JPS62124777A - Semiconductor dynamic-quantity sensor - Google Patents

Abstract

PURPOSE:To mass-produce dynamic-quantity sensors having uniform charac teristics by precisely forming the thickness of a cantilever as a dynamic-quantity responding section and a diaphragm. CONSTITUTION:A groove 8 in depth corresponding to the thickness of a cantilever is formed from the surface of an Si substrate 1, and piezo-resistors 16 for detecting strain are shaped previously on both sides of the groove 8, but the piezo-resistors are formed where shorter than 0.7 times as long as the depth of the groove from the groove. A groove oxide 9, a surface insulating film 11 and a back insulating film 12 are shaped and oxidizing the surface and back of the Si substrate 1, and a packing as a beam structure 10 is buried into the groove 8. One parts of the back insulating film 12 are removed, and a hole 13 for forming a beam and a hole 14 for shaping an air gap are formed, but remaining section in the back insulating film 12 function as masks 15 for etching the back. The Si substrate 1 is etched in an anisotropic manner from the back. Etching progresses in sections to which the groove oxide 9 is not shaped, the air gaps 18 are formed, Si is left obliquely on both side walls of the groove, and the Si sections serve as the piezo-resistor sections 16.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor mechanical quantity sensor, such as a pressure sensor or an acceleration sensor.

[Prior art]

Examples of conventional semiconductor acceleration sensors include:

There is one proposed by Roylance et al. (L
, M. Roylance and J. B. Angel.
l IEEHE Electron Devices,
VolJD-26, No. 12. p, 1911. D
ec, 1979”A Batch-Fabricate
d 5ilicon Accelerometer).

FIG. 7 is a perspective view and a sectional view of the above semiconductor sensor.

In FIG. 7, 71 is an n-type Si substrate, 72 is an St cantilever, 73 is a Si weight, and 74 is a diffused resistor.

In the semiconductor acceleration sensor described above, when acceleration is applied, the Si weight 73 is deflected, so that the Si cantilever 7
2 causes distortion.

A diffused resistor 74 is formed near the support portion of the Si cantilever 72, and when the cantilever is strained, the resistance value of the diffused resistor 74 changes due to the piezoresistance effect.

Acceleration can be detected by detecting this change in resistance value.

When manufacturing a semiconductor acceleration sensor with a cantilever structure as described above, an anisotropic etching solution such as KOH is used to etch S.
By etching the back side of the i-board 71,
A method of forming a Si cantilever 72 is used.

Next, FIG. 8 is an example of a conventional semiconductor pressure sensor, and shows a cross-sectional view of a diaphragm type pressure sensor.
In the figure, 81 is a Si diaphragm, 82 is a Si substrate, 83 is a diffused resistor, 84 is a metal electrode, 85 is a surface insulating film, and 86 is a surface protective film.

In the above pressure sensor, when pressure is applied to the diaphragm 81, the diaphragm 81 is distorted, and therefore the resistance value of the diffusion resistor 83 changes, so that pressure can be detected.

In the method of manufacturing such a diaphragm pressure sensor, a method is used in which the diaphragm is formed by anisotropic etching using KOH or the like from the back side, similar to the device shown in FIG.

[Problem that the invention seeks to solve]

In semiconductor dynamic quantity sensors as shown in Figures 7 and 8 above, the thickness of the cantilever beam and the thickness of the diaphragm are the most important parameters that determine the sensing ability of the sensor, and if the thickness changes, resonance may occur. Frequency and sensitivity change.

Therefore, if the thickness cannot be precisely controlled, the characteristics of the sensor cannot be made uniform.

However, the S used to manufacture the above sensor
The thickness of the i-substrate varies by at least ±5t1m, so even if etching is performed under the same conditions, the thickness of the cantilever beam or diaphragm will vary to the same extent as the variation in the thickness of the Si substrate. Put it away.

In addition, in anisotropic etching using a KOH, etc., the etching speed changes depending on changes in the etching solution temperature, solution stirring state, solution composition, etc., so it is difficult to precisely control the thickness of the cantilever beam or diaphragm. Very difficult.

Therefore, there was a problem in that the variation in product characteristics increased and the yield decreased.

The present invention was made in order to solve the problems of the prior art as described above, and an object of the present invention is to provide a semiconductor dynamic quantity sensor that can precisely set the thickness of a cantilever beam and a diaphragm. It is something.

[Means to solve the problem]

In order to achieve the above object, one aspect of the present invention is as follows.

Mechanical quantity-responsive parts in semiconductor substrates (cantilevers and diaphragms)
One or more grooves having a depth corresponding to the thickness of the dynamic quantity responsive part from the surface of the semiconductor substrate are provided in a part of the part that will become the mechanical quantity responsive part, and the inner surface of the groove is oxidized to form a filling material that becomes the dynamic quantity responsive part. After filling the groove with etching, the semiconductor substrate is etched from the back side to form a mechanical quantity responsive portion having a thickness corresponding to the depth of the groove.

As described above, in the present invention, by oxidizing the inner surface of the groove, etching from the back surface is stopped at the surface of the groove, so the thickness of the mechanical quantity responsive part can be arbitrarily set depending on the depth of the groove. I can do it.

