or
etching a layer on each of the substrates.
22. The method of claim 16, wherein the gas injector extends into a
central portion of the chamber and the gas outlets inject the
process gas in multiple zones between the exposed surface of the
substrate and the interior surface of the dielectric member.
23. The method of claim 16, wherein the gas outlets include a
central on-axis gas outlet in the distal end of the gas injector
and a plurality of off-axis gas outlets surrounding the on-axis gas
outlet, the off-axis gas outlets injecting the process gas in a
plurality of different directions.
24. The method of claim 16, comprising plasma etching an aluminum
layer on the substrate by injecting a chlorine containing gas
through the gas outlets, at least some of the gas outlets injecting
the gas in a direction which is not perpendicular to the exposed
surface of the substrate.
25. The method of claim 16, comprising plasma etching a polysilicon
layer on the substrate by injecting a chlorine and/or bromine
containing gas through a central gas outlet in an axial direction
which is perpendicular to the exposed surface of the substrate and
through a plurality of angled gas outlets surrounding the central
outlet, the angled gas outlets injecting the gas in directions
oriented at an angle of 10 to 90.degree. to the axial
direction.
26. The method of claim 16, comprising plasma etching a silicon
oxide layer on the substrate by injecting a fluorine containing gas
through a central gas outlet in an axial direction which is
perpendicular to the exposed surface of the substrate and/or
through a plurality of angled gas outlets surrounding the central
outlet, the angled gas outlets injecting the gas in directions
oriented at an angle of 10 to 90.degree. to the axial
direction.
27. The method of claim 16, comprising plasma etching a polysilicon
layer on the substrate by injecting a chlorine and/or bromine
containing gas through a central gas outlet in an axial direction
which is perpendicular to the exposed surface of the substrate and
through a plurality of angled gas outlets surrounding the central
outlet, the angled gas outlets injecting the gas in directions
oriented at an angle of 10 to 45.degree. to the axial
direction.
28. The method of claim 16, comprising plasma etching a silicon
oxide layer on the substrate by injecting a fluorine containing gas
through a central gas outlet in an axial direction which is
perpendicular to the exposed surface of the substrate and/or
through a plurality of angled gas outlets surrounding the central
outlet, the angled gas outlets injecting the gas in directions
oriented at an angle of 10 to 45.degree. to the axial
direction.
29. The method of claim 16, wherein a single main gas supply is
split into multiple gas supply lines to feed the gas outlets.
30. The method of claim 16, wherein the ratio of gas flow through
at least some of the gas outlets is independently varied using
variable flow restriction devices.
31. The method of claim 16, wherein the ratio of gas flow through
at least some of the gas outlets is independently varied using a
network of valves and throttling elements.
32. The method of claim 16, wherein the ratio of gas flow through
at least some of the gas outlets is independently varied to etch a
layer on the substrate so as to achieve uniformity in
center-to-edge etching of the layer.
33. The method of claim 16, wherein the ratio of gas flow through
at least some of the gas outlets is independently varied to deposit
a layer on the substrate so as to achieve uniformity in
center-to-edge deposition of the layer.
34. The method of claim 16, wherein the gas injector is further
provided with an electrically conductive shield which minimizes
plasma ignition within gas passages located in the gas
injector.
35. A gas injector for supplying process gas into a semiconductor
processing chamber comprising: an injector body which includes at
least first and second gas inlets, at least first and second gas
passages, and at least first and second gas outlets, the first gas
passage being in fluid communication with the first inlet and first
outlet, the second gas passage being in fluid communication with
the second inlet and second outlet, the first and second gas
passages being discrete from each other so as to provide
independently adjustable flow rates of gas through the first and
second outlets.
36. The injector of claim 35, wherein the at least one first gas
outlet comprises a single on-axis outlet in an axial end surface of
the injector body and the at least one second gas outlet comprises
a plurality of off-axis outlets in a side surface of the injector
body.
37. The injector of claim 35, wherein the injector body includes a
planar axial end face and a conical side surface, the at least one
first gas outlet comprising an on-axis outlet in the axial end face
and the at least one second gas outlet comprising off-axis outlets
in the conical side surface, the on-axis outlet connected to a
central passage in the injector and the off-axis outlets connected
to an annular passage surrounding the central passage.
38. The injector of claim 35, further comprising an electrically
conducting shield which minimizes plasma ignition within gas
passages located in the gas injector.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to a system and a method for
delivering reactants to a substrate in a plasma processing system
for semiconductor substrates such as semiconductor wafers. More
particularly, the present invention relates to a system and a
method for injecting gas from a localized region over the center of
the substrate to maximize processing uniformity and efficiency.
BACKGROUND OF THE INVENTION
[0002] Vacuum processing chambers are generally used for etching or
chemical vapor depositing (CVD) of materials on substrates by
supplying process gas to the vacuum chamber and applying a radio
frequency (RF) field to the gas. The method of injection of process
gasses into the chamber may have a dramatic effect on the
distribution of chemically reactive species above the substrate
surface and thus the overall process. Showerhead gas injection and
diffusive transport systems are commonly used to ensure even
distribution of the process gas over the substrate. In the case of
inductively coupled plasma etch chambers, for example, the
evolution of etched features is largely governed by the spatially
dependent density of these reactive species over the substrate and
the distribution of energetic ions incident on the substrate.
[0003] U.S. Pat. No. 4,691,662 to Roppel et al. discloses a dual
plasma microwave apparatus for etching and deposition in which
process gas is fed by conduits mounted on a side wall of a
processing chamber, extending over a portion of the substrate. U.S.
