JPH0830718B2 - Semiconductor acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Object of the Invention (Industrial field of application) The present invention relates to a cantilever type semiconductor acceleration sensor.

(Prior Art) As a conventional cantilever type semiconductor acceleration sensor, for example, there is one as shown in FIGS.
tch-Fabricated Silicon A ccelerometer '' IEEE ED-26,
No. 12, p1911, Dec. 1979).

In FIG. 10, reference numeral 41 denotes a Si substrate, and the Si substrate 41 is subjected to etching processing from its back surface side and front surface side so that a gap portion 42 is penetrated between both surfaces of the substrate and one end is supported by a fixing portion 43. A cantilever 44 is formed, and a mass portion 45 to which a detected acceleration is applied is formed at the tip of the cantilever 44. Reference numeral 46 is a backside etching mask. A piezoresistor for acceleration detection is formed on the cantilever 44 by a diffusion layer resistance not shown. As described above, in the conventional semiconductor acceleration sensor, the cantilever 44, the mass portion 45, and the like are planarly formed on the Si substrate 41.

When acceleration is applied to the mass portion 45 during use, the mass portion 45 is displaced and the cantilever 44 is bent, and a stress proportional to the acceleration is generated on the surface portion of the cantilever 44. Due to this stress, the resistance value of the piezoresistor changes, and the acceleration is detected from the change in the resistance value.

As described above, in the semiconductor acceleration sensor, the cantilever 44 bends when the acceleration is applied, and the mass portion 45 is vertically displaced. For this reason, as shown in FIG. 11, an upper stopper 47 and a lower stopper 48 for protecting the cantilever 44 from the excessive G are formed on the front surface and the back surface of the Si substrate 41 by the displacement of the mass portion 45. It is installed at a certain interval.

(Problems to be Solved by the Invention) The conventional semiconductor acceleration sensor requires etching processing from the back side and the front side of the Si substrate, and therefore requires complicated processes such as double-sided alignment, and the mass portion and minute Since it is necessary to add a stopper that needs to be installed at a certain interval in a later step, the installation is difficult, which leads to a decrease in yield and an increase in cost.

Moreover, since the cantilever and the mass portion are formed on the surface of the Si substrate in a plane, only a semiconductor acceleration sensor that detects acceleration in the direction perpendicular to the surface can be manufactured. A single sensor unit with sensitivity in the dimension
It could not be formed on the Si substrate at the same time.

Further, as shown in FIG. 12, since the center of gravity 49 of the mass portion 45 is located at a position shifted downward by h from the extension of the cantilever 44, the sensitivity to the other axis, that is, the acceleration Ax in the x direction is also high. Will occur. To further explain this, assuming that the sensitivities in the x and y directions are Sx and Sy, respectively, and the distance from the support portion of the cantilever 44 to the center of gravity 49 is 1, although the other axis sensitivity Sx = 0 is desirable, There was a problem that the other axis sensitivity of SxSy · h / l would occur.

Therefore, the present invention improves the process yield by forming the stopper at the same time as the cantilever, the mass part, etc., and at the same time, it is possible to reduce the cost by eliminating the complicated process such as double-sided alignment. An object of the present invention is to provide a semiconductor acceleration sensor in which a sensor section having a sensitivity in a two-dimensional direction can be simultaneously formed on a semiconductor substrate, and further, the sensitivity of another axis does not occur.

[Structure of the Invention] (Means for Solving the Problems) In order to solve the above-mentioned problems, the present invention relates to a semiconductor acceleration sensor formed on a semiconductor substrate using etching processing from the surface of the semiconductor substrate. , A cantilever beam formed at an appropriate depth position from the surface of the semiconductor substrate in a direction perpendicular to the surface and toward the surface, and parallel to the surface formed at the tip of the cantilever beam. Direction, the mass portion to which the detected acceleration is applied, the side wall portion which is formed at a side portion of the mass portion at a required interval and serves as a stopper, and the both side portions of the mass portion and the side wall facing each other are provided with the detected acceleration. The gist of the present invention is to have a detection unit that detects the displacement of the mass unit according to the change as a capacitance change.

