U.S. patent application number 12/013907 was filed with the patent office on 2009-07-16 for flow control system and method for multizone gas distribution.
This patent application is currently assigned to TOKYO ELECTRON LIMITED. Invention is credited to Stefan Sawusch.
Application Number | 20090178714 12/013907 |
Document ID | / |
Family ID | 40849626 |
Filed Date | 2009-07-16 |
United States Patent
Application |
20090178714 |
Kind Code |
A1 |
Sawusch; Stefan |
July 16, 2009 |
FLOW CONTROL SYSTEM AND METHOD FOR MULTIZONE GAS DISTRIBUTION
Abstract
A multizone gas distribution system configured to be coupled to
a process chamber is described. The multizone gas distribution
system comprises a first gas distribution element and a second gas
distribution element. Additionally, the multizone gas distribution
system comprises a flow control system configured to divide a flow
of process gas between the first gas distribution element and the
second gas distribution element. Further, a system controller
coupled to the flow control system is configured to adjust the flow
of process gas to the first gas distribution element and the second
gas distribution element according to a target flow condition.
Further yet, the system controller is configured to monitor the
flow control system in order to perform at least one of monitoring
a flow rate, adjusting a flow rate, controlling a flow rate,
determining a fault condition, and determining an erroneous fault
condition.
Inventors: |
Sawusch; Stefan; (Pirna,
DE) |
Correspondence
Address: |
WOOD, HERRON & EVANS, LLP (TOKYO ELECTRON)
2700 CAREW TOWER, 441 VINE STREET
CINCINNATI
OH
45202
US
|
Assignee: |
TOKYO ELECTRON LIMITED
Tokyo
JP
|
Family ID: |
40849626 |
Appl. No.: |
12/013907 |
Filed: |
January 14, 2008 |
Current U.S.
Class: |
137/12 ;
137/861 |
Current CPC
Class: |
F17D 5/00 20130101; Y10T
137/2562 20150401; Y10T 137/7761 20150401; Y10T 137/7759 20150401;
Y10T 137/2501 20150401; Y10T 137/0379 20150401; Y10T 137/2529
20150401; Y10T 137/877 20150401 |
Class at
Publication: |
137/12 ;
137/861 |
International
Class: |
F17D 3/00 20060101
F17D003/00; F16K 11/00 20060101 F16K011/00 |
Claims
1. A multizone gas distribution system configured to be coupled to
a process chamber, comprising: a multizone gas distribution
assembly comprising a first gas distribution element configured to
introduce a first flow rate of process gas to said process chamber
and a second gas distribution element configured to introduce a
second flow rate of process gas to said process chamber; a flow
control system coupled to said multizone gas distribution system,
said flow control system comprising: a process gas supply system
configured to supply said process gas, a process gas supply line
having an inlet end coupled to said process gas supply system and
an outlet end that splits into a first gas supply branch that
supplies said process gas to said first gas distribution element
and a second gas supply branch that supplies said process gas to
said second gas distribution element, a flow rate controller
coupled to said process gas supply line and configured to control
the total sum of said first flow rate and said second flow rate, a
first flow control valve coupled to said first gas supply branch
and configured to adjust said first flow rate, a second flow
control valve coupled to said second gas supply branch and
configured to adjust said second flow rate, a first pressure
measurement device coupled to said first gas supply branch and
configured to measure a first pressure, and a second pressure
measurement device coupled to said second gas supply branch and
configured to measure a second pressure; and a system controller
coupled to said flow control system and configured to control said
first flow rate and said second flow rate according to a target
flow condition by adjusting said first flow control valve and said
flow second control valve and monitoring said first pressure and
said second pressure.
2. The multizone gas distribution system of claim 1, wherein said
first pressure measurement device is located on an outlet side of
said first flow control valve, and said second pressure measurement
device is located on an outlet side of said second flow control
valve.
3. The multizone gas distribution system of claim 1, wherein said
multizone gas distribution assembly comprises a showerhead gas
distribution system, and said first gas distribution element is
arranged in a first region while said second gas distribution
element is arranged in a second region.
4. The multizone gas distribution system of claim 3, wherein said
first region comprises a substantially central region of said
shower gas distribution system and said second region comprises a
substantially peripheral region surrounding said central
region.
5. The multizone gas distribution system of claim 3, wherein said
first gas distribution element is pneumatically isolated from said
second gas distribution element.
6. The multizone gas distribution system of claim 3, wherein said
first gas distribution element comprises a first gas plenum
configured to receive said first flow rate of said process gas from
said first gas supply branch and a first array of openings formed
through a gas injection plate that is configured to introduce said
process gas from said first plenum to a process space in said
process chamber, and wherein said second gas distribution element
comprises a second gas plenum configured to receive said second
flow rate of said process gas from said second gas supply branch
and a second array of openings formed through said gas injection
plate that is configured to introduce said process gas from said
second plenum to said process space in said process chamber.
7. The multizone gas distribution system of claim 1, wherein said
system controller is configured to determine a fault condition or
an erroneous fault condition by monitoring said first pressure, or
said second pressure, or a combination of said first pressure and
said second pressure.
8. The multizone gas distribution system of claim 1, wherein said
system controller is configured to determine a service condition by
monitoring said first pressure, or said second pressure, or a
combination of said first pressure and said second pressure.
9. A method of supplying a process gas to a process chamber,
comprising: initiating a known flow rate of a process gas to a
process chamber; dividing said known flow rate of said process gas
into a first flow of said process gas at a first flow rate and a
second flow of said process gas at a second flow rate; measuring a
first pressure associated with said first flow of said process gas;
measuring a second pressure associated with said second flow of
said process gas; and controlling said first flow rate and said
second flow rate according to a target flow condition by adjusting
a first conductance of said first flow of said process gas and a
second conductance of said second flow of said process gas and
monitoring said first pressure and said second pressure.
10. The method of claim 9, further comprising: establishing a first
correlation between the sum of said first pressure and said second
pressure and the sum of said first flow rate and said second flow
rate.
11. The method of claim 10, further comprising: establishing a
second correlation between a ratio of said first flow rate to said
second flow rate and a ratio of said first pressure to said second
pressure.
12. The method of claim 11, further comprising: determining said
first flow rate or said second flow rate or both by using said
first correlation, said second correlation, said measurement of
said first pressure and said measurement of said second
pressure.
