JP2001267588A - Capacitance-type semiconductor sensor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a capacitance-type semiconductor sensor which is low-cost and small and which is of high sensitivity by improving the shape of a diaphragm to be used as a sensor detection part. SOLUTION: A glass wafer 2 is formed, in such a way that a circular thin- film fixed electrode 2a is formed on the rear surface and that a through-hole 2b is formed in its outer circumferential region. A diaphragm block 1 is formed, in such a way that a low-resistance thin-film diaphragm which faces the fixed electrode by keeping a very small gap is formed on the surface side of the silicon wafer, that a wafer material on the rear surface of the diaphragm is removed, and that the diaphragm block is overlapped with the glass wafer so as to be bonded. A sensor chip is constituted of an assembly which is composed of the glass wafer 2 and the diaphragm block 1. The thin-film diaphragm is formed as a corrugated diaphragm 4, where a low-resistance polysilicon film is used as a structure material, a flat zone in its central part is used as a moving electrode part 4a, a corrugated ring 4b which is arranged in a concentric circle shape is formed in its outer circumferential region, and a dust trap 4c which faces a part directly under the through-hole 2a is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type semiconductor sensor applied to a pressure sensor, an acceleration sensor, and the like used for automobiles and industries.

[0002]

2. Description of the Related Art In recent years, various types of sensors, such as pressure sensors, acceleration sensors, and flow sensors for automobiles and industrial use, are mainly semiconductor type sensors manufactured by a micromachining technique using silicon as a structural material. That is, silicon has excellent properties as a structural material of the sensor, such as high strength and high repetition of deformation repetition, and can be downsized by a semiconductor process and integrated with a control circuit.

In such a semiconductor sensor, a mechanical sensor (mechanical sensor) such as a pressure sensor or an acceleration sensor detects strain (stress) due to pressure or acceleration in a minute portion, and thus a diaphragm serving as a detecting element thereof. In processing, it is necessary to process as thin as possible and no residual stress remains. for that reason,
Conventionally, dry etching such as wet etching with an alkaline solution and plasma etching has been mainly used as a processing method for bulk silicon.

Next, taking a capacitance type semiconductor pressure sensor as an example, the structure of a conventional sensor chip is shown in FIGS. 9 (a) and 9 (b).
Shown in In the figure, 1 is a diaphragm block made of silicon, 2 is a glass wafer provided with a thin film fixed electrode 2a at the center of the lower surface, and 3 is a glass pedestal to which the diaphragm block 1 is attached. Here, the diaphragm block 1 has the following configuration. That is, the resistivity is 0.
For a P-type silicon wafer 1a of 2 to 0.3 .OMEGA.cm, a shallow circular recess 1b of about 2 .mu.m is formed on the upper surface side of the wafer by a plasma etching method, and a ring-shaped deep groove 1 is formed on the back surface side.
The movable electrode 1d is formed in a central region surrounded by a thin diaphragm and a ring-shaped deep groove by processing c.

A glass wafer (substrate) 2 made of borosilicate glass (glass having a thermal expansion coefficient very close to that of silicon) is provided on the upper surface of the diaphragm block 1.
Are formed by electrostatic bonding, and a circular thin film fixed electrode 2a that faces the movable electrode 1a with a small gap formed in the center of the lower surface of the glass substrate 2. The fixed electrode 2a is an aluminum sputter film having a thickness of about 0.7 μm, and a capacitor is formed between the movable electrode 1d and the fixed electrode 2a with the recess 1b as a gap. Further, a through hole 2b communicating with the inside of the sensor chip is formed at the outer peripheral corner of the glass wafer 2, and an aluminum metallized layer 2c is formed on the inner surface thereof so that the leads of the fixed electrode 2a are placed on the upper surface of the glass wafer 2. I'm pulling out. Further, an inclined through hole is formed in a corner portion opposite to the through hole 2b, and an aluminum metallized layer 2d is formed therein. The metallized layer 2d is used as a lead terminal of the movable electrode 1d and the glass wafer 2 is used as a lead terminal.
To the top side of the The assembly of the diaphragm block 1 and the glass wafer 2 is made of a glass pedestal 3 made of borosilicate glass having a pressure guiding hole 3a opened at the center.
And is assembled in a case (not shown), and the pressure sensor is formed by wire bonding between the sensor chip and the terminal on the case side.

When a measurement pressure is applied from the lower surface side of the silicon wafer 1a through the pressure guiding hole 3a formed in the glass pedestal 3 in such a configuration, the thin diaphragm portion is bent in accordance with the magnitude of the pressure and fixed to the movable electrode 1d. The gap with the electrode 2a changes, which changes the capacitance between the electrodes.

