JPH04181136A - Pressure detector and its manufacture - Google Patents

Abstract

PURPOSE:To enable highly sensitive and highly accurate pressure measurement by constituting a pressure receiving diaphragm and a distortion gage element of a single crystal. CONSTITUTION:Oxide film 8, 2 are sequentially formed on a silicon substrate while a single crystal silicon 3 and a reference pressure chamber 1 are formed on the oxide film 2. A pressure receiving diaphragm 21 is formed on the pressure chamber 1 and a piezo-resistant element 6 being a distortion gage element is formed inside the chamber 1 at a predetermined portion. An oxide film 4 is formed between a passivation film 5 and the silicon 3. When the element 6 detects pressure, the detection signal is output via an Al wiring layer 7 to a signal processing circuit such as an externally provided CPU. Thus pressure can be measured highly sensitively and highly accurately.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a pressure detector and a method for manufacturing the same, for example, a pressure detector having a reference pressure chamber and a method for manufacturing the same.

[Conventional technology]

2. Description of the Related Art Conventionally, a pressure sensor having a reference pressure chamber in a sensor chimp is disclosed in, for example, Japanese Patent Laid-Open No. 1-136043. In this publication, a pressure receiving diaphragm that receives pressure is formed of a silicon nitride film, and a strain gauge is formed of a polycrystalline film.

[Problems to be Solved by the Invention] However, in the conventional device described above, since the pressure receiving diaphragm is formed of a silicon nitride film, variations due to temperature characteristics become large and changes over time occur. There is a problem that pressure measurement cannot be performed with high precision.

Furthermore, since the strain gauge element is made of polysilicon, the output signal level of the strain gauge element is low, making it difficult to operate with high sensitivity.

The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to improve the accuracy of pressure measurement and to provide a highly sensitive pressure detector and a method for manufacturing the same.

(Means for Solving the Problems) Therefore, in the invention according to claim 1, the present invention includes: a single crystal layer formed on a substrate; and a predetermined portion of the single crystal layer is removed as a reference pressure chamber. The method is characterized by comprising: a formed cavity region; a pressure-receiving diaphragm formed in the single crystal layer on the cavity region; and a strain gauge element formed in the pressure-receiving diaphragm and detecting displacement of the pressure-receiving diaphragm. In the invention according to claim 2, a pressure detector is adopted, and in the first substrate surface formed of a single crystal,
a first step of forming a hole with a depth corresponding to the film thickness of the pressure receiving diaphragm by etching; a pressure chamber forming region in which the hole and a reference pressure chamber are formed;
a second step of etching the pressure chamber forming region and a communication path communicating the hole to form the hole as an etching hole; a third step of forming an oxide film in at least the etching hole; and the third step. A fourth step of bonding the side of the first substrate that has undergone the process on which the pressure chamber forming region is formed and the second substrate.
and a fifth step of polishing the back surface of the first substrate until the oxide film formed in the etched hole is exposed from the back surface of the first substrate. This method adopts the method of manufacturing pottery.

[Effect]

With the above configuration, in the invention according to claim 1, a single crystal layer is formed on the substrate, and a cavity region in this single crystal layer is formed by removing a predetermined portion of the single crystal layer as a reference pressure chamber. A pressure receiving diaphragm is formed on the single crystal layer above the cavity region, and a strain gauge element is formed on the pressure receiving diaphragm to detect displacement of the pressure receiving diaphragm.

Further, in the invention according to claim 2, a hole having a depth corresponding to the thickness of the pressure receiving diaphragm is formed on the surface of the first substrate formed of a single crystal in the first step, and the hole is formed in the second step. The hole is formed as an etched hole by etching a pressure chamber forming region in which a reference pressure chamber is formed and a communication path communicating the pressure chamber forming region and the hole.

Then, in a fourth step, the side of the first substrate that has gone through the third step, on which the pressure chamber forming region is formed, is bonded to the second substrate, and in a fifth step, the etching holes are etched from the back surface of the first substrate. The back surface of the first substrate is polished until the oxide film formed on the first substrate is exposed.

〔Effect of the invention〕

As described above, in the invention according to claim 1, since the pressure receiving diaphragm is formed of a single crystal, it is difficult to cause changes over time, so an excellent effect is achieved in that the accuracy of pressure measurement can be improved. be. Furthermore, since the strain gauge element is also formed of a single crystal, the output signal level is increased, so it has the excellent effect of being able to operate with high sensitivity.

