JPH09246569A - Manufacture of silicon structure, silicon structure and acceleration sensor having silicon structure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form a silicon structure in an intended shape by controlling the bending moment generated in a polycrystalline silicon film forming the silicon structure. SOLUTION: When the beam structure comprising a polycristalline film is formed, an amorphous silicon layer, wherein she film is formed under the state without a crystalline structure, and a high-temperature polysilicon layer, wherein the film is formed under the state having the polycrystalline structure, are overlapped, and the polycrystalline silicon film is formed. In the amorphous silicon layer, tensile stress as the remaining stress is generated when the layer is crystallized. In the high-temperature polysilicon layer, compressive stress as the remaining stress is generated. Therefore, a bending moment M acting on the entire polycrystalline film can be controlled by the ratio between the film thickness t1 of the amorphous silicon layer and the film thickness t2 of the high-temperature polysilicon layer. When the above described film thickness ratio is determined so that the bending moment M becomes 0, the beam structure without warping is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a silicon structure, a silicon structure, and an acceleration sensor having the silicon structure. More specifically, a polycrystalline silicon film formed on a substrate is formed into a desired shape. The present invention relates to a method for manufacturing a silicon structure including the steps of :, a silicon structure, and an acceleration sensor including the silicon structure.

[0002]

2. Description of the Related Art Conventionally, as a method of manufacturing a silicon structure of this type, a silicon oxide film is formed on a single crystal silicon substrate, and a CVD (Chemical Vapor) film is further formed on the oxide film.
NIKKEI ELECTRONICS 1991.11.11 (No.540) 223 is a method of laminating a polycrystalline silicon film by the Deposition method.
Pp.-231. The polycrystalline silicon film thus laminated is subjected to a predetermined forming process such as etching to form a silicon structure. According to such a method for manufacturing a silicon structure, it is possible to process a complicated shape as compared with the conventional method for manufacturing a silicon structure by performing a molding process such as etching on a single crystal silicon bulk. Therefore, the degree of freedom in designing the silicon structure is increased. For example, when manufacturing a sensor that detects changes in acceleration and pressure as such a silicon structure,
It is possible to manufacture a sensor that is smaller and has higher performance than the case where a sensor is manufactured by molding a single crystal silicon bulk.

As described above, a sensor manufactured by subjecting a laminated polycrystalline silicon film to a molding treatment is usually
A movable electrode plate and a fixed electrode plate formed of polycrystalline silicon laminated on the surface of single crystal silicon are provided. When external conditions such as acceleration and pressure that the sensor is trying to detect change,
Along with this, the movable electrode plate is displaced, and the differential capacitance between the movable electrode plate and the two fixed electrode plates changes. This change in the differential capacitance is converted into an analog voltage to detect acceleration or the like.

[0004]

However, as described above, when a polycrystalline silicon film laminated on a substrate is molded to manufacture a silicon structure such as an electrode plate of a sensor, the polycrystalline silicon film thus formed has the following structure. Had a problem that residual stress was distributed and a bending moment was generated, which deformed the silicon structure. An adverse effect caused by such a bending moment will be described in the beam structure that constitutes the sensor. A silicon structure having a beam structure such as a polar plate forming a sensor can be divided into a cantilever beam and a double-supported beam depending on a method of supporting the same. The cantilever has a structure in which one end is a fixed end and the other end is a free end, and the cantilever has a structure in which both ends are fixed. When forming these structures with a polycrystalline silicon layer, a desired beam structure is obtained by forming a polycrystalline silicon layer on a silicon oxide film serving as a sacrificial layer and removing the sacrificial layer by etching. When residual stress is distributed in such a cantilever beam and a cantilever beam, a bending moment is generated and they are deformed. Such deformation causes a problem such as a decrease in sensor sensitivity when the silicon structure is an electrode plate of the sensor. Here, a method for forming the polycrystalline silicon layer and residual stresses generated in the cantilever beam and the cantilever beam will be described.

As a method for laminating a polycrystalline silicon layer, first, an amorphous silicon layer having no crystal structure is formed, and then the amorphous silicon layer is crystallized, or a silicon layer is formed in a polycrystalline state from the beginning. There is a method of filming. Amorphous silicon has a structure formed when a film is formed at a temperature of 600 ° C. or lower when a silicon layer is deposited by a CVD method, and is processed at a high temperature of about 1000 ° C. (this process is annealed). It can be polycrystalline silicon.

In the case of such a method for forming an amorphous silicon layer having no crystal structure, a force acts to reduce the size of the entire silicon layer as crystallization progresses during annealing, and as a result, the residual stress causes tensile stress. Stress is generated. However, on the side in contact with the oxide film which is the sacrificial layer, it becomes difficult to crystallize because it comes into contact with the oxide film having different properties, and many crystals are formed in a small size in the vicinity of the interface with the sacrificial layer. On the side of such a sacrificial layer having a small crystal size, compressive stress is eventually generated as residual stress. FIG. 7 shows a state of distribution of residual stress generated in a cantilever formed by a method of forming an amorphous silicon layer. Compressive stress occurs on the side that was in contact with the sacrificial layer, and the tensile stress increases as the distance from the boundary surface increases. Therefore, in the cantilever thus formed, the residual moment acts in different directions on both surfaces of the polycrystalline silicon film, so that a bending moment M occurs and the free end side warps. Therefore, when the cantilever forming the electrode plate of the sensor is manufactured by such a method, the detection accuracy of the sensor may be deteriorated.