Pat. No. 5,522,934 to Suzuki et al. discloses a gas injector
arrangement including a plurality of gas supply nozzles positioned
in a plurality of levels in a direction substantially perpendicular
to the substrate wherein inert (rather than process) gas is
injected through the center of the chamber ceiling. The gas supply
nozzles at upper levels extend further toward the center of the
substrate than those at lower levels. The injection holes are
located at the distal ends of the gas supply nozzles. These systems
are effective in delivering the process gas to the region above the
substrate. However, because the conduits extend over the substrate
surface between the substrate and the primary ion generation
region, as the ions diffuse from the generation region toward the
substrate the conduits can cast shadows of ion nonuniformity onto
the substrate surface. This can lead to an undesirable loss in etch
and deposition uniformity.
[0004] Other approaches employ gas supply conduits which do not
extend over the substrate surface. "Electron Cyclotron Resonance
Microwave Discharges for Etching and Thin-film Deposition," J.
Vacuum Science and Technology A, Vol. 7, pp. 883-893 (1989) by J.
Asmussen shows conduits extending only up to the substrate edge.
"Low-temperature Deposition of Silicon Dioxide Films from Electron
Cyclotron Resonant Microwave Plasmas," J. Applied Physics, Vol. 65,
pp. 2457-2463 (1989) by T. V. Herak et al. illustrates a plasma CVD
tool including a plurality of gas injection conduits that feed
separate process gases. One set of conduits is mounted in the lower
chamber wall with gas delivery orifices located just outside the
periphery of the substrate support and at the distal ends of the
conduits. These conduit arrangements can cause process drift
problems as a result of heating of the ends of the conduits.
[0005] "New Approach to Low Temperature Deposition of High-quality
Thin Films by Electron Cyclotron Resonance Microwave Plasmas," J.
Vac. Sci. Tech, B, Vol. 10, pp. 2170-2178 (1992) by T. T. Chau et
al. illustrates a plasma CVD tool including a gas inlet conduit
mounted in the lower chamber wall, located just above and outside
the periphery of the substrate support. The conduit is bent so that
the injection axis is substantially parallel to the substrate. An
additional horizontal conduit is provided for a second process gas.
The gas injection orifices are located at the distal ends of the
conduits. Injectors with the orifices located at the distal ends of
the injector tubes may be prone to clogging after processing a
relatively small batch of substrates, e.g., less than 100. This
injector orifice clogging is detrimental as it can lead to
nonuniform distribution of reactants, nonuniform film deposition or
etching of the substrate, shifts in the overall deposition or etch
rate, as well as economic inefficiency vis-a-vis tool downtime due
to required maintenance.
[0006] Various systems have been proposed to improve process
uniformity by injecting process gas at sonic or supersonic velocity
using, for example, a single nozzle aimed at the center of the
substrate as disclosed in commonly-owned U.S. Pat. No. 6,230,651 to
Ni et al. Other schemes utilize a showerhead arrangement with a
distribution of small holes designed to produce supersonic
injection. This second design can improve reactive neutral
densities over the substrate but requires the presence of a
conducting gas distribution and baffle system which may degrade
inductive coupling and can be a source of process
contamination.
[0007] U.S. Pat. No. 4,270,999 to Hassan et al. discloses the
advantage of injecting process gases for plasma etch and deposition
applications at sonic velocity. Hassan et al. notes that the
attainment of sonic velocity in the nozzle promotes an explosive
discharge from the vacuum terminus of the nozzle which engenders a
highly swirled and uniform dissipation of gas molecules in the
reaction zone surrounding the substrate. U.S. Pat. No. 5,614,055 to
Fairbairn et al. discloses elongated supersonic spray nozzles that
spray reactant gas at supersonic velocity toward the region
overlying the substrate. The nozzles extend from the chamber wall
toward the substrate, with each nozzle tip having a gas
distribution orifice at the distal end. U.S. Pat. No. 4,943,345 to
Asmussen et al. discloses a plasma CVD apparatus including
supersonic nozzles for directing excited gas at the substrate. U.S.
Pat. No. 5,164,040 to Eres et al. discloses pulsed supersonic jets
for CVD. While these systems are intended to improve process
uniformity, they suffer from the drawbacks noted above, namely
clogging of the orifices at the distal ends of the injectors, which
can adversely affect film uniformity on the substrate.
[0008] Several systems have been proposed to improve process
uniformity by injecting process gas using multiple injection
nozzles. Commonly owned U.S. Pat. No. 6,013,155 to McMillin et al.
discloses an RF plasma processing system wherein gas is supplied
through injector tubes via orifices located away from the high
electrical field line concentrations found at the distal tip of the
tubes. This arrangement minimizes clogging of the orifices because
the orifices are located away from areas where build-up of process
byproducts occurs.
[0009] U.S. Pat. No. 4,996,077 to Moslehi et al. discloses an
electron cyclotron resonance (ECR) device including gas injectors
arranged around the periphery of a substrate to provide uniform
distribution of non-plasma gases. The non-plasma gases are injected
to reduce particle contamination, and the injectors are oriented to
direct the non-plasma gas onto the substrate surface to be
processed.
[0010] U.S. Pat. No. 5,252,133 to Miyazaki et al. discloses a
multi-wafer non-plasma CVD apparatus including a vertical gas
supply tube having a plurality of gas injection holes along a
longitudinal axis. The injection holes extend along the
longitudinal side of a wafer boat supporting a plurality of
substrates to introduce gas into the chamber. Similarly, U.S. Pat.
