JP5884999B2 - Manufacturing method of pressure sensor - Google Patents

Description

The present invention relates to a vibration type differential pressure sensor.
More specifically, the present invention relates to a vibration type differential pressure sensor that has high measurement accuracy, is easy to manufacture, and can be manufactured at low cost.

  FIG. 13 is an explanatory diagram showing the structure of a main part of a conventional example that has been generally used, and is disclosed in, for example, Japanese Utility Model Laid-Open No. 01-171337. In the figure, reference numerals 11 and 111 denote a silicon diaphragm and a silicon diaphragm fixing portion disposed in a predetermined fluid 112. In this case, silicon oil is used as the fluid 112.

  In this case, the vibrator-type strain gauge 12 has an H shape, and a cross section near its fixed end appears in FIG. Reference numeral 30 denotes a vibration suppressing body provided with one surface close to at least one surface of the diaphragm 11 so that the silicon diaphragm 11 does not resonate with the vibratory strain gauge 12 due to the density and viscosity of the fluid 112 between the diaphragm 11 and the fluid. .

  In this case, the yoke 131 of the magnet 13 including the yoke 131 and the permanent magnet 132 functions as the vibration suppressing body 30. Reference numeral 113 denotes a recess formed of a silicon diaphragm 11 and a silicon diaphragm fixing portion 111.

  Reference numeral 40 denotes a silicon substrate which is fixed to one surface of the fixing portion 111 of the silicon diaphragm and forms the chamber 114 together with the recess 113. Reference numeral 141 denotes a pressure introducing hole provided in the silicon substrate 40 for introducing pressure into the chamber 114.

  50 is provided in the external opening of the pressure introducing hole 41 so that the fixed portion 111 of the silicon diaphragm does not resonate with the vibrator-type strain gauge 12 due to the density and viscosity of the fluid 112 between the silicon substrate 40. This is a pressure contact that is fixed in close proximity to the silicon substrate 40 via a spacer 42.

  In this case, the spacer 42 is formed integrally with the silicon substrate 40. A communication hole 51 is provided in the pressure connection 50 and communicates with the pressure introduction hole 41 of the silicon substrate 40. Reference numeral 60 denotes a cover that covers the magnet 13, the diaphragm 11, the fixed portion 111, the substrate 40, and the spacer 42, is attached to the pressure contact 50, and is filled with the fluid 112 therein.

  In the above configuration, when an external force is applied to the diaphragm 11, the natural frequency of the vibratory strain gauge 12 changes corresponding to the external force. The vibration of the vibratory strain gauge 12 is detected by the vibration detecting means, and the detected frequency is taken out as an output signal.

  As a result, the external force applied to the diaphragm 11 can be detected. In addition, since the vibration suppressing body 30 provided with one surface close to at least one surface of the diaphragm 11 is provided, the silicon diaphragm 11 does not resonate with the vibratory strain gauge 12.

  That is, the diaphragm 11 has a resonance frequency determined by its shape, but is braked by the silicon oil 112 in the gap between the diaphragm 11 and the yoke 131, so that the oscillation frequency of the vibrator-type strain gauge 12 is the resonance frequency of the diaphragm 11. The diaphragm 11 can be made not to resonate even if it matches. For example, in this embodiment, this condition is sufficiently achieved when the gap a <0.1 mm between the yoke 131 and the diaphragm 11 in 100 cs silicon oil.

FIG. 14 is an example in which the relationship between the Q of the diaphragm 11 and the gap a in various fluids was measured. It has been found that the influence of resonance of the diaphragm 11 is substantially eliminated when Q <0.7.
A shows the case where the fluid 112 is the atmosphere, B shows the case of Freon, and C shows the case of silicon oil.

  FIG. 15 is an explanatory diagram showing the structure of a main part of a conventional example that has been generally used, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 02-032224. In the figure, reference numeral 19 denotes a damping base made of a silicon single crystal that can be accommodated in the recess 13. A flow hole 20 is formed in the center, and a base chip 16 is formed so that the bottom thereof communicates with the through hole 15. It is thermally oxidized and bonded.

  The upper part holds a predetermined gap Δ from the bottom of the diaphragm 13. Reference numeral 21 denotes silicon oil. By sealing the silicon oil inside the recess 11, the influence of the self-excited vibration of the vibration type strain gauge 14 is damped by a narrow gap Δ and removed.

FIG. 16 to FIG. 23 are explanatory views of the configuration of the main part of a conventional example that is generally used conventionally, and is disclosed in, for example, Japanese Patent Laid-Open No. 06-244438. In the figure,
(A) As shown in FIG. 16, a spinel epi layer 12 is formed on one surface side of the semiconductor substrate 11.
(B) As shown in FIG. 17, a silicon oxide film 13 is formed on the surface of the semiconductor substrate 11 in contact with the spinel epilayer 12.

The spinel epilayer is described, for example, in “SOI structure formation technology” P259 published by Shizujiro Furukawa, published on October 23, 1987. The spinel epi layer 12 is a film that accepts the crystallinity of silicon.
(C) As shown in FIG. 18, a polysilicon layer 14 is formed on the surface of the spinel epi layer 12, and the polysilicon layer 14 is annealed to be single crystallized.

(D) As shown in FIG. 19, by photolithography and etching (RIE method (reactive ion etching method, etc.)), the polysilicon layer 14, the spinel epi layer 12, and the silicon oxide film 13 other than the portion corresponding to the diaphragm 3 Remove. Reference numeral 15 denotes a resist.

(E) A silicon epitaxial growth layer 16 is formed on the surfaces of the semiconductor substrate 11 and the polysilicon layer 14 as shown in FIG.
(F) As shown in FIG. 21, the strain detection sensor 17 is formed in the silicon epitaxial growth layer 16. In this case, a piezoresistive element is formed.

(G) As shown in FIG. 22, a communication hole 18 reaching the silicon oxide film 13 from the other surface of the semiconductor substrate 11 is formed by etching.
(H) As shown in FIG. 23, the silicon oxide film 13 is removed by selective etching through the communication hole 18.
Thus, the diaphragm 3 and the gap chamber 4 are configured.

  In short, in this type of vibration-type differential pressure sensor, the diaphragm is strained by the deformation of the diaphragm due to the application of pressure, and the resonance frequency of the vibrator-type strain gauge is changed. By detecting this frequency change, the pressure input to the diaphragm can be measured.

  In such a vibratory differential pressure sensor using a vibratory strain gauge, the vibratory strain gauge is self-excited using an external circuit, and the energy supplied from the circuit is limited to the vibration of the vibratory strain gauge. It is desirable to be used.

  However, at a frequency where the resonance frequency of the diaphragm and the self-excited vibration frequency of the vibratory strain gauge are the same, part of the energy input to the vibratory strain gauge is consumed as the resonance energy of the diaphragm. As a result, the Q value (output) of the transducer-type strain gauge element decreases, so theoretically, the pressure and frequency are in a quadratic proportional relationship, but the error from this proportional relationship becomes large and the input / output characteristics, etc. There is a problem that various characteristics of the above become worse. As a means for solving such a problem, there has been proposed a technique for suppressing diaphragm resonance by using a narrow gap filled with oil.

  As a concrete example for realizing the above, a method of forming a gap by arranging a machined part on the side where a vibrator-type strain gauge is arranged (Japanese Utility Model Laid-Open No. 01-171337, FIG. 1A), A method of arranging a convex portion on a part facing the concave portion of the diaphragm (Japanese Patent Laid-Open No. 02-032224, FIG. 1B), a method of forming a gap by etching an oxide film layer (Japanese Patent Laid-Open No. 6-244438, FIG. 1). (C)) has been proposed.

  Next, as a manufacturing method of such a conventional example, in particular, as a method of forming a diaphragm, a method of forming a diaphragm using alkaline etching of deep moat used in Japanese Utility Model Laid-Open No. 01-171337 and Japanese Patent Laid-Open No. 02-032224, and There is a method of forming a diaphragm using an oxide film used in JP-A-6-244438 as an etch stop.

  In the method of forming a diaphragm using deep etching of alkali, the single crystal silicon wafer 101 is processed by anisotropic wet etching so that the diaphragm 102 has a desired thickness. The thickness is controlled by the etching rate and etching time. In this method, as shown in FIG. 24, a recess constituted by the (111) plane is formed.

  In the method of forming a diaphragm using an oxide film as an etch stop as used in JP-A-6-244438, etching with an alkaline solution and plasma etching can be used. However, since an oxide film can be used as an etch stop, The film thickness can be controlled more precisely than the method using alkaline etching.

