JPH0758345A - Manufacture of semiconductor acceleration sensor and photomask for the same - Google Patents

Abstract

PURPOSE:To avoid unevennesses produced on bending parts by a method wherein an anisotropic etching mask pattern is composed of a basic mask pattern whose shape is the same as the shape of a weight and T-shaped correction mask patterns which are connected to the respective corners of the basic mask pattern and so arranged that their horizontal projecting parts overlap through-hole forming parts. CONSTITUTION:An anisotropic etching mask pattern is composed of a rim part mask pattern 40 for forming a rim part, a basic mask pattern 50 whose shape is approximately the same as the shape of a weight which is the object of etching and T-shaped correction patterns 51C which are connected to the respective corners of the basic mask pattern 50 and have their horizontal projecting parts arranged in regions 30 where through-holes are to be formed in a process afterwards. Therefore, the correction patterns 51C are not provided in bending part forming parts 20. With this constitution, unevenness produced by the correction pattern is not produced on the bending part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor acceleration sensor using a single crystal silicon substrate and a photomask, and more particularly to a thick weight portion for converting acceleration into force and an electric force for converting the converted force. A thin flexible portion for converting into a signal and a through-hole for increasing acceleration detection sensitivity are provided in (10
0) A method for manufacturing a semiconductor acceleration sensor formed by utilizing anisotropic etching of plane-oriented single crystal silicon, and a photomask used for the manufacturing.

[0002]

2. Description of the Related Art In a semiconductor acceleration sensor of this type, as shown in the perspective view of FIG. 2 (a), a rectangular and thick weight portion 1 is usually provided on one surface of a single crystal silicon substrate.
The thin bending portion 2 provided in parallel with two opposite sides of the weight portion 1, the through hole 3 provided in parallel with another pair of opposite sides of the weight portion 1, and the bending portion 2 are supported. And a thick rim portion 4 that is formed. Further, on the other surface of the silicon substrate, as shown in the schematic perspective view of FIG. 2 (b), a plurality of resistors 5 are formed at the portions corresponding to the flexures 2, and these resistors 5 receive a current from the outside. The pad 6 and the metal wiring 7 are provided so that the current can flow. In the above structure, the weight portion 1 has a law of dynamics F = Mα (where F is a force, M is a mass of the weight portion, when an acceleration having a component in a direction perpendicular to the crystal plane is applied to the sensor).
α is a portion that converts acceleration into force according to (acceleration). The flexure portion 2 is a portion that supports the weight portion 1 and bends due to the force generated in the weight portion 1, and causes the resistance 5 formed on the other surface of the silicon substrate to change in resistance value due to the piezoresistive effect due to the deflection. Is. The change in resistance value of the resistor 5 is taken out from the pad 6 as a change in voltage when a constant current flows.

The manufacturing process of the acceleration sensor having the above structure will be described below. 3A to 3E show a weight portion 1, a flexure portion 2, a through hole 3 and a rim portion 4 of the acceleration sensor.
FIG. 6 is a diagram showing a cross-section of a main part of FIG. First, (1
00) plane orientation on both sides of the n-type silicon substrate 8, for example,
The protective films _9a and _9b are formed by _a thermal oxidation method (see FIG. 3).
(A)). Next, the protective film 9 _a on one surface of the silicon substrate 8 is patterned by a photolithography technique, and the protective films 9 _W and 9 _R are left in the portions to be the weight portion and the rim portion (see FIG. b)). Further, when this silicon substrate is etched with an alkaline etching solution such as an aqueous potassium hydroxide solution, the silicon in the portion not covered with the masks (protective films 9 _W and 9 _R ) is etched, and the thick weight portion 1 Also, the rim portion 4 and the thinned flexible portion 2 are formed (FIG. 3C). This etching of single crystal silicon with an alkaline aqueous solution is called anisotropic etching because the etching rate depends on the crystal orientation of the silicon substrate. Then, etched by photolithography with respect to the protective film 9 _b on the other surface of the silicon substrate, removing the protective film in a portion to be a through hole (FIG. 3 (d)). This silicon substrate is treated with an alkaline etching solution such as an aqueous solution of potassium hydroxide or an etching solution obtained by mixing a hydrofluoric acid solution, a nitric acid solution and an acetic acid solution to form a portion (through hole formation) not covered with the mask (protective film 9 _b ). Part) is etched to form a through hole 3 for facilitating vertical movement of the weight part 1 (FIG. 3 (e)).

