JPS62232171A - Semiconductor acceleration sensor - Google Patents

Abstract

PURPOSE:To set the width of a cantilever in the vicinity of a supporting part, which gives large effects on the characteristics of a semiconductor accleration sensor in correspondence with a mask shape in etching, by making the width of the cantilever in the vicinity of the supporting part, which is formed in a semiconductor substrate, smaller than the thickness of the semiconductor substrate. CONSTITUTION:A groove 3, which penetrates a semiconductor substrate from its upper surface to lower surface, is provided in the Si semiconductor substrate 1. with this groove 3, a cantilever 2, which is separated from the outer semiconductor substrate, is formed at a part other than the vicinity of a supporting part. The width W1 of the cantilever 2 in the vicinity of the supporting part, i.e., the size of the cantilever in the horizontal direction with respect to the plane of the Si semiconductor substrate 1, is set so that W1 is smaller than the size w2 of the Si semiconductor substrate 1 in the thickness direction. Therefore, the cantilever 2 is not displaced by acceleration in the direction orthogonal to the plane of the Si semiconductor substrate 1, but displaced by accleration in the direction horizontal to the plane. By providing a means for detecting the displacement, the acceleration in the direction horizontal to the plane of the Si semiconductor substrate can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a semiconductor acceleration sensor having a single cantilever structure.

[Prior art]

As a conventional semiconductor acceleration sensor, for example, IEEE TRANSACTIONS ON ELECTRON DEVICES (IEEE TRANSACTIONS
ELECTRON DEVICES, Vol, HD-
26, No. 12. There is one described in DHC1979ρ1911).

FIG. 6 is a diagram showing the above semiconductor acceleration sensor,
(A) is a sectional view, and (B) is a plan view.

In the device shown in FIG. 6, the groove 35 is removed by etching the Si semiconductor substrate 31 from both the upper and lower directions, and a cantilever beam 32 is formed which is partitioned from the outside by the groove 35.

Note that a weight portion 36 is provided at the tip of each cantilever 32, and the thickness near the support portion of the cantilever 32 (the dimension in the direction perpendicular to the surface of the semiconductor substrate) is also etched by etching. It is formed to be thinner than other parts, so that it is displaced in response to acceleration in the thickness direction (direction perpendicular to the surface) of the semiconductor substrate.

In addition, the cantilever beam 32 due to acceleration in the direction perpendicular to the above plane
In order to detect the displacement of the cantilever beam 32, a diffused resistor 33 is provided near the support portion of the cantilever beam 32, and the displacement of the cantilever beam due to the application of acceleration is detected by the piezoresistance effect of the diffused resistor 33. ing.

Further, in order to prevent the cantilever beam 32 from breaking due to excessive impact, both sides of the Si semiconductor substrate 31 are protected by glass coverrs 34.

Next, FIG. 7 is a diagram showing a manufacturing process of a conventional semiconductor acceleration sensor as shown in FIG. 6 above.

First, in (A), a silicon oxide film 37 with a thickness of approximately 1.5-1.5 mm is formed on both sides of an n-type Si semiconductor substrate 31 whose surface is the (100) crystal plane using a thermal oxidation method, and then photo-etched. A p-type diffused resistance layer 38 and a high concentration P+ diffused layer 39 are formed by performing thermal diffusion treatment twice.

Next, in (B), an An wiring M440 is formed by photoetching and vacuum evaporation, and a phosphorus glass film 41 is further formed by chemical vapor deposition.

Next, in (C), the silicon oxide film 37 in a predetermined region on the back surface is removed, and using this as a mask, a crystal plane selective etching method using a KOH solution is performed to obtain a thickness approximately twice the thickness of the target cantilever. The Si semiconductor substrate 31 is etched until it is thick.

Next, in (D), the phosphorus glass film 41 and the silicon oxide film 37 at a predetermined portion of the surface are removed by etching, and using this as a mask, etching is performed from both sides of the Si semiconductor substrate 31 using a KOH solution. The cantilever beam 32 is formed by removing the groove 35 portion.

At this time, the thickness near the support portion of the single cantilever beam 32 is also etched and thinned to a desired thickness.

Further, by etching, a predetermined portion of the phosphor glass film 41 is etched.
is removed to form a contact hole 42.