Japanese Utility Model Publication No. 01-171337 Japanese Patent Laid-Open No. 02-032224 Japanese Patent Laid-Open No. 06-244438

Such an apparatus has the following problems.
In Japanese Utility Model Laid-Open No. 01-171337, since the diaphragm is manufactured by deep alkaline etching, it is difficult to control the thickness of several um to several tens of um in units of several um, and it is difficult to suppress variations in sensitivity.

  In forming the gap, since machined parts are used, it is difficult to accurately produce a narrow gap of several tens of um or less, and there is a limit in suppressing the resonance of the diaphragm. In addition, since machined parts are used, foreign matter enters when gaps are formed, and the movable range of the diaphragm is limited, which may affect various characteristics such as input / output characteristics. Furthermore, the shape of the diaphragm cannot be freely selected due to the influence of crystal plane orientation due to alkali etching during the formation of the diaphragm. For this reason, restrictions are imposed on the shape when designing the diaphragm, and a diaphragm having a free shape cannot be designed.

  In Japanese Patent Laid-Open No. 02-032224, since the diaphragm is manufactured by deep alkaline etching, it is difficult to control the thickness of several um to several tens of um in units of several um. In the gap formation, it is difficult to accurately process the recess by alkali etching, and the processing error of the opposed convex parts deteriorates the accuracy, so it is difficult to accurately manufacture a gap of several um, There is also a limit to suppressing diaphragm resonance.

  Further, since the shape of the diaphragm cannot be freely selected due to the influence of the crystal plane orientation due to alkali etching during the formation of the diaphragm, the shape is restricted when designing the diaphragm, and the diaphragm cannot be designed in a free shape.

  In Japanese Patent Laid-Open No. 6-244438, an oxide film layer is used for manufacturing a gap, so that stress may be generated at the boundary between the oxide film and silicon, and the wafer may be warped or the oxide film may be cracked. In order to avoid such a state, an oxide film thickness of about 3 to 4 μm is a limit, and a gap of 3 to 4 μm or more cannot be formed.

  For this reason, the movable range of the diaphragm is limited to the gap, and a restriction is imposed on the sensor design of the pressure range that requires a displacement of 4 μm or more. In addition, since the diaphragm is produced by epitaxial growth and is affected by the crystal plane, when designing a diaphragm with no crystal defects at the boundary between the substrate and the diaphragm and having a high fracture stress, the design must be made in consideration of the crystal plane. I must. Therefore, it is not possible to design a diaphragm with a free shape that is not restricted by the crystal orientation.

Next, problems of such a conventional manufacturing method, particularly, a diaphragm forming method will be described.
The problems of deep alkali etching used in Japanese Utility Model Laid-Open No. 01-171337 and Japanese Patent Laid-Open No. 02-032224 are that it is easily affected by the temperature of the chemical solution and the thickness is difficult to control. In other words, high accuracy of the diaphragm film thickness is required and control is difficult, and it is necessary to protect the element surface side from the chemical solution during etching.

  On the other hand, in the method using an oxide film as an etch stop as used in JP-A-6-244438, a gap is formed by the oxide film thickness. For this reason, it is impossible to form a gap of about 3 to 4 μm or more where the wafer warps or the oxide film cracks. As a result, the diaphragm comes into contact with the opposing structure, and the movable range of the diaphragm is restricted. That is, there is a great restriction on the sensor design for the pressure range that requires a displacement of 4 μm or more.

  Further, in deep etching, as shown in FIG. 25, when the same mask shape is used to finish the same diaphragm thickness, the finished shape of the diaphragm differs for wafers having different thicknesses due to the difference in the etching rate of the plane orientation.

  For this reason, in wafers having different inch sizes, since the thickness of the wafer is different, it is necessary to change the etching conditions and the mask pattern. This means that after making a prototype with a small wafer of 4 inches or the like in the R & D stage, when manufacturing a large wafer with an inch size of 8 inches or 12 inches in mass production, the mask is remade and manufactured. Indicates that the conditions need to be changed. This means that a huge amount of time must be spent to move from prototype to commercialization.

  Furthermore, in the differential pressure sensor, it is necessary to change the design of the shape and thickness of the diaphragm according to the pressure range. In order to realize various diaphragm thicknesses corresponding to such various pressure ranges by deep alkaline etching, the mask pattern and manufacturing conditions must be individually managed for each corresponding diaphragm thickness. Don't be.

  In addition, even a diaphragm manufactured using epitaxial growth as disclosed in Japanese Patent Laid-Open No. 6-244438 is affected by the plane orientation and cannot be designed into a free shape that is not restricted by the crystal orientation.

An object of the present invention is to solve the above-described problems, and to provide a sensor and a method for manufacturing the same as follows.
1) For the structure of the vibration type differential pressure sensor,
Structure with good controllability of diaphragm thickness that can suppress variations in sensitivity.
A structure that can realize a gap (sub um to several tens of um or more) to prevent diaphragm resonance with sub um accuracy.

2) For the manufacturing method of the vibration type differential pressure sensor,
A method for manufacturing a vibration-type differential pressure sensor independent of the inch size of a wafer.
A method of manufacturing a vibration-type differential pressure sensor that can be manufactured with the same mask even if the diaphragms have different thicknesses.
A method of manufacturing a vibration type differential pressure sensor having a diaphragm with a uniform sensitivity with little variation in diaphragm thickness.

A method for manufacturing a vibration type differential pressure sensor capable of producing a narrow gap for suppressing diaphragm resonance.
A manufacturing method of a vibration type differential pressure sensor that is a simple process that does not include a pre-process for completing a vibratory strain gauge element in a process after a grinding and polishing process and a bonding process.

(1) A method for manufacturing a pressure sensor, comprising the following steps. (A) A step of forming a strain gauge element on the element surface of the sensor wafer. (B) An attaching step in which a support wafer is attached to the element surface of the sensor wafer on which the strain gauge element is already formed. (C) Grinding polishing surface is ground and polished by grinding and polishing process diaphragm is formed. (D) A patterning step of forming a recess having a predetermined gap on the ground and polished surface. (E) A joining step for joining the ground and polished surface to the base wafer. (F) A support wafer peeling step of peeling the support wafer from the element surface.

(2) A method for manufacturing a pressure sensor, comprising the following steps. (A) A step of forming a strain gauge element on the element surface of the sensor wafer. (B) An attaching step in which a support wafer is attached to the element surface of the sensor wafer on which the strain gauge element is already formed. (C) Grinding polishing surface is ground and polished by grinding and polishing process diaphragm is formed. (D) A patterning step of forming a recess having a predetermined gap on the ground and polished surface. (E) the grinding polishing surface and the bonding step of bonding the base Suueha. (F) A support wafer peeling step of peeling the support wafer from the element surface.

(3) In the step (a) of forming the strain gauge element, a metal wiring is formed on the element surface, wherein the pressure sensor manufacturing method according to ( 1 ) or ( 2 ).

( 4 ) In the affixing step (b), the affixing material is any one of a thermoplastic adhesive, a chemical solution-type adhesive, a UV adhesive, a double-sided tape, and WAX, and the affixing accuracy is within the wafer surface. The pressure according to (3) or (4), wherein the support wafer is one of sapphire, glass, and silicon, which is controlled by a difference between a minimum value and a maximum value of thickness or warpage in a wafer surface. Sensor manufacturing method.

( 5 ) A cleaning step is provided after the grinding and polishing step (c). In this cleaning step, either physical cleaning or acid-alkali cleaning is performed at a temperature lower than the heat resistant temperature of the material for bonding, The method for manufacturing a pressure sensor according to (3) or (4), wherein the material is a chemical solution having chemical resistance, and the physical cleaning is CO2 cleaning or two-fluid cleaning.

( 6 ) In the joining step (e), the ground and polished surface and the base wafer are joined at a temperature lower than the heat resistance temperature of the material for bonding, and any of room temperature direct joining, metal diffusion joining and plasma activated joining The method for manufacturing a pressure sensor according to (3) or (4), wherein the pressure sensor is joined.

( 7 ) In the support wafer peeling step (f), heat is applied to the sensor wafer and the support wafer, and after the support wafer peeling step (f), the element surface is cleaned by spin cleaning or chemical immersion. (3) Or the manufacturing method of the pressure sensor as described in (4) characterized by the above-mentioned.