Further, in the invention as set forth in claim 2, the thickness of the pressure receiving diaphragm is set by etching performed in the first step. Furthermore, since the amount of etching is extremely small as the film thickness of the pressure-receiving diaphragm, it is possible to use an etching method that allows precise etching control such as dry etching. Therefore, the thickness of the pressure receiving diaphragm can be formed with high precision, and there is an excellent effect that the precision of pressure measurement can be improved.

〔Example〕

Hereinafter, the present invention will be explained based on embodiments shown in the drawings.

FIG. 1 is a sectional view of a pressure detector representing an embodiment of the present invention, and FIG. 2 is a plan view of the pressure detector. In addition,
The AA' section in FIG. 2 corresponds to the sectional view shown in FIG.

In FIG. 1, an oxide film 8 and an oxide film 2 are sequentially formed on a silicon substrate 16, and on this oxide film 2, a single crystal silicon 3 and a reference pressure chamber 1 are formed.

The inside of this reference pressure chamber 1 is in a vacuum state or filled with a predetermined gas, and is sealed with single crystal silicon 3 and a passivation film 5.

A pressure receiving diaphragm 21 is formed above the reference pressure chamber 1, and a piezoresistive element 6, which is a strain gauge element, is formed at a predetermined portion inside the pressure diaphragm 21. When the piezoresistive element 6 detects pressure, the detection signal is outputted via the A1 wiring layer 7 to a signal processing circuit such as a CPU provided outside.

Further, an oxide film 4 is formed between the passivation film 5 and the single crystal silicon 3. Note that the piezoresistive element 6 does not need to be provided inside the pressure receiving diaphragm 21.

The pressure detector having the above configuration actually has a form as shown in FIG. That is, four piezoresistive elements 6 are formed on the reference pressure chamber 1, and around the reference pressure chamber 1, etching holes 9 and an etching liquid introduction path 12, which were used in the process of manufacturing this pressure sensor, are formed. Each of them is filled with the above-mentioned passivation film 5 (FIG. 1).

In this way, in the pressure detector of this embodiment, since the pressure receiving diaphragm is formed of single crystal silicon, variations due to temperature characteristics and changes over time can be suppressed as much as possible. Furthermore, since the strain gauge element is made of single crystal silicon, the detection signal level is high (and pressure can be measured with high sensitivity).

Next, the manufacturing procedure (first manufacturing method) of the pressure detector shown in FIG. 1 mentioned above will be explained using FIGS. 3(a) to (j). Note that FIGS. 3(a) to 3(j) are cross-sectional views of the pressure detector shown in the order of manufacturing steps.

(Diaphragm Formation Step) First, as shown in FIG. 3(a), a resist film 10 is applied on the single crystal silicon 3, and then a prototype of the etched hole 9 is formed by etching.

The amount of etching performed in this step ultimately corresponds to the film thickness of the pressure receiving diaphragm. Furthermore, since the amount of etching is very small, dry etching can be used and precise etching control can be easily performed. In this example, the etching amount is 1 μm.
It is said that

Note that this diaphragm forming step corresponds to the first step.

(Reference pressure chamber formation step) Next, as shown in FIG. 3(b), after removing the resist film 10, a resist film 11 is applied again to form a further 1 μm.
Perform etching with the etching amount.

Through this step, a prototype of the reference pressure chamber 1 is formed.

(Etching solution introduction path forming process) Next, as shown in FIG.
Patterning is performed with an enching amount of .

Through this step, the etching liquid introduction path 12 is formed.

At this stage, the depth of the etching liquid introduction path 12 is 0.5 μm.
m, the depth of the reference pressure chamber 1 is 1.5 μm, and the depth of the etching hole 9 is 2.5 μm. Note that the above-described reference pressure chamber forming step and this etching liquid introduction path forming step correspond to the second step.

(Oxide film formation step) Next, as shown in Figure 3(d), when an etching solution is added in the later process, the film thickness of the pressure receiving diaphragm is prevented from becoming too thin, and moreover, it is performed in the later process. In order to play the role of a stopper during polishing, a thermal oxidation process is performed to form an oxide film 14 with a thickness of 1000 nm. Note that this oxide film forming step corresponds to the third step.

(Polycrystalline film deposition step) Next, as shown in FIG. 3(e), polycrystalline silicon 15 is deposited on the oxide film 14, and approximately 5,000 layers of this polycrystalline silicon 15 are left on the surface of the oxide film 14. Then, as shown in Fig. 3, a thermal oxidation treatment is performed to form an oxide film 2.

