Device member including cavity and method of producing the device member including cavity

A device member including a cavity, includes a base member, an interlayer, an upper layer, an opening portion, and a gas-permeable sealing layer. The base member includes a first semiconductor. The interlayer is formed on the base member and is non-conductive. The upper layer is formed on the interlayer and includes a second semiconductor. The opening portion is formed at the upper layer. The gas-permeable sealing layer is formed to seal the opening portion formed at the upper layer. The cavity is formed by removing the interlayer with an etching gas that penetrates through the sealing layer.

TECHNICAL FIELD

The invention belongs to the technical field of MEMS (Micro Electro Mechanical Systems) and relates to a device member comprising cavity and a method of producing the device member comprising cavity.

The device member, in which such a cavity is provided, can be used, for instance, as a micro passage device that is used for the pressure sensor of the capacitance type, the inkjet printer head, the medical treatment, and biotechnology etc.

BACKGROUND ART

The pressure sensor of such a capacitance type is used for various usages, for example, such as refrigerant pressure sensor for freezing, refrigeration, and air-conditioning equipment; hydraulic pressure sensors for water supplies and industrial pumps; vapor pressure sensor for steam boiler; air pressure/oil pressure sensor for air pressure/oil pressure industrial apparatus and pressure sensor for cars.

By the way, conventionally, as a device member, in which this kind of cavity is provided, for instance, as for the pressure sensor of the capacitance type, the producing method disclosed in Patent Document 1 (JP 2004-260187, A) is proposed.

FIG. 9-FIG. 13is a schematic view showing the process of the method of producing the device member, in which such a conventional cavity is provided.

For instance, as shown inFIG. 9(A), a device material101including the SOI (Silicon On Insulator) wafer, comprising a substrate member102including Si, an interlayer104including SiO2formed on this substrate member102, and an upper layer106including Si formed on the interlayer104, is prepared.

Next, as shown inFIG. 9(B), for instance, a photoresist layer108of the positive type is formed on the upper layer106.

Moreover, as shown inFIG. 9(C), through a photomask110having the predetermined pattern, the photoresist layer108is exposed, for instance, by using ultraviolet (UV) from the upper surface of this photoresist layer108.

Thereafter, for instance, it is developed by the developer such as TMAH (Tetra Methyl Ammonium Hydroxide).

As a result, as shown inFIG. 10(A), the photoresist of the exposed portion is removed, so that the photoresist layer108is remained in the form of the predetermined pattern.

Under such a condition, as shown inFIG. 10(B), the photoresist layer108is used as a mask and the upper layer106is processed by using the method of Deep Reactive RIE (Deep Reactive Ion Etching).

That is to say, for instance, “the process in which the etching by SF6 and the passivation by C4F8is alternately are performed”, that is called “Process of Bosch” is performed.

As a result, an opening portion112, which is the same pattern as the photoresist layer108remained in the form of the predetermined pattern, is formed to the upper layer106.

Moreover, as shown inFIG. 11(A), for instance, the interlayer104is etched by using the HF gas, so that a gap114having the predetermined pattern is formed to the interlayer104.

Moreover, as shown inFIG. 11(B), from the upper surface in the upper layer106, for instance, metal such as aluminum, semiconductor such as polysilicon, or plastic such as parylene is deposited, so that a sealing layer116is formed.

As a result, a part of sealing layer116is entered into the opening portion112formed to upper layer106and is sealed, so that a cavity118is formed.

Next, as shown inFIG. 11(C), for instance, photoresist layer120of the positive type is spin-coated on the upper surface of the sealing layer116.

Thereafter, as shown inFIG. 12(A), through a photomask122having the predetermined pattern, the photoresist layer120is exposed by, for instance, by using ultraviolet (UV) from the upper surface of this photoresist layer120.

Thereafter, for instance, it is developed by the developer such as TMAH (Tetra Methyl Ammonium Hydroxide).

As a result, as shown inFIG. 12(B), the photoresist of the exposed portion is removed, so that the photoresist layer120is remained in the form of the predetermined pattern.

Next, for instance, where the sealing layer116is aluminum, the aluminum etching fluid is used, or where the sealing layer116is a plastic, the O2ashing by using the O2plasma is used.

As a result, as shown inFIG. 12(C), an unnecessary portion is removed from the sealing layer116.

Consequently, as shown inFIG. 13, a device member100, in which the sealing layer116is formed in the form of the predetermined pattern, is obtained.

Though not shown in the drawing, in the device member100, predetermined circuit, strain gauge (Strain gauge), and counter electrode, etc. are formed to the upper layer106according to the usage.

FIG. 15is a schematic drawing that shows the schematic when the device member100manufactured from a conventional producing method is used as a pressure sensor of the capacitance type.

As shown inFIG. 15, in a pressure sensor200, the upper layer106, which is sealed by the above-mentioned sealing layer116, is used as a diaphragm202.

Moreover, the diaphragm202is used as a counter electrode204.

In addition, the substrate member102consisting of Si is used as a counter electrode206.

Moreover, as shown inFIG. 15(A), andFIG. 15(B), when the pressure of the cavity118is P1and the pressure exerted to the diaphragm202from the outside is P2, it is a pressure sensor to detect this pressure difference.

Moreover, the cavity118is sealed to enter the state of the vacuum in the cavity118.