(Function) A side wall portion serving as a stopper is simultaneously formed on the semiconductor substrate together with the cantilever and the mass portion by etching processing only from the surface portion thereof. Therefore, the process yield is improved, and complicated processes such as double-sided alignment are not necessary. Also, the cantilever is perpendicular to the substrate surface,
Since the acceleration parallel to the substrate surface is detected, it is possible to simultaneously form a sensor section having sensitivity in a two-dimensional direction such as X and Y on a single semiconductor substrate. Furthermore, since the mass portion can be formed symmetrically with respect to the cantilever and the center of gravity of the mass portion can be located on the extension of the cantilever, the sensitivity of the other axis is lost.

Then, when the mass part is displaced according to the detected acceleration,
The displacement is taken out as a capacitance change from the detection unit and the acceleration is detected.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

1 to 3 are views showing a first embodiment of the present invention.

First, the configuration of the semiconductor acceleration sensor will be described.
In the figure, reference numeral 1 denotes a Si semiconductor substrate, and a cantilever, a mass portion, and a side wall portion serving as a stopper, which will be described below, are simultaneously formed by etching the substrate surface 1a.

That is, the cantilever 2 is formed at an appropriate depth position from the substrate surface 1a in a direction perpendicular to the surface. Cantilever 2
A mass portion 3 to which the acceleration to be detected is applied is formed at the tip of the symmetric shape with respect to the cantilever 2. Also, the mass part 3
Side wall portions 4 serving as stoppers are formed at required intervals on both side portions. The stopper is for protecting the cantilever 2 from excessive G. Then, electrodes 5 serving as detecting portions are respectively attached to the facing both surface portions of the mass portion 3 and the side wall portion 4. The detection unit detects the displacement of the mass unit 3 according to the detected acceleration as a capacitance change.

Next, an example of the manufacturing method will be described with reference to FIG. 2 to further detail the configuration. In the following description, the item symbols (a) to (e) correspond to (a) to (e) in FIG.

(A) A Si semiconductor substrate 1 having a (100) plane is prepared.

(B) The trench 6 is formed perpendicularly to the substrate surface 1a by masking the planned region of the mass part and the like and using anisotropic etching such as RIE.

(C) After forming the insulating film 7 on the entire surface by a method such as thermal oxidation and opening the contact holes 8, a method such as MOCVD is used.
A metal film to be the electrode 5 is formed on the substrate surface 1a and the sidewalls of the trench 6.

(D) The trench 6a is dug down again by anisotropic etching such as RIE.

(E) By anisotropic etching of KOH, hydrazine, etc.,
Only the lower trench 6a is etched to form the cantilever 2 and the mass portion 3. 9 is an etched void.

In this way, the cantilever 2, the mass portion 3 and the side wall portion 4 serving as a stopper are simultaneously formed by the etching process.

Next, the operation will be described with reference to FIG. When acceleration g is applied in the direction of the arrow parallel to the substrate surface 1a, the mass part 3
Is displaced, and the distance between the electrodes 5 in the detection unit changes.
The changes in the distance between the electrodes 5 are (d−δ) and (d +
δ), the dielectric constant of the gap (air) between the electrodes 5 is ε, and the area of the electrode 5 is S, the change in capacitance between (C-C ₁ ) and (C-C ₂ ) is ε ・S / (d−δ) ε · S / (d + δ), and if this difference ΔC is taken, then ΔC2ε · S · δ / d ² (1) and acceleration can be detected as a capacitance change.

As described above, according to this embodiment, the following effects can be obtained.

