U.S. patent application number 09/798959 was filed with the patent office on 2002-02-14 for anticorrosive vacuum sensor.
Invention is credited to Esashi, Masayoshi, Kitamura, Yasuyuki, Miyashita, Haruzo.
Application Number | 20020019711 09/798959 |
Document ID | / |
Family ID | 26586936 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020019711 |
Kind Code |
A1 |
Miyashita, Haruzo ; et
al. |
February 14, 2002 |
Anticorrosive vacuum sensor
Abstract
The present invention concerns the capacitive vacuum sensor that
includes an elastic diaphragm electrode and rigid fixed electrodes
disposed to face opposite the elastic diaphragm electrode, with an
internal space being delimited between the elastic diaphragm
electrode and rigid fixed electrodes, wherein the elastic diaphragm
electrode deflects elastically in response to any change in the
pressure of a gas applied on the said elastic diaphragm electrode,
and wherein the capacitive vacuum sensor is responsive to any
change in the capacitance between the elastic diaphragm electrode
and rigid fixed electrodes that may occur in accordance with the
deflection of the elastic diaphragm electrode so that it can
measure the pressure of the gas. In the present invention, the
capacitive vacuum sensor is provided as the anticorrosion vacuum
sensor that includes an anticorrosive diaphragm electrode that can
resist the corrosive action of the reactive gas when it is exposed
to such gas, and is fabricated by the micromachining technology.
Thereby, the capacitive vacuum sensor that has the resistance to
the reactive gases as well as the high quality, and can be
manufactured on the massive production basis is provided.
Inventors: |
Miyashita, Haruzo;
(Yamanashi, JP) ; Kitamura, Yasuyuki; (Miyagi,
JP) ; Esashi, Masayoshi; (Miyagi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
26586936 |
Appl. No.: |
09/798959 |
Filed: |
March 6, 2001 |
Current U.S.
Class: |
702/52 |
Current CPC
Class: |
G01L 9/0073
20130101 |
Class at
Publication: |
702/52 |
International
Class: |
G01F 001/00; G01F
007/00; G06F 019/00; G01L 007/00; G01N 011/00; G01F 017/00; G01F
023/00 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 7, 2000 |
JP |
2000-62095 |
Jan 12, 2001 |
JP |
2001-4387 |
Claims
What is claimed is:
1. An anticorrosive vacuum sensor of the class of the capacitive
vacuum sensor manufactured by the micromachining technique,
including: an elastic diaphragm electrode elastically deflects in
response to any change in the pressure of a gas applied on the said
elastic diaphragm electrode; and rigid fixed electrodes disposed to
face opposite said elastic diaphragm electrode, said elastic
diaphragm electrode and said rigid fixed electrodes defining a
closed space therebetween, and said capacitive vacuum sensor being
responsive to any change in the capacitance between said elastic
diaphragm electrode and said rigid fixed electrodes that occurs in
response to the deflection of said elastic diaphragm electrode, for
measuring said pressure of the gas, wherein said elastic diaphragm
electrode is formed to be anticorrosive.
2. The anticorrosive vacuum sensor as defined in claim 1, wherein
said elastic diaphragm electrode is formed like a thin film
diaphragm that is slightly stressed to provide the tensile
stress.
3. The anticorrosive vacuum sensor as defined in claim 1, wherein
said elastic diaphragm electrode contains doped impurities that
enhance the conductivity of said elastic diaphragm electrode.
4. The anticorrosive vacuum sensor as defined in claim 2, wherein
said elastic diaphragm electrode contains doped impurities that
enhance the conductivity of said elastic diaphragm electrode.
5. The anticorrosive vacuum sensor as defined in claim 1, further
including an electrically conductive thin film deposited on the
side of said elastic diaphragm electrode facing said rigid fixed
electrodes.
6. The anticorrosive vacuum sensor as defined in claim 2, further
including an electrically conductive thin film deposited on the
side of said elastic diaphragm electrode facing said rigid fixed
electrodes.
7. The anticorrosive vacuum sensor as defined in claim 1, wherein
said elastic diaphragm electrode is formed from any one of silicon
carbide, alumina and aluminum nitride.
