JP2007292658A - Pressure sensor and manufacturing method of same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To compose a diaphragm as a pressure receiving plane by using a movable electrode, simplify a structure, and improve the detection precision. <P>SOLUTION: A capacitive pressure sensor has the movable electrode 3 for composing the diaphragm, a cavity 4, a fixed electrode 8, and first and second extraction electrodes 7, 9. The movable electrode 3 comprises a doped layer embedded in a silicon substrate 1, and is exposed from an opening 2 in the silicon substrate 1 at a diaphragm portion. The fixed electrode 8 comprises a doped layer bonded to the cavity and sealing the cavity 4. The first extraction electrode 7 is formed on a back face of the silicon substrate 1, and electrically connected to the movable electrode 3. The second extraction electrode 9 is formed on the back face of the fixed electrode 8, and electrically connected to the fixed electrode 8. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a capacitive pressure sensor in which a capacitance between electrodes changes depending on an applied pressure, and a manufacturing method thereof.

  Conventionally, as a technique related to a capacitive pressure sensor, for example, there are those described in the following documents.

Japanese Patent Laid-Open No. 10-332510

  This patent document 1 discloses a silicon wafer having a buried impurity region and a concave portion reaching the buried impurity region on a first surface, and a first surface formed on a second surface on the back side of the silicon wafer. A thin-film diaphragm made of silicon bonded so as to close the opening of the recess, and a second electrode formed on the diaphragm, and the cavity is closed by the recess being closed by the diaphragm A capacitive pressure sensor in which (air gap) is formed and a manufacturing method thereof are described.

  In this pressure sensor, when a pressure is applied, the diaphragm is bent, and the capacitance between the first electrode and the second electrode changes due to the bending, and the applied pressure is determined by measuring the change in the capacitance. It can be measured. And in a manufacturing process, it becomes unnecessary to join a glass pedestal to a silicon wafer by an anodic bonding method, and there exists an advantage that a pressure sensor can be manufactured, without generating Na ion which causes the pressure-resistant defect of a pressure sensor.

  The anodic bonding method is a bonding technique often used for mounting microsensors such as a pressure sensor. For example, when a voltage of about 1 KV is applied by connecting silicon to a positive electrode and a heat-resistant glass to a negative electrode, about 300 Bonding can be performed at an ambient temperature of ˜400 ° C. There is an advantage that strong bonding can be performed in a temperature range in which the electronic circuit on the silicon side is not broken, and a different material is not required at the bonding interface. However, there is a drawback in that Na ions contained in the glass are generated at the time of bonding, causing a pressure-resistant defect of the pressure sensor, and the technique of Patent Document 1 solves this.

  However, in the conventional pressure sensor described in Patent Document 1 and the like, since the second electrode is provided immediately above the diaphragm which is the pressure receiving surface, there is no problem in applications such as dry air, but acid, alkaline In this atmosphere, the wiring to the second electrode is corroded, or the displacement of the diaphragm is suppressed by the second electrode provided directly above this, adversely affecting the pressure detection characteristics and improving the reliability. There was a problem that it was difficult.

  The pressure sensor and the manufacturing method of the present invention have a movable electrode, a cavity, a fixed electrode, and first and second lead electrodes.

  The movable electrode is embedded in a semiconductor substrate having a first surface on the pressure receiving surface side and a second surface on the back side, and the first surface of the first surface and the second surface on the back side is the first surface. The impurity layer is exposed from the first surface. The cavity is opened on the second surface side of the second surface. The fixed electrode has a third surface on the bonding surface side and a fourth surface on the back side, and is composed of an impurity layer that seals the cavity by bonding the third surface to the cavity portion. The first lead electrode is formed on the second surface and is electrically connected to the movable electrode. Further, the second lead electrode is formed on the fourth surface and is electrically connected to the fixed electrode.

  Another pressure sensor of the present invention and this manufacturing method include a movable electrode, first and second connecting portions, a cavity, a fixed electrode, and first and second extraction electrodes.

  The movable electrode is embedded in a first semiconductor substrate having a first surface on the pressure-receiving surface side and a second surface on the back side, and the first surface and the second surface on the back side are the first surface. The surface is made of an impurity layer exposed from the first surface. The first connection portion is formed in the first semiconductor substrate, and includes an impurity region that is electrically connected to the movable electrode and exposed from the second surface. The second connection portion is formed in the first semiconductor substrate and includes an impurity region exposed from the second surface. The cavity is opened on the second surface side of the second surface.