Another method for laminating the polycrystalline silicon layer is, as described above, a method of forming the silicon layer in a polycrystalline state from the beginning. When a silicon layer is laminated by the CVD method, if the film is formed at a temperature higher than 600 ° C., the silicon is laminated while being crystallized. Since then
The silicon layer laminated by such a method will be referred to as a high temperature polysilicon layer. Even when a cantilever is formed by such a method, a bending moment still occurs and the free end side warps. When forming a cantilever with a high-temperature polysilicon layer, tensile stress does not occur due to annealing as in the case of an amorphous silicon layer, but polycrystalline silicon is used between the oxide film side and the surface side, which are sacrificial layers. Due to the different crystallization states, the residual stresses distributed have different magnitudes. On the side in contact with the oxide film, crystallization is unlikely to proceed, and a larger compressive stress acts, as in the case of amorphous silicon. As described above, the difference in residual stress distribution causes a bending moment in the entire high-temperature polysilicon layer. Therefore, even when the cantilever is formed by the high temperature polysilicon layer, the cantilever is deformed, and when the cantilever forms the electrode plate of the sensor, the detection sensitivity of the sensor deteriorates. there were.

Furthermore, when the above-mentioned doubly supported beam is formed by a method of forming an amorphous silicon layer,
The residual stress of the whole doubly supported beam after the annealing process becomes tensile stress, but if this tensile stress is too large, the reactivity of the doubly supported beam will decrease. When the doubly supported beam forms the electrode plate of the sensor, a decrease in the reactivity of the doubly supported beam may lead to deterioration in the detection sensitivity of the sensor. Further, when the doubly supported beam is formed by the method of depositing the high temperature polysilicon layer, the residual stress of the entire doubly supported beam becomes the compressive stress, but the compressive stress is generated in the doubly supported beam. It leads to deformation and is difficult to adopt.

As described above, when a silicon structure is manufactured by laminating silicon layers under a certain condition, regardless of whether the silicon layers are laminated at a state of amorphous silicon or high-temperature polysilicon, they occur inside. There is a problem that the manufactured silicon structure is deformed by the residual stress, and a desired shape cannot be obtained.

The silicon structure manufacturing method, the silicon structure, and the acceleration sensor having the silicon structure according to the present invention solve these problems and control the bending moment generated in the polycrystalline silicon film forming the silicon structure. The following constitution was adopted for the purpose of forming a silicon structure into a desired shape.

[0011]

Means for Solving the Problem and Its Action / Effect: A method for manufacturing a silicon structure according to the present invention comprises a polycrystalline film forming step of forming a polycrystalline silicon film on a substrate, and a step of forming the polycrystalline silicon film. In the method for manufacturing a silicon structure, which comprises a polycrystalline film shape forming step of forming a desired shape, the polycrystalline film forming step comprises forming a first silicon layer in a state of amorphous silicon. A silicon layer forming step,
A second silicon layer forming step of forming a second silicon layer on the first silicon layer while having a polycrystalline structure.

In the method of manufacturing a silicon structure of the present invention having the above-described structure, when the polycrystalline silicon film is formed on the substrate, the first silicon layer is first formed in the state of amorphous silicon. Then on this first silicon layer,
The second silicon layer is formed so as to have a polycrystalline structure. The polycrystalline silicon film thus formed is formed into a desired shape.

According to such a method for manufacturing a silicon structure, the formed polycrystalline silicon film is formed by stacking a high temperature polysilicon layer on an amorphous silicon layer, and the residual stress is different between the silicon layers. To work. In the amorphous silicon layer, the residual stress is a tensile stress as a whole, and in the high temperature polysilicon layer, the residual stress is a compressive stress as a whole. Therefore, by overlaying the high temperature polysilicon layer on the amorphous silicon layer,
Bending moments can be offset by residual stresses acting in different directions, and thus the shape of the polycrystalline silicon film can be stabilized.

Here, the film thickness of the first silicon layer,
The film thickness ratio to the film thickness of the second silicon layer is the average residual stress and the radius of curvature of the polycrystalline silicon layer formed in the same amorphous silicon state as the first silicon layer, and the second Obtained using the average residual stress and the radius of curvature of the polycrystalline silicon layer formed in the state of having the same polycrystalline structure as the silicon layer, in the polycrystalline silicon film formed into the desired shape, the bending moment is predetermined. The value may be determined to be

In such a case, first, the polycrystalline silicon layer formed in the state of amorphous silicon like the first silicon layer and the polycrystalline silicon layer formed in the same state as the second silicon layer are formed. And a filmed polycrystalline silicon layer. The average residual stress and the radius of curvature of each produced polycrystalline silicon layer are measured. Based on these values, the film thickness ratio of each silicon layer is determined so that the bending moment generated as a whole when the amorphous silicon layer and the high temperature polysilicon layer are overlaid becomes a predetermined value. Therefore, the bending moment can be canceled by the residual stress generated in each layer, and a polycrystalline silicon film having a desired bending moment can be obtained.

