U.S. patent application number 10/653153 was filed with the patent office on 2004-03-04 for delivery of liquid precursors to semiconductor processing reactors.
Invention is credited to MacNeil, John.
Application Number | 20040040505 10/653153 |
Document ID | / |
Family ID | 10861584 |
Filed Date | 2004-03-04 |
United States Patent
Application |
20040040505 |
Kind Code |
A1 |
MacNeil, John |
March 4, 2004 |
Delivery of liquid precursors to semiconductor processing
reactors
Abstract
This invention relates to methods and apparatus for delivering
liquid precursors to semi-conductor processing apparatus. The
liquid precursor delivery system is generally indicated at 10 and
includes a source 11, an inlet tube 12, a two-way valve 13, a pump
assembly 14, an outlet tube 15, a shut-off valve 16 and a flash
evaporator 17. The pump assembly 14 is in the form of a syringe or
variable volume pump and is controlled by a combination of a step
motor 27 and a linear encoder 30. The arrangement is such that
unused liquid precursor can be returned to the source.
Inventors: |
MacNeil, John; (Cardiff,
GB) |
Correspondence
Address: |
VOLENTINE FRANCOS, P.L.L.C.
SUITE 150
12200 SUNRISE VALLEY DRIVE
RESTON
VA
20191
US
|
Family ID: |
10861584 |
Appl. No.: |
10/653153 |
Filed: |
September 3, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10653153 |
Sep 3, 2003 |
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09667329 |
Sep 21, 2000 |
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6640840 |
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Current U.S.
Class: |
118/715 ; 141/1;
257/E21.241; 257/E21.279 |
Current CPC
Class: |
C23C 16/401 20130101;
Y02E 60/34 20130101; F04B 19/04 20130101; C23C 16/56 20130101; H01L
21/3105 20130101; H01L 21/31612 20130101 |
Class at
Publication: |
118/715 ;
141/001 |
International
Class: |
B65B 001/04 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 25, 1999 |
GB |
9922691.2 |
Claims
1. Apparatus for delivering a liquid precursor to a semiconductor
processing reactor including a source for the liquid precursor, a
volume calibrated positive displacement pump for drawing liquid
precursor from the source via an input path and for delivering
along an output path a known volume of liquid precursor to the
reactor.
2. Apparatus as claimed in claim 1 further including a valve for
connecting the pump to the input path or the output path.
3. Apparatus as claimed in claim 2 further including control means
for controlling the pump and valve whereby the pump draws liquid
in, whilst the reactor is not processing with this precursor.
4. Apparatus as claimed in claim 2 or claim 3 further including
control means for controlling the pump and the valve whereby the
pump returns some or all of the undelivered precursor to the
source.
5. Apparatus as claimed in any one of the preceding claims wherein
the pump is a syringe pump.
6. Apparatus as claimed in any of the preceding claims wherein the
source includes a bottle or reservoir of liquid precursor.
7. Apparatus as claimed in claim 6 wherein the source includes at
least two bottles or reservoirs and means for automatically
connecting one bottle or reservoir to the inlet path as the other
becomes empty.
8. A method of delivering a liquid precursor to a semiconductor
processing reactor including: (i) Drawing a liquid precursor along
an input path, into a volume calibrated positive displacement pump
from a source of liquid precursor; and (ii) Delivering, along an
output path, a known volume of liquid precursor.
9. A method as claimed in claim 8 including alternately connecting
the pump to the input path and the output path.
10. A method as claimed in claim 8 or claim 9 wherein is after each
volume delivery the pump returns some or all of the remaining
liquid to the source, before drawing a fresh charge.
Description
[0001] This invention relates to methods and apparatus for
delivering liquid precursors to semiconductor processing
reactors.
[0002] There is a good discussion of various prior art proposals
for delivering such precursors in the preamble of U.S. Pat. No.
5,620,524 and the reader is referred to this. In general a liquid
precursor will be a gas at the low pressures, which typically exist
in the reactor (e.g. 1 torr), but at atmospheric pressure (15 torr)
they will be in their liquid state. This gives rise to practical
delivery and measurement problems, which are exacerbated by the
highly reactive nature of many of these precursors, which limit the
choice of engineering materials that may be used. Most liquid
precursor delivery systems, which are used in wafer processing, are
of one of the following three types:
[0003] 1. There is vaporisation of the liquid and the use of a gas
mass flow controller.
[0004] 2. Use of a liquid mass flow controller.
[0005] 3. A carrier gas is passed through a liquid in a "bubbler"
to vaporise some of the liquid in the carrier gas bubbles.