  The fixed electrode is formed on the third surface side of a second semiconductor substrate having a third surface on the bonding surface side and a fourth surface on the back side, and is bonded to the cavity portion to seal the cavity. And an impurity layer electrically connected to the second connection portion. The first lead electrode is formed on the second surface and is electrically connected to the first connection portion. Further, the second lead electrode is formed on the second surface and is electrically connected to the second connection portion.

  The pressure sensor according to the first to third aspects of the present invention has the following effects (a) and (b).

  (A) Since the diaphragm, which is the pressure receiving surface, is composed of movable electrodes, the structure is simplified and the pressure detection characteristics can be improved.

  (B) Both the first extraction electrode of the movable electrode and the second extraction electrode of the fixed electrode are provided on the second surface of the semiconductor substrate and the fourth surface of the fixed electrode opposite to the pressure receiving surface. Therefore, it can be strong in humid, acidic and alkaline atmospheres. This is because it is easy to protect the extraction electrode portion that is most susceptible to corrosion from the atmosphere.

  According to the pressure sensor of the inventions according to claims 4 and 5, there are the same effects as the effects (a) of the inventions according to claims 1 to 3, and further, there are the following effects.

  Since both the first extraction electrode of the movable electrode and the second extraction electrode of the fixed electrode are provided on the second surface of the first semiconductor substrate opposite to the pressure receiving surface, the humidity, acidity, Can be strong in alkaline atmospheres. This is because it is easy to protect the extraction electrode portion that is most susceptible to corrosion from the atmosphere.

  According to the manufacturing method of the invention which concerns on Claim 6, 7, there exists an effect as following (c)-(f).

  (C) Since the thickness of the movable electrode constituting the diaphragm serving as the pressure receiving surface can be controlled by the thickness of the buried impurity layer, the movable electrode having a predetermined thickness can be formed with high accuracy.

  (D) It is easy to control the thickness of the cavity.

  (E) When the semiconductor substrate on which the movable electrode constituting the diaphragm is formed and the fixed electrode are bonded to each other, the movable electrode constituting the diaphragm is already processed even if the processing temperature is raised. Changes in the density profile (contour) are not a problem.

  (F) Since the bonding surface between the semiconductor substrate on which the movable electrode constituting the diaphragm is formed and the fixed electrode can be made uniform, bonding is easy and bonding strength can be improved. In particular, since the second lead electrode of the fixed electrode is provided on the fixed electrode side, conduction at the joint surface is unnecessary, and the joint surface can be made uniform. Therefore, any method such as anodic bonding or direct bonding can be adopted as the bonding method, and the manufacturing becomes easy.

  According to the manufacturing method of the invention concerning Claims 8 and 9, there are substantially the same effects as the effects (c) to (f) of the invention according to Claims 6 and 7, and further, there are the following effects.

  Since the position where the first and second lead electrodes are provided is on the second surface side of the first semiconductor substrate, it is easier to process than the inventions according to the sixth and seventh aspects.

  In the method of manufacturing a capacitive pressure sensor, first, a first surface of a movable electrode made of an impurity layer embedded in a silicon substrate having a first surface on the pressure-receiving surface side and a second surface on the back side, and Of the second surface, the silicon substrate on the first surface side is etched to expose the first surface from the first surface. Further, a cavity is formed by opening the second surface side of the second surface by etching. Next, the third surface of the fixed electrode made of an impurity layer having a third surface on the bonding surface side and a fourth surface on the back side is bonded to the cavity portion to seal the cavity. Thereafter, a first extraction electrode is formed on the second surface and electrically connected to the movable electrode, and a second extraction electrode is formed on the fourth surface and electrically connected to the fixed electrode. Connecting.

(Pressure sensor of Example 1)
FIGS. 1A and 1B are schematic configuration diagrams of a capacitive pressure sensor showing Embodiment 1 of the present invention, where FIG. 1A is a plan view and FIG. 2B is the same figure. It is the II-II sectional view taken on the line in (2).