Finally, by attaching glass covers (not shown) to both sides of the Si semiconductor substrate 31, the semiconductor acceleration sensor as shown in FIG. 6 is completed.

[Problem that the invention seeks to solve]

In the conventional semiconductor acceleration sensor as described above, the composition of the etching solution is important in order to make the thickness uniform near the support part of the cantilever beam formed by etching the semiconductor substrate from both the top and bottom directions.

It is necessary to maintain constant etching environmental conditions such as temperature and stirring conditions, but it is extremely difficult to maintain the above conditions uniformly over all parts of the semiconductor substrate surface, so it is necessary to maintain sufficient etching conditions. It is difficult to ensure accuracy.

Therefore, there has been a problem in that it is difficult to mass-produce semiconductor acceleration sensors with uniform characteristics.

Also, in conventional semiconductor acceleration sensors.

Since it is possible to form only a cantilever beam that is displaced in the direction perpendicular to the surface of the semiconductor substrate, 1.
That is, when it is desired to detect acceleration in two mutually perpendicular directions, a member 43 is installed as shown in FIG.
Since it is necessary to arrange and fix the two semiconductor acceleration sensors 44 and 45 so that the movable directions of their cantilevers are perpendicular to each other, the assembly and mounting method becomes complicated and the size increases. was there.

Furthermore, in conventional semiconductor acceleration sensors, the cantilever beam may break due to m* acceleration that occurs during the semiconductor device manufacturing process after the cantilever structure is formed or during the assembly and mounting process until the glass cover is attached. Therefore, there was a problem in that the manufacturing yield was significantly reduced.

The present invention was made in order to solve the problems of the prior art as described above, and has uniform characteristics and a high manufacturing yield.
Moreover, it is an object of the present invention to provide a semiconductor acceleration sensor that can easily realize a structure that detects acceleration in multiple directions.

[Means to solve the problem]

In order to achieve the above object, in the present invention, a cantilever beam is formed in a semiconductor substrate and is partitioned from the outside except for the support portion by a groove penetrating the semiconductor substrate from the upper surface to the lower surface, and By making the width (dimension in the direction horizontal to the surface of the semiconductor substrate) of the supporting beam smaller than the dimension in the direction perpendicular to the surface of the semiconductor substrate, displacement due to acceleration in the direction parallel to the surface of the semiconductor substrate can be reduced. It is configured to form a cantilever beam.

[Effect]

As mentioned above, in the semiconductor acceleration sensor of the present invention,
The thickness near the support part of a conventional semiconductor acceleration sensor (the dimension perpendicular to the surface of the semiconductor substrate) corresponds to the width near the support part of the cantilever beam, i.e., the width parallel to the surface of the semiconductor substrate. Since the dimensions are in the same direction, the dimensions can be precisely controlled by changing the shape of the mask during etching.

For example, one method is reactive ion etching using CBrF, etc. as an etching gas.
By using an etching method that exhibits a sharp anisotropic pressure in the depth direction of the semiconductor substrate, the width of the cantilever near the supporting portion can be made to accurately match the dimensions of the mask. Another method is to form a cantilever beam on a Si semiconductor substrate having a (110) plane using a crystal plane selective etching method, thereby increasing the crystal plane selectivity between the (110) plane and the (111) plane. It is possible to set the convergence near the support part of the cantilever beam with high accuracy determined by .

Therefore, it becomes possible to mass-produce semiconductor acceleration sensors with uniform characteristics.

In addition, the first semiconductor acceleration sensor of the present invention is sensitive to acceleration in a direction parallel to the surface of the semiconductor substrate. By forming the semiconductor acceleration sensor so as to be sensitive to both directions, it is possible to commonly form semiconductor acceleration sensors that are mutually sensitive to acceleration in the vertical direction, or even semiconductor acceleration sensors that are sensitive to acceleration in a plurality of directions, on one semiconductor substrate. It becomes possible.

Furthermore, in the semiconductor acceleration sensor of the present invention, since the displacement direction of the cantilever beam is parallel to the surface of the semiconductor substrate,
The structure is such that the periphery of the cantilever beam in the displacement direction is surrounded by a semiconductor substrate. Therefore, a protective structure for the cantilever is also formed at the same time as the cantilever is formed, so there is a risk that the cantilever will break due to impact acceleration applied during the manufacturing process and assembly mounting process after the cantilever is formed. It also disappears.

