U.S. patent application number 09/729779 was filed with the patent office on 2001-06-14 for mini-environment control system and method.
Invention is credited to Bernard, Roland, Chevalier, Eric.
Application Number | 20010003572 09/729779 |
Document ID | / |
Family ID | 9553053 |
Filed Date | 2001-06-14 |
United States Patent
Application |
20010003572 |
Kind Code |
A1 |
Bernard, Roland ; et
al. |
June 14, 2001 |
Mini-environment control system and method
Abstract
A mini-environment control device includes an individual
enclosure to contain a sample and to isolate it from the external
environment. An array of micropumps attached to the individual
enclosure generates and maintains a controlled vacuum in the
individual enclosure. Transfer means introduce the sample into the
individual enclosure and extract it therefrom. The micropumps of
the array of micropumps can be of a type employing the thermal
transpiration effect. Temperature and pressure microsensors and a
gas analyzer enable the operation of the array of micropumps to be
controlled by an onboard microcomputer. The atmosphere surrounding
a sample is therefore controlled.
Inventors: |
Bernard, Roland;
(Viuz-La-Chiesaz, FR) ; Chevalier, Eric; (Annecy
Le Vieux, FR) |
Correspondence
Address: |
SUGHRUE, MION, ZINN, MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, N.W., Suite 800
Washington
DC
20037-3213
US
|
Family ID: |
9553053 |
Appl. No.: |
09/729779 |
Filed: |
December 6, 2000 |
Current U.S.
Class: |
417/53 ; 417/207;
417/244; 417/322 |
Current CPC
Class: |
H01L 21/67393 20130101;
F04B 19/006 20130101 |
Class at
Publication: |
417/53 ; 417/207;
417/244; 417/322 |
International
Class: |
F04B 019/24 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 9, 1999 |
FR |
99 15 528 |
Claims
There is claimed:
1. A method of testing samples or of transforming samples by
etching and deposition, said method including a step of
transporting the sample individually in a controlled vacuum in an
individual enclosure.
2. A device for controlling the atmosphere which surrounds a
sample, said device including: a sealed individual enclosure
conformed to contain said sample and to isolate it from the
external atmosphere with a small volume interior atmosphere around
said sample, an array of micropumps, fastened to said individual
enclosure and adapted to generate and maintain a controlled vacuum
in said individual enclosure, said array of micropumps being
adapted to be connected to an electrical power supply, transfer
means for introducing said sample into said individual enclosure
and extracting it therefrom.
3. The device claimed in claim 2 wherein the combination of said
individual enclosure and said array of micropumps constitutes a
portable self-contained system including an internal electrical
power supply for supplying power at least temporarily to said array
of micropumps.
4. The device claimed in claim 2 wherein said combination of said
individual enclosure and said array of micropumps is fixed and
constitutes a transfer chamber in a semiconductor fabrication
installation.
5. The device claimed in claim 2 wherein said array of micropumps
comprises thermal transpiration micropumps.
6. The device claimed in claim 5 wherein said array of micropumps
comprises a succession of chambers linked by channels of which at
least one transverse dimension is approximately equal to or less
than the mean free path of the gas molecules present in said
micropumps, and means for creating and maintaining a temperature
difference between said successive chambers in order to generate a
pumping effect.
7. The device claimed in claim 6 wherein said means for creating
and maintaining a temperature difference between said successive
chambers include an electrical resistance in the vicinity of the
inlet of the second of two successive chambers.
8. The device claimed in claim 6 wherein said means for creating
and maintaining a temperature difference comprise Peltier-effect
junctions accommodated in the vicinity of the inlets of the
successive chambers.
9. The device claimed in claim 2 wherein said array of micropumps
comprises micromembrane micropumps.
10. The device claimed in claim 2 wherein said array of micropumps
comprises piezo-electric micropumps.
11. The device claimed in claim 2 wherein said array of micropumps
comprises a series of at least one primary stage of thermal
transpiration micropumps and at least one secondary stage of
piezo-electric micropumps.
12. The device claimed in claim 2 further including a temperature
microsensor, a pressure microsensor and a gas analyzer, for
controlling said atmosphere in said individual enclosure and for
controlling said array of micropumps via an onboard microcomputer.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to devices and methods for
controlling the atmosphere surrounding a sample such as a substrate
wafer for fabricating semiconductors, for example, or any other
item, during testing or manufacture.
[0003] 2. Description of the Prior Art
[0004] In the semiconductor industry, for example, substrate
handling systems are currently used to isolate the substrates from
contaminating agents in white rooms. Several substrates are placed
in a common collective box containing nitrogen or another neutral
gas under pressure, as taught in the documents EP 0 582 018 A or
U.S. Pat. No. 5,988,233 A. The atmosphere in the box is not
controlled. The presence of the nitrogen or other neutral gas,
which requires a transient step of degassing before vacuum
treatment of the substrate, in an interface like that described in
the same document EP 0 532 018 A, constitutes a problem. Another
problem is the contamination resulting from gas flows during return
to the treatment pressure, as a result of which a purge device like
that described in the document U.S. Pat. No. 5,988,233 A may be
provided.
[0005] In the documents U.S. Pat. No. 5,255,783 A and EP 0 854 498
A, several substrates can be transported in a common collective
box, the atmosphere in which is at a reduced pressure established
by an external source and which can contain a substitute neutral
gas. The atmosphere of the box is not controlled. At the very most,
the document EP 0 854 498 A teaches continuous agitation and
filtering of the internal atmosphere, and the generation of an
internal overpressure on opening the access door. All the above
documents encourage collective transportation of the samples by
grouping several of them in a common collective box.
[0006] Various micropump designs are known in the art, including
thermal transpiration micropumps described in the document U.S.
Pat. No. 5,871,336 A when applied to generating vacuum in a
miniature gas analyzer employing a mass spectrograph or other
miniature sensor; thermal gas expansion micropumps described in the
document U.S. Pat. No. 5,375,979 A; piezo-electric membrane
micropumps described in the document U.S. Pat. No. 4,938,742 A for
pumping liquids or gases in the fields of medication, biology,
cooling and fuel supply; micropumps which function by varying the
volume of gases using Peltier-effect junctions described in the
document U.S. Pat. No. 5,975,856 A when applied to acceleration,
pressure or chemical composition sensors or to fluid control in the
pharmaceutical or aerospace industry. None of the above documents
describes or suggests an application to controlling the atmosphere
in the treatment of samples such as semiconductor wafers.
[0007] An object of the invention is to design a device for placing
the sample in a controlled atmosphere, and maintaining it therein,
which is as close as possible to the conditions under which the
sample is treated or used, and to eliminate or significantly reduce
transient steps of atmosphere modification and adaptation that have
previously been necessary between successive sample treatment or
test operations.
[0008] The invention aims to bring the sample as close as possible
to the conditions of use or treatment and to maintain it there.
SUMMARY OF THE INVENTION
[0009] To this end, the invention provides a method of testing
samples or of transforming samples by etching and deposition, said
method including a step of transporting the sample individually in
a controlled vacuum in an individual enclosure. This significantly
reduces the risk of contaminating the samples.
[0010] The size of the individual enclosure is preferably only
slightly greater than that of the sample to be transported, so that
the sample placed in the enclosure is surrounded by a small volume
of atmosphere constituting a mini-environment.
[0011] The invention also provides a device for controlling the
atmosphere which surrounds a sample, notably for using these
methods, said device including:
[0012] a sealed individual enclosure conformed to contain said
sample and to isolate it from the external atmosphere with a small
volume interior atmosphere around said sample,
[0013] an array of micropumps fastened to said individual enclosure
and adapted to generate and maintain a controlled vacuum in said
individual enclosure, said array of micropumps being adapted to be
connected to an electrical power supply,
[0014] transfer means for introducing said sample into said
individual enclosure and extracting it therefrom.
[0015] The above device produces a mini-environment around the
sample, significantly reducing the risk of contamination of the
sample.
[0016] In a first embodiment, the combination of said individual
enclosure and said array of micropumps constitutes a portable
self-contained system including an internal electrical power supply
for supplying power at least temporarily to said array of
micropumps. It is therefore possible to move the sample between two
successive workstations without necessitating any transient
degassing operation such as has been necessary with pressurized
nitrogen containers.
[0017] In another application, said combination of said individual
enclosure and said array of micropumps is fixed and constitutes a
transfer chamber in a semiconductor fabrication installation.
[0018] According to one advantageous facility, in particular for
constituting a portable self-contained system, said array of
micropumps comprises thermal transpiration micropumps. The heat
sources for producing the thermal transpiration effect can be
electrical resistances or Peltier-effect junctions. An advantage of
these micropumps is that they have no moving parts, and therefore
no parts that can be worn by friction. This can therefore achieve
excellent reliability, and freedom from losses caused by
friction.
[0019] Also, these micropumps do not release unwanted particles
into the atmosphere.
[0020] Micromembrane micropumps, piezo-electric micropumps or gas
thermal expansion micropumps in which the gases can be heated by
electrical resistances or by Peltier effect junctions can be used
instead.
[0021] The interior atmosphere can be controlled by temperature and
pressure microsensors and a gas analyzer controlling the micropumps
via an onboard microcomputer.
[0022] Other objects, features and advantages of the present
invention will emerge from the following description of particular
embodiments, which is given with reference to the accompanying
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1 is a diagram showing in section an array of thermal
transpiration micropumps that can be used in accordance with the
present invention.
[0024] FIG. 2 is a diagrammatic view in section of an embodiment of
an atmosphere control device in accordance with the present
invention.
[0025] FIG. 3 shows the use of a portable implementation of an
atmosphere control device in accordance with the invention for
fabricating semiconductors.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0026] Referring more particularly to FIG. 2, a device in
accordance with the invention for controlling the atmosphere in a
mini-environment includes an individual enclosure 1 with a sealed
peripheral wall 2 conformed to contain a sample 3 and to isolate it
from the external atmosphere with a small volume 4 around the
sample 3 inside the individual enclosure 1. For a semiconductor
substrate wafer, for example, the peripheral wall 2 can define a
flat parallelepiped-shaped interior chamber whose dimensions are
only slightly greater than those of the substrate wafer.
[0027] An array of micropumps 5, attached to the individual
enclosure 1, is adapted to generate and maintain a controlled
vacuum in the individual enclosure 1. The array of micropumps 5 can
be connected to an electrical power supply.
[0028] Transfer means shown diagrammatically as a door 6 and a
transfer plate 19, which can be motorized and slides longitudinally
as shown by the double-headed arrow 20, insert the sample 3 in the
individual enclosure 1 or extract it therefrom.
[0029] In the FIG. 2 embodiment, the combination of the individual
enclosure 1 and the array of micropumps 5 is a portable
self-contained system including an internal electrical power supply
7 for supplying power at least temporarily to the array of
micropumps 5 and its control units. A portable configuration of the
device as a whole can have a diameter of approximately 200 mm to
approximately 500 mm, and a thickness from approximately 30 mm to
approximately 50 mm.
[0030] In the FIG. 2 embodiment, the device further includes
microsensors such as, for example, a temperature microsensor 8, a
pressure microsensor 9, and a gas analyzer 10, for controlling the
atmosphere in the individual enclosure 1 and for controlling the
array of micropumps 5 via an onboard microcomputer 11. The
microcomputer 11 is programmed to control the operation of the
micropumps 5 to stabilize the atmosphere in the individual
enclosure 1 around the sample 3.
[0031] In the embodiment shown in FIG. 1, the array of micropumps 5
comprises micropumps operating by the thermal transpiration effect.
As demonstrated by Knudsen, thermal transpiration establishes a
pressure difference between two large volumes at different
temperatures linked by a channel with very small transverse
dimensions, the radius of which is less than the mean free path of
the molecules. A succession of channels and volumes can therefore
generate a pressure difference from atmospheric pressure down to a
hard vacuum.
[0032] Considering two successive chambers 12 and 13 connected by a
small-section channel 14, for example, as shown in FIG. 1, if the
second chamber 13 is at a higher temperature than the first chamber
12, for example with a first chamber 12 at 300.degree. K and a
second chamber 13 at 600.degree. K, the pressure in the second
chamber 13 can be 1.4 times greater than the pressure in the first
chamber 12. The ratio of the pressures is substantially
proportional to the square root of the ratio of the absolute
temperatures in the two chambers 12 and 13.
[0033] This effect is produced even if the channel 14 is short but
sufficiently long to maintain the temperature difference between
the two chambers 12 and 13.
[0034] Clearly a plurality of chambers linseed by a plurality of
channels can be provided.
[0035] Accordingly, the array of micropumpls 5 can advantageously
comprise a succession of chambers 12, 13 connected by channels 14
of which at least one transverse dimension is approximately equal
to or less than the mean free path of the gas molecules present in
the micropumps 5, and with means for creating and maintaining a
temperature difference between the successive chambers 12, 13 in
order to generate a pumping effect.
[0036] This plurality of chambers and channels can be formed on
substrates by micromachining processes routinely used in
microtechnology. Multiple sequences (thousands of sequences) can
then be performed on an entire wafer, which significantly increases
the pumping capacity of the array, which can be as high as several
hundred mbar.L/s, with nominal and redundant sequences. It is
important to note that there are no moving parts.
[0037] In an array of micropumps 5 of this kind using the thermal
transpiration effect it is necessary to create and to maintain a
temperature difference between the successive chambers such as the
chambers 12 and 13 in order to generate a pumping effect.
[0038] As shown to a larger scale in FIG. 2, an array of thermal
transpiration micropumps 5 according to the invention can include a
pump inlet 15 connected to the interior volume 4 of the individual
enclosure 1 and a pump outlet 16 connected to atmospheric pressure.
The array of micropumps 5 receives a gas at a low pressure via its
inlet 15 and exhausts the gas at atmospheric pressure via its
outlet 16.
[0039] Each of the connecting channels such as the channel 14 can
have a rectangular cross section, which is easier to produce by
micromachining, and at least one dimension that is approximately
equal to or less than the mean free path of the gas molecules under
the conditions present in the channel 14.
[0040] To generate the pumping effect, the means for creating and
maintaining a temperature difference between the successive
chambers can include an electrical resistance 17 for heating the
gases in the second chamber 13. The electrical resistance 17 can
advantageously be disposed near the inlet of the second chamber 13
and fed by control and regulation means.
[0041] Alternatively, the means for creating and maintaining a
temperature difference can include Peltier effect junctions located
near the inlets of the successive chambers 12 and 13, for
example.
[0042] The substrate in which the chambers 12 and 13 and the
channels 14 are formed is preferably made of a semiconductor
material such as silicon, silica, gallium arsenide or silicon
carbide.
[0043] For ease of manufacture, channels of rectangular cross
section may be preferred, in which one dimension, such as the
width, is approximately equal to or less than the mean free path of
the molecules.
[0044] The gases pumped out of the individual enclosure 1 pass
through a plurality of stages within the array of micropumps 5.
Because the mean free path of the molecules decreases as the gas
pressure increases, the chambers and the channels can be made
smaller as the gas pressure increases. The typical dimensions used
in thermal transpiration micropumps of the above kind are from a
few hundreds of microns to less than one micron.
[0045] To avoid the more complex production of chambers and
channels with very small dimensions when the pressure of the gas to
be exhausted is approaching atmospheric pressure, an array of
micropumps 5 can advantageously comprise in series at least one
primary stage of thermal transpiration effect micropumps and at
least one secondary stage of piezo-electric micropumps.
[0046] FIG. 3 shows one use of the device according to the
invention.
[0047] In this use, the individual enclosure 1 shown is in the form
of a flat parallelepiped-shaped box. The figure also shows the
sample 3 and a door device 6. The individual enclosure 1 can be the
size of a cassette, depending on the size of the sample 3, for
example it can have a diameter from approximately 200 mm to
approximately 500 mm and a thickness from approximately 30 mm to
approximately 50 mm.
[0048] The individual enclosure 1 containing the sample 3 can
easily be moved manually to a workstation 1E, in which the sample 3
is extracted from the individual enclosure 1 but remains at a
pressure similar to that in the individual enclosure 1, for example
for a vacuum deposition or etching step of the fabrication of a
semiconductor.
[0049] Another example of a use of the device according to the
invention is the encapsulation of a satellite onboard optical
system detector to protect it from moisture and other contaminating
agents during dedicated control tests prior to launch.
[0050] The present invention is not limited to the embodiments
explicitly described but includes variants and generalizations
thereof that will be evident to the skilled person.
* * * * *