  This capacitive pressure sensor includes a semiconductor substrate (for example, an N-type silicon substrate) 1 having a first surface (for example, a front surface) 1a on the pressure-receiving surface side and a second surface (for example, a back surface) 1b on the back side. A substantially circular movable electrode 3 constituting a diaphragm is embedded in the silicon substrate 1. The movable electrode 3 is composed of an impurity layer (for example, a P + type diffusion layer in which P + type impurity ions such as boron (B) are diffused), and the first surface (for example, the surface) 3a and the second side on the back side. A surface 3 a of the surface (for example, the back surface) 3 b is exposed from the opening 2 formed in the surface 1 a of the silicon substrate 1. On the back surface 1 b of the silicon substrate 1, the back surface 3 b side of the movable electrode 3 is opened to form a cavity 4. For this reason, the movable electrode 3 constituting the diaphragm is more greatly curved when pressure is applied.

  The movable electrode 3 is provided with a band-like connection portion 5 made of an impurity region (for example, a P + type region), and an end portion of the connection portion 5 extends from an opening 6 formed on the back surface 1 b of the silicon substrate 1. Exposed. A first extraction electrode 7 is formed at the exposed portion with aluminum (Al) or the like and is electrically connected to the connection portion 5.

  The cavity 4 is sealed by a fixed electrode 8 disposed to face the movable electrode 3. The fixed electrode 8 is an electrode that generates a capacitance with the movable electrode 3 and is formed of an impurity layer (for example, a silicon substrate in which N + type impurity ions such as phosphorus (P) are diffused at a high concentration). It has a third surface (for example, a front surface) 8a on the bonding surface side and a fourth surface (for example, a back surface) 8b on the back side, and the surface 8a is bonded to the cavity to seal the cavity 4. Yes. A second extraction electrode 9 such as Al is electrically connected to the back surface 8 b of the fixed electrode 8.

  In the pressure sensor having such a configuration, when a pressure is applied to the movable electrode 3 that is a diaphragm, the movable electrode 3 is curved in a concave shape to change the distance from the fixed electrode 8, and the movable electrode 3 and the fixed electrode 8 are changed. The capacitance between them changes. By measuring this change in capacitance, the applied pressure can be detected.

(Manufacturing method of pressure sensor of Example 1)
FIGS. 2-1 to 2-7 are schematic cross-sectional views of a manufacturing process showing an example of a manufacturing method of the pressure sensor of FIG. FIG. 3 is a schematic plan view showing a silicon wafer for fixed electrodes used in the manufacturing process of FIGS. 2-5.

  The pressure sensor of FIG. 1 is manufactured by, for example, the steps (1) to (20) shown in FIGS. 2-1 to 2-7.

  First, in step (1), insulating protective films (for example, oxide films or nitride films) 11 and 12 are respectively formed on the front surface and the back surface of an N-type silicon wafer (hereinafter simply referred to as “wafer”) 10. Form.

  In the step (2), the sensor formation portion in the protective film 11 on the surface side of the wafer 10 is etched by a photolithography process to form the opening 11a. Then, in the step (3), P + type impurity ions are formed from the opening 11a. (For example, B) is implanted, and the diaphragm movable electrode 3 made of a P + type diffusion layer is formed in the surface of the wafer 10. In step (4), the protective film 11 on the wafer surface is removed with an etching solution or the like, and then in step (5), single crystal silicon is grown on the wafer surface by a cavity height h by epitaxial growth to thereby move the movable electrode 3. Embed.

  In step (6), an insulating protective film (eg, oxide film or nitride film) 13 is formed on the surface of the grown wafer. The wafer 10 is turned upside down from the subsequent step (6-1). In step (7), an opening 13a is formed by etching a predetermined portion of the protective film 13 on the back surface of the wafer that has been turned upside down by a photolithography process. In step (8), P + type impurity ions (for example, B) are implanted from the opening 13a, and a connection portion 5 made of a P + type diffusion layer is formed in a region reaching the movable electrode 3 from the back surface of the wafer.

  In step (9), the protective film 13 is formed again on the back surface of the wafer to close the opening 13a. In step (10), an opening 12a is formed in the protective film 12 on the wafer surface at the movable electrode formation site and an opening 13b is formed in the protective film 13 on the back surface of the wafer by etching in the photolithography process.

