U.S. patent application number 10/840288 was filed with the patent office on 2005-02-03 for controlling pressure in a process chamber by variying pump speed and a regulator valve, and by injecting inert gas.
This patent application is currently assigned to ALCATEL. Invention is credited to Bernard, Roland, Desbiolles, Jean-Pierre, Munari, Sebastien, Rousseau, Claude.
Application Number | 20050025634 10/840288 |
Document ID | / |
Family ID | 32982389 |
Filed Date | 2005-02-03 |
United States Patent
Application |
20050025634 |
Kind Code |
A1 |
Bernard, Roland ; et
al. |
February 3, 2005 |
Controlling pressure in a process chamber by variying pump speed
and a regulator valve, and by injecting inert gas
Abstract
A gas pumping system of the invention enables gas to be pumped
from a process chamber (1) in order to regulate its pressure as a
function of process steps. The system comprises a primary pump (2),
a secondary pump (8), an inert gas injection device (6), and a
regulator valve (4). The primary and/or secondary pump (2 and/or 8)
is controlled in speed in order to regulate variations of greater
amplitude. The regulator valve (4) is controlled in opening in
order to regulate variations that are small amplitude and fast. The
inert gas injection (6) is controlled in flow rate in order to
regulate medium amplitude variations. This provides great reaction
stability and a wide range of possible variation for the conditions
in the process chamber (1).
Inventors: |
Bernard, Roland;
(Viuz-La-Chiesaz, FR) ; Desbiolles, Jean-Pierre;
(Cruseilles, FR) ; Munari, Sebastien;
(Cran-Gevrier, FR) ; Rousseau, Claude; (Annecy Le
Vieux, FR) |
Correspondence
Address: |
SUGHRUE MION, PLLC
Suite 800
2100 Pennsylvania Avenue, N.W.
Washington
DC
20037-3213
US
|
Assignee: |
ALCATEL
|
Family ID: |
32982389 |
Appl. No.: |
10/840288 |
Filed: |
May 7, 2004 |
Current U.S.
Class: |
417/279 ;
417/300; 417/572 |
Current CPC
Class: |
F04B 41/06 20130101;
F04D 19/046 20130101; F04B 49/08 20130101; G05D 16/208
20130101 |
Class at
Publication: |
417/279 ;
417/300; 417/572 |
International
Class: |
F04B 049/00; F04B
039/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 9, 2003 |
FR |
03 05 615 |
Claims
What is claimed is:
1. A system for pumping gas from a process chamber (1), the system
comprising a primary pump (2), a secondary pump (8), an inert gas
injection device (6), and a regulator valve (4), in which: the
primary and/or secondary pump (2 and/or 8) is controlled in speed;
the regulator valve (4) is controlled in opening and is connected
to the inlet of the primary pump (2); and the inert gas injection
(6) is controlled in flow rate, and is provided upstream from the
regulator valve (4).
2. A pumping system according to claim 1, in which the regulator
valve (4) is controlled so as to compensate for fast variations of
small amplitude in conditions of pressure and gas injection flow
rate in the process chamber (1), inert gas injection (6) is
controlled to compensate for larger amplitude variations in
conditions of pressure and gas injection flow rate in the process
chamber (1), and primary and/or secondary pump (2 and/or 8) speed
is controlled so as to compensate for longer-term trends and
greater variations in the amplitude of conditions of pressure and
gas injection flow rate in the process chamber (1).
3. A pumping system according to claim 2, in which the speed(s) of
the primary and/or secondary pump (2 and/or 8) and the rate of
inert gas injection (6) are determined so as to place the regulator
valve (4) in a mean position of appropriate intermediate opening in
which the regulator valve presents appropriate reaction
sensitivity.
4. A pumping system according to claim 1, in which: the primary
and/or secondary pump (2 and/or 8) is connected to control means (3
or 11) for controlling the primary and/or secondary pump (2 and/or
8) at adjustable speed; the regulator valve (4) is associated with
control means (5) for controlling the regulator valve (4); the
inert gas injection (6) injects inert gas from an inert gas source
(7) via an injection pipe (7a) provided with an injection valve
(7b) and control means (7c) for controlling the injection valve
(7b); and central control means (10) such as a microprocessor or a
microcontroller control the respective control means (3, 11, 5, 7c)
for the primary and/or secondary pump (2 and/or 8), for the
regulator valve (4), and for the injection valve (7b).
