JPH0845896A - Under-etching correction method in anisotropic etching - Google Patents

Abstract

(57) [Summary] [Objective] When forming a rectangular trapezoid by anisotropic etching, an under-etching correction method that can suppress the amount of under-etching that occurs at the corners of the rectangular trapezoid by a correction mask with a small shape is provided. suggest. A first correction mask 2D is formed from each corner of a rectangular mask 2B for forming a rectangular trapezoidal portion 7 on a semiconductor substrate 1 toward a mask 2A for forming a frame, and the first correction mask 2D. 2 for forming the frame 5 on both sides of the
Masks for forming second correction masks 2E and 2F extended from A and forming between the tip of the first correction mask and the mask for forming the frame and between the tip of the second correction mask and the rectangular trapezoidal portion. And R1 and R2 are formed between them.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for correcting under-etching in anisotropic etching which can be used, for example, when manufacturing various sensors and the like with semiconductors.

[0002]

2. Description of the Related Art First, referring to FIGS.
Anisotropic etching using the [0] plane will be described.
First, [100] of the semiconductor substrate 1 such as silicon
A rectangular mask hole 3 is formed on the surface by the etching mask 2. Each side of the mask hole 3 is [11] of the semiconductor substrate 1.
It is made to be parallel to the [0] plane. When etching is performed using this etching mask 2, a triangular hole 4 protruding downward is formed in the semiconductor substrate 1 as shown in FIG. Each surface of the hole 4 is surrounded by an inclined surface 4A, and each inclined surface 4A
Is the [111] plane. The reason is that the etching rate of the [111] plane is slower than the etching rates of other crystal planes.

Assuming that the width of the mask hole 4 is X (see FIG. 5), the periphery of the hole 4 becomes a [111] plane at a depth of (X / 2) / tan (90 ° -54.74 °). , The etching will stop automatically. Therefore, when the through hole is formed by etching, the width X of the mask hole 3 must be selected to be larger than the state shown in FIG. The thickness of the semiconductor substrate 1 t, the and the width of the mask hole 3 required to form a through hole and _{X A (X A /2)/tan(90°-54.74°)=t, X} A = 2t · tan (90 ° -54.74 °)
≈1.41t = √2t.

That is, when the through hole is formed in the semiconductor substrate 1 having the thickness t, the width X _A of the mask hole 3 must be selected so that X _A ≧ √2t. By the way, an acceleration sensor having a structure as shown in FIG. 7 is considered as one example of the sensor. This acceleration sensor includes spring members 6A to 6A in a frame body 5.
The weight 7 is supported via D, and the strain sensor 8 is adhered and formed on the spring members 6A to 6D.

When the acceleration is applied in the direction orthogonal to the plane of the weight 7, the spring members 6A to 6D are bent, and the strain sensor 8 detects the amount of the bending, thereby generating an electric signal corresponding to the applied acceleration. Can be sent. In order to make the acceleration sensor of this structure small and highly sensitive, the frame body 5, weight 7 and spring members 6A to 6D are
Forming is performed from a single semiconductor substrate.

The anisotropic etching described above is used to manufacture an acceleration sensor having this structure.
The manufacturing method will be described with reference to FIGS. 8 to 10. The semiconductor substrate 1 is covered with the etching mask 2. The etching mask 2 is removed in a square ring shape to form a square ring mask hole 9. Each side of the square annular mask hole 9 is formed on the semiconductor substrate 1 [11
[0] plane. By forming the square annular mask hole 9, the etching mask 2 is a mask 2A for forming the frame 5 and a mask 2B for forming the weight 7.
Is separated into

When etching is performed according to the shape of the rectangular annular mask hole 9, a concave groove 11 as shown in FIGS. 9 and 10 is formed. On both sides of the concave groove 11, the inclined surfaces 10 having [111] surfaces exposed are formed. A frame 5 is formed on the outer side of the groove 11, and a weight 7 (the portion of the weight 7 is rectangular and has a trapezoidal shape is hereinafter referred to as a rectangular trapezoidal portion) is formed on the inner side. When the thickness of the bottom surface of the recessed groove 11 reaches a desired value (the state of FIG. 10), the etching is temporarily stopped, the portions to be left as the spring members 6A to 6D are covered with a mask, and the etching is performed again. Other parts are penetrated leaving 6A to 6D. By forming the spring members 6A to 6D by etching in this way, it is possible to form the extremely thin spring members 6A to 6D, and to obtain a spring member that can be largely bent with respect to the acceleration applied to the rectangular trapezoidal portion 7. You can As a result, by forming the strain sensor 8 on the spring members 6A to 6D, an acceleration sensor with high detection sensitivity can be obtained.