13. The method of claim 11, wherein said determining said first
flow rate comprises: computing the ratio of said first pressure to
said second pressure, determining a flow ratio from said second
correlation using the ratio of said first pressure to said second
pressure, computing the sum of said first pressure and said second
pressure, determining a total flow rate using the sum of said first
pressure and said second pressure, and computing said first flow
rate using said determined flow ratio and said determined total
flow rate or said known flow rate.
14. The method of claim 9, wherein said target flow condition
comprises a target ratio of said first flow rate to said known flow
rate or a target ratio of said second flow rate to said known flow
rate or a target ratio of said first flow rate to said second flow
rate, and wherein said controlling said first flow rate and said
second flow rate comprises comparing a ratio of said first pressure
to said second pressure with said target ratio.
15. The method of claim 9, further comprising: determining a fault
condition during the supply of said process gas to said process
chamber by monitoring said first pressure, or said second pressure,
or a combination of said first pressure and said second
pressure.
16. The method of claim 15, wherein said determining said fault
condition comprises correlating a temporal variation in said first
pressure or said second pressure or a combination of said first
pressure and said second pressure with a variation in said known
flow rate.
17. The method of claim 9, further comprising: determining an
erroneous fault condition during the supply of said process gas to
said process chamber by monitoring said first pressure, or said
second pressure, or a combination of said first pressure and said
second pressure.
18. The method of claim 17, wherein said determining said fault
condition comprises correlating a substantially small temporal
variation in said first pressure or said second pressure or a
combination of said first pressure and said second pressure with a
variation in said known flow rate.
19. The method of claim 9, further comprising: determining a
service condition during the supply of said process gas to said
process chamber by monitoring said first pressure, or said second
pressure, or a combination of said first pressure and said second
pressure.
20. The method of claim 19, wherein said determining said fault
condition comprises detecting a gradual temporal variation in said
first pressure or said second pressure or a combination of said
first pressure and said second pressure while not varying said
known flow rate.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The invention relates to a flow control system for
controlling the flow of process gas to a process chamber and a
method of operating and, in particular, a flow control system for
and method of controlling a multizone gas distribution system.
[0003] 2. Description of Related Art
[0004] The fabrication of integrated circuits (IC) in the
semiconductor industry typically employs plasma to create and
assist surface chemistry within a processing chamber necessary to
remove material from and deposit material on a substrate. In
general, plasma is formed within the processing chamber under
vacuum conditions by heating electrons in the presence of an
electric field to energies sufficient to sustain ionizing
collisions with a supplied process gas. Moreover, the heated
electrons can have energy sufficient to sustain dissociative
collisions and, therefore, a specific set of gases under
predetermined conditions (e.g., chamber pressure, gas flow rate,
etc.) are chosen to produce a population of charged species and
chemically reactive species suitable to the particular process
being performed within the chamber (e.g., etching processes where
materials are removed from the substrate or deposition processes
where materials are added to the substrate).
[0005] In plasma processing systems, the uniformity of process
results across the substrate are affected by spatial variations in
plasma density within the process space above the substrate,
typically expressed as a spatial distribution of electron density
n.sub.e(r,.theta.), spatial variations in process chemistry (i.e.,
spatial distribution of chemical species), and spatial variations
of the substrate temperature. Often times, the residence time
.tau.(r,.theta.) of chemical species in the process space may be
correlated with the amount of plasma dissociation occurring due to
interactions between chemical constituents and energetic electrons
and, hence, the residence time may be correlated with process
chemistry; i.e., the greater the residence time, the greater the
amount of dissociation of chemical constituents and the lesser the
residence time, the lesser the dissociation of chemical
constituents.
[0006] Common to many of these systems, the process gas is
introduced to the process chamber through a showerhead gas
distribution system having a plurality of gas passages formed there
through. Therefore, in an effort to affect spatial variations in
the process space above a substrate, multizone gas distribution
systems have been contemplated. However, there remains a need to
control the flow properties of the multizone gas distribution
system.
[0007] Furthermore, the processes described above are sensitive to
the conditions achieved within the plasma processing system and, in
order to meet expected yields, precise control of these conditions
is now required. For example, changes in these conditions due to
either abrupt changes (or faults), or gradual changes require
constant monitoring. Therefore, it is of increasing importance to
detect fault conditions, determine whether the fault is real or
erroneous, and determine if a service condition is present.
SUMMARY OF THE INVENTION
[0008] The invention relates to a flow control system for
controlling the flow of process gas to a process chamber and a
method of operating and, in particular, a flow control system for
and method of controlling a multizone gas distribution system.
[0009] According to one embodiment, a multizone gas distribution
system configured to be coupled to a process chamber is described.
The multizone gas distribution system comprises a first gas
distribution element and a second gas distribution element.
Additionally, the multizone gas distribution system comprises a
flow control system configured to divide a flow of process gas
between the first gas distribution element and the second gas
distribution element. Further, a system controller coupled to the
flow control system is configured to adjust the flow of process gas
to the first gas distribution element and the second gas
distribution element according to a target flow condition. Further
yet, the system controller is configured to monitor the flow
control system in order to perform at least one of monitoring a
flow rate, adjusting a flow rate, controlling a flow rate,
determining a fault condition, and determining an erroneous fault
condition.
[0010] According to another embodiment, a multizone gas
distribution system configured to be coupled to a process chamber
is described, comprising: a multizone gas distribution assembly
comprising a first gas distribution element configured to introduce
a first flow rate of process gas to the process chamber and a
second gas distribution element configured to introduce a second
flow rate of process gas to the process chamber; a flow control
system coupled to the multizone gas distribution system, the flow
control system comprising: a process gas supply system configured
to supply the process gas, a process gas supply line having an
inlet end coupled to the process gas supply system and an outlet
end that splits into a first gas supply branch that supplies the
process gas to the first gas distribution element and a second gas
supply branch that supplies the process gas to the second gas
distribution element, a flow rate controller coupled to the process
gas supply line and configured to control the total sum of the
first flow rate and the second flow rate, a first flow control
valve coupled to the first gas supply branch and configured to
adjust the first flow rate, a second flow control valve coupled to
the second gas supply branch and configured to adjust the second
flow rate, a first pressure measurement device coupled to the first
gas supply branch and configured to measure a first pressure, and a
second pressure measurement device coupled to the second gas supply
branch and configured to measure a second pressure; and a system
controller coupled to the flow control system and configured to
control the first flow rate and the second flow rate according to a
target flow condition by adjusting the first flow control valve and
the second flow control valve and monitoring the first pressure and
the second pressure.