At this time, it is also preferable that the radius of curvature of the polycrystalline silicon layer corresponding to the second silicon layer is infinite when determining the film thickness ratio.

The polycrystalline silicon layer corresponding to the second silicon layer formed in the state of having a polycrystalline structure is warped due to a bending moment caused by uneven distribution of residual stress. As described above, in the vicinity of the interface with the silicon oxide film having different properties, the degree of compression of residual stress is different because the crystalline state is different. On the other hand, when the amorphous silicon layer is overlaid, it is considered that the silicon layer hardly bends due to such a cause. Since the amorphous silicon layer is much closer in nature to the second silicon layer than the silicon oxide film,
This is because it seems that the crystal structure of the boundary surface is less likely to affect the distribution of residual stress. Therefore, the second
As the radius of curvature of the polycrystalline silicon layer corresponding to the silicon layer of, by using infinity instead of the measured value in the polycrystalline silicon layer formed on the silicon oxide film,
The value of the film thickness ratio can be brought closer to a desired condition.

Further, when the film thickness ratio is determined, the predetermined value of the bending moment may be zero. In such a case, a bending moment does not occur in the polycrystalline silicon film formed into a desired shape,
A silicon structure having no warp can be obtained.

Further, in the above method for manufacturing a silicon structure, the polycrystalline silicon film is formed into a desired shape, and when the polycrystalline silicon film is displaced according to an external force, the displaced amount is output as an electric signal. It is also possible to form an operating portion of the sensor to enable the detection of the external force.

In such a case, when forming the operating portion of the sensor, the bending moment is offset by stacking two silicon layers having different residual stresses to stabilize the shape of the operating portion of the sensor. be able to.

The silicon structure of the present invention is a silicon structure formed on a substrate and provided with a polycrystalline silicon film having a predetermined shape, wherein the average residual stress of the polycrystalline silicon film is tensile stress. It is composed of a certain first polycrystalline silicon layer and a second polycrystalline silicon layer overlaid on the first polycrystalline silicon layer and having an average residual stress of compressive stress, and a predetermined bending moment is generated in the polycrystalline silicon film. That is the summary.

In the silicon structure constructed as described above, the first polycrystalline silicon layer whose average residual stress is tensile stress and the second polycrystalline silicon layer whose average residual stress is compressive stress are laminated. By forming the polycrystalline silicon film, a predetermined bending moment is generated in this polycrystalline silicon film. Therefore, according to such a silicon structure, it is possible to cancel the bending moment generated by stacking two types of silicon layers that generate different residual stresses.

At this time, the value of the predetermined bending moment may be zero. In this case, since no bending moment is generated in the polycrystalline silicon film having the predetermined shape, the polycrystalline silicon film is not deformed.

Further, it is also preferable that the average residual stress of the polycrystalline silicon film is a tensile stress. With such a structure, when the polycrystalline silicon film forms a doubly supported beam, the doubly supported beam does not deform due to the residual stress of the doubly supported beam being a compressive stress.

Further, the polycrystalline silicon film may be displaced in accordance with an external force, and an operating portion of a sensor capable of detecting the external force by outputting the displaced amount as an electrical signal may be formed. .

In such a case, by forming the operating part of the sensor by two layers of polycrystalline silicon layers having different residual stresses, the operating part of the sensor that produces a predetermined bending moment can be obtained. Here, if the film thickness ratio of each silicon layer is determined by setting a predetermined bending moment to 0, a sensor operation unit without warpage can be obtained by controlling the film thickness ratio. Therefore, the sensitivity of the sensor does not deteriorate due to the warp of the sensor operating unit.

Further, the gist of the acceleration sensor of the present invention is that it is an acceleration sensor provided with a silicon structure forming the operating portion of the above-mentioned sensor. In such an acceleration sensor, the shape of the operation part of the acceleration sensor is stabilized by forming the operation part of the acceleration sensor by two polycrystalline silicon layers having different residual stresses.
Therefore, there is no problem that an undesired bending moment is generated in the operating portion of the acceleration sensor, which deforms the operating portion of the acceleration sensor and reduces the sensor sensitivity.

[0028]

Other Embodiments of the Invention The present invention can also take the following other embodiments. As a first other aspect of the present invention, in the method for producing a silicon structure of the present invention, the second silicon layer is formed on the second silicon layer by the second silicon layer forming step. A method of manufacturing a silicon structure in which the first silicon layer formed in the state of amorphous silicon by the first silicon layer forming step is overlaid.

According to such a manufacturing method, the polycrystalline silicon film formed into a desired shape has a larger size than a case where a single amorphous silicon film or a polycrystalline silicon film is formed. A bending moment can be generated, and this bending moment can be used to form a curved surface structure.

Here, the film thickness ratio between the film thickness of the second silicon layer and the film thickness of the first silicon layer is the same as that of the first silicon layer. The average residual stress and the radius of curvature of the silicon layer and the average residual stress and the radius of curvature of the polycrystalline silicon layer formed in the state of having the same polycrystalline structure as the second silicon layer are used to obtain the desired value. In the polycrystalline silicon film formed in the above shape, the bending moment may be determined to have a predetermined value.

In this case, since the value of the bending moment generated is controlled by the film thickness ratio of the first silicon layer and the second silicon layer, a polycrystalline silicon film having a desired warp can be obtained.