The present invention has the following effects.
Since the amount of polishing can be adjusted for each wafer in consideration of individual wafer thickness variations, for example, the diaphragm thickness can be easily controlled with an accuracy of about several um to sub um. Therefore, a vibration type differential pressure sensor that can suppress variation in sensitivity is obtained.
Since different materials are not used for bonding, the bonded portion can achieve a fracture strength equivalent to the strength of the base metal of silicon. Therefore, a vibration type differential pressure sensor having excellent breakdown voltage characteristics can be obtained.

In addition, since thermal distortion due to the difference in thermal expansion coefficient can be suppressed, a vibration type differential pressure sensor with good temperature characteristics can be obtained.
An internal residual strain between different types of materials caused by temperature and pressure history is also suppressed, and a vibration type differential pressure sensor capable of realizing a structure without hysteresis is obtained.

For example, a gap of several tens of um or less can be formed between the concave portion of the base substrate and the diaphragm. Therefore, resonance of the diaphragm can be prevented, and a vibration type differential pressure sensor having favorable characteristics such as input / output characteristics can be obtained without restricting the movable range of the diaphragm due to the inclusion of foreign matter.
Since the etching amount when forming the gap in the concave portion of the base substrate is small, a highly accurate vibration type differential pressure sensor with good controllability of the gap can be obtained.

For example, since the shape of the concave portion of the base substrate, for example, several tens of um or less becomes the shape of the diaphragm as it is, compared with the case where the diaphragm is formed by anisotropic etching of deep digging with an alkaline solution from the back surface of the wafer on which the element is formed, Since there is no change in diaphragm size or shape due to the (111) crystal plane, a free shape that is not restricted by crystal orientation, such as a circle, can be produced.
In particular, if etching using plasma is used, the manufacturing process is simplified, and a vibration type differential pressure sensor with reduced cost and uniform sensitivity can be obtained.

The present invention has the following effects.
Since the amount of polishing can be adjusted for each wafer in consideration of individual wafer thickness variations, for example, the diaphragm thickness can be easily controlled with an accuracy of about several um to sub um. Therefore, a vibration type differential pressure sensor that can suppress variation in sensitivity is obtained.
Since different materials are not used for bonding, the bonded portion can achieve a fracture strength equivalent to the strength of the base metal of silicon. Therefore, a vibration type differential pressure sensor having excellent breakdown voltage characteristics can be obtained.

In addition, since thermal distortion due to the difference in thermal expansion coefficient can be suppressed, a vibration type differential pressure sensor with good temperature characteristics can be obtained.
An internal residual strain between different types of materials caused by temperature and pressure history is also suppressed, and a vibration type differential pressure sensor capable of realizing a structure without hysteresis is obtained.

For example, a gap of several tens of um or less can be formed between the recess of the sensor substrate provided on the polishing surface side of the diaphragm and the base substrate. Therefore, resonance of the diaphragm can be prevented, and a vibration type differential pressure sensor having favorable characteristics such as input / output characteristics can be obtained without restricting the movable range of the diaphragm due to the inclusion of foreign matter.
Since the etching amount at the time of forming the gap in the concave portion of the sensor substrate is small, a vibration type differential pressure sensor with high controllability of the high-precision gap can be obtained.

For example, since the shape of the recess of the sensor substrate, for example, several tens of um or less becomes the shape of the diaphragm as it is, compared to the case where the diaphragm is formed by anisotropic etching of deep digging with an alkaline solution from the back surface of the substrate on which the element is formed, Since there is no change in diaphragm size or shape due to the (111) crystal plane, a free shape that is not restricted by crystal orientation, such as a circle, can be produced.
In particular, if isotropic etching using plasma is used, the manufacturing process is simplified, the stress concentration portion around the diaphragm can be rounded, and the breakdown voltage increases. Therefore, a vibration type differential pressure sensor with reduced cost and high sensitivity can be obtained.

The present invention has the following effects.
Since the thickness of the diaphragm is substantially determined by the grinding and polishing process, a mask that takes into consideration the difference in the shape of the diaphragm depending on the etching depth is not required, unlike deep etching by alkali etching. Also, unlike alkali etching, the same mask is used even when products are manufactured using large wafers (8 inches, 12 inches, etc.) using large wafers (8 inches, 12 inches, etc.) using small wafers (4 inches wafers, etc.). Since the same process as the pattern can be applied, mass production can be transferred efficiently. Therefore, a method of manufacturing a vibration type differential pressure sensor that does not depend on the inch size of the wafer can be obtained.

Since the amount of polishing can be adjusted for each wafer in consideration of variations in individual wafer thicknesses, the thickness can be easily controlled with an accuracy of a few um, unlike the depth of deep etching by alkali etching. Therefore, a method of manufacturing a vibration type differential pressure sensor capable of manufacturing a diaphragm with uniform sensitivity can be obtained.
Since the gap can be determined by the depth of the concave portion of the base wafer with a small etching amount, for example, a gap from several tens of um to sub um or less can be easily created. Further, since the etching amount is small, the accuracy can be controlled with a high accuracy of about sub um. As a result, a method of manufacturing a vibration type differential pressure sensor capable of manufacturing a narrow gap for suppressing diaphragm resonance in a state where controllability is good is obtained.

  Diaphragm fabrication processes using room temperature direct bonding or metal diffusion bonding, which can directly bond silicon wafers near room temperature, are lower than the heat resistance temperature of the metal wiring placed on the sensor wafer. Bonding is possible with the metal wiring process of the child strain gauge element completed. In addition, even when the shape and thickness of the diaphragm are changed according to the pressure range, the diaphragm formation using the above-described bonding can be realized by the same process and the same mask without depending on the shape and thickness of the diaphragm.

Lowering the bonding temperature has many other advantages. In general, if a high-temperature process of 800 ° C or higher is performed after creating a transducer-type strain gauge, redistribution of impurity elements, rearrangement of atoms, recrystallization, etc. may cause deterioration of sensor device characteristics. There is.
The diaphragm manufacturing process by the above-described normal temperature direct bonding or metal diffusion bonding can be configured at, for example, 400 degrees or less, so that no silicon creep or thermal strain that adversely affects the characteristics of the differential pressure sensor remains. Therefore, a method for manufacturing a vibration type differential pressure sensor having good characteristics can be obtained.

The present invention has the following effects.
Since the thickness of the diaphragm is substantially determined by the grinding and polishing process, a mask that takes into consideration the difference in the shape of the diaphragm depending on the etching depth is not required, unlike deep etching by alkali etching. Also, unlike alkali etching, the same mask pattern is used when products are manufactured with large wafers (8 inches, 12 inches, etc.) using large wafer sizes (8 inches, 12 inches, etc.) using prototype results with small wafers (4 inches, etc.). Because the same process can be applied, mass production can be transferred efficiently. Therefore, a method of manufacturing a vibration type differential pressure sensor that does not depend on the inch size of the wafer can be obtained.

Since the amount of polishing can be adjusted for each wafer in consideration of variations in individual wafer thicknesses, the thickness can be easily controlled with an accuracy of a few um, unlike the depth of deep etching by alkali etching. Therefore, a method of manufacturing a vibration type differential pressure sensor capable of manufacturing a diaphragm with uniform sensitivity can be obtained.
Since the gap can be determined by the depth of the concave portion of the base wafer with a small etching amount, for example, a gap from several tens of um to sub um or less can be easily created. Further, since the etching amount is small, the accuracy can be controlled with a high accuracy of about sub um. As a result, a method of manufacturing a vibration type differential pressure sensor capable of manufacturing a narrow gap for suppressing diaphragm resonance in a state where controllability is good is obtained.

  In addition, if isotropic etching using plasma is used, the manufacturing process becomes simple, the stress concentration portion around the diaphragm can be rounded, and the breakdown voltage increases. Therefore, a vibration type differential pressure sensor with reduced cost and high sensitivity can be obtained.

  Diaphragm fabrication processes using room temperature direct bonding or metal diffusion bonding, which can directly bond silicon wafers near room temperature, are lower than the heat resistance temperature of the metal wiring placed on the sensor wafer. Bonding is possible with the metal wiring process of the child strain gauge element completed. In addition, even when the shape and thickness of the diaphragm are changed according to the pressure range, the diaphragm formation using the above-described bonding can be realized by the same process and the same mask without depending on the shape and thickness of the diaphragm.

In general, if a high-temperature process of 800 ° C or higher is performed after creating a transducer-type strain gauge, redistribution of impurity elements, rearrangement of atoms, recrystallization, etc. may cause deterioration of sensor device characteristics. There is.
The diaphragm manufacturing process by the above-described normal temperature direct bonding or metal diffusion bonding can be configured at, for example, 400 degrees or less, so that no silicon creep or thermal strain that adversely affects the characteristics of the differential pressure sensor remains. Therefore, a method for manufacturing a vibration type differential pressure sensor having good characteristics can be obtained.

