WO2016066106A1

WO2016066106A1 - All-silicon mems methane sensor, fuel gas detection application, and manufacturing method

Info

Publication number: WO2016066106A1
Application number: PCT/CN2015/093096
Authority: WO
Inventors: 马洪宇; 丁恩杰; 刘晓文; 赵小虎; 赵端
Original assignee: 中国矿业大学
Priority date: 2014-10-31
Filing date: 2015-10-28
Publication date: 2016-05-06
Also published as: CN104316575A; CN104316575B

Abstract

An all-silicon microelectromechanical systems (MEMS) methane sensor, a fuel gas detection application, and a manufacturing method, applicable in mining environments, related to methane sensors, manufacturing methods for same, and detection methods therefor, and specifically related to a methane sensor employing a MEMS processing technique and a methane detection method for the sensor. The all-silicon MEMS sensor employs monocrystalline silicon to serve as a heating material of a heating component, the heating component also serves as a methane-sensitive component, and detection of low-concentration methane can be implemented without requiring a catalyst carrier and a catalyst material. The all-silicon MEMS methane sensor is processed by employing a MEMS process with an SOI wafer serving as a substrate. The processing process is compatible with a CMOS process. The all-silicon MEMS sensor has the characteristics of having a low power consumption and high sensitivity, being free from effects of oxygen deficiency, and being free from effects brought forth by a catalyst, such as carbon deposition and poisoning.

Description

All-silicon MEMS methane sensor and gas detection application and preparation method

Technical field

The invention relates to a methane sensor and a gas detecting application and a preparation method, and is particularly suitable for an all-silicon MEMS methane sensor and a gas detecting application and a preparation method used for gas prevention in industrial and mining production.

Background technique

At present, catalytic combustion methane sensors based on traditional platinum wire heating are still widely used in coal mines. The principle is based on the catalytic heat release effect of methane gas, which has many disadvantages due to the use of the catalyst. For example, the short calibration cycle, carbon deposition, poisoning, activation, etc. are fundamentally derived from the use of catalysts and catalyst supports. The existing catalytic combustion type methane sensor uses a coil wound with a noble metal such as platinum wire as a heating element, which is difficult to mass-produce, has poor consistency, and has a large power consumption. Therefore, the application requirements of the Internet of Things for methane sensors cannot be well met. Existing thermal conductivity methane sensors are used in coal mines to detect high concentrations of methane-based gas. For methane-based gas with a low concentration of less than 4%, it cannot be used to detect alarms due to its low sensitivity.

Summary of the invention

Technical Problem: The object of the present invention is to provide a silicon-based MEMS methane sensor which is simple in structure, can detect a gas gas having a concentration of less than 4% by methane without using a catalyst, and adopts a CMOS-compatible MEMS process to produce a convenient. And gas detection applications and preparation methods.

Technical Solution: The all-silicon MEMS methane sensor of the present invention comprises a silicon component, a fixed end and a silicon frame support; the silicon frame support is an SOI substrate, comprising a silicon substrate and a buried silicon oxide disposed on the silicon substrate And the top layer of silicon on the buried silicon oxide, the top layer of silicon is single crystal silicon;

The fixed end is on the buried silicon oxide on the silicon frame support; the fixed end comprises a silicon layer, a silicon oxide layer outside the silicon layer, and a metal layer serving as an electrical extraction pad Pad; the fixed end silicon layer is disposed at a buried silicon oxide layer; a doped silicon layer is disposed in the supporting silicon layer of the fixed end; a metal layer of the electric extraction pad Pad is disposed on the silicon oxide layer above the silicon layer; and the metal layer is mixed with the fixed end The heterosilicon layer is in direct contact with and constitutes an ohmic contact, and the contact portions of the two have no silicon oxide layer;

The silicon component includes a silicon layer, a silicon oxide layer outside the silicon layer, and a passivation protective layer, the silicon element is provided with a silicon heater, two symmetrically arranged for supporting the silicon heater and providing electrical connection for the silicon heater Silicon cantilever having a length of at least 300 um; one end of the single silicon cantilever is connected to the silicon heater, and the other end is connected to a fixed end on the silicon frame support, and the two silicon cantilevers suspend the silicon heater In the air; the two silicon cantilevers are preferably parallel side by side, and form a U-shaped cantilever structure integrally with the silicon heater; the silicon heater may be a parallel connection of a plurality of silicon heating strips to have a larger surface area; the passivation protective layer a silicon oxide, or hafnium oxide, or a silicon oxide/alumina composite layer, or a hafnium oxide/alumina composite layer, or a hafnium oxide/silicon nitride composite layer, or an aluminum oxide/silicon nitride composite layer, or a silicon oxide/ a silicon nitride composite layer, or a composite layer formed by combining materials of silicon oxide, hafnium oxide, aluminum oxide, silicon nitride; wherein the thickness of the silicon oxide is at least 10 nm, the thickness of the hafnium oxide is at least 5 μm, and the thickness of the aluminum oxide is at least 6 nm. Silicon nitride thickness of at least 10nm, the whole Passivated protective layer The thickness does not exceed 1um;

The silicon layer of the silicon component and the silicon layer of the fixed end are both part of the top silicon of the SOI substrate, that is, part of the top silicon of the silicon frame support, which is formed by the top silicon and has the same thickness; but not The other top silicon of the silicon frame support is in communication; the silicon layers of the two fixed ends are only in communication with the silicon layer of the silicon component.