Since the stopper is formed simultaneously with the formation of the cantilever 2 and the mass portion 3, the process yield is improved. in this way,
Since it is not necessary to add an external stopper in a subsequent process, the cost can be kept low. Processing such as etching is the substrate surface
Since it is performed only from 1a, complicated processes such as double-sided alignment are unnecessary. Since the acceleration detection direction is parallel to the substrate surface 1a, it is possible to simultaneously form a two-dimensional sensor section on a single semiconductor substrate. Further, since the shape of the mass part 3 is symmetrical with respect to the cantilever 2, it becomes possible to position the center of gravity of the mass part 3 on the extension of the cantilever 2, and the sensitivity of the other axis can be almost zero. it can.

Next, FIGS. 4 to 6 show a second embodiment of the present invention.

In this embodiment, a p ⁺ etch stop layer is used to form a cantilever, a very thin and highly accurate cantilever is formed, and detection sensitivity is increased.

 An example of the manufacturing method will be described with reference to FIG.

(A) An n ^- epitaxial layer is grown on the Si semiconductor substrate 11 having the p ⁺ (100) plane.

(B) The trench 13 is formed from the surface by anisotropic etching such as RIE until the semiconductor substrate 11 is reached. Trench 13
The opening is in the <110> direction.

(C) After the mask patterning, the shallow trench 14 is formed again by RIE or the like.

(D) High concentration p ^{+ on the} substrate surface and the side walls of each trench 13 and 14
Form layer 15. An insulating film 16 is deposited on the entire surface and patterned, and then an electrode 17 connected to the p ⁺ layer 15 via an opening is formed. The electrode 18 is also formed on the back surface of the semiconductor substrate 11.

(E) The shallow trench 14 formed in the step (c) is
Further trenches are formed by anisotropic etching such as RIE until the p ⁺ semiconductor substrate 11 is reached to form trenches 14a.

(F) Anisotropic etching using KOH or the like is performed. p ⁺ layer 15
In this case, since etching does not proceed, the cantilever 15a and the mass portion 19 are formed by the p ⁺ layer 15.

As described above, since the p ⁺ etch stop layer is used for forming the cantilever, a very thin and highly accurate cantilever 15a is formed, and at the same time, the mass portion 19, the side wall portion 21 serving as a stopper, and the detecting portion are formed. The electrode 15b forming the electrode is formed.

 Next, the operation will be described with reference to FIG.

The displacement Δy of the tip of the mass portion 19 when the acceleration g is applied to the mass portion 19 is expressed by the following equation.

Δy [(2m · g) / (E · w · d 3) ] · (2l ³ + 9l ² ·
C + 12l · C ² ) (2) m: mass of mass part 19, E: Young's modulus, w: width of cantilever beam 15a, d: thickness of cantilever beam 15a, l: length of cantilever beam 15a , 2C: the size of the mass part 19, and from the above formula (2), the cantilever 15a is formed to be very thin and highly accurate, so that the detection sensitivity can be improved.

Then, the acceleration can be detected as a capacitance change by taking the capacitance difference between both electrodes in exactly the same manner as in the case of the equation (1) of the first embodiment.

In this embodiment, both mass parts 19 are displaced as shown in FIG. 6 when acceleration in the direction perpendicular to the substrate surface is applied, but the capacitance difference ΔCY between C ₁ and C ₂ shown in FIG. = by taking C ₁ -C ₂ = 0, the other axis sensitivity can be made zero. In FIG. 6, 22 is the center of gravity of each mass part 19.

FIGS. 7 and 8 show a third embodiment of the present invention. In FIGS. 7 and 8, the same or equivalent members and parts as those in FIGS. 4 and 5 are designated by the same reference numerals as those used above, and a duplicate description will be omitted.

As shown in the equation (2), the width w of the cantilever may be narrowed in order to improve the detection sensitivity. Therefore,
In this embodiment, the width w of the cantilever in the second embodiment is narrowed to further enhance the detection sensitivity.