It is principal part structure explanatory drawing of one Example of this invention. It is operation | movement explanatory drawing of FIG. It is a manufacturing process explanatory drawing of FIG. It is process flowchart explanatory drawing of FIG. It is principal part structure explanatory drawing of the other Example of this invention. It is operation | movement explanatory drawing of FIG. FIG. 6 is an explanatory diagram of the manufacturing process of FIG. 5. It is process flowchart explanatory drawing of FIG. It is principal part structure explanatory drawing of the other Example of this invention. It is operation | movement explanatory drawing of FIG. FIG. 10 is an explanatory diagram of the manufacturing process of FIG. 9. It is process flowchart explanatory drawing of FIG. It is principal part structure explanatory drawing of the prior art example generally used conventionally. It is operation | movement explanatory drawing of FIG. It is principal part structure explanatory drawing of the other conventional example generally used conventionally. It is principal part manufacture explanatory drawing of the other conventional example generally used conventionally. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of FIG. It is principal part manufacture explanatory drawing of the other conventional example generally used conventionally. It is principal part manufacture explanatory drawing of the other conventional example generally used conventionally.

Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram of the main part configuration of one embodiment of the present invention, FIG. 2 is an explanatory diagram of the main part configuration of FIG. 1, FIG. 3 is an explanatory diagram of the manufacturing process of FIG. is there.

  In FIG. 1, the sensor substrate 410 is provided with a vibrator-type strain gauge element 411 on one surface, and the other surface is polished to a thickness corresponding to the diaphragm 412 and is made of silicon. The base substrate 430 is made of silicon having one surface directly bonded to the other surface of the sensor substrate 410.

  The concave portion 435 is provided at a joint portion between the base substrate 430 and the sensor substrate 410, substantially forms the diaphragm 412 in the sensor substrate 410, and the movable range of the diaphragm 412 is not limited by contamination of foreign matter, and A predetermined gap is provided for performing a braking action by a fluid 446 described later against the resonance of the diaphragm 412 excited by the vibration of the vibratory strain gauge element 411.

  The introduction hole 445 introduces a measurement pressure into the recess 435. The fluid 446 propagates pressure to the recess 435 through the introduction hole 445 and brakes the diaphragm 412.

  That is, the vibration-type differential pressure sensor 400 includes a sensor substrate 410 and a base substrate 430. The base substrate 430 is provided with an introduction hole 445 by plasma etching or alkali etching. The shape of this hole may be any hole as long as it is an introduction hole. The vibratory strain gauge element 411 is manufactured on the upper surface 415 of the diaphragm 412.

  The thickness 420 of the diaphragm is determined by the thickness of the sensor substrate 410. Therefore, the diaphragm thickness 420 is adjusted by grinding and polishing to a desired thickness. Since the polishing amount can be finely adjusted for each wafer, the thickness of each wafer can be accurately controlled in units of several um. The sensor substrate 410 and the base substrate 430 are silicon, and the substrates are bonded without using an oxide film or other different materials. Therefore, the fracture strength equivalent to the strength of the silicon base material can be realized even at the joint surface. In addition, the vibration type differential pressure sensor 400 having good temperature characteristics can be realized.

  The concave portion 435 of the base substrate 430 becomes a gap 435 formed after bonding. The recess 435 is formed by plasma etching, wet etching, or the like. Since this recess 435 does not require deep etching using an alkaline chemical (KOH, TMAH, etc.), a gap of sub um to several tens of um or less can be easily realized with high accuracy. Therefore, it is possible to give a degree of freedom to the design of the gap in consideration of the mixing of foreign matter and the design in consideration of the movable range of the diaphragm 412. The dimension of the diaphragm 412 is the dimension 440 of the concave portion 435 of the base substrate 430.

  As specific shapes, as shown in FIG. 2, a quadrangle 460, a circle 465, a polygon 470, and the like are conceivable. Since the concave portion 435 of the base substrate 430 is a narrow gap of sub um to several tens of um or less, unlike the method of forming a diaphragm using an alkaline chemical solution (KOH, TMAH, etc.), the substrate surface due to the etching surface There is no restriction on the size of the inward direction. Therefore, the shape can be freely designed without being limited by the crystal orientation of the diaphragm.

  In the above configuration, FIG. 3 is a production process explanatory diagram of FIG. 1, and FIG. 4 is a process flowchart explanatory diagram of FIG. (a)-(g) shows the same process in FIG.3 and FIG.4. FIG. 3A shows a manufacturing process of the sensor wafer 510.

  A sensor-type strain gauge element 411 is arranged on one surface of the sensor wafer 510 that has undergone this process, and the formation of the vibrator-type strain gauge element 411 and the metal wiring are already completed. That is, the processing of the surface on which the vibratory strain gauge element 411 is arranged has already been completed, and there is no need for processing in the subsequent steps. Since the transducer-type strain gauge element 411 is small and cannot be displayed, the arrangement area of the transducer-type strain gauge element 411 is indicated by hatching different from that of the sensor wafer 510.

FIG. 3B shows a sensor wafer attaching process.
The element surface of the sensor wafer 510 and the support wafer 521 are attached using the attaching material 522. Here, the pasting material 522 is a thermoplastic adhesive, a chemical solution-dissolving adhesive, a UV adhesive, a double-sided tape, WAX or the like. Since the pasting accuracy affects variations in the thickness of subsequent grinding and polishing, it is necessary to control TTV (total thickness variation, the difference between the minimum value and the re-maximum value of the wafer surface thickness) and warpage. A material such as sapphire, glass, or silicon is used for the support wafer 521. Further, the shape of the support wafer is not particularly limited.

FIG. 3C shows a sensor wafer back surface grinding / polishing step.
A surface 531 opposite to the vibratory strain gauge element 411 of the sensor wafer 510 attached to the support wafer 521 is thinned to a desired thickness by grinding and polishing. At this time, it is necessary to carry out polishing until there is no crushed layer or grinding mark during grinding.

  On the thinned sensor wafer 510, the uneven pattern of the vibratory strain gauge element 411 appears as an uneven pattern on the ground surface after grinding. Since the unevenness of the ground and polished surface generates an unbonded portion at the time of bonding or generates a bonding strain in the sensor, it is preferable that the unevenness of the element surface of the sensor wafer 510 is as flat as possible. When the sensor wafer 510 is ground and polished to 100 μm or less, if the wafer is handled alone, the wafer is easily broken, but with the support wafer 521 attached, the sensor wafer 510 of several tens of μm or less can also be handled.

After grinding and polishing, it is desirable to carry out a cleaning process (not shown) in order to improve the cleanliness of the ground and polished surface. The cleaning process may be physical cleaning (CO ₂ cleaning, two-fluid cleaning), acid-alkali cleaning, etc., but it must be performed at a temperature lower than the heat resistance temperature of the material for attachment, and it is necessary to use a chemical solution that has chemical resistance. is there.

FIG. 3D shows a base wafer manufacturing process.
A pressure introduction hole 541 and a recess 542 are formed in the base wafer 540. The base wafer 540 may use any technique as long as it can form the pressure introducing hole 541 such as plasma etching and wet etching. Further, this hole may have any shape as long as it is an introduction hole. Similarly, the concave portion 542 is formed using plasma etching, wet etching, or the like.

FIG. 3E shows a wafer direct bonding process.
The base wafer 540 in which the pressure introducing hole 541 and the concave portion 542 are manufactured and the ground and polished sensor wafer 510 attached to the support wafer 521 are bonded.
At that time, it is necessary to bond the base wafer 540 and the sensor wafer 510 with the bonding material having a temperature lower than the heat resistant temperature.

  Specifically, the upper limit temperature is about 100 to 200 ° C. for an adhesive and about 150 ° C. for a double-sided tape. Further, from the viewpoint of simplifying the process, it is desirable that the ground and polished surface be bonded in a state where the film formation and the modification process are not performed. Joining satisfying such conditions includes room temperature direct joining and metal diffusion joining.

  In the room temperature direct bonding, the surface of the wafer is etched with an ion gun or an FAB (fast atom beam) gun to increase the activity, and then the wafer is bonded in a high vacuum. The feature of this technique is that bonding is possible at room temperature and the surface is suitable for bonding silicon to each other. Since the gas emitted from the bonding material reattaches to the surface and causes a significant drop in the bonding force, it is necessary to select a material that does not have any gas to be bonded.