[0008]

In the manufacturing process shown in FIGS. 8 to 10, the mask is formed at each corner of the rectangular trapezoidal portion 7 in the step of forming the concave groove 11 as shown by the dotted line in FIG. The phenomenon that etching progresses to the lower side of 2B occurs. Hereinafter, this phenomenon will be referred to as under etching. This under-etching causes the corners of the rectangular trapezoidal portion 7 to be scraped off at the four corners, so the weight is reduced by the scraped-off portion, and the detection sensitivity of the acceleration sensor is reduced. . It is possible to add a weight to supplement or increase the weight of the rectangular trapezoidal portion 7, but since a large number of the frame 5 and the rectangular trapezoidal portion 7 are formed on the semiconductor wafer and their shapes are extremely small, The work of sticking weights is extremely troublesome.

Therefore, conventionally, as shown in FIG. 12, correction masks 2C are formed at the four corners of the mask 2B for forming the rectangular trapezoidal portion 7, and the formation of the correction masks 2C suppresses the occurrence of under-etching. ing. The size of the correction mask 2C is determined by the amount y (see FIG.
1)). That is, the correction mask 2C has a length of the diagonal line which is twice the amount y of under-etching, and is set to a shape in which the intersection of the diagonal lines is located at the corner of the mask 2B (see FIG. 12).

Under-etching amount y is [100]
It is about 2.3 times the amount of etching. For this reason
The projection amount X of the correction mask 2C_BIs X_B≒ 2.3t
It This protrusion amount X_BTo form the through hole described above
Required groove width X_AAgainst X_A<X_BIt becomes a relationship. this
Result Groove width X required to form through hole_AWhereas, Anda
-Protrusion amount X required to correct etching_BCorrection with
If the mask 2C is formed, the state shown in FIG. 13 is obtained.
It Perform etching in the state shown in FIG.
However, the concave groove 11 is not continuous in an annular shape, and the correction mass
2C does not work as the original correction mask.
It For this reason, conventionally, the groove width of the concave groove 11 is set to the originally required groove width.
X_AThe projection amount X of the correction mask 2C is larger than_BThan
Groove width X _CMust be selected for
It

Since the groove width of the concave groove 11 must be selected to be X _C (X _A <X _B <X _C ) larger than the originally required groove width X _{A in} this way, it is necessary to reduce the size of the acceleration sensor. Is an obstacle. According to the conventional shape of the correction mask 2C, if the rectangular trapezoidal portion 7 is selected to have a long and thin shape for downsizing, as shown in FIG. 14, the correction masks 2C overlap each other. . In this case, [1
[00] reaches a set value, the under-etching that occurs under the correction mask 2C becomes the shape indicated by the dotted line, which causes the inconvenience that the groove 11 cannot be formed. In this case, the width a of the rectangular trapezoidal portion 7 must be selected so that a> √2y, where the amount of underetching is y. Therefore, also from this point, there is a disadvantage that the shape of the acceleration sensor cannot be reduced.

The object of the present invention is to suppress the occurrence of under-etching on the rectangular trapezoidal portion 7 as much as possible, and to make the concave groove 1
The present invention proposes an under-etching correction method in anisotropic etching that can take the groove width of 1 to the minimum value required to form a through hole.

[0013]

According to the present invention, when a rectangular annular groove is formed by etching and a rectangular trapezoidal portion is formed by forming the annular groove, each of the masks for forming the trapezoid is formed. A strip-shaped first correction mask having a dimension shorter than the groove width of the concave groove is formed at the corner of the groove, and the groove width of the concave groove is formed on both sides of the first correction mask from the masks left outside the concave groove. Second strip-shaped with shorter dimensions
A correction mask is formed, under-etching is started from a corner portion of the second correction mask, and the under-etching is carried over from the second correction mask to the first correction mask, so that the corner of the rectangular trapezoidal portion is formed. We propose a method for correcting under-etching in anisotropic etching, characterized by delaying the time for etching to reach a portion, and by delaying this time, the amount of under-etching that occurs in the rectangular trapezoid can be reduced. .