Here, in the above manufacturing process, when a silicon substrate is etched with an alkaline etching solution, its etching rate depends on the crystal orientation, as described above, and the etching rate for the {111} plane is different. It is extremely slow compared to the etching rate on any surface. Therefore, the shape of the weight part is
If a rectangle is formed which is parallel to the ridge line in the [011] direction formed by the intersection of the (0) plane and the {111} plane, FIG.
As shown in, the {111} plane appears from the rim portion 4 and the weight portion 1 to the flexible portion 2 and the through hole 3 due to anisotropic etching of silicon.

Next, a method of detecting acceleration in the semiconductor acceleration sensor will be described with reference to the schematic perspective view shown in FIG. Referring to FIG. 2B, before the anisotropic etching is performed in the manufacturing process described above,
A resistor 5 formed by thermally diffusing or ion-implanting boron, and a metal wiring 7 and a pad 6 for transmitting the resistance change of the resistor 5 to the outside are formed. When an upward acceleration perpendicular to the (100) plane acts on this sensor, the weight portion 1 is pulled downward due to inertia, so that the bending portion 2 is bent. At this time, of the resistors 5 formed on the flexible portion 2, the resistance on the side closer to the rim portion 4 is increased,
On the other hand, the resistance close to the weight portion 1 contracts. Since the resistance changes due to the piezoresistive effect with respect to the expansion and contraction of the resistance, it is possible to detect the change in acceleration as a change in voltage by supplying a constant current from the pad portion 6 to the resistance in advance. .

By the way, when the weight portion or the bending portion of the acceleration sensor is formed, anisotropic etching of silicon is used as described above. At this time, a mask pattern having the same shape as the desired weight shape (hereinafter referred to as a basic mask) is used. When etching is performed with a pattern), side etching occurs in the corner convex portion, and the problem that the desired weight shape cannot be obtained at the end of etching occurs. A correction mask pattern for anisotropic etching is added to the pattern.

FIG. 4A shows an example of such a correction mask pattern for anisotropic etching, which is disclosed in Japanese Patent Laid-Open No. 1-28.
This is disclosed in Japanese Patent No. 4764. Referring to FIG. 4A, the etching mask has a rim portion mask pattern 40 for forming a rim portion and a basic mask pattern 50 for determining a target weight shape.
And the correction mask pattern 5 which is projected in a rectangular shape in advance.
The shape is a combination of 1A and 1A. The correction mask pattern 51A protruding in a rectangular shape is arranged so as to hang over the bending portion forming portion 20 and the through hole forming portion 30 due to its shape.

In FIG. 2B, when anisotropic etching is performed using an etching mask having a shape in which a correction mask pattern protruding in a rectangular shape is added to the corner convex portion of the basic mask pattern, The progress of etching viewed from the 100> direction is shown with time. Since the etching rate of the convex portion of the protruding portion in the rectangular shape is the highest, the etching starting from the three protruding corner convex portions of the correction mask pattern 51A is A1-B1-C1-D1.
-Go to the shape indicated by the polygonal line connecting E1. Then
When the etching progresses to the line connecting the points A2-B2-C2-D2-E2 and the line connecting the points A2 and B2 reaches the ridge line where the (110) face and the (100) face intersect, the etching rate of this face increases. Point A2-A3-
Etching proceeds like a line connecting B3-C3-D3-E3-E2. Then, a right-angled convex portion indicated by a line connecting the points A2-0-E2 is formed to obtain a desired weight shape.

