JPH0854414A - Semiconductor acceleration sensor and manufacturing method thereof - Google Patents

Abstract

(57) [Abstract] [Purpose] To mass-produce a high-sensitivity cantilever structure or double-supported beam semiconductor acceleration sensor at low manufacturing cost. A thin-walled portion 21 is formed on the back surface of the silicon substrate 10 so as to extend from one end to the other by forming a channel-shaped recess 17 that crosses from one end to the other. A diffusion resistance layer 13 is formed near the upper surface of 21. A glass plate 30 is joined to the back surface of the silicon substrate 10 by anodic bonding, and a slit portion 31 is provided corresponding to the thin portion 21 to divide the glass plate 30 into two independent portions.
One side sandwiching the thin portion 21 is fixed as a pedestal portion 51 and the other side is a free end, whereby a cantilever structure is formed. The free end side is a weight portion 61, and the acceleration applied to this portion gives a bending stress to the thin portion 21 reaching from end to end of the silicon substrate 10 and greatly changes the resistance in the diffusion resistance layer 13.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor acceleration sensor used for acceleration detection / control in automobiles, aircrafts, various industrial robots, home electric appliances and the like, and a manufacturing method thereof.

[0002]

2. Description of the Related Art A semiconductor acceleration sensor is composed of a semiconductor strain gauge utilizing the piezoresistive effect of silicon, and obtains an output corresponding to the acceleration by applying a bending stress to the semiconductor strain gauge by the acceleration. .
That is, in a semiconductor acceleration sensor, usually, a diffusion resistance region serving as a strain gauge is provided on the front surface side of a silicon substrate, and a recess is provided by etching from the back surface side of the portion where the diffusion resistance region is formed. This forms a thin portion. One of both side portions sandwiching the thin portion is fixed to form a pedestal portion, and the other portion is a free end to form a cantilever structure. The free end is used as a weight portion that moves according to acceleration, and bending stress is applied to the thin portion due to the movement, and the resistance value of the diffusion resistance region changes due to the piezoresistance effect.

The sensitivity of the semiconductor acceleration sensor is determined by how much bending stress is applied to the semiconductor strain gauge by a constant acceleration, that is, how much bending stress is applied to the thin portion where the semiconductor strain gauge is formed. Therefore, the mass of the weight portion and the thickness of the thin portion are important factors that determine the sensitivity. That is, the sensitivity of the semiconductor acceleration sensor is improved as the mass of the weight portion is increased and as the thickness of the thin portion which is a cantilever is reduced.

[0004]

However, in the semiconductor acceleration sensor, if the thickness of the thin portion is made thin, problems occur in terms of strength and durability, and in order to increase the mass of the weight portion, another member is required. In the case of attachment, the manufacturing process becomes complicated, the manufacturing cost rises, and mass production becomes difficult.

In view of the above, it is an object of the present invention to provide a highly sensitive semiconductor acceleration sensor having a cantilever structure or a double-supported beam structure, which can be mass-produced easily and can be manufactured at low cost. .

Further, according to the present invention, a weight having a large mass can be easily formed by a simple manufacturing process, and thus a semiconductor acceleration of a cantilever structure or a cantilever structure having high sensitivity at low manufacturing cost. An object of the present invention is to provide a method for manufacturing a semiconductor acceleration sensor, which enables mass production of sensors.

[0007]

To achieve the above object, in a semiconductor acceleration sensor according to the present invention, a thin portion is formed by a silicon substrate and a channel-shaped recess formed from one end to the other in a direction crossing the silicon substrate. And a diffusion resistance layer serving as a strain gauge provided in the thin portion, and a glass of borosilicate glass separated at a position corresponding to the thin portion and anodically bonded to the silicon substrate and having a thermal expansion coefficient close to that of the silicon substrate. It has a cantilever structure in which a plate is provided and one side of the thin portion sandwiches the pedestal portion and the other side has a free end portion.

In this semiconductor acceleration sensor, the silicon substrate is formed in a square shape, and the side of the square portion which is the free end portion in the same direction as the length direction of the channel-shaped recess is the other side. Can be longer than.