As a result, a pressure sensor of the absolute pressure type is composed as a pressure standard room where pressure P1in the cavity118becomes a vacuum.

By the way, capacity C of the general capacitor composed of two electrodes, which are separated mutually through the dielectric substance (insulator), is shown by a formula listed below.

In this formula, ∈ is a dielectric constant of the dielectric substance (insulator) of interelectrode, and S is an area of the electrode, and d is a distance of interelectrode.

As it is clear from this formula, capacity C is proportional to dielectric constant ∈ of the dielectric substance (insulator) of interelectrode and to area S of the electrode respectively, and is in inverse proportion to distance d of interelectrode.

Similarly, the pressure sensor200of the capacitance type shown inFIG. 15(A) andFIG. 15(B) comprises the counter electrode204and counter electrode206, which is two electrodes separated mutually through the interlayer104that is dielectric substance (insulator).

In this case, the counter electrode204that composes one of the electrodes is used as the diaphragm202, which is displaced by the change in the pressure that is exerted to the counter electrode204.

As a result, the distance d of the interelectrode between the counter electrode204that functions as the diaphragm.202and the counter electrode206that composes the other electrode is changed.

Therefore, as it is clear from the above formula, in the pressure sensor200of the capacitance type, the pressure, which is exerted to the counter electrode204that functions as the diaphragm202, is changed.

As a result, the distance d of the interelectrode between the counter electrode204and the counter electrode206is changed. Accordingly, it can be considered as a variable capacity capacitor, in which capacity C is changed in inverse proportion to the distance d of interelectrode.

Moreover, as shown inFIG. 15(A) andFIG. 15(B), a part of a wire208is connected to the counter electrode204and apart of a wire210is connected to the counter electrode206.

In addition, each other end of these wires208,210are connected to the measuring control device not shown in the drawing.

As a result, through these wire208and wire206, the voltage can be applied to the counter electrode204and the counter electrode206by the measuring control device.

As a result, as it is clear from the above formula, displacement of the counter electrode204by change in pressure which is exerted to the counter electrode204that functions as the diaphragm202can be perceived as a change in capacity C in inverse proportion to the distance d of interelectrode.

That is, change in the distance d of the interelectrode between the counter electrode204and the counter electrode206by displacement of the counter electrode204, can be perceived as a change in capacity C in inverse proportion to the distance d of interelectrode.

Therefore, if the relation between this change in capacity C and the change of the pressure which is exerted to the counter electrode204that functions as the diaphragm202is previously recognized, the pressure, which is exerted to the counter electrode204at that time by measuring capacity C, can be perceived.

As a result, it can be used as a pressure sensor.

The pressure sensor by such a principle is generally called “Pressure sensor of the capacitance type”.

Moreover, though not shown in the drawing, as a pressure sensor, besides the pressure sensor of the capacitance type, the pressure sensor of the piezoresistance type is existed.

In this pressure sensor of the piezoresistance type, strain gauge (Strain gauge) is formed on the surface of the diaphragm and the diaphragm is transformed by pressure from the outside, so that the change in electric resistance according to the generated piezoresistance effect is converted into pressure.

PRIOR ART REFERENCE

Patent Document

SUMMARY OF INVENTION

Problems to be Solved by the Invention

However, in the producing method of the device member comprising the cavity described in conventional Patent Document 1, as shown inFIG. 13, the enclosing material invades in the gap114(see reference numeral124), and the gap114might be buried.

As a result, there is a case that the cavity118which has the predetermined shape to be aimed cannot be formed.

In this specification, “gap114” means the space formed by removing a part of the interlayer before it is sealed by the enclosing material.

In addition, “cavity118” means the space formed after it is sealed by the sealing layer116.

In this case, for instance, when using it as a device member of the pressure sensor of the capacitance type, it is difficult to form the diaphragm structure to have the cavity118having the predetermined shape internally.

The predetermined capacitance change according to the change of pressure cannot be measured.

As a result, the pressure sensor of high accuracy cannot be provided.

Moreover, the enclosing material should be prevented from invading in the gap114as much as possible to avoid such a state. Therefore, in the conventional producing method of the device member comprising the cavity118, the sealing layer116should have been formed by rigid conditions.

Moreover, the production cost cannot help rising since the complicate step is necessary.

In view of considering such a current state, the object of the invention is to provide the device member that has an expected function and the method of producing thereof, in which, such as the conventional method of producing the device member comprising a cavity, an unnecessary enclosing material is not invaded in the gap, and the gap might not be buried, and the cavity which has the predetermined shape to be aimed can be formed by an easy step.

Moreover, the invention is to provide the pressure sensor of high accuracy, in which, in case using it as a device member of the pressure sensor of the capacitance type, the diaphragm structure to have the cavity of the predetermined shape internally can be obtained, and the predetermined capacitance change according to the change of pressure can be measured.

Solution to Problem

The invention was invented to solve the problems and to achieve the object in the above-mentioned prior art,

the device member of the invention is a device member comprising a cavity comprising:

a base member including the semiconductor,

an interlayer, which is formed on the base member and has the nonconductivity,

an upper layer, which is formed on the interlayer and includes the semiconductor,

an opening portion formed to the upper layer,

a gas-permeable sealing layer, which is formed to seal the opening portion formed to the upper layer,

wherein the cavity is a cavity which is formed by removing the interlayer with an etching gas that is penetrated through the sealing layer.