5. A pumping system according to claim 4, in which the central
control means (10) generate the signals which control the
respective control means (3, 11, 5, 7c) as a function of a
reference signal received from reference means (13), as a function
of information concerning the opening positions of the regulator
valve (4) and of the injection valve (7b), and as a function of
measurements of the pressure in the process chamber (1) as issued
by a pressure sensor (12).
6. A system for fabricating semiconductor or microelectronic
mechanical systems (MEMS), the installation including at least one
process chamber (1) and a pumping system according to claim 1.
7. A method of fabricating semiconductor or microelectronic
mechanical systems (MEMS), in which the atmosphere inside a process
chamber (1) is pumped using a pumping system according to claim
1.
8. A method according to claim 7, characterized in that the opening
of the regulator valve (4) is controlled in such a manner as to
compensate for rapid variations of small amplitude in the
conditions of pressure and gas injection flow rate in the process
chamber (1), the inert gas injection (6) is controlled in flow rate
so as to compensate for larger amplitude variations in the
conditions of pressure and gas injection flow rate in the process
chamber (1), and the speed of the primary and/or secondary pump (2
and/or 8) is controlled in such a manner as to compensate for
longer-term trends and for variations of large amplitude in the
conditions of pressure and/or gas injection flow rate into the
process chamber (1).
Description
[0001] The invention described in this document relates to
controlling the pressure of gas in a process chamber used in
particular in the semiconductor industry.
[0002] Methods of fabricating semiconductors and microelectronic
mechanical systems (MEMS) generally comprise successive steps which
take place in a process chamber under an atmosphere at low
pressure. Each step is characterized by a gas pressure that needs
to be regulated, e.g. in order to maintain a plasma or a particle
bombardment acting on a semiconductor substrate.
[0003] Certain steps include simultaneous injection of treatment
gas into the process chamber.
[0004] Most of the steps of the process take place in the presence
of a suitable vacuum, generated and maintained by a vacuum line
that includes vacuum pumps connected to the process chamber.
[0005] In traditional manner, pressure in process chambers has been
controlled by operating a regulator valve placed directly at the
outlet from the chamber prior to the secondary pump and the primary
pump. A problem then arises with a risk of the regulator valve
becoming dirty, and a risk of pollution being scattered back from
the regulator valve into the process chamber.
[0006] A solution to this problem, consisting in simultaneously
controlling the speeds of the primary and secondary pumps,
constitutes the subject matter of U.S. Pat. No. 6,419,455.
Difficulties arise when the primary pump is remote, being separated
from the secondary pump by a pipe that is relatively long. The
response time of the regulation system is then too long.
[0007] Also known, from document WO 99/04325, are a large number of
solutions of varying complexity, making use:
[0008] sometimes of controlling the speed of the primary pump while
injecting an inert gas upstream from the primary pump and
downstream from an outlet valve from the secondary pump; and
[0009] sometimes injecting inert gas upstream from a control valve
connected to the inlet of the primary pump whose speed is not
controlled.
[0010] However, that document does not describe a solution in which
a regulator valve is engaged between a primary pump and a secondary
pump, the speed of the primary pump being controlled, and an inert
gas being injected upstream from the regulator valve. Nor does that
document describe a solution in which the speed of the secondary
pump is controlled.
[0011] A difficulty in controlling the atmosphere in process
chambers for fabricating microtechnical and microelectronic
components lies in the wide variety of machining steps making use
of plasmas or other gaseous elements, and the wide variety of
physical conditions for the atmosphere that is present in the
process chamber. The control device must be capable of following
these variations which are of relatively large amplitude. It is
also necessary for the control device to follow variations quickly
so as to provide machining steps that are performed correctly,
complying from the beginning to the end of each step with the
appropriate conditions for the machining. Otherwise, a machining
step cannot begin until after the atmosphere in the process chamber
has stabilized, thereby reducing the fabrication throughput rate
and increasing the cost of production.
