JP2007033304A - Production method of pressure sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a production method of pressure sensors forming pressure detector elements with high fineness by avoiding focus gap on photo engraving caused by distortion of diaphragms in the pressure sensors where pressure detector elements are prepared in a diaphragm. <P>SOLUTION: The production method of pressure sensors is made to include: a process of thinning a layer from the rear side after forming a pressure detector element 5 on a front side of a first semi-conductor substrate 1, where the pressure detector element 5 of the first semi-conductor substrate 1 is not formed; a process of establishing a recess portion by removing a part of an insulated layer 2 after forming an insulated layer 2 on a second semi-conductor substrate 3; and a process of forming a diaphragm by joining the first semi-conductor substrate 1 thinning-layered with the insulated layer 2 on the second semi-conductor substrate 3. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention belongs to the technical field of pressure sensors in which a diaphragm is provided with a pressure detector, and particularly relates to a method of manufacturing a pressure sensor in which the pressure detector is formed with high definition.

  As a pressure sensor using a semiconductor, a sensor using a diaphragm in which a semiconductor substrate is thinned by etching is used as a deformation portion with respect to pressure. The diaphragm is provided with a pressure detection unit in order to detect a pressure change based on the amount of deformation.

  In a conventional pressure sensor manufacturing method, after forming a cavity in the first semiconductor substrate, the cavity side is bonded to the second semiconductor substrate in a vacuum, and the first semiconductor substrate is thinned by etching, whereby the diaphragm is formed. Is forming. At this time, the inside of the cavity becomes a pressure reference chamber. After the diaphragm is formed, a pressure sensor is formed using a normal IC manufacturing process to obtain a pressure sensor (see, for example, Patent Document 1).

JP 2000-39371 A (paragraph numbers 0016 to 0024, FIGS. 3 and 4)

  However, in the conventional pressure sensor manufacturing method, after bonding the first semiconductor substrate and the second semiconductor substrate, the first semiconductor substrate is thinned to a desired thickness to form a diaphragm. In this case, particularly when the pressure reference chamber is a vacuum, the diaphragm is distorted due to the difference in pressure between the pressure reference chamber and the outside air as the first semiconductor substrate becomes thinner. For this reason, it is necessary to pattern the pressure detection portion by lithography on the distorted surface of the diaphragm, and lithography shifts in focus. Therefore, there is a problem that it is difficult to form the pressure detection portion with high definition.

  The present invention has been made to solve the above-mentioned problems, and a pressure sensor manufacturing method for forming a pressure detection unit with high definition by avoiding lithography focus deviation caused by diaphragm distortion. I will provide a.

  In the pressure sensor manufacturing method according to the present invention, after the pressure detector is formed on the front side of the first semiconductor substrate, the thickness of the first semiconductor substrate is reduced from the back side where the pressure detector is not formed. And after forming an insulating layer on the second semiconductor substrate, removing a part of the insulating layer to provide a recess, and on the thinned first semiconductor substrate and the second semiconductor substrate Forming a diaphragm so that the position of the pressure detection unit matches the region of the recess when the insulating layer is bonded.

  According to the present invention, the first semiconductor substrate is thinned after forming the pressure detection portion on the first semiconductor substrate, and then the thinned first semiconductor substrate and the insulating layer of the second semiconductor substrate are Since the diaphragm is formed by bonding, the pressure sensor manufacturing method can be provided in which the focus detection of the lithography due to the distortion of the diaphragm is avoided and the pressure detection part is formed with high definition.

Embodiment 1
FIG. 1 is a cross-sectional view of a pressure sensor for explaining the first embodiment. This pressure sensor is an absolute pressure sensor and has a three-layer structure including a single crystal silicon thin plate 1 as a first semiconductor substrate, an insulating layer 2 and a single crystal silicon support substrate 3 as a second semiconductor substrate. The recess provided by removing a part of the insulating layer 2 is sandwiched between the single crystal silicon thin plate 1 and the single crystal silicon support substrate 3 to form a cavity region, and this cavity region functions as the pressure reference chamber 4. A region corresponding to the pressure reference chamber 4 in the single crystal silicon thin plate 1 functions as a diaphragm that deforms according to the pressure difference between the pressure reference chamber 4 and the outside air. The strain gauge 5 as the pressure detection unit can convert the deformation amount of the diaphragm into a resistance change. The atmospheric pressure can be detected from this resistance change.