Moreover, the method of producing the device member of the invention is a method of producing the device member comprising a cavity comprising:

a step of preparing a device material, the device material comprising,

a base member including the semiconductor,

an interlayer which is formed on the base member and has the nonconductivity, and

an upper layer which is formed on the interlayer and includes the semiconductor;

a step of forming an opening portion to the upper layer;

a step of sealing the opening portion which is formed to the upper layer with a gas-permeable sealing layer; and

a step of forming the cavity by removing the interlayer with penetrating an etching gas through the gas-permeable sealing layer.

By composing like this, the opening portion formed to the upper layer is sealed with the gas-permeable sealing layer, so that the etching gas is penetrated through this sealing layer.

As a result, the cavity is formed by removing the interlayer.

In addition, for instance, where the interlayer includes SiO2, if reaction formula with the etching gas is shown as the expression listed below.
SiO2+4HF (gas)→SiF4(gas)+H2O (gas)

Therefore, if consider the case where the pressure sensor of the absolute pressure type is produced by the SOI (Silicon On Insulator) wafer, this sealing layer is desirable that gassy SiF4and H2O is penetrated thereinto, besides condition that HF gas that is etching gas should be penetrated absolutely in this sealing layer.

That is, it is desirable that this sealing layer has the gas permeability, in which the gas generated by etching the interlayer having nonconductivity with the etching gas can be also penetrated.

Therefore, such as the conventional method of producing the device member comprising the cavity, the enclosing material is not invaded in the gap, and the gap might not be buried.

As a result, the cavity which has the predetermined shape to be aimed can be formed by an easy step and the device member that has an expected function can be provided.

Moreover, when the opening portion, which is formed to the upper layer, is sealed with the gas-permeable sealing layer, for instance, the enclosing material is spin-coated by using the liquid photoresist as for the enclosing material.

As a result, the enclosing material is entered into the opening portion by the capillary action of the liquid and all part of the opening portion is sealed.

Therefore, the sealing layer need not be formed by rigid conditions conventionally.

Moreover, the complicate step is unnecessary, and the manufacturing cost can be reduced.

Furthermore, the device member of an excellent extremely stable quality can be provided.

Moreover, the device member of the invention is characterized in that a gas-impermeable overcoating layer is provided on the sealing layer.

Moreover, the method of producing the device member of the invention is characterized in that a step of forming the gas-impermeable overcoating layer is included.

By composing like this, since the gas-impermeable overcoating layer is provided on the sealing layer, the gas would not be invaded in the cavity of the device member from the outside, so that it is never polluted in the cavity.

Moreover, the ingress or egress of the gas in the cavity is not also occurred, so that the internal pressure in the cavity is not changed.

Therefore, the device member that has an expected function can be provided.

Moreover, the device member of the invention is characterized in that the cavity is in the state of the vacuum.

Moreover, the method of producing the device member of the invention is characterized in that,

a step of forming the gas-impermeable overcoating layer is performed under the vacuum condition, so that the cavity is to be a state of the vacuum.

In this case, “vacuum” is meant that, comprising absolute vacuum state, absolutely near the vacuum state, or decompressed state compared with the atmospheric pressure to the extent that it can be used as a pressure sensor.

By composing like this, in the conventional method of producing the device member, the vacuum chamber is formed by using LPCVD (Low Pressure Chemical Vapor Deposition) or by burning the hydrogen that remains in the cavity.

Therefore, for instance, the device material including the SOI (Silicon On Insulator) wafer etc. had to be made at a high temperature.

Therefore, the material without the resistance to the high temperature cannot be used.

The material is limited, and there is a problem of the lack of generality and versatility etc.

On the contrary, according to the invention, in order to make the cavity to the vacuum, for instance, a very easy process of vacuum evaporation etc. of the metal is used, so that the gas-impermeable overcoating layer can be formed on the sealing layer.

In addition, the device member comprising the pressure standard room, in which an impure gas etc. is not remained in the cavity, and which is sealed in the state of the vacuum, can be provided.

Therefore, for instance, the pressure sensor etc. of the absolute pressure type of the capacitance type can be easily manufactured at low cost.

Moreover, the pressure sensor etc. which has the stable quality compared with conventional can be manufactured.

Moreover, the device member of the invention is characterized in that the base member is Si, the interlayer is SiO2, and the upper layer is Si.

Moreover, the method of producing the device member of the invention is characterized in that the device member is SOI (Silicon On Insulator) wafer, in which the base member is Si, the interlayer is SiO2, and the upper layer is Si.

Thus, in the invention, the SOI (Silicon On Insulator) wafer, in which the base member is Si, the interlayer is SiO2, and the upper layer is Si, is as the device material.

In such a SOI (Silicon On Insulator) wafer, in the wafer manufacturing process, the thickness of the interlayer of SiO2(that is, the gap between the base member and the upper layer) can be easily constant.

Therefore, SiO2that is the interlayer is removed by using such a SOI (Silicon On Insulator) wafer as the device material.

As a result, in the cavity forming, the difference of the gap between the base member and the upper layer is small and the cavity of a uniform gap can be formed.