  In step (11), the openings 12a and 13b (for example, the crystal axes 100 and 110) on both surfaces of the wafer reach the movable electrode 3 by a wet etching step using an alkaline etching solution such as potassium hydroxide (KOH). Remove. Thereby, the wafer 10 at the opening 12a on the front surface side is etched into a substantially inverted truncated cone at an oblique angle, the opening 2 on the pressure receiving surface side is formed, and the surface 3a of the movable electrode 3 is exposed, and the back surface side The wafer 10 at the position of the opening 13b is etched into a substantially frustoconical shape to form an opening for the cavity 4, and the back surface 3b of the movable electrode 3 is exposed. Since the rate of wet etching decreases when reaching the movable electrode 3 (for example, the crystal axis 111) made of the buried P + type diffusion layer, the thickness of the movable electrode 3 for the diaphragm is the thickness of the buried P + type diffusion layer. Determined by

  In step (12), the protective films 12 and 13 on both surfaces of the wafer are removed with an etching solution or the like. In step (13), protective films (for example, thermal oxide films or nitride films) 14 and 15 are formed on both surfaces of the wafer again, and then in step (14), the opening 2 on the wafer surface and the cavity 4 on the back surface of the wafer. The protective films 14 and 15 at portions other than the opening for etching are removed by etching.

  In step (15), a silicon wafer (hereinafter simply referred to as “wafer”) 20 for forming a fixed electrode as shown in FIG. 3 is prepared in advance. The entire wafer 20 is diffused with N + type impurity ions (for example, P) at a high concentration, and a large number of vertical and horizontal grooves 21 are cut in a half cut state on the surface to form a large number of rectangular fixed electrodes. Region 22 is formed. Note that the width of the groove 21 in step (15) in FIG. 2-5 is drawn larger than the corresponding portion in FIG. 3 in order to make the drawing easier to see. The fixed electrode forming region 22 on the front surface side of the wafer 20 and the cavity opening on the back surface on the wafer 10 side are overlapped and bonded in a vacuum. Since conduction at this joining surface is not required, any joining method such as a direct joining method by heating or an anodic joining method can be adopted.

  For example, the direct bonding method is suitable for silicon (Si) -silicon (Si) bonding, no intermediate material is required or silicon dioxide (Si02), heating and pressure are required, the interface is a solid phase, Although the applied pressure is low, a high temperature (for example, 1000 ° C. or higher) is required, and it can be applied to metals and ceramics in addition to Si (in this case, generally referred to as diffusion bonding).

  When the fixed electrode forming region 22 is joined to the cavity opening in a vacuum, the cavity opening is sealed to form the vacuum cavity 4. The reason why the inside of the cavity 4 is in a vacuum state is to use it as a reference for absolute pressure, and it is important in terms of sensor accuracy that there is no leakage in the cavity 4 and that no stress remains. Next, in step (16), the vertical and horizontal grooves 21 are cut from the back surface of the wafer 20 to separate the fixed electrode formation regions 22 to form the fixed electrodes 8, respectively. In step (17), Protective films (for example, thermal oxide films or nitride films) 16 and 17 are formed on both surfaces of the wafer with fixed electrodes, respectively.

  In step (18), the protective film 17 at the location of the connection portion 5 on the back surface side of the wafer 10 is removed by etching in the photolithography process to form the opening 6 and the protective film 17 on the back surface side of the fixed electrode 8. Is removed by etching to form an opening 17a. After a metal film such as Al is formed on the entire back surface of the wafer 10 and the fixed electrode 8, the portions other than the openings 6 and 17a are removed by etching to form a lead electrode 7 in the opening 6 and lead out to the opening 17a. Electrode 9 is formed.

  In step (19), after each fixed electrode portion 10a in wafer 10 is cut by dicing and separated into silicon substrates 1, in step (20), if a protective film is deposited, a plurality of pressure sensors are obtained. Is completed.

(Effect of Example 1)
The pressure sensor according to the first embodiment has the following effects (a) and (b).

  (A) Since the diaphragm which is the pressure receiving surface is constituted by the movable electrode 3, the structure becomes simple and the pressure detection characteristics can be improved.

  (B) Since both the extraction electrode 7 of the movable electrode 3 and the extraction electrode 9 of the fixed electrode 8 are provided on the back surface of the silicon substrate 1 opposite to the pressure receiving surface and the back surface of the fixed electrode 8, It can be strong against acidic and alkaline atmospheres. This is because it is easy to protect the extraction electrode portion that is most susceptible to corrosion from the atmosphere.

  According to the manufacturing method of the first embodiment, the following effects (c) to (f) are obtained.

  (C) In step (3), since the thickness of the movable electrode 3 constituting the diaphragm which is the pressure receiving surface can be controlled by the thickness of the embedded impurity, the movable electrode 3 having a predetermined thickness can be formed with high accuracy.