  Metal diffusion bonding is a technique in which metal is attached to the surface of a substrate at the atomic layer level instead of increasing the surface activity by etching at room temperature direct bonding. Bonding is performed under high vacuum in the same way as normal temperature direct bonding. In this joining, since the dissimilar materials are only very thin and attached at the atomic layer level, they can be joined without deteriorating the characteristics of the differential pressure sensor.

As a bonding technique at a low temperature, there is plasma activated bonding in addition to the technique described above. Plasma activated bonding is performed with a plasma using a gas such as Ar, N ₂ , O _{2, and the} like, in a state where OH groups are arranged on the surfaces. The bonding strength is increased by annealing. In this technology, moisture generated during bonding causes voids, but in structures like diaphragms where the bonding area is small, moisture can be released from the bonding interface, and even when silicon is bonded, there is no void. Can be realized.

  FIG. 3F shows a support wafer peeling process. The sensor wafer 510 and the base wafer 540 directly bonded after being thinly polished are separated from the support wafer 521. The method of peeling from the support wafer 521 differs depending on the adhesive used. For example, a thermoplastic adhesive is peeled off by sliding in a state where temperature is applied. In addition, the heat-releasable double-sided tape can be easily peeled off simply by applying heat. Although not shown, after peeling, it is desirable to clean the sensor element surface by spin cleaning, chemical immersion, or the like in order to remove the residue of the bonding material.

FIG. 3G shows a dicing process.
As a final wafer process, dicing is performed on the bonded wafer 560 from which the support wafer 521 has been peeled off after bonding. Thereby, the vibration type differential pressure sensor 400 is completed.

  As a result, since the thickness of the diaphragm 412 is adjusted by the amount of grinding and polishing, the thickness can be finely adjusted for each wafer. For example, the diaphragm thickness can be easily controlled with an accuracy of about several um to sub um. Therefore, a vibration type differential pressure sensor that can suppress variation in sensitivity is obtained. Since different materials are not used for bonding, the bonded portion can achieve a fracture strength equivalent to the strength of the base metal of silicon. Therefore, a vibration type differential pressure sensor having excellent breakdown voltage characteristics can be obtained.

  In addition, since thermal distortion due to the difference in thermal expansion coefficient can be suppressed, a vibration type differential pressure sensor with good temperature characteristics can be obtained. An internal residual strain between different types of materials caused by temperature and pressure history is also suppressed, and a vibration type differential pressure sensor capable of realizing a structure without hysteresis is obtained.

  Since the gap can be determined by the depth of the concave portion of the base substrate 540, a gap of, for example, several tens of um or less can be formed between the concave portion 435 of the base substrate and the diaphragm 412. Therefore, resonance of the diaphragm 412 can be prevented, and a vibration type differential pressure sensor with favorable characteristics such as input / output characteristics can be obtained without restricting the movable range of the diaphragm due to the inclusion of foreign matter.

  The shape of the concave portion of the base substrate 430, for example, of several tens of um or less becomes the shape of the diaphragm 412 as it is, and therefore, by anisotropic etching of deep trenches with an alkaline solution from the back surface of the wafer on which the vibratory strain gauge element 411 is formed. Compared to the case where a diaphragm is formed, there is no change in the diaphragm size or shape due to the (111) crystal plane, so that a free shape such as a circle that is not restricted by crystal orientation can be produced. In particular, if etching using plasma is used, the manufacturing process is simplified, and a vibration type differential pressure sensor with reduced cost and uniform sensitivity can be obtained.

  In addition, since the thickness of the diaphragm 412 is substantially determined by the grinding and polishing process, there is provided a method of manufacturing a vibration type differential pressure sensor that eliminates the need for a mask that takes into consideration the difference in the shape of the diaphragm depending on the depth of etching unlike deep etching by alkali etching. can get. Unlike alkaline etching, the same mask pattern is the same even if the product is produced on a large wafer (8 inches, 12 inches, etc.) using a prototype of a small wafer (4 inches, etc.). Since the process can be applied, the transition to mass production can be performed efficiently.

Therefore, a method of manufacturing a vibration type differential pressure sensor that does not depend on the inch size of the wafer can be obtained.
Similarly, in response to a request to change the shape and thickness of the diaphragm 412 in accordance with the pressure range, the diaphragm formation using the above-described bonding does not depend on the shape and thickness of the diaphragm 412 and uses the same process with the same mask. realizable.

  Since the diaphragm manufacturing process including the direct bonding at normal temperature or the metal diffusion bonding for directly bonding silicon wafers is a process lower than the heat resistance temperature of the metal wiring arranged on the sensor wafer 510, first, the vibrator-type distortion Bonding is possible after the metal wiring process of the gauge element is completed.

  In addition, since the diaphragm manufacturing process including room temperature direct bonding or metal diffusion bonding can be configured at, for example, 400 degrees or less, silicon creep or thermal strain that affects the characteristics of the differential pressure sensor does not remain. Therefore, a method for manufacturing a vibration type differential pressure sensor having good characteristics can be obtained.

  FIG. 5 is a diagram illustrating the configuration of the main part of another embodiment of the present invention, FIG. 6 is a diagram illustrating the configuration of the main part of FIG. 5, FIG. 7 is an explanatory diagram of the manufacturing process of FIG. FIG. In FIG. 5, a sensor substrate 610 is provided with a transducer-type strain gauge element 611 on one surface, and the other surface is polished to a thickness corresponding to a diaphragm 612, and then a recess 635 is formed, which is made of silicon.

  Base substrate 630 is made of silicon having one surface directly bonded to the other surface of sensor substrate 610. The concave portion 635 is provided in the sensor substrate 610 at the joint portion with the base substrate 630, and substantially forms the diaphragm 612 in the sensor substrate 610, and the movable range of the diaphragm 612 due to the mixing of foreign matters is not limited, and vibration is generated. The diaphragm 612 is excited by the vibration of the child strain gauge element 611 and has a predetermined gap for performing a braking action by a fluid 646 described later.

  The introduction hole 645 introduces a measurement pressure into the recess 635. The fluid 646 propagates pressure to the recess 635 through the introduction hole 645 and brakes the diaphragm 612.

  That is, the vibration type differential pressure sensor 600 includes a sensor substrate 610 and a base substrate 630. The base substrate 630 is provided with an introduction hole 645 by plasma etching or alkali etching. The shape of this hole may be any hole as long as it is an introduction hole. The vibratory strain gauge element 611 is manufactured on the upper surface 615 of the diaphragm 612.

  The thickness 620 of the diaphragm is determined by a value obtained by subtracting the etching amount of the recess 635 on the back surface of the sensor substrate 610 from the thickness of the sensor substrate 610. Therefore, the thickness accuracy of the diaphragm 612 is expressed by the sum of the accuracy of several um of grinding and polishing and the accuracy of the sub-um of etching, and as a result, has a processing accuracy of several um.

  The sensor substrate 610 and the base substrate 630 are made of silicon, and the substrates are bonded without using an oxide film or other different materials. Therefore, the fracture strength equivalent to the strength of the silicon base material can be realized even at the joint surface. In addition, a sensor having good temperature characteristics can be realized.

  Further, the stress concentration of the diaphragm 612 can be dispersed by applying isotropic etching to the recess 635 of the sensor substrate 610 and adding a roundness 650. As a result, the breakdown voltage of the sensor increases. A gap is formed after the concave portion 635 of the sensor substrate is joined to the base substrate 630. The recess 635 is formed by plasma etching, wet etching, or the like.

  Since this recess 635 does not need to be deep etched using an alkaline chemical (KOH, TMAH, etc.), a gap of sub um to several tens of um or less can be easily realized with high accuracy. Therefore, it is possible to give a degree of freedom to the design of the gap in consideration of the mixing of foreign matter and the design in consideration of the movable range of the diaphragm 612. The dimension of the diaphragm 612 is determined by the dimension 640 of the concave portion 635 of the sensor substrate 610.

  As specific shapes, as shown in FIG. 6, a quadrangle 660, a circle 665, a polygon 670, and the like are conceivable. Since the concave portion 635 of the sensor substrate 610 is a narrow gap of sub um to several tens of um or less, unlike the method of forming a diaphragm by deep etching using an alkaline chemical (KOH, TMAH, etc.), the substrate surface due to the etching surface There is no restriction on the size of the inward direction. Therefore, the shape can be freely designed without being limited by the crystal orientation of the diaphragm.

  In the above configuration, FIG. 7 is a production process explanatory diagram of FIG. 5, and FIG. 8 is a process flowchart explanatory diagram of FIG. (a)-(h) shows the same process in FIG.7 and FIG.8.