2 to 4 are process diagrams for explaining the manufacturing method of the pressure sensor.
In FIG. 2A, a strain gauge 5 is formed on a single crystal silicon substrate 1 as a first semiconductor substrate before being thinned by a semiconductor process. Here, the side on which the strain gauge 5 is formed is the front side of the single crystal silicon substrate 1. The strain gauge 5 may be a metal thin film such as a NiCr thin film, or can be formed by providing a conductive region opposite to the single crystal silicon substrate 1 by ion implantation. For example, the strain gauge 5 can be formed by injecting boron into an N-type substrate to form a P region.

  In FIG. 2B, the single crystal silicon thin plate 1 is formed by thinning from the back side where the strain gauge 5 of the single crystal silicon substrate 1 is not formed. An example of the thinning method is mechanical chemical polishing (CMP). In this case, since the processing surface is applied to the extreme outermost surface of the polished surface, the mechanical strength decreases. Therefore, it is desirable to use wet etching in order to remove the processing strain layer after CMP. For example, the processing strain layer on the polished surface can be removed by spraying a mixed solution of hydrofluoric acid, nitric acid, and water (by volume ratio, hydrofluoric acid: nitric acid: water = 5: 3: 125). In this manner, the single crystal silicon thin plate 1 thinned to a desired thickness is obtained. The thickness of the single crystal silicon thin plate 1 varies depending on the specifications of the pressure sensor, but when the diaphragm is 400 μm square, a thickness of about 10 μm is suitable for a pressure sensor in the 1 atm range. In addition, by combining CMP and wet etching, the thickness accuracy of the single crystal silicon thin plate 1 can be achieved within ± 1 μm, and the stability of the sensitivity of the pressure sensor is improved.

  In FIG. 3A, the insulating layer 2 is formed on the single crystal silicon support substrate 3. As the insulating layer 2, borosilicate glass having a thermal expansion coefficient close to that of silicon is suitable. As a method of forming the insulating layer 2, a sputtering method or a method of sintering by spin coating is suitable. In the formation of the insulating film 2 made of borosilicate glass by the sputtering method, a sputtering method by plasma excitation by a high frequency power source is suitable, and a mixed gas atmosphere of argon and oxygen (gas flow ratio, argon: oxygen = 9: 1). ) Is good. Furthermore, a smooth glass thin film can be obtained by annealing at about 300 ° C. after film formation.

  In FIG. 3B, a part of the insulating layer 2 is removed by etching to provide a recess. As an etching technique, hydrofluoric acid wet etching using a photosensitive resin as an etching mask and plasma etching using SF6 gas are suitable. Here, there is no problem if not only the insulating layer 2 but also the surface layer of the single crystal silicon supporting substrate 3 is etched. However, since it is an absolute pressure sensor, it must not penetrate the single crystal silicon support substrate 3.

  Next, in FIG. 4A, the back side of the single crystal silicon thin plate 1 obtained in FIG. 2 and the insulating layer 2 on the single crystal silicon support substrate 3 obtained in FIG. Are bonded in a vacuum so as to fit in the region of the recess. As a result, a diaphragm is formed. Here, when the borosilicate glass as the insulating layer 2 contains about 4% by weight of sodium oxide, an anodic bonding method can be applied as a bonding method, which facilitates bonding between silicon and glass, and reliability of vacuum sealing. Will increase. As an example of the anodic bonding method, a negative voltage is applied to the insulating layer 2 and a positive voltage or 0 V is applied to the single crystal silicon thin plate 1, and a voltage of 300 V is applied in a vacuum atmosphere at about 400 ° C. for about 2 hours. As a result, the hollow region composed of the recesses is joined in a vacuum state, and the pressure reference chamber 4 is formed. The amount of deformation of the diaphragm single crystal silicon thin plate 1 is determined by the pressure difference between the pressure reference chamber 4 and the outside air, and the pressure reference chamber 4 is maintained in a vacuum state, so that this configuration functions as an absolute pressure sensor.