[0012] Prior art documents do not give satisfactory teaching on
achieving reaction speeds and adjustment ranges that are
appropriate for all of the steps that are necessary.
[0013] Thus, the invention seeks simultaneously to avoid the
drawbacks of prior art systems, in particular by making it possible
significantly to reduce the regulation response time of the system
and to reduce risks of instability, while also increasing
adjustment range, and simultaneously avoiding any risk of
back-scattering pollution which might result from a control valve
being present at the outlet from the process chamber.
[0014] The invention thus seeks to replace the regulator valve at
the outlet from the chamber by satisfactory means which achieve
appropriate reaction speed and amplitude even in the presence of a
long pipe between the primary and secondary pumps.
[0015] The invention also seeks to guarantee satisfactory
regulation stability, avoiding the appearance of the instabilities
that are frequently encountered in regulated systems when it is
desired to increase the amplitude and the speed of reaction.
[0016] The essential idea of the invention is to perform regulation
by three complementary means whose reaction speeds complement one
another:
[0017] controlling the speed of the primary and/or secondary pump,
thus making it possible to respond to very long-term trends;
[0018] injecting inert gas under flow rate control, at a point
located upstream from a regulator valve itself, and upstream from
the primary pump, thereby responding to medium-term trends; and
[0019] controlling the opening of the regulator valve, thus
providing a reaction that is very fast when placed under
appropriate operating conditions by injecting gas and regulating
the speed of the primary pump.
[0020] To achieve these objects amongst others, the invention
provides a system for pumping gas from a process chamber, the
system comprising a primary pump, a secondary pump, an inert gas
injection device, and a regulator valve, in which:
[0021] the primary and/or secondary pump is controlled in
speed;
[0022] the regulator valve is controlled in opening and is
connected to the inlet of the primary pump; and
[0023] the inert gas injection is controlled in flow rate, and is
provided upstream from the regulator valve.
[0024] The combination of these elements gives great flexibility in
adjustment, making it possible to achieve a very fast reaction
speed and a broad range of possible adjustments.
[0025] The invention is preferably applied to a speed-controlled
secondary pump of the turbo, drag, or turbo/drag pump type.
[0026] In a preferred embodiment, the regulator valve is controlled
so as to compensate for fast variations of small amplitude in
conditions of pressure and gas injection flow rate in the process
chamber, inert gas injection is controlled to compensate for larger
amplitude variations in conditions of pressure and gas injection
flow rate in the process chamber, and primary and/or secondary pump
speed is controlled so as to compensate for longer-term trends and
greater variations in the amplitude of conditions of pressure and
gas injection flow rate in the process chamber.
[0027] In this case, the speed(s) of the primary and/or secondary
pump and the injection of gas are preferably determined so as to
place the regulator-valve in an appropriate intermediate opening
position, which is a function of the selected valve. The person
skilled in the art can adapt the mean position of the regulator
valve as a function of response curves provided by the valve
manufacturer. The regulator valve is thus placed in the mean
position that gives the valve its most appropriate reaction
sensitivity over the fluid it controls as a function of its
position.
[0028] Likewise, the person skilled in the art will preferably
chose to adapt the pump speeds or the injection of gas as a
function of the sensitivity desired for regulation purposes,
preferring to adapt gas injection in order to achieve high
regulation sensitivity, or to adapt gas injection and pump speed in
order to reduce regulation sensitivity.
[0029] In a practical embodiment, the pumping system of the
invention may be such that:
[0030] the primary and/or secondary pump is connected to control
means for controlling the primary and/or secondary pump at
adjustable speed;
[0031] the regulator valve is associated with control means for
controlling the regulator valve;
[0032] the inert gas injection injects inert gas from an inert gas
source via an injection pipe provided with an injection valve and
control means for controlling the injection valve; and
[0033] central control means such as a microprocessor or a
microcontroller control the respective control means for the
primary and/or secondary pump, for the regulator valve, and for the
injection valve.
