JP2000252476A - Method for manufacturing semiconductor sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily handle a wafer even if its diameter is large when manufacturing a semiconductor sensor. SOLUTION: The thickness of a silicon wafer 1 to be prepared is made larger than the design value (300 μm) of a sensor. First, an integrated circuit part 3 is formed on the surface of the silicon wafer 1. Then, the reverse side of the silicon wafer 1 is ground, and the thickness is set to 400 μm. After that, the ground surface is subjected to wet etching by a fluoric nitric acid, and the thickness of the silicon wafer 1 is set to 300 μm. Then, a deformation part 2 is formed on the reverse side of the silicon wafer 1 by anisotropic wet etching.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a semiconductor sensor formed by processing a semiconductor substrate.

[0002]

2. Description of the Related Art Examples of a semiconductor sensor formed by processing a semiconductor substrate include an acceleration sensor and a pressure sensor.
As a conventional example of an acceleration sensor, as shown in FIG. 1F, a deformed portion 2 is formed on one surface of a silicon substrate 1,
In some cases, the integrated circuit section 3 is formed on the other surface.
As shown in FIG. 1 (g), this acceleration sensor is used in a state where a glass substrate 4 is fixed to the back surface on which the deformed portion 2 is formed. The deformation part 2 of the acceleration sensor includes a support 21 fixed to the glass substrate 4 and a swingable weight 22.
And a thin beam 23 connecting the support 21 and the weight portion 22
It is composed of

As shown in FIG. 1 (g), for example, the integrated circuit section 3 includes a piezo resistor (detection element) formed by a p-type diffusion layer.
3A and a signal processing circuit 3B for converting a change in piezoresistance into an electric signal. The integrated circuit unit 3 also has
Wiring and the like for extracting the electric signal processed by the signal processing circuit 3B to the outside are also formed. Accordingly, when an acceleration (external force) is applied to the silicon substrate 1, the weight 22 swings, and the beam 23 is deformed accordingly. The resistance value of the piezoresistor 3A of the integrated circuit unit 3 changes according to the amount of deformation of the beam 23, and an electric signal corresponding to the acceleration value is output by the signal processing circuit. Therefore, the acceleration can be detected by extracting this output signal from the pad electrode to the outside.

Conventionally, when manufacturing such a semiconductor sensor, a silicon wafer having a thickness corresponding to the design value of the sensor is prepared, and an integrated circuit portion 3 is first formed on the surface thereof, and then a deformed surface is formed on the back surface. A part 2 is formed. Thereafter, a glass substrate is placed on the back surface of the silicon wafer, and the silicon substrate 1 and the glass substrate 4 are anodically bonded at the support 21 of the deformed portion 2.

[0005]

However, since the thickness of the silicon substrate for the semiconductor sensor is designed to be thinner than other semiconductor devices, cracks occur in the wafer especially when the diameter of the wafer is large. Easy and difficult to handle. The present invention has been made in view of such a problem of the related art, and when manufacturing a semiconductor sensor, by using a wafer thicker than the design value of the sensor, even when the diameter of the wafer is large, An object of the present invention is to provide a method for manufacturing a semiconductor sensor capable of facilitating the handling of a semiconductor sensor.

[0006]

According to the present invention, there is provided a deformed portion forming step of forming a deformed portion composed of a weight, a support, and a beam deformed by an external force on a semiconductor substrate by photolithography and etching. An integrated circuit unit including a detection element for electrically detecting a physical quantity such as acceleration or pressure from the deformation amount of the beam, and a signal processing circuit for processing an electric signal detected by the detection element is provided on a surface of a semiconductor substrate. In order to solve the above-mentioned problem, in a method of manufacturing a semiconductor sensor having an integrated circuit portion forming step of forming a wafer, a wafer having a thickness larger than a design value of the sensor is prepared as a semiconductor substrate, and integrated with this wafer. After performing the circuit portion forming step, performing a back side removing step of removing the back side of the wafer to reduce the thickness to the design value of the sensor, and then performing a deformed portion forming step And it features.

According to the method of the present invention, the thickness of the wafer is made larger than the design value of the sensor until the step of forming the integrated circuit is completed. As compared with the conventional method in which the thickness is reduced according to the design value, the handling of the wafer becomes easier. In the method of the present invention, when an anisotropic wet etching method is employed as the etching method of the deformed portion forming step, as the back side removal step, a grinding step of mechanically grinding the back surface of the wafer, and after the grinding step, It is preferable to perform a flattening step of flattening the ground surface by wet etching.

When the back surface of the wafer is mechanically ground, irregularities of about several tens nm are generated on the ground surface, and crystal defects are generated. If a crystal defect exists, accurate etching by anisotropic wet etching cannot be performed. Also, it is difficult to perform anodic bonding on a surface having irregularities of about several tens nm. These problems can be solved by performing the above-described grinding step and flattening step as the back side removing step. That is, since crystal defects on the ground surface are removed by wet etching in the flattening step, accurate etching by anisotropic wet etching can be performed. In addition, since the back surface of the wafer is flattened (surface roughness becomes, for example, 1 nm or less) by wet etching in the flattening step, anodic bonding between the back surface of the semiconductor substrate and the glass substrate becomes possible.

[0009]

Embodiments of the present invention will be described below. FIG. 1 is a view for explaining a method corresponding to an embodiment of the present invention in the order of steps. First, a wafer having a thickness larger than the design value of the sensor is prepared as the semiconductor substrate 1. For example, as a semiconductor substrate 1 for an acceleration sensor having a designed thickness of 300 μm, a diameter of 6 inches and a thickness of 60
An n-type silicon wafer having a thickness of 0 μm and a crystal plane of (100) is prepared. FIG. 1A shows this state.