It should be noted that, compared to the conventional method described above, in which an extremely thin pressure-responsive part is left by etching from the back surface of the semiconductor substrate, when a shallow groove is formed on the surface of the semiconductor substrate by etching as in the present invention, , the depth of the groove can be set precisely.

Therefore, since the thickness of a single cantilever beam or diaphragm can be precisely controlled, it is possible to mass-produce products with uniform characteristics.

[Embodiments of the invention]

1 and 2 are diagrams of a first embodiment of the present invention,
1 is a perspective view, and FIG. 2(A) is a sectional view taken along the line AA' in FIG. 1, showing a case where the present invention is applied to a cantilever type semiconductor acceleration sensor.

(B) shows a B-B' cross-sectional view.

In FIGS. 1 and 2, 1 is a Si substrate, 2 is a filling material in the groove (PSG, poly-Si, Sin, Si3N).
, etc.); 3 is a Si cantilever; 4 is a Si weight; 5 is a gap separating the Si substrate 1 from the Si cantilever 3 and the Si weight 4; 6 is a piezoresistor; is a mask for backside etching.

In the above device, the main portion of the Si cantilever 3 is constituted by the groove region 2, and the piezoresistor 6 is formed in the SL portion around the groove region 2.

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

First, in (A), a groove 8 having a depth corresponding to the thickness of the cantilever beam is formed in the surface of the Si substrate 1.

This groove 8 is formed by an etching method such as reactive ion etching (RIE).

Note that the piezoresistors 16 for strain detection are formed on both sides of the groove 8, but they must be formed at a position closer to the groove than 0.7 times the depth of the groove.

Next, in (B), the front and back surfaces of the Si substrate 1 are oxidized to form the groove oxide 91, the front insulating film 11, and the back insulating film 12.

Next, the groove 8 is filled with filling material (Sin, . . .
Si, N4. embed PSG, poly-Si, etc.).

Next, in (C), a portion of the back insulating film 12 is removed by photoetching to form a beam forming hole 13 and a gap forming hole 14.

At this time, the remaining portion of the back insulating film 12 becomes the mask 15 for back etching.

Next, in CD), the Si substrate 1 is anisotropically etched from the back side.

As the etching solution, ethylenediamine/pyrocatechol, KOH, hydrazine, etc. are used.

When etching is performed using the above etching solution, the etching stops at the groove oxide 9 on the lower surface of the portion that will become the cantilever.

However, in the portions where trench oxide 9 is not provided, etching progresses and voids 18 are formed.

At this time, Si is left diagonally on both side walls of the groove, and this part becomes the piezoresistive part 16.The width of the part where the SL is left is equal to 0 of the depth of the groove.
．． Since it is about 7 times as large, the above-mentioned piezoresistor must be formed within this range.

As described above, in the semiconductor acceleration sensor of the present invention, the thickness and width of the cantilever are determined by the depth and width of the groove formed from the front surface of the Si substrate, and the thickness and width of the cantilever are determined by the depth and width of the groove formed from the front surface of the Si substrate. It is hardly affected by the temperature, etching time, stirring state of the etching solution, variations in the thickness of the Si substrate, etc.

Therefore, the thickness and shape of the cantilever beam can be precisely set, making it possible to mass-produce products with uniform characteristics.
The effect is that the yield is improved.

Next, FIG. 4 is a diagram showing a second embodiment of the present invention, in which a cantilever-type acceleration sensor similar to the one described above is constructed in which both the cantilever portion and the Si weight portion are formed using grooves. An example of the configuration is shown below.

4(A) is a perspective view, FIG. 4(B) is a sectional view taken along the line AA', and FIG. 4(C) is a sectional view taken along the line BB'.

In the embodiment shown in FIG. 4, a cantilever beam and a Si weight are formed in a groove region similar to that described above (the groove is filled with a material serving as a structure).

Note that a plurality of groove regions 41 are provided in the cantilever section, but if the interval between these groove regions is made smaller than 1.4 times the depth, SL between the grooves can be left. Therefore, a cantilever beam can be formed continuously.

As described above, by forming the Si weight portion as a groove region, the degree of freedom in designing a single weight increases, and it becomes possible to precisely form weights having various thicknesses and weights.

Next, FIG. 5 is a diagram showing a third embodiment of the present invention, in which the present invention is applied to a diaphragm type semi-solid pressure sensor.

In FIG. 5, 50 is a Si substrate, 51 is a diffused resistance section,
52 is a groove region, 53 is a diaphragm, and 54 is a backside etching mask.

In the semiconductor pressure sensor shown in FIG.
3 is formed with a groove region 52 similar to the above, and
A diffused resistor 51 is formed in the Si portion left between the groove regions.

Similarly to the above, if the distance between the grooves is less than 1.4 times the depth of the grooves, SL will remain in that area when anisotropic etching is performed from the back side. It becomes possible to form a diffused resistance for negative detection in the portion.

Next, the manufacturing process of the semiconductor pressure sensor shown in FIG. 5 will be explained based on FIG. 6.