Further, in the semiconductor acceleration sensor according to the present invention, the silicon substrate, the two elongated thin portions formed by the channel-shaped recesses formed from one end to the other in the direction traversing the silicon substrate, and the thin portion are respectively provided. And a diffusion resistance layer serving as a strain gauge, and a glass plate of borosilicate glass which is separated at a position corresponding to each of the thin portions and has a coefficient of thermal expansion anodically bonded to the silicon substrate which is close to that of the silicon substrate. It is also possible to adopt a double-supported beam structure in which portions on both outer sides of the two thin portions are pedestal portions and portions sandwiched by the two thin portions are movable portions.

Further, in this semiconductor acceleration sensor, a step of forming a diffusion resistance layer serving as a strain gauge on a silicon substrate and a step of forming a channel-shaped recess near the diffusion resistance layer of the silicon substrate to provide a thin portion. When,
A step of joining a glass plate to the silicon substrate by anodic bonding, and forming a slit portion parallel to the length direction of the channel-shaped recess in the glass plate for separating the glass plate at a position corresponding to the thin portion And a step of cutting the silicon substrate and the glass plate at least at a cutting plane perpendicular to the lengthwise direction of the channel-shaped recess to separate into individual sensor chips having a cantilever structure or a cantilever structure. It is manufactured by carrying out.

In this method of manufacturing a semiconductor acceleration sensor, after cutting into individual sensor chips by cutting, the portion of the cut surface where the end of the thin portion is located is etched to chip the portion. A step of removing can be added.

[0012]

The glass plate is anodically bonded to the silicon substrate, and the mass of this part is increased. Therefore, a large force is applied to this part due to the acceleration, which allows sufficient bending stress to be applied to the thin part,
A large resistance change due to the piezoresistive effect can be generated in the diffusion resistance layer. Therefore, the sensitivity to acceleration can be increased without thinning the thin portion.
Since the thin portion does not have to be thin, the strength and durability are improved.

The thin portion is formed by forming a channel-shaped recess in a silicon substrate. Since the channel-shaped recess is formed so as to cross the silicon substrate from end to end, the thin portion becomes a bent portion. A cantilever structure or a cantilever structure can be easily realized.

If the silicon substrate is formed in a square shape, the free end portion also becomes a square shape. At the free end portion of the square shape, the side in the same direction as the length direction of the channel-shaped recess is the other side. By making the length longer than this, it is possible to prevent the thin portion from bending in the lateral direction when a force is applied to the free end in the lateral direction (the length direction of the channel-shaped recess), and the thin portion has its thickness direction. You can bend only to. Therefore, only when the free end is subjected to acceleration in the thickness direction of the thin portion,
An output sensitive to this can be generated, and the acceleration in the specific direction can be detected without being influenced by the acceleration in the other directions.

The steps of forming a diffusion resistance layer to be a strain gauge on a silicon substrate and forming a channel-shaped recess to form a thin portion are the same as the steps of manufacturing a pressure sensor, etc. Can be done by. Then, an individual sensor chip having a cantilever structure or a double-supported beam structure can be obtained by only performing a step of anodic bonding a glass plate to a silicon substrate that has undergone such a process, and then performing a step of forming a slit portion and a cutting step. Can be manufactured. Therefore, the manufacturing process is simple as a whole and is suitable for mass production. It is easy to increase the mass of the weight portion by joining the glass plates, and thereby the sensitivity can be increased, and thus a highly sensitive semiconductor acceleration sensor can be manufactured at low cost.

