JPH11186565A - Semiconductor acceleration sensor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor acceleration sensor which capable of reducing fluctuations in hinge thickness to reduce variations in detection sensitivity. SOLUTION: In a semiconductor acceleration sensor including a semiconductor substrate 21 having a frame 11, an overlap 12 and a hinge 13 are integrally formed therein, the silicon substrate 21 is etched to form hinge parts 23. Thereafter, the hinge parts 23 are heated and oxidized to form oxidation films 24a and 24b having a predetermined thickness. The oxidation films 24a and 24b thus formed are etched and removed to form a hinge 13. The reproducibility of the oxidation film thickness by thermal oxidization is extremely satisfactory, and thus a thickness T1 of the hinge 13 can be accurately adjusted to target value.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor acceleration sensor using a silicon substrate, and more particularly, to a method for reducing variations in detection sensitivity.

[0002]

2. Description of the Related Art FIG. 2 shows an example of the configuration of a semiconductor acceleration sensor of this type. A weight 12 is positioned within a frame of a rectangular frame 11, and the weight 12 is connected to and supported by the frame 11 via a hinge 13. In this example, two hinges 13 are provided on one side of the square weight 12,
The thickness is, for example, 10 so that the required elastic deformation is possible.
It is extremely thin, about μm.

A frame 11, a weight 12, and a pair of hinges 13 are formed by chemically etching a silicon substrate with an alkaline solution, that is, are constituted by an integral silicon substrate. In this example, a piezoresistive element 14 is formed on each hinge 13 as a detecting element. Although not shown in the drawing, each piezoresistive element 14 is provided with required wiring.

In the semiconductor acceleration sensor 15 having the above configuration, when an acceleration is input, for example, in a direction indicated by an arrow in FIG. 2B, the weight 12 is displaced in accordance with the input acceleration, and Accordingly, the hinge 13 is deformed and stress is applied to the piezoresistive element 14. Therefore, the resistance value of the piezoresistive element 14 changes according to the input acceleration, and the input acceleration can be detected by detecting the change in the resistance value.

[0005]

In the semiconductor acceleration sensor 15 having the above-described detection structure, the detection sensitivity is greatly affected by the thickness (shape and size) of the hinge 13. Therefore, in order to obtain good and stable detection sensitivity with little variation, it is necessary to form the hinge 13 with high accuracy in the manufacture of the acceleration sensor 15.

However, in the conventional hinge forming method using chemical etching, the thickness of the hinge is controlled by controlling the etching time. Depending on conditions such as concentration and stirring state, reproducibility is not always excellent. Therefore, the thickness of the hinge varies, for example, about ± 2 to 3 μm between wafers, which is a major factor of the detection sensitivity. Was. The number of the acceleration sensors 15 is, for example, about 400 per wafer.

On the other hand, as another conventional manufacturing method,
A method of forming an hinge by leaving only an epitaxial layer by electrochemical etching using an epitaxial substrate as a silicon substrate and improving the thickness accuracy of the hinge is also adopted. Although the thickness accuracy of the hinge is improved as compared with the etching method, there is still a variation of about ± 1 μm between wafers.

[0008] For example, when the final thickness adjustment is performed in order to accurately adjust the thickness of the hinge to the target value by the above-described chemical etching method, the etching is frequently performed while repeating the thickness measurement. Must be advanced, and the process becomes extremely complicated and time-consuming. SUMMARY OF THE INVENTION An object of the present invention is to provide a good method of manufacturing a semiconductor acceleration sensor capable of reducing variation in hinge thickness and, thus, variation in detection sensitivity in view of the above-described problems.

[0009]

According to the present invention, there is provided a frame integrally formed from a silicon substrate, a weight located in the frame, and a hinge connecting the weight and the frame, and comprising: In a method of manufacturing a semiconductor acceleration sensor having a structure in which a weight is displaced by an input,
After etching the silicon substrate to form the hinge,
An oxide film of a predetermined thickness is formed on the hinge portion by thermal oxidation,
The hinge is formed by removing the formed oxide film by etching.

[0010]

Embodiments of the present invention will be described with reference to the accompanying drawings. FIG. 1 shows an embodiment of the present invention in the order of steps. Hereinafter, each of steps A to G will be described. First, the silicon substrate 21 is thermally oxidized,
Oxide films 22a and 22b are formed on both surfaces (A). One of the oxide films 22b is patterned (B),
The silicon substrate 21 is etched using the masks a and 22b as a mask (C). The etching is performed by chemical etching using an alkaline solution as in the conventional case, and the hinge portion 23 is formed as shown in the figure by this etching. The thickness T ₀ of the silicon substrate 21 in the hinge portion 23 is the final thickness T _{1 of the} hinge 13 (see FIG. 1G).
It is made larger.

Next, the oxide films 22a and 22b are removed by etching (D), and the thickness T ₀ of the hinge portion 23 is accurately measured by an optical method or the like. Then, a difference ΔT from the final thickness T ₁ of the hinge 13 is calculated. ΔT = T ₀ −T ₁ Next, the silicon substrate 21 is thermally oxidized to form oxide films 24a and 24b on both surfaces thereof (E). Oxide films 24a, 24
The total thickness t of b is a value obtained by the following equation.

T = ΔT × K (K is a coefficient) The coefficient K is determined by the volume expansion when silicon is oxidized, and is generally about 1.6. That is, the total thickness t of the oxide films 24a and 24b is a value obtained when the silicon having the thickness ΔT is oxidized, and this oxidation causes the hinge portion 2
The thickness of the silicon of No. 3 is reduced by ΔT.

Next, the formed oxide films 24a and 24b are removed by etching (F). Thereby, the hinge portion 23
The thickness of the by removing an unnecessary portion of the T _1, and the hinge portion 23, hinge 13 having a predetermined thickness T ₁ is completed (G). In the figure, reference numeral 11 denotes a frame, and reference numeral 12 denotes a weight. The frame 11, the weight 12, and the hinge 13 have the same planar shape as the semiconductor acceleration sensor 15 shown in FIG.

As described above, in this example, as in the prior art, the hinge portion 23 formed by chemical etching is removed by forming and removing an oxide film having a predetermined thickness.
3 and the reproducibility of the oxide film thickness by thermal oxidation is generally good and can be controlled to a predetermined thickness within an error range of several percent. T ₁ can be very precisely adjusted to the target value.

An example of numerical values in the above process is as follows.
₀ = 12 μm and T ₁ = 10 μm. At this time, the variation between the wafers of the hinge thickness T ₁ is about ± 0.2 to 0.3 μm, which is reduced to about one tenth of the conventional chemical etching method. Note that the above manufacturing method can be similarly used when an epitaxial substrate is used as a silicon substrate.

[0016]

As described above, according to the present invention, variation in hinge thickness can be greatly reduced, and a semiconductor acceleration sensor having less variation in detection sensitivity can be obtained. As a result, measurement accuracy can be reduced. Improvement can be achieved.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining an embodiment of the present invention.

FIG. 2 is a diagram showing an example of the configuration of a semiconductor acceleration sensor, FIG.
Is a plan view, and B is a sectional view thereof.

Claims (1)

[Claims] 1. A structure having a frame integrally formed from a silicon substrate, a weight located in the frame, and a hinge connecting the weight and the frame, wherein the weight is displaced by acceleration input. Forming a hinge portion by etching the silicon substrate, forming an oxide film of a predetermined thickness on the hinge portion by thermal oxidation, and etching away the formed oxide film. Forming the hinge by the method described above.