Further, as a second other aspect of the present invention,
In the silicon structure of the present invention, the polycrystalline silicon film is formed by stacking the first polycrystalline silicon layer having an average residual stress of tensile stress on the second polycrystalline silicon layer having an average residual stress of compressive stress. It can be configured as follows.

With this structure, a predetermined bending moment can be generated by laminating silicon layers having different residual stresses. Therefore, it is possible to obtain a silicon structure provided with a polycrystalline silicon film that forms a curved surface by this bending moment.

[0034]

BEST MODE FOR CARRYING OUT THE INVENTION In order to further clarify the structure and operation of the present invention described above, the embodiments of the present invention will be described below based on Examples. FIG. 2A shows an acceleration sensor 10 manufactured by the method for manufacturing a silicon structure according to the present invention.
FIG. 3 is an exploded perspective view of FIG. The acceleration sensor 10 can be divided into a lid portion 20 and a sensor portion 30. The lid portion 20 is formed of a Pyrex glass substrate having a thermal expansion coefficient close to that of the silicon substrate, and the edge portion 2 coated with the low melting point glass.
At 2, it is bonded to the sensor unit 30. FIG. 2B is a perspective view showing the shape of the surface of the lid portion 20 opposite to the surface shown in FIG. 2A. As shown in FIG. 2B, the lid 2
At 0, the inside of the edge portion 22 has a concave structure,
When the lid portion 20 covers the sensor portion 30 and is bonded to the sensor portion 30 at the peripheral edge portion 22, the recess structure protects the structure formed on the surface of the sensor portion 30. In the sensor section 30, an operation section 34 made of polycrystalline silicon is formed on a sensor substrate 32 made of single crystal silicon, as will be described later.

First, the operation unit 3 in the sensor unit 30.
A method of forming No. 4 will be described. FIG. 3 shows the sensor unit 30.
2 is an exploded perspective view showing the configuration of FIG. As shown in FIG. 3, the operating unit 34 includes a first layer 40, a second layer 42, and a second layer 42 made of polycrystalline silicon on a sensor substrate 32 made of single crystal silicon.
It has a structure in which the third layer 44 is laminated. Such a structure is formed by repeating a cycle of forming a silicon oxide film, forming a polycrystalline silicon film, forming a resist pattern, etching using a resist as a mask, and removing the resist, and finally removing the silicon oxide film.

FIG. 4 shows the operation unit 34 in the sensor unit 30.
FIG. 4A is an explanatory view schematically showing a step of forming a groove, and corresponds to a section 4-4 in FIG. In FIG. 4, only a part of the cross section of the operation unit 34 is shown, but when actually manufactured, a large number of sensor units 30 arranged vertically and horizontally are simultaneously formed on one silicon wafer. The size of each sensor unit 30 formed on the silicon wafer was 2000 μm × 1700 μm in this embodiment. First, a silicon oxide film 36 of 500 n is formed by thermal oxidation on a sensor substrate 32 made of a single crystal silicon wafer.
m thick, and CV is formed on the silicon oxide film 36.
A silicon nitride film 38 is formed to a thickness of 250 nm by the D method.

Next, the first layer 4 is formed on the silicon nitride film 38.
The polycrystal silicon layer which becomes 0 is 400n by the CVD method.
m. Since the first layer 40 is formed at 620 ° C., it is formed as a high temperature polysilicon layer. Then, a resist is applied on this polycrystalline silicon layer, and the resist is patterned into a predetermined shape. When etching is performed using this resist as a mask, only the polycrystalline silicon layer in the region covered with the resist remains, and the first layer 40 having a desired shape is formed. In the present embodiment, as the etching method, plasma etching in which active radicals are generated in plasma using CF ₄ is adopted. Next, a PSG film to be the first sacrificial layer 41 is formed on the first layer 40.
After all, it is formed with a thickness of 2 μm by the CVD method. PS
The G film is a silicon oxide film containing phosphorus, and the sacrifice layer formed of this PSG film is removed by etching in a later step. Since the PSG film is formed with a uniform thickness, its surface has irregularities corresponding to the shape of the first layer 40. After that, a resist is applied on the PSG film to pattern the resist. FIG. 4 (a)
This shows a state where the patterning of the resist is completed.

When etching is performed using this resist as a mask, only the PSG film in the region covered by the resist remains, and the first sacrificial layer 41 having a desired shape is formed. Then, a polycrystalline silicon layer to be the second layer 42 is formed with a thickness of 2 μm on the first sacrificial layer 41. At this time, the surface of the formed polycrystalline silicon layer has the first layer 40 and the first layer 40.
Irregularities corresponding to the shape of the sacrificial layer 41 are formed. The polycrystalline silicon layer that becomes the second layer 42 and the polycrystalline silicon layer that becomes the third layer 44 described later actually consist of an amorphous silicon layer and a high-temperature polysilicon layer, but here, for convenience, It is called a crystalline silicon layer. A resist is further applied to the surface of the polycrystalline silicon layer thus formed, and the resist is patterned. FIG.
(B) shows a state where the patterning of the resist is completed.

