U.S. patent application number 10/157180 was filed with the patent office on 2003-01-02 for apparatus and method of gas injection sequencing.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Strang, Eric J..
Application Number | 20030000924 10/157180 |
Document ID | / |
Family ID | 26853877 |
Filed Date | 2003-01-02 |
United States Patent
Application |
20030000924 |
Kind Code |
A1 |
Strang, Eric J. |
January 2, 2003 |
Apparatus and method of gas injection sequencing
Abstract
An apparatus and method for gas injection sequencing in order to
increase the gas injection total pressure while satisfying an upper
limit to the process gas flow rate, thereby achieving gas flow
uniformity during a sequence cycle and employing practical orifice
configurations. The gas injection system includes a gas injection
electrode having a plurality of regions, through which process gas
flows into the process chamber. The gas injection system further
includes a plurality of gas injection plenums, each independently
coupled to one of the aforesaid regions and a plurality of gas
valves having an inlet end and an outlet end, where the outlet end
is independently coupled to one of the aforesaid plurality of gas
injection plenums. The gas injection system includes a controller
coupled to the plurality of gas valves for sequencing the flow of
process gas through the aforesaid plurality of regions.
Inventors: |
Strang, Eric J.; (Chandler,
AZ) |
Correspondence
Address: |
OBLON SPIVAK MCCLELLAND MAIER & NEUSTADT PC
FOURTH FLOOR
1755 JEFFERSON DAVIS HIGHWAY
ARLINGTON
VA
22202
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
26853877 |
Appl. No.: |
10/157180 |
Filed: |
May 30, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60301434 |
Jun 29, 2001 |
|
|
|
Current U.S.
Class: |
216/86 |
Current CPC
Class: |
H01J 37/3244 20130101;
C23C 16/45523 20130101; Y10T 137/0324 20150401; C23C 16/45574
20130101; Y10T 137/0318 20150401 |
Class at
Publication: |
216/86 |
International
Class: |
C23F 001/00; B44C
001/22; C03C 015/00; C03C 025/68 |
Claims
1. A plasma processing device comprising a processing surface and a
gas injection system, the gas injection system comprising: a
plurality of gas valves having an inlet configured to receive a
process gas and an outlet; a process chamber; a gas injection
electrode provided within the process chamber; a plurality of gas
injection plenums provided on the gas injection electrode, the
plurality of gas injection plenums being independently coupled to
the outlet of a respective one of the plurality of gas valves; a
plurality of regions provided on the gas injection electrode, each
region of the plurality of regions includes at least one gas
injection orifice coupled to a respective one of the plurality of
gas injection plenums; and a controller coupled to the plurality of
gas valves for sequencing a flow of process gas through the
plurality of regions into the process chamber.
2. The apparatus according to claim 1, wherein at least one region
of the plurality of regions is substantially parallel to the
processing surface, and wherein the at least one gas injection
orifice of the at least one region is configured to discharge
process gas into the process chamber in a direction substantially
normal to the processing surface.
3. The apparatus according to claim 1, wherein the plurality of
regions are substantially parallel to the processing surface, and
wherein the at least one gas injection orifice of the plurality of
regions is configured to discharge process gas into the process
chamber in a direction substantially normal to the processing
surface.
4. The apparatus according to claim 1, further comprising: a common
gas line; and a gas supply system, wherein the inlet of each of the
plurality of the gas valves is coupled to the common gas line, and
wherein the common gas line is coupled to the gas supply
system.
5. The apparatus according to claim 1, further comprising: a
plurality of gas lines; and a plurality of gas supplies, wherein
the inlet of at least one of the plurality of gas valves is
independently coupled to one of the plurality of gas lines, and
wherein the plurality of gas lines are coupled to the plurality of
gas supplies.
6. The apparatus according to claim 1, wherein the at least one gas
injection orifice is substantially cylindrical.
7. The apparatus according to claim 6, wherein the at least one gas
injection orifice is a sonic orifice.
8. The apparatus according to claim 6, wherein the at least one gas
injection orifice has a length between 0.025 mm and 20 mm, and a
diameter between 0.025 mm and 2 mm.
9. The apparatus according to claim 1, wherein the at least one gas
injection orifice comprises: a throat section having a
substantially cylindrical cross section and a throat diameter; a
divergent section connected to the throat section, the divergent
section having an inlet with an inlet diameter and an exit with an
exit diameter, the exit diameter being at least as large as the
inlet diameter, wherein the inlet diameter of the divergent section
is equivalent to the throat diameter of throat section.
10. The apparatus according to claim 9, wherein the divergent
section is conically divergent.
11. The apparatus according to claim 10, wherein the divergent
section has a half-angle that is at most 18 degrees.
12. The apparatus according to claim 10 wherein the divergent
section has a half-angle that is between 12 degrees and 18
degrees.
13. The apparatus according to claim 9, wherein the divergent
section includes a concave wall, wherein the concave wall extends
from the inlet to the exit.
14. The apparatus according to claim 9 wherein the divergent
section is a minimum-length nozzle.
15. The apparatus according to claim 9 wherein the divergent
section is a perfect nozzle.
16. A gas injection system for a plasma processing device, the gas
injection system comprising: a first gas valve having an inlet
configured to receive a process gas and an outlet; a second gas
valve having an inlet configured to receive a process gas and an
outlet; a gas injection electrode provided within a process
chamber; a first gas injection plenum provided on the gas injection
electrode, the first gas injection plenum being coupled to the
outlet of the first gas valve; a second gas injection plenum
provided on the gas injection electrode, the second gas injection
plenum being coupled to the outlet of the second gas valve; a first
gas injection orifice provided on the gas injection electrode, the
first gas injection orifice being coupled to the first gas
injection plenum; a second gas injection orifice provided on the
gas injection electrode, the second gas injection orifice being
coupled to the second gas injection plenum; and a controller
coupled to the first gas valve and the second gas valve for
sequencing a flow of process gas through the first gas injection
plenum and the second gas injection plenum into the process
chamber.