  (D) Since the thickness of the cavity 4 is determined by the accumulation distance (cavity height h) of epitaxial growth in the step (5), the thickness can be easily controlled. Further, in the epitaxial growth, the step difference of the wafer 10 due to the growth rate of Si between the place where there is buried diffusion and the place where there is no buried diffusion is not a problem because the cavity portion is removed by etching in the step (11).

  (E) Even in the step (15), when the wafer 10 on which the movable electrode 3 constituting the diaphragm is formed and the wafer 20 grooved in the vertical and horizontal directions at a predetermined interval are bonded, the processing temperature may be increased. Since the movable electrode 3 constituting the diaphragm is already processed, a change in the profile of the impurity concentration is not a problem.

  (F) In the step (15), since the bonding surface between the wafer 10 and the wafer 20 is a uniform surface, the bonding is easy and the bonding strength can be improved. In particular, since the lead electrode 9 of the fixed electrode 8 is provided on the back surface side of the fixed electrode 8, conduction at the joint surface is not necessary, and the joint surface can be made uniform. Therefore, any method such as anodic bonding or direct bonding can be adopted as the bonding method, and the manufacturing becomes easy.

(Pressure sensor of Example 2)
FIGS. 4A and 4B are schematic configuration diagrams of a capacitive pressure sensor showing Example 2 of the present invention, where FIG. 4A is a plan view and FIG. It is the III-IV sectional view taken on the line in (1). 4 (1) and 4 (2), elements common to those in FIG. 1 showing the first embodiment are denoted by common reference numerals.

  As in the first embodiment, the capacitive pressure sensor includes a first semiconductor substrate (a first surface (for example, a front surface) 1a on the pressure-receiving surface side and a second surface (for example, a back surface) 1b on the back side. For example, an N-type silicon substrate) 1 is provided, and a substantially circular movable electrode 3 constituting a diaphragm is embedded in the silicon substrate 1. Similar to the first embodiment, the movable electrode 3 is formed of an impurity layer (for example, a P + type diffusion layer in which P + type impurity ions such as B are diffused), and the first surface (for example, the surface) 3a and the back side thereof. The surface 3a of the second surface (for example, the back surface) 3b is exposed from the opening 2 formed in the surface 1a of the silicon substrate 1. Similar to the first embodiment, the cavity 4 is formed on the back surface 1 b of the silicon substrate 1 by opening the back surface 3 b side of the movable electrode 3. For this reason, the movable electrode 3 constituting the diaphragm is more greatly curved when pressure is applied.

  Unlike the first embodiment, the movable electrode 3 is provided with a strip-shaped first connection portion 5-1 made of an impurity region (for example, a P + type region), and further, an impurity region separated from the movable electrode 3 ( For example, a second connection portion 5-2 for connecting a fixed electrode made of a P + type region) is provided. The end of the first connection portion 5-1 is exposed from the opening 6-1 formed in the back surface 1b of the silicon substrate 1, and the second connection portion 5-2 is further connected to the back surface 1b of the silicon substrate 1. It is exposed from the opening 6-2 formed in. A first extraction electrode 7-1 is formed of Al or the like at the exposed portion of the opening 6-1 and is electrically connected to the connection portion 5-1, and also at the exposed portion of the opening 6-2. The second extraction electrode 7-2 is formed of Al, etc., and is electrically connected to the connection portion 5-2.

  Unlike the first embodiment, the cavity 4 is sealed with a second semiconductor substrate (for example, an N-type silicon substrate) 20A-1 disposed so as to face the movable electrode 3. The silicon substrate 20A-1 has a third surface (for example, a front surface) 20A-1a that seals the cavity 4, and a fourth surface (for example, a back surface) 20A-1b on the back side, and the surface 20A. The fixed electrode 8A is formed in -1a. The fixed electrode 8A is an electrode that generates a capacitance with the movable electrode 3, and is formed by an impurity layer (for example, a diffusion layer in which P + type impurity ions such as P are diffused at a high concentration). The fixed electrode 8A is electrically connected to the connection portion 5-2 in the silicon substrate 1, and the connection portion 5-2 is electrically connected to the extraction electrode 7-2 through the opening 6-2. .