[0011] According to yet another embodiment, a method of supplying a
process gas to a process chamber is described, comprising:
initiating a known flow rate of a process gas to a process chamber;
dividing the known flow rate of the process gas into a first flow
of the process gas at a first flow rate and a second flow of the
process gas at a second flow rate; measuring a first pressure
associated with the first flow of the process gas; measuring a
second pressure associated with the second flow of the process gas;
and controlling the first flow rate and the second flow rate
according to a target flow condition by adjusting a first
conductance of the first flow of the process gas and a second
conductance of the second flow of the process gas and monitoring
the first pressure and the second pressure.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] In the accompanying drawings:
[0013] FIG. 1 shows a plasma processing system according to an
embodiment;
[0014] FIG. 2 shows a schematic diagram of a gas distribution
system according to another embodiment;
[0015] FIG. 3 illustrates a plasma processing system according to
another embodiment;
[0016] FIG. 4 illustrates a plasma processing system according to
another embodiment;
[0017] FIG. 5 illustrates a plasma processing system according to
another embodiment;
[0018] FIG. 6 illustrates a plasma processing system according to
another embodiment;
[0019] FIG. 7 illustrates a plasma processing system according to
another embodiment;
[0020] FIGS. 8A through 8D show exemplary data for operating a gas
distribution system; and
[0021] FIG. 9 illustrates a method of operating a gas distribution
system according to yet another embodiment.
DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS
[0022] In the following description, for purposes of explanation
and not limitation, specific details are set forth, such as a
particular geometry of the plasma processing system and
descriptions of various components. However, it should be
understood that the invention may be practiced in other embodiments
that depart from these specific details.
[0023] Nonetheless, it should be appreciated that, contained within
the description are features which, notwithstanding the inventive
nature of the general concepts being explained, are also of an
inventive nature.
[0024] According to an embodiment, a multizone gas distribution
system configured to be coupled to a process chamber is described.
The multizone gas distribution system comprises a first gas
distribution element and a second gas distribution element.
Additionally, the multizone gas distribution system comprises a
flow control system configured to divide a flow of process gas
between the first gas distribution element and the second gas
distribution element. Further, a system controller coupled to the
flow control system is configured to adjust the flow of process gas
to the first gas distribution element and the second gas
distribution element according to a target flow condition. Further
yet, the system controller is configured to monitor the flow
control system in order to perform at least one of monitoring a
flow rate, adjusting a flow rate, controlling a flow rate,
determining a fault condition, and determining an erroneous fault
condition.
[0025] According to another embodiment, a plasma processing system
101 is depicted in FIG. 1 comprising a process chamber 110, a
substrate holder 120, upon which a substrate 125 to be processed is
affixed, a vacuum pumping system 130, and a system controller 190.
Substrate 125 can be a semiconductor substrate, a wafer, a flat
panel display, or a liquid crystal display.
[0026] A multizone gas distribution system comprising a multizone
gas distribution assembly 150 is coupled to the process chamber 110
and is configured to introduce an ionizable gas or mixture of
process gases. The multizone gas distribution assembly 150
comprises a first gas plenum 142 that may be configured to
introduce process gas to process space 141 at a substantially
central location 144 above substrate 125. Additionally, the
multizone gas distribution assembly 150 comprises a second gas
plenum 143 that may be configured to introduce process gas to
process space 141 at a substantially peripheral location 145 above
substrate 125. The first gas plenum 142 and the second gas plenum
143 may be pneumatically isolated from one another, or they may be
partially or fully open to one another.
[0027] Each of the first gas plenum 142 and the second gas plenum
143 is configured to receive an independent flow of process gas
through an inlet and distribute each flow of process gas in a
process space 141. Each of the first gas plenum 142 and the second
gas plenum 143 of the multizone gas distribution assembly 150 may
comprise a showerhead gas distribution plate 170 having a supply
side that interfaces with the respective gas plenum 142 or 143, a
process side that interfaces with the process space 141, and a
plurality of gas passages formed from the supply side to the
process side. The showerhead gas distribution plate 170 may include
a monolithic structure coupled to both the first gas plenum 142 and
the second gas plenum 143, or it may include separate plates
independently coupled to each gas plenum.
[0028] Referring still to FIG. 1, a flow control system 152 is
coupled to the multizone gas distribution assembly 150, and
configured to introduce one or more process gases to the first gas
plenum 142 and the second gas plenum 143. The flow control system
152 is configured to perform at least one of monitoring the flow to
the first plenum 142 and the second plenum 143, adjusting the flow
to the first plenum 142 and the second plenum 143, controlling the
flow to the first plenum 142 and the second plenum 143, determining
a fault condition for the flow of process gas to the first plenum
142 or the second plenum 143 or both, determining an erroneous
fault condition for the flow of process gas to the first plenum 142
or the second plenum 143 or both, or determining a service
condition for the flow of process gas to the first plenum 142 or
the second plenum 143 or both.
[0029] A plasma generation system 140 is coupled to the process
chamber 110 and is configured to facilitate the generation of
plasma in process space 141 in the vicinity of a surface of
substrate 125. Plasma can be utilized to create materials specific
to a pre-determined materials process, and/or to aid the removal of
material from the exposed surfaces of substrate 125. The plasma
processing system 101 can be configured to process substrates of
any desired size, such as 200 mm substrates, 300 mm substrates, or
larger. The plasma generation system 140 comprises at least one of
a capacitively coupled plasma source, an inductively coupled plasma
source, a transformer coupled plasma source, a microwave plasma
source, a surface wave plasma source, or a helicon wave plasma
source.
[0030] For example, the plasma generation system 140 may comprise
an upper electrode to which radio frequency (RF) power is coupled
via a RF generator 146 through an optional impedance match network.
Electromagnetic (EM) energy at a radio frequency is capacitively
coupled from the upper electrode to plasma in process space 141. A
typical frequency for the application of RF power to the upper
electrode can range from about 10 MHz to about 100 MHz. Further,
for example, the upper electrode may be integrated with the
multizone gas distribution system 150.
[0031] An impedance match network may serve to improve the transfer
of RF power to plasma by reducing the reflected power. Match
network topologies (e.g. L-type, .pi.-type, T-type, etc.) and
automatic control methods are well known to those skilled in the
art.