An all-silicon MEMS methane sensor methane detection application method: applying a voltage or a current through two fixed ends of a silicon component of the all-silicon MEMS methane sensor to operate the silicon component on the left side of the current-resistance characteristic curve In the working point area, the silicon heater of the silicon component is heated, the heating temperature is above 500 degrees Celsius, and the power consumption of a single silicon component is about 80-90 mW; the turning point is the maximum resistance of the resistor as the current or voltage increases. Point, when the current or voltage continues to increase, the resistance does not continue to increase but decreases; when there is methane gas, the temperature of the silicon heater of the all-silicon MEMS methane sensor decreases, causing the resistance of the silicon element to change; The silicon components of the two all-silicon MEMS methane sensors constitute a Wheatstone bridge detection bridge arm for detecting methane concentration, wherein the silicon component of one all-silicon MEMS methane sensor is in contact with ambient air, and the silicon component of another all-silicon MEMS methane sensor For hermetic packaging, the gas inside the package is sealed from the ambient air, and the output voltage of the bridge is detected by Wheatstone when methane gas is present. Due to the change in the resistance of the silicon element in contact with the ambient air, the output voltage of the Wheatstone detection bridge decreases as the methane concentration increases, enabling the detection of methane gas for low concentration methane gas (0 to 4%). The detection sensitivity can reach 10mV/CH ₄ %, and the response time can reach 40ms.

The method for preparing an all-silicon MEMS methane sensor according to claim 1, comprising three preparation methods, specifically:

The steps of the preparation method (1) are as follows:

In the first step, a silicon oxide layer is formed on the top silicon on the front side of the SOI substrate;

In the second step, the silicon oxide layer on the top layer of silicon is patterned to form a window required for doping or ion implantation;

In the third step, doping or ion implantation forms a doped silicon layer;

In the fourth step, a metal layer is formed on the front surface of the SOI substrate by deposition, sputtering or evaporation;

In the fifth step, the metal layer formed in the fourth step is patterned to form a metal pad of the electrical extraction pad, and an ohmic contact is formed after annealing;

In the sixth step, the front etch window pattern is formed by photolithography, and the silicon oxide layer in the front etch window pattern is removed by etching, and then the RIE (Reactive Ion Etching) method is used for dry etching to remove the top layer. Silicon, the etching stops at the buried silicon oxide, and after etching, a silicon element, a structure pattern of the fixed end is formed on the buried silicon oxide layer, and the remaining silicon oxide layer in the window corresponding to the back etching window is removed by etching and The top silicon, the formed silicon component and the two fixed ends connected thereto are not connected to the remaining top silicon on the buried silicon oxide layer, and the two fixed ends of the same silicon component are not connected to the remaining top silicon on the silicon frame support Connected and not connected through the remaining top silicon on the silicon frame support;

In the seventh step, an etch protection layer is prepared on the front surface of the SOI substrate, and a photoresist or PSG (phosphorus silicate glass) is used as an etch protection layer, and the etch protection layer covers the front surface of the entire SOI silicon wafer;

In the eighth step, after the back surface etching window pattern is formed by photolithography on the back side of the SOI substrate, wet etching or ICP (Inductively Coupled Plasma) or DRIE (Deep Reactive Ion Etching) is used. Etching and other dry etching method to remove the silicon substrate of the SOI substrate exposed by the back etching window, the etching stops at the buried silicon oxide; the back etching window and the front etching window are in the SOI silicon The center of the pattern projected on the back side of the substrate coincides, and the back etching window is larger than the front etching window;

In the ninth step, the buried silicon oxide layer exposed from the back surface of the SOI substrate is wet-etched by hydrofluoric acid solution or hydrofluoric acid gas mist to release the silicon component;

In the tenth step, the etching protection layer prepared in the seventh step is removed and dried;

In the eleventh step, the exposed silicon is oxidized to form a thin silicon oxide layer;

In the twelfth step, the front surface of the SOI substrate is covered with a protective layer covering the remaining portion of the front surface of the SOI substrate except the silicon component; the photoresist may be used as a protective layer; and the micro-printing device may be used after precise positioning Preparing a photoresist for use as a protective layer; the photoresist used as a protective layer may also be prepared by spraying using a masking plate overlying the front side of the SOI substrate, the masking plate exposing only the silicon component, and the rest The front part of the SOI substrate is obscured by the masked version;

In the thirteenth step, the arsenic oxide film is prepared by using the ALD method, or the aluminum oxide film is prepared, or the yttrium oxide/alumina composite film is prepared, or the silicon oxide/yttria/alumina composite film is prepared, and the eleventh step and the step are performed. Or forming a passivation protective layer by one of the steps in the eleventh step; the prepared passivation protective layer covers the outer surface of the silicon component;

In the fourteenth step, the protective layer used in the twelfth step is removed and dried;

In the fifteenth step, the SOI substrate is diced along the scribe groove, and the shard is obtained to obtain a large amount of the methane sensor according to the present invention;

Or the steps of the preparation method (2) are:

In the third step, doping or ion implantation forms a doped silicon layer;

In the fourth step, the front etch window pattern is formed by photolithography, the silicon oxide layer in the front etch window pattern is removed by etching, and then the top silicon is removed by RIE etching, and the etching stops at the buried silicon oxide. After forming a silicon element, a structure pattern of the fixed end on the buried silicon oxide layer, and etching away the remaining silicon oxide layer and the top silicon in the window corresponding to the back etching window, the formed silicon element and the two connected thereto The fixed ends are not connected to the remaining top silicon on the buried silicon oxide layer, and the two fixed ends of the same silicon component are not connected to the remaining top silicon on the silicon frame support, nor to the remaining top layer on the silicon frame support. Silicon connected;