  In the pressure sensor having such a configuration, as in the first embodiment, when pressure is applied to the movable electrode 3 that is a diaphragm, the movable electrode 3 is curved in a concave shape and the distance from the fixed electrode 8A is changed. The electrostatic capacitance between the movable electrode 3 and the fixed electrode 8A changes. By measuring this change in capacitance, the applied pressure can be detected.

(Manufacturing method of pressure sensor of Example 2)
FIGS. 5-1 to 5-7 are schematic cross-sectional views of the manufacturing process showing an example of the manufacturing method of the pressure sensor of FIG. 4, and FIGS. 2-1 to 2-7 showing the manufacturing process of the first embodiment. Elements common to the elements inside are given common reference numerals.

  The pressure sensor of FIG. 4 is manufactured by, for example, the steps (1) to (20) shown in FIGS.

  First, in step (1), insulating protective films (for example, oxide films or nitride films) 11 and 12 are respectively formed on the front surface and the back surface of an N-type silicon wafer (hereinafter simply referred to as “wafer”) 10. The steps from the forming step to the step (6-1) are the same as the steps (1) to (6-1) of the first embodiment.

  In step (7), a predetermined portion of the protective film 13 on the reverse side of the wafer that has been turned over is etched by a photolithography process to form an opening 13a, and an opening 13b is also formed at a position away from the opening 13a. . In step (8), P + type impurity ions (for example, B) are implanted from the openings 13a and 13b, and the connection portion 5 made of a P + type diffusion layer is formed in the region reaching the movable electrode 3 from the back surface of the wafer via the opening 13a. -1 is formed, and a connection portion 5-2 made of a P + type diffusion layer is formed in a predetermined region from the back surface of the wafer through the opening 13b.

  In step (9), the protective film 13 is formed again on the back surface of the wafer to close the openings 13a and 13b. In the step (10), as in the step (10) of the first embodiment, an opening 12a is formed in the protective film 12 on the front surface of the wafer at the position where the movable electrode is formed by etching in the photolithography process, and the protective film on the rear surface of the wafer is formed. An opening 13 b is formed in 13.

  In the step (11), the openings 12a and 13b on both surfaces of the wafer are removed until reaching the movable electrode 3 by a wet etching step using an etching solution such as KOH as in the step (11) of the first embodiment. Thereby, the opening 2 on the pressure receiving surface side is formed and the surface 3a of the movable electrode 3 is exposed, and the opening for the cavity 4 is formed and the back surface 3b of the movable electrode 3 is exposed.

  In the step (12), unlike the step (12) of the first embodiment, only the protective film 12 on the wafer surface is removed by etching. In step (13), after forming protective films (for example, thermal oxide film or nitride film) 14 and 13 on both surfaces of the wafer again, the wafer in step (14) is different from step (14) in the first embodiment. The front surface is coated (coated) with a protective material, and the protective film 13 on the back surface of the wafer is removed by wet etching such as hydrofluoric acid.

  In step (15), an N-type silicon wafer (hereinafter simply referred to as “wafer”) 20A different from that of the first embodiment is prepared in advance. A P + type diffusion layer for a fixed electrode in which P + type impurity ions (for example, P) are diffused at a high concentration is formed in the surface of the wafer 20A, and the vertical direction and the horizontal direction with respect to the P + type diffusion layer. A large number of grooves 21 are cut in a half-cut state to form a large number of rectangular fixed electrodes 8A, and a protective film (for example, an oxide film or a nitride film) 23 is formed on the back surface of the wafer 20A. In addition, the width | variety of the groove | channel 21 in the process (15) of FIGS. 5-5 is drawn larger than the corresponding location of FIG. 3 similarly to FIG. 2-5.

  The fixed electrode 8A on the front surface side of the wafer 20A and the cavity opening and the connection portion 5-2 on the back surface on the wafer 10 side are overlapped and bonded in a vacuum. On this bonding surface, conduction between the fixed electrode 8A and the connection portion 5-2 is necessary, and therefore, a direct bonding method by heating is desirable as a bonding method. When the fixed electrode 8A is joined to the cavity opening and the connection part 5-2 in vacuum, the cavity opening is sealed to form the cavity 4 in a vacuum state, and the fixed electrode 8A and the connection part 5-2 are also formed. Are electrically connected.