No. 4,992,301 to Shishiguchi et al. discloses a plurality of
vertical gas supply tubes with gas emission holes along the length
of the tube.
[0011] U.S. Pat. No. 6,042,687 to Singh et al. describes a system
with two independent gas supplies. The primary supply injects gas
towards the substrate and the secondary supply injects gas at the
periphery of the substrate. The gas supplies represent separate
assemblies and are fed from separate gas supply lines that may
carry different gas mixtures. Other systems comprising independent
gas sources and independent gas flow control are disclosed in U.S.
Pat. Nos. 5,885,358 and 5,772,771.
[0012] With the industry trend toward increasing substrate sizes,
methods and apparatus for ensuring uniform etching and deposition
are becoming increasingly important. This is particularly evident
in flat panel display processing. Conventional showerhead gas
injection systems can deliver gases to the center of the substrate,
but in order to locate the orifices close to the substrate, the
chamber height must be reduced which can lead to an undesirable
loss in uniformity. Radial gas injection systems may not provide
adequate process gas delivery to the center of large area
substrates typically encountered, for example, in flat panel
processing. This is particularly true in bottom-pumped chamber
designs commonly found in plasma processing systems.
[0013] The above-mentioned Fairbairn et al. patent also discloses a
showerhead injection system in which injector orifices are located
on the ceiling of the reactor. This showerhead system further
includes a plurality of embedded magnets to reduce orifice
clogging. U.S. Pat. No. 5,134,965 to Tokuda et al. discloses a
processing system in which process gas is injected through inlets
on the ceiling of a processing chamber. The gas is supplied toward
a high density plasma region.
[0014] In addition to the systems described above, U.S. Pat. No.
4,614,639 to Hegedus discloses a parallel plate reactor supplied
with process gas by a central port having a flared end in its top
wall and a plurality of ports about the periphery of the chamber.
U.S. Pat. Nos. 5,525,159 (Hama et al.), 5,529,657 (Ishii),
5,580,385 (Paranjpe et al.), 5,540,800 (Qian) and 5,531,834
(Ishizuka et al.) disclose plasma chamber arrangements supplied
process gas by a showerhead and powered by an antenna which
generates an inductively coupled plasma in the chamber. Apparatus
and systems for providing a uniform distribution of gas across a
substrate are disclosed in U.S. Pat. Nos. 6,263,829; 6,251,187;
6,143,078; 5,734,143; and 5,425,810.
[0015] In spite of the developments to date, there still is a need
for optimizing uniformity and deposition for radio frequency plasma
processing of a substrate while preventing clogging of the gas
supply orifices and build up of processing by-products and
improving convective transport above the substrate.
SUMMARY OF THE INVENTION
[0016] The invention provides a plasma processing system which
includes a plasma processing chamber, a vacuum pump connected to
the processing chamber, a substrate support on which a substrate is
processed within the processing chamber, a dielectric member having
an interior surface facing the substrate support, wherein the
dielectric member forms a wall of the processing chamber, a gas
injector extending through the dielectric member such that a distal
end of the gas injector is exposed within the processing chamber,
the gas injector including a plurality of gas outlets supplying
process gas that is independently varied between at least some of
the outlets into the processing chamber, and an RF energy source
which inductively couples RF energy through the dielectric member
and into the chamber to energize the process gas into a plasma
state to process the substrate. The system is preferably a high
density plasma chemical vapor deposition system or a high density
plasma etching system.
[0017] The RF energy source can comprise an RF antenna and the gas
injector can inject the process gas toward a primary plasma
generation zone in the chamber. The gas outlets can be located in
an axial end surface of the gas injector thus forming several gas
outlet zones. For instance, the gas outlets can include a center
gas outlet (on-axis zone) extending in an axial direction
perpendicular to the exposed surface of the substrate and a
plurality of angled gas outlets (off axis zones) extending at an
acute angle to the axial direction. The injector outlets are
positioned to improved uniformity of reactive species over the
substrate. A single gas supply is split to feed each of the
injection zones.
[0018] Gas injection can be partitioned between one or more than of
the injector outlets using variable flow restriction devices in
each of the separate gas lines that supply the different injection
zones. By independently varying the setting of the flow restriction
devices, the ratio of flows through multiple zones can be varied in
order to create jets of varying size and at various angles with
respect to the axis of the process chamber. This balance between on
and off-axis injection determines the convective flow field
downstream from the nozzle tip. This flow field can be used to
modify the total flow in the chamber, which includes convective and
diffuse components. As a result, the spatial density dependence of
reactive species can be modulated with a goal of improving process
uniformity.
[0019] The gas injector can inject the process gas at a subsonic,
sonic, or supersonic velocity. In one embodiment, the gas injector
includes a planar axial end face which is flush with the interior
surface of the dielectric window. In another embodiment, the gas
injector is removably mounted in the dielectric window and/or
supplies the process gas into a central region of the chamber. The
gas outlets can have various configurations and/or spatial
arrangements. For example, the gas injector can include a closed
distal end and the gas outlets can be oriented to inject process
gas at an acute angle relative to a plane parallel to an exposed
surface of the substrate. In the case where the gas injector is
removably mounted in the opening in the dielectric window, at least
one O-ring provides a vacuum seal between the gas injector and the
dielectric window.