In the fifth step, an etch protection layer is prepared on the front side of the SOI substrate, and a photoresist or PSG (phosphorus silicate glass) is used as an etch protection layer, and the etch protection layer covers the front surface of the entire SOI silicon wafer;

In the sixth step, after the backside etching window pattern is formed on the back surface of the SOI substrate, the silicon of the SOI substrate exposed by the back etching window is removed by wet etching or dry etching such as ICP or DRIE. Substrate, the etching stops at the buried silicon oxide;

In the seventh step, the buried silicon oxide layer exposed from the silicon substrate is wet-etched by hydrofluoric acid solution or hydrofluoric acid gas mist to release the suspended silicon component;

In the eighth step, the etch protection layer formed in the fifth step is removed;

In the ninth step, the exposed silicon is oxidized to form a thin layer of silicon oxide;

In the tenth step, the front surface of the SOI substrate is covered by a protective layer covering the remaining portion of the front surface of the SOI substrate except the suspended silicon component; the photoresist may be used as a protective layer; and the micro-printing device may be used after precise positioning Preparing a photoresist for use as a protective layer; the photoresist used as a protective layer may also be prepared by spraying using a masking plate overlying the front side of the SOI substrate; the masking plate exposes only the silicon component, and the rest The front part of the SOI substrate is obscured by the masked version;

In the eleventh step, an aluminum oxide or hafnium oxide film is prepared on the outer surface of the silicon component by an ALD method;

In the twelfth step, silicon nitride is prepared on the outer surface of the suspended silicon component by PECVD at 400-450 ° C; and silicon oxide is prepared by combining the ninth step, the eleventh step with this step or the above three steps. Silicon nitride composite film, or silicon oxide/alumina/silicon nitride composite film, or yttria/silicon nitride composite film, or silicon oxide/yttria/alumina/silicon nitride conforming film to form a passivation protective layer The prepared passivation protective layer covers the outer surface of the silicon component;

In the thirteenth step, the protective layer used in the tenth step is removed and dried;

In the fourteenth step, a photoresist is prepared on the front side of the SOI substrate, and a pattern of the metal pad of the electrical extraction pad is formed after photolithography;

In the fifteenth step, preparing a metal layer by sputtering or deposition;

In the sixteenth step, the photoresist prepared in the fourteenth step is removed, and only the metal pad (22) of the electrical extraction pad is formed on the fixed end (102), dried, and annealed to form an ohmic contact;

In the seventeenth step, the SOI substrate is diced along the scribe groove, and the shard is obtained to obtain a large amount of the methane sensor according to the present invention;

Or the steps of the preparation method (3) are:

The first step to the thirteenth step are the first step to the thirteenth step of the preparation method,

In a fourteenth step, a masking plate is prepared, the pattern of the masking plate being the same as the pattern of the metal pad of the electrical extraction pad on the SOI substrate;

In the fifteenth step, the metal pad of the electrical extraction pad is prepared, the masking plate of the fourteenth step is placed on the front surface of the SOI substrate and the metal is sputtered after the alignment, and the electrical extraction pad is formed only on the fixed end. Metal pad, forming an ohmic contact after annealing;

In the sixteenth step, the SOI substrate is diced along the scribe groove, and the number of the present invention is obtained after the cleavage More methane sensors.

Advantageous Effects: The silicon component and the silicon heater of the all-silicon MEMS methane sensor of the present invention use silicon as a heating material, instead of using metal as a heating material, the silicon heater is supported by the silicon cantilever and is suspended from the silicon substrate and can be energized in the air. It is heated to a high temperature of 500 ° C or higher, and is compatible with CMOS without using a catalyst and using a MEMS process. Due to the adoption of the above scheme, the following effective effects are obtained:

The silicon heater released from the SOI wafer is suspended in the air, which greatly reduces the heat loss through the SOI wafer, and can heat the silicon heater to a temperature higher than 500 ° C at a lower power; The methane sensor does not contain a catalyst and a catalytic carrier. Therefore, the performance of the sensor is not affected by the catalyst, and there is no problem of sensitivity reduction, poisoning, activation, etc. caused by a decrease in catalyst activity; it is particularly important for a low concentration methane gas; the methane of the present invention The sensor has a high sensitivity of up to 10mV/CH ₄ %. This sensitivity has been able to directly push the instrument to meet the requirements of national standards.

1. The all-silicon MEMS methane sensor of the present invention uses a silicon component as a heating element and a methane detecting component, and can detect a low-concentration methane gas (0 to 5%) without using a catalyst; the silicon heater of the present invention has a plurality of structures The parallel form of the silicon heating strip has a large surface area in contact with air, and can detect low concentration methane with high sensitivity; the sensitivity of the all-silicon MEMS methane sensor of the invention can reach 10 mV/CH ₄ %, which can directly push the meter Meet the requirements of national standards.

2. The methane sensor of the present invention does not contain a catalyst and a catalytic carrier. Therefore, the performance of the sensor is not affected by the catalyst, and there is no problem of sensitivity reduction, poisoning, activation, etc. caused by a decrease in catalyst activity; and the methane sensor of the present invention is methane. The detection does not require oxygen to participate, so it is not affected by oxygen in the air;

3. The silicon heater of the all-silicon MEMS methane sensor of the present invention is suspended in the air by the support of the silicon cantilever and away from the silicon substrate, and the distance is more than 300 um, and the silicon heater can be heated to 500 ° C or higher with a lower power. The high temperature, therefore, has the advantage of low power consumption, and the power consumption of a single silicon component is about 80 to 90 mW.