8. The anticorrosive vacuum sensor as defined in claim 2, wherein
said elastic diaphragm electrode is formed from any one of silicon
carbide, alumina and aluminum nitride.
9. The anticorrosive vacuum sensor as defined in claim 3, wherein
said elastic diaphragm electrode is formed from any one of silicon
carbide, alumina and aluminum nitride.
10. The anticorrosive vacuum sensor as defined in claim 4, wherein
said elastic diaphragm electrode is formed from any one of silicon
carbide, alumina and aluminum nitride.
11. The anticorrosive vacuum sensor as defined in claim 5, wherein
said elastic diaphragm electrode is formed from any one of silicon
carbide, alumina and aluminum nitride.
12. The anticorrosive vacuum sensor as defined in claim 6, wherein
said elastic diaphragm electrode is formed from any one of silicon
carbide, alumina and aluminum nitride.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a capacitive vacuum sensor,
and more particularly to an anticorrosive vacuum sensor of the
class of the capacitive vacuum sensor. The said anticorrosive
vacuum sensor includes a diaphragm electrode section, which has the
high resistance to the corrosive action of any gas that would
affect the performance of the diaphragm electrode, when it is
exposed to such gas, and can measure the degree of vacuum under
such gaseous environment with high reliability and stability over a
long-term lifetime.
[0003] 2. Prior Art
[0004] The manufacture of electronics components or semiconductor
devices or products involves the thin film deposition or etching
process that must be carried out within the strictly controlled
vacuum equipment. This process usually proceeds within the vacuum
equipment that is kept at a constant pressure. The pressures that
exist within the vacuum equipment are often measured by means of
capacitive vacuum sensors that provide the accurate pressure
measuring capabilities regardless of the type of gases used.
[0005] Most of the existing capacitive vacuum sensors that are
commercially available are manufactured by the mechanical machining
technique, but the micromachining technique may be used to produce
more compact sensors on the massive production basis and at the
reduced costs.
[0006] Referring to FIG. 3, there is one typical example of the
conventional capacitive vacuum sensor that may be manufactured by
using the micromachining technique. This capacitive vacuum sensor
includes a non-conducting substrate 2 made of glass (referred to as
glass substrate) and a silicon substrate 3 that are bonded
together, wherein the glass substrate 2 has electrically conductive
leads 1 that extend through the substrate 2 for providing
respective electrical paths between the top and bottom sides
thereof, and the silicon substrate 3 has a recess formed on either
side thereof.
[0007] There is a reference pressure space 4 that is internally
delimited by the silicon substrate 3 and glass substrate 2, and is
kept at high vacuum. A getter 5 is provided within the recess on
the silicon substrate 3, and is communicative with the reference
pressure space 4 so that it can absorb any part of the gas that
remains within the reference pressure space 4. In this way, the
reference pressure space 4 may be kept at high vacuum.
[0008] The silicon substrate 3 includes a boron diffused silicon
layer 7 that is formed on the upper surface by diffusing boron over
the depth of 2 .mu.m to 8 .mu.m. On the bottom side, the silicon
substrate 3 is partially etched, thereby exposing the above boron
diffused silicon layer 7 from the bottom side. This exposed boron
diffused silicon layer 7 acts as a diaphragm electrode 6. That is,
the diaphragm electrode 6 is formed from silicon that contains
boron diffused over the depth of 2 .mu.m to 8 .mu.m.
[0009] The diaphragm electrode 6 may deflect when a certain gas
pressure from any external source is applied upon the diaphragm
electrode 6. This deflection may occur in accordance with the
applied gas pressure, which causes the corresponding change in the
capacitance between the rigid fixed electrode 8 and diaphragm
electrode 6. The change in the capacitance may be provided in the
form of the corresponding electrical signal. The electrical signal
is transmitted from the fixed electrodes 8 through the electrically
conductive leads 1 to electrode pads 9, respectively. The electrode
pads 9 are coupled to the signal processing circuit (not shown),
where the signal may be processed to determine the current pressure
of the gas applied from the external source.
[0010] FIG. 5(a) through FIG. 5(e) depict the process of
manufacturing the conventional capacitive vacuum sensor in FIG. 3
by means of the micromachining technique.