  In the step (16), substantially in the same manner as in the step (16) of the first embodiment, the vertical and horizontal grooves 21 are cut from the back surface of the wafer 20A to form silicon substrates 20A-1 in which the respective fixed electrodes 8A are separated. After that, in step (17), as in step (17) of the first embodiment, protective films (for example, thermal oxide films or nitride films) 16 and 17 are formed on both surfaces of the wafer with fixed electrodes, respectively.

  In the step (18), unlike the step (18) in the first embodiment, the protective film 17 at the connection portions 5-1 and 5-2 on the back side of the wafer 10 is removed by etching and opened by a photolithography step. The parts 6-1 and 6-2 are formed, respectively. After a metal film such as Al is formed on the back surface of the wafer 10, the portions other than the openings 6-1 and 6-2 are removed by etching to form a lead electrode 7-1 in the opening 6-1 and the opening. The extraction electrode 7-2 is formed on 6-2.

  In step (19), the inter-sensor portions 10a of the wafer 10 are cut by dicing and separated into silicon substrates 1 in substantially the same manner as in step (19) of the first embodiment. As in the first step (20), when a protective film is deposited, a plurality of pressure sensors are completed.

(Effect of Example 2)
The pressure sensor according to the second embodiment has the following effects (a) and (b).

  (A) Since the diaphragm which is a pressure receiving surface is comprised by the movable electrode 3 similarly to Example 1, a structure becomes simple and the characteristic of pressure detection can be improved.

  (B) In substantially the same manner as in Example 1, both the extraction electrode 7-1 of the movable electrode 3 and the extraction electrode 7-2 of the fixed electrode 8A are provided on the back surface of the silicon substrate 1 opposite to the pressure receiving surface. Therefore, it can be strong in humid, acidic and alkaline atmospheres. This is because it is easy to protect the extraction electrode portion that is most susceptible to corrosion from the atmosphere.

  According to the manufacturing method of Example 2, the following effects (c) to (g) are obtained.

  (C) In the same manner as in the first embodiment, in the step (3), the thickness of the movable electrode 3 constituting the diaphragm which is the pressure receiving surface can be controlled by the thickness of the embedded impurity, and therefore the movable electrode 3 having a predetermined thickness. Can be formed with high accuracy.

  (D) As in Example 1, the thickness of the cavity 4 is determined by the stacking distance (cavity height h) of the epitaxial growth in the step (5), so that the thickness can be easily controlled. Further, in the epitaxial growth, the step difference of the wafer 10 due to the growth rate of Si between the place where there is buried diffusion and the place where there is no buried diffusion is not a problem because the cavity portion is removed by etching in the step (11).

  (E) When joining the wafer 10 on which the movable electrode 3 constituting the diaphragm is formed and the wafer 20A grooved in the vertical and horizontal directions at a predetermined interval in the step (15), as in the first embodiment. In addition, even if the processing temperature is raised, since the movable electrode 3 constituting the diaphragm is already processed, a change in the impurity concentration profile does not become a problem.

  (F) In substantially the same manner as in Example 1, in the step (15), since the bonding surface between the wafer 10 and the wafer 20A is made uniform, the bonding is easy and the bonding strength can be improved. In particular, since the lead electrode 7-2 of the fixed electrode 8A is provided on the back side of the wafer 10, conduction at the joint surface between the lead electrode 7-2 and the connection portion 5-2 is required. Therefore, the direct bonding method is desirable as the bonding method, which facilitates manufacturing.

  (G) Since the positions where the first and second lead electrodes 7-1 and 7-2 are provided are on the same plane on the back surface of the wafer, the processing is easier than in the first embodiment.

(Modification)
The present invention is not limited to the first and second embodiments, and various usage forms and modifications are possible. For example, there are the following forms (i) and (ii) as usage forms and modifications.

  (I) The shape and structure of the pressure sensor of FIGS. 1 and 4 may be changed to other shapes and structures. For example, the fixed electrode 8A in FIG. 4 may be formed on the entire silicon substrate 20A-1 like the fixed electrode 8 in FIG.

  (Ii) In the manufacturing steps of FIGS. 2-1 to 2-7 and FIGS. 5-1 to 5-7, the materials used, the manufacturing method, the manufacturing conditions, and the like can be arbitrarily changed.

It is a block diagram of the pressure sensor which shows Example 1 of this invention. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is a top view which shows the silicon wafer for fixed electrodes used at the manufacturing process of FIGS. 2-5. It is a block diagram of the pressure sensor which shows Example 2 of this invention. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG. It is sectional drawing of the manufacturing process which shows the example of a manufacturing method of the pressure sensor of FIG.