4. The silicon element of the all-silicon MEMS methane sensor of the present invention is processed by a MEMS process using a stable single crystal silicon, which makes the methane sensor of the invention have good stability and long life under high temperature operation. This is because monocrystalline silicon does not have the disadvantages of low temperature, sublimation, migration, etc. of a metal heating material such as platinum or tungsten at a high temperature of 500 degrees Celsius or higher, and there is no disadvantage that the polycrystalline silicon resistor is easily changed at a high temperature and cannot be controlled. At the same time, the passivation layer provided on the outer surface of the silicon element of the present invention also reduces the influence of the external environment on the above components, thereby further improving the stability of the performance of the methane sensor of the present invention.

5. The silicon component of the all-silicon MEMS methane sensor of the invention is obtained by MEMS processing, and the processing technology is uniform, simple, and compatible with the SOI-CMOS process, and has the advantages of low production cost.

6. The all-silicon MEMS methane sensor of the invention has small size, low power consumption, fast response, up to 40ms, and good linearity of the output signal.

7. The methane sensor of the present invention can be mass-produced in a CMOS process, has good consistency and interchangeability, and can be batch-calibrated, thereby further improving sensor performance and reducing the cost of sensor calibration.

Advantages: The all-silicon MEMS methane sensor provided by the invention has high sensitivity response signal to low-concentration methane, and the preparation method thereof is compatible with the CMOS process, has low cost, is easy to mass-produce and calibrate, and has good consistency and interchangeability. The methane sensor of the invention has small size, fast response speed, low sensor power consumption, high sensitivity, good linearity of output signal and long service life; sensor performance is not affected by the catalyst, and the performance of the sensor is comprehensively optimized and compensated without considering the catalyst. Complex effects, simple and easy.

DRAWINGS

1 is a top plan view of an all-silicon MEMS methane sensor of the present invention on an SOI substrate.

2 is a top plan view of the all-silicon MEMS methane sensor of the present invention after dicing.

Figure 3 is a cross-sectional view taken along line A-A of Figures 1 and 2 of the present invention.

4 is a schematic view showing the structure of a silicon heater of the present invention.

Figure 5 is a graph showing the current-resistance characteristics of a silicon component of an all-silicon MEMS methane sensor of the present invention.

Figure 6 is a graph showing the methane response characteristics of the all-silicon MEMS methane sensor of the present invention.

In the figure: 101-silicon component, 102-fixed end, 103-silicon frame holder, 104-front etch window, 105-back etch window, 106-long scribe groove, 1011-silicon heater, 1012-silicon Cantilever, 1013-silicon heating strip, 21-silicon layer, 22-electrode-extracting pad metal, 23-silicon oxide layer, 24-doped silicon layer, 25-passivation protective layer, 31-silicon substrate, 32- Buried silicon oxide, 33-top silicon.

detailed description

The embodiments of the present invention are further described below with reference to the accompanying drawings:

Embodiments: In FIG. 1, FIG. 2, FIG. 3, the all-silicon MEMS methane sensor comprises a silicon component 101, a fixed end 102 and a silicon frame support 103; the silicon frame support 103 is an SOI substrate, including a silicon liner. a bottom 31, a buried silicon oxide 32 disposed on the silicon substrate 31 and a top silicon 33 over the buried silicon oxide 32, the top silicon 33 being single crystal silicon;

The fixed end 102 is on the buried silicon oxide 32 on the silicon frame support 103; the fixed end 102 includes a silicon layer 21, a silicon oxide layer 23 outside the silicon layer 21, and a metal pad 22 serving as an electrical extraction pad. The silicon layer 21 of the fixed end 102 is disposed on the buried silicon oxide 12; the doped silicon layer 24 is disposed in the supporting silicon layer 21 of the fixed end 102; the metal pad 22 of the electrical extraction pad is disposed on the silicon On the silicon oxide layer 23 above the layer 21; the metal layer 22 is in direct contact with the doped silicon layer 24 of the fixed end 102 and constitutes an ohmic contact, the contact portion of the two without the silicon oxide layer 23;

The silicon element 101 includes a silicon layer 21, a silicon oxide layer 23 outside the silicon layer 21, and a passivation protective layer 25. The silicon element 101 is provided with a silicon heater 1011, two symmetrically arranged for supporting the silicon heater 1011. And providing a silicon heater 1011 with an electrically connected silicon cantilever 1012 having a length of at least 300 um; one end of the single silicon cantilever 1012 is coupled to the silicon heater 1011 and the other end is coupled to the silicon frame support 103. The fixed ends 102 are connected, and the two silicon cantilevers 1012 suspend the silicon heater 1011 in the air; the two silicon cantilevers 1012 are preferably parallel side by side, and form a U-shaped cantilever structure integrally with the silicon heater 1011; the passivation protective layer 25 a silicon oxide, or hafnium oxide, or a silicon oxide/alumina composite layer, or a hafnium oxide/alumina composite layer, or a hafnium oxide/silicon nitride composite layer, or an aluminum oxide/silicon nitride composite layer, or a silicon oxide/ a silicon nitride composite layer, or a composite layer formed by combining materials of silicon oxide, hafnium oxide, aluminum oxide, silicon nitride; wherein the thickness of the silicon oxide is at least 10 nm, the thickness of the hafnium oxide is at least 5 μm, and the thickness of the aluminum oxide is at least 6 nm. Silicon nitride thickness of at least 10nm, the entire passivation protection The thickness of the layer does not exceed 1 um;

The silicon layer 21 of the silicon element 101 and the silicon layer 21 of the fixed end 102 are both part of the top layer silicon 33 of the SOI substrate, that is, part of the top layer silicon 33 of the silicon frame holder 103, which is processed by the top layer silicon 33. The shaped, the same thickness; but not in communication with the other top silicon 33 of the silicon frame support 103; the silicon layers 21 of the two fixed ends 102 are only in communication with the silicon layer 21 of the silicon component.