[0032] A substrate bias system 180 may be coupled to the process
chamber 110 and may be configured to electrically bias substrate
125. For example, substrate holder 120 can comprise an electrode
through which RF power is coupled to substrate 125 in order to
adjust and/or control the level of energy for ions incident upon
the upper surface of substrate 125. For example, substrate holder
120 can be electrically biased at a RF voltage via the transmission
of RF power from a RF generator 186 through an optional impedance
match network to substrate holder 120. The substrate bias system
180 may serve to heat electrons to form and maintain plasma.
Additionally, the substrate bias system 180 may serve to adjust
and/or control the ion energy at the substrate. A typical frequency
for the RF bias can range from about 0.1 MHz to about 100 MHz. RF
systems for plasma processing are well known to those skilled in
the art.
[0033] Vacuum pumping system 130 may include a turbo-molecular
vacuum pump (TMP) capable of a pumping speed up to about 5000
liters per second (and greater) and a gate valve for throttling the
chamber pressure. In conventional plasma processing devices
utilized for dry plasma etch, a 1000 to 3000 liter per second TMP
can be employed. TMPs are useful for low pressure processing,
typically less than about 50 mtorr. For high pressure processing
(i.e., greater than about 100 mtorr), a mechanical booster pump and
dry roughing pump can be used.
[0034] Furthermore, a device for monitoring chamber pressure (not
shown) can be coupled to the process chamber 110. The pressure
measuring device can be, for example, a Type 628B Baratron absolute
capacitance manometer commercially available from MKS Instruments,
Inc. (Andover, Mass.).
[0035] System controller 190 may comprise a microprocessor, memory,
and a digital I/O port capable of generating control voltages
sufficient to communicate and activate inputs to plasma processing
system 101 as well as monitor outputs from plasma processing system
101. Moreover, system controller 190 can be coupled to and can
exchange information with multizone gas distribution system 150,
flow control system 152, plasma generation system 140, substrate
holder 120, substrate bias system 180, and vacuum pumping system
130. For example, a program stored in the memory can be utilized to
activate the inputs to the aforementioned components of plasma
processing system 101 according to a process recipe in order to
perform a plasma assisted process on substrate 125.
[0036] System controller 190 may be locally located relative to the
plasma processing system 101, or it may be remotely located
relative to the plasma processing system 101. For example, system
controller 190 can exchange data with plasma processing system 101
using a direct connection, an intranet, and/or the internet. System
controller 190 can be coupled to an intranet at, for example, a
customer site (i.e., a device maker, etc.), or it can be coupled to
an intranet at, for example, a vendor site (i.e., an equipment
manufacturer). Alternatively or additionally, system controller 190
can be coupled to the internet. Furthermore, another computer
(i.e., controller, server, etc.) can access system controller 190
to exchange data via a direct connection, an intranet, and/or the
internet.
[0037] Furthermore, embodiments of this invention may be used as or
to support a software program executed upon some form of processing
core (such as a processor of a computer, e.g., system controller
190) or otherwise implemented or realized upon or within a
machine-readable medium. A machine-readable medium includes any
mechanism for storing information in a form readable by a machine
(e.g., a computer). For example, a machine-readable medium can
include a read only memory (ROM); a random access memory (RAM); a
magnetic disk storage media; an optical storage media; and a flash
memory device, etc.
[0038] Referring now to FIG. 2, a schematic illustration of a
multizone gas distribution system 200 is provided. The multizone
gas distribution system 200 may be configured to be coupled to a
process chamber. The multizone gas distribution system 200
comprises a multizone gas distribution assembly 250 to which a flow
control system 252 is coupled.
[0039] The multizone gas distribution assembly 250 comprises a
first gas distribution element 242 configured to introduce a first
flow rate (Q.sub.1) of process gas to the process chamber and a
second gas distribution element 244 configured to introduce a
second flow rate (Q.sub.2) of process gas to the process chamber.
The flow control system 252 is coupled to the multizone gas
distribution assembly 250, wherein the flow control system 252
comprises a process gas supply system 264 configured to supply the
process gas at a known total flow rate (Q) through a process gas
supply line 260. The process gas supply line 260 has an inlet end
coupled to the process gas supply system 264 and an outlet end that
splits into a first gas supply branch 270 that supplies the process
gas to the first gas distribution element 242 and a second gas
supply branch 280 that supplies the process gas to the second gas
distribution element 244.
[0040] Additionally, the flow control system 252 comprises a flow
rate controller 262 coupled to the process gas supply line 260 and
configured to control the known total flow rate (Q), i.e., the sum
of the first flow rate (Q.sub.1) and the second flow rate
(Q.sub.2). A first flow control valve 272 coupled to the first gas
supply branch 270 is configured to adjust the first flow rate
(Q.sub.1), and a second control valve 282 coupled to the second gas
supply branch 280 is configured to adjust the second flow rate
(Q.sub.2).
[0041] For a given known total flow rate (Q), the first flow rate
(Q.sub.1) may be increased by adjusting the first flow control
valve 272 to a more open state or adjusting the second flow control
valve 282 to a more closed state or a combination of both actions.
Additionally, for a given known total flow rate (Q), the first flow
rate (Q.sub.1) may be decreased by adjusting the first flow control
valve 272 to a more closed state or adjusting the second flow
control valve 282 to a more open state or a combination of both
actions. Additionally yet, for a given known total flow rate (Q),
the second flow rate (Q.sub.2) may be increased by adjusting the
first flow control valve 272 to a more closed state or adjusting
the second flow control valve 282 to a more open state or a
combination of both actions. Furthermore, for a given known total
flow rate (Q), the second flow rate (Q.sub.2) may be decreased by
adjusting the first flow control valve 272 to a more open state or
adjusting the second flow control valve 282 to a more closed state
or a combination of both actions.
[0042] The multizone gas distribution assembly 250 may comprise a
showerhead gas distribution system, and the first gas distribution
element 242 is arranged in a first region while the second gas
distribution element 244 is arranged in a second region. The first
region may comprise a substantially central region of the shower
gas distribution system and the second region may comprise a
substantially peripheral region surrounding the central region.