[0011] Specifically, the process is described by referring to FIG.
5(a) to FIG. 5(e). In step of FIG. 5(a), a thermally oxidized layer
10 is first formed on the surface of the silicon substrate 3 having
a recess on the upper side thereof, and the portion of the
thermally oxidized layer 10 located on the upper side of silicon
substrate 3 is then patterned by masking.
[0012] In step of FIG. 5(b), boron is doped into the silicon
substrate 3 on its upper side so that it can diffuse over the
thickness of 2 .mu.m to 8 .mu.m. The result is the boron-diffused
layer 7.
[0013] In step of FIG. 5(c), the thermally oxidized layer 10 on the
upper side of the silicon substrate 3 is removed, and the thermally
oxidized layer 10 on the lower side of the silicon substrate 3 is
then patterned by masking.
[0014] In step of FIG. 5(d), a getter 5 is inserted between the
silicon substrate 3 obtained through the steps FIG. 5(a) through
FIG. 5(c) and the glass substrate 2 that carries the electrode pads
9 on one side (upper side, in this case) and the fixed electrodes 8
on the other side (lower side) that are interconnected with each
other by the electrically conducting leads 1, respectively, and the
silicon substrate 3 and glass substrate 2 are anodically bonded
together into a single unit substrate under the vacuum atmosphere.
The single unit substrate thus obtained includes a reference
pressure space 4 that is internally delimited by the silicon
substrate 3 and glass substrate 2.
[0015] In step of FIG. 5(e), when the single unit substrate
including the glass substrate 2 and silicon substrate 3 bonded
together is immersed in an etching liquid, such as
ethylenediaminepyrocatechol (EDP) water, the glass substrate 2 and
the thermally oxidized layer 10 thereon will remain not to be
etched, while the exposed area of the silicon substrate 3 that is
not covered with the thermally oxidized layer 10 will be removed by
etching. This etching will progresses deep into the silicon
substrate 10 until the boron diffused silicon layer 7 is exposed.
As the ethylenediaminepyrocatechol water has no etching effect on
the boron-doped silicon, the etching will stop where and when the
boron diffused silicon layer 7 has been exposed. Finally, the
capacitive vacuum sensor is thus obtained, which includes a
diaphragm electrode 6 formed by the boron diffused silicon layer 7
that is 2 .mu.m to 8 .mu.m thick.
[0016] Various types of gases may be utilized during the process of
manufacturing semiconductor devices or electronics components. Some
of the gases may contain reactive gases that have the corrosive
action. When the diaphragm electrode is exposed to the reactive
gases, it may be affected by the corrosive action. If the
capacitive vacuum sensor includes such diaphragm electrode that is
easy to be affected by the corrosive action, it may have a shorter
lifetime. Thus, the capacitive vacuum sensor cannot provide the
long-term reliable pressure measuring capabilities.
[0017] Particularly, in the dry etching equipment, some gases that
contain fluorine reactive gases may be used in manufacturing
silicon-based semiconductor devices. In this case, the capacitive
vacuum sensor including the silicon-based diaphragm electrode may
be used to measure the pressures in the fluorine gas atmosphere.
During the process, the diaphragm electrode is always exposed to
the fluorine reactive gases that have the etching effect on the
diaphragm electrode. Thus, the diaphragm electrode may be damaged
seriously.
SUMMARY OF THE INVENTION
[0018] An object of the present invention is to provide a
capacitive vacuum sensor that may be manufactured by using the
micromachining technology that allows for the manufacture of
compact products on the massive production basis, wherein the
capacitive vacuum sensor thus manufactured can guarantee the
long-term, reliable and stable operation by providing the high
resistance to the corrosive action of any reactive gases even when
it is exposed to such reactive gases during the process of
manufacturing the semiconductor devices or electronics
components.
[0019] The present invention proposes to solve the problems of the
prior art in several aspects by providing the anticorrosive vacuum
sensor of the class of the capacitive vacuum sensor.
[0020] In one aspect, the anticorrosive vacuum sensor according to
the present invention may be manufactured by using the
micromachining technique, and includes the diaphragm electrode that
is highly resistant to the corrosive action.