[0007]

However, the above-mentioned capacitance type semiconductor pressure sensor having the conventional structure has the following problems to be solved in terms of manufacturing and function. (1) In order to promote the miniaturization and high sensitivity of the sensor, if the diaphragm is formed as thin as possible, strict processing accuracy is required for the etching performed on the back side of the silicon wafer 1a, and quality control is difficult. Become. Therefore, the processing accuracy of bulk silicon reaches the limit in the sensor chip having the conventional structure, and it is extremely difficult to meet the demand for high sensitivity and miniaturization of the sensor without reducing the yield. The dry etching method is widely used because it has the advantages of less stress concentration and less damage due to cracks than the wet etching method.
The processing accuracy is lower than that of wet etching, and in particular, variation in etching processing accuracy is a problem in quality control in making the diaphragm thinner.

(2) On the other hand, in the case of a thermal semiconductor sensor represented by a gas sensor or a flow sensor, the thickness of a sensing element mounting portion has conventionally been reduced to a submicron to 1 μm level in order to improve its thermal response. A thin film diaphragm is known. The thin film diaphragm is formed by depositing a silicon nitride film or the like to a uniform thickness on the flat upper surface of a silicon wafer and then using the difference in the etching selectivity with silicon to remove the wafer material on the lower surface side of the thin film. A method has been used in which the diaphragm portion is formed by removing the silicon wafer by anisotropic etching and releasing it from the silicon wafer.

A diaphragm formed by forming a silicon nitride film or the like on a silicon wafer as described above has the advantage that the film thickness can be reduced, but the generation of residual stress inside the diaphragm is avoided. I can't. For this reason, when the thin film diaphragm formed by the above method is used as a mechanical sensor that measures the displacement of the diaphragm, such as a capacitance type pressure sensor, the following problems occur in the operation aspect. . In other words, when tensile stress is generated as an internal residual stress in the diaphragm, the displacement of the diaphragm (displacement when pressure is applied in a direction perpendicular to the diaphragm surface) becomes extremely small, and vice versa. Becomes When the internal residual stress of the thin film changes due to a temperature change, the spring constant, sensor sensitivity, and offset of the diaphragm change. As a result, it is difficult to ensure high linearity, stable sensor sensitivity, and measurement accuracy required as output characteristics of the mechanical sensor.

(3) In order to obtain high linearity in the capacitance type semiconductor sensor, the movable electrode formed in a part of the diaphragm is not distorted by the flexural deformation of the diaphragm, and is displaced in parallel with the fixed electrode. Therefore, the movable electrode portion generally adopts a structure formed thick as shown in FIG. However, when the sensitivity is increased by reducing the thickness of the diaphragm, the influence of the mass of the thick movable electrode portion cannot be ignored, and the output of the sensor fluctuates due to its mounting direction, vibration, and the like, causing a measurement error.

(4) Further, in a mechanical sensor such as a capacitance type pressure sensor, the processing accuracy with respect to the diameter of the diaphragm affects the sensor sensitivity. That is, within the range considered by the linear theory, the displacement w _{0 of the} movable electrode with respect to the pressure is expressed by the following equation.

[0012]

(Equation 1) Here, P: pressure, a: diaphragm outer diameter, b: diaphragm inner diameter, E: diaphragm Young's modulus, h: diaphragm thickness, ν: diaphragm Poisson's ratio As can be seen from the above equation, the diaphragm inner and outer diameters. If there is a variation in the dimensions (a dimensional error based on the processing accuracy), the variation appears as a variation in the sensor sensitivity. In this case, in the conventional processing method, the dimensional accuracy of the inner and outer diameters of the diaphragm is determined depending on the processing accuracy of the deep dry etching performed from the back side of the silicon wafer, and the processing accuracy of the dry etching is wet as described above. As compared with the etching method or the like, the diameter size of the diaphragm tends to vary.

(5) As another problem, as shown in FIG. 9, a detecting portion of a pressure sensor is constituted by a fixed electrode and a movable electrode of a diaphragm which are opposed to each other with a small gap therebetween, and a detecting portion of the pressure sensor is provided on the diaphragm block. In the case of a capacitive semiconductor sensor with a through-hole for leading the lead of the fixed electrode formed on the combined glass wafer, foreign matter such as dust from the outside passes between the diaphragm and the glass wafer through the through-hole during the sensor assembly process etc. When the foreign matter moves into the surface area between the fixed electrode and the movable electrode formed at the center of the pressure detection unit, the foreign matter not only directly disturbs the displacement of the movable electrode, but also causes a capacitance between the electrodes. Will affect the measurement accuracy.