〔Example〕

FIG. 1 is a perspective view of the present invention, and FIG. 2 is a plan view and a sectional view.

In FIGS. 1 and 2, the Si semiconductor base Fil has the following:
A groove 3 penetrating the semiconductor substrate from the upper surface to the lower surface is formed by etching, and this groove 3 forms a cantilever beam 2 that is partitioned from the external semiconductor substrate except for the vicinity of the support portion.

Note that the width W1° of the cantilever beam 2 near the support part, that is, the dimension of the beam in the horizontal direction with respect to the surface of the Si semiconductor substrate 1 is as follows:
It is set to be smaller than the dimension W2 in the thickness direction of the Si semiconductor substrate 1.

Therefore, the cantilever beam 2 is not displaced in response to acceleration in a direction perpendicular to the surface of the Si semiconductor substrate 1, but is displaced in response to acceleration in a direction horizontal to the surface.

Therefore, by providing a means for detecting the above-mentioned displacement (details will be described later), it is possible to detect acceleration in the direction horizontal to the surface of the Si semiconductor substrate 1.

Note that 19 is a weight portion of the cantilever beam.

Next, the manufacturing process of the semiconductor acceleration sensor of the present invention will be explained based on FIG.

Note that FIG. 3 shows a cross-sectional view of the semiconductor acceleration sensor during the manufacturing process and a plan view of the main parts.

First, in (A), a silicon oxide film 5 with a thickness of approximately 70 on- is formed on an n-type Si semiconductor substrate 1 by thermal oxidation, and the silicon oxide 1115 in a predetermined region 6 is removed by photoetching. .

Next, in (B), the Sl semiconductor substrate 1 is removed from the upper surface to the lower surface using the silicon oxide llA3 as a mask by reactive ion etching using, for example, CBrF as an etching gas, thereby forming a groove 11. .

Next, p-type impurity diffusion JFJ12 and the source 13 and drain 14 of the p-channel MOS transistor are formed by photoetching and impurity diffusion.

Next, in (C), a gate oxide film 15 is formed by photoetching and thermal oxidation, and an M wiring layer 16 is further formed by vacuum evaporation.

For example, by atmospheric pressure chemical vapor deposition method, phosphorus glass Il'J
form 17.

Next, in CD), a cantilever pattern is formed on the phosphor glass film 17 by photoetching, and using this as a mask, the upper surface of the Si semiconductor substrate 1 is etched by a reactive ion etching method using, for example, CBrF as an etching gas. The cantilever beam 2 is formed by removing until the bottom surface is reached.

Finally, a contact hole 18 for external wiring is formed by photoetching, thereby completing the semiconductor acceleration sensor as shown in FIG.

In addition, as shown in FIG. 3(D), the weight part 19 of the cantilever beam
A p-type diffusion layer 12 is provided on both side surfaces and the portion facing the side surfaces.

A portion of the p-type diffusion layer 12 provided on the surface of the weight portion 19 becomes the beam-like electrode 20, and a portion provided on the surface opposite thereto becomes the substrate electrode 21.

Then, by detecting a change in the capacitance formed between the beam-shaped electrode 20 and the substrate electrode 21.

The displacement of the cantilever beam 2 can be detected.

Next, FIG. 4 is a diagram illustrating a method for detecting the displacement of the cantilever beam.

In FIG. 4, the mass of the weight portion 19 of the cantilever beam 2 is M, the width of the cantilever beam 2 near the support portion ( The dimension (horizontal to the surface of the semiconductor substrate) is t, and the length of the cantilever is from the support end to the weight part 1.
9) is L, Young's modulus is E, and
If the distance between the beam electrode 20 provided on the side surface of the weight part 19 and the substrate electrode 21 provided on the opposite surface is d, and the acceleration of gravity is g, then the static current between the beam electrode 20 and the substrate electrode 21 is The rate of change ΔC/C per 1 g in capacitance tc is as follows (1)
It is expressed by the formula.

In the above equation (1), 1 For example, the mass of the weight M = 2
．． 45X10-'g, cantilever thickness b = 500am,
Width near the support part of the cantilever beam t = 54, length of the cantilever beam L = 1
000,, the distance between both electrodes d=10. Then, Young's modulus E = 1.7 x 10"dyne/aJ, acceleration of gravity g = 980ell/see", so the rate of change in capacitance C per 1g is ΔC/C = 0.0
02&.