Another example of the conventional correction mask pattern for anisotropic etching is the Institute of Electrical Science.
Electrical Engineers of
"The 4th International Conference on Solid State Sensors and Actuators" sponsored by Japan (The 4th Intern)
national Conference on Sol
id-State Sensors and Actu
Attors), Tokyo, June 2-5, 1987 Proceedings "Transducers '87" (TRANSDUC)
ERS'87) 126-129.
FIG. 5A is a diagram showing an etching mask pattern when the correction mask pattern described in the above-mentioned abstract is applied to the manufacture of a semiconductor acceleration sensor. Referring to the figure, the etching mask pattern shown in this figure has a rim portion mask pattern 40 for forming a rim portion, a basic mask pattern 50 for defining a target weight shape, and a vertex of the basic mask pattern 50. It is formed from the added triangular correction mask pattern 51B. Here, the correction mask pattern 51B in the shape of a triangle is arranged so as to hang over the bending portion forming portion 20 and the through hole forming portion 30 due to its shape as in the previous example.

FIG. 5B shows the progress of etching when anisotropic etching is performed using the etching mask having the pattern shown in FIG. With the start of etching, etching progresses from the tip and the periphery of the protruding portion of the triangular correction mask pattern 51B, and after a certain period of time, a desired weight shape is obtained via a rectangular pattern connecting points ABCDE. Obtainable.

Further, Japanese Patent Laid-Open No. 2-280325 discloses another example of a correction mask pattern for anisotropic etching. The silicon substrate used for the acceleration sensor described in the above publication is different from those described so far,
Although it is a single crystal silicon substrate having a (110) plane orientation, it is formed by connecting a (110) plane and a (111) plane to a basic mask pattern for obtaining a target shape, which is connected to the apex of this basic mask pattern. The configuration in which a correction pattern having a side parallel to the ridgeline is added is the same. Also in this case, when the correction mask pattern is applied to the manufacture of the semiconductor acceleration sensor, the correction mask pattern is arranged so as to hang over the flexible portion forming portion and the through hole forming portion, as in the previous two examples. It

[0012]

All of the correction mask patterns of the conventional semiconductor acceleration sensor described above are arranged so as to hang on the bending portion forming portion. Here, in the anisotropic etching of the (100) plane-oriented silicon substrate in the flexure formation portion other than the correction mask pattern portion, the (100) plane is etched while leaving the {111} plane.
A flexure having a uniform thickness can be obtained. On the other hand, in the etching just below the correction mask pattern, since the flexure is formed while etching the other etching surface, the etching rate is different. Therefore, unevenness is generated on the surface of the flexure at the end of etching. As a result, when the flexure portion bends due to acceleration, stress concentrates on the uneven portion, and the reliability of the sensor decreases. Also,
Due to the unevenness, the thickness of the flexible portion becomes non-uniform, so that the output characteristics of each sensor vary.

Therefore, an object of the present invention is a method of manufacturing a semiconductor acceleration sensor in which a weight portion and a bending portion are formed by using anisotropic etching of single crystal silicon, and the bending portion surface caused by the correction mask pattern is formed. It is an object of the present invention to provide a manufacturing method in which no unevenness is generated.

[0014]

According to a method of manufacturing a semiconductor acceleration sensor of the present invention, a single crystal silicon substrate having a (100) plane as a main surface is subjected to anisotropic etching so that the plane shape is a right-angled parallelogram. A method of manufacturing a semiconductor acceleration sensor comprising a thick weight portion, a thick rim portion surrounding the weight portion, a through hole provided between the weight portion and the rim portion, and a thin deflection portion, An etching mask forming step of forming an etching mask for leaving the weight portion and the rim portion in the anisotropic etching on the main surface of the single crystal silicon substrate; Forming in the etching mask forming step, including an etching step of thinning the flexure forming area and the through hole forming area that have been subjected to isotropic etching. Among the etching masks, the etching mask for forming the weight portion is composed of a basic pattern having a shape corresponding to the target weight shape, and a correction pattern arranged at each vertex of the basic pattern. Each of the patterns has a planar shape within the through hole formation region with two sides extending from each vertex of the basic pattern in the through hole formation region direction and a part of the side along the through hole formation region. A method of manufacturing a semiconductor acceleration sensor, characterized in that it reaches a right-angled parallelogram.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 1A is a diagram showing a mask pattern of an etching mask for anisotropic etching according to an embodiment of the present invention. Referring to FIG. 1A, in the present embodiment, a rim portion mask pattern 40 for forming a rim portion is formed.
And a basic mask pattern 50 having substantially the same shape as the target weight shape, and a portion connected to each apex of the basic mask pattern 50, and a lateral overhanging portion 52 where a through hole is formed during silicon etching in a later step ( Through hole forming part 3
The pattern is a combination of the T-shaped correction pattern 51C arranged in 0). Therefore, the correction pattern 51C is not arranged in the flexure forming portion 20.