The present invention has been made in view of the above points, and has as its object to suppress the effects of internal residual stress of a thin film diaphragm formed by film formation and etching on a silicon wafer, and changes in gravity, vibration, and the like. It is an object of the present invention to provide a high-sensitivity, high-precision capacitive semiconductor sensor with improved diaphragm shape and a manufacturing method suitable for manufacturing the same.

[0015]

According to the present invention, there is provided a glass wafer having a thin film fixed electrode formed in the center of a lower surface thereof, and a fine gap formed on the upper surface of a silicon wafer by the fixed electrode. To form a thin film diaphragm integrated with a movable electrode that faces each other, and removes the wafer material on the back side of the thin film diaphragm to form an assembly with a diaphragm block superimposed on a glass wafer. The flat zone is formed as a movable electrode portion by a corrugated diaphragm having a plurality of corrugated rings formed concentrically in the outer peripheral area thereof (claim 1).

According to the above configuration, the residual stress generated during the film formation of the diaphragm is absorbed by the flexible wave ring and hardly affects the spring constant of the diaphragm. Is also absorbed, so that the spring constant of the diaphragm hardly changes, whereby stable sensitivity and linear sensor output characteristics can be secured.

Further, according to the present invention, each of the above-described structures can be configured in the following manner. (1) The outer diameter of the thin-film fixed electrode formed on the lower surface of the glass wafer is set so that the outer peripheral edge thereof faces the valley of the corrugated ring arranged on the innermost periphery of the corrugated diaphragm.

Thus, it is possible to prevent the burrs generated on the periphery of the fixed electrode from directly contacting the movable electrode facing the other via a minute gap when forming the fixed electrode in a state where the diaphragm block and the glass wafer are assembled. . (2) A through hole for leading out the lead of the fixed electrode is formed on the outer periphery of the glass wafer, and a concave dust trap is formed on the outer periphery of the corrugated diaphragm so as to face immediately below the through hole (claim 3). .

As a result, foreign matter that has entered from the outside through the through-hole is settled and adsorbed in the dust trap, so that it is possible to effectively prevent the foreign matter from moving into the gap between the electrodes and obstructing the sensor function. (3) The wave depth of the wave ring of the wave diaphragm is set to at least five times the gap between the thin film fixed electrode and the movable electrode part, and the wave pitch is set to one to two times the wave depth. .

With this setting, the wall surface does not grow during the film formation of the thin film diaphragm by the CVD method or the like, so that the valleys of the grooves formed in advance in the silicon wafer are not filled or the wall thickness becomes non-uniform. The yield is improved. (4) A corrugated diaphragm is formed as a structural material by using a polysilicon provided with conductivity by doping the corrugated diaphragm with an impurity element, and the diaphragm can be used as a movable electrode as it is (claim 5).

(5) A rib-like reinforcing beam is formed on the back side of the movable electrode section formed at the center of the corrugated diaphragm, and the wafer material on the back side of the electrode section is removed. According to this configuration, it is possible to increase the rigidity of the movable electrode portion without giving the movable electrode portion a large mass (the wafer material portion bonded to the back surface of the movable electrode portion), thereby maintaining the parallel displacement of the movable electrode portion. In addition, the influence of fluctuations in the sensor output due to the mounting direction, vibration, and the like is suppressed, and the sensor sensitivity and measurement accuracy are further improved.

On the other hand, according to the present invention, the diaphragm block having the above configuration is manufactured by the following method. That is, a concave portion corresponding to a gap between electrodes and a concentric multiple groove corresponding to a corrugated ring of a corrugated diaphragm are formed on the upper surface of a silicon wafer by etching, and a silicon oxide film and a diaphragm structural material are laminated on the upper surface of the wafer. After forming the film, the wafer material in the lower surface region of the diaphragm is removed from the back surface side of the silicon wafer by dry etching using the silicon oxide film as an etching stop layer to form a corrugated diaphragm (claim 7).

According to this method, when the thin film of the diaphragm structure material formed on the upper surface of the silicon wafer is subjected to dry etching from the back surface side of the silicon wafer to release the thin film as a diaphragm, the silicon oxide film is formed. Since it functions as an etching stop layer, a corrugated diaphragm having a uniform thickness and almost no internal stress remains can be formed with high yield.