The silicon wafer 1 may have both surfaces mirror-finished, or may have only one surface mirror-finished. Next, the integrated circuit section 3 is formed on the surface (mirror-finished surface) of the silicon wafer 1 by a conventionally known method. FIG. 1B shows this state. Note that this integrated circuit unit 3 corresponds to FIG.
As shown in (g), similarly to the above-described conventional acceleration sensor, a bridge circuit including a piezoresistor (detection element) 3A and a signal processing circuit 3B for processing a voltage signal generated in the bridge circuit are provided. ing. In addition, silicon wafer 1
A pad electrode portion is formed at a predetermined position on the surface of the device, and wirings and the like for connecting the signal processing circuit 3B and the pad electrode are also formed in the integrated circuit portion 3. The detection element is formed of, for example, a PMOS transistor, and the signal processing circuit is formed of, for example, CMOS.

Next, the back surface of the silicon wafer 1 (the surface on which the integrated circuit portion 3 is not formed) is formed by a conventionally known method.
Mechanical grinding with a grinder. Thus, the thickness of 200 μm on the back side of the silicon wafer 1 is removed. By this grinding, the thickness of the silicon wafer 1 becomes 400
μm. FIG. 1C shows this state. When the roughness of the ground surface was measured with an atomic force microscope,
m.

Next, the ground surface is subjected to wet etching using a hydrofluoric-nitric acid-based etchant,
The thickness of 100 μm on the back side of the silicon wafer 1 is removed. By this etching, the thickness of the silicon wafer 1 becomes 300 μm, which is the design value of the sensor. FIG.
(D) shows this state. After this etching, the roughness of the ground surface was measured by an atomic force microscope and found to be 1 nm or less.

Next, a silicon nitride film is deposited on the back surface of the silicon wafer 1 by a plasma CVD method, and a resist film is formed thereon. A resist pattern is formed by transferring a mask pattern for forming a deformed portion to the resist film. Thereafter, the silicon nitride film is dry-etched using the resist pattern as a mask. Thereby, an etching mask 5 made of silicon nitride is formed on the back surface of the silicon wafer 1. FIG. 1E shows this state.

Next, the back surface of the silicon wafer 1 is subjected to anisotropic wet etching using a KOH (potassium hydroxide) aqueous solution via the etching mask 5,
Deformation part 2 composed of support 21, weight 22 and beam 23
To form After that, the etching mask 5 is removed by dry etching. FIG. 1F shows this state.

Next, the glass substrate 4 is overlaid on the back surface of the silicon wafer 1 and anodically bonded at the support 21 of the deformed portion 2 of each chip. A concave portion 41 is provided on the surface of the glass substrate 4 facing the weight 22, and the peripheral portion thereof is formed on the silicon substrate 1.
With the support 21 of FIG. With this concave portion 41,
A space that allows the weight 22 to move is formed below the weight 22. FIG. 1 (g) shows this state.

As described above, according to the method of this embodiment, the thickness of the silicon wafer 1 is made larger than the design value of the sensor until the formation of the integrated circuit portion 3 is completed.
The handling of the wafer is easier than in the conventional method. In addition, in the method of this embodiment, since the crystal defects generated on the back surface of the silicon wafer 1 by the grinding are removed at the time of the wet etching in the flattening step, the anisotropic wet etching at the time of forming the deformed portion 2 is performed accurately. Done in Further, since the back surface of the silicon wafer 1 is flattened, anodic bonding with the glass substrate 4 can be performed.

In the above embodiment, the method for manufacturing the acceleration sensor is described. However, the present invention can be applied to a method for manufacturing other semiconductor sensors (such as a pressure sensor).

[0018]

As described above, according to the method of the present invention, even when the diameter of the wafer is large, the handling of the wafer becomes easier as compared with the conventional method. In particular, according to the method of the second aspect, the anisotropic wet etching at the time of forming the deformed portion is accurately performed, and the anodic bonding of the glass substrate to the back surface of the semiconductor substrate becomes possible.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a method corresponding to an embodiment of the present invention in the order of steps.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 silicon wafer (silicon substrate, semiconductor substrate) 2 deformed portion 3 integrated circuit portion 4 glass substrate 5 etching mask 21 support 22 weight 23 beam 41 concave portion

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F055 AA40 BB20 CC02 DD05 EE13 FF43 GG01 GG12 4M112 AA01 AA02 BA01 CA24 DA04 DA05 EA03 FA20

Claims (2)

[Claims] 1. A deformed portion forming step of forming a deformed portion composed of a weight, a support, and a beam deformed by an external force on a semiconductor substrate by a photolithography method and an etching method; Forming an integrated circuit section including a detection element for electrically detecting a physical quantity such as pressure and a signal processing circuit for processing an electric signal detected by the detection element on a surface of a semiconductor substrate A semiconductor wafer having a thickness greater than the design value of the sensor as a semiconductor substrate, performing an integrated circuit portion forming step on the wafer, A method of manufacturing a semiconductor sensor, comprising: performing a back surface side removing step of reducing the thickness to a design value of the sensor by removing the surface, followed by performing a deformed portion forming step. 2. An anisotropic wet etching method is employed as an etching method of a deformed portion forming step, and a grinding step of mechanically grinding the back surface of the wafer as a back surface removing step, and a wet etching after the grinding step. 2. The method according to claim 1, further comprising: performing a flattening step of flattening a surface.