Further, the chipping generated in the cutting process for individualizing the sensor chip may cause cracks, but the portion of the cut surface where the end of the thin portion is located is etched. By doing so, chipping is removed. Since the thin portion bends in accordance with the acceleration, if there is chipping in the thin portion, cracks are likely to occur, but there is no chipping in the thin portion, and the possibility of such cracks is eliminated. Therefore, the life and durability are improved.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the drawings. 1A is a schematic plan view seen from above the semiconductor acceleration sensor according to one embodiment of the present invention, and FIG. 1B is a schematic plan view seen from the side of the acceleration sensor. It is a side view. As shown in these figures, a channel-shaped recess 17 is provided on the back surface side of the silicon substrate 10. The recessed portion 17 forms the thin portion 21 of the silicon substrate 10. As shown in FIG. 1A, the channel-shaped recess 17 is formed from end to end in the direction crossing the silicon substrate 10, so that the thin portion 21 also crosses the silicon substrate 10 from end to end. Become. A diffusion resistance layer 13 is formed near the upper surface of the thin portion 21.
This diffusion resistance layer 13 functions as a strain gauge,
As shown in FIG. 1A, the thin portion 21 is not formed in the central portion but in a position slightly deviated to the left side.

On the back surface of the silicon substrate 10, a glass plate 30 made of borosilicate glass such as Pyrex glass (trademark) having a thermal expansion coefficient substantially equal to that of the silicon substrate 10.
Are strongly bonded by anodic bonding. The glass plate 30 is provided with a slit portion 31 corresponding to the channel-shaped recess 17 (that is, the thin portion 21). Since the slit portion 31 is formed so as to traverse the glass plate 30 from one end to the other like the channel-shaped recess 17, the slit portion 31 divides the glass plate 30 into two independent portions. .

Including the glass plate 30 divided into these two, one side of the silicon substrate 10 sandwiching the thin portion 21 is fixed as a pedestal portion 51, and the other side is a free end. . This forms a cantilever structure. On the free end side, the silicon substrate 10 is also thick, and the weight 61
However, the weight of the weight portion 61 is increased by further joining the glass plate 30.

In the semiconductor acceleration sensor having such a structure, acceleration is applied to the weight portion 61, so that the thin portion 21
Will turn. Since the channel-shaped concave portion 17 is formed from end to end in the direction crossing the silicon substrate 10 and the thin portion 21 also crosses the silicon substrate 10 from end to end, the thin portion 21 is bent mainly. . As a result, an output according to acceleration can be obtained from the diffusion resistance layer 13 that functions as a strain gauge. With a very simple structure in which the channel-shaped recess 17 is formed from end to end of the silicon substrate 10, a cantilever structure having a thin wall portion 21 that bends when acceleration is applied is formed, which facilitates manufacturing.

Further, the glass plate 30 is the silicon substrate 10.
Since the heavy weight portion 61 having a large mass is formed by being joined to the back surface of the anode by anodic bonding, even if the thin portion 21 is not thinned, the thin portion 21 is sufficiently bent by the acceleration, and the acceleration is accelerated. Sensitivity to. Thin part 2
Since 1 does not have to be thin, the strength can be increased. By forming the diffusion resistance layer 13 functioning as a strain gauge at a position biased toward the side closer to the pedestal 51 rather than at the center of the thin portion 21 as described above, the strain gauge is formed at a position where more stress is applied. As a result, the sensitivity can be further increased.

The chip of this semiconductor acceleration sensor has a length (horizontal direction in FIG. 1 (a)) 3 mm × width (FIG. 1).
(A in the up-down direction of (a)) A rectangular shape having a size of about 1 mm can be used. Then, for example, the thin portion 21
Has a thickness of about 15 μm, and the glass plate 30 has a thickness of 1 mm to
It can be about 3 mm. However, the shape is not limited to such a shape, and various shapes such as a square can be used. For example, as shown in Figure 2, length (left and right direction)
It may be a square of 2.5 mm × width (up and down direction) 2.5 mm. In this case, since the length of the thin portion 21 (the length in the vertical direction, that is, the length of the channel-shaped recess) becomes long,
It is possible to prevent a shake in the vibration direction of the cantilever.
That is, since the thin portion 21 is formed to be long in the vertical direction in FIG. 2, the thin portion 21 easily bends in the direction (thickness direction) with respect to the acceleration in the direction perpendicular to the paper surface of FIG. , It is more difficult to bend in the lateral direction (vertical direction in FIG. 2). Therefore, even if the lateral acceleration is applied to the weight portion 61, the thin portion 21 does not bend in that direction, so that it is less affected by the acceleration in such a direction.
Only the acceleration in the thickness direction of the thin portion 21 will be more sensitive. Therefore, it is effective as an acceleration sensor that detects acceleration in a specific direction.