[0034] Preferably, the central control means generate the signals
which control the respective control means as a function of a
reference signal received from reference means, as a function of
information concerning the opening positions of the regulator valve
and of the injection valve, and as a function of measurements of
the pressure in the process chamber as issued by a pressure
sensor.
[0035] The invention may advantageously be applied to making an
installation for fabricating semiconductors or microelectronic
mechanical systems (MEMS).
[0036] In another aspect, the invention provides a method of
fabricating semiconductor or microelectronic mechanical systems
(MEMS) in which the atmosphere inside a process chamber is pumped
by means of a pumping system as defined above.
[0037] Preferably, the opening of the regulator valve is controlled
in such a manner as to compensate for rapid variations of small
amplitude in the conditions of pressure and gas injection flow rate
in the process chamber, the inert gas injection is controlled in
flow rate so as to compensate for larger amplitude variations in
the conditions of pressure and gas injection flow rate in the
process chamber, and the speed of the primary and/or secondary pump
is controlled in such a manner as to compensate for longer-term
trends and for variations of large amplitude in the conditions of
pressure and/or gas injection flow rate into the process
chamber.
[0038] Other objects, characteristics, and advantages of the
present invention appear from the following description of
particular embodiments described with reference to the accompanying
figures, in which:
[0039] FIG. 1a is a timing diagram showing an example of variation
in the reference pressure for a process chamber, together with the
real variation in pressure;
[0040] FIG. 1b shows an example of simultaneously varying flow
rates of gas introduced into the process chamber during
treatment;
[0041] FIG. 1c then shows a curve for variation in the opening of a
valve in order to follow small-amplitude pressure and flow rate
variations in the process chamber;
[0042] FIG. 1d is a curve showing how the variation in gas
injection that needs to be implemented in order to follow long-term
trends or variations of greater amplitude;
[0043] FIG. 1e is a curve showing variation in the speed of the
primary pump;
[0044] FIG. 2 is a block diagram of apparatus for controlling
pressure in a process chamber in an embodiment of the present
invention; and
[0045] FIG. 3 shows regulation sensitivity curves as a function of
valve opening for different pump speed and gas flow rate
conditions.
[0046] In the embodiment shown in FIG. 2, in a vacuum line for
controlling the vacuum in a process chamber 1, there are provided a
primary pump 2 connected to means 3 for controlling the primary
pump 2 at adjustable speed. A regulator valve 4 is provided at the
inlet to the primary pump 2, in association with means 5 for
controlling the regulator valve 4. Inert gas injection 6 under flow
rate control is provided by injecting the inert gas upstream from
the regulator valve 4 from an inert gas source 7 via an injection
pipe 7a provided with an injection valve 7b and with means 7c for
controlling the injection valve 7b. The primary pump 2 is connected
to a secondary pump 8 which is itself connected to the process
chamber 1 possibly via an isolating valve 9. The secondary pump 8
is itself connected to means 11 for controlling the secondary pump
8 at variable speed.
[0047] The means 3 and 11 respectively for controlling the primary
pump 2 and the secondary pump 8 define the speed of rotation of the
primary pump 2 or of the secondary pump 8,.and they stabilize on a
determined value as explained below. Similarly, the means 7c for
controlling inert gas injection 6 define the rate at which inert
gas is injected upstream from the regulator valve 4 at a rate that
is appropriate, as defined below. Finally, the means for
controlling the regulator valve define an appropriate opening
position for the regulator valve 4.
[0048] For a given speed of the primary pump 2 and/or the secondary
pump 8, the inert gas injection means 6 are programmed to inject a
quantity of inert gas that enables an appropriate mean gas pressure
to be achieved downstream from the secondary pump 8, thereby
determining a mean pressure in the process chamber 1 that
corresponds to the mean pressure required by the current step of
the method, for a mean position of the regulator valve which is
intermediate being in a zone of sensitivity that is appropriate for
the adjustment.
[0049] The adjustment sensitivity of the regulator valve is
illustrated by curve A in FIG. 3 which shows the slope of pressure
variation in the process chamber 1 as a function of the opening
position of the regulator valve 4 for given downstream pressure.
