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.

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 μm to 8 μm. 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 μm to 8 μm.  
           [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]    [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 μm to 8 μm. 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 μm to 8 μm 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]    [0037]FIG. 1 represents one preferred embodiment of the present invention;  
         [0038]    [0038]FIG. 2 represents another preferred embodiment of the present invention;  
         [0039]    [0039]FIG. 3 represents one typical example of the prior art capacitive vacuum sensor;  
         [0040]    [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]    [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]    [0042]FIG. 4( b ) represents how a silicon carbide layer is formed on the upper side of the silicon substrate;  
         [0043]    [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]    [0044]FIG. 4( d ) represents how an electrically conductive thin film is formed on the silicon carbide layer;  
         [0045]    [0045]FIG. 4( e ) represents how the glass substrate and silicon substrate are bonded together into a single unit substrate; and  
         [0046]    [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]    [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]    [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]    [0049]FIG. 5( b ) represents how a boron diffused layer is deposited on the upper side of the silicon substrate;  
         [0050]    [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]    [0051]FIG. 5( d ) represents how the glass substrate and silicon substrate are bonded together into a single unit substrate; and  
         [0052]    [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]    [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 μm to 8 μm 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]    [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 μm to 8 μm. 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 μm to 8 μm-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]    [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° 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.