Next, a method of manufacturing such a semiconductor acceleration sensor will be described. First, the crystal orientation of the surface is (1
The n-type silicon substrate 10 which is 00) is oxidized,
As shown in FIG. 3, silicon oxide films 11 are formed on both front and back surfaces. Next, a window 12 is provided in the silicon oxide film 11 on the front surface side by photolithography. These windows 12 are diffusion windows, and by diffusing boron or the like through these windows 12, a diffusion resistance layer (P
Layer) 13 is formed. The diffusion resistance layer 13 serves as a strain gauge.

Then, the silicon oxide film 11 (integrated with the previous silicon oxide film 11) is provided on both front and back surfaces of the silicon substrate 10 by oxidizing again, and further nitrided to form the silicon nitride film 15 as shown in FIG. (Note that the silicon nitride film 15 may not be formed in some cases).

Then, the silicon nitride film 15 and the silicon oxide film 11 are sequentially etched by photolithography on the back surface to form a window 16 in the silicon oxide film 11 and the silicon nitride film 15 on the back surface as shown in FIG. Set up. The window 16 is a window for selective etching used to selectively provide the recess 17 for forming the thin portion 21. Silicon etching is performed through the window 16 to form a channel-shaped recess 17 as shown in FIG. The thin portion (about 15 μm) formed by forming the recess 17 becomes the thin portion 21. Since the recess 17 has a channel shape extending in the direction perpendicular to the paper surface of FIG. 6, the thin portion 21 is also an elongated shape extending in the direction perpendicular to the paper surface of FIG.

Further, on the front surface side, the silicon nitride film 15 and the silicon oxide film 11 are sequentially etched by photolithography to form a window 26 in the front silicon oxide film 11 and the silicon nitride film 15 as shown in FIG. Set up. The window 26 serves as a contact hole for forming an electrode. Then, after aluminum (or Au-Cr, Au-Ti, etc.) is vapor-deposited on the entire surface, aluminum is photolithographically applied to the contact hole window 26.
The electrode 27 as shown in FIG. 7 is provided by etching and removing it, leaving only the vicinity thereof.

Next, the silicon nitride film 15 and the silicon oxide film 11 on the back surface side are removed, and the glass plate 30 is bonded to the back surface of the silicon substrate 10 as shown in FIG. The glass plate 30 is made of borosilicate glass having a thermal expansion coefficient substantially equal to that of the silicon substrate 10, such as Pyrex glass (trademark) having a thickness of 1 mm to 3 mm. The bonding between the silicon substrate 10 and the glass plate 30 is performed by so-called anodic bonding. That is, for example, these silicon substrate 10 and glass plate 30 are superposed in a vacuum and sandwiched by electrodes, and a voltage of 600 V is applied at a temperature of 400 ° C. The silicon substrate 10 and the glass plate 30 are only weighted in the direction of being sandwiched by the electrodes, but are attracted by the plus or minus electrostatic force and firmly joined.

Thus, the glass plate 30 becomes the silicon substrate 10.
After being firmly bonded to the back surface of the glass plate 30, a slit portion 31 is provided to divide the glass plate 30 as shown in FIG. The slit portion 31 has a channel-shaped recess 17 (that is, the thin portion 2
At a position corresponding to 1), the channel-shaped recess 17 is formed so as to extend in the length direction (direction perpendicular to the paper surface). The slit portion 31 is formed by cutting only the glass plate 30 with a dicing saw or the like. Then, the individual sensor chips are formed by cutting both the silicon substrate 10 and the glass plate 30 along the cutting surface 32 that is perpendicular to the paper surface using a dicing saw or the like.