The silicon heater 1011 shown in FIG. 4 is a parallel connection of a plurality of silicon heating bars 1013 to increase the high temperature surface area in contact with air, and the silicon heater 1011 may also have a ring shape.

Figure 5 is a graph showing the current-resistance characteristics of the all-silicon MEMS methane sensor of the present invention.

A method for detecting methane in an all-silicon MEMS methane sensor by applying a voltage or a current to the two fixed ends 102 of the silicon element 101 of the all-silicon MEMS methane sensor to operate the silicon element 101 on a current-resistance characteristic curve The working point area on the left side of the turning point causes the silicon heater 1011 of the silicon element 101 to generate heat, the heating temperature is above 500 degrees Celsius, and the power consumption of the single silicon element 101 when operating is about 80-90 mW; the turning point is the resistance with current or voltage. Increasing the maximum point of resistance, when the current or voltage continues to increase, the resistance does not continue to increase but decreases; when methane gas occurs, the temperature of the silicon heater 1011 of the all-silicon MEMS methane sensor decreases, making silicon The resistance of the element 101 is varied; the silicon element 101 of the two described all-silicon MEMS methane sensor is used to form a Wheatstone bridge detection bridge arm to detect methane concentration, wherein the silicon element 101 of an all-silicon MEMS methane sensor is in contact with ambient air, The silicon component 101 of another all-silicon MEMS methane sensor is hermetically sealed, and the gas in the package is sealed from the ambient air when methane gas is present. The output voltage of the Wheatstone detection bridge changes due to the decrease in the resistance of the silicon element 101 in contact with the ambient air. The output voltage of the Wheatstone detection bridge decreases as the methane concentration increases, achieving detection of methane gas, which is low. The detection sensitivity of the concentration methane gas (0~4%) can reach 10mV/CH ₄ %, and the response time can reach 40ms.

The preparation method of the all-silicon MEMS methane sensor includes three preparation methods, specifically:

The steps of the preparation method (1) are as follows:

a first step, preparing a silicon oxide layer 23 on the top layer of silicon 33 on the front side of the SOI substrate;

In the second step, the silicon oxide layer 23 on the top layer of silicon 33 is patterned to form a window required for doping or ion implantation;

The third step, doping or ion implantation to form a doped silicon layer 24;

In the fifth step, the metal layer formed in the fourth step is patterned to form a metal pad 22 of the electrical extraction pad, and an ohmic contact is formed after annealing;

In the sixth step, the front etching window 104 is formed by photolithography, and the silicon oxide layer 23 in the pattern of the front etching window 104 is removed by etching, and then the top silicon 33 is removed by RIE dry etching, and the etching is stopped. After the etching, the silicon oxide layer 32 is formed on the buried silicon oxide layer 32, and the structural pattern of the fixed end 102 is formed on the buried silicon oxide layer 32, and the remaining silicon oxide layer 23 and the top layer in the window corresponding to the back etching window are removed by etching. The silicon 33, the formed silicon element 101 and the two fixed ends 102 connected thereto are not connected to the remaining top silicon on the buried silicon oxide layer 32, and the two fixed ends 102 of the same silicon element 101 are not connected to the silicon frame support. The remaining top silicon on 103 is connected and is not connected through the remaining top silicon on the silicon frame support 103;

In the eighth step, after the back surface etching window 105 pattern is formed on the back surface of the SOI substrate, the SOI substrate exposed by the back etching window is removed by wet etching or dry etching such as ICP or DRIE. The silicon substrate 31 is etched and stopped in the buried silicon oxide 32; the back etching window 105 coincides with the center of the pattern of the front etching window 104 projected on the back side of the SOI silicon substrate, and the back etching window 105 is larger than the front etching Window 104;

The ninth step, using a hydrofluoric acid solution or hydrofluoric acid aerosol wet etching of the buried silicon oxide layer 32 exposed from the back side of the SOI substrate, releasing the silicon element 101;

In a twelfth step, the front surface of the SOI substrate is covered with a protective layer covering the rest of the front surface of the SOI substrate except the silicon component 101; the photoresist can be used as a protective layer; and the micro-printing device can be used for precise positioning. The photoresist used as a protective layer is then prepared; the photoresist used as a protective layer can also be prepared by spraying using a masking plate overlying the front side of the SOI substrate, the masking plate exposing only the silicon component 101, and The remaining portion of the remaining SOI substrate is obscured by the masked version;

In the thirteenth step, the yttrium oxide film is prepared by using the ALD atomic layer deposition method, or the aluminum oxide film is prepared, or the yttrium oxide/alumina composite film is prepared, or the silicon oxide/yttria/alumina composite film is prepared, and the eleventh step is adopted. Forming a passivation protective layer 25 with this step or by one of the steps of the eleventh step; the passivation protective layer 25 is prepared to cover the outer surface of the silicon element 101;

In the fifteenth step, the SOI substrate is diced along the scribe groove 106, and a large number of methane sensors according to the present invention are obtained after cleavage.