FIG. 7A shows a manufacturing process of the sensor wafer 710.
The sensor wafer 710 that has undergone this process has a vibratory strain gauge 611 disposed on one surface of the sensor wafer 710, and the vibratory strain gauge element 611 is formed and the metal wiring is already completed. In other words, the processing of the surface on which the vibratory strain gauge element 611 is arranged has already been completed, and there is no need for processing in the subsequent steps.

FIG. 7B shows a process for attaching the sensor wafer 710.
The element surface of the sensor wafer 710 and the support wafer 721 are attached using the attaching material 722. Here, the pasting material 722 is a thermoplastic adhesive, a chemical solution-dissolving adhesive, a UV adhesive, a double-sided tape, WAX or the like.

  Since the pasting accuracy affects variations in the thickness of subsequent grinding and polishing, it is necessary to control TTV (total thickness variation, the difference between the minimum value and the re-maximum value of the wafer surface thickness) and warpage. A material such as sapphire, glass, or silicon is used for the support wafer 721. Further, the shape of the support wafer 721 is not particularly limited.

FIG. 7C shows a sensor wafer back surface grinding / polishing step.
A surface 731 opposite to the vibratory strain gauge element 611 of the sensor wafer 710 attached to the support wafer 721 is thinned to a desired thickness by grinding and polishing. At this time, it is necessary to carry out polishing until there is no crushed layer or grinding mark during grinding.

Further, on the thinned wafer 710, the concave / convex pattern of the vibrator-type strain gauge element 611 appears as a concave / convex pattern on the ground / polished surface after grinding / polishing. Since the unevenness of the ground surface of the grinding causes unbonded portions to be formed in the bonded portions or causes bonding distortion in the sensor, the unevenness of the element surfaces of the sensor wafer 710 is preferably as flat as possible.
When grinding and polishing the sensor wafer 710 to 100 μm or less, the wafer is easily broken if it is handled as a single wafer. However, with the support wafer 721 attached, the sensor wafer 710 of several tens of μm or less can be handled.

After grinding and polishing, it is desirable to carry out a cleaning process (not shown) in order to improve the cleanliness of the ground and polished surface. The cleaning process may be physical cleaning (CO ₂ cleaning, two-fluid cleaning), acid-alkali cleaning, or the like, but it is performed at a temperature below the temperature at which the pasting material is thermally decomposed, and this material uses a chemical solution with chemical resistance. There is a need.

FIG. 7D shows a sensor wafer back surface pattern forming process.
An opening is provided on the ground and polished surface by photolithography using a resist, and the opening is etched by a technique such as dry etching. After etching, the resist wafer is removed to form the recess 742 of the sensor wafer.

FIG. 7E shows a base wafer manufacturing process.
A pressure introducing hole 741 is formed in the base wafer 740. Any method may be used for the pressure introduction hole 741 as long as the pressure introduction hole can be formed, such as plasma etching and wet etching. Further, this hole may have any shape as long as it is an introduction hole.

FIG. 7F shows a wafer direct bonding process.
The base wafer 740 having the pressure introducing hole 741 and the sensor wafer 710 having the recess 742 are bonded. At that time, it is necessary to bond the base wafer and the sensor wafer below the heat-resistant temperature of the bonding material.

  Specifically, the upper limit temperature is about 100 to 200 ° C. for an adhesive and about 150 ° C. for a double-sided tape. Further, from the viewpoint of simplifying the process, it is desirable that the ground and polished surface be bonded in a state where the film formation and the modification process are not performed. Joining satisfying such conditions includes room temperature direct joining and metal diffusion joining.

  In the room temperature direct bonding, the surface of the wafer is etched with an ion gun or an FAB (fast atom beam) gun to increase the activity, and then the wafer is bonded in a high vacuum. The feature of this technique is that bonding is possible at room temperature and the surface is suitable for bonding silicon to each other. Since the gas emitted from the bonding material reattaches to the surface and causes a significant drop in the bonding force, it is necessary to select the bonding material that does not have any gas emitted.

  Metal diffusion bonding is a technique in which metal is attached to the surface of a substrate at the atomic layer level instead of increasing the surface activity by etching at room temperature direct bonding. Bonding is performed under high vacuum in the same way as normal temperature direct bonding. In this joining, since the dissimilar materials are only very thin and attached at the atomic layer level, they can be joined without deteriorating the characteristics of the differential pressure sensor.

As a bonding technique at a low temperature, there is plasma activated bonding in addition to the technique described above.
Plasma activated bonding is performed with a plasma using a gas such as Ar, N ₂ , O _{2 and the} like, with OH groups arranged on the surfaces, and after temporary bonding (simply pasting) the surfaces to each other at a temperature of about 400 ° C. This is a technique for increasing the bonding strength by annealing. In this technology, moisture generated due to OH groups at the time of bonding causes voids. However, in a structure like a diaphragm with a small bonding area, moisture can be released from the bonding interface, resulting in good bonding without voids. it can.

FIG. 7G shows a support wafer peeling process.
The sensor wafer and the base wafer bonded directly after being thinly polished are separated from the support wafer. The method of peeling from the support wafer differs depending on the adhesive used. For example, a thermoplastic adhesive is peeled off by sliding in a state where temperature is applied.

  In addition, the heat-releasable double-sided tape can be easily peeled off simply by applying heat. Although not shown, after peeling, it is desirable to clean the sensor element surface by spin cleaning, chemical immersion, or the like in order to remove the residue of the bonding material.

FIG. 7H shows a dicing process.
As a final wafer process, dicing is performed on the bonded wafer 760 from which the support wafer has been peeled off after bonding. Thereby, the vibration type differential pressure sensor 600 is completed.

  As a result, since the thickness of the diaphragm 612 is adjusted by fine adjustment of the grinding / polishing amount for each wafer and dry etching, for example, the diaphragm thickness can be easily controlled with an accuracy of about several um to sub um. Therefore, a vibration type differential pressure sensor that can suppress variations in sensitivity can be obtained.

  Since different materials are not used for bonding, the bonded portion can achieve a fracture strength equivalent to the strength of the base metal of silicon. Therefore, a vibration type differential pressure sensor having excellent breakdown voltage characteristics can be obtained. In addition, since thermal distortion due to the difference in thermal expansion coefficient can be suppressed, a vibration type differential pressure sensor with good temperature characteristics can be obtained.

  An internal residual strain between different types of materials caused by temperature and pressure history is also suppressed, and a vibration type differential pressure sensor capable of realizing a structure without hysteresis is obtained.

  Since the gap can be determined by the depth of the concave portion of the sensor substrate, the thickness of the diaphragm can be easily controlled between the concave portion 635 of the sensor substrate and the base substrate with an accuracy of about several tens of um to sub um. Further, since the etching amount is small, the accuracy can be controlled with a high accuracy of about sub um. As a result, the resonance of the diaphragm 612 can be prevented, and the movable range of the diaphragm is not limited by the inclusion of foreign matter, so that a vibration-type differential pressure sensor with favorable characteristics such as input / output characteristics can be obtained.

In addition, if isotropic etching using plasma is used, the manufacturing process becomes simple, the stress concentration portion around the diaphragm can be rounded, and the breakdown voltage increases.
Therefore, a vibration type differential pressure sensor with reduced cost and high sensitivity can be obtained.

  For example, the shape of the recess 635 of several tens of um or less of the sensor substrate 610 becomes the shape of the diaphragm 612 as it is. Compared to the case where a diaphragm is formed, there is no change in the diaphragm size and shape due to the (111) crystal plane, so that a free shape such as a circle that is not restricted by the crystal orientation can be produced.

  In particular, if isotropic etching using plasma is used, the manufacturing process is simplified, the stress concentration portion around the diaphragm can be rounded, and the breakdown voltage increases. Therefore, a vibration type differential pressure sensor with reduced cost and high sensitivity can be obtained.

  Moreover, since the diaphragm thickness can be determined by grinding and polishing and plasma etching, a method of manufacturing a vibration type differential pressure sensor that eliminates the need for a mask that takes into consideration the difference in the shape of the diaphragm depending on the etching depth is obtained unlike the deep etching by alkali etching. .

  In other words, unlike alkaline etching, the same mask is used even when a product with a large inch size wafer (8 inches, 12 inches, etc.) is produced using a prototype result with a small inch size wafer (4 inches wafer, etc.). Since the same process as the pattern can be applied, the shift to mass production can be performed efficiently.