The regulator valve 4 is preferably placed in a position of
intermediate opening in the range O running from 40% to 60%,
corresponding to a satisfactory variation slope for the combined
transfer function of the valve and the secondary pump 8.
[0050] During the process steps, the mean pressure in the process
chamber, and the mean flow rate of gas injected into the process
chamber can vary. To track said variation in mean pressure and flow
rate, it would be necessary to cause the rate at which inert gas is
injected upstream from the regulator valve 4 to be caused to vary
considerably. In order to avoid reaching flow rates that are too
high or zero, the means 3 and/or 11 for controlling the primary
pump 2 and/or the secondary pump 8 at adjustable speed adapt the
speed of the primary and/or secondary pumps 2 and/or 8 so as to
achieve an appropriate mean pressure at the inlet to the primary
pump 2 for a mean inert gas flow rate 6 and for a mean opening of
the regulator valve 4.
[0051] In addition, because of the satisfactory adjustment and
above all because of the wide range of adjustment possibilities, it
is possible to perform regulation quickly in a very broad range of
variation in the conditions present in the process chamber 1.
[0052] The means for regulating inert gas injection and the means
for controlling the regulator valve 4 can be combined with
regulating the speed of the primary pump 2 alone, or with
regulating the speed of the secondary pump 8 alone, or with
regulating the speeds of both the primary pump 2 and the secondary
pump 8. This two-pump possibility makes it possible to further
increase the range of variation that is possible in the conditions
that exist inside the process chamber, and make it possible to
further increase the reaction speed of control.
[0053] FIGS. 1a to 1e show an example of how operating conditions
in a system for controlling pressure in a process chamber can vary
as a function of time in an embodiment of the invention.
[0054] FIG. 1a shows firstly the reference pressure for the inside
of the process chamber during a process sequence that is taken by
way of example. It should be observed that the reference pressure
begins at a relatively high value, of the order of 90 millitorr
(mTorr), after which it falls very low, subsequently to rise to
about 20 mTorr for a period until time mark 50.00, after which it
falls very low again for a period subsequently rising to about 20
mTorr. Thereafter the reference pressure rises to about 40 mTorr
round about time mark 100.00, falling subsequently to a low value
and subsequently rising to about 60 mTorr prior to falling very low
and subsequently rising to about 90 mTorr.
[0055] FIG. 1a also shows the pressure actually achieved in the
process chamber, and it can be seen that pressure drops quickly for
negative steps in the reference pressure, but increases more slowly
for positive steps in the reference pressure.
[0056] FIG. 1b shows simultaneous variations in the flow rate of
treatment gas introduced into the process chamber, said flow rate
sometimes going against the variations in the reference pressure.
The pumping system must then evacuate the process gas flow rate in
order to track the reference pressure.
[0057] FIG. 1c shows variations in the opening of the regulator
valve 4.
[0058] FIG. 1d shows variations in the rate at which inert gas is
injected upstream from the regulator valve 4, while FIG. 1e shows
variations in the speed of the secondary pump.
[0059] Particular consideration can be given to the event which
takes place around time mark 100.00. There is then simultaneously a
decrease in the treatment gas injection flow rate into the process
chamber (FIG. 1b) and an increase in the reference pressure for the
inside of the process chamber (FIG. 1a). In order to achieve the
desired pressure inside the process chamber, the regulator valve 4
is initially closed quickly, as indicated by negative step O1 in
FIG. 1c. Simultaneously, or slightly later as shown in the figures,
the inert gas injection flow rate 6 is increased quickly upstream
from the regulator valve 4, as represented by positive step F1.
Given that the variations in injection flow rate and valve opening
do not suffice to track the positive step in the reference pressure
when in the presence of a decrease in the treatment gas flow rate
into the process chamber, a variation in pump speed is also
applied, as represented by negative step V1. The system responds
correctly because of the three variations: in valve opening O1, in
injection flow rate F1, and in pump speed V1. This enables the
invention to follow variations of great amplitude.
[0060] A second advantage of the invention is explained below with
reference to FIG. 3 showing how selecting which elements to
regulate makes it possible to act on the overall regulation
sensitivity of the system.