[0006] Whilst gas mass flow measuring instruments are widely used,
they present problems when the liquid has to be vaporised for mass
flow measurement. A large reservoir of vaporised liquid is
required, which increases the residence time of the vaporised
liquid at a raised temperature. For peroxide, which is a useful
precursor, decomposition may commence before it reaches the process
chamber. Liquid mass flow controllers are capable of giving good
flow control but are liable to instabilities, believed to be caused
by bubbles forming in the mass flow controller whilst in its idle
state and the cold liquid cooling the controller can cause
calibration drift. Bubblers require a carrier gas and the lower the
vapour pressure, the less liquid that is taken up as vapour by the
bubbles. Therefore, for low vapour pressure liquids, a high flow of
carrier gas is required and that may be incompatible with the
process.
[0007] As alternatives to these approaches, an arrangement similar
to that shown in U.S. Pat. No. 5,620,524 has been tried comprising
a positive displacement pump in combination with a narrow bore
outlet pipe, but as well as difficulties in selecting appropriate
materials for such pumps and other parts, flow variations are
experienced due to variations in bore of the narrow bore pipe,
necessary to buffer the low pressure chamber from the pump. Such
arrangements are susceptible to variations because the flow
restriction of the narrow bore pipe dominates as the pump is
essentially only a pressurisation device. The results of this
method are referred to as "standard" in FIG. 3 below.
[0008] A simpler version of this system can be used if a pre-set or
fixed flow is acceptable. The system then entirely depends on the
action of ambient pressure upon the liquid to replace the use of
the pump and the flow restricting tubing to control flow. This
system makes use of the fact that clean rooms are pressure
controlled environments at slightly above atmospheric pressure. The
system is still however dependent on the internal bore diameter of
the pipe being accurate and in suitably compatible materials this
is not often the case. Specific system calibration can therefore
become necessary and different pipe lengths may need to be used
depending on the actual bore diameter. The results of this method
are referred to as "fixed flow" in FIG. 3 below.
[0009] U.S. Pat. No. 5,620,524 describes an alternative using
out-of-phase piston pumps, but it relies on the system knowing
various characteristics of the precursor and monitoring the
temperature and pressure of the precursor in order to deliver a
desired mass of precursor.
[0010] U.S. Pat. No. 5,098,741 describes the use of a positive
displacement pump to feed a liquid precursor to a CVD chamber, but
the system requires the use of a pressure metre controlling a
variable orifice valve to overcome the problem of dissolved
gases.
[0011] From one aspect the invention consists in apparatus for
delivering a liquid precursor to a semiconductor processing reactor
comprising a source of a liquid precursor, a volume calibrated
positive displacement pump drawing liquid precursor from the source
via an input path and for delivering, along an output path,
(preferably without any pressure control and/or pulsing) a known
volume of liquid precursor to the reactor. Either just prior to the
reactor or within the reactor the liquid precursor may be
evaporated, for example by a flash evaporator.
[0012] The apparatus may further include a valve for connecting the
pump to the input path or the output path. The apparatus may
further comprise control means for controlling the pump and the
valve whereby the pump draws liquid in, whilst the reactor is not
processing with this precursor. Additionally or alternatively the
apparatus may further include control means for controlling the
pump and the valve whereby the pump returns any undelivered
precursor to the source. This recucling, particularly when combined
with the pump only being charged when needed, significantly reduces
the presence of dissolved gases.
[0013] The pump may be in the form of a syringe pump.
[0014] The source may include another reservoir of liquid precursor
and preferably the source may include at least two bottles or
reservoirs and means for automatically connecting one bottle or
reservoir to the inlet path as the other becomes empty.
[0015] The apparatus preferably includes a linear encoder
controlled stepper motor for driving the pump to deliver the known
volume.
[0016] From another aspect the invention consists in a method of
delivering a liquid precursor to a semiconductor processing reactor
including:
[0017] 1. Delivering a liquid precursor, along an input path, into
a volume calibrated positive displacement pump from a source of
liquid precursor;
[0018] 2. Delivering, along an output path, preferably without
pressure control and/or pulsing a known volume of liquid precursor
to the reactor.
[0019] The liquid precursor may be evaporated either just before it
reaches the reactor or within the reactor.
[0020] This may further include permanently connecting the pump to
the input path and the output path. Additionally or alternatively,
after each volume delivery, the pump may return any remaining
liquid to the source, before drawing a fresh charge.
[0021] Although the invention has been defined above it is to be
understood it includes any inventive combination of the features
set out above or in the following description.
[0022] The invention may be performed in various ways and specific
embodiments will now be described, by way of example, with
reference to the accompanying drawing in which:
[0023] FIG. 1 is a schematic view of a liquid precursor delivery
system;
[0024] FIG. 2 is a graph indicating flow rate from the system;
and
[0025] FIG. 3 is a further graph indicating variations in
deposition rates using a variety of liquid precursor delivery
systems.
[0026] A liquid precursor delivery system is generally indicated at
10 in FIG. 1. The system 10 includes a precursor source generally
indicated at 11, an inlet tube 12, a two-way valve 13, a pump
assembly, generally indicated at 14, an outlet tube 15, a shut off
valve 16, and a flash evaporator 17.