At this time, thermal oxidation treatment is performed until oxidation WX2 of polycrystalline silicon 15 reaches oxidation Wi14 on the surface of single crystal silicon 3. As a result, the film thickness of oxidized [2] becomes approximately 1 μm.

(Bonding process) Next, as shown in FIG. 3(g), a silicon substrate 16 having an oxide film 8 with a thickness of about 1 μm on the surface and the single crystal silicon 3 that has gone through the above process are bonded together by wafer direct bonding. match. Subsequently, polishing is performed until the oxide film 14 formed in the etching hole 9 (FIG. 3(C)) is exposed.

At this time, by using selective polishing for surface polishing, polishing can be stopped when the oxide film 14 is exposed.
The pressure receiving diaphragm 21 has a desired thickness. Note that this bonding step corresponds to the fourth step and the fifth step.

(Piezoresistive Element Forming Step) Next, as shown in FIG. 3(5), a piezoresistive element 6 and an oxide film 4 are formed on the reference pressure chamber 1 using a normal IC manufacturing process.

(Cavity region forming step) Next, as shown in FIG. 3(i), the oxide film 4 formed on the etching hole 9 is removed by photoetching or the like.
Subsequently, polycrystalline silicon 15 formed in the reference pressure chamber l
is removed by wet etching. Then, wet etching is further performed to remove the oxide film 14. Here, since the film thickness of the oxide film 2 is formed much thicker than the film thickness of the oxide film 14, a part of the oxide film 2 is removed, but most of it remains.

(Sealing process) Next, as shown in FIG. 3(j), an Affi wiring layer 7 is formed on the piezoresistive element 6, a passivation film 5 is further deposited, and AI! , covering the wiring layer 7 and sealing the etching hole 9 with passivation WjI5.

At this time, since the atmosphere in which the passivation film 5 is formed is close to a vacuum state, the etching hole 9 is closed while the reference pressure chamber is maintained in a vacuum state. In addition, selective CVD
The etching hole 9 may be sealed by selective tungsten CVD (for example, selective tungsten CVD).

As described above, the thickness of the pressure receiving diaphragm is determined by the initial etching (etching performed in the diaphragm forming process). Moreover, since the amount of etching is very small, it is possible to use an etching method that allows precise etching control, such as dry etching. Therefore, it becomes possible to form the thickness of the pressure receiving diaphragm with high precision.

Furthermore, by using the above manufacturing method, it is possible to manufacture a pressure sensor in which a pressure receiving diaphragm and a strain gauge element are formed of a single crystal film, which cannot be realized by the manufacturing process disclosed in the above publication (Japanese Patent Laid-Open No. 1-136043). becomes possible.

In other words, when attempting to substitute a nitride film for a single crystal film (for example, single crystal silicon) using the manufacturing method described in the above publication, an oxide film must be formed on a polycrystalline polysilicon film and single crystal silicon must be formed by recrystallization growth. Must be. but,
For this purpose, a seed portion of single crystal silicon is required, which poses a problem in that the number of manufacturing steps increases. Moreover, the pressure-receiving diaphragm constructed by recrystallization growth is
It has low mechanical strength and is not suitable for pressure detectors where pressure is applied at any time.

However, the above manufacturing method makes it possible to manufacture a pressure sensor in which the pressure receiving diaphragm and the strain gauge element are formed of a single crystal film.

Next, the manufacturing procedure (second manufacturing method) of the pressure detector described above will be explained.

FIGS. 4(a) to 4(d) are cross-sectional views of the pressure detector shown in the order of manufacturing steps. Note that this second manufacturing method is performed after forming a pressure sensor as shown in the cross-sectional view of FIG. 3(d) in the first manufacturing method.

First, as shown in FIG. 4(a), polycrystalline silicon 15 is deposited on oxide film 14.

Next, as shown in FIG. 4 et al., a thermal oxidation treatment is performed to form an oxide film 2 on the surface of the single crystal silicon 3, and a silicon substrate 16 having an oxide film 8 with a thickness of about 1 μm on the surface is formed. The single-crystal silicon 3 that has passed through the process is bonded to the wafer by direct bonding.

Subsequently, the surface is polished until the oxide film 14 formed in the etching hole 9 (FIG. 3(C)) is exposed. Note that the polishing at this time uses selective polishing so that the polishing is stopped when the oxide film 14 is exposed.