Etching is performed using this resist as a mask to form the second layer 42 having a desired shape. afterwards,
The PSG film, the resist pattern, and the etching are performed again on the second layer 42, and the second sacrificial layer 43 is formed.
To form In FIG. 4C, the PS serving as the second sacrificial layer 43 is formed.
The state where the patterning of the resist is completed on the G film is shown.

Next, a polycrystalline silicon layer to be the third layer 44 is formed to a thickness of 2 μm on the second sacrificial layer 43, the resist pattern formation and etching are repeated, and the third layer 44 having a desired shape is formed. To form. FIG. 4D shows a state where the patterning of the resist is completed on the polycrystalline silicon layer which becomes the third layer 44. A PSG film having a thickness of 2 μm is further formed on the third layer 44 formed by etching to form a third sacrificial layer. After forming the third sacrificial layer, the entire silicon wafer is annealed.

Here, the annealing will be described. Annealing is a process of stabilizing a polycrystalline silicon layer by treating it at a high temperature, and at the same time, it has an action of lowering the resistance value of the polycrystalline silicon layer. As described above, amorphous silicon is polycrystallized and stabilized by annealing. Since the high-temperature polysilicon layer has a polycrystalline structure from the time of film formation, annealing is not an essential step for crystallization, but annealing is required to reduce the resistance value. If the sacrificial layer to be removed in a later step is formed of a PSG film which is a silicon oxide layer containing phosphorus as in this embodiment, when annealing is performed in contact with this sacrificial layer,
Phosphorus contained in the sacrificial layer diffuses inside the silicon layer. Originally, both the amorphous silicon layer and the high temperature polysilicon layer
Although the resistance value is too high as a member forming the electrode plate of the sensor, such an annealing treatment reduces the resistance value including phosphorus, so that the sensor has an appropriate resistance value. The PSG film is excellent as a sacrificial layer because it is quickly etched by hydrofluoric acid, but it also functions as a source of phosphorus to the polycrystalline silicon layer.

After the annealing, the entire silicon wafer is etched with hydrofluoric acid to remove the first to third sacrificial layers to complete the sensor section 30. FIG. 4E shows a state after each sacrificial layer is removed by etching. The hydrofluoric acid has the effect of etching the silicon oxide film as well as the PSG layer. However, since the silicon nitride film 38 is formed on the silicon oxide film 36 here, the etching solution of hydrofluoric acid is used as the silicon oxide film. Does not soak into 36. Therefore, even if the first to third sacrificial layers are removed by the etching process, the silicon oxide film 36 is not affected.

The steps of forming the sensor section 30 have been outlined above. Next, the steps of forming a polycrystalline silicon layer corresponding to the main part of the present invention will be described. When forming the sensor unit 30, as described above, three layers of polycrystalline silicon layers from the first layer to the third layer are formed. Among these, the second layer and the third layer having a thickness of 2 μm are the lower 1.8 μm.
And the upper 0.2 μm differ in the conditions for forming a film by the CVD method. The lower layer with a thickness of 1.8 μm is 60
The film is formed at 0 ° C. or lower (505 ° C. in this embodiment) and is formed as an amorphous silicon layer having no crystal structure. The upper layer having a thickness of 0.2 μm is formed at a temperature exceeding 600 ° C. (620 ° C. in this embodiment), and is formed as a high temperature polysilicon layer having a polycrystalline structure from the time of film formation. FIG. 5 shows film forming conditions in this embodiment. Here, the film thickness of each layer was controlled by the reaction time with the gas when the film was formed by the CVD method.

In the acceleration sensor 10 of this embodiment, the second layer 42 functions as a movable electrode plate and the third layer 44 functions as a fixed electrode plate. As shown in FIG. 3, the second layer is supported at one central position and has a cantilever structure. Further, the third layer is supported at six places around and has a doubly supported beam-like structure. In this embodiment, when forming the second layer and the third layer,
By forming the amorphous silicon layer and the high-temperature polysilicon layer with the above-mentioned film thicknesses respectively, it is possible to suppress the occurrence of bending moment in these cantilevered or doubly supported beam-like structures and prevent the layers from warping. are doing.

Here, a method for calculating the film thickness ratio between the amorphous silicon layer and the polysilicon layer to be laminated will be described. FIG. 1 is an explanatory diagram that schematically shows the residual stress distributed inside a cantilever made of a polycrystalline silicon film that is divided into two layers, an amorphous silicon layer and a high-temperature polysilicon layer. In the present embodiment, in the cantilever beam shown in FIG. 1, the film thickness ratio when the bending moment becomes 0 is obtained, and the obtained film thickness ratio is applied at the time of forming the second layer and the third layer. , Prevents the deformation of these structures forming the working part of the sensor.

As described above, when the amorphous silicon layer is crystallized by annealing, the average residual stress becomes tensile stress. The high temperature polysilicon layer has an average residual stress of compressive stress before and after annealing. In the cantilever shown in FIG. 1, the compressive stress, which is the residual stress generated in the high-temperature polysilicon layer, and the tensile stress, which is the residual stress generated in the amorphous silicon layer, cancel each other out, and the bending moment in the entire polycrystalline silicon layer is reduced. A method for calculating the film thickness ratio of each layer when it becomes 0 will be described below.