This embodiment is manufactured by the same manufacturing process as in the conventional method of manufacturing a semiconductor acceleration sensor described above. That is, an etching protection film such as silicon dioxide is formed on both surfaces of a single crystal silicon substrate having a (100) plane as a main surface, and the etching protection film is patterned by photolithography or the like to form a weight portion forming region and a rim portion forming region. Leave the protective film. At this time, a photomask having the pattern shown in FIG. 1A is used. Then, using the remaining portion of the protective film as an etching mask, the silicon substrate is anisotropically etched with an alkaline aqueous solution such as potassium hydroxide.

FIG. 1 (b) is a view of the anisotropic etching process in this embodiment as seen from the <100> direction. In the etching, the etching rate of the convex portion of the laterally extending portion 52 of the T-shaped correction mask pattern 51C is high,
Etching proceeds from both ends as indicated by a line connecting points A1-B1-C1 and points D1-E1-F1. Then, etching proceeds as represented by a line connecting points A2-B2-C2 and points D2-E2-C2. And
If the etching surface tips from both ends collide with each other at the point C2, the laterally projecting portion 52 of the correction mask pattern 51C is formed.
Etching proceeds in the direction of the vertically extending portion 53 that connects the basic mask pattern 50 defining the weight shape. After this, from the line connecting points B3-C3-E3 to point B4
A desired weight shape can be obtained when the etching reaches the point where the line connecting points C5-D5 is reached after passing through the line connecting -C4-D4. At this time, the unevenness on the etching surface caused by the difference in the etching rate of the single crystal silicon under the correction mask pattern described above is different from that in the conventional manufacturing method, and is different from that in the bending portion 2 and not in the through hole forming portion 3.
0 above.

Next, the protective film is patterned on the other surface of the silicon substrate by the photolithography technique. Then, the through hole forming portion is subjected to silicon etching with an alkaline etching solution such as potassium hydroxide or a mixed etching solution of hydrofluoric acid water, a nitric acid solution and an acetic acid solution to form a through hole. At this time, the unevenness generated on the surface of the through hole forming portion 30 by the anisotropic etching in the previous step is accompanied by the silicon layer which is etched and removed as the through hole is completed and opened. It is removed and disappears. Therefore, in this embodiment, there is no unevenness on any part of the silicon substrate surface of the completed sensor, which deteriorates reliability and causes variations in output characteristics.

In this embodiment, the lateral overhang portion 52 in the correction mask pattern is formed at the time when the etching in the depth direction is completed in the anisotropic etching process, that is,
This is for adjusting so that the etching of the silicon layer under the correction mask pattern is just finished when the thickness of the silicon layer in the flexure reaches a predetermined thickness. It is designed to have an appropriate length according to the etching time. In this case, as can be seen from the state of the progress of etching shown in FIG. 1B, the etching of the silicon layer under the correction mask pattern is finally performed in the direction along the longitudinal direction of the vertical overhang portion 53. However, depending on the time required for anisotropic etching, the lateral overhanging portion 52 is not always necessary, and the vertical overhanging portion 53 alone can achieve the object of the present invention.