In addition, concerning the SOI (Silicon On Insulator) wafer, a large amount of the SOI wafer of the uniform quality can be obtained and has generality and versatility.

As a result, the producing method is easily, so that the manufacturing cost can be reduced.

Moreover, because the upper layer is Si, in the step of forming the opening portion to the upper layer, for instance, the pattern that includes the portion exposed and the portion not exposed is formed by the photolithography.

In addition, after developing, the etching processing is performed by using the method of Deep RIE (Deep Reactive Ion Etching).

Consequently, the opening portion can be formed to the upper layer.

Therefore, because the photolithography is used, the patterning is easy.

As a result, by using this pattern, the predetermined pattern can be formed to the upper layer with a large amount of excellent reproducibilities.

Moreover, because the interlayer is SiO2, the opening portion formed to the upper layer is sealed in a gas-permeable sealing layer and for instance, the etching gas that includes the HF gas is penetrated through this gas-permeable sealing layer.

As a result, the cavity can be easily formed by removing the interlayer.

Therefore, the complicate step is unnecessary, and the manufacturing cost can be reduced.

Furthermore, the device member of an excellent extremely stable quality can be provided.

Moreover, the invention is a pressure sensor of the capacitance type wherein any one of the device member described above is used.

Moreover, the invention is a pressure sensor of the capacitance type wherein the device member obtained by any one of the method of producing the device member described above is used.

By composing like this, the pressure sensor of high accuracy can be provided, in which in case using it as a device member of the pressure sensor of the capacitance type, the diaphragm structure having the cavity of the predetermined shape internally can be obtained, and the predetermined capacitance change according to the change of pressure can be measured.

Advantageous Effects of Invention

According to the invention, the opening portion formed to the upper layer is sealed with the gas-permeable sealing layer, so that the etching gas is penetrated through this sealing layer.

As a result, the cavity is formed by removing the interlayer.

Therefore, such as the conventional method of producing the device member comprising the cavity, the enclosing material is not invaded in the gap, and the gap might not be buried.

As a result, the cavity which has the predetermined shape to be aimed can be formed by an easy step and the device member that has an expected function can be provided.

Moreover, when the opening portion, which is formed to the upper layer, is sealed with the gas-permeable sealing layer, for instance, the enclosing material is spin-coated by using the liquid photoresist as for the enclosing material.

As a result, the enclosing material is entered into the opening portion by the capillary action of the liquid and the opening portion is sealed, so that the entire opening portion is sealed with the enclosing material of the gas permeability.

Therefore, the sealing layer need not be formed by rigid conditions conventionally.

Moreover, the complicate step is unnecessary, and the manufacturing cost can be reduced.

Furthermore, the device member of an excellent extremely stable quality can be provided.

DESCRIPTION OF EMBODIMENTS

Hereafter, the embodiment of the invention (Embodiment) is described in the detail or more on the basis of the drawing.

FIG. 1is a partial enlarged sectional view of the device member comprising the cavity of the invention.

InFIG. 1, reference numeral10shows the device member comprising the cavity of the invention as a whole.

As shown inFIG. 1, the device member10of the invention comprises a base member12including the semiconductor.

In addition, an interlayer14is formed on the base member12which has the nonconductivity,

Moreover, on this interlayer14, an upper layer16which includes the semiconductor is formed.

In addition, in the upper layer16, an opening portion18, which is formed in the state of the predetermined pattern configuration, is provided.

Moreover, a gas-permeable sealing layer20, which is formed to seal the opening portion18formed to the upper layer16, is provided.

Moreover, as shown inFIG. 1, a cavity22is formed to the partial part of the interlayer14which is corresponding to this gas-permeable sealing layer20.

In this case, this cavity22is formed by the etching gas which is penetrated through the gas-permeable sealing layer20.

Moreover, as for the substrate member12, for instance, the semiconductor such as Si can be used.

It may be elected arbitrarily according to the usage of device member10, and it is not limited especially.

On the other hand, as for the interlayer14, it may be used that has nonconductivity and is etched with the etching gas which is penetrated through the gas-permeable sealing layer20.

It may be elected arbitrarily according to the kind of the etching gas used.

For instance, where the HF gas is selected as the etching gas, for instance, as for the interlayer14, the oxide etc. such as SiO2can be used.

In addition, as for the upper layer16, for instance, the semiconductor such as Si can be used as well as the substrate member12.

Moreover, it can be selected arbitrarily according to the usage of the device member10and it is not especially limited.

Moreover, as for the gas-permeable sealing layer20, according to the kind of the etching gas used, it can be selected arbitrarily from the one to penetrate this etching gas and it is not especially limited.

For instance, where the HF gas is selected as for the etching gas, such as the photoresist of the negative type “SU-8 (brand name)” made by Microchem company can be used as the gas-permeable sealing layer20.

In addition, for instance, where the interlayer14includes SiO2, if the cavity forming with the etching gas is shown by reaction formula, it is expressed like a formula listed below.
SiO2+4HF (gas)→SiF4(gas)+H2O (gas)

Therefore, if consider the case where the pressure sensor of the absolute pressure type is produced by the SOI (Silicon On Insulator) wafer, as for the sealing layer20, besides condition that HF gas which is etching gas should penetrate absolutely, it is desirable that gassy SiF4and H2O can be penetrated through the sealing layer20.