[0020] The invention also provides a method of plasma processing a
substrate comprising placing a substrate on a substrate support in
a processing chamber, wherein an interior surface of a dielectric
member forming a wall of the processing chamber faces the substrate
support, supplying process gas into the processing chamber from a
gas injector extending through the dielectric member such that a
distal end of the gas injector is exposed within the processing
chamber, the gas injector including a plurality of gas outlets
supplying process gas into the processing chamber, and energizing
the process gas into a plasma state by inductively coupling RF
energy produced by an RF energy source through the dielectric
member into the processing chamber, the process gas being plasma
phase reacted with an exposed surface of the substrate. According
to a preferred embodiment of the invention, the outlet holes in the
injector are fed by multiple gas supply lines, which are fed by a
single gas source. The fraction of total flow through each of the
supply lines may be varied with a control valve arrangement, e.g.,
a network of valves and throttling elements located outside the
plasma chamber; thus, the flow pattern in the chamber is modulated
by varying the ratio of conductances for each injection zone within
the injector.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 illustrates a plasma processing system according to
the present invention.
[0022] FIGS. 2a-b show details of a two-zone injector supplied
process gas by a single main gas supply which is split to
independently feed gas to both injection zones.
[0023] FIG. 2c shows a two-zone injector provided with an
electrically conducting outer jacket.
[0024] FIGS. 3a-c show gas distribution effects in an inductively
coupled plasma reactor using a gas injection arrangement in
accordance with the present invention.
[0025] FIGS. 4a-c show the effect of flow ratio on blanket
polysilicon etch rate using a gate etch process.
[0026] FIGS. 5a-c show the effect of flow ratio on blanket silicon
etch rate using an shallow trench isolation process.
[0027] FIGS. 6a-b and 7a-b illustrate an improvement in critical
dimension uniformity for polysilicon gate and trimmed photoresist
mask by adjusting the flow ratio.
[0028] FIGS. 8a-b show that mean etch characteristics can be tuned
by adjusting process gas flow ratios.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] The present invention provides an improved gas injection
system for plasma processing of substrates such as by etching or
CVD. The injection system can be used to inject gases such as gases
containing silicon, halogen (e.g., F, Cl, Br, etc.), oxygen,
hydrogen, nitrogen, etc. The injection system can be used alone or
in addition to other reactant/inert gas supply arrangements.
[0030] According to a preferred embodiment of the invention, a gas
injection arrangement is provided for an inductively coupled plasma
chamber. In the preferred arrangement, a gas injector is centrally
located in an upper wall of the chamber and one or more gas outlets
direct process gas into the chamber above a semiconductor substrate
such as a wafer or flat panel display to be processed. The gas
injector in accordance with the invention can improve
center-to-edge uniformity and mean etch or deposition
characteristics, e.g., critical dimension (CD), CD bias, profile
and/or profile microloading.
[0031] The method of process gas injection into inductively coupled
plasma etch chambers impacts the distribution of chemically
reactive species above the substrate surface. The evolution of
etched features is largely governed by the spatially dependent
density of these reactive species over the substrate and the
distribution of energetic ions incident on the substrate. The
invention relates to a method for injecting gas from a localized
region over the center of the substrate being processed which
improves process performance.
[0032] Process performance can be measured by uniformity of etch
rate, feature width and profile, fidelity of pattern transfer, and
uniformity of pattern transfer. Improved performance can be
achieved by partitioning process gas injection between injector
outlets designed to create jets of varying size and at varying
angles with respect to the axis of the process chamber, e.g., the
injector outlets are preferably positioned to improve uniformity of
reactive species over the substrate. Optimal gas injection and
hence optimal process performance can be achieved by adjusting the
ratio of flow through the injector outlets. In a preferred
implementation the ratio of flow through on-axis and off-axis
outlets may be varied. This balance between on-axis and off-axis
injection determines the convective flow field downstream from the
nozzle tip. This flow field can be used to modify the total flow in
the chamber which includes convective and diffuse components. As a
result, the spatial density dependence of reactive species can be
modulated. The injection scheme is thus tunable, and furthermore
minimizes significant contamination of the injector and gas
injection lines via diffusion of plasma species generated in the
interior of the chamber by maintaining at least a minimum flow of
process gas through the outlets. For example, it may be desirable
to maintain choked flow through the outlets. The injection scheme
also provides the ability to tune gas injection for optimized
performance with a single set of hardware. For example, for
different etch applications (and different recipe steps within an
etch application) that demand different ratios of on-axis to
off-axis flow for optimum uniformity, the gas injection scheme
allows for variation of this ratio without tool modification.
[0033] The gas outlets can be provided in a surface of the gas
injector which is below, flush or above the surface of the upper
chamber wall. For example, the gas injector can comprise a
cylindrical member having gas outlets in a sidewall and a single
gas outlet in an axial end thereof, the gas outlets being located
between the upper wall and the exposed surface of the semiconductor
substrate. In accordance with the invention, improved etch results
can be achieved with a single gas injector located centrally in the
upper chamber wall. However, more than one gas injector can be
provided in the upper wall of the chamber, especially in the case
where the plasma is generated by an antenna separated from the
interior of the chamber by a dielectric layer or window and/or the
chamber is used to process large substrates or a plurality of
substrates.
[0034] The number of gas outlets and/or the angle of injection of
gas flowing out of the gas outlets can be selected to provide
desired gas distribution in a particular substrate processing
regime. For instance, in the case of single wafer processing, the
number, size, angle of injection and/or location of the outlets
within the chamber can be adapted to a particular antenna design
used to inductively couple RF energy into the chamber, the gap
between the upper wall and the exposed surface of the substrate,
and etch process to be performed on the substrate.
[0035] FIG. 1 shows a plasma etch reactor 10 such as the TCP
9100.TM. made by Lam Research Corporation, the assignee of the
present application. According to the invention, the gas injector
is mounted in an opening extending through the dielectric window.