[0021] In another aspect, the anticorrosive vacuum sensor according
to the present invention includes the anticorrosive diaphragm
electrode that may be formed like a thin film diaphragm that is
slightly stressed to provide the tensile stress. This permits the
sensor to measure the pressures accurately.
[0022] In still another aspect, the anticorrosive vacuum sensor of
the present invention can determine any change in the capacitance
accurately, even if the anticorrosive diaphragm electrode has
relatively less conductive owing to the type of material used for
forming it. To this end, an electrically conductive thin film may
be deposited on the side of the diaphragm electrode facing the
fixed electrodes, or the diaphragm electrode may contain any doped
impurities that enhance the conductivity of the diaphragm
electrode. This permits the sensor to respond accurately to any
change in the capacitance that develops between the diaphragm
electrode and fixed electrodes.
[0023] The present invention concerns the capacitive vacuum sensor
that includes an elastic diaphragm electrode and rigid fixed
electrodes disposed to face opposite the elastic diaphragm
electrode, with an internal space being delimited between the
elastic diaphragm electrode and rigid fixed electrodes, wherein the
elastic diaphragm electrode deflects elastically in response to any
change in the pressure of a gas applied on the said elastic
diaphragm electrode, and wherein the capacitive vacuum sensor is
responsive to any change in the capacitance between the elastic
diaphragm electrode and rigid fixed electrodes that may occur in
accordance with the deflection of the elastic diaphragm electrode
so that it can measure the pressure of the gas.
[0024] More specifically, the present invention provides the
anticorrosive vacuum sensor of the class of the capacitive vacuum
sensor that may be manufactured by using the micromachining
technique and includes an anticorrosive elastic diaphragm
electrode.
[0025] In this specification, the term "anticorrosive" means that
the diaphragm electrode can resist the corrosive action of the gas
that would affect the diaphragm electrode.
[0026] The anticorrosive diaphragm electrode may be formed from any
materials that show the chemical stability. For example, in cases
where the capacitive vacuum sensor that includes the silicon-based
elastic diaphragm electrode as the essential part of it is used on
the vacuum equipment to measure the pressure of a gas within the
vacuum equipment. And the gas used in the said vacuum equipment is
the reactive gas, such as fluorine gas, that generates halogen
radicals such as fluorine radicals. Any materials, such as silicon
carbide, alumina, aluminum nitride and the like, that show the
chemical stability and have the high resistance to the halogen
radicals such as fluorine radicals may be used to form the
anticorrosive diaphragm electrode.
[0027] The anticorrosive vacuum sensor according to the present
invention may be manufactured by using the micromachining
technique, which allows high-precision and compact-size vacuum
sensors to be manufactured on the massive production basis.
[0028] In the present invention, the anticorrosive diaphragm
electrode that is the essential part of capacitive vacuum sensor is
formed from any of the chemically stabilized materials such as
those mentioned above. Therefore, even when the vacuum sensor is
used in the reactive gas atmosphere under which semiconductor
devices or electronics components are fabricated, and is always
exposed to the corrosive action of the reactive gas, there is no
risk that the diaphragm electrode within the vacuum sensor will be
affected by the corrosive action of the reactive gas. Thus, the
vacuum sensor can have the long-term lifetime, and can measure the
degree of vacuum with high reliability and high stability.
[0029] Preferably, the anticorrosive diaphragm electrode may be
formed like a thin-film diaphragm that is slightly stressed to
provide the tensile stress. In this way, the anticorrosive
diaphragm electrode formed like the thin-film diaphragm can be
maintained to be in its flat state under the applied tensile
stress. This permits the vacuum sensor to measure the pressures
accurately.
[0030] The anticorrosive diaphragm electrode that is formed as the
thin-film diaphragm electrode being slightly stressed to provide
the tensile stress is manufactured by the following method. For
example, a thin film that is composed of any anticorrosive material
may be deposited on the side of the diaphragm electrode being
formed that is located facing the rigid fixed electrodes, by using
the chemical vapor deposition (CVD) method, evaporation method,
sputtering method or the like, under the conditions in which the
type of gas used, ambient temperature, power supply, deposition
time (processing time) and other parameters are well controlled.