The steps of the preparation method (2) are as follows:

The third step, doping or ion implantation to form a doped silicon layer 24;

In the fourth step, lithography forms a front etch window 104 pattern, and the silicon oxide layer 23 in the pattern of the front etch window 104 is etched away, and then the top silicon 33 is removed by RIE dry etching, and the etch stops at the burying. After the etching, the silicon oxide layer 32 is formed on the buried silicon oxide layer 32, and the structural pattern of the fixed end 102 is formed on the buried silicon oxide layer 32, and the remaining silicon oxide layer 23 and the top layer in the window corresponding to the back etching window are removed by etching. The silicon 33, the formed silicon element 101 and the two fixed ends 102 connected thereto are not connected to the remaining top silicon on the buried silicon oxide layer 32, and the two fixed ends 102 of the same silicon element 101 are not connected to the silicon frame support. The remaining top silicon on 103 is connected and is not connected through the remaining top silicon on the silicon frame support 103;

In the fifth step, an etch protection layer is formed on the front top silicon of the SOI substrate, and a photoresist or PSG (phosphorus glass) is used as an etch protection layer covering the front surface of the entire SOI wafer. ;

In the sixth step, after the back surface etching window 105 pattern is formed on the back surface of the SOI substrate, the SOI substrate exposed by the back etching window is removed by wet etching or dry etching such as ICP or DRIE. Silicon substrate 31, etching stops at buried silicon oxide 32;

In the seventh step, the buried silicon oxide layer 32 exposed from the silicon substrate 31 is wet-etched by using a hydrofluoric acid solution or a hydrofluoric acid gas mist to release the suspended silicon element 101;

In the tenth step, the front surface of the SOI substrate is covered with a protective layer covering the remaining portion of the front surface of the SOI substrate except the suspended silicon component 101; the photoresist may be used as a protective layer; and the micro-printing device may be used for precise positioning. Thereafter, a photoresist used as a protective layer is prepared; the photoresist used as a protective layer may also be prepared by spraying using a masking plate overlying the front surface of the SOI substrate; the masking plate exposes only the silicon component 101, and The remaining portion of the remaining SOI substrate is obscured by the masked version;

In the eleventh step, an aluminum oxide or hafnium oxide film is prepared on the outer surface of the silicon element 101 by an ALD atomic layer deposition method;

In the twelfth step, silicon nitride is prepared on the outer surface of the suspended silicon element 101 by a PECVD (Plasma Enhanced Chemical Vapor Deposition) at 400 to 450 ° C; through the ninth step, the eleventh step The step is combined with this step or the above three steps to prepare a silicon oxide/silicon nitride composite film, or a silicon oxide/alumina/silicon nitride composite film, or a hafnium oxide/silicon nitride composite film, or silicon oxide/oxidation.铪/alumina/silicon nitride conforms to the film to form a passivation protective layer 25; the prepared passivation protective layer 25 covers the outer surface of the silicon element 101;

In the fourteenth step, a photoresist is prepared on the front side of the SOI substrate, and after lithography, a pattern of the metal pad 22 of the electrical extraction pad is formed;

In the fifteenth step, preparing a metal layer by sputtering or deposition;

In the seventeenth step, the SOI substrate is diced along the scribe groove 106, and a large number of methane sensors according to the present invention are obtained after cleavage.

The steps of the preparation method (3) are as follows:

The first step to the thirteenth step are the first step to the thirteenth step of the preparation method (2),

In a fourteenth step, a masking plate is prepared, the pattern of the masking plate and the gold of the electrical extraction pad on the SOI substrate The graphics of Pad 22 are the same;

In the fifteenth step, the metal pad 22 of the electrical extraction pad is prepared, the masking plate of the fourteenth step is placed on the front surface of the SOI substrate and the metal is sputtered after alignment, and the electrical extraction is formed only on the fixed end 102. The metal pad 22 of the pad forms an ohmic contact after annealing;

In a sixteenth step, the SOI substrate is diced along the scribe groove 106, and the shard is obtained to obtain a plurality of methane sensors according to the present invention.

Claims

An all-silicon MEMS methane sensor, comprising: a silicon component (101), a fixed end (102) and a silicon frame support (103); the silicon frame support (103) is an SOI substrate, including silicon a substrate (31), a buried silicon oxide (32) disposed on the silicon substrate (31) and a top silicon (33) over the buried silicon oxide (32), the top silicon (33) being single crystal silicon;

The fixed end (102) is disposed on the buried silicon oxide (32) on the silicon frame support (103); the fixed end (102) includes a silicon layer (21), a silicon oxide outside the silicon layer (21) a layer (23) and a metal pad (22) serving as an electrical extraction pad; a silicon layer (21) of the fixed end (102) is disposed over the buried silicon oxide (12); and the silicon of the fixed end (102) a layer (21) is provided in the layer (21); the metal pad (22) of the electrical extraction pad is disposed on the silicon oxide layer (23) above the silicon layer (21); the metal layer (22) Directly contacting the doped silicon layer (24) of the fixed end (102) and forming an ohmic contact, the contact portion of the two having no silicon oxide layer (23);