The vacuum processing chamber 10 includes a substrate holder 12
providing an electrostatic clamping force via electrostatic chuck
16 to a substrate 13 as well as an RF bias to a substrate supported
thereon and a focus ring 14 for confining plasma in an area above
the substrate while it is He back-cooled. A source of energy for
maintaining a high density (e.g. 10.sup.11-10.sup.12 ions/cm.sup.3)
plasma in the chamber such as an antenna 18 powered by a suitable
RF source and associated RF impedance matching circuitry 19
inductively couples RF energy into the chamber 10 so as to provide
a high density plasma. The chamber includes suitable vacuum pumping
apparatus (not shown) connected to outlet 15 for maintaining the
interior of the chamber at a desired pressure (e.g. below 50 mTorr,
typically 1-20 mTorr). A substantially planar dielectric window 20
of uniform thickness is provided between the antenna 18 and the
interior of the processing chamber 10 and forms the vacuum wall at
the top of the processing chamber 10. A gas injector 22 is provided
in an opening in the window 20 and includes a plurality of gas
outlets such as circular holes (not shown) for delivering process
gas supplied by the gas supply 23 to the processing chamber 10. An
optional conical or cylindrical liner 30 extends from the window 20
and surrounds the substrate holder 12.
[0036] In operation, a semiconductor substrate such as a wafer is
positioned on the substrate holder 12 and is typically held in
place by an electrostatic clamp, a mechanical clamp, or other
clamping mechanism when He back-cooling is employed. Process gas is
then supplied to the vacuum processing chamber 10 by passing the
process gas through the gas injector 22. The window 20 can be
planar and of uniform thickness as shown in FIG. 1 or have other
configurations such as non-planar and/or non-uniform thickness
geometries. A high density plasma is ignited in the space between
the substrate and the window by supplying suitable RF power to the
antenna 18. After completion of etching of an individual substrate,
the processed substrate is removed from the chamber and another
substrate is transferred into the chamber for processing
thereof.
[0037] The gas injector 22 can comprise a separate member of the
same or different material as the window. For instance, the gas
injector can be made of metal such as aluminum or stainless steel
or dielectric materials such as quartz, alumina, silicon nitride,
silicon carbide, etc. According to a preferred embodiment, the gas
injector is removably mounted in an opening in the window. However,
the gas injector can also be integral with the window. For example,
the gas injector can be brazed, sintered or otherwise bonded into
an opening in the window or the gas injector can be machined or
otherwise formed in the window, e.g. the window can be formed by
sintering a ceramic powder such as Al.sub.2O.sub.3 or
Si.sub.3N.sub.4 with the gas injector designed into the shape of
the window.
[0038] FIGS. 2a-b show an embodiment of the invention wherein the
injector 22 provides multi-zone gas injection. In the embodiment
shown, the injector 22 includes on-axis injection outlet 24 to
supply process gas to a first zone to which process gas is supplied
in an axial direction perpendicular to the substrate surface and an
off-axis injection outlet 26 to supply process gas to a second zone
to which process gas is supplied in an angled direction which is
not perpendicular to the substrate. Both zones can be supplied with
the same process gas (e.g., process gas from a gas manifold in
which one or more process gases are combined). For example, main
gas supply 32 can be split with a T-connector 34 to feed both
injection zones. To control the gas flow in each line, flow
controllers such as variable flow-restriction devices 36a and 36b
can be placed in each of the separate gas lines that supply the
different injection zones. The devices 36a and 36b can be set
manually or operated automatically by suitable electronic controls.
By independently varying the settings of the flow-restriction
devices 36a and 36b the ratio of flows through the two outlets 24
and 26 can be varied. Alternative implementations include multiple
outlets and variable flow-restriction valves and/or networks of
fixed restrictors and valves, which would enable the total
conductance to each injection zone to be adjusted to one or more
preset dynamically controlled values.
[0039] In the FIG. 2a embodiment, the center gas injection outlet
is shown as a continuation of central bore 25 which allows the
bore/outlet 24,25 to be used for interferometry measurements. For
example, the upper end of the bore 25 can be sealed by a window 27
arranged to communicate with monitoring equipment 29 such as a
lamp, spectrometer, optical fiber and lens arrangement as disclosed
in U.S. Pat. No. 6,052,176, the disclosure of which is hereby
incorporated by reference. In such an arrangement, the on-axis
outlet has a larger diameter than the off-axis outlets, e.g., 1 cm
on-axis outlet diameter and 1 mm diameter off-axis outlets. In the
FIG. 2b embodiment, the on-axis outlet has a smaller diameter than
the bore 25. The relative sizes of the on-axis and off-axis outlets
can be selected to achieve a desired gas flow distribution. For
example, the total cross-sectional area of the off-axis outlets can
be less than, equal to, or greater than the total cross-sectional
area of the on-axis outlet.
[0040] According to an embodiment of the invention, the injector
can be provided with an electrically conducting shield that
minimizes plasma ignition within the gas passages of the injector.
If the injector is made of a non-conducting material such as
quartz, a plasma discharge within the injector can be sustained by
electric fields generated by the antenna. Reactive species
generated within the injector may cause undesirable deposition on
or etching of the injector interior. Thus, referring to FIG. 2c, in
order to minimize the formation of sustained discharges, injector
22 can be provided with a conducting shield 40 or coated with an
electrically conducting film. The conducting shield can be located
on the outer surface of the injector, e.g. along the sidewall of
the injector. The shield can significantly reduce electric fields
inside the injector so as to prevent plasma ignition and/or
maintenance of a plasma within gas passages of the injector. As
shown in FIG. 2c, the conducting shield 40 can be designed as a
tubular element such as an annular ring or an open ended
cylindrical jacket. The shield can optionally comprise an
electrically conductive coating on the side and/or top (e.g. 40')
of the injector. The conducting jacket may be electrically grounded
or floating in order to further reduce electric field strength
inside the injector depending on the proximity of other grounded
and RF driven conducting surfaces.
[0041] FIGS. 3a-c illustrate the impact of injector flow ratio on
reactive species densities in an inductively coupled plasma reactor
which includes a gas injector 22 mounted in an opening in the
window 20 (increasing reactant density contours are shown by arrows
A and increasing product density contours are shown by arrows B).
In FIG. 3a, the flow restriction devices (not shown) are set to
direct the gas supply mostly through the on-axis outlet. In FIG.
3b, the flow restriction devices (not shown) are set to direct the
gas supply mostly through the off-axis outlets. In FIG. 3c, the
ratio of the supply gas flow through the on-axis outlet and the
off-axis outlets is tuned to produce flat density contours for both
the reactant and product reactive species. These diagrams do not
account for interaction between the injection flow distribution and
plasma generation/density profile. The impact of reactant
utilization is also not shown. It is reasonable to assume that such
interactions do exist and can also impact plasma and reactive
neutral density profiles over the substrate. The ratio of flows
through the injector outlets can be chosen to optimize uniformity
of one or more of the plasma and reactive species.
[0042] According to a preferred embodiment, the gas injector
includes a single on-axis outlet and a plurality of off-axis
outlets (e.g., 3 outlets arranged at 120.degree. apart, 4 outlets
arranged at 90.degree. apart, etc.) The outlet arrangement is
useful for a polysilicon etching process or an aluminum etching
process. For instance, the off-axis outlets can be spaced
45.degree. apart and located on a tapered side surface extending
from the outer periphery of the axial end. The off-axis angles can
form an acute, right, or obtuse angle with the axial direction. A
preferred angle of the off-axis outlets is 10 to 90.degree. with
respect to the axial direction, more preferably 10 to
60.degree..
[0043] The most preferred mounting arrangement for the gas injector
is a removable mounting arrangement. For instance, the gas injector
could be screwed into the window or clamped to the window by a
suitable clamping arrangement. A preferred removable mounting
arrangement is one in which the gas injector is simply slidably
fitted in the window with only one or more O-rings between the
window and gas injector. For example, an O-ring can be provided in
a groove around a lower part of the gas injector to provide a seal
between the gas injector and the opening in the window. If desired,
another O-ring can be provided in a groove in an upper part (not
shown) of the gas injector to provide a seal between the gas
injector and an exterior surface of the window.
[0044] The gas injector advantageously allows an operator to modify
a process gas supply arrangement for a plasma etch reactor to
optimize gas distribution in the reactor. For example, in plasma
etching aluminum it is desirable to distribute the process gas into
the plasma rather than direct the process gas directly towards the
substrate being etched. In plasma etching polysilicon it is
desirable to distribute the process gas into the plasma and direct
the process gas directly towards the substrate being etched.
Further optimization may involve selecting a gas injector which
extends a desired distance below the inner surface of the window
and/or includes a particular gas outlet arrangement. That is,
depending on the etching process, the number of gas outlets, the
location of the gas outlets such as on the axial end and/or along
the sides of the gas injector as well as the angle(s) of injection
of the gas outlets can be selected to provide optimum etching
results. For example, the angle of injection is preferably larger
for larger size substrates.
[0045] The gas injector can be used to plasma etch aluminum by
injecting the process gas into the interior of the chamber such
that the gas is provided in a desired distribution scheme. As an
example, the process gas can include 100 to 500 sccm of a mixture
of Cl.sub.2 and BCl.sub.3 or Cl.sub.2 and N.sub.2 or BCl.sub.3,
Cl.sub.2 and N.sub.2.
[0046] The gas injector can also be used to plasma etch polysilicon
by injecting the process gas into the interior of the chamber such
that the gas is provided in a desired distribution scheme. As an
example, the process gas can include 100 to 500 sccm of a mixture
of Cl.sub.2 and HBr or C1.sub.2 only, or HBr only, with or without
a carrier such as He and/or an additive such as O.sub.2.
[0047] In processing a semiconductor substrate, the substrate is
inserted into the processing chamber 10 and clamped by a mechanical
or electrostatic clamp to a substrate support. The substrate is
processed in the processing chamber by energizing a process gas in
the processing chamber into a high density plasma. A source of
energy maintains a high density (e.g., 10.sup.9-10.sup.12
ions/cm.sup.3, preferably 10.sup.10-10.sup.12 ions/cm.sup.3) plasma
in the chamber. For example, an antenna 18, such as the planar
multiturn spiral coil, a non-planar multiturn coil, or an antenna
having another shape, powered by a suitable RF source and suitable
RF impedance matching circuitry inductively couples RF energy into
the chamber to generate a high density plasma. However, the plasma
can be generated by other sources such as ECR, parallel plate,
helicon, helical resonator, etc., type sources. The chamber may
include a suitable vacuum pumping apparatus for maintaining the
interior of the chamber at a desired pressure (e.g., below 5 Torr,
preferably 1-100 mTorr). A dielectric window, such as the planar
dielectric window 20 of uniform thickness or a non-planar
dielectric window is provided between the antenna 18 and the
interior of the processing chamber 10 and forms the wall at the top
of the processing chamber 10.
[0048] A gas supply supplying process gas into the chamber includes
the gas injector described above. The process gases include
reactive gasses and optional carrier gases such as Ar. Due to small
orifice size and number of gas outlets, a large pressure
differential can develop between the gas injector and the chamber
interior. For example, with the gas injector at a pressure of >1
Torr, and the chamber interior at a pressure of about 10 mTorr, the
pressure differential is about 100:1. This results in choked, sonic
flow at the gas outlets. If desired, the interior orifice of the
gas outlets can be contoured to provide supersonic flow at each
outlet.
[0049] Injecting the process gas at sonic velocity inhibits the
plasma from penetrating the gas outlets. In the case of deposition
of materials such as doped or undoped silicon dioxide, such a
design prevents plasma decomposed gases such as SiH.sub.4 from
entering the injector from the interior of the chamber. This avoids
subsequent formation of amorphous silicon residues within the gas
outlets. The plasma processing system according to this embodiment
can provide an increased deposition rate and improved uniformity on
the substrate, compared to conventional gas distribution systems,
by concentrating the silicon-containing process gas above the
substrate and by preferentially directing the process gas onto
specific regions of the substrate.
[0050] According to the invention, etch uniformity of metal such as
aluminum, conductive semiconductor materials such as polysilicon
and dielectric materials such as silicon dioxide including
photoresist and selectivity to underlying materials using halogen
and halocarbon based chemistries can be improved. In contrast,
conventional injection through a showerhead incorporated in or
below a dielectric window can result in nonuniform etching across
the substrate, e.g., "center fast resist etching", which can lead
to poor control of the etched features and profiles, and
differences in features at the substrate center and edge. In
addition, polymer formation on the showerhead can lead to
undesirable particle flaking and contamination on the substrate.
Other problems associated with showerhead arrangements include the
additional costs associated with providing a sandwich type
structure for delivering gas across the window, temperature
control, the effects of gas/plasma erosion of the showerhead,
ignition of plasma in the showerhead gas outlets or gap between the
showerhead and the overlying window, lack of process repeatability,
process drift, etc. In contrast, edge injection via a gas injection
ring can result in "edge fast etching" and polymer deposition on
the chamber walls. Photoresist to oxide selectivities are typically
only 1-4 in these cases, where 5-10 would be desirable. The gas
injector according to the invention can provide improvement in the
uniformity of the resist etch rate (typically 6% 3.sigma.) with
simultaneous resist to oxide selectivities of at least 5,
preferably 10 or more. The present preferred injection design thus
can provide a much more uniform flux of reactive intermediates and
chemical radicals to the substrate surface, including both etch
species, such as atomic chlorine and fluorine, and polymerizing
species, such as C.sub.xF.sub.yH.sub.z gases, e.g., CF, CF.sub.2,
CF.sub.3, etc.
[0051] As the substrate size increases, so does the need for center
fed gas. Injection systems supplying gas from gas ring arrangements
cannot provide adequate process gas delivery to the center of large
area substrates typically encountered in flat panel processing.
This is particularly true in bottom-pumped chamber designs commonly
found in plasma processing systems. In the case of plasma etching,
without center gas feeding in accordance with the invention, etch
by-products may stagnate above the center of the substrate in which
case transport is essentially through diffusion alone. This can
lead to undesirable nonuniform etching across the substrate.
According to the invention, process gas is injected within the
plasma region facing and in close proximity to, the center of the
substrate. For instance, gas outlets of the gas injector can be
located far enough below the inner surface of the window such that
the gas outlets are immersed within the plasma. The gas outlets are
preferably located such that there is adequate diffusion of the
ions and neutral species in order to ensure a uniform etch or
deposition rate. Accordingly, the gas injector can be located in a
region where the azimuthal electric field induced by the TCP.TM.
coil falls to zero, which minimizes perturbations of the plasma
generation zone. Furthermore, it is preferable that the gas
injector is immersed a suitable distance such as no more than about
80% of the distance between the chamber ceiling and the substrate.
This ensures that the ion diffusion from upper regions of the
chamber have sufficient space to fill in the lower ion density
immediately beneath the gas injector. This will minimize any
"shadow" of the gas injector in the ion flux to the substrate.
[0052] Using the immersed gas injector allows for independent
selection of the center gas feed location and the chamber aspect
ratio. This facilitates efficient utilization of process gas and
improves process gas delivery to the central region of large area
substrates with minimal disturbance to plasma uniformity. This
configuration is also advantageous because locating the gas outlets
close to the substrate increases the convective transport relative
to diffusive transport in the region immediately above the
substrate. In addition to improving the delivery of the reactants,
the gas injector facilitates efficient transport of etch
by-products out of the substrate region, which can favorably impact
etch uniformity and profile control, particularly in chemically
driven applications such as aluminum etching.
[0053] The gas outlets can have any desired shape such as uniform
diameter along the entire length thereof or other shape such as
conically tapered, flared surfaces or radially contoured surfaces.
The gas outlets can be oriented to inject the gas in any direction,
including directly at the substrate, at an acute angle with respect
to the substrate, parallel to the substrate or back toward the
upper plasma boundary surface (at an oblique angle with respect to
the longitudinal axis of the nozzle), or combinations thereof. It
is desired to achieve a uniform flux of chemical radicals and
reactive intermediate species onto the substrate surface to
facilitate uniform etch and deposition rates across the large area
substrate. If desired, additional gas injection arrangements can
also be provided near the periphery of the substrate or from other
chamber walls.
[0054] Preferably, no sharp corners exist at the distal end of the
gas injector in order to reduce local electric field enhancement
near the tip. However, there may be cases where such field
enhancement can be advantageous.
EXAMPLE 1
[0055] Polysilicon etch depth statistics (mean, standard deviation,
and range) were measured as a function of on-axis:off-axis gas flow
ratio. FIGS. 4a-c show etch profiles for a gate etch process
wherein FIG. 4a shows the effect of higher on-axis gas injection
and FIG. 4c shows the effect of higher off-axis injection.
Predominately on-axis flow conditions produced an etch depth of
212.9.+-.4.7 nm (.+-.2.2%) and a range of 18.3 nm (.+-.1.4%) (see
polysilicon etch results in FIG. 4a). Predominately off-axis flow
conditions produced an etch depth of 212.6.+-.5.3 nm (.+-.2.5%) and
a range of 22.3 nm (.+-.1.7%) (see polysilicon etch results in FIG.
4c). A mixed gas flow condition, in contrast, produced a dramatic
improvement in etch uniformity (see polysilicon etch results in
FIG. 4b). Under the mixed flow conditions, the mean etch depth was
213.5.+-.2.3 nm (.+-.1.1%), with a range of only 7.7 nm (.+-.0.6%).
The polysilicon etch used a Cl.sub.2/HBr/O.sub.2 flow mixture at a
total flow of 420 sccm and a chamber pressure of 10 mT. The RF
antenna (top) power was 800 W, with a -155 V bias on the bottom
electrode. The injector angle was 60.degree..
EXAMPLE 2
[0056] Silicon etch depth statistics (mean, standard deviation, and
range) were measured as a function of on-axis:off-axis gas flow
ratio. FIGS. 5a-c show etch rate profiles for a gate etch process
wherein FIG. 5a shows the effect of higher on-axis gas injection
and FIG. 5c shows the effect of higher off-axis injection.
Predominately on-axis flow conditions produced an etch depth of
1299 A.+-.27 A (.+-.2.1%) and a range of 74 A (.+-.1.0%) (see
polysilicon etch results in FIG. 5a). A mixed gas flow condition
produced an etch depth of 1295 A.+-.23 A (.+-.1.8%) and a range of
76 A (.+-.1.0%) (see polysilicon etch results in FIG. 5b).
Predominately off-axis flow conditions produced a dramatic
improvement in etch uniformity (see polysilicon etch results in
FIG. 5c). Under the off-axis flow conditions, the mean etch depth
was 1272 A.+-.14 A (.+-.1.1%), with a range of 41 A (.+-.0.53%).
The silicon etch used an HBr/O.sub.2 flow mixture at a chamber
pressure of 40 mT and a bottom electrode temperature of 60.degree..
The RF antenna (top) power was 1200 W, with a -320 V bias on the
bottom electrode. The injector angle was 45.degree..
EXAMPLE 3
[0057] FIGS. 6a-b show polysilicon gate critical dimension (CD)
variation as a difference between pre- and post-etch for two
different gas flow ratios. Increased on-axis flow is shown in FIG.
6a in comparison with increased off-axis flow shown in FIG. 6b. The
use of tunable injection results in better CD uniformity. In
particular, the results shown in FIG. 6a provided a mean CD
variation of -3.9 nm, standard deviation of 2.1 nm and range of 7.5
nm whereas the results shown in FIG. 6b provided a CD variation of
-3.4 nm, standard deviation of 1.6 nm and range of 5.9 nm.
EXAMPLE 4
[0058] FIGS. 7a-b show photoresist trim CD variation as a
difference between pre- and post-etch for two different gas flow
ratios. The use of tunable injection results in better CD
uniformity. The process used a Cl.sub.2/O.sub.2 flow mixture with
100 sccm total flow at a chamber pressure of 5 mT and a bottom
electrode temperature of 60.degree.. The RF antenna (top) power was
385 W, with a -34 V self bias on the bottom electrode. The injector
angle was 45.degree.. In particular, the results shown in FIG. 7a
provided a mean CD variation of -49.3 nm, standard deviation of 2.5
nm and range of 9.1 nm whereas the results shown in FIG. 7b
provided a CD variation of -47.6 nm, standard deviation of 2.0 nm
and range of 7.5 nm.
EXAMPLE 5
[0059] FIGS. 8a-b show polysilicon gate critical dimension (CD)
variation as a difference between pre- and post-etch for two
different gas flow ratios. FIG. 8a demonstrates that the mean CD
variation can be adjusted solely by adjusting the gas flow ratios.
A two step process using a Cl.sub.2/HBr/He/O.sub.2 mixture was
used: in step 1 the chamber pressure was 15 mT with 400 sccm total
flow, 575 W antenna (top/inductive) power, and -138 V self bias on
bottom electrode; in step 2 the chamber pressure was 30 mT with 575
sccm total flow, 750 W antenna power, -80 V self bias on the bottom
electrode. In particular, the results shown in. FIG. 8a provided a
mean CD variation of 0.1 nm, standard deviation of 2.4 nm and range
of 9.5 nm whereas the results shown in FIG. 8b provided a CD
variation of 13.3 nm, standard deviation of 2.4 nm and range of 8.9
nm.
[0060] The foregoing has described the principles, preferred
embodiments and modes of operation of the present invention.
However, the invention should not be construed as being limited to
the particular embodiments discussed. Thus, the above-described
embodiments should be regarded as illustrative rather than
restrictive, and it should be appreciated that variations may be
made in those embodiments by workers skilled in the art without
departing from the scope of the present invention as defined by the
following claims.
* * * * *