  In such a pressure sensor manufacturing method, since the strain gauge 5 is formed on the sufficiently thick single crystal silicon substrate 1 before being thinned, no focus shift occurs when the strain gauge 5 is patterned by lithography. That is, the strain gauge 5 can be formed with high definition while avoiding the focus shift of lithography due to the distortion of the diaphragm. In addition, since the strain gauge 5 is exposed to the outside air, the strain gauge 5 and the external circuit can be easily connected.

  Furthermore, since the polishing is performed in a state where the diaphragm is not bent due to the pressure difference from the outside, the thickness of the diaphragm can be uniformly controlled, and a method for manufacturing a pressure sensor with small performance variation can be provided.

  In FIG. 4B, an insulating protective film 6 is formed on the surface of the strain gauge 5. Thereby, the environmental resistance is improved. For example, it is possible to prevent electrical leakage from occurring due to adhesion of a conductive liquid to the strain gauge 5.

Embodiment 2
FIG. 5 is a cross-sectional view of a pressure sensor for explaining the second embodiment. This embodiment is a modification in which the strain gauge 5 in the first embodiment is provided in the pressure reference chamber 4. That is, in FIG. 5, the front side of the single crystal silicon thin plate 1 obtained in FIG. 2 and the insulating layer 2 on the single crystal silicon support substrate 3 obtained in FIG. 3 are joined in a vacuum to form a diaphragm. ing.

  Thus, by providing the strain gauge 5 in the pressure reference chamber 4, sufficient environmental resistance can be obtained without covering the strain gauge 5 with the insulating protective film. Since there is no insulating protective film, good sensitivity as a pressure detection part of the strain gauge 5 can be maintained.

  Here, in order to take out the resistance change of the strain gauge 5 to the external circuit, a configuration shown in FIG. 6 will be described as a first example of electrical connection between the strain gauge 5 and the external circuit. In FIG. 6, on the front side of the single crystal silicon thin plate 1, an electrode pad 11 is formed around the junction between the single crystal silicon thin plate 1 and the insulating layer 2 on the single crystal silicon support substrate 3. The strain gauge 5 and the electrode pad 11 are electrically connected through a wiring 7 made of a diffusion resistor formed on the front side of the single crystal silicon thin plate 1. The electrode pad 11 and the wiring 7 are formed by a semiconductor process.

  Here, the layout and the sheet resistance are devised so that the wiring 7 has a sufficiently low resistance as compared with the strain gauge 5. If the sheet resistance of the wiring 7 is set to several tens of Ω / □, the resistance change amount with respect to the strain generated in the diffusion resistance portion can be sufficiently reduced with respect to the resistance change amount generated in the strain gauge 5.

  An electrode pad 13 is also formed on the mounting substrate 12 on which the pressure sensor is mounted. If the electrode pad 11 and the electrode pad 13 are connected using the solder 14, the sensor mounting by the flip chip becomes easy.

  Furthermore, in order to take out the resistance change of the strain gauge 5 to the external circuit, a configuration shown in FIG. 7 will be described as a second example of electrical connection between the strain gauge 5 and the external circuit. In FIG. 7, on the single crystal silicon support substrate 3, an electrode pad 16 is formed around the junction between the single crystal silicon thin plate 1 and the insulating layer 2 on the single crystal silicon support substrate 3. The strain gauge 5 and the electrode pad 16 are electrically connected via a conductive sheet 15 and a wiring 7 made of a diffusion resistor formed on the front side of the single crystal silicon thin plate 1. The conductive sheet 15 is sandwiched between the single crystal silicon thin plate 1 and the single crystal silicon support substrate 3 when the single crystal silicon thin plate 1 and the insulating layer 2 are joined.

  In such a pressure sensor, connection from the electrode pad 16 on the single crystal silicon support substrate 3 to an external circuit is performed by wire bonding. Therefore, it can be easily connected.

Embodiment 3
FIG. 8 is a cross-sectional view of a pressure sensor for explaining the third embodiment. This embodiment is a modification in which a differential pressure sensor is formed by forming a through hole in the single crystal silicon support substrate 3 in the first embodiment. That is, in FIG. 8, after part of the insulating layer 2 of the single crystal silicon support substrate 3 is removed and provided in the recess, the single crystal silicon support substrate 3 is also etched, so that the entire region or part of the bottom surface of the recess is formed. A through hole 17 passing through the region is formed.

  As an etching method of the single crystal silicon substrate 3, there is high-density plasma etching. For example, the through hole 17 can be formed by reactive etching mainly using SF 6 gas by an inductive coupling type plasma excitation method. Other methods include wet etching with an alkaline solution.

  After the through hole 17 is formed in this way, the single crystal silicon thin plate 1 and the insulating layer 2 on the single crystal silicon support substrate 3 are bonded by, for example, an anodic bonding method. The pressure sensor manufactured according to this embodiment functions as a differential pressure sensor because the deformation amount of the diaphragm is determined by the pressure difference between the front side and the back side of the single crystal silicon thin plate 1.

3 is a cross-sectional view of a pressure sensor for explaining the first embodiment. FIG. FIG. 6 is a process diagram for illustrating the method for manufacturing the pressure sensor in the first embodiment. FIG. 6 is a process diagram for illustrating the method for manufacturing the pressure sensor in the first embodiment. FIG. 6 is a process diagram for illustrating the method for manufacturing the pressure sensor in the first embodiment. FIG. 5 is a cross-sectional view of a pressure sensor for explaining a second embodiment. It is a block diagram of the 1st example for demonstrating the electrical connection of the strain gauge in Embodiment 2, and an external circuit. It is a block diagram of the 2nd example for demonstrating the electrical connection of the strain gauge and external circuit in Embodiment 2. FIG. FIG. 10 is a cross-sectional view of a pressure sensor for explaining a third embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Single crystal silicon substrate (thin board), 2 Insulating layer, 3 Single crystal silicon support substrate, 4 Pressure reference chamber, 5 Strain gauge, 6 Insulating protective substrate, 7 Wiring, 11 Electrode pad, 12 Mounting substrate, 13 Electrode pad, 14 Solder, 15 Conductive sheet, 16 Electrode pad, 17 Through hole.

Claims (8)

After forming the pressure detection part on the front side of the first semiconductor substrate, thinning from the back side where the pressure detection part of the first semiconductor substrate is not formed, and
Forming an insulating layer on the second semiconductor substrate and then removing a part of the insulating layer to provide a recess;
Forming a diaphragm so that the position of the pressure detection unit is adapted to the region of the recess when the thinned first semiconductor substrate and the insulating layer on the second semiconductor substrate are bonded together; A method for manufacturing a pressure sensor.   2. The pressure sensor according to claim 1, wherein borosilicate glass containing sodium oxide is used as the insulating layer, and the first semiconductor substrate and the insulating layer on the second semiconductor substrate are bonded by an anodic bonding method. Production method.   2. The method of manufacturing a pressure sensor according to claim 1, wherein the back side of the first semiconductor substrate is bonded to an insulating layer on the second semiconductor substrate.   The method of manufacturing a pressure sensor according to claim 3, further comprising a step of forming an insulating protective film on a surface of the pressure detection unit.   2. The method of manufacturing a pressure sensor according to claim 1, wherein the front side of the first semiconductor substrate is bonded to an insulating layer on the second semiconductor substrate.   Forming an electrode pad electrically connected to the pressure detection unit on the front side of the first semiconductor substrate and around the junction between the first semiconductor substrate and the insulating layer on the second semiconductor substrate; The method of manufacturing a pressure sensor according to claim 5.   Forming an electrode pad electrically connected to the pressure detection unit on the second semiconductor substrate and around a junction between the first semiconductor substrate and the insulating layer on the second semiconductor substrate; The method of manufacturing a pressure sensor according to claim 5. 2. The method of manufacturing a pressure sensor according to claim 1, further comprising a step of forming a through hole passing through the bottom surface of the recess in the second semiconductor substrate.

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