That is, it is desirable that the sealing layer20has gas-permeable, in which the gas generated when interlayer14is etched with the etching gas can be penetrated.

Like this, in the invention, “gas-permeable” of “gas-permeable sealing layer20” means that all gases, which are generated when the etching gas and the interlayer14are etched with the etching gas, can be penetrated.

For instance, where the SOI (Silicon On Insulator) wafer is used as for as the device material and the HF gas is used as the etching gas, as for the gas-permeable requested to the gas-permeable sealing layer20, for instance, it is desirable that the etching gas include the HF gas and the reactive gases by the etchings such as the SiF4gas and H2O gas can be penetrated.

About the method of producing the device member10of the invention composed like this, in accordance withFIG. 2-FIG. 5, explanation is described as follows.

First of all, as shown inFIG. 2(A), a device material1that includes the SOI (Silicon On Insulator) wafer is prepared. In this case, the device material1comprises, for instance, the substrate member12including Si, the interlayer14including SiO2formed on this substrate member12, and the upper layer16including Si formed on the interlayer14.

Next, as shown inFIG. 2(B), for instance, a photoresist layer24of the positive type is formed on the upper layer16.

Moreover, as shown inFIG. 2(C), from the upper surface of this resist layer24, through a photomask26having the predetermined pattern, for instance, the photoresist layer24is exposed by ultraviolet (UV).

Thereafter, for instance, it is developed with the developer such as TMAH (Tetra Methyl Ammonium Hydroxide).

As a result, as shown inFIG. 3(A), the photoresist of the portion exposed is removed, so that the photoresist layer24is remained in the form of the predetermined pattern.

Under such a condition, as shown inFIG. 3(B), the photoresist layer24is used as a mask and the upper layer16is processed by using the method of Deep Reactive RIE (Deep Reactive Ion Etching).

That is to say, for instance, “the process in which the etching by SF6and the passivation by C4F8is alternately are performed”, that is called “Process of Bosch” is performed.

As a result, an opening portion18, which is the same pattern as the photoresist layer24remained in the form of the predetermined pattern, is formed to the upper layer16.

Moreover, as shown inFIG. 4(A), for instance, enclosing material, which includes the photoresist of the negative type “SU-8 (brand name)” made by Microchem company, is spin-coated on the upper layer16, so that a gas-permeable sealing layer20is formed.

In this case, “SU-8 (brand name)” is originally a liquid, so that “SU-8 (brand name)” is entered into the opening portion18by the capillary action of the liquid in the opening portion18formed to the upper layer16and all part of the opening portion18is sealed.

Moreover, thereafter, after baking at 95° C., it is developed by using, for instance, the developer such as PGMEA (Propylene Glycol Monomethyl Ether Acetate).

As a result, as shown inFIG. 4(C), “SU-8 (brand name)”, which is the enclosing material of the exposed portion, is remained.

Consequently, the gas-permeable sealing layer20is remained in the form of the predetermined pattern.

Under such a condition, as shown by the arrow ofFIG. 5, the etching gas is penetrated to the gas-permeable sealing layer20.

As a result, for instance, the HF gas is used and the interlayer14is etching-processed, so that a part of the interlayer14is removed, and a cavity22is formed in the form of the predetermined pattern.

As a result, as shown inFIG. 1, the device member10, in which the cavity22is formed, can be manufactured.

In this case, between the upper layer16including Si and the substrate members12including Si, the cavity22is formed.

Therefore, the upper layer16is used as a diaphragm, which is displaced by the change in pressure.

In addition, the upper layer16is used as a counter electrode that composes the other electrode.

Moreover, the substrate member12is used as a counter electrode that composes the other electrode.

As a result, it can be considered as the variable capacity capacitor.

FIG. 14is a schematic view that shows the schematic when the device member10manufactured by the producing method of the invention is used as a pressure sensor of the capacitance type.

As shown inFIG. 14, in a pressure sensor50, the upper layer16, which is sealed by the above-mentioned sealing layer20, is used as a diaphragm52.

Moreover, the diaphragm52is used as a counter electrode54.

In addition, the substrate member12that includes Si is also used as a counter electrode56.

Moreover, as shown inFIG. 14(A) andFIG. 14(B), where the pressure of cavity18is P1and the pressure, which is exerted on the diaphragm52from the outside, is P2, it is a pressure sensor in which this pressure difference is detected.

Moreover, in order to enter the state of the vacuum in the cavity18, the cavity18is sealed.

As a result, it is a pressure sensor of the absolute pressure type that it is composed as a pressure standard room where pressure P1in the cavity18became a vacuum.

By the way, capacity C of the general capacitor composed of two electrodes, which are separated mutually through the dielectric substance (insulator), is shown by a formula listed below.

In this formula, ∈ is a dielectric constant of the dielectric substance (insulator) of interelectrode, and S is an area of the electrode, and d is a distance of interelectrode.

As it is clear from this formula, capacity C is proportional to dielectric constant ∈ of the dielectric substance (insulator) of interelectrode and to area S of the electrode respectively, and is in inverse proportion to distance d of interelectrode.

Similarly, the pressure sensor50of the capacitance type shown inFIG. 14(A) andFIG. 14(B) comprises the counter electrode54and counter electrode56, which is two electrodes separated mutually through the interlayer14that is dielectric substance (insulator).