17. A method for supplying at least one process gas to a plasma
processing device using a gas injection system, the method
comprising the steps of: (i) cyclically providing the at least one
process gas at a first gas flow rate for a first period of time
within the plasma processing device at a first region of the gas
injection system; (ii) cyclically providing the at least one
process gas at a second gas flow rate for a second period of time
within the plasma processing device at a second region of the gas
injection system; and (iii) performing steps (i) and (ii) for a
third period of time, wherein the first gas flow rate and the
second gas flow rate are maintained substantially constant during
the third period of time.
18. The method according to claim 17, wherein a first process gas
is provided in step (i) and a second process gas is provided in
step (ii), and wherein the first process gas is different from the
second process gas.
19. The method according to claim 17, further comprising the steps
of: (iv) cyclically providing the at least one process gas at a
third gas flow rate for a fourth period of time within the plasma
processing device at a third region of the gas injection system;
and (v) performing step (iv) for the third period of time.
20. The method according to claim 19, wherein the a first process
gas is provided in step (i), a second process gas is provided in
step (ii) and a third process gas is provided in step (iv), and
wherein the first process gas, the second process gas and the third
process gas are different.
21. A method according to claim 17 wherein the first period of time
and the second period of time range between 1 and 5 seconds.
22. A method for supplying at least one process gas to a plasma
processing device using a gas injection system, the method
comprising the steps of: (i) cyclically providing the at least one
process gas at a first gas flow rate for a first period of time
within the plasma processing device at a first region of the gas
injection system; (ii) cyclically providing the at least one
process gas at a second gas flow rate for a second period of time
within the plasma processing device at a second region of the gas
injection system; and (iii) performing steps (i) and (ii) for a
third period of time, wherein a gas mass flux into the plasma
processing device is maintained substantially constant during the
third period of time.
23. The method according to claim 22, wherein a first process gas
is provided in step (i) and a second process gas is provided in
step (ii), and wherein the first process gas is different from the
second process gas.
24. The method according to claim 22, further comprising the steps
of: (iv) cyclically providing the at least one process gas at a
third gas flow rate for a fourth period of time within the plasma
processing device at a third region of the gas injection system;
and (v) performing step (iv) for the third period of time.
25. The method according to claim 24, wherein the a first process
gas is provided in step (i), a second process gas is provided in
step (ii) and a third process gas is provided in step (iv), and
wherein the first process gas, the second process gas and the third
process gas are different.
26. The method according to claim 22 wherein the first period of
time and the second period of time range between 1 and 5
seconds.
27. A method for supplying at least one process gas to a plasma
processing device using a gas injection system, the method
comprising the steps of: (i) cyclically providing the at least one
process gas at a first gas flow rate for a first period of time
within the plasma processing device at a first region of the gas
injection system; (ii) cyclically providing the at least one
process gas at a second gas flow rate for a second period of time
within the plasma processing device at a second region of the gas
injection system; and (iii) performing steps (i) and (ii) for a
third period of time, wherein a start of the second period of time
overlaps an end of the first period of time.
28. The method according to claim 27, wherein a first process gas
is provided in step (i) and a second process gas is provided in
step (ii), and wherein the first process gas is different from the
second process gas.
29. The method according to claim 27, further comprising the steps
of: (iv) cyclically providing the at least one process gas at a
third gas flow rate for a fourth period of time within the plasma
processing device at a third region of the gas injection system;
and (v) performing step (iv) for the third period of time.
30. The method according to claim 29, wherein the a first process
gas is provided in step (i), a second process gas is provided in
step (ii) and a third process gas is provided in step (iv), and
wherein the first process gas, the second process gas and the third
process gas are different.
31. The method according to claim 27, wherein the first period of
time and the second period of time range between 1 and 5
seconds.
32. The method according to claim 27, wherein the overlap of the
first period of time and the second period of time ranges between
0.1 and 1 second.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. application Ser.
No. 60/301,434 filed Jun. 29, 2001, and is related to U.S.
application Ser. No. 60/272,452, filed Mar. 2, 2001 entitled
"SHOWER-HEAD GAS INJECTION APPARATUS WITH SECONDARY HIGH PRESSURE
PULSED GAS INJECTION" and co-pending PCT International Application
Serial No. PCT/US02/03405, filed Feb. 26, 2002 entitled
"SHOWER-HEAD GAS INJECTION APPARATUS WITH SECONDARY HIGH PRESSURE
PULSED GAS INJECTION". The contents of those applications are
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to plasma processing and more
particularly to a system including a gas injection component for
improved plasma processing.
[0004] 2. Discussion of the Background
[0005] Typically, during materials processing, plasma is employed
to facilitate the addition and removal of material films when
fabricating composite material structures. For example, in
semiconductor processing, a (dry) plasma etch process is utilized
to remove or etch material along fine lines or within vias or
contacts patterned on a silicon substrate. The plasma etch process
generally involves positioning a semiconductor substrate with an
overlying patterned, protective layer (for example, a photoresist
layer) into a processing chamber. Once the substrate is positioned
within the chamber, an ionizable, dissociative gas mixture is
introduced within the chamber at a pre-specified flow rate, while a
vacuum pump is throttled to achieve an ambient process
pressure.