Next, as shown in FIG. 4(C), trenches 17 are formed by etching. This trench 17 has a depth that reaches the oxide film 2.

Next, as shown in FIG. 4(d), the surface of the single crystal silicon 3 is oxidized, and the trench 17 is filled with an oxide film 18. After this, by going through the piezoresistive element forming step and the hollowing step in the above example,
Manufactures pressure detectors.

Since the pressure sensor in this embodiment is surrounded by the trench 17 and the oxide film 2, it can be insulated and isolated from other regions.

Therefore, for example, a semiconductor element such as a transistor can be formed in a region adjacent to this pressure sensor.

Next, the manufacturing procedure (third manufacturing method) of the pressure detector will be explained.

FIGS. 5(a) and 5(a) are sectional views of the pressure detector shown in the order of manufacturing steps. Note that this third manufacturing method is performed after forming a pressure sensor as shown in the cross-sectional view of FIG. 3(d) in the first manufacturing method.

First, as shown in FIG. 5(a), polycrystalline silicon 15 is deposited on oxide film 14. Next, as shown in FIG. Then polish the surface,
After that, a resist film 19 is applied. Next, resist film 1
Boron (B') is implanted at a high concentration into the areas where 9 is not coated to form a high concentration polycrystalline silicon 20.

Next, as shown in FIG. 5(b), after removing the resist layer 9, a thermal oxidation treatment is performed to form an oxide film 2 on the surface of the single crystal silicon 3, and an oxide film 8 with a thickness of approximately lum is formed. The silicon base Fi 16 on the surface and the single crystal silicon 3 that has gone through the above steps are bonded together by wafer direct bonding.

Subsequently, the surface is polished until the oxide film 14 formed in the etching hole 9 (FIG. 3(C)) is exposed. Note that the polishing at this time uses selective polishing so that the polishing is stopped when the oxide film 14 is exposed. After this, the pressure sensor is manufactured by passing through the piezoresistive element forming step and the hollowing step in the above embodiment.

In this hollowing step, selective etching is performed using the concentration difference between polycrystalline silicon 15 and polycrystalline silicon 20. This is because polycrystalline silicon 20 having a high concentration is difficult to be etched by alkali etching (KOH2NaOH, etc.), so polycrystalline silicon 15 is removed using this etching.

When this manufacturing method is used, there is no need to control the thermal oxidation treatment performed in the process of forming a pressure sensor as shown in the cross-sectional view of FIG. 3(f).

[Brief explanation of drawings]

FIG. 1 is a sectional view of a pressure detector representing one embodiment of the present invention, FIG. 2 is a plan view of the pressure detector in the above-mentioned embodiment, and FIGS. FIG. 4 (a
) to (c) are cross-sectional views of the pressure detector shown in the order of manufacturing steps according to the second manufacturing method, and FIGS. 5(a) and 5(b) are sectional views showing the manufacturing steps according to the third manufacturing method. FIG. 3 is a cross-sectional view of the pressure detector shown in sequence. DESCRIPTION OF SYMBOLS 1... Reference pressure chamber, 3... Single crystal layer, 6... Piezo resistance element (strain gauge element), 21... Pressure receiving diaphragm. Representative patent attorney Takashi Okabe (one idiot) Figure 1 A' / Figure 2 Figure 3 (j)

Claims (2)

[Claims] (1) A single crystal layer formed on a substrate; a cavity region formed by removing a predetermined portion of the single crystal layer as a reference pressure chamber; and a cavity region formed in the single crystal layer on the cavity region. A pressure detector comprising: a pressure receiving diaphragm; and a strain gauge element formed on the pressure receiving diaphragm and detecting displacement of the pressure receiving diaphragm. (2) A first step of forming a hole with a depth corresponding to the film thickness of the pressure receiving diaphragm on the surface of the first substrate formed of single crystal by etching, and a pressure at which the hole and the reference pressure chamber are formed. a chamber-forming region;
a second step of etching the pressure chamber forming region and a communication path communicating the hole to form the hole as an etching hole; a third step of forming an oxide film in at least the etching hole; and the third step. A fourth step of bonding the side of the first substrate that has undergone the process on which the pressure chamber forming region is formed and the second substrate.
and a fifth step of polishing the back surface of the first substrate until the oxide film formed in the etching hole is exposed from the back surface of the first substrate. manufacturing method.