These steps are simultaneously performed on a large number (for example, about 1000) of sensor chips by using a silicon wafer having a diameter of about 100 mm, for example. That is, for example, on the circular silicon substrate 10 as shown in FIG. 10, the diffusion resistance layer 13 and the thin portion 2 as described above are formed.
Many 1 and the like are formed at the same time, and then glass plates 30 having the same diameter are joined. After the joining, the slit portion 31 is provided only on the glass plate 30 so as to correspond to the thin portion 21 using the dicing saw, and along the cut surface 32 in the direction parallel to the thin portion 21 and at the right angle. The silicon substrate 10 and the glass plate 30 bonded thereto are cut to obtain individual sensor chips 33. The size of each sensor chip 33 is, for example, 3 mm in the direction perpendicular to the thin portion 21 (left-right direction in FIG. 1A), and the thin portion 2
1 in the direction parallel to 1 (vertical direction in FIG. 1 (a))
It can be mm. Further, stoppers for limiting the movement of the weight portion 61 may be formed of silicon or the like above and below the sensor chip 33, if necessary.

After the strain gauge and the thin portion 21 are formed by using the normal semiconductor manufacturing process as described above, the glass plate 30 for increasing the weight of the weight portion 61 is firmly joined by anodic bonding and further dicing. A large number of chips of a semiconductor acceleration sensor having a cantilever structure having a thin portion 21 that bends due to acceleration can be obtained only by forming the slit portion 31 and cutting the individual sensor chips 33 into individual pieces by a cutting process using saws or the like. it can. Therefore, it can be said that a large number of highly sensitive semiconductor acceleration sensor chips having a cantilever structure can be manufactured at one time from a single silicon wafer by an extremely simple manufacturing process, which is a manufacturing method suitable for mass production.

Since the sensor chip 33 is finally cut by a dicing saw or the like, innumerable fine chippings are formed on the cut surface around the sensor chip 33 as shown in FIG. Since the thin portion 21 bends due to the acceleration as described above, cracking may occur due to this chipping, which may cause a decrease in durability. Therefore, it is effective to remove this chipping at least in the vicinity of the bent thin portion 21. Since the chipping is about 30 μm in width (width in the direction parallel to the plane of the paper, depth from the end face), FIG.
As shown in FIG. 5, it is desirable to form the curved concave portion 71 having a depth of 30 μm or more from the end face by, for example, the RIE (reactive ion etching) method.

Although the semiconductor acceleration sensor having a cantilever structure has been described above, it goes without saying that a double-supported beam structure can be easily formed as shown in FIGS. 12 (a) and 12 (b). The semiconductor acceleration sensor shown in FIG. 12 is
A large wafer is cut so that two sets of the recess 17, the thin portion 21, the diffusion resistance layer 13 on the thin portion 21, and the slit portion 31 for separating the glass plate 30 are present in one sensor chip. , Made a sensor chip. Then, both ends are fixed as the pedestal portion 51, and the two thin portions 2
The central portion sandwiched by 1 is used as a weight 61 so that it can move freely. As in the case of the above-mentioned cantilever structure, the process of manufacturing the semiconductor acceleration sensor chip having the both-support beam structure is extremely simple and suitable for mass production. That is, a semiconductor acceleration sensor chip having a doubly supported beam structure can be manufactured only by a normal semiconductor manufacturing process and a cutting process, and a large number can be manufactured at once from one silicon wafer.

Also in this double-supported beam semiconductor acceleration sensor, it is desirable that the diffusion resistance layer 13 serving as a strain gauge is provided at a position where bending stress is further generated. Therefore, as shown in FIG. And each thin part 2
It is arranged not at the central portion of 1 but at a position biased to the side closer to the pedestal portion 51. In addition, the respective directions (length direction) of the diffusion resistance layer 13 serving as the strain gauge are also shown in FIG.
Not only those that are at right angles to each other as shown in (a) of Fig. 13, but also those that are parallel to a direction (horizontal direction in the figure) perpendicular to the length direction of the thin portion 21 (vertical direction in the figure) as shown in FIG. May be

Needless to say, the specific structure, materials, etc. can be variously modified without departing from the spirit of the present invention.