That is to say, during the thin film deposition process, the before
mentioned parameters are controlled to avoid the minimum
requirement that the thin film being deposited is stressed to
provide the compressive stress.
[0031] In the anticorrosive vacuum sensor of the present invention
as described above, the anticorrosive diaphragm electrode
preferably may contain any doped impurities, such as boron (B),
phosphorous (P) and the like, that may enhance the conductivity of
the diaphragm electrode, or an electrically conductive thin film
preferably may be deposited on the side of the anticorrosive
diaphragm electrode facing the rigid fixed electrodes. For the
latter case, the diaphragm electrode may include the anticorrosive
diaphragm electrode coupled with the electrically conductive thin
film.
[0032] If the anticorrosive diaphragm electrode might become less
conductive, depending upon the type of material used for forming
the anticorrosive diaphragm electrode, or depending upon the
condition under which the thin film for the anticorrosive diaphragm
electrode is deposited and allowed to grow on the side of the
diaphragm electrode facing the rigid fixed electrodes, by using the
chemical vapor deposition (CVD) or sputtering process, as a result,
the vacuum sensor including such diaphragm electrode might fail to
respond to any change in the capacitance between the fixed
electrodes and diaphragm electrode accurately.
[0033] According to the present invention, the anticorrosive
diaphragm electrode can operate and determine any change in the
capacitance that develops between the diaphragm electrode and fixed
electrodes under such situations by and through forming the
anticorrosive diaphragm electrode containing any doped impurities
as described above.
[0034] It may be understood from the foregoing description that the
anticorrosive vacuum sensor according to the present invention
includes the elastic diaphragm electrode that may be formed from
any chemically stabilized materials, such as silicon carbide,
alumina or aluminum nitride. Therefore, when the vacuum sensor is
placed in the reactive gas atmosphere where it is exposed to the
corrosive action of a reactive gas, such as fluorine gases, that
produces halogen radicals such as fluorine radicals, the diaphragm
electrode within the vacuum sensor can resist the corrosive action
of the reactive gas. Thus, the vacuum sensor can provide the
reliable and accurate pressure measuring capabilities for a
long-term period.
[0035] It may also be understood that the vacuum sensor according
to the present invention may be manufactured by the micromachining
technique. Thus, the vacuum sensor thus obtained can have the
uniform quality and high precision.
[0036] While retaining the features of the compactness and massive
production offered by the micromachining technique, the
anticorrosive vacuum sensor may be provided simply by modifying
some of the conventional silicon-based diaphragm electrode
manufacturing process. Thus, the costs required to modify the
conventional process into the inventive process for manufacturing
the anticorrosive vacuum sensor of the present invention can be
minimized.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 represents one preferred embodiment of the present
invention;
[0038] FIG. 2 represents another preferred embodiment of the
present invention;
[0039] FIG. 3 represents one typical example of the prior art
capacitive vacuum sensor;
[0040] FIG. 4(a) to FIG. 4(f) depict the process of manufacturing
the anticorrosive vacuum sensor of FIG. 1 according to the present
invention, including the following steps:
[0041] FIG. 4(a) represents how a thermally oxidized layer is
formed on the silicon substrate, and the portion of the thermally
oxidized layer located on the upper side of the silicon substrate
is then patterned by masking;
[0042] FIG. 4(b) represents how a silicon carbide layer is formed
on the upper side of the silicon substrate;
[0043] FIG. 4(c) represents how the portion of the thermally
oxidized layer located on the upper side of the silicon substrate
is removed, with the portion of the thermally oxidized layer
exposed on the lower side being patterned by masking;
[0044] FIG. 4(d) represents how an electrically conductive thin
film is formed on the silicon carbide layer;
[0045] FIG. 4(e) represents how the glass substrate and silicon
substrate are bonded together into a single unit substrate; and
[0046] FIG. 4(f) represents the finished anticorrosive vacuum
sensor after having been processed through the steps FIG. 4(a)
through FIG. 4(e); and
[0047] FIG. 5(a) to FIG. 5(e) depict the process of manufacturing
the prior art capacitive vacuum sensor by using the micromachining
technique, including the following steps:
[0048] FIG. 5(a) represents how a thermally oxidized layer is
deposited on the silicon substrate, and the portion of the
thermally oxidized layer located on the upper side of the silicon
substrate is then patterned by masking;
[0049] FIG. 5(b) represents how a boron diffused layer is deposited
on the upper side of the silicon substrate;
[0050] FIG. 5(c) represents how the portion of the thermally
oxidized layer located on the upper side of the silicon substrate
is removed, with the portion of the thermally oxidized layer
exposed on the lower side being patterned by masking;
[0051] FIG. 5(d) represents how the glass substrate and silicon
substrate are bonded together into a single unit substrate; and
[0052] FIG. 5(e) represents the finished capacitive vacuum sensor
after having been processed through the steps FIG. 5(a) through
FIG. 5(d).
DETAILED DESCRIPTION OF THE INVENTION
[0053] Referring now to FIG. 1, a preferred embodiment of the
present invention is described.
[0054] FIG. 1 shows the anticorrosive vacuum sensor according to
the present invention, which may be manufactured by the
micromachining technique and which includes a glass substrate 2 and
a silicon substrate 3 that are bonded together into a single unit
substrate having the dimensions of several mm to several 10 mm
square and 1 mm thick.
[0055] The glass substrate 2 is a non-conducting substrate having
rigid fixed electrodes 8 and electrode pads 9 on the lower and
upper sides thereof, respectively. The rigid fixed electrodes 8 and
the corresponding electrode pads 9 are interconnected by way of
electrically conducting leads 1 extending through the glass
substrate 2 and across the same. The silicon substrate 3 is a
monocrystalline substrate having a recess formed on each of the
upper and lower sides thereof. There is a reference pressure space
4 that is formed between the glass substrate 2 and silicon
substrate 3 when they are anodically bonded together under the
vacuum atmosphere. The reference pressure space 4 is delimited by
the two substrates 2 and 3, and is kept at high vacuum.
[0056] It may be seen from FIG. 1 that the glass substrate 2 has a
recess that communicates with the reference pressure space 4 and
within which a getter 5 is provided. This getter 5 acts so that it
can absorb any part of the gas that remains in the reference
pressure space 4 and kept reference pressure space 4 at the high
vacuum.
[0057] The silicon substrate 3 further includes a silicon carbide
layer 11 on the side thereof facing the glass substrate 2 that is
deposited to a thickness of 2 .mu.m to 8 .mu.m by the chemical
vapor deposition (CVD) method. The silicon substrate 3 has a deep
recess partially formed on the side thereof opposite the side on
which the silicon carbide layer 11 is located, from which the
silicon carbide layer 11 is exposed. This exposed portion of the
silicon carbide layer 11 acts as the elastic diaphragm electrode
6.
[0058] It may be seen from FIG. 1 that an electrically conductive
thin film 12 such as metal may be deposited on the side of the
silicon carbide layer 11 facing the rigid fixed electrodes 8. Part
of the electrically conductive thin film 12 makes contact with the
electrically conducting leads 1 extending through the glass
substrate 2. Thereby, electrically conductive thin film 12 and the
electrode pads 9 on the upper side of the glass substrate 2 are
interconnected by way of electrically conductive leads 1.
[0059] In some cases, the silicon carbide layer 11 may become less
conductive, depending upon the particular condition under which the
silicon carbide layer 11 is to be deposited and grown on the side
of the silicon substrate 3 facing the glass substrate 2 by using
the chemical vapor deposition (CVD) method. In such cases, the
silicon carbide layer 11 alone is not sufficient to work as the
electrode, but when the silicon carbide layer 11 is coupled with
the electrically conductive thin film 12, any deflection of the
silicon carbide layer 11 can be sensed by the electrically
conductive thin film 12.
[0060] In the embodiment in which the electrically conductive thin
film 12 is deposited on the side of the silicon carbide layer 11
facing the rigid fixed electrodes 8, as described above, the
diaphragm electrode 6 may include the silicon carbide layer 11 and
the electrically conductive thin film 12 deposited thereon.