In this case, the counter electrode54that composes one of the electrodes is used as the diaphragm52, which is displaced by the change in the pressure that is exerted to the counter electrode54.

As a result, the distance d of the interelectrode between the counter electrode54that functions as the diaphragm52and the counter electrode56that composes the other electrode is changed.

Therefore, as it is clear from the above formula, in the pressure sensor50of the capacitance type, the pressure, which is exerted to the counter electrode54that functions as the diaphragm52, is changed.

As a result, the distance d of the interelectrode between the counter electrode54and the counter electrode56is changed. Accordingly, it can be considered as a variable capacity capacitor, in which capacity C is changed in inverse proportion to the distance d of interelectrode.

Moreover, as shown inFIG. 14(A) andFIG. 14(B), a part of a wire58is connected to the counter electrode54and a part of a wire60is connected to the counter electrode56.

In addition, each other end of these wires58,60are connected to the measuring control device not shown in the drawing.

As a result, through these wire58and wire60, the voltage can be applied to the counter electrode54and the counter electrode56by the measuring control device.

As a result, as it is clear from the above formula, displacement of the counter electrode54by change in pressure which is exerted to the counter electrode54that functions as the diaphragm52can be perceived as a change in capacity C in inverse proportion to the distance d of interelectrode.

That is, change in the distance d of the interelectrode between the counter electrode54and the counter electrode56by displacement of the counter electrode54, can be perceived as a change in capacity C in inverse proportion to the distance d of interelectrode.

Therefore, if the relation between this change in capacity C and the change of the pressure which is exerted to the counter electrode54that functions as the diaphragm52is previously recognized, the pressure, which is exerted to the counter electrode54at that time by measuring capacity C, can be perceived.

As a result, it can be used as a pressure sensor.

The pressure sensor by such a principle is generally called “Pressure sensor of the capacitance type”.

Moreover, though not shown in the drawing, as a pressure sensor, besides the pressure sensor of the capacitance type, the invention can be applied to the pressure sensor of the piezoresistance type.

In this pressure sensor of the piezoresistance type, strain gauge (Strain gauge) is formed on the surface of the diaphragm and the diaphragm is transformed by pressure from the outside, so that the change in electric resistance according to the generated piezoresistance effect is converted into pressure.

By composing like this, the opening portion18formed to the upper layer16is sealed with the gas-permeable sealing layer20, so that the etching gas is penetrated through this sealing layer20. As a result, the cavity22is formed.

Therefore, such as the conventional method of producing the device member comprising the cavity, the enclosing material is not invaded in the gap, and the gap might not be buried.

As a result, the cavity22which has the predetermined shape to be aimed can be formed by an easy step and the device member10that has an expected function can be provided.

Moreover, when the opening portion18, which is formed to the upper layer16, is sealed with the gas-permeable sealing layer20, for instance, the enclosing material is spin-coated by using the liquid photoresist as for the enclosing material.

As a result, the enclosing material20is entered into the opening portion18by the capillary action of the liquid and all part of the opening portion18is sealed.

Therefore, the sealing layer need not be formed by rigid conditions conventionally.

Moreover, the complicate step is unnecessary, and the manufacturing cost can be reduced.

Furthermore, the device member10of an excellent extremely stable quality can be provided.

In addition, thus, the SOI (Silicon On Insulator) wafer, in which the base member12is Si, the interlayer14is SiO2, and the upper layer16is Si, is as the device material.

In such a SOI (Silicon On Insulator) wafer, in the wafer manufacturing process, the thickness of the interlayer14of SiO2(that is, the gap between the base member12and the upper layer16) can be easily constant.

Therefore, SiO2that is the interlayer14is removed by using such a SOI (Silicon On Insulator) wafer as the device material.

As a result, in the cavity22forming, the difference of the gap between the base member12and the upper layer16is small and the cavity22of a uniform gap can be formed.

In addition, concerning the SOI (Silicon On Insulator) wafer, a large amount of the SOI wafer of the uniform quality can be obtained and has generality and versatility

As a result, the producing method is easily, so that the manufacturing cost can be reduced.

Moreover, because the upper layer16is Si, in the step of forming the opening portion18to the upper layer16, for instance, the pattern that includes the portion exposed and the portion not exposed is formed by the photolithography.

In addition, after developing, the etching processing is performed by using the method of Deep RIE (Deep Reactive Ion Etching).

Consequently, the opening portion18can be formed to the upper layer16.

Therefore, because the photolithography is used, the patterning is easy.

As a result, by using this pattern, the predetermined pattern can be formed to the upper layer16with a large amount of excellent reproducibilities.

Moreover, because the interlayer14is SiO2, the opening portion18formed to the upper layer16is sealed in a gas-permeable sealing layer20.

In addition, the etching gas is penetrated through this gas-permeable sealing layer20, so that, for instance, the interlayer14is etched by using the HF gas.

As a result, the cavity22can be easily formed by removing the interlayer14.

Therefore, the complicate step is unnecessary, and the manufacturing cost can be reduced.

Furthermore, the device member10of an excellent extremely stable quality can be provided.

FIG. 6is a partial enlarged sectional view of another Embodiment of the device member comprising the cavity of the invention.