[0043] Referring still to FIG. 2, the flow control system 252
further comprises a first pressure measurement device 274 coupled
to the first gas supply branch 270 and configured to measure a
first pressure (P.sub.1), and a second pressure measurement device
284 coupled to the second gas supply branch 280 and configured to
measure a second pressure (P.sub.2). A system controller 290
coupled to the flow control system 252 is configured to control the
first flow rate (Q.sub.1) and the second flow rate (Q.sub.2)
according to a target flow condition by adjusting the first flow
control valve 272 and the second flow control valve 282 and
monitoring the first pressure (P.sub.1) and the second pressure
(P.sub.2).
[0044] The first pressure measurement device 274 is located on an
outlet side of the first flow control valve 272, and the second
pressure measurement device 284 is located on an outlet side of the
second flow control valve 282. For example, if the first flow
control valve 272 is adjusted to a more open state (while the
second flow control valve 282 remains substantially unchanged), the
first pressure (P.sub.1) is expected to increase to accommodate the
increase in the first flow rate (Q.sub.1). Additionally, for
example, if the first flow control valve 272 is adjusted to a more
closed state (while the second flow control valve 282 remains
substantially unchanged), the first pressure (P.sub.1) is expected
to decrease to accommodate the decrease in the first flow rate
(Q.sub.1). Additionally yet, for example, if the second flow
control valve 282 is adjusted to a more open state (while the first
flow control valve 272 remains substantially unchanged), the second
pressure (P.sub.2) is expected to increase to accommodate the
increase in the second flow rate (Q.sub.2). Furthermore, for
example, if the second flow control valve 282 is adjusted to a more
closed state (while the first flow control valve 272 remains
substantially unchanged), the second pressure (P.sub.2) is expected
to decrease to accommodate the decrease in the second flow rate
(Q.sub.2).
[0045] By measuring the first pressure (P.sub.1) and the second
pressure (P.sub.2), the first flow rate (Q.sub.1) and the second
flow rate (Q.sub.2) may be estimated. For instance, the sum of the
first pressure and the second pressure (P.sub.1+P.sub.2) may be
correlated with the known (total) flow rate (Q), and the ratio of
the first pressure and the second pressure (P.sub.1/P.sub.2) may be
correlated with the ratio between the first flow rate and the
second flow rate (Q.sub.1/Q.sub.2).
[0046] According to an example, as shown in FIGS. 8A and 8B, the
sum of the first pressure and the second pressure (P.sub.1+P.sub.2)
is presented as a function of the known (total) flow rate (Q)
(standard cubic centimeters per minute, sccm). In FIGS. 8A and 8B,
the process gas comprises a mixture of gas, including a first
process gas (process gas #1) that constitutes a majority of the
process gas composition and a second process gas (or mixture of
gases) that constitutes a minority of the process gas composition.
The first process gas comprises argon, and the second process gas
comprises several gases including oxygen and one or more
fluorocarbon gases.
[0047] As illustrated in FIG. 8A, the flow rate of the first
process gas (argon) is varied from about 900 sccm to about 1080
sccm, while the flow rate of each constituent of the second process
gas remains substantially unchanged. The sum of the pressures
correlates well with the known flow rate as indicated by the
grouping of data labeled "Process gas #1". Also, as illustrated in
FIGS. 8A and 8B, the flow rate of each constituent of the second
process gas (i.e., Gas #1, Gas #2, Gas #3) is varied plus or minus
10% from its nominal value, while the flow rate of the first
process gas remains substantially unchanged and the flow rate of
each of the remaining constituents of the second process gas remain
substantially unchanged.
[0048] As observed in FIGS. 8A and 8B, when varying one constituent
of a process gas mixture, a correlation between the sum of the
first pressure and the second pressure (P.sub.1+P.sub.2) and the
known (total) flow rate (Q) is achieved. However, when other
constituents are varied, the relationship between the sum of the
pressures (P.sub.1+P.sub.2) and the known flow rate (Q) changes.
Therefore, the relationship between pressure and flow rate may be
obtained for each constituent utilized in the process gas
composition.
[0049] As shown in FIG. 8C, the sum of the first pressure and the
second pressure (P.sub.1+P.sub.2) is presented as a function of the
ratio of the first flow rate and the (total) known flow rate
(Q.sub.1/Q) (%). Data is presented for different process gas
compositions as described in FIGS. 8A and 8B. As observed in FIG.
8C, the sum of the pressures exhibits a similar behavior for each
process gas composition.
[0050] According to yet another example, as shown in FIG. 8D, the
ratio of the first pressure and the second pressure
(P.sub.1/P.sub.2) (%) is presented as a function of the ratio of
the first flow rate and the (total) known flow rate (Q.sub.1/Q)
(%). In a first set of data, the flow ratio (Q.sub.1/Q) is varied
from 0% to 100% for a first process gas composition. The first
process gas composition comprises 600 sccm of oxygen (O.sub.2). In
a second set of data, the flow ratio (Q.sub.1/Q) is varied from 0%
to 100% for a second process gas composition. The second process
gas composition comprises 600 sccm of argon (Ar). The first and
second sets of data are presented in FIG. 8D. As observed in FIG.
8D, a relationship between the pressure ratio and the flow ratio
may be achieved for different process gas compositions. Therefore,
using the data of FIGS. 8A and 8B, the total flow rate (Q) may be
determined from the sum of the pressures, and the division of the
flow rate (Q) into a first flow rate (Q.sub.1) and a second flow
rate (Q.sub.2) may be determined from FIG. 8D.
[0051] FIG. 3 illustrates a plasma processing system according to
another embodiment. Plasma processing system 1 a comprises a
process chamber 10, substrate holder 20, upon which a substrate 25
to be processed is affixed, and vacuum pumping system 30. Substrate
25 can be a semiconductor substrate, a wafer or a liquid crystal
display. Process chamber 10 can be configured to facilitate the
generation of plasma in process space 15 adjacent a surface of
substrate 25. An ionizable gas or mixture of gases is introduced
via a multizone gas distribution system including a multizone gas
distribution assembly 50 and a flow control system 52, and the
process pressure is adjusted. For example, a control mechanism (not
shown) can be used to throttle the vacuum pumping system 30. Plasma
can be utilized to create materials specific to a pre-determined
materials process, and/or to aid the removal of material from the
exposed surfaces of substrate 25. The plasma processing system 1a
can be configured to process a substrate of any size, such as 200
mm substrates, 300 mm substrates, or larger.