[0047]

[Equation 1]

The above equation (1) is an equation representing the bending moment M generated in the cantilever beam shown in FIG. In order to obtain the film thickness ratio between the high temperature polysilicon layer and the amorphous silicon layer when the value of M becomes 0,
Equation (1) is modified. In order to obtain this film thickness ratio, it is necessary to substitute a variable representing the state of the high temperature polysilicon layer and the amorphous silicon layer, but here, as a measurable variable regarding the magnitude of strain in each silicon layer, The radius of curvature and the average residual stress were used. When the bending moment M is set to 0 in the equation (1) and the equation is modified based on the relationship between the radius of curvature and the average residual stress, the following equation (2) is obtained.

[0049]

[Equation 2]

By substituting the numerical values of the radius of curvature and the average residual stress of each layer into the equation (2), the ratio r of the thickness t ₁ of the amorphous silicon layer to the total thickness t of the polycrystalline silicon layer can be obtained. In order to obtain the values of the radius of curvature and the average residual stress to be substituted, the amorphous silicon layer or the high temperature polysilicon layer is formed under the same conditions as in FIG. 5, and the amorphous silicon layer or the high temperature polysilicon layer is formed alone. It is necessary to form a cantilever. To form a cantilever, a silicon oxide layer to be a sacrificial layer is first formed on a silicon wafer on which a silicon oxide film and a silicon nitride film are formed, and then a high-temperature polysilicon layer or an amorphous silicon layer is formed thereon. Is formed to a thickness of 2 μm, and the sacrifice layer is removed by etching. The average residual stress and the radius of curvature of each cantilever beam thus formed were measured and substituted into the equation (2). Here, the radius of curvature can be obtained from the length of the produced cantilever (beam length) and the amount of warpage on the free end side.

FIG. 5 shows the average residual stress and the radius of curvature of each cantilever formed by separately forming a cantilever made of a high temperature polysilicon layer or an amorphous silicon layer. The amorphous silicon layer is formed on the sacrificial silicon oxide film both when the cantilever is formed independently and when the cantilever is formed by stacking the high temperature polysilicon layers. Considered the same. Therefore, as the values of the average residual stress and the radius of curvature to be substituted into the equation (2), the measured values of the cantilever formed only by the amorphous silicon layer were used as they were. However, in the case of the high-temperature polysilicon layer, the conditions are different between the case where the film is formed on the silicon oxide film which is the sacrificial layer and the case where the film is formed as a multilayer on the amorphous silicon layer.
Therefore, in this embodiment, the value to be substituted for the radius of curvature of the high-temperature polysilicon layer is set to be approximately infinity instead of the actually measured value.

When the cantilever is formed only by the high-temperature polysilicon layer, the crystal state is different between the boundary side with the silicon oxide film and the surface side, so that the residual stress distribution becomes non-uniform and a bending moment occurs. The cantilever deforms and warps. However, when forming high-temperature polysilicon on amorphous silicon, which has properties closer to those of silicon oxide film, it is considered that such bending moment does not occur due to the difference in crystalline state at the interface with the lower layer. To be It is not easy to measure how much warp actually occurs and what the actual value of the radius of curvature is. Therefore, in this embodiment, assuming that there is no warp, infinity is substituted as the radius of curvature in the equation (2). As a result of substituting these values into the equation (2), 0.91 was obtained as the value of r when the bending moment M was set to 0. That is, the film thickness ratio between the amorphous silicon layer and the high temperature polysilicon layer when the bending moment M was set to 0 was 9: 1. When a cantilever having a thickness of 2 μm was actually formed under these conditions, even if the beam length of the cantilever exceeded 300 μm, the warp was 1 μm or less, and the occurrence of bending moment could be suppressed. FIG. 6 is a diagram comparing the amounts of warpage of a cantilever formed by stacking an amorphous silicon layer and a high-temperature polysilicon layer according to the value of r and a cantilever formed by using the amorphous silicon layer alone. .

As described above, the residual stress and the radius of curvature of the cantilever made of the amorphous silicon layer alone or the high temperature polysilicon layer alone were measured, and these values were substituted into the equation (2) By assuming the radius of curvature in the polysilicon layer to be infinite) and determining the film thickness ratio between the amorphous silicon layer and the high temperature polysilicon layer, a cantilever without warpage can be manufactured. The film thickness ratio thus obtained is effective not only for a cantilever beam but also for a cantilever beam.

As described above, the doubly supported beam may be deformed when the average residual stress is compressive stress. Further, when a strong tensile stress is generated as the average residual stress, the sensor sensitivity may be deteriorated. Therefore, it is desirable that a tensile stress of about 0 to 50 MPa is generated in the doubly supported beam that forms the electrode plate of the sensor as an average residual stress that does not cause deformation and does not reduce sensitivity. The average residual stress of the entire polycrystalline silicon layer having the two-layer structure shown in FIG. 1 can be calculated by the following equation (3).

[0055]

(Equation 3)

By substituting the value of the film thickness ratio calculated as described above and the measured value of the average residual stress in the cantilever formed by the amorphous silicon layer or the high temperature polysilicon layer alone into the equation (3), it is formed. The average residual stress of the obtained polycrystalline silicon film becomes a tensile stress of 56 MPa, and a desired residual stress is obtained.