Therefore, a method for manufacturing a vibration type differential pressure sensor independent of the inch size can be obtained.
Similarly, to meet the demand for changing the shape and thickness of the diaphragm according to the pressure range, the above-described diaphragm forming method using bonding is realized by the same mask and the same process regardless of the shape and thickness of the diaphragm. it can.

Since the diaphragm manufacturing process including the room temperature direct bonding or the metal diffusion bonding for directly connecting the silicon wafers is a process lower than the heat resistance temperature of the metal wiring disposed on the sensor wafer 710, the vibratory strain gauge element 611 is used. Bonding is possible with the metal wiring process completed.
Since the diaphragm manufacturing process including room temperature direct bonding or metal diffusion bonding can be configured at, for example, 400 degrees or less, silicon creep or thermal strain that affects the characteristics of the differential pressure sensor does not remain. Therefore, a method for manufacturing a vibration type differential pressure sensor having good characteristics can be obtained.

FIG. 9 is an explanatory diagram of the main part configuration of another embodiment of the present invention, FIG. 10 is an explanatory diagram of the main part configuration of FIG. 9, FIG. 11 is an explanatory diagram of the manufacturing process of FIG. FIG.
It is.

FIG. 9 shows a structure 800 of a vibration type differential pressure sensor.
The vibration type differential pressure sensor 800 includes a sensor substrate 810 and a base substrate 830. The base substrate 830 is provided with an introduction hole 845 by plasma etching and alkali etching. The shape of this hole may be any hole as long as it is an introduction hole. The vibrator-type strain gauge element 811 is manufactured on the upper surface 815 of the diaphragm.

  The thickness of the diaphragm is determined by the thickness of the sensor substrate 810. Therefore, the diaphragm thickness 820 is adjusted by grinding and polishing to a desired thickness. Since the amount of grinding / polishing can be finely adjusted for each wafer, the thickness of each wafer can be accurately controlled in units of several um.

  The sensor substrate 810 and the base substrate 830 are made of silicon, and the wafers are bonded without using an oxide film or other different materials. Therefore, the fracture strength equivalent to the strength of the silicon base material can be realized even at the joint surface. In addition, a sensor having good temperature characteristics can be realized.

  A recess 835 of the base substrate 830 is provided as a gap formed after bonding. The gap is formed by plasma etching, wet etching, or the like. Since this gap does not require deep etching using an alkaline chemical (KOH, TMAH, etc.), a gap of sub um to several tens of um or less can be realized with high accuracy. Therefore, it is possible to give a degree of freedom to the design of the gap in consideration of mixing of foreign matters and the design in consideration of the movable range of the diaphragm 812.

The dimension of the diaphragm 812 is determined by the dimension 840 of the concave portion of the base substrate 830.
As specific shapes, as shown in FIG. 10, a quadrangle 860, a circle 865, a polygon 870, and the like are conceivable. Since the concave portion 835 portion of the base substrate 830 is a narrow gap of sub um to several tens of um or less, unlike a method of forming a diaphragm using an alkaline chemical solution (KOH, TMAH, etc.), a mask pattern depending on the etching plane orientation There are no shape restrictions.

  Therefore, the shape can be freely designed without being limited by the crystal orientation of the diaphragm. Further, the ring-shaped roundness 850 formed on the sensor substrate 810 can alleviate the stress concentration on the diaphragm, so that the breakdown voltage can be improved.

  In the above configuration, FIG. 11 shows a schematic diagram of the process, and FIG. 12 shows a process flowchart.

FIG. 11A shows a manufacturing process of the sensor wafer 910.
The sensor wafer 910 that has undergone this process is a wafer in which the transducer-type strain gauge element 811 is arranged on one surface 911 of the sensor wafer 910, and the formation of the transducer-type strain gauge element 811 and the metal wiring are already completed. That is, the processing of the surface 911 on which the vibratory strain gauge element 811 is arranged has already been completed, and there is no need for processing in the subsequent steps.

FIG. 11B shows a process for attaching the sensor wafer 910.
The element surface of the sensor wafer 910 and the support wafer 921 are attached using the attaching material 922. Here, the pasting material 922 is a thermoplastic adhesive, a chemical solution-soluble adhesive, a UV adhesive, a double-sided tape, WAX, or the like.

  Since the pasting accuracy affects variations in the thickness of subsequent grinding and polishing, it is necessary to control TTV (total thickness variation, the difference between the minimum value and the re-maximum value of the wafer surface thickness) and warpage. A material such as sapphire, glass, or silicon is used for the support wafer 921. Further, the shape of the support wafer is not particularly limited.

FIG. 11C shows a sensor wafer back surface grinding / polishing step.
The surface 931 opposite to the vibratory strain gauge element 811 of the sensor wafer 910 attached to the support wafer 921 is thinned to a desired thickness by grinding and polishing. At this time, it is necessary to carry out polishing until there is no crushed layer or grinding mark during grinding.

  In the thinned sensor wafer 910, the uneven pattern of the vibrator-type strain gauge element 811 appears as an unevenness and pattern on the ground surface after grinding. Since the unevenness of the ground surface of the grinding causes an unbonded portion to be formed in the bonded portion or causes bonding distortion in the sensor, the unevenness of the element surface of the sensor wafer 910 should be as flat as possible. When the sensor wafer 910 is ground and polished to 100 μm or less, the wafer is easily broken if it is handled as a single wafer. However, with the support wafer 921 attached, it is possible to handle even a wafer of several tens of μm or less.

After grinding and polishing, it is desirable to carry out a cleaning process (not shown) in order to improve the cleanliness of the ground and polished surface. The cleaning process may be physical cleaning (CO ₂ cleaning, two-fluid cleaning), acid-alkali cleaning, etc., but it must be performed at a temperature lower than the heat resistance temperature of the material for attachment, and it is necessary to use a chemical solution that has chemical resistance. is there.

FIG. 11D shows a sensor wafer back surface pattern forming process.
An opening is provided on the ground and polished surface by photolithography using a resist, and the opening is etched by a technique such as dry etching. After the etching, the resist is removed to form a rounded portion 932 of the sensor wafer.

FIG. 11E shows a base wafer manufacturing process.
A pressure introduction hole 941 and a recess 942 are formed in the base wafer 940. For the base wafer 940, any technique such as plasma etching and wet etching can be used as long as the pressure introduction hole can be formed. Further, this hole may have any shape as long as it is an introduction hole. Similarly, the concave portion 942 is formed using plasma etching, wet etching, or the like.

FIG. 11 (f) shows a wafer direct bonding process.
The base wafer 940 having the pressure introducing hole 941 and the concave portion 942 and the sensor wafer 910 having the rounded portion 932 are bonded. At that time, it is necessary to bond the base wafer 940 and the sensor wafer 910 below the heat resistant temperature of the bonding material.

  Specifically, the upper limit temperature is about 100 to 200 ° C. for an adhesive and about 150 ° C. for a double-sided tape. Further, from the viewpoint of simplifying the process, it is desirable that the ground and polished surface be bonded in a state where the film formation and the modification process are not performed. Joining satisfying such conditions includes room temperature direct joining and metal diffusion joining.

  In the room temperature direct bonding, the surface of the wafer is etched with an ion gun or an FAB (fast atom beam) gun to increase the activity, and then the wafer is bonded in a high vacuum. The feature of this technique is that bonding is possible at room temperature and the surface is suitable for bonding silicon to each other. Since the gas emitted from the bonding material is reattached to the surface and causes a significant drop in the bonding force, it is necessary to select a gas that does not generate the bonding material.

Metal diffusion bonding is a technique in which metal is attached to the surface of a substrate at the atomic layer level instead of increasing the surface activity by etching at room temperature direct bonding.
Bonding is performed under high vacuum in the same way as normal temperature direct bonding. In this joining, since different materials are only very thin and attached at the atomic layer level, joining can be performed without deteriorating the characteristics of the differential pressure sensor.

As a bonding technique at a low temperature, there is plasma activated bonding in addition to the technique described above.
Plasma activated bonding is performed with a plasma using a gas such as Ar, N ₂ , O _{2, and the} like, in a state where OH groups are arranged on the surfaces. The bonding strength is increased by annealing. In this technique, moisture generated due to OH groups causes voids. However, in a structure like a diaphragm having a small bonding area, moisture can be released from the bonding interface, and good bonding without voids can be realized.

FIG. 11G shows a peeling process of the support wafer 921.
The sensor wafer 910 and the base wafer 940 that are directly bonded after being thinly polished are separated from the support wafer 921. The method of peeling from the support wafer 921 differs depending on the adhesive used. For example, a thermoplastic adhesive is peeled off by sliding in a state where temperature is applied.