First, in (A), a groove 60 having a depth corresponding to the thickness of the diaphragm is formed from the surface of the Si substrate 61.

Note that the width of the region 62 left between the grooves is set to be smaller than 1.4 times the depth of the grooves, and a diffused resistor is formed in this portion.

Next, in (B), the front and back surfaces of the Si substrate 61 are oxidized to form a trench oxide film 63. A back insulating film 65 and a front insulating film 66 are formed, and a filling material (Sin2, PSG, poly-Si, Si3N4) that becomes a diaphragm structure is formed inside the groove.
etc.).

Next, in (C), a mask for etching is formed by removing a portion of the back insulating film 65 where the diaphragm forming hole 67 is to be formed.

Next, in (D), the Si substrate 61 is etched from the back surface using the above mask.

Note that KOH, ethylenediamine/pyrocatechol, or the like is used as the etching solution.

The above etching stops when it reaches the groove oxide 63 provided on the inner surface of the groove, and in the Si portion between the grooves,
A V-shaped groove corresponding to the width is formed and etching automatically stops.

As mentioned above, in this example as well, the thickness of the diaphragm is determined by the depth of the groove formed from the front surface, so the temperature of the anisotropic etching solution from the back side, the etching time, and the stirring state of the etching solution are The thickness of the diaphragm can be precisely controlled without being affected by variations in the thickness of the Si substrate or the like.

Note that, as described above, the Si surrounded by the groove regions
Since a V-shaped groove is formed in this part when etching from the back side, this part is particularly susceptible to distortion. Therefore, if a diffused resistance part that becomes a piezoresistance is formed in this part, high sensitivity can be achieved. This makes it possible to realize a sensor with a wide range of functions.

〔Effect of the invention〕

As explained above, in the present invention, a groove having a depth corresponding to the thickness of the mechanical quantity responsive part from the surface of the semiconductor substrate is provided in a part of the semiconductor substrate that becomes the mechanical quantity responsive part, and the groove is After oxidizing the inner surface of the groove and filling the groove with a filler that will become the structure of the dynamic quantity responsive part, the semiconductor substrate is etched from the back side to form a dynamic quantity responsive part having a thickness corresponding to the depth of the groove. Since the structure is such that the thickness of the cantilever beam and diaphragm, which serve as the mechanical quantity responsive portion, can be precisely formed. This makes it possible to mass-produce mechanical quantity sensors with uniform characteristics.

The effect is that the yield is improved.

In addition, a V-shaped groove is formed in the area sandwiched between the groove areas when etching from the back side, and as that area becomes thinner, it is easier to receive distortion, and piezoresistance can be formed in that area. This makes it possible to realize a highly sensitive sensor.

[Brief explanation of drawings]

FIG. 1 and FIG. 2 are diagrams of a first embodiment of the present invention. 3 is a manufacturing process diagram of the first embodiment, FIG. 4 is a diagram of the second embodiment of the present invention, FIG. 5 is a diagram of the third embodiment of the present invention, and FIG. 6 is a diagram of the third embodiment of the invention. The manufacturing process diagrams of the embodiment, FIGS. 7 and 8, each show an example of a conventional device. <Explanation of symbols> 1...Si substrate 2...Groove region 3...S
i Cantilever beam 4...SL weight 5...Gap
6... Piezoresistor 7... Patent attorney representing the mask for back etching Junnosuke Nakamura 1 Figure day B' 1---- 5. -Ki-o and 2-11-ra v1! Print 3----5 piece P! Early 4----- S 11th 5-111 Jukubayashi 6---- Piezo Discharge 7----- Emmen work, $>rii's mass feed 2 Interval (A) (B ) Middle 5 Figures 4 50----- Sノ "Kunsai IE 51----- i Scattered part 52--1 Spelling 53----- Da A Ah Um

Claims (3)

[Claims] 1. A semiconductor mechanical quantity, which has a mechanical quantity responsive part formed in a semiconductor substrate to have a thickness thinner than the thickness of the semiconductor substrate, and a detection part that detects strain in the mechanical quantity responsive part when a mechanical quantity is applied. In the sensor, one or more grooves having a depth corresponding to the thickness of the mechanical quantity responsive part from the surface of the semiconductor substrate are provided in a part of the semiconductor substrate that becomes the mechanical quantity responsive part; A mechanical quantity having a thickness corresponding to the depth of the groove is formed by oxidizing the inner surface of the groove and filling the groove with a filler that becomes the structure of the mechanical quantity responsive part, and then etching the semiconductor substrate from the back side. A semiconductor dynamic quantity sensor characterized by forming a responsive part. 2. The mechanical quantity responsive part is a cantilever beam supported at one end, and a piezoresistor serving as the detection part is formed around the groove provided in the cantilever beam. A semiconductor mechanical quantity sensor according to scope 1. 3. Claim 1, wherein the mechanical quantity responsive part is a diaphragm, and a piezoresistor serving as the detection part is formed in a portion surrounded in at least two directions by the groove provided in the diaphragm. The semiconductor mechanical quantity sensor described above.