[0052] Substrate 25 can be affixed to the substrate holder 20 via a
mechanical clamping system or an electrical clamping system, such
as an electrostatic clamping system. Furthermore, substrate holder
20 can further include a cooling system or heating system that
includes a re-circulating fluid flow that receives heat from
substrate holder 20 and transfers heat to a heat exchanger system
(not shown) when cooling, or receives heat from a heat exchanger
and transfers heat to substrate holder 20 when heating.
[0053] Moreover, gas can be delivered to the back-side of substrate
25 via a backside gas system to improve the gas-gap thermal
conductance between substrate 25 and substrate holder 20. Such a
system can be utilized when temperature control of the substrate 25
is required at elevated or reduced temperatures. For example, the
backside gas system can comprise a two-zone gas distribution
system, wherein the backside gas (e.g., helium) pressure can be
independently varied between the center and the edge of substrate
25. In other embodiments, heating/cooling elements, such as
resistive heating elements, or thermo-electric heaters/coolers can
be included in the substrate holder 20, as well as the chamber wall
of the process chamber 10 and any other component within the plasma
processing system 1a.
[0054] In the embodiment shown in FIG. 3, substrate holder 20 can
comprise an electrode through which RF power is coupled to plasma
in process space 15. For example, substrate holder 20 can be
electrically biased at a RF voltage via the transmission of RF
power from a RF generator 40 through an optional impedance match
network 42 to substrate holder 20. The RF bias can serve to heat
electrons to form and maintain plasma, or affect the ion energy
distribution function within the sheath, or both. In this
configuration, the system can operate as a reactive ion etch (RIE)
reactor, wherein the process chamber 10 and an upper gas injection
electrode serve as ground surfaces. A typical frequency for the RF
bias can range from 0.1 MHz to 100 MHz. RF systems for plasma
processing are well known to those skilled in the art.
[0055] Furthermore, impedance match network 42 serves to improve
the transfer of RF power to plasma in process chamber 10 by
reducing the reflected power. Match network topologies (e.g.
L-type, z-type, T-type, etc.) and automatic control methods are
well known to those skilled in the art.
[0056] Referring still to FIG. 3, plasma processing system 1a
further comprises an optional direct current (DC) power supply (not
shown) coupled to an upper electrode, that may include the
multizone gas distribution assembly 50, opposing substrate 25. The
upper electrode may comprise an electrode plate. The electrode
plate may comprise a silicon-containing electrode plate. Moreover,
the electrode plate may comprise a doped silicon electrode plate.
The DC power supply can include a variable DC power supply.
Additionally, the DC power supply can include a bipolar DC power
supply. The DC power supply can further include a system configured
to perform at least one of monitoring, adjusting, or controlling
the polarity, current, voltage, or on/off state of the DC power
supply. Once plasma is formed, the DC power supply facilitates the
formation of a ballistic electron beam. An electrical filter may be
utilized to de-couple RF power from the DC power supply.
[0057] For example, the DC voltage applied to the upper electrode
by DC power supply may range from approximately -2000 volts (V) to
approximately 1000 V. Desirably, the absolute value of the DC
voltage has a value equal to or greater than approximately 100 V,
and more desirably, the absolute value of the DC voltage has a
value equal to or greater than approximately 500 V. Additionally,
it is desirable that the DC voltage has a negative polarity.
Furthermore, it is desirable that the DC voltage is a negative
voltage having an absolute value greater than the self-bias voltage
generated on a surface of the upper electrode. The surface of the
upper electrode facing the substrate holder 20 may be comprised of
a silicon-containing material.
[0058] Referring still to FIG. 3, plasma processing system 1a
further comprises a system controller 90 as described above. System
controller 90 comprises a microprocessor, memory, and a digital I/O
port capable of generating control voltages sufficient to
communicate and activate inputs to plasma processing system 1a as
well as monitor outputs from plasma processing system 1a. Moreover,
system controller 90 can be coupled to and can exchange information
with RF generator 40, impedance match network 42, optional DC power
supply, multizone gas distribution assembly 50, flow control system
52, a diagnostic system 32, vacuum pumping system 30, as well as
the backside gas delivery system (not shown), the
substrate/substrate holder temperature measurement system (not
shown), and/or the electrostatic clamping system (not shown).
[0059] The diagnostic system 32 can include an optical diagnostic
subsystem (not shown). The diagnostic system 32 can be configured
to provide an endpoint signal that may indicate the completion of a
specific etch process. Additionally, for example, the diagnostic
system 32 can be configured to provide a metrology signal that may
provide data indicating the state of etch processes performed on
the substrate (e.g., profile data for a feature, structure, deep
trench, etc.). For instance, diagnostic system 32 may include an
optical emission spectrometry system for etch process endpoint
detection, or a scatterometer, incorporating beam profile
ellipsometry (ellipsometer) and beam profile reflectometry
(reflectometer) for pattern profile determination, or both.
[0060] The optical diagnostic subsystem can comprise a detector
such as a (silicon) photodiode or a photomultiplier tube (PMT) for
measuring the light intensity emitted from the plasma. The
diagnostic system 32 can further include an optical filter such as
a narrow-band interference filter. In an alternate embodiment, the
diagnostic system 32 can include a line CCD (charge coupled
device), a CID (charge injection device) array, or a light
dispersing device such as a grating or a prism. Additionally,
diagnostic system 32 can include a monochromator (e.g.,
grating/detector system) for measuring light at a given wavelength,
or a spectrometer (e.g., with a rotating grating) for measuring the
light spectrum.
[0061] The diagnostic system 32 can include a high resolution
Optical Emission Spectroscopy (OES) sensor such as from Peak Sensor
Systems, or Verity Instruments, Inc. Such an OES sensor can have a
broad spectrum that spans the ultraviolet (UV), visible (VIS), and
near infrared (NIR) light spectrums. The resolution can be
approximately 1.4 Angstroms, that is, the sensor can be capable of
collecting about 5550 wavelengths from about 240 to about 1000 nm.
For example, the OES sensor can be equipped with high sensitivity
miniature fiber optic UV-VIS-NIR spectrometers, which are, in turn,
integrated with 2048 pixel linear CCD arrays.