[0006] Thereafter, a plasma is formed when a fraction of the gas
species present are ionized by electrons heated via the transfer of
radio frequency (RF) power either inductively or capacitively, or
microwave power using, for example, electron cyclotron resonance
(ECR). Moreover, the heated electrons serve to dissociate some
species of the ambient gas species and create reactant specie(s)
suitable for the exposed surface etch chemistry. Once the plasma is
formed, any exposed surfaces of the substrate are etched by the
plasma. The process is adjusted to achieve optimal conditions,
including an appropriate concentration of desirable reactant and
ion populations to etch various features (e.g., trenches, vias,
contacts, etc.) in the exposed regions of the substrate. Such
substrate materials where etching is required include silicon
dioxide (SiO.sub.2), poly-silicon and silicon nitride.
[0007] As the feature size shrinks and the number and complexity of
the etch process steps used during integrated circuit (IC)
fabrication escalate, the ability to control the transport of
reactive materials to and effluent etch products from etch features
becomes more stringent. The ability to control such processes must
insure achievement of the proper chemical balance necessary to
attain high etch rates with good material selectivity.
[0008] The etch rate in most dry etch applications (for example,
oxide (SiO.sub.2) etch applications) includes a physical component
and a chemical component. The plasma chemistry should create a
population of positively charged (for example, relatively heavy,
singly charged argon ions) utilized as the physical component and a
population of chemical radicals (such as atomic fluorine F, and CF,
CF.sub.2, CF.sub.3 or more generally CF.sub.x species in a
fluorocarbon plasma) utilized for the chemical component. Moreover,
the chemical reactants (CF.sub.x) act as reactants in the surface
etch chemistry and the (heavy) positively charged ions (Ar.sup.+)
provide energy to catalyze the surface reactions.
[0009] As feature sizes progressively shrink, they do so at a rate
greater than the shrinking oxide and other film thicknesses.
Therefore, the etch feature aspect ratio (depth-to-width) is
greatly increased with shrinking sizes, for example on the order
10:1. As the aspect ratio increases, the directionality of chemical
reactant and ion transport local to the etch features becomes
increasingly important in order to preserve the anisotropy of the
etch feature.
[0010] The transport of electrically charged species such as ions
can be affected by an electric force and, therefore, it is
conventional in the industry to provide a substrate holder or chuck
with an RF bias to attract and accelerate ions to the substrate
surface through the plasma sheath such that they arrive moving in a
direction substantially normal to the substrate surface. However,
the transport of neutral, chemically reactive species is not
amenable to the application of an electric force to assert their
directionality at the substrate surface. In order to affect the
same, gas species are injected under high pressure to preserve
their directionality upon expanding into the low-pressure
environment and the ambient pressure is sufficiently reduced to
further maintain a narrow angular distribution of the velocity
field near the substrate surface.
[0011] In order to affect changes in the transport of neutral
species local to the substrate surface and, thus, affect the etch
rate of high aspect ratio features, the gas injection total
pressure can be increased. One way to increase the gas injection
total pressure is to increase the mass flow rate of process gas
into the process chamber. However, in order to achieve the same
process pressure, the pumping speed to the processing region must
be proportionately increased. For example, when utilizing a
shower-head gas injection system including approximately
three-hundred-and-sixty 0.5 mm diameter orifices of 1 cm in length
with a typical process gas flow rate, for example, of 400 sccm
(standard cubic centimeters per minute) argon, the gas injection
total pressure can be approximately 6 Torr. In order to increase
the gas injection total pressure by a factor of ten (e.g., from 6
to 60 Torr), the mass flow rate must be increased by a factor of
ten (e.g., from 400 to 4000 sccm argon) and, therefore to achieve
the same process pressure of, for example, 20 mTorr, the pumping
speed at the processing region must also be increased by a factor
of ten (e.g., from 250 to 2500 liters per second).
[0012] A turbo-molecular pump (TMP) with a minimum inlet pumping
speed of 5000 liters per second is employed to achieve this demand
for pumping speed. The TMP includes a vacuum chamber configured to
have at least a flow conductance equivalent to that of the inlet
pumping speed to the TMP. However, these high-speed pumps are
cumbersome, and extremely expensive (e.g., currently such pumps
cost approximately $100,000 per pump with an additional $50,000 for
an appropriately sized gate valve). Moreover, to accommodate their
size and enable the aforesaid flow conductance, the process chamber
footprint must be increased. Consequently, they are not an
economically viable solution. Therefore, what is needed is a way to
substantially increase the gas injection total pressure while
satisfying an upper limit to the process gas flow rate.
[0013] Another technique is to pulse the gas in short bursts as it
enters the process chamber. However, this technique results in
transient pressure waves due to the large volume of gas introduced
to the chamber with each pulse. In particular, there is an abrupt
increase in chamber pressure followed by a slow decay as the vacuum
pump struggles to bring the pressure back to specification. What is
needed is a way to increase the gas injection total pressure
without creating a substantially non-stationary process.
[0014] A further method of increasing the gas injection total
pressure, while not affecting the mass flow rate or process chamber
pressure, involves reducing the number and/or size of the gas
injection orifices (i.e. reducing the total injection flow-through
area). However, this reduction can seriously jeopardize process
uniformity over large substrates, for example, 200 to 300 mm and
greater. Conventional systems achieve uniform etching of substrates
by maintaining a uniform gas flow over the substrate surface (in
addition to other requirements). In order to achieve a uniform
introduction of the process gas to the process environment,
materials processing devices utilize a showerhead gas distribution
system comprising a plurality of gas orifices, for example, on the
order 100 to 1000 gas injection orifices of 0.5 mm in diameter.