[0027] The liquid precursor source 11 comprises a pair of bottles
18, 19 contained within a temperature controlled chamber 20, level
sensors, schematically indicated at 21 detect the level of liquid
in the respective bottles 18, 19. The bottles 18, 19 are connected
to a valve 22 and thence to the inlet tube 12. The valve 22 is
arranged to connect one or other of the bottles 18, 19 to the tube
12.
[0028] The pump assembly 14 is of the type generally known as a
syringe or variable volume pump, such as, for example, made by Lee
Products in their LPV series. Such pumps have a syringe 24
comprising a tube 25 and a piston 26. The piston is linked to a
stepper motor 27 and in general means are provided for detecting
the linear movement of the piston to determine the volume of liquid
expelled from the syringe.
[0029] In the illustrated arrangement the stepper motor 27 drives a
lead screw 28 which in turn linearly moves a carriage 29 that is
connected to the free end of the piston 26. The linear position of
the carriage 29 is detected by a linear encoder 30. As the position
of the carriage 29 is revealed very precisely by the linear encoder
30, the position of the piston 26, and hence the volume of liquid
displaced, can be very tightly controlled and without relying on
the pump being operated over a precisely set time period. Further
the whole arrangement enables liquid to be expelled at high
pressure.
[0030] The pump assembly 14 and valves 13, 16 and 22 are all under
the control of a control circuit 31, which is in turn responsive to
the linear encoder 30 and the level sensors 21, as well as other
processing information from the associated reactor.
[0031] In use the stepper motor 27 initially draws the carriage 29
in a downward direction, which moves the piston in a withdrawing
sense within the tube 25. With the valve 13 set to connect the pump
24 to the liquid source 11, the liquid precursor can be drawn from
one or other of the bottles 18, 19 depending on the position Of the
valve 22. Once the pump 24 is charged, the stepper motor 27 stops.
The valve 13 is then switched to connect the syringe pump 24 to the
outlet tube 15 and at the right moment, in processing, the shut off
valve 16 is opened and the stepper motor reverses the motion to
drive the piston 26 back within the tube 25 causing liquid
precursor to be delivered into the flash evaporator 17. The volume
of liquid expelled is directly related to the travel of the piston
26 and hence of the carriage 29. This can be monitored by the
control circuit 31 via the linear encoder 30 and as soon as the
desired volume is achieved, the stepper motor 27 is turned off.
Thus it will be seen that very precise volumes of liquid precursor
can be delivered at high pressure into the evaporator without the
problems which arise with other systems.
[0032] It is preferred that the syringe is filled with more than
the required volume to prevent any shortage in delivery.
Conveniently, then the unexpelled liquid can be returned to the
bottles 18, 19 via a valve 13, tube 12 and valve 23 so that the
liquid precursor can be kept in the best conditions possible.
[0033] The provision of two bottles enables one bottle to be
switched over when it becomes empty, without any interruption in
processing being necessary.
[0034] It is thus anticipated that wafers or batches of wafers can
be introduced into the reactor chamber, a precise volume of liquid
precursor delivered into the chamber via the flash evaporator 17
and thereafter the pump can be emptied and recharged ready for the
next wafer or batch.
[0035] FIG. 2 illustrates the linearity in flow rate that can be
achieved with the system of the invention and hence the accuracy of
volume delivery.
[0036] FIG. 3 illustrates the resultant benefits in terms of
repeatability deposition rate. It will be seen that the syringe
produces a very repeatable level of deposition using a hydrogen
peroxide system as compared with earlier delivery proposals.
[0037] The system has a number of advantages:
[0038] 1. It can be self primed at the beginning of a run and hence
clear any lines of degraded hydrogen peroxide and bubbles from the
line and syringe.
[0039] 2. The syringe need only be filled immediately prior to the
process avoiding degradation of the liquid precursor.
[0040] 3. The delivery rate can be fully programmable.
[0041] 4. The delivery rate can be fully monitored by the linear
encoder.
[0042] 5. Any excess liquid precursor is returned to the source at
the end of the process.
[0043] 6. Continuous running through the automatic bottle
changeover can be easily achieved. These benefits have been
particularly noted with such precursors as hydrogen peroxide which
do tend to degrade when not kept under suitable conditions. The
delivery system also works very well with hydrogen peroxide being
accurate to below 1 gram per minute. Flow rates can be easily
changed without any significant loss of accuracy simply by changing
the pump tubes and the matching pistons.
[0044] Experiments, which are reported, in our copending UK Patent
application 0001179.1 entitled "Method and Apparatus for forming a
film on a substrate" using conventional systems and then a syringe
pump to deliver cyclohexyldimethoxymethylsilane show that for at
least some precursors and processes acceptable results are only
obtained when a syringe pump assembly as described is used. This
disclosure is incorporated herein by reference.
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