The device member10of this Embodiment is basically similar composition of the device member10shown inFIG. 1.

Like reference numeral is refer to the same composition member, and the detailed explanation is omitted.

In the device member10of this Embodiment, as shown inFIG. 6, a gas-impermeable overcoating layer30is provided on the gas-permeable sealing layer20.

In this case, as for the gas-impermeable overcoating layer30, it may be selected arbitrarily according to the usage of the device member10and it is not especially limited.

However, for instance, by the deposition etc., metal such as aluminum, semiconductor such as polysilicon, or plastic such as parylene can be used to form the overcoating layer30.

In this case, “gas impermeability” of “gas-impermeable overcoating layer30” means that the gas is not penetrated through the overcoating layer30and gas-permeable sealing layer20, and the gas is not invaded into the cavity22from the outside.

As a result, the cavity22is not polluted and the ingress or egress of the gas in cavity22is not occurred, so that internal pressure in the cavity22is not changed.

Moreover, about the film thickness of the overcoating layer30, it may be selected arbitrarily according to the usage of the device member10and it is not especially limited.

However, it is desirable to prevent the gas from invading in the cavity22that it is within the range of, for instance, 100 nm-5 μm, preferably 100 nm-200 nm when overcoating layer30is aluminum, and 2 μm-5 μm when the overcoating layer30is parylene.

According to the device member10composed like this, since the gas-impermeable overcoating layer30is provided on the sealing layer20, the gas would not be invaded in the cavity22of the device member10from the outside, so that it is never polluted in the cavity22.

Moreover, the ingress or egress of the gas in the cavity is not also occurred, so that the internal pressure in the cavity is not changed.

Therefore, the device member10that has an expected function can be provided.

In this case, it is desirable that the cavity22is in the state of the vacuum.

That is, it is desirable that a step of forming the gas-impermeable overcoating layer30is performed under the vacuum condition, so that the cavity22is to be a state of the vacuum.

In this case, “vacuum” is meant that, comprising absolute vacuum state, absolutely near the vacuum state, or decompressed state compared with the atmospheric pressure to the extent that it can be used as a pressure sensor.

By composing like this, in the conventional method of producing the device member, the vacuum chamber is formed by using LPCVD (Low Pressure Chemical Vapor Deposition) or by burning the hydrogen that remains in the cavity.

Therefore, for instance, the device material including the SOI (Silicon On Insulator) wafer etc. had to be made a high temperature.

Therefore, the material without the resistance to the high temperature cannot be used.

The material is limited, and there is a problem of the lack of generality and versatility etc.

On the contrary, according to the invention, in order to make the cavity22to the vacuum, for instance, a very easy process of vacuum evaporation etc. of the metal is used, so that the gas-impermeable overcoating layer30can be formed on the sealing layer20.

In addition, the device member10comprising the pressure standard room, in which an impure gas etc. is not remained in the cavity22, and which is sealed in the state of the vacuum, can be provided.

Therefore, for instance, the pressure sensor etc. of the absolute pressure type of the capacitance type can be easily manufactured at low cost.

Moreover, the pressure sensor etc. which has the stable quality compared with conventional can be manufactured.

About the method of producing the device member10of the invention composed like this, in accordance withFIG. 7-FIG. 8, explanation is described as follows.

First of all, the step ofFIG. 2-FIG. 5is the same as the method of producing the device member10of the above-mentioned Embodiment 1.

As shown inFIG. 5, the etching gas is penetrated to the gas-permeable sealing layer20, so that a part of the interlayer14is removed, and the cavity22is formed in the form of the predetermined pattern.

Thereafter, as shown inFIG. 7(A), on this gas-permeable sealing layer20, for instance, by the deposition etc., an overcoating layer30is formed by using metal such as aluminum, semiconductor such as polysilicon, or plastic such as parylene.

Next, as shown inFIG. 7(B), for instance, a photoresist layer32of the positive type is spin-coated on the overcoating layer30.

Moreover, as shown inFIG. 7(C), through a photomask34having the predetermined pattern, the photoresist layer32is exposed, for instance, by using ultraviolet (UV) from the upper surface of this photoresist layer32.

Thereafter, for instance, it is developed by the developer such as TMAH (Tetra Methyl Ammonium Hydroxide).

As a result, as shown inFIG. 8(A), the photoresist of the exposed portion is removed, so that the photoresist layer32is remained in the form of the predetermined pattern.

Under such a condition, as shown inFIG. 8(B), the photoresist layer32is used as a mask and the upper layer16is etched for instance, by using the aluminum etchant such as mixed acid.

As a result, the overcoating layer30is removed in the state of the predetermined pattern.

As a result, as shown inFIG. 8(C), the device member10, in which the gas-impermeable overcoating layer30is provided on the sealing layer20, can be manufactured.

As well as the above-mentioned Embodiment 1 and Embodiment 2, the device member10comprising the gas-impermeable overcoating layer30is manufactured.

That is, as shown inFIG. 2(A), a device material1that includes the SOI (Silicon On Insulator) wafer is prepared.

In this case, the device material1comprises the substrate member12including Si, the interlayer14including SiO2formed on this substrate member12, and the upper layer16including Si formed on the interlayer14.

This device material1is cleaned by using the ammonia hydrogen peroxide water.