However, to maintain conventional process recipes (i.e. chamber
pressure and gas flow rate) optimal for etch applications such as
oxide etch applications, the injection pressure is limited and
neutral flow directionality suitable for high aspect ratio feature
etch is sacrificed. What is needed is a way to increase the gas
injection total pressure while achieving specifications for process
uniformity and employing practical gas injection orifice
geometry.
SUMMARY OF THE INVENTION
[0015] The present invention utilizes a gas injection system that
overcomes the aforementioned problems for processing a workpiece in
a plasma processing chamber.
[0016] According to an embodiment of the present invention, the gas
injection system advantageously includes a gas injection electrode
having a plurality of regions, through which process gas flows into
the process chamber, wherein each region includes one or more gas
injection orifices. The gas injection system further includes a
plurality of gas injection plenums, each independently connected to
one of the above regions of the gas injection electrode and a
plurality of gas valves having an inlet end and an outlet end,
wherein the outlet end is independently connected to one of the
plurality of gas injection plenums of the gas injection system. The
gas injection system further includes a controller coupled to the
plurality of gas valves for sequencing the flow of process gas
through the plurality of regions of the gas injection system.
[0017] Furthermore, an additional embodiment of the present
invention advantageously provides a method for cyclically supplying
at least one gas through at least two regions of the gas injection
system to a plasma processing device for processing a substrate.
The method includes the steps of (i) injecting a first gas in a
first region of the gas injection system for a first period of
time, (ii) injecting a second gas in a second region of the gas
injection system for a second period of time, and (iii) performing
steps (i) and (ii) for a third period of time, wherein the gas flow
rate above the substrate is kept substantially constant during the
third period of time.
[0018] The flow of process gas to the process chamber can
additionally include the steady flow of a third gas in a third
region of the gas injection system for the third period of
time.
[0019] Furthermore, the gas injection sequencing can further
include the overlapping of gas sequences to different regions
within the gas injection system in order to allow for modulation of
the chamber pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] A more complete appreciation of the invention and many of
the attendant advantages thereof will become readily apparent with
reference to the following detailed description, particularly when
considered in conjunction with the accompanying drawings, in
which:
[0021] FIG. 1 is a schematic view of a plasma processing device
with a gas injection system according to a first embodiment of the
present invention;
[0022] FIG. 2 is a schematic view of a plasma processing device
with a gas injection system according to a second embodiment of the
present invention;
[0023] FIG. 3 is a plan view of a first gas injection zoning
pattern according to the embodiments of FIGS. 1 and 2;
[0024] FIG. 4 is a plan view of a second gas injection zoning
pattern according to the embodiments of FIGS. 1 and 2;
[0025] FIG. 5 is a cross-sectional view of an individual gas
injection orifice, illustrating a first geometry;
[0026] FIG. 6 is a cross-sectional view of an individual gas
injection orifice, illustrating a second geometry;
[0027] FIG. 7 is a cross-sectional view of an individual gas
injection orifice, illustrating a third geometry;
[0028] FIG. 8 illustrates a first timing diagram for gas injection
sequencing in accordance with an embodiment of the present
invention;
[0029] FIG. 9 illustrates a second timing diagram for gas injection
sequencing in accordance with an embodiment of the present
invention; and
[0030] FIG. 10 illustrates a third timing diagram for gas injection
sequencing in accordance with an embodiment of the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0031] A plasma processing device 1 is depicted in FIG. 1 including
chamber 10, gas injection system 20, substrate holder 40 upon which
a substrate 45 to be processed is affixed, pumping duct 50, and
vacuum pumping system 55. Chamber 10 is configured to facilitate
the generation of plasma 60 adjacent a surface of substrate 45,
wherein plasma 60 is formed via collisions between heated electrons
and an ionizable gas. An ionizable gas or mixture of gases is
introduced via gas injection system 20 and the process pressure is
adjusted using a gate valve (not shown) to throttle the vacuum
pumping system 55. For example, plasma 60 is utilized to create
materials specific to a pre-determined materials process, and to
aid either the deposition of material to a substrate 45 or the
removal of material from the exposed surfaces of substrate 45.
[0032] Substrate 45 is transferred into and out of chamber 10
through a slot valve (not shown) and chamber feed-through (not
shown) via robotic substrate transfer system where it is received
by substrate lift pins (not shown) housed within chuck 40 and
mechanically translated by devices housed therein. Once substrate
45 is received from substrate transfer system, it is lowered to an
upper surface of chuck 40 and affixed to chuck 40 via an
electrostatic clamp (not shown). Moreover, gas may be delivered to
the back-side of the substrate to improve the gas-gap thermal
conductance between the substrate 45 and the chuck 40.
[0033] In an alternate embodiment, the chuck 40 can further include
a cooling system including a re-circulating coolant flow that
receives heat from chuck 40 and transfers heat to a heat exchanger
system (not shown), or when heating, transfers heat from the heat
exchanger system. Such a system can be utilized when temperature
control of the substrate is required at elevated or reduced
temperatures. For example, temperature control of the substrate may
be useful at temperatures in excess of the steady-state temperature
achieved due to a balance of the heat flux delivered to the
substrate from the plasma and the heat flux removed from substrate
by conduction to the chuck 40. In other embodiments, heating
elements, such as resistive heating elements, can be included.
[0034] In a preferred embodiment, plasma 60 is utilized to process
substrate 45. For example, chuck 40 is electrically biased at a RF
voltage via the transmission of RF power from RF generator 42
through impedance match network 44 to chuck 40. The RF bias can
serve to heat electrons and, thereby, capacitively couple power to
plasma 60. In this configuration, it can operate as a reactive ion
etch (RIE) reactor, wherein the chamber and upper gas injection
electrode serve as ground surfaces. A typical frequency for the RF
bias is 13.56 MHz. In another example, chuck electrode 40 can serve
to bias the substrate 45 to control the ion energy during
processing steps, wherein an additional electrode (e.g., inductive
coil or electrode opposite the substrate) serves to generate a high
density plasma (HDP).