Explanation of symbols

1,20A silicon substrate 3 movable electrode 4 cavity 5,5-1,5-2 connection portion 7,7-1,7-2,9 lead electrode 8,8A fixed electrode

Claims (9)

The first surface is embedded in a semiconductor substrate having a first surface on the pressure-receiving surface side and a second surface on the back side, and the first surface of the first surface and the second surface on the back side is separated from the first surface. A movable electrode comprising an exposed impurity layer;
A cavity opened on the second surface side of the second surface;
A fixed electrode comprising an impurity layer having a third surface on the bonding surface side and a fourth surface on the back side, the third surface being bonded to the cavity portion and sealing the cavity;
A first extraction electrode formed on the second surface and electrically connected to the movable electrode;
A second lead electrode formed on the fourth surface and electrically connected to the fixed electrode;
A pressure sensor comprising:   2. The pressure sensor according to claim 1, wherein the first lead electrode is electrically connected to the movable electrode through a connection portion including an impurity region.   The pressure sensor according to claim 1, wherein the semiconductor substrate and the fixed electrode are silicon substrates. The first surface is embedded in a first semiconductor substrate having a first surface on the pressure-receiving surface side and a second surface on the back side, and the first surface of the first surface and the second surface on the back side is the first surface. A movable electrode comprising an impurity layer exposed from the surface of
A first connecting portion formed in the first semiconductor substrate and made of an impurity region that is electrically connected to the movable electrode and exposed from the second surface;
A second connection portion formed in the first semiconductor substrate and made of an impurity region exposed from the second surface;
A cavity opened on the second surface side of the second surface;
Formed on the third surface side of a second semiconductor substrate having a third surface on the bonding surface side and a fourth surface on the back side, and bonded to the cavity portion to seal the cavity and A fixed electrode made of an impurity layer electrically connected to the two connecting portions;
A first extraction electrode formed on the second surface and electrically connected to the first connection portion;
A second lead electrode formed on the second surface and electrically connected to the second connection portion;
A pressure sensor comprising:   The pressure sensor according to claim 4, wherein the first and second semiconductor substrates are silicon substrates. Of the first surface of the movable electrode made of an impurity layer embedded in the semiconductor substrate having the first surface on the pressure-receiving surface side and the second surface on the back side, and the second surface on the back side, the first surface Etching the semiconductor substrate on the surface side to expose the first surface from the first surface;
Forming a cavity by opening the second surface side of the second surface by etching; and
Bonding the third surface of the fixed electrode composed of an impurity layer having a third surface on the bonding surface side and a fourth surface on the back side to the cavity portion and sealing the cavity;
A first lead electrode is formed on the second surface and electrically connected to the movable electrode, and a second lead electrode is formed on the fourth surface and electrically connected to the fixed electrode. Process,
A method for manufacturing a pressure sensor, comprising:   The pressure sensor according to claim 6, wherein the semiconductor substrate and the fixed electrode are silicon substrates, and the third surface and the cavity portion are bonded by a direct bonding method or an anodic bonding method by heating. Manufacturing method. Of the first surface of the movable electrode made of an impurity layer embedded in the first semiconductor substrate having the first surface on the pressure-receiving surface side and the second surface on the back side, and the second surface on the back side, Etching the first semiconductor substrate on the first surface side to expose the first surface from the first surface;
A first connection portion made of an impurity region electrically connected to the movable electrode is formed in the first semiconductor substrate and exposed from the second surface, and a second connection portion made of the impurity region is formed. Forming a connection portion in the first semiconductor substrate and exposing the connection portion from the second surface;
Forming a cavity by opening the second surface side of the second surface by etching; and
A fixed electrode made of an impurity layer formed on the third surface side of the second semiconductor substrate having a third surface on the bonding surface side and a fourth surface on the back side is bonded to the cavity portion, Sealing the cavity and electrically connecting to the second connection;
A first lead electrode is formed on the second surface and electrically connected to the first connection portion, and a second lead electrode is formed on the second surface to form the second connection portion. Electrically connecting with
A method for manufacturing a pressure sensor, comprising:   9. The method of manufacturing a pressure sensor according to claim 8, wherein the first and second semiconductor substrates are silicon substrates, and the fixed electrode and the cavity portion are bonded by a direct bonding method by heating.

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