After the polycrystalline silicon layer is formed on the basis of the film thickness ratio obtained as described above and the operating portion 34 is formed on the sensor substrate 32, the sensor portion 30 and the lid portion 20 are adhered to each other. To do. As described above, the sensor portion 30 is formed vertically and horizontally on the silicon wafer, and the lid portion 20 is vertically and horizontally formed on the glass substrate made of Pyrex glass. Sensor part 3 formed on these silicon wafers
0 and the lid portion 20 formed on the glass substrate,
The silicon wafer and the glass substrate are superposed so that the respective positions correspond correctly. The direction of superposition is the same as the surface on which the operating unit 34 is formed in the sensor unit 30,
The direction in which the surface of the lid 20 on which the above-described recessed structure is formed faces is opposite. Since the low melting point glass is applied to the bonding portion of the glass substrate, the silicon wafer and the glass substrate can be bonded to each other by heating both of them thus stacked together to about 400 ° C. When a silicon wafer and a glass substrate are bonded together, a large number of acceleration sensors are formed vertically and horizontally. After the adhesion, a large number of acceleration sensors 10 can be obtained at the same time by performing dicing. Dicing is realized by sawing or division with a laser cutter.

In the acceleration sensor 10 manufactured as described above, the first layer 40 formed on the sensor substrate 32 made of single crystal silicon and the third layer 44 having a doubly supported beam-like structure.
And act as fixed electrodes. In addition, the second layer 42 having a cantilever-like structure having a supporting portion in the central portion functions as a movable electrode plate. When operating as a sensor, an independent capacitor is formed between the movable plate and each fixed plate. The second layer is held in the middle of the first and third layers when no acceleration is applied. When acceleration is applied, the second layer is displaced according to the magnitude of acceleration. At this time, the distance between the first and third layers that are the fixed electrode plates and the second layer that is the movable electrode plate changes, and the capacitance between the electrode plates changes. A complementary square wave is applied to each fixed electrode plate, and when the capacitance between the electrode plates changes, a voltage corresponding to the amount of change in the capacitance is generated in the movable electrode plate. Since the acceleration sensor 10 is connected to another chip including a signal processing circuit such as a compensation circuit and an amplification circuit, the voltage output from the acceleration sensor 10 is processed by these circuits and detected as acceleration.

According to the acceleration sensor 10 of the present embodiment, a beam structure formed of a polycrystalline silicon layer (a structure in which a space is provided between the beam and a lower layer and is supported by one or more supporting portions)
When forming, the layer formed as amorphous silicon and the layer formed as high-temperature polysilicon layer are overlaid, so that residual stress generated in each layer cancels each other out and suppresses the occurrence of bending moment, thus forming a sensor. The deformation of the beam structure can be prevented. Here, in order to obtain the film thickness ratio of each layer to be measured based on the average residual stress and the radius of curvature of the cantilever formed by the amorphous silicon layer alone or the high-temperature polysilicon layer alone, the bending moment is calculated. It is possible to predetermine the condition for making
At this time, regarding the high temperature polysilicon layer which is the upper layer,
Infinity is used as the radius of curvature instead of the measured value. This corrects the difference in conditions between the case of forming a cantilever by itself and the case of forming a cantilever by stacking on an amorphous silicon layer, and a more desirable value as the ratio of film thickness to be laminated Obtainable.

In the present embodiment, the film forming temperature of the amorphous silicon layer was set to 505 ° C. and the film forming temperature of the high temperature polysilicon layer was set to 620 ° C. These temperatures are the same as those of the amorphous silicon layer and the high temperature polysilicon layer, respectively. It may be any range as long as it can form a film. In the case of forming a film at a temperature different from that of this example, a cantilever beam formed at a desired temperature was prepared in the same manner as in the example, and values such as residual stress and radius of curvature were measured for them and described above. By substituting into the equation (2), the film thickness ratio between the amorphous silicon layer and the high temperature polysilicon layer can be obtained.

In this embodiment, the layer formed as the high temperature polysilicon layer is laminated directly on the layer formed as the amorphous silicon, but the layer formed as the amorphous silicon and the high temperature polysilicon layer are stacked. A layer made of another material may be sandwiched between the layer formed as above. Further, although the silicon oxide film 36 is formed on the sensor substrate 32 in this embodiment, the present invention can be achieved without forming the silicon oxide film.

In the acceleration sensor of this embodiment, as shown in FIGS. 2 and 3, the second layer 42 whose central point serves as a supporting portion.
A movable electrode plate composed of a third electrode, and a third electrode having a plurality of supporting portions around the movable electrode plate.
Although the fixed electrode plate including the layer 44 is provided, the movable electrode plate and the fixed electrode plate may have different shapes. For example,
The movable electrode plate may have a plurality of supporting portions around it and may be in the form of a doubly supported beam.

As described above, by changing the film formation temperature when forming a silicon film, different residual stresses are produced in the upper layer and the lower layer, and the bending is performed by utilizing the fact that these residual stresses cancel each other out. The method of suppressing the moment can be applied to various sensors other than the acceleration sensor described in this embodiment. For example, a yaw rate sensor or a pressure sensor may be used as long as it can be manufactured by molding a polycrystalline silicon film formed on a substrate into a desired shape.

Further, by using the method of forming the polycrystalline silicon film from two kinds of silicon layers having different residual stresses, not only the bending moment M is set to 0 but the warp of the silicon layer is suppressed but also the bending moment M is set to a predetermined value. It is also possible to set the value to calculate the film thickness ratio of each silicon layer and form a silicon layer having a desired warp amount.