[0062] The spectrometers receive light transmitted through single
and bundled optical fibers, where the light output from the optical
fibers is dispersed across the line CCD array using a fixed
grating. Similar to the configuration described above, light
passing through an optical vacuum window can be focused onto the
input end of the optical fibers via a convex spherical lens. Three
spectrometers, each specifically tuned for a given spectral range
(UV, VIS and NIR), form a sensor for a process chamber. Each
spectrometer includes an independent A/D converter. And lastly,
depending upon the sensor utilization, a full emission spectrum can
be recorded every 0.1 to 1.0 seconds.
[0063] The diagnostic system 32 can include a metrology system that
may be either an in-situ or ex-situ device. For example, the
metrology system may include a scatterometer, incorporating beam
profile ellipsometry (ellipsometer) and beam profile reflectometry
(reflectometer), commercially available from Therma-Wave, Inc.
(1250 Reliance Way, Fremont, Calif. 94539) or Nanometrics, Inc.
(1550 Buckeye Drive, Milpitas, Calif. 95035), which is positioned
within a transfer chamber (not shown) to analyze substrates. For
instance, the metrology system may include an integrated optical
digital profile (iODP) scatterometry system.
[0064] In the embodiment shown in FIG. 4, the plasma processing
system 1b can be similar to the embodiment of FIG. 3 and further
comprise either a stationary, or mechanically or electrically
rotating magnetic field system 60, in order to potentially increase
plasma density and/or improve plasma processing uniformity, in
addition to those components described with reference to FIG. 3.
Moreover, controller 90 can be coupled to magnetic field system 60
in order to regulate the speed of rotation and field strength. The
design and implementation of a rotating magnetic field is well
known to those skilled in the art.
[0065] In the embodiment shown in FIG. 5, the plasma processing
system 1c can be similar to the embodiment of FIG. 3 or FIG. 4, and
can further comprise an RF generator 70 configured to couple RF
power to an upper electrode, that may include multizone gas
distribution assembly 50, through an optional impedance match
network 72. A typical frequency for the application of RF power to
upper electrode can range from about 0.1 MHz to about 200 MHz.
Additionally, a typical frequency for the application of power to
the substrate holder 20 (or lower electrode) can range from about
0.1 MHz to about 100 MHz. For example, the RF frequency coupled to
the upper electrode can be relatively higher than the RF frequency
coupled to the substrate holder 20. Optionally, the RF power to the
upper electrode from RF generator 70 can be amplitude modulated, or
the RF power to the substrate holder 20 from RF generator 40 can be
amplitude modulated, or both RF powers can be amplitude modulated.
The RF power at the higher RF frequency can be amplitude modulated.
Moreover, system controller 90 is coupled to RF generator 70 and
impedance match network 72 in order to control the application of
RF power to upper electrode. The design and implementation of an
upper electrode is well known to those skilled in the art.
[0066] Referring still to FIG. 5, the optional DC power supply may
be directly coupled to the upper electrode, or it may be coupled to
the RF transmission line extending from an output end of impedance
match network 72 to the upper electrode. An electrical filter may
be utilized to de-couple RF power from the DC power supply.
[0067] In the embodiment shown in FIG. 6, the plasma processing
system 1d can, for example, be similar to the embodiments of FIGS.
3, 4 and 5, and can further comprise an inductive coil 80 to which
RF power is coupled via RF generator 82 through an optional
impedance match network 84. RF power is inductively coupled from
inductive coil 80 through a dielectric window (not shown) to
process space 15. A typical frequency for the application of RF
power to the inductive coil 80 can range from about 10 MHz to about
100 MHz. Similarly, a typical frequency for the application of
power to the lower electrode can range from about 0.1 MHz to about
100 MHz. In addition, a slotted Faraday shield (not shown) can be
employed to reduce capacitive coupling between the inductive coil
80 and plasma. Moreover, controller 90 is coupled to RF generator
82 and impedance match network 84 in order to control the
application of power to inductive coil 80. In an alternate
embodiment, inductive coil 80 can be a "spiral" coil or "pancake"
coil in communication with the process space 15 from above as in a
transformer coupled plasma (TCP) reactor. The design and
implementation of an inductively coupled plasma (ICP) source, or
TCP source, is well known to those skilled in the art.
[0068] Alternately, the plasma can be formed using electron
cyclotron resonance (ECR). In yet another embodiment, the plasma is
formed from the launching of a Helicon wave. In yet another
embodiment, the plasma is formed from a propagating surface wave.
Each plasma source described above is well known to those skilled
in the art.
[0069] In the embodiment shown in FIG. 7, the plasma processing
system 1e can, for example, be similar to the embodiments of FIGS.
3, 4 and 5, and can further comprise a second RF generator 44
configured to couple RF power to substrate holder 20 through
another optional impedance match network 46. A typical frequency
for the application of RF power to substrate holder 20 can range
from about 0.1 MHz to about 200 MHz for either the first RF
generator 40 or the second RF generator 44 or both. The RF
frequency for the second RF generator 44 can be relatively greater
than the RF frequency for the first RF generator 40. Furthermore,
the RF power to the substrate holder 20 from RF generator 40 can be
amplitude modulated, or the RF power to the substrate holder 20
from RF generator 44 can be amplitude modulated, or both RF powers
can be amplitude modulated. The RF power at the higher RF frequency
can be amplitude modulated. Moreover, system controller 90 is
coupled to the second RF generator 44 and impedance match network
46 in order to control the application of RF power to substrate
holder 20. The design and implementation of an RF system for a
substrate holder is well known to those skilled in the art.
[0070] Referring now to FIG. 9, a flow chart 500 of a method for
operating a multizone gas distribution system is presented. Flow
chart 500 begins in 510 with initiating a known flow rate (Q) of a
process gas to a process chamber. For example, the multizone gas
distribution system may include any one of the systems described in
FIGS. 1 through 7, or may include any combination of components
described in these FIGS.
[0071] In 520, the known flow rate (Q) of the process gas is
divided into a first flow of the process gas at a first flow rate
(Q.sub.1) and a second flow of the process gas at a second flow
rate (Q.sub.2). For example, as illustrated in FIG. 2, a first flow
control valve and a second control valve may be utilized to divide
the known flow rate (Q) into the first flow rate (Q.sub.1) and the
second flow rate (Q.sub.2).
[0072] In 530, a first pressure (P.sub.1) associated with the first
flow of the process gas is measured. For example, the first
pressure (P.sub.1) may be measured downstream from the outlet of
the first flow control valve.