[0035]

As described above, according to the embodiment,
According to the present invention, a semiconductor acceleration sensor having a cantilever structure or a double-supported beam structure that is easy to manufacture and has high sensitivity can be obtained. Furthermore, according to the manufacturing method of the present invention, a highly sensitive semiconductor acceleration sensor having a cantilever structure or a double-supported beam structure can be mass-produced at a low manufacturing cost.

[Brief description of drawings]

FIG. 1 is a schematic external view of an embodiment of the present invention.

FIG. 2 is a schematic plan view of a modified example viewed from above.

FIG. 3 is a sectional view of the first manufacturing process of the embodiment of the present invention.

FIG. 4 is a cross-sectional view in the second manufacturing process of the same embodiment.

FIG. 5 is a sectional view in the third manufacturing process of the embodiment.

FIG. 6 is a cross-sectional view in the fourth manufacturing process of the same embodiment.

FIG. 7 is a sectional view in the fifth manufacturing process of the embodiment.

FIG. 8 is a cross-sectional view in the sixth manufacturing process of the embodiment.

FIG. 9 is a sectional view in the final manufacturing process of the embodiment.

FIG. 10 is a plan view of the wafer before cutting as seen from above.

FIG. 11 is a schematic plan view of another modification seen from above.

FIG. 12 is a schematic external view of another embodiment.

FIG. 13 is a schematic plan view of still another modification viewed from above.

[Explanation of symbols]

 10 silicon substrate 11 silicon oxide film 12, 16, 26 window 13 diffusion resistance layer 15 silicon nitride film 17 recess 21 thin portion 27 electrode 30 glass plate 31 slit part 32 cut surface 33 sensor chip 51 pedestal 61 weight part 71 curved recess

Claims (5)

[Claims] 1. A silicon substrate, a thin-walled portion formed by a channel-shaped recess formed from one end to the other in a direction traversing the silicon substrate, a diffusion resistance layer provided in the thin-walled portion and serving as a strain gauge, and the thin-walled portion. A borosilicate glass plate having a coefficient of thermal expansion close to that of the silicon substrate anodically bonded to the silicon substrate, and one side sandwiching the thin portion is a pedestal part, and the other side is free. A semiconductor acceleration sensor having a cantilever structure which is an end portion. 2. The silicon substrate is formed in a square shape, and a side of the square portion which is a free end portion in the same direction as the length direction of the channel-shaped recess is longer than other sides. The semiconductor acceleration sensor according to claim 1, wherein: 3. A silicon substrate, two thin thin portions formed by channel-shaped recesses formed from one end to the other in a direction crossing the silicon substrate, and a diffusion resistance layer serving as a strain gauge provided in each thin portion. And a glass plate of borosilicate glass having a coefficient of thermal expansion close to that of the silicon substrate, which is separated at positions corresponding to the thin portions, and is anodically bonded to the silicon substrate. A semiconductor acceleration sensor having a double-supported beam structure in which a portion is a pedestal portion and a portion sandwiched by the two thin portions is a movable portion. 4. A step of forming a diffusion resistance layer to be a strain gauge on a silicon substrate, a step of forming a thin portion by forming a channel-shaped recess near the diffusion resistance layer of the silicon substrate, and a step of forming the silicon substrate on the silicon substrate. A step of joining the glass plate by anodic bonding, and a step of separating the glass plate at a position corresponding to the thin portion, a step of forming a slit portion parallel to the length direction of the channel-shaped recess in the glass plate, A step of cutting the silicon substrate and the glass plate at least in a cutting plane perpendicular to the longitudinal direction of the channel-shaped recess to separate into individual sensor chips having a cantilever structure or a double-supported beam structure. And method for manufacturing a semiconductor acceleration sensor. 5. A step of, after the step of separating into individual sensor chips by cutting, etching a portion of the cut surface where the end of the thin portion is located to remove chipping of the portion. The method for manufacturing a semiconductor acceleration sensor according to claim 4, further comprising: