Pressure sensor element and method of manufacturing the same

Abstract

To prevent metal formed on a bottom surface of a diaphragm from diffusing to a strain sensing element forming area.SOLUTION: A second semiconductor layer 103 is formed on a first semiconductor layer 102, covering an opening 112. The second semiconductor layer 103 is formed with a diaphragm 121, which uses an area of the opening 112 as a pressure receiving section. The second semiconductor layer 103 is also formed with an embedded insulating layer 106 in a position deeper than where strain sensing elements 104 are formed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a pressure sensor element and a manufacturing method thereof. [Background technology]

[0002] For example, pressure sensors that output a pressure value from the amount of deflection, or displacement, of a diaphragm subjected to pressure are widely used in industrial applications, including semiconductor equipment. This type of pressure sensor includes a pressure sensor element that uses a strain element that uses the piezoresistance effect to detect the displacement of the diaphragm as stress and outputs a pressure value from the detected stress. In this type of pressure sensor element, the strain element is formed in the semiconductor layer on which the diaphragm is formed (Patent Document 1).

[0003] This pressure sensor element is mounted on a meter body. To insulate and separate the element section made of a semiconductor from the meter body, it is bonded to a support substrate made of an insulator such as glass. In order to fix the semiconductor layer to the support substrate such as glass in this way, a metal layer is formed at the bonding interface between them to improve bonding strength, and the metal layers are then bonded together. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-171318 Summary of the Invention [Problem to be solved by the invention]

[0005] In forming the metal layer described above, the metal is generally deposited from the bottom side of the semiconductor layer by a deposition method such as vacuum evaporation or sputtering. As a result, the metal is also deposited on the bottom surface of the diaphragm exposed in the opening of the semiconductor layer, forming a metal layer. When heat is applied in a later process, the thin metal film formed on the bottom surface of the diaphragm diffuses through the diaphragm (semiconductor layer) and reaches the strain element, creating a current leakage path and affecting the operation of the strain element.

[0006] The present invention has been made to solve the above problems, and has as its object to suppress the diffusion of the metal formed on the bottom surface of the diaphragm into the strain element forming region. [Means for solving the problem]

[0007] The pressure sensor element of the present invention comprises a support substrate having a through hole, a first semiconductor layer having an opening and formed on the support substrate, a second semiconductor layer formed on the first semiconductor layer to cover the opening and having a diaphragm with the area of ​​the opening as a pressure receiving portion, a strain element formed in the second semiconductor layer to measure the strain of the diaphragm, metal layers formed on each of the bonding surfaces of the support substrate with the first semiconductor layer and the bonding surface of the first semiconductor layer with the support substrate to bond the support substrate and the first semiconductor layer, and a buried insulating layer formed at a location deeper than the location where the strain element is formed in the second semiconductor layer.

[0008] In one configuration example of the pressure sensor element, the buried insulating layer is made of an oxide of the second semiconductor layer.

[0009] In one configuration example of the pressure sensor element, the support substrate and the first semiconductor layer are bonded to each other via a metal layer formed on their bonding surfaces.

[0010] The method for manufacturing a pressure sensor element according to the present invention includes a first step of preparing a support substrate having a through-hole, and forming an element portion including a first semiconductor layer having an opening, a second semiconductor layer formed on the first semiconductor layer to cover the opening and having a diaphragm with the area of ​​the opening as a pressure-receiving portion, a strain element formed in the second semiconductor layer to measure the strain of the diaphragm, and a buried insulating layer formed at a location deeper than the location where the strain element is formed in the second semiconductor layer; a second step of forming a metal layer on the bonding surface of the support substrate with the first semiconductor layer, and forming a metal layer on the bonding surface of the first semiconductor layer with the support substrate; and a third step of abutting the metal layer forming surface of the first semiconductor layer and the metal layer forming surface of the support substrate to bond them together.

[0011] In one configuration example of the above-described method for manufacturing a pressure sensor element, the second step forms a metal layer by depositing a metal. [Effects of the Invention]

[0012] As described above, according to the present invention, the buried insulating layer is provided in the second semiconductor layer in which the strain element is formed, so that diffusion of the metal formed on the bottom surface of the diaphragm into the strain element forming region can be suppressed. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a cross-sectional view showing the configuration of a pressure sensor element according to an embodiment of the present invention. [Figure 2] FIG. 2 is a plan view showing a partial configuration of the pressure sensor element according to the embodiment of the present invention. [Figure 3A] FIG. 3A is a cross-sectional view illustrating a state of the pressure sensor element in the middle of a process for explaining a method of manufacturing the pressure sensor element according to the embodiment of the present invention. [Figure 3B] FIG. 3B is a cross-sectional view showing a state of the pressure sensor element in the middle of a process, for explaining the method of manufacturing the pressure sensor element according to the embodiment of the present invention. [Figure 3C] FIG. 3C is a cross-sectional view showing a state of the pressure sensor element in the middle of a process, for explaining the method of manufacturing the pressure sensor element according to the embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] A pressure sensor element according to an embodiment of the present invention will be described below with reference to Figures 1 and 2. This pressure sensor element includes a support substrate 101, a first semiconductor layer 102, a second semiconductor layer 103, a strain element 104, and a buried insulating layer 106.

[0015] The support substrate 101 has a through hole 111. The support substrate 101 can be made of an insulating material such as glass (heat-resistant glass), quartz, or sapphire. The support substrate 101 can also be made of gold, aluminum, copper, GaAs, or the like. The support substrate 101 is made of a different material from that of the first semiconductor layer 102 described below.

[0016] The first semiconductor layer 102 is formed on a support substrate 101. The first semiconductor layer 102 has an opening 112. The first semiconductor layer 102 can be made of silicon, for example. The first semiconductor layer 102 and the support substrate 101 are bonded together via a metal layer 105.

[0017] The second semiconductor layer 103 is formed on the first semiconductor layer 102, covering the opening 112. The second semiconductor layer 103 also has a diaphragm 121 formed thereon, with the region of the opening 112 serving as a pressure-receiving portion. As illustrated in FIG. 2, the opening 112 may have a rectangular (square) shape in plan view when viewed from the normal direction to the plane of the second semiconductor layer 103. In this case, the shape of the diaphragm 121 in plan view is rectangular (square). The opening 112 may also have a circular shape in plan view. In this case, the shape of the diaphragm 121 in plan view is circular. The second semiconductor layer 103 may be made of single-crystal silicon whose main surface is a (100) plane.

[0018] The strain elements 104 are formed on the second semiconductor layer 103 and measure the strain of the diaphragm 121. For example, as illustrated in Fig. 2, the strain elements 104 can be arranged at four locations at equal intervals around the circumference of the diaphragm 121. When the shape of the diaphragm 121 in a plan view is square, the strain elements 104 can be arranged near the center of each of the four sides.

[0019] The strain element 104 can be, for example, a piezo-strain element that uses the piezo-resistance effect to measure the strain of the diaphragm 121. For example, the piezo-strain element can be configured by a piezo-resistance region formed from a p-type region by introducing boron (B), which is a p-type impurity, into a predetermined location of the diaphragm 121 made of single crystal silicon.

[0020] Furthermore, strain element 104 can be made of a material whose resistance value changes with strain and can be used to measure the strain of diaphragm 121. The strain element includes a detection layer whose resistance value changes with strain and a reference layer that serves as a reference for the detection layer, and measures the strain of diaphragm 121 by comparing the change in resistance between the detection layer and the reference layer. The reference layer is, for example, a layer whose change due to pressure is fixed, and whose resistance value does not change with strain.

[0021] Furthermore, the second semiconductor layer 103 has a buried insulating layer 106 formed at a location deeper than the location where the strain element 104 is formed. For example, the second semiconductor layer 103 can be formed by processing a well-known SOI (Silicon on Insulator) substrate. The second semiconductor layer 103 can be formed by forming the strain element 104 in the surface silicon layer of the SOI substrate and thinning the base portion of the SOI substrate from the back surface side. The second semiconductor layer 103 made from the SOI substrate is a silicon layer, and the buried insulating layer 106 is made of an oxide (silicon oxide) of the second semiconductor layer 103.

[0022] According to the above-described embodiment, the buried insulating layer 106 is provided in the second semiconductor layer 103 on which the strain element 104 is formed. Therefore, even if a metal deposited to bond the support substrate 101 is deposited on the back surface of the second semiconductor layer 103 (diaphragm 121), the deposited metal can be prevented from diffusing into the region where the strain element 104 is formed. The metal deposited on the back surface of the second semiconductor layer 103 will diffuse into the second semiconductor layer 103 when heat is applied in a later process, for example. However, according to the embodiment, the buried insulating layer 106 is formed, and the diffusion of the metal stops at the buried insulating layer 106. Therefore, the above-described metal does not diffuse into the region where the strain element 104 is formed, and does not affect the operation of the strain element 104.

[0023] Next, a method for manufacturing the pressure sensor element according to the embodiment will be described with reference to FIGS. 3A, 3B, and 3C.

[0024] 3A, an element section is fabricated, which includes a frame-shaped first semiconductor layer 102 with an opening 112, a second semiconductor layer 103 in which a diaphragm 121 is formed, a strain element 104 formed in the second semiconductor layer 103, and a buried insulating layer 106 formed in a location of the second semiconductor layer 103 deeper than the location where the strain element 104 is formed. The element section can be fabricated by bonding together the first semiconductor layer 102, which is formed by processing a silicon substrate, and the second semiconductor layer 103, which is formed by processing another SOI substrate. Furthermore, although not shown, a support substrate 101 with a through hole 111 formed therein is prepared (first step).

[0025] For example, an SOI substrate with an n-type surface silicon layer is prepared, and a mask pattern having openings in areas to be the strain elements 104 is formed on the SOI substrate (surface silicon layer) by known photolithography techniques. Next, a p-type impurity such as boron is introduced by known ion implantation techniques into the surface silicon layer exposed in the openings of the mask pattern to form piezoresistance elements, which are the strain elements 104.

[0026] Next, after removing the mask pattern, a mask pattern having openings in regions to be lead-out wiring portions connected to the strain element 104 is formed on the surface silicon layer again. Next, by a known ion implantation method, impurities are introduced at a higher concentration into the surface silicon layer exposed through the openings of the mask pattern to form a lead-out wiring structure.

[0027] Next, after removing the above-mentioned mask pattern, the silicon base portion of the SOI substrate is thinned by known chemical mechanical polishing (CMP) or dry etching techniques to form a second semiconductor layer 103 having the strain element 104 using the above-mentioned piezoresistance element and further having a buried insulating layer 106.

[0028] Meanwhile, another silicon substrate is prepared, and a mask layer having an opening corresponding to the region where the opening 112 will be formed is formed thereon by a known photolithography technique. Next, the silicon substrate is etched using the mask layer as a mask in a state of high vertical anisotropy by well-known reactive ion etching, thereby forming the first semiconductor layer 102 having the opening 112. The second semiconductor layer 103 and the first semiconductor layer 102 formed as described above are bonded together to form the element portion.

[0029] Next, as shown in FIG. 3B, a metal layer 105 is formed on the surface of the first semiconductor layer 102 that will be the bonding surface with the support substrate 101 (second step). At this time, a metal layer (not shown) is also formed on the back surface of the second semiconductor layer 103 (diaphragm 121). Although not shown in FIG. 3B, a metal layer 105 is also formed on the bonding surface of the prepared support substrate 101. For example, the metal layer 105 can be formed by depositing a predetermined metal by sputtering or vacuum deposition.

[0030] Thereafter, the surface of the first semiconductor layer 102 on which the metal layer is to be formed and the surface of the support substrate 101 on which the metal layer is to be formed are brought into contact with each other, and the two are bonded together as shown in FIG. 3C (third step).

[0031] As described above, according to the embodiment of the present invention, the second semiconductor layer in which the strain element is formed is provided with a buried insulating layer, thereby making it possible to suppress the diffusion of metal formed on the bottom surface of the diaphragm into the strain element formation region.

[0032] It should be noted that the present invention is not limited to the embodiments described above, and it is clear that many modifications and combinations can be made by a person having ordinary knowledge in the art within the technical concept of the present invention. [Explanation of symbols]

[0033] 101...support substrate, 102...first semiconductor layer, 103...second semiconductor layer, 104...strain element, 105...metal layer, 106...buried insulating layer, 111...through hole, 112...opening, 121...diaphragm.

Claims

1. a support substrate having a through hole; a first semiconductor layer formed on the support substrate and having an opening; a second semiconductor layer on which a diaphragm is formed, the second semiconductor layer covering the opening and using the opening region as a pressure receiving portion; a strain element formed on the second semiconductor layer for measuring strain of the diaphragm; a metal layer formed on a bonding surface of the support substrate with the first semiconductor layer and a bonding surface of the first semiconductor layer with the support substrate, in order to bond the support substrate and the first semiconductor layer; a buried insulating layer formed in a portion of the second semiconductor layer deeper than a portion in which the strain element is formed; A pressure sensor element comprising:

2. 2. The pressure sensor element according to claim 1, The pressure sensor element, wherein the buried insulating layer is made of an oxide of the second semiconductor layer.

3. 3. The pressure sensor element according to claim 1, The support substrate and the first semiconductor layer are bonded to each other via a metal layer formed on their bonding surfaces.

4. a first step of forming an element portion including a first semiconductor layer having an opening, a second semiconductor layer formed on the first semiconductor layer to cover the opening and having a diaphragm formed thereon with the region of the opening as a pressure receiving portion, a strain element formed in the second semiconductor layer to measure strain of the diaphragm, and a buried insulating layer formed in a position deeper than the position where the strain element is formed in the second semiconductor layer, and preparing a support substrate having a through hole; a second step of forming a metal layer on a bonding surface of the support substrate with the first semiconductor layer, and forming a metal layer on a bonding surface of the first semiconductor layer with the support substrate; a third step of bringing the metal layer formation surface of the first semiconductor layer and the metal layer formation surface of the support substrate into contact with each other and bonding them together; A method for manufacturing a pressure sensor element comprising:

5. 5. The method for manufacturing a pressure sensor element according to claim 4, The second step is a method of manufacturing a pressure sensor element, in which a metal layer is formed by depositing a metal.

Images