Moreover, with the HF solution (diluted to 1/100), the device material1is cleaned for one minute.

Moreover, the primer is applied on the upper layer16of the device material1.

In addition, on the surface, as shown inFIG. 2(B), on the upper layer16, by using the photoresist “S1805G (brand name)” of the positive type made by SHIPLEY company is used, it is spin-coated under the condition of 4000 rpm/30 sec.

As a result, the photoresist layer24is formed.

Next, as shown inFIG. 2(C), from the upper surface of this resist layer24, through a photomask26having the predetermined pattern, for instance, the photoresist layer24is exposed by ultraviolet (UV) for 3 seconds.

Thereafter, it is developed for 1 minute with the developer such as TMAH (Tetra Methyl Ammonium Hydroxide) (developer “NMD-3 (brand name)” manufactured by TOKYO OHKA KOGYO CO., LTD).

As a result, as shown inFIG. 3(A), the photoresist of the portion exposed is removed, so that the photoresist layer24is remained in the form of the predetermined pattern.

Under such a condition, as shown inFIG. 3(B), the photoresist layer24is used as a mask and the upper layer16is processed by using the method of Deep Reactive RIE (Deep Reactive Ion Etching).

That is to say, “the process in which the etching by SF6 and the passivation by C4F8is alternately are performed”, that is called “Process of Bosch” is performed.

As a result, an opening portion18, which is the same pattern as the photoresist layer24remained in the form of the predetermined pattern, is formed to the upper layer16.

Next, as shown inFIG. 3(C), all photoresist layers24are removed by O2ashing that uses O2plasma for 2 minutes.

Moreover, as shown inFIG. 4(A), enclosing material, which includes the photoresist of the negative type “SU-8 (brand name)” made by Microchem company, is spin-coated on the upper layer16under the condition of 2000 rpm/sec, so that a gas-permeable sealing layer20is formed.

In this case, “SU-8 (brand name)” is originally a liquid, so that “SU-8 (brand name)” is entered into the opening portion18by the capillary action of the liquid in the opening portion18formed to the upper layer16and all part of the opening portion18is sealed.

Moreover, thereafter, after baking at 95° C. for 3 minutes, it is developed by using, for instance, the developer such as PGMEA (Propylene Glycol Monomethyl Ether Acetate) for 1 minute.

As a result, as shown inFIG. 4(C), “SU-8 (brand name)”, which is the enclosing material of the exposed and baked portion, is remained.

Consequently, the gas-permeable sealing layer20is remained in the form of the predetermined pattern.

Under such a condition, as shown by the arrow ofFIG. 5, the etching gas, i.e. HF gas is penetrated to the gas-permeable sealing layer20for 20 minutes.

As a result, a part of the interlayer14is removed, and a cavity22is formed in the form of the predetermined pattern.

Next, as shown inFIG. 7(A), on this gas-permeable sealing layer20, an overcoating layer30of the thickness of 200 nm is formed by using aluminum by vacuum evaporation.

Moreover, the primer is applied on the overcoating layer30.

In addition, on the surface, as shown inFIG. 7(B), on the overcoating layer30, by using the photoresist “S1818G (brand name)” of the positive type made by SHIPLEY company is used, it is spin-coated under the condition of 3000 rpm/30 sec.

As a result, the photoresist layer32is formed.

Next, as shown inFIG. 7(C), from the upper surface of this resist layer32, through a photomask34having the predetermined pattern, the photoresist layer32is exposed by ultraviolet (UV) for 3 seconds.

Thereafter, it is developed for 1 minute with the developer such as TMAH (Tetra Methyl Ammonium Hydroxide) (developer “NMD-3 (brand name)” manufactured by TOKYO OHKA KOGYO CO., LTD).

As a result, as shown inFIG. 8(A), the photoresist of the portion exposed is removed, so that the photoresist layer32is remained in the form of the predetermined pattern.

Under such a condition, as shown inFIG. 8(B), the photoresist layer32is used as a mask and the upper layer16is etched by using the aluminum etchant (mixed acid aluminum) for 3 minutes.

As a result, the overcoating layer30is removed in the form of the predetermined pattern.

As a result, as shown inFIG. 8(C), the device member10, in which the gas-impermeable overcoating layer30is provided on the sealing layer20, can be manufactured.

By using this device member10, it used as a pressure sensor of the absolute pressure type and experiment is performed.

There is a linear correlation between the pressure and the electrostatic capacity.

It is clear that there is the reliability as a pressure sensor.

Although a preferable of the invention is described above, the invention is not limited to this embodiment.

The device member10of the invention can be used, for instance, as a micro passage device that is used for the pressure sensor of the capacitance type, the inkjet printer head, the medical treatment, and biotechnology etc.

However, the device member10of the invention can be used as various device members.

Therefore, various changes are possible in the scope in which it does not deviate from the object of the invention.

INDUSTRIAL APPLICABILITY

The invention belongs to the technical field of MEMS (Micro Electro Mechanical Systems) and relates to a device member comprising cavity and a method of producing the device member comprising cavity.

The device member, in which such a cavity is provided, can be used, for instance, as a micro passage device that is used for the pressure sensor of the capacitance type, the inkjet printer head, the medical treatment, and biotechnology etc.

EXPLANATION OF LETTERS OR NUMERALS

DRAWING