[0073] In 540, a second pressure (P.sub.2) associated with the
second flow of the process gas is measured. For example, the second
pressure (P.sub.2) may be measured downstream from the outlet of
the second flow control valve.
[0074] In 550, the first flow rate (Q.sub.1) and the second flow
rate (Q.sub.2) are controlled according to a target flow condition
by adjusting a first conductance of the first flow of the process
gas and a second conductance of the second flow of the process gas
and monitoring the first pressure (P.sub.1) and the second pressure
(P.sub.2).
[0075] The target flow condition may include any flow parameter
associated with the flow control system. For example, the target
flow condition may include a first flow rate (Q.sub.1), a second
flow rate (Q.sub.2), a total flow rate (Q, Q.sub.1+Q.sub.2) (i.e.,
sum of the first flow rate and the second flow rate), or a flow
ratio such as a ratio of the first flow rate to the second flow
rate (Q.sub.1/Q.sub.2), a ratio of the first flow rate to the total
flow rate (Q.sub.1/Q) or a ratio of the second flow rate to the
total flow rate (Q.sub.2/Q), or any mathematical combination
thereof. Additionally, for example, the target flow condition may
include a first pressure (P.sub.1), a second pressure (P.sub.2), a
total pressure (P.sub.1+P.sub.2) (i.e., sum of the first pressure
and the second pressure), or a pressure ratio such as a ratio of
the first pressure to the second pressure (P.sub.1/P.sub.2), a
ratio of the first pressure to the total pressure
(P.sub.1/P.sub.1+P.sub.2) or a ratio of the second pressure to the
total pressure (P.sub.2/P.sub.1+P.sub.2), or any mathematical
combination thereof.
[0076] As described above, a first correlation between the sum of
the first pressure and the second pressure (P.sub.1+P.sub.2) and
the sum of the first flow rate and the second flow rate (Q,
Q.sub.1+Q.sub.2) may be established. Also, as described above, a
second correlation between the ratio of the first pressure to the
second pressure (P.sub.1/P.sub.2) and the ratio of the first flow
rate to the second flow rate (Q.sub.1/Q.sub.2) may be established.
The first flow rate (Q.sub.1) or the second flow rate (Q.sub.2) or
both may be computed by using the first correlation, the second
correlation, the measurement of the first pressure (P.sub.1) and
the measurement of the second pressure (P.sub.2). Alternatively,
the sum of the first flow rate and the second flow rate
(Q.sub.1+Q.sub.2) may not be determined from the first correlation
and the known flow rate (Q) may be used. The known flow rate (Q)
and the flow ratio determined using the measured pressure ratio and
the second correlation may be utilized to compute the first flow
rate (Q.sub.1) and the second flow rate (Q.sub.2).
[0077] As an example, the first flow rate (Q.sub.1) may be
determined by the following procedure:computing the ratio of the
first pressure to the second pressure (P.sub.1/P.sub.2),
determining a flow ratio (Q.sub.1/Q.sub.2) from the second
correlation using the ratio of the first pressure to the second
pressure (P.sub.1/P.sub.2), computing the sum of the first pressure
and the second pressure (P.sub.1+P.sub.2), optionally determining
the total flow rate (Q, Q.sub.1+Q.sub.2) using the sum of the first
pressure and the second pressure (P.sub.1+P.sub.2), and computing
the first flow rate (Q.sub.1) using the determined flow ratio
(Q.sub.1/Q.sub.2) and either the determined total flow rate
(Q.sub.1+Q.sub.2) or the known flow rate (Q).
[0078] In 560, the first pressure (P.sub.1), the second pressure
(P.sub.2), or any mathematical combination thereof is utilized to
determine a fault condition, an erroneous fault condition, or a
service condition, or any combination of two or more thereof.
[0079] In one example, the first pressure (P.sub.1), the second
pressure (P.sub.2), the sum of the first pressure and the second
pressure (P.sub.1+P.sub.2), or the ratio of the first pressure and
the second pressure (P.sub.1/P.sub.2), or a mathematical
combination thereof is monitored during the execution of a process
in the plasma processing system. When the change in the chosen
parameter (or parameters) during the execution of a process on a
substrate exceeds a pre-determined threshold value, an operator of
the plasma processing system may be alerted to the occurrence of a
fault condition associated with the variation in the flow
conditions. For instance, the threshold value may include an
absolute value (known to be always greater than or less than the
typical range of values for the chosen parameter), an upper control
limit and lower limit set at a fraction (i.e., 20%) of the mean
value of the parameter during processing, or an upper control limit
and a lower control limit set at an integer number (i.e., 3) of
root mean square (rms) values of the fluctuation of the flow
parameter during processing.
[0080] In another example, the first pressure (P.sub.1), the second
pressure (P.sub.2), the sum of the first pressure and the second
pressure (P.sub.1+P.sub.2), or the ratio of the first pressure and
the second pressure (P.sub.1/P.sub.2), or a mathematical
combination thereof is monitored during the execution of a process
on the substrate in the plasma processing system. During the
process, the chosen parameter indicates no abrupt change; however,
the mass flow controller that sets the known flow rate (Q) reports
a sudden change in mass flow rate. Based upon this data, an
operator may identify the change reported from the mass flow
controller as an erroneous fault condition, and continue to process
substrates in the plasma processing system. Alternatively, the
operator may identify the change reported from the mass flow
controller as an erroneous fault condition, and discontinue to
process substrates in the plasma processing system in order to
investigate the mass flow controller.
[0081] In yet another example, the first pressure (P.sub.1), the
second pressure (P.sub.2), the sum of the first pressure and the
second pressure (P.sub.1+P.sub.2), or the ratio of the first
pressure and the second pressure (P.sub.1/P.sub.2), or a
mathematical combination thereof is monitored during the sequential
execution of a plurality of substrates through a process in the
plasma processing system. During the processing of each substrate,
the chosen parameter is monitored as a function of substrate
number, lot number, or radio frequency (RF) hours in the plasma
processing system. When the value of the chosen parameter, or rate
of change in the chosen parameter becomes greater than (or less
than) a pre-determined value, an operator may be notified of a
service condition. The service condition may include, for instance,
re-calibrating the multizone gas distribution system or cleaning
the plasma processing system in order to remove residue accumulated
on the internal surfaces of the plasma processing system.
[0082] Although only certain embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
embodiments without materially departing from the novel teachings
and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention.
* * * * *