[0061] In this figure, curve A is a transfer or pressure variation
curve for the process chamber 1 for various opening positions of
the regulator valve 4 under given and constant conditions of speed
in the pumps 2 and 8 and of inert gas injection flow rate 6
upstream from the regulator valve 4. From curve A, it will be
understood that it is advantageous to place the regulator valve 4
in an intermediate opening position, advantageously in the range
40% to 60% of fully open, so as to conserve sensitivity that is
sufficient but not too great.
[0062] Curve B shows that the transfer curve A is shifted towards
higher pressures in the presence of variations in the inert gas
injection flow rate 6 upstream from the regulator valve 4. Curve B
remains relatively parallel to curve A. Similarly, curve C shows
the transfer curve A being shifted towards high pressures for
additional variation in the inert gas injection flow rate 6
upstream from the regulator valve 4.
[0063] Curve D shows how the transfer curve becomes deformed in the
event of simultaneously varying the inert gas injection flow rate
upstream from the regulator valve 4 and the speed of the primary
pump 2. Finally, curve E shows how the transfer curve is deformed
in the event of the speed of the primary pump 2 and the inert gas
injection flow rate 6 upstream from the regulator valve 4 being
caused to vary for a greater injection flow rate.
[0064] These curves can be interpreted as follows: if the valve is
placed at a mean opening of 50%, a progressive increase in the
inert gas injection flow rate 6 upstream from the regulator valve 4
causes the transfer curve to shift from a point A1 towards a point
B1 and then towards a point C1 on the respective curves A, B, and
C. It can be seen that at point B1, the slope of the curve B is
steeper than it is at point A1 on curve A, and that it is even
steeper at point C1 on curve C. This means that by increasing the
inert gas injection flow rate 6 upstream from the regulator valve
4, regulation sensitivity is progressively increased. In some
cases, this can lead to instabilities, due to excess reaction
gain.
[0065] Still for an opening at 50% for the valve, consideration is
given to point D1 on curve D and point E1 on curve E, to which it
can be seen that curves D and E present much shallower slope for
the same pressure conditions in the process chamber. Thus, by
choosing also to vary the speed of the primary pump, in order to
move onto curves D and E, it is possible to reduce regulation
sensitivity and thus to occupy a zone of improved stability.
[0066] Advantage can thus be taken of the means of the invention to
adapt pump speed(s) or inert gas injection in preferred manner as a
function of the sensitivity desired for regulation purposes. A
constant pump speed enables greater regulation sensitivity to be
achieved merely by adapting gas injection while also adapting the
opening of the regulator valve 4. In contrast, changing pump speed
while simultaneously adapting inert gas injection 6 upstream from
the regulator valve 4 makes it possible to reduce regulation
sensitivity so as to improve regulation stability.
[0067] With reference again to FIG. 2, there can be seen a diagram
for a practical organization of the means for controlling the
various members of the vacuum line of the invention.
[0068] The control means 5 and 7c for respective valves 4 and 7b
may be electromagnetic interfaces which move the shutter means of
the respective valves mechanically as a function of a reference
value received from central control means 10 such as a
microprocessor or a microcontroller to which they are connected.
The same microprocessor or microcontroller 10 also controls the
supply of electricity to the primary pump 2 and/or to the secondary
pump 8 via the control means 3 and/or the control means 11
corresponding thereto and thus constituting power supply control
means connected to the central control means 10.
[0069] The central control means 10 such as the microprocessor or
microcontroller may optionally receive information concerning the
opening position of the regulator valve 4 and the injection valve
7b, and concerning the speed(s) of the primary and/or secondary
pumps 2 and/or 8, via sensors that are not shown in the figure. A
sensor may also be provided for picking up the injection flow rate
into the pipe 7a. The microcontroller also receives signals
representing pressure measurements made in the process chamber 1
and issued by a pressure sensor 12, and it also receives the
pressure reference signal as generated by reference means 13.
[0070] Alternatively, the central control means 10 could issue
control signals in an open loop configuration without receiving
measurement signals.
[0071] The present invention is not limited to the embodiments
described above, but it includes the variants and generalizations
that are within the competence of the person skilled in the
art.
* * * * *