[0020]

As described above, according to the method of manufacturing a semiconductor acceleration sensor of the present invention, the pattern of the etching mask for anisotropic etching is the basic mask pattern having substantially the same shape as the predetermined weight shape. Of the correction mask pattern which is connected to the apex of the above and is arranged so that the laterally extending portion is formed in a T shape so as to hang on the through hole forming portion. Therefore, it is possible to prevent the unevenness caused by the correction mask pattern from being generated on the flexible portion without being applied on the flexible portion, and it is possible to form the flexible portion having a uniform thickness. The irregularities generated on the through-hole forming portion are removed and disappear during the silicon etching for forming the through-hole in the subsequent process.

As a result, according to the present invention, it is possible to obtain a flexure having a uniform thickness without unevenness.
It is possible to supply a semiconductor acceleration sensor having high reliability and uniform output characteristics.

Incidentally, the correction mask pattern may be only the vertically extending portion depending on the depth of anisotropic etching.

[Brief description of drawings]

FIG. 1A is a diagram showing the shape of an etching mask according to an embodiment of the present invention. Diagram (b) is a diagram showing the progress state of the etched surface when the silicon substrate is anisotropically etched using the etching mask shown in diagram (a), as viewed from the <100> axis direction.

FIG. 2A is a perspective view of the semiconductor acceleration sensor as viewed from the side where the weight portion is formed. Diagram (b) is a schematic perspective view of the semiconductor acceleration sensor shown in diagram (b) as seen from the circuit formation surface side.

3A to 3C are process diagrams sequentially showing a manufacturing process of a semiconductor acceleration sensor.

FIG. 4A is a diagram showing an example of the shape of a conventional etching mask. Diagram (b) is a diagram showing the progress state of the etched surface when the silicon substrate is anisotropically etched using the etching mask shown in diagram (a), as viewed from the <100> axis direction.

FIG. 5A is a diagram showing another example of the shape of a conventional etching mask. Diagram (b) is a diagram showing the progress state of the etched surface when the silicon substrate is anisotropically etched using the etching mask shown in diagram (a), as viewed from the <100> axis direction.

[Explanation of symbols]

1 weight portion 2 flexures 3 through holes 4 rim fifth resistor 6 pads 7 metal wiring 8 silicon substrate _{9 a, 9 b, 9 W} , 9 R protective film 20 flexures forming section 30 through hole forming portion 40 rim mask pattern 50 Basic Mask Patterns 51A, 51B, 51C Correcting Mask Patterns 52 Horizontal Overhangs 53 Vertical Overhangs

Claims (4)

[Claims] 1. A single-crystal silicon substrate having a (100) plane as a principal surface is anisotropically etched to form a thick weight portion having a right-angled parallelogram in plan view, and a thick rim surrounding the weight portion. Section and a method for manufacturing a semiconductor acceleration sensor including a through-hole provided between the weight section and the rim section and a thin flexure section, in the anisotropic etching on the main surface of the single crystal silicon substrate. An etching mask forming step of forming an etching mask for leaving the weight portion and the rim portion, and a bending portion forming region and a through hole forming region which are anisotropically etched on the single crystal silicon substrate using the etching mask. An etching step for forming a weight portion in the etching mask formed in the etching mask forming step, Mask,
A basic pattern having a shape corresponding to a target weight shape, and a correction pattern arranged at each vertex of each of the basic patterns, and each of the correction patterns has a planar shape of each of the vertexes of the basic pattern. From a side extending in the direction of the through-hole forming region and a part of the side along the through-hole forming region as two sides, and a right-angled parallelogram reaching the inside of the through-hole forming region. Method for manufacturing semiconductor acceleration sensor. 2. The method for manufacturing a semiconductor acceleration sensor according to claim 1, wherein each of the correction patterns has a planar shape arranged in the through-hole forming region in addition to the right-angled parallelogram. A method of manufacturing a semiconductor acceleration sensor, wherein the semiconductor acceleration sensor has a T-shape with a right-angled parallelogram orthogonal to the quadrangle. 3. The method of manufacturing a semiconductor acceleration sensor according to claim 1, wherein in the etching mask forming step, the etching mask is formed by a photo-etching method using a photomask. Manufacturing method of semiconductor acceleration sensor. 4. A photomask having a shape formed by the method for manufacturing a semiconductor acceleration sensor according to claim 3.