According to the under-etching correction method of the present invention, the first correction mask and the second correction mask only have to have a dimension shorter than the groove width of the concave groove, so that the groove width of the concave groove forms a through hole. It may be selected to the minimum required size. Therefore, there is an advantage that the shape can be reduced including the frame body.

[0015]

FIG. 1 shows an embodiment of a method for correcting under-etching in anisotropic etching according to the present invention. In the figure, 2A is a mask for forming the frame body 5 shown in FIG.
B shows a mask for forming the rectangular trapezoidal part 7 shown in FIG. In the present invention, a strip shape is formed from each corner of the mask 2B for forming the rectangular trapezoidal portion 7, in the illustrated example, from the corners at both ends of the short side 12 of the mask 2B toward the mask 2A for forming the frame body 5. The first correction mask 2D is formed so as to project. Further, strip-shaped second correction masks 2E and 2F are formed on both sides of the first correction mask 2D so as to project and extend from the mask 2A.
The first correction mask 2D and the second correction masks 2E and 2F
The projecting lengths L1 and L2 are formed to have dimensions L <L1 and L <L2 smaller than the groove width L of the concave groove 11. By selecting this dimension, the distance between the first correction mask 2D and the mask 2A and the second correction mask 2D
Spaces R1 and R2 are formed between the correction masks 2E and 2F and the mask 2B. The distances R1 and R2 may be as small as possible, and it is sufficient that the surface of the semiconductor substrate 1 is exposed even slightly.

By forming the intervals R1 and R2, under-etching starts from the lower portion of the corners A and A'of the second correction masks 2E and 2F. FIG. 2 shows the progress of etching. The under-etching starting from points A and A'progresses toward point B in the shape shown by the dotted line in FIG. 2 at the beginning. Since the etching operation on the A ', B', and C'sides is symmetrical with respect to the A, B, and C point sides shown in FIG. 2 and the center line 13 as a boundary, only the A, B, and C point sides will be described here. I will explain.

When the end of the etching reaches the point B, the etching takes the shape of and progresses toward the point C. At this time, on the XX line shown in FIG. 2, as shown in FIG.
The inclined surface 15 whose surface 1] is exposed is about to be formed. When the etching reaches the point C, a part of the etching passes through the point C and proceeds to the point F. On the other hand, since the space R1 is formed between the end of the first correction mask 2D and the mask 2A, the semiconductor substrate 1 is etched by this space R1 and the hole 14 is formed. The hole 14 is [11
1] Automatically stops with the surface exposed. When the etching reaches the C point in this state, [111] at the C point.
Since the surfaces are not determined on the cross line formed by the convex surfaces intersecting with each other, the etching progresses rapidly, and the shape shown in FIG.
Etching progresses toward the point. When the etching reaches the point D, the etching shape becomes. Etching in the shape of (3) proceeds similarly on the opposite side with the center line 13 as line symmetry. As a result, the etching proceeds in the plane shape as shown in FIG. 4 at the position of the line YY shown in FIG.

When the etching contacts the portion of the rectangular trapezoid portion 7, the etching on the points A ', B', and C'abuts the [111] plane, so that the etching stops at the portion of the rectangular trapezoid portion 7. However, the etching on the points A, B and C hits the corners of the rectangular trapezoid. Therefore, underetching starts from this corner. This under-etching amount Z is Z = W _1/2 . Where W ₁ is the first correction mask 2D
Indicates the width of. Therefore, the smaller the width W ₁ of the first correction mask 2D, the smaller the final under-etching amount Z can be made. However, there are limits. That is, the inclined surface 15 having the exposed [111] surface is formed below the second correction masks 2E and 2F in a state where the etching is directed from the point A to the point C. Since it is exposed, it is etched though the etching amount is small. In order to carry out the etching for correction to the end without any trouble, the [111] surface is etched because the portion in contact with the back surface of the first correction mask 2D must not disappear while the etching proceeds to a predetermined depth. Quantity J
Then, the width W ₁ of the first correction mask 2D must be selected so that W ₁ ≧ 2J.