Further, in the present invention, there is the following manufacturing method as an embodiment based on the above manufacturing method. (a) For a silicon oxide film formed over the entire upper surface of a silicon wafer, a film of a diaphragm structure is formed after removing a film of another region while leaving a film of a multi-groove region, and the silicon oxide film is formed. After the wafer material in the lower surface region of the diaphragm is removed from the back surface side of the silicon wafer as an etching stop layer by dry etching, the silicon oxide film remaining on the back surface of the diaphragm is removed by wet etching.

According to this method, the inner and outer diameters of the corrugated diaphragm released from the silicon wafer (the inner and outer peripheral edges of the corrugated ring forming region) do not depend on the processing accuracy of the silicon wafer by the dry etching method. Photolithography in which a silicon oxide film formed on an upper surface of a silicon wafer is processed so as to function as an etching stop layer (a process for removing a part of the silicon oxide film formed on an upper surface of a silicon wafer is generally performed by a photo process. The processing is performed using masking, and the processing accuracy is determined by the accuracy of submicron order and higher than dry etching). Thereby, a stable sensitivity can be ensured by forming a waveform diaphragm with high processing accuracy.

Further, by leaving the silicon oxide film in the range of the formation of the corrugated ring of the diaphragm as described above, after the silicon wafer is subjected to deep etching, the silicon oxide film remaining on the back surface of the diaphragm is wetted with a hydrofluoric acid or the like. By performing the etching process, the silicon oxide film is completely removed, so that the effect of suppressing the occurrence of distortion due to the difference in linear expansion coefficient from the silicon wafer can be obtained.

(B) In the above item (a), the silicon oxide film remaining on the back surface of the diaphragm is removed by a wet etching method, and then the etching solution is replaced with ethanol at normal temperature and normal pressure. Drying by replacing with carbon dioxide (claim 9). That is,
In the state where the silicon oxide film is removed by wet etching, stiction occurs when the etchant that has entered the gap (a trace of the silicon oxide film) formed on the overlapping surface between the thin film diaphragm (polysilicon film) and the silicon wafer dries. The sticking phenomenon due to surface tension may occur, but by replacing the etching solution with ethanol having good wettability as described above, and further replacing it with liquid carbon dioxide having a small surface tension in a high pressure environment and drying it. And stiction can be reliably prevented.

(C) In the present invention, as a method of forming the dirt trap of the diaphragm block described in the above item (2), a step of forming multiple grooves concentrically arranged in the silicon wafer includes the steps of: A concave groove serving as a dust trap is formed at the corner at the same time.
0). (d) In addition, there is a method of performing an annealing treatment after the formation of the corrugated diaphragm in order to alleviate the internal stress of the corrugated diaphragm itself.

(E) Further, as a manufacturing method for forming a reinforcing beam of the movable electrode portion described in the above item (6), the present invention provides:
A slit-shaped concave groove corresponding to the reinforcing beam is formed in advance in the electrode forming region of the silicon wafer, and when forming the diaphragm structure material, the concave groove is filled to form a reinforcing beam for the movable electrode portion. Item 12), wherein the groove width of the concave groove is determined by the film thickness of the silicon oxide film and the diaphragm structure material formed on the upper surface of the wafer (the film thickness of the silicon oxide film and the polysilicon film as the diaphragm structure material). (Total thickness) is set to twice or less (claim 13).

According to this method, when the thin film diaphragm is formed on the upper surface of the silicon wafer, the diaphragm structure material fills the slit-shaped grooves at the same time, and the thin film diaphragm and the thin film diaphragm are etched in a subsequent deep etching step of the silicon wafer.
And when the wafer material on the back side of the movable electrode part is removed,
A movable electrode part with a reinforcing beam released from the silicon wafer is formed.

[0031]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure of an embodiment of the present invention and a method of manufacturing the same will be described below with reference to the illustrated embodiment, taking a capacitance type pressure sensor as an example. [Embodiment 1] First, an embodiment according to claims 1 to 5 of the present invention will be described with reference to FIGS. 1 is a sectional view of the configuration of the sensor chip, FIG. 2 is an enlarged view of a main part of FIG. 1, and FIGS.
(b) is a perspective view of the disassembled and assembled state of the sensor chip.

The sensor chip of the illustrated embodiment is basically the same as the conventional structure shown in FIG. 9, but the diaphragm formed on the upper surface side of the diaphragm block 1 is a thin film diaphragm having a thickness of submicron to several μm. And a waveform diaphragm 4 whose section becomes a waveform. That is,
A general corrugated diaphragm made of a metal material has a higher effect of absorbing internal stress (strain) and increasing the amount of displacement than a flat diaphragm, and as shown in the pressure-displacement characteristic diagram