  In addition, the heat-releasable double-sided tape can be easily peeled off simply by applying heat. Although not shown, after peeling, it is desirable to clean the sensor element surface by spin cleaning, chemical immersion, or the like in order to remove the residue of the bonding material.

FIG. 11H shows a dicing process.
As a final wafer process, dicing is performed on the bonded wafer 960 from which the support wafer 921 has been peeled off after bonding. Thereby, the vibration type differential pressure sensor 800 is completed.

  As a result, the embodiment in FIG. 9 can realize a structure that further suppresses the stress concentration on the diaphragm 812 without reducing the effect of the embodiment in FIG.

The present invention has the following effects.
Since the thickness of the diaphragm 812 can be adjusted by grinding and polishing before joining, for example, the thickness of the diaphragm 812 can be easily controlled with an accuracy of about several um to sub um. Therefore, a vibration type differential pressure sensor that can suppress variation in sensitivity is obtained.

  Since different materials are not used for bonding, the bonded portion can achieve a fracture strength equivalent to the strength of the base metal of silicon. Therefore, a vibration type differential pressure sensor having excellent breakdown voltage characteristics can be obtained. In addition, since thermal distortion due to the difference in thermal expansion coefficient can be suppressed, a vibration type differential pressure sensor with good temperature characteristics can be obtained.

  An internal residual strain between different types of materials caused by temperature and pressure history is also suppressed, and a vibration type differential pressure sensor capable of realizing a structure without hysteresis is obtained. Since the gap can be determined by the depth of the recess 942 of the base wafer, a gap of, for example, several tens of um to sub um or less can be formed between the recess 835 of the base substrate and the diaphragm 812. Further, since the etching amount is small, the accuracy can be controlled with a high accuracy of about sub um.

As a result, the resonance of the diaphragm 812 can be prevented, and the movable range of the diaphragm is not limited due to foreign matter mixing in, so that a vibration type differential pressure sensor with excellent characteristics such as input / output characteristics can be obtained. In addition, if isotropic etching using plasma is used, the manufacturing process becomes simple, the stress concentration portion around the diaphragm can be rounded, and the breakdown voltage increases.
Therefore, a vibration type differential pressure sensor with reduced cost and high sensitivity can be obtained.

  For example, the shape of the recess 835 of several tens of um or less in the base substrate 830 becomes the shape of the diaphragm 812 as it is. Since there is no change in the diaphragm size or shape due to the (111) crystal plane, a free shape that is not restricted by the crystal orientation, such as a circle, can be produced.

  In particular, if isotropic etching using plasma is used, the manufacturing process becomes simple, a cost can be reduced, and a vibration type differential pressure sensor with high sensitivity can be obtained.

  In addition, since the thickness of the diaphragm 812 is determined by grinding and polishing, a mask that takes into consideration the difference in the shape of the diaphragm depending on the etching depth is not required unlike deep etching by alkali etching.

In other words, unlike alkaline etching, the same mask is used even when a product with a large inch size wafer (8 inches, 12 inches, etc.) is produced using a prototype result with a small inch size wafer (4 inches wafer, etc.). Since the same process as the pattern can be applied, the shift to mass production can be performed efficiently. Therefore, a method for manufacturing a vibration type differential pressure sensor independent of the inch size can be obtained.
Similarly, in response to a request to change the shape and thickness of the diaphragm 812 according to the pressure range, the diaphragm formation using the above-described room temperature direct bonding or metal diffusion bonding or the like depends on the shape and thickness of the diaphragm 812. It can be realized by the same process with the same mask.

  Since the manufacturing process of the diaphragm 812 including room temperature direct bonding or metal diffusion bonding for directly bonding silicon wafers is lower than the resistance temperature of the metal wiring disposed on the sensor wafer 910, the vibratory strain gauge Bonding is possible with the metal wiring process of the element completed.

  In addition, since the diaphragm manufacturing process including room temperature direct bonding or metal diffusion bonding can be configured at, for example, 400 degrees or less, silicon creep or thermal strain that affects the characteristics of the differential pressure sensor does not remain. Therefore, a method for manufacturing a vibration type differential pressure sensor having good characteristics can be obtained.

  The above description merely shows a specific preferred embodiment for the purpose of explanation and illustration of the present invention. Therefore, the present invention is not limited to the above-described embodiments, and includes many changes and modifications without departing from the essence thereof.

101 Monocrystalline silicon wafer 102 Diaphragm 400 Vibration type differential pressure sensor 410 Sensor substrate 411 Vibrating strain gauge element 412 Diaphragm 415 Upper surface 420 Diaphragm thickness 430 Base substrate 435 Concave portion 440 Concave portion size 445 Introduction hole 446 Fluid 460 Square 465 Circular 470 Polygon 510 Sensor wafer 521 Support wafer 522 Pasting material 531 Opposite surface 540 Base wafer 541 Pressure introduction hole 542 Recess 560 Bonded wafer 600 from which the port wafer is peeled Vibration type differential pressure sensor 610 Sensor substrate 611 Oscillator type Strain gauge element 612 Diaphragm 615 Upper surface 620 Diaphragm thickness 630 Base substrate 635 Recess 640 Size of recess 645 Introduction hole 646 Fluid 650 Round 660 Square 665 Yen 670 Polygon 710 Sensor wafer 721 Support wafer 722 Adhesive material 731 Opposite surface 740 Base wafer 741 Pressure introduction hole 742 Concave 760 Bonded wafer with peeled port wafer 800 Vibration type differential pressure sensor 810 Sensor substrate 811 Oscillator distortion Gauge element 812 Diaphragm 815 Upper surface 820 Diaphragm thickness 830 Base substrate 835 Recess 840 Size of recess 845 Introduction hole 846 Fluid 850 Round 860 Square 865 Circular 870 Polygon 910 Sensor wafer 921 Support wafer 922 Adhesive material 931 Opposite surface 932 Roundness 940 Base wafer 941 Pressure introduction hole 942 Recess 960 Bonded wafer with the port wafer peeled off

Claims (7)

A pressure sensor manufacturing method comprising the following steps.
(A) A step of forming a strain gauge element on one element surface of the sensor wafer.
(B) An attaching step in which a support wafer is attached to the element surface of the sensor wafer on which the strain gauge element is already formed.
(C) Grinding polishing surface is ground and polished by grinding and polishing process diaphragm is formed.
(D) A recess forming step of forming a recess having a predetermined gap on one surface of the base wafer.
(E) A bonding step of bonding the ground and polished surface and one surface of the base wafer.
(F) A support wafer peeling step of peeling the support wafer from the element surface. A pressure sensor manufacturing method comprising the following steps.
(A) A step of forming a strain gauge element on the element surface of the sensor wafer.
(B) An attaching step in which a support wafer is attached to the element surface of the sensor wafer on which the strain gauge element is already formed.
(C) Grinding polishing surface is ground and polished by grinding and polishing process diaphragm is formed.
(D) A patterning step of forming a recess having a predetermined gap on the ground and polished surface.
(E) the grinding polishing surface and the bonding step of bonding the base Suueha.
(F) A support wafer peeling step of peeling the support wafer from the element surface. In the step (a) of forming the strain gauge element,
Method of manufacturing a pressure sensor according to claim 1 or 2, characterized in that the metal wiring is formed on the element surface. In the pasting step (b),
The material for pasting is one of a thermoplastic adhesive, a chemical solution dissolving adhesive, a UV adhesive, a double-sided tape, and WAX,
The pasting accuracy is controlled by the difference between the minimum and maximum thickness in the wafer surface or the warpage in the wafer surface.
The method for manufacturing a pressure sensor according to claim 1, wherein the support wafer is one of sapphire, glass, and silicon. A cleaning step is provided after the grinding and polishing step (c),
In this cleaning step, either physical cleaning or acid-alkali cleaning is used, and the heat treatment is performed at a temperature lower than the heat resistant temperature of the pasting material.

The pressure sensor manufacturing method according to claim 1, wherein the physical cleaning is CO 2 cleaning or two-fluid cleaning. In the joining step (e),
2. The ground and polished surface and the base wafer are bonded at a temperature lower than the heat resistance temperature of the bonding material, and bonded by any one of normal temperature direct bonding, metal diffusion bonding, and plasma activated bonding. Or the manufacturing method of the pressure sensor of 2. In the support wafer peeling step (f), heat is applied to the sensor wafer and the support wafer,
3. The method of manufacturing a pressure sensor according to claim 1, wherein the element surface is cleaned by spin cleaning or chemical immersion after the support wafer peeling step (f).