The method for manufacturing a silicon structure according to the present invention can be applied not only to the various sensors described above, but also to the formation of silicon structures that form various other actuators. In addition to the cantilever beam and the double-supported beam shown in the embodiment, in a gear-shaped rotating body having no fixed end, the bending moment M can be set to 0 to suppress the warp at the end portion. Further, in addition to suppressing the warp of such a silicon structure, it can be applied to the formation of a silicon structure having a curved surface. In this case, the bending moment M is set to a predetermined value and the film thickness ratio between the amorphous silicon layer and the high temperature polysilicon layer is calculated. If a polycrystalline silicon layer is formed according to this film thickness ratio, a desired bending moment is generated and a silicon structure that forms a curved surface can be obtained. Here, if the high temperature polysilicon layer is formed as the lower layer and the amorphous silicon layer is formed as the upper layer,
Bending moment M can be set to a larger value,
It is possible to manufacture silicon structures with varying degrees of curvature.

The embodiments of the present invention have been described above.
It is needless to say that the present invention is not limited to these embodiments and can be implemented in various modes without departing from the scope of the present invention.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a state of distribution of residual stress generated inside a cantilever formed by stacking an amorphous silicon layer and a high temperature polysilicon layer.

FIG. 2 is an exploded perspective view showing a configuration of an acceleration sensor 10 and a perspective view of a lid portion 20.

FIG. 3 is an exploded perspective view showing a configuration of a sensor unit 30.

FIG. 4 is an explanatory diagram illustrating a manufacturing process of the sensor unit 30.

FIG. 5 is an explanatory diagram showing film forming conditions of an amorphous silicon layer and a high temperature polysilicon layer, and properties of a cantilever manufactured under each condition.

FIG. 6 is an explanatory diagram showing that no warp is observed in a cantilever formed by stacking an amorphous silicon layer and a high temperature polysilicon layer at a predetermined film thickness ratio.

FIG. 7 is an explanatory diagram showing a state of distribution of residual stress generated inside a cantilever formed by forming a film in a state of amorphous silicon.

[Explanation of reference numerals] 10 ... Acceleration sensor 20 ... Lid 22 ... Edge 30 ... Sensor 32 ... Sensor substrate 34 ... Operating part 36 ... Silicon oxide film 38 ... Silicon nitride film 40 ... First layer 41 ... First sacrifice Layer 42 ... Second layer 43 ... Second sacrificial layer 44 ... Third layer

Claims (10)

[Claims] 1. A silicon structure comprising: a polycrystalline film forming step of forming a polycrystalline silicon film on a substrate; and a polycrystalline film shape forming step of forming the polycrystalline silicon film into a desired shape. In the manufacturing method, the polycrystalline film forming step includes a first silicon layer forming step of forming a first silicon layer in a state of amorphous silicon, and a polycrystalline structure on the first silicon layer. And a second silicon layer forming step of forming a second silicon layer in the state of having the second silicon layer. 2. The method for manufacturing a silicon structure according to claim 1, wherein a film thickness ratio between the film thickness of the first silicon layer and the film thickness of the second silicon layer is the first film thickness. Of the polycrystalline silicon layer formed in the same amorphous silicon state as that of the second silicon layer and the average residual stress and the radius of curvature of the polycrystalline silicon layer formed in the state of having the same polycrystalline structure as the second silicon layer. A method for manufacturing a silicon structure, which is obtained by using an average residual stress and a radius of curvature that are possessed, and is determined so that a bending moment has a predetermined value in the polycrystalline silicon film formed into the desired shape. 3. The method for manufacturing a silicon structure according to claim 2, wherein when determining the film thickness ratio, infinity is used as a radius of curvature of the polycrystalline silicon layer corresponding to the second silicon layer. 4. The method of manufacturing a silicon structure according to claim 2, wherein a predetermined value of the bending moment is 0 when the film thickness ratio is determined. 5. The method for manufacturing a silicon structure according to claim 1, wherein the polycrystalline silicon film is formed into a desired shape, and when the polycrystalline silicon film is displaced according to an external force, the displacement is caused. A method for manufacturing a silicon structure, wherein an operating portion of a sensor that outputs an amount as an electric signal is formed, and the external force can be detected. 6. A silicon structure formed on a substrate, comprising a polycrystalline silicon film having a predetermined shape, wherein the polycrystalline silicon film is a first polycrystalline silicon whose average residual stress is tensile stress. A silicon structure comprising a layer and a second polycrystalline silicon layer which is overlaid on the first polycrystalline silicon layer and has an average residual stress of compressive stress, and which produces a predetermined bending moment in the polycrystalline silicon film. 7. The silicon structure according to claim 6, wherein the value of the predetermined bending moment is zero. 8. The silicon structure according to claim 7, wherein the average residual stress of the polycrystalline silicon film is tensile stress. 9. The silicon structure according to claim 6, wherein the polycrystalline silicon film is displaced according to an external force, and the external force can be detected by outputting the displaced amount as an electric signal. A silicon structure forming the working part of the sensor. 10. An acceleration sensor comprising the silicon structure according to claim 9.