[0035] The process gas is introduced to the plasma reactor via gas
injection system 20 including gas injection electrode 21, gas valve
manifold 26, mass flow controller manifold 30, and a gas supply 34.
Process gas originates from the gas supply 34. Preferably, the gas
supply 34 is a cabinet that houses a plurality of compressed gas
cylinders, each of which stores a gas. The gas supply 34 preferably
further includes pressure regulators for safe gas handling
practices known to those of ordinary skill in the art. The gas
supply 34 is also coupled to a controller 90.
[0036] The mass flow controller manifold 30 is coupled to the gas
supply 34. The mass flow controller manifold 30 includes a
plurality of mass flow controllers 32A, 32B, 32C, 32D. In a
preferred embodiment, each mass flow controller 32A, 32B, 32C, 32D
monitors and controls the mass flow rate of a single processing gas
being supplied by gas supply 34. For example, four processing gases
can be used. In an oxide etch process (e.g., a SiO.sub.2 etch
process), processing gases include Ar, C.sub.4F.sub.8 and O.sub.2,
wherein a fourth gas nitrogen (N.sub.2) is available for chamber
purging. An exemplary process recipe is a gas composition with flow
rates Ar/C.sub.4F.sub.8/O.sub.2=400/7/12 sccm (standard cubic
centimeters per minute). Although provisions in FIG. 1 are made for
four gases, either more than four gases or less than four gases can
be used in alternate embodiments. Other gases can include
C.sub.5F.sub.8, C.sub.4F.sub.6, HF, NH.sub.3, H.sub.2, Cl.sub.2,
SF.sub.6, HBr, CO, etc. The gate valve located adjacent vacuum pump
55 in pumping duct 50 can be partially open in order to adjust the
chamber process pressure to approximately 20 mTorr.
[0037] The mass flow controller manifold 30 is coupled to the
controller 90. In a preferred embodiment, each mass flow controller
32A, 32B, 32C, 32D is coupled to the controller 90. The mass flow
controllers 32A, 32B, 32C, 32D are preferably commercially
available mass flow controllers capable of regulating the flow rate
of gas ranging from 1 sccm to 2000 sccm (the mass flow controller
is calibrated per the process specifications as discussed above).
For example, 500 sccm, 40 sccm and 20 sccm mass flow controllers
would be suitable for the above gas composition and flow rates,
respectively.
[0038] The valve manifold 26 is coupled to mass flow controller
manifold 30 via gas pipe 38. In a preferred embodiment, processing
gases are mixed along the length of gas pipe 38. The valve manifold
26 includes gas inlets 28A 28B, 28C, a number of control valves
27A, 27B, 27C, and a number of outlet manifolds 29A, 29Bb, 29C. In
a preferred embodiment, each gas inlet 28A, 28B, 28C is coupled to
the gas pipe 38 and to a respective control valve 27A, 27B, 27Cc.
In addition, each control valve 27A, 27B, 27C is coupled to a
respective outlet manifold 29A, 29B, 29C. In a preferred
embodiment, the valves 27A, 27B, 27C are each electrically actuated
two-way valves. An exemplary valve is a pneumatically-activated
valve such as a Nupro SS-BNVCR4-C valve. Moreover, the
pneumatically-activated valves are opened and closed via activation
from an array of electro-mechanical valves (e.g., SMC
VQ-110U-5F).
[0039] The valve manifold 26 is coupled to the gas injection
electrode 21, which includes a number of gas injection plenums 23A,
23B, 23C. In a preferred embodiment, each outlet manifold 29A, 29B,
29C is coupled to at least one gas injection plenum. In the
embodiment depicted in FIG. 1, outlet manifold 29A is coupled to
gas injection plenum 23A, outlet manifold 29B is coupled to gas
injection plenum 23B, and outlet manifold 29C is coupled to gas
injection plenum 23C. The valve manifold 26 is also coupled to the
controller 90.
[0040] In a preferred embodiment, a first gas injection plenum 23A
is a cylindrical volume, a second gas injection plenum 23B is an
annular (ring-like) volume, and a third gas injection plenum 23C is
an annular (ring-like) volume. Each gas injection plenum 23A, 23B,
23C is independently connected to a region of gas injection
orifices 24A, 24B, 24C, respectively. For example, in a gas
injection electrode 21 including "N" gas injection orifices, each
gas injection plenum can be coupled to "N/3" gas injection orifices
and, more generally, if "M" injection plenums (and M corresponding
gas valves 27) were employed, each region can be coupled to N/M gas
injection orifices. However, the number of gas injection plenums
and gas injection orifices is not limited in any way by these
exemplary embodiments.
[0041] When gas valve(s) 27A, 27B, 27C is/are open, process gas
flows to the respective gas injection plenum(s) 23A, 23B, 23C, and
process gas is introduced to the process chamber via at least one
region of gas injection orifices 24A, 24B, 24C. When gas valve(s)
27A, 27B, 27C is/are closed, process gas does not flow to the
respective gas injection plenum(s) 23A, 23B, 23C, and process gas
is not introduced to the process chamber via one of the regions of
gas injection orifices 24A, 24B, 24C. In a preferred embodiment,
the timing for gas valves 27A, 27B, 27C opening and closing and the
sequencing of gas valves are utilized to affect process conditions
suitable for improved materials processing applications.
[0042] Controller 90 includes a microprocessor, memory, and a
digital I/O port capable of generating control voltages sufficient
to activate valves 27A, 27B, 27C as well as mass flow controllers
32A, 32B, 32C, 32D. Moreover, controller 90 exchanges status data
with the gas supply 34. In addition, controller 90 sends and
receives control signals to and from vacuum pump 55. For example, a
gate valve can be controlled. A program stored in the memory
includes a process recipe with which to activate the valves and the
respective gas flow rate when desired. One example of controller 90
is a Model#SBC2486DX PC/104 Embeddable Computer Board commercially
available from Micro/sys, Inc., 3730 Park Place, Glendale, Calif.
91020.
[0043] In a second embodiment shown in FIG. 2, plasma processing
device 100 includes the same components as described in reference
to FIG. 1 except for several elements as part of the gas injection
system 120 to be described below. The same reference numerals will
be used to identify identical components present in both the first
embodiment and the second embodiment. As described in FIG. 1 and
again shown in FIG. 2, the process gas arriving at entrance to
valve manifold 26 is distributed to different regions within gas
injection electrode 21 via gas valves 27A, 27B, 27C. Each valve
27A, 27B, 27C is independently coupled to a separate gas line 38,
138 and 238, respectively. Each gas line 38, 138, 238 is connected
to an independent mass flow controller manifold 30, 130, 230 and
gas supply 34, 134, 234, respectively.
[0044] Process gas carried in gas line 38 originates from gas
supply 34. For example, gas supply 34 can be a cabinet that houses
a plurality of compressed gas cylinders, each of which stores a
gas. The flow rate of processing gas is monitored and controlled
via mass flow controllers 32A, 32B, 32C, 32D, which are assembled
as mass flow controller manifold 30.
[0045] Similarly, process gas carried in gas line 138 originates
from gas supply 134. For example, gas supply 134 can be a cabinet
that houses a plurality of compressed gas cylinders, each of which
stores a gas. The flow rate of processing gas is monitored and
controlled via mass flow controllers 132A, 132B, 132C, 132D, which
are assembled as mass flow controller manifold 130.
[0046] Process gas carried in gas line 238 originates from gas
supply 234. For example, gas supply 234 can be a cabinet that
houses a plurality of compressed gas cylinders, each of which
stores a gas. The flow rate of processing gas is monitored and
controlled via mass flow controllers 232A, 232B, 232C, 232D
assembled as mass flow controller manifold 230.
[0047] Controller 90 includes a microprocessor, memory, and a
digital I/O port capable of generating control voltages sufficient
to activate valves 27A, 27B, 27C, as well as mass flow controllers
32, 132 and 232. Moreover, controller 90 exchanges status data with
the gas supplies 34, 134 and 234. In addition, controller 90 sends
and receives control signals to and from vacuum pump 55 controller.
For example, a gate valve can be controlled. A program stored in
the memory includes a process recipe with which to activate the
valves and the respective gas flow rate when desired. One example
of controller 90 is a Model#SBC2486DX PC/104 Embeddable Computer
Board commercially available from Micro/sys, Inc., 3730 Park Place,
Glendale, Calif. 91020.
[0048] In an alternate embodiment, gas injection electrode 21
includes heating/cooling and electrical systems in order to serve
as a RF powered electrode. Similar to the chuck electrode 40, the
(upper) gas injection electrode is energized via application of RF
power from a RF generator (not shown) through an impedance match
network (not shown) and coaxial transmission line (not shown). Gas
injection electrode 22 is conventionally configured to serve as an
electrode through which RF power (e.g. 2 to 3 kW of 60 MHz RF
power) is coupled to sustain plasma 60. The powered electrode is
electrically insulated from the grounded chamber wall.
[0049] In a further alternative embodiment, gas injection electrode
21 further includes a gas inject plate (not shown) attached to the
lower surface 22 of gas injection electrode 21. The gas inject
plate can be machined from a metal such as aluminum and, for those
surfaces in contact with the plasma, anodized to form an aluminum
oxide protective coating or spray coated with Y.sub.2O.sub.3.
Furthermore, the gas inject plate may be fabricated from silicon or
carbon to act as a scavenging plate, or it can be fabricated from
silicon carbide to promote greater erosion resistance. The gas
inject plate includes gas orifices substantially aligned with those
orifices extending through bottom surface 22 of gas injection
electrode 21.
[0050] Vacuum pump 55 is preferably a turbo-molecular vacuum pump
(TMP) capable of a pumping speed up to 5000 liters per second or
greater. In conventional plasma processing devices utilized for dry
plasma etch, a 1000 to 3000 liter per second TMP is employed. TMPs
are useful for low pressure processing, typically less than 50
mTorr. At higher pressures, the TMP pumping speed falls off
dramatically. For high pressure processing (e.g., processing
greater than 100 mTorr), a mechanical booster pump and dry roughing
pump is recommended.
[0051] In FIGS. 1 and 2, the regions of gas injection orifices 24A,
24B, 24C are associated with gas injection plenums 23A, 23B, 23C
such that the pattern created forms annular rings. A plan view of
this configuration is presented in FIG. 3. The pattern described in
FIG. 3 enables radial control of the gas flow rate above substrate
45. However, other configurations are possible including the five
zone gas injection system of FIG. 4 including zones 24D, 24E, 24F,
24G, 24H. The pattern described in FIG. 4 further enables azimuth
control of the gas flow rate above substrate 45. In FIGS. 3 and 4,
three zones 24A, 24B, 24C, and five zones 24D, 24E, 24F, 24G, 24H
are shown; however, the number of zones and their pattern is not
limited. And more generally, the volume of space defining each
plenum 23A, 23B, 23C is a simply connected or non-simply connected
domain.
[0052] In order to facilitate changes in the neutral gas transport
local to the surface of substrate 45, process gas injection is
oriented such that the flow of gas is substantially normal to the
surface of substrate 45. Therefore, the lower surface 22 of gas
injection electrode system 21 is substantially parallel with the
surface of substrate 45. Moreover, the gas injection should be made
proximate the substrate surface 45; for example, directly above the
surface of substrate 45.
[0053] With continuing reference to FIGS. 1 and 2, regions of gas
injection orifices 24A, 24B, 24C each include a plurality of gas
injection orifices. Three exemplary orifice cross-sections are
depicted in FIGS. 5-7.
[0054] In FIG. 5, a cross-sectional schematic of a preferred gas
injection orifice 250 is shown, including an orifice throat 252
substantially cylindrical in cross-section with length L and
diameter d.sub.th and having inner cylindrical wall 253. The
orifice throat 252 is defined as the minimum area cross-section. A
typical range for length L is between 0.025 mm and 20 mm and
diameter d.sub.th is between 0.025 mm and 2 mm. The inlet 254 to
cylindrical orifice 252 has a cross-section substantially similar
to the outlet 255.
[0055] In a second configuration presented in FIG. 6, the gas
injection orifice 260 includes a first section substantially
cylindrical in cross-section having an orifice throat 262 with
inlet 264, outlet 265 and inner cylindrical wall 263. Beyond the
orifice throat 262 extends a substantially divergent section with
inlet 265, inner conical wall 266 and outlet 268 of diameter
d.sub.e, wherein diameter d.sub.e is greater than or equal to the
throat diameter d.sub.th. This geometry is referred to as a
divergent nozzle. Preferably, the half-angle .alpha. of the
conically divergent section wall 266 does not exceed eighteen
degrees in order to minimize radial flow losses within the
divergent nozzle, and more preferably, the angle .alpha. is between
twelve degrees and eighteen degrees.
[0056] In a third configuration presented in FIG. 7, the gas
injection orifice 270 includes a first section substantially
cylindrical in cross-section having an orifice throat 272 with
inlet 274, outlet 275 and inner cylindrical wall 273. Beyond the
orifice throat 272 extends a substantially divergent section with
inlet 275, inner concave wall 280 and outlet 278 of diameter
d.sub.e, wherein diameter d.sub.e is greater than or equal to the
throat diameter d.sub.th. This geometry is referred to as a
"minimum-length" nozzle; a simplified version of a "perfect"
nozzle. Minimum-length and perfect nozzles are well known to those
skilled in the art. The latter two configurations may serve to
restrain the rate of expansion of process gas from the total
pressure in the gas injection plenums 23A, 23B, 23C to the process
chamber pressure, if configured properly using the Method of
Characteristics. The Method of Characteristics is a well-known
method used to design a divergent nozzle and, more specifically, it
is used to tailor the divergent nozzle shape (particularly those
divergent nozzles with a non-zero second derivative of the wall
coordinate) to avoid nozzle shock losses. The use of the Method of
Characteristics can lead to what are known as "perfect" and
"minimum-length" nozzles. This method and such nozzles are well
known to one of ordinary skill in the art.
[0057] Utilizing the embodiments shown in FIGS. 1 and 2, the
present invention describes a method to cyclically sequence the
process gas flow through regions of gas injection orifices 24A,
24B, 24C (as shown in FIGS. 1 and 2) in order to increase the gas
injection total pressure while satisfying an upper limit to the
process gas flow rate, achieving gas flow uniformity during a
sequence cycle and employing practical orifice configurations. For
example, gas injection electrode 21 can include M regions of gas
injection orifices 250, wherein gas injection electrode 21 includes
a total number of N gas injection orifices 250 and each region
includes a fraction of the total number of gas injection orifices
250 in gas injection electrode 21. Preferably, the fraction of the
total number of gas injection orifices 250 is N/M. In this system,
the gas injection total pressure is approximately M times greater
in each gas injection plenum 23A, 23B, 23C than the total pressure
in a single gas injection plenum coupled to all N gas injection
orifices 250.
[0058] FIG. 8 illustrates a preferred first timing diagram 300 for
gas injection sequencing using a gas sequencing method wherein the
process gas flow is cyclically sequenced, for simplicity, between
regions of gas injection orifices 24A, 24B, 24C. A first valve 27A,
pneumatically connected to a first region of gas injection orifices
24A follows sequence 302. A second valve 27B, coupled to a second
region of gas injection orifices 24B follows sequence 306. And, a
third valve 27C, coupled to a third region of gas injection
orifices 24C follows sequence 310. Gas injection sequencing
proceeds when; in sequence 302, valve 27A opens for a time
(t.sub.1) 303, flows process gas at a gas flow rate Q.sub.1 through
a region of total flow-through area of A.sub.1 and then closes; in
sequence 306, gas valve 27B opens for a time (t.sub.2) 307, flows
process gas at a gas flow rate Q.sub.2 through a region of total
flow-through area of A.sub.2 and closes; and, in sequence 310, gas
valve 27C opens for a time (t.sub.3) 311, flows process gas at a
gas flow rate Q.sub.3 through a region of total flow-through area
of A.sub.3 and closes. The three sequences are repeated throughout
the duration of a substrate processing time T.
[0059] In the preferred method, the gas injection sequencing is
such that the gas flow rate is substantially steady (or stationary)
during the substrate processing time, viz.
Q.sub.1=Q.sub.2=Q.sub.3=Q,
[0060] where Q is a substantially steady process gas flow rate, as
opposed to gas injection pulsing where the gas flow rate is
unsteady (or non-stationary) during the substrate processing time.
During the gas sequencing, process gas is injected locally above
the substrate according to the activated region of gas injection
orifices.
[0061] In an alternate embodiment, the gas injection sequencing is
such that the gas mass flux is substantially steady (or stationary)
during the substrate processing time, viz.
Q.sub.1*t.sub.1/A.sub.11=Q.sub.2*t.sub.2/A.sub.2=Q.sub.3*t.sub.3/A.sub.3=Q-
*T/A.sub.tot,
[0062] where A.sub.tot is the sum of the region total flow-through
area for all regions of gas injection orifices 24A, 24B and 24C;
i.e. A.sub.tot=A.sub.1+A.sub.2+A.sub.3.
[0063] In an alternate method, the period of time where each region
of gas injection orifices is activated, i.e. 303, 307 and 311, can
be adjusted to optimize the spatial uniformity of the materials
process. Typically, the sequence times 303, 307 and 311 vary
between one to five seconds.
[0064] FIG. 9 presents an alternate timing diagram 400 for gas
injection sequencing using an alternative gas sequencing method
wherein the process gas flow is cyclically sequenced between
regions of gas injection orifices 24A, 24B, 24C; however, the gas
sequences are overlapped. A first valve 27A, coupled to a first
region of gas injection orifices 24A follows sequence 402. A second
valve 27B, pneumatically connected to a second region of gas
injection orifices 24B follows sequence 406. And, a third valve
27C, pneumatically connected to a third region of gas injection
orifices 24C follows sequence 410.
[0065] Gas injection sequencing proceeds when; in sequence 402,
valve 27A opens for a time (t.sub.1) 403, flows process gas at a
gas flow rate Q.sub.1 through a region of total flow-through area
of A.sub.1 and closes; in sequence 406, gas valve 27B opens for a
time (t.sub.2) 407, flows process gas at a gas flow rate Q.sub.2
through a region of total flow-through area of A.sub.2 and closes
wherein the beginning of time period 407 of sequence 406 overlap
with end of time period 403 in sequence 402 for a time period 415;
and, in sequence 410, gas valve 27C opens for a time (t.sub.3) 311,
flows process gas at a gas flow rate Q.sub.3 through a region of
total flow-through area of A.sub.3 and closes wherein the beginning
of time period 411 of sequence 410 overlaps with end of time period
407 in sequence 406 for a time period 420. The three sequences are
repeated throughout the duration of the substrate processing time
T.
[0066] During the gas sequencing, process gas is injected locally
above the substrate according to the activated region of gas
injection orifices. In an alternate method, the period of time
where each region of gas injection orifices is activated, i.e. 403,
407 and 411, may be adjusted to optimize the spatial uniformity of
the materials process according to substrate processing results.
However, in addition to the set of control parameters available for
the first gas injection sequencing scheme 300, the second gas
injection sequencing scheme offers the ability to modulate the
chamber pressure according to the signal 425 in FIG. 9 wherein the
pressure "modulation" has time periods 430 and 435 mirroring the
occurrence of valve sequence overlaps 415 and 420,
respectively.
[0067] In order to facilitate the chamber pressure modulation, the
gate valve used in conjunction with vacuum pump 55 must remain
stationary (i.e. it must not adjust itself in response to the
pressure variations). These pressure "modulations" can further
affect the neutral transport local to the upper surface of
substrate 45. The system will behave as depicted in FIG. 9 when the
time periods 430 and 435 are sufficiently small relative to the
sequence time periods 403, 407 and 411. Typically, the sequence
times 403, 407 and 411 vary between 1 to 5 seconds and the overlap
time periods vary between 0.1 to 1 second.
[0068] FIG. 10 presents an alternate timing diagram 500 for gas
injection sequencing using an alternative gas sequencing method
wherein the process gas flow is cyclically sequenced between
regions of gas injection orifices 24A, 24B, 24C. A first valve 27A,
coupled to a first region of gas injection orifices 24A remains
open during processing according to sequence 502. A second valve
27B, coupled to a second region of gas injection orifices 24B
follows sequence 506. And, a third valve 27C, coupled to a third
region of gas injection orifices 24C follows sequence 510.
[0069] Gas injection sequencing proceeds when; in sequence 502,
valve 27A remains open during processing for time T and flows
process gas at a gas flow rate of Q.sub.1 through a region of total
flow-through area of A.sub.1; in sequence 506, gas valve 27B opens
for a time (t.sub.2) 507, flows process gas at gas flow rate of
Q.sub.2 through a region of total flow-through area of A.sub.2 and
closes; and, in sequence 510, gas valve 27C opens for a time
(t.sub.3) 511, flows process gas at a gas flow rate of Q.sub.3
through a region of total flow-through area A.sub.3 and closes. The
three sequences are repeated throughout the duration of the
substrate processing time T. During the gas sequencing, process gas
is injected locally above the substrate according to the activated
region of gas injection orifices. Moreover, the period of time
where each region of gas injection orifices is activated, i.e. 507
and 511, may be adjusted to optimize the spatial uniformity of the
materials process. Typically, the sequence times 507 and 511 vary
between one to five seconds.
[0070] Although three specific gas sequencing diagrams 300, 400 and
500 and methods have been presented with reference to FIGS. 8, 9
and 10, it will be appreciated by those skilled in the art that
other alternatives are possible including combinations thereof.
[0071] It should be noted that the exemplary embodiments depicted
and described herein set forth the preferred embodiments of the
present invention, and are not meant to limit the scope of the
claims hereto in any way.
[0072] Numerous modifications and variations of the present
invention are possible in light of the above teachings. It is
therefore to be understood that, within the scope of the appended
claims, the invention may be practiced otherwise than as
specifically described herein.
* * * * *