When the etching reaches the portion of the rectangular trapezoidal portion, FIG. 4 is shown below the center line 13 of the first correction mask 2D.
Etching starts downward from the mountain-shaped apex portion shown in FIG. 1, and the first correction mask 2D and the second correction masks 2E and 2F are formed.
On the lower side portion, the concave groove 11 having the same shape as the place where these correction masks 2D, 2E and 2F do not exist is formed.
Although the first correction mask 2D and the second correction masks 2E and 2F are formed on the short sides of the mask 2B for forming the rectangular trapezoidal portion 7 in the embodiment shown in FIG. It may be formed on the side corner. Further, the long side corners and the short side corners may be alternately formed, or even if the long side corners and the short side corners are formed, the same action and effect can be obtained.

[0020]

As described above, according to the present invention, the first correction mask 2D and the second correction masks 2E and 2F are formed to have a width smaller than the width L of the opening of the mask in which the concave groove 11 is to be formed. Since it is sufficient to form the opening intervals R1 and R2 at the end portions, the width L of the opening portion of the mask in which the concave groove 11 is to be formed.
Since it suffices to adopt the dimension X _A ≈√2t necessary for forming the through hole in the semiconductor substrate having the thickness t μm, the dimension L of the groove width can be minimized. Therefore, there is an advantage that the shape of the acceleration sensor as shown in FIG. 7 can be reduced.

Further, the amount Z of under-etching into the rectangular trapezoidal portion 7 can be controlled by the value of the width W ₁ of the first correction mask 2D. As a result, the amount Z of under-etching can be reduced, and a large reduction in the weight of the rectangular trapezoidal portion 7 can be prevented. Therefore, in this respect, it is possible to obtain the practical benefit of making an acceleration sensor having high sensitivity.

When the amount of under-etching is y, the width a of the rectangular trapezoidal portion 7 can be selected as a <√2y, and the shape of the rectangular trapezoidal portion 7 can be selected as an elongated shape. Is obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of the present invention.

FIG. 2 is a plan view for explaining an underetching correction method according to the present invention.

FIG. 3 is a cross-sectional view taken along line XX shown in FIG.

FIG. 4 is a plan view on line YY shown in FIG.

FIG. 5 is a plan view for explaining anisotropic etching.

6 is a cross-sectional view taken along the line AA shown in FIG.

FIG. 7 is a perspective view for explaining the structure of an acceleration sensor manufactured by using anisotropic etching.

FIG. 8 is a plan view for explaining the method of manufacturing the acceleration sensor shown in FIG.

9 is a plan view showing a state after the etching process from the state of FIG.

10 is a cross-sectional view taken along the line BB shown in FIG.

FIG. 11 is a partially enlarged plan view for explaining the inconvenience of the conventional technique.

FIG. 12 is a partially enlarged plan view for explaining a conventional under-etching correction method.

FIG. 13 is a partially enlarged cross-sectional view for explaining the inconvenience of the conventional under-etching correction method.

FIG. 14 is a plan view similar to FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Etching mask 2A Mask for forming a frame 2B Mask for forming a rectangular trapezoid 2D 1st correction mask 2E, 2F 2nd correction mask 5 Frame 7 Rectangular trapezoid 9 Square ring-shaped mask hole 11 concave groove 12 short side

Claims (2)

[Claims] 1. A semiconductor substrate is provided with a rectangular annular groove,
In anisotropic etching for forming a rectangular trapezoid inside the groove and forming a rectangular trapezoid inside the groove, the frame is formed from each corner of a rectangular mask for forming the rectangular trapezoid. Strip-shaped first formed to be shorter than the groove width of the mask opening surface for forming the concave groove toward the mask for forming
A correction mask and a second strip-shaped correction formed from the masks for forming the frame body on both sides of the first correction mask toward the masks for forming the rectangular trapezoidal portion with a width shorter than the groove width. A method for correcting under-etching in anisotropic etching, characterized in that a mask is provided to suppress the amount of under-etching that goes into each corner of the rectangular trapezoidal portion. 2. The rectangular annular groove according to claim 1, wherein each side is parallel to the [110] plane of the semiconductor substrate, and the plane parallel to the surface of the semiconductor substrate is the [100] plane. Correction method for underetching in anisotropic etching.