The silicon element (101) includes a silicon layer (21), a silicon oxide layer (23) outside the silicon layer (21), and a passivation protective layer (25). The silicon element (101) is provided with a silicon heater (1011). a two symmetrically disposed silicon cantilever (1012) for supporting the silicon heater (1011) and providing an electrical connection to the silicon heater (1011), the silicon cantilever (1012) having a length of at least 300 um; the single One end of the silicon cantilever (1012) is connected to the silicon heater (1011), the other end is connected to the fixed end (102) on the silicon frame holder (103), and the two silicon cantilevers (1012) suspend the silicon heater (1011). In the air, the two silicon cantilevers (1012) are preferably parallel side by side, and form a U-shaped cantilever structure integrally with the silicon heater (1011); the passivation protective layer (25) is silicon oxide, or yttrium oxide, or oxidized. a silicon/alumina composite layer, or a yttria/alumina composite layer, or a yttria/silicon nitride composite layer, or an aluminum oxide/silicon nitride composite layer, or a silicon oxide/silicon nitride composite layer, or silicon oxide, a composite layer formed by combining materials of cerium oxide, aluminum oxide and silicon nitride; wherein the thickness of the silicon oxide is at least 10 nm, the thickness of the cerium oxide is at least 5 um, and the thickness of the aluminum oxide is at least 6 nm, nitriding The thickness of the silicon is at least 10 nm, and the thickness of the entire passivation protective layer is not more than 1 um;

The silicon layer (21) of the silicon component (101) and the silicon layer (21) of the fixed end (102) are both part of the top silicon (33) of the SOI substrate, that is, the same as the silicon frame support (103). A portion of the top silicon (33) is formed from the top silicon (33) and has the same thickness; but is not in communication with the other top silicon (33) of the silicon frame support (103); the two fixed ends (102) The silicon layer (21) is only in communication with the silicon layer (21) of the silicon component.
An all-silicon MEMS methane sensor methane detection application method is characterized in that a silicon element (101) is operated on a current-resistance characteristic by applying a voltage or current on two fixed ends (102) of the all-silicon MEMS methane sensor. The working point area on the left side of the turning point in the curve causes the silicon heater (1011) of the silicon component (101) to generate heat, and the heating temperature is above 500 degrees Celsius; the turning point is the maximum point of resistance which occurs when the resistance increases with current or voltage. When the current or voltage continues to increase, the resistance does not continue to increase but decreases; when methane gas occurs, the temperature of the silicon heater (1011) of the all-silicon MEMS methane sensor decreases, causing the resistance of the silicon element to change; The silicon element (101) of the two described all-silicon MEMS methane sensors is used to form a Wheatstone bridge detection bridge arm to detect methane concentration, wherein the silicon element (101) of an all-silicon MEMS methane sensor is in contact with ambient air, and the other is The silicon component (101) of the silicon MEMS methane sensor is hermetically sealed, and the gas inside the package is sealed from the ambient air. When methane gas is present, the output voltage of the Wheatstone detection bridge is due to The resistance of the silicon element (101) in contact with the ambient air is lowered, and the output voltage of the Wheatstone detection bridge is lowered as the methane concentration is increased to realize the detection of methane gas.
A method of fabricating an all-silicon MEMS methane sensor according to claim 1, comprising Three preparation methods;

The steps of the preparation method (1) are as follows:

a first step, preparing a silicon oxide layer (23) on the top silicon (33) on the front side of the SOI substrate;

In the second step, the silicon oxide layer (23) above the top silicon (33) is patterned to form a window required for doping or ion implantation;

The third step, doping or ion implantation to form a doped silicon layer (24);

In the fourth step, a metal layer is formed on the front surface of the SOI substrate by deposition, sputtering or evaporation;

In the fifth step, the metal layer formed in the fourth step is patterned to form a metal pad (22) of the electrical extraction pad, and an ohmic contact is formed after annealing;

In the sixth step, photolithography forms a front etch window (104) pattern, and the silicon oxide layer (23) in the front etch window (104) pattern is removed by etching, followed by RIE (Reactive Ion Etching). Method The dry etching further removes the top silicon (33), the etching stops at the buried silicon oxide (32), and after etching, the silicon element (101) and the fixed end (102) are formed on the buried silicon oxide layer (32). a structural pattern, and etching to remove the remaining silicon oxide layer (23) and the top silicon (33) in the window corresponding to the back etching window, the formed silicon component (101) and the two fixed ends connected thereto (102) not connected to the remaining top silicon on the buried silicon oxide layer (32), the two fixed ends (102) of the same silicon component (101) are not connected to the remaining top silicon on the silicon frame support (103) Nor is it connected through the remaining top silicon on the silicon frame support (103);

In the seventh step, an etch protection layer is formed on the front surface of the SOI substrate, and the etch protection layer covers the front surface of the entire SOI silicon wafer;

In the eighth step, after the back side etching window (105) pattern is formed by photolithography on the back side of the SOI substrate, wet etching or ICP (Inductively Coupled Plasma) or DRIE (Deep Reactive Ion Etching) is used. Dry etching method such as reactive ion etching removes the silicon substrate (31) of the SOI substrate exposed by the back etching window, and the etching stops at the buried silicon oxide (32); the back etching The window (105) coincides with the front etch window (104) on the center of the pattern projected on the back side of the SOI silicon substrate, and the back etch window (105) is larger than the front etch window (104);