For example, by converting the capacitance change described above into an electrical signal using a detection circuit composed of a p-channel MQS transistor as shown in FIGS. 1 and 3, the acceleration applied to the cantilever beam is converted into an electrical signal. Can be detected.

Next, FIG. 5 is a diagram showing another embodiment of the present invention.

In the embodiment of FIG. 5, one Si semiconductor substrate 22
2 shows an example in which two cantilevers 23 and 24 are formed.

These two cantilever beams 23 and 24 are arranged so that the movable directions of the beams are perpendicular to each other.

Therefore, acceleration in two mutually perpendicular directions can be detected.

In addition, in the present invention, since the movable direction of the cantilever beam can be set according to the mask pattern during etching, it is possible to easily install multiple semiconductor sensors that detect acceleration in various directions on one semiconductor substrate. It becomes possible to form.

In addition, in the above embodiments, the case where a reactive etching method was used was explained, but by appropriately selecting the etching mask pattern, the crystal plane using the Si semiconductor substrate having the (100) crystal plane as the surface can be etched. Selective etching methods can also be used.

〔Effect of the invention〕

As explained above, in the present invention, by making the width of the cantilever beam formed on the semiconductor substrate near the support part smaller than the thickness of the semiconductor substrate, the cantilever beam can be displaced by acceleration in a direction parallel to the surface of the semiconductor substrate. Since it is configured to form a beam, the width near the support portion, which has a large effect on the characteristics of the semiconductor acceleration sensor, can be precisely set according to the shape of the mask used in etching.

For example, by forming beams using a reactive ion etching method or using a crystal plane selective etching method on a Si semiconductor substrate with a (110) plane as a surface, etching anisotropy or crystal plane selectivity can be improved. It is possible to set the width near the support part of the cantilever beam with high accuracy determined by .

Therefore, it becomes possible to easily produce semiconductor acceleration sensors with uniform characteristics.

Furthermore, in the present invention, a plurality of cantilevers can be formed on one semiconductor substrate so that the displacement directions are different from each other, so that, for example, acceleration in two mutually perpendicular directions can be separated. A device capable of detection can be easily constructed.

In addition, since the side surface of the cantilever beam in the displacement direction is surrounded by the semiconductor substrate, a protective structure is also formed at the same time as the cantilever beam is formed. Many excellent effects can be obtained, such as being able to prevent the cantilever beam from breaking due to impact acceleration applied during the mounting process.

[Brief explanation of drawings]

Fig. 1 is a perspective view of an embodiment of the present invention, Fig. 2 is a plan view and sectional view of an embodiment of the invention, Fig. 3 is a manufacturing process diagram of an embodiment of the invention, and Fig. 4 is a diagram of the manufacturing process of an embodiment of the invention. FIG. 3 is an explanatory diagram of a method for detecting displacement of a cantilever beam in the present invention. Fig. 5 is a diagram of another embodiment of the present invention, Fig. 6 is a sectional view and a plan view of an example of a conventional device, Fig. 7 is a manufacturing process diagram of the conventional device, and Fig. 8 is a diagram of another example of the conventional device. It is. Explanation of symbols> 1... SL semiconductor substrate 2... Cantilever beam 3... Groove 19... Cantilever weight section Patent attorney Junnosuke Nakamura Figure 1 Figure 2 Figure 1-- -5i main conductor board 2 - cantilevered mound 3 - one groove 19 - one single piece of wooden beam part Fig. 3 Fig. 6 3475 Siber 33m2'WLNL No. 8
Figure 43 Mamata is a talented person

Claims (1)

[Claims] In a semiconductor acceleration sensor that detects applied acceleration by detecting displacement of a cantilever provided in a semiconductor substrate, a supporting portion is removed by a groove penetrating the semiconductor substrate from the top surface to the bottom surface of the semiconductor substrate. to form a cantilever beam partitioned from the outside, and the width of the cantilever beam near the support part, that is, the dimension in the direction horizontal to the surface of the semiconductor substrate,
A semiconductor acceleration sensor characterized in that a cantilever beam is formed that is displaced by acceleration in a direction horizontal to the surface of the semiconductor substrate by making the dimension smaller than the dimension in the direction perpendicular to the surface of the semiconductor substrate.