[0061] In operation, when any change in the pressure occurs outside
the vacuum sensor, it causes the pressure within the region located
below the diaphragm electrode 6 (FIG. 1) and leading to the vacuum
equipment to change accordingly. The change in the pressure within
the region causes the diaphragm electrode 6 to be deflected
accordingly. In response, the capacitance that develops between the
diaphragm electrode 6, or electrically conductive thin film 12, and
the rigid fixed electrodes 8 will change according to the
deflection of the diaphragm electrode 6. The change in the
capacitance is provided in the form of an electrical signal which
appears at the electrode pads 9 that may be coupled with any
suitable signal processing circuit (not shown), where the
electrical signal may be processed to determine the current
pressure applied from the external source.
[0062] In the anticorrosive vacuum sensor according to the current
embodiment, the part of the diaphragm electrode 6 that is exposed
to the reactive gas, more specifically, the silicon carbide layer
11 located beneath the diaphragm electrode 6 that has the chemical
stability as well as the strong resistance to the corrosive action
of the reactive gas. For example, when the anticorrosive vacuum
sensor of the current embodiment is used on the dry etching
equipment, in which silicon is usually processed in the fluorine
reactive gas atmosphere, it can operate and measure the pressures
for an extended period of time with stability and without being
affected by the corrosive action of the reactive gas.
[0063] FIG. 4(a) through FIG. 4(f) depict the process of
manufacturing the anticorrosive vacuum sensor according to the
present invention that has been described so far by referring to
FIG. 1. The anticorrosive vacuum sensor shown in FIG. 1 may be
manufactured by the micromachining technique method, which includes
the following steps that are described below.
[0064] In step FIG. 4(a), a thermally oxidized layer 10 is formed
on the silicon substrate 3 having a recess on the upper side
thereof, and the portion of the thermally oxidized layer 10 located
on the upper side of silicon substrate 3 is then patterned by
masking.
[0065] In step FIG. 4(b), a silicon carbide layer 11 is deposited
on the upper side of the silicon substrate 3 by the chemical vapor
deposition (CVD) method so that it can have a thickness of 2 .mu.m
to 8 .mu.m. When the silicon carbide layer 11 is deposited, the
conditions such as the flow rate of a gas, the ambient temperature,
and the stoichiometric ratio are controlled, so that the formed
silicon carbide layer 11 has a slight tensile stress.
[0066] In step FIG. 4(c), the portion of the thermally oxidized
layer 10 on the upper side of the silicon substrate 3 is removed,
and the portion of the thermally oxidized layer 10 located beneath
the silicon substrate 3 is then patterned by masking.
[0067] In step FIG. 4(d), an electrically conductive thin film 12
such as metal is deposited on part of the upper side of the silicon
carbide layer 11.
[0068] In step FIG. 4(e), the glass substrate 2 and the silicon
substrate 3 being processed through the step of FIG. 4(a) to FIG.
4(d) are anodically bonded together into a single unit substrate
under the vacuum atmosphere, with a getter 5 being inserted between
the two substrates 2 and 3. The single unit substrate thus obtained
includes a reference pressure space 4 delimited by the two
substrates 2 and 3 and that is kept under the vacuum condition. The
glass substrate 2 has a rigid fixed electrodes 8 and electrode pads
9 on the lower and upper sides thereof, respectively. The rigid
fixed electrodes 8 and the corresponding electrode pads 9 are
interconnected by way of electrically conducting leads 1 extending
through the glass substrate 2.
[0069] In step FIG. 4(f), the single unit substrate thus obtained
is then immersed in any suitable etching liquid such as potassium
hydroxide (KOH) solution. The glass substrate 2 and the portion of
the thermally oxidized layer 10 on the upper side of the silicon
substrate 3 remain not to be etched, with only the exposed silicon
on the silicon substrate 3 being etched in the direction of the
depth. This etching progresses until it reaches the rear side of
the silicon substrate 3 (that is, the bottom side of the silicon
substrate 3 in FIG. 4(e)) where the silicon carbide layer 11 will
be exposed. As the potassium hydroxide solution has no etching
effect on the silicon carbide layer 11, the etching stops where and
when the silicon carbide layer 11 has been exposed. The final
result is the anticorrosive vacuum sensor of the present invention
that includes the diaphragm electrode 6 having the 2 .mu.m to 8
.mu.m-thick silicon carbide layer 11 and the electrically
conductive thin film 12 deposited thereon.