In the ninth step, the buried silicon oxide layer (32) exposed from the back side of the SOI substrate is wet-etched using a hydrofluoric acid solution or a hydrofluoric acid gas mist to release the silicon element (101);

In the tenth step, the etching protection layer prepared in the seventh step is removed and dried;

In the eleventh step, the exposed silicon is oxidized to form a thin silicon oxide layer;

In a twelfth step, a front surface of the SOI substrate is covered with a protective layer covering a front portion of the SOI substrate other than the silicon component (101);

In the thirteenth step, an ALD (atomic layer deposition) method is used to prepare a ruthenium oxide film, or an aluminum oxide film is prepared, or a yttrium oxide/alumina composite film is prepared, or a silicon oxide/yttria/alumina composite film is prepared. Forming a passivation protective layer (25) by the eleventh step and this step or by the eleventh step and one of the steps; the prepared passivation protective layer (25) covers the outer surface of the silicon element (101);

In the fourteenth step, the protective layer used in the twelfth step is removed and dried;

In the fifteenth step, the SOI substrate is diced along the scribe groove (106), and the shard is obtained to obtain a large amount of the methane sensor according to the present invention;

Or the steps of the preparation method (2) are:

a first step, preparing a silicon oxide layer (23) on the top silicon (33) on the front side of the SOI substrate;

In the second step, the silicon oxide layer (23) above the top silicon (33) is patterned to form a window required for doping or ion implantation;

The third step, doping or ion implantation to form a doped silicon layer (24);

In the fourth step, photolithography forms a front etch window (104) pattern, and the silicon oxide layer (23) in the front etch window (104) pattern is removed by etching, followed by RIE (Reactive Ion Etching). Method The dry etching further removes the top silicon (33), the etching stops at the buried silicon oxide (32), and after etching, the silicon element (101) and the fixed end (102) are formed on the buried silicon oxide layer (32). a structural pattern, and etching to remove the remaining silicon oxide layer (23) and the top silicon (33) in the window corresponding to the back etching window, the formed silicon component (101) and the two fixed ends connected thereto (102) not connected to the remaining top silicon on the buried silicon oxide layer (32), the two fixed ends (102) of the same silicon component (101) are not connected to the remaining top silicon on the silicon frame support (103) Nor is it connected through the remaining top silicon on the silicon frame support (103);

In the fifth step, an etch protection layer is formed on the front side of the SOI substrate (above the top silicon), and the etch protection layer covers the front surface of the entire SOI silicon wafer;

In the sixth step, after the back surface etching window (105) pattern is formed by photolithography on the back side of the SOI substrate, wet etching or ICP (Inductively Coupled Plasma) or DRIE (Deep Reactive Ion Etching) is used. a dry etching method such as reactive ion etching to remove the silicon substrate (31) of the SOI substrate exposed by the back etching window, and the etching stops at the buried silicon oxide (32);

In the seventh step, the buried silicon oxide layer (32) exposed from the silicon substrate (31) is wet-etched by hydrofluoric acid solution or hydrofluoric acid gas mist to release the suspended silicon component (101);

In the eighth step, the etch protection layer formed in the fifth step is removed;

In the ninth step, the exposed silicon is oxidized to form a thin layer of silicon oxide;

In the tenth step, the front surface of the SOI substrate is covered with a protective layer covering the front portion of the SOI substrate except the suspended silicon component (101)

In the eleventh step, an aluminum oxide or hafnium oxide film is prepared on the outer surface of the silicon element (101) by an ALD (Atomic Layer Deposition) method;

The twelfth step is to use PECVD (Plasma Enhanced Chemical Vapor Deposition, Plasma enhanced chemical vapor deposition method) preparing silicon nitride on the outer surface of the suspended silicon component (101) at 400-450 ° C; preparing by the combination of the ninth step, the eleventh step and the step or the above three steps a silicon oxide/silicon nitride composite film, or a silicon oxide/alumina/silicon nitride composite film, or a hafnium oxide/silicon nitride composite film, or a silicon oxide/yttria/alumina/silicon nitride conforming film, formed Passivating the protective layer (25); the prepared passivation protective layer (25) covers the outer surface of the silicon component (101);

In the thirteenth step, the protective layer used in the tenth step is removed and dried;

In the fourteenth step, a photoresist is prepared on the front side of the SOI substrate, and after lithography, a pattern of the metal pad (22) of the electrical extraction pad is formed;

In the fifteenth step, preparing a metal layer by sputtering or deposition;

In the sixteenth step, the photoresist prepared in the fourteenth step is removed, and only the metal pad (22) of the electrical extraction pad is formed on the fixed end (102), dried, and annealed to form an ohmic contact;

In the seventeenth step, the SOI substrate is diced along the scribe groove (106), and the shard is obtained to obtain a large amount of the methane sensor according to the present invention;

Or the steps of the preparation method (3) are:

The first step to the thirteenth step are the first step to the thirteenth step of the preparation method (2),

In a fourteenth step, a masking plate is prepared, the pattern of the masking plate being the same as the pattern of the metal pad (22) of the electrical extraction pad on the SOI substrate;

In the fifteenth step, a metal pad (22) for electrically extracting the pad is prepared, and the masking plate of the fourteenth step is placed on the front surface of the SOI substrate and aligned to sputter the metal, only at the fixed end (102). Forming a metal pad (22) on the electrical extraction pad, forming an ohmic contact after annealing;

In a sixteenth step, the SOI substrate is diced along the scribe groove (106), and the shards are obtained to obtain a plurality of methane sensors according to the present invention.