In FIG. 7, reference numeral 25 denotes a cantilever having a narrow width w, and the width w is formed to be about 10 μm and the thickness d is formed to be about 0.1 μm. When the other values are set to the required values in the equation (2), the displacement Δy of the tip end portion of the mass portion 19 is given by the following equation.

Δy 0.2 μm / 1G (3) This equation (3) corresponds to the capacitance change ΔC2fF.

FIG. 8 shows an example of the manufacturing method of this embodiment. Trench etching of the central portion is performed twice (FIGS. 8B and 8C) to form a narrow p ⁺ layer. This narrow p ⁺ layer is formed as the width of the cantilever 25.

FIG. 9 shows a fourth embodiment of the present invention. This embodiment is the same as the semiconductor acceleration sensor of the first embodiment.
In order to increase the mass m of the mass part 3, a metal mass part 26 made of a substance having a high density such as metal is added to the upper part of the mass part 3. As the mass m of the mass part increases, the displacement of the tip of the mass part becomes large and the detection sensitivity is further enhanced, as shown in the equation (2).

In each of the above-described embodiments, since anisotropic etching is used for etching when forming the cantilever and the mass portion (steps such as FIG. 2E), the orientation of the substrate surface and the trench opening Although the direction is limited to some extent, a cantilever or the like can be formed using isotropic etching.

[Effects of the Invention] As described above, according to the present invention, it is possible to simultaneously form a side wall portion serving as a stopper with a cantilever beam and a mass portion on a semiconductor substrate by etching only the surface portion thereof. As a result, the process yield is improved, and at the same time, a complicated process such as double-sided alignment is not necessary and the cost can be reduced. Further, since the cantilever is perpendicular to the substrate surface and detects the acceleration in the direction parallel to the substrate surface, a sensor section having a two-dimensional sensitivity is simultaneously formed on a single semiconductor substrate. be able to. Furthermore, since the mass part can be made symmetrical with respect to the cantilever and the center of gravity of the mass part can be positioned on the extension of the cantilever, the sensitivity of the other axis should be almost zero. You can

[Brief description of drawings]

1 to 3 show a first embodiment of a semiconductor acceleration sensor according to the present invention. FIG. 1 is a sectional view of the structure, FIG. 2 is a process drawing showing an example of a manufacturing method, and FIG. FIGS. 4 to 6 are views for explaining the operation of the second embodiment of the present invention.
FIG. 4 shows an embodiment, FIG. 4 is a process chart showing an example of the manufacturing method, FIGS. 5 and 6 are views for explaining the action respectively, and FIG. 7 shows a third embodiment of the present invention. FIG. 8 is a perspective view of an essential part, FIG. 8 is a process drawing showing an example of the manufacturing method of the third embodiment, and FIG. 9 is a configuration drawing showing the fourth embodiment of the present invention.
1 to 12 show a conventional semiconductor acceleration sensor, FIG. 10 is a view showing a sensor chip, FIG. 11 is a view showing a state in which an upper stopper and a lower stopper are attached to the sensor chip, and FIG. It is a figure for demonstrating a problem. 1: semiconductor substrate, 1a: substrate surface, 2, 15a, 25: cantilever,
3, 19: Mass part, 4, 21: Side wall part that serves as stopper, 5, 15
b: An electrode that constitutes the detection unit.

Claims (1)

[Claims] 1. A semiconductor acceleration sensor formed on a semiconductor substrate by using an etching process from the surface of the semiconductor substrate, wherein the semiconductor acceleration sensor is provided at an appropriate depth position from the surface of the semiconductor substrate in a direction perpendicular to the surface. In addition, a cantilever formed toward the surface, a mass portion formed at the tip of the cantilever and to which a detected acceleration in a direction parallel to the surface is applied, and a side portion of the mass portion are required. It has a side wall portion which is formed at intervals and serves as a stopper, and a detection portion which is formed on both opposing surfaces of the mass portion and the side wall portion and detects a displacement of the mass portion according to a detected acceleration as a capacitance change. Characteristic semiconductor acceleration sensor.