[0070] As described in the step FIG. 4(b) above, the silicon
carbide layer 11 is stressed to provide the slight tensile stress
when it is deposited so that it can be maintained in its flat
condition even when the diaphragm electrode 6 is finally formed
like a thin film diaphragm as shown in FIG. 4(f). This permits the
accurate pressure measurement.
[0071] More specifically, for example, if the silicon carbide layer
11 is stressed to provide the compressive stress when it is
deposited, it might become so flexible that it cannot be maintained
to be flat when the diaphragm electrode 6 is finally formed like
the thin film diaphragm as shown in FIG. 4(f). If this occurs, the
diaphragm electrode 6 might deflect easily even in the absence of
the applied gas pressure. This would prevent the accurate pressure
measurement.
[0072] To avoid that such situation occurs, the diaphragm electrode
6 according to present invention is formed such that its silicon
carbide layer 11 is stressed to provide the slight tensile stress
when it is deposited.
[0073] FIG. 2 represents another embodiment of the anticorrosive
vacuum sensor according to the present invention, wherein a silicon
carbide layer 13 is deposited on the silicon substrate 3, but
includes no such electrically conductive thin film 12 as the one in
the preceding embodiment. In the embodiment shown in FIG. 2, the
anticorrosive vacuum sensor is able to respond to any deflection of
the silicon carbide layer 13 even if there is no electrically
conductive thin film 12 on the silicon carbide layer 13.
[0074] In this variation, when the silicon carbide layer is
deposited as described in the step FIG. 4(b), any suitable
impurities such as boron (B) or phosphorus (P) may be doped into
the silicon carbide layer 13 as it is usually done when
semiconductor chips or devices are fabricated. The silicon carbide
layer 13 containing those doped impurities can provide the high
conductivity by itself. In other words, a diaphragm electrode 14
may be provided by the silicon carbide layer 13 that contains the
impurities, such as boron or phosphorus, that enhance the
conductivity of the silicon carbide layer 13.
[0075] In accordance with the diaphragm electrode shown in FIG. 2
and obtained as above, whether the electrically conductive thin
film 12 is present on the silicon carbide layer 13 or not, or
regardless of the particular type of material from which the
silicon carbide layer may be made, or regardless of the particular
conditions of the chemical vapor deposition (CVD) method under
which the silicon carbide layer may be deposited and allowed to
grow on the side of the silicon substrate 3 facing the glass
substrate 2, it is possible for the vacuum sensor to respond to any
deflection of the diaphragm electrode 14 since it or the silicon
carbide layer can have the good conductivity by itself.
[0076] In the embodiment and variation thereof as described above,
the silicon carbide layer is composed of the chemically stabilized
materials, and is deposited by using the chemical vapor deposition
(CVD) method. Any other materials can be used as the chemically
stabilized materials and any other method can be used for forming a
thin film. For example, alumina, diamond, aluminum nitride, boron
nitride and the like can be used as the chemically stabilized
materials, and a thin film that forms the elastic diaphragm
electrode may be obtained by depositing any of those materials by
the injection, sputtering or vapor deposition method.
[0077] For example, when a thin film of aluminum nitride is
deposited for forming the diaphragm electrode 14, the reactive
sputtering method may be used. The reactive sputtering method
consists of depositing the thin film by causing the gas introduced
into the vacuum equipment to react with a particular target
material. In this example, the target material may be aluminum, and
nitrogen gas may be fed into the chamber, where the nitrogen gas is
allowed to react with the target, i.e., aluminum. Then, the thin
film may be deposited by sputtering.
[0078] Those target materials and gases are utilized in the usual
semiconductor manufacturing process. When a thin film is deposited
on the substrate by using those target materials and gases, the
deposition can occur while the substrate is maintained at the
temperature of below 500.degree. C., which is less than the
temperature at which the silicon carbide layer described above is
deposited by the chemical vapor deposition (CVD) method. Thus, the
process may be simplified, by which an anticorrosive thin film may
be deposited.
[0079] Although the present invention has been described with
reference to the particular embodiment and variation thereof, it
should be understood that various changes and modifications may be
made without departing from the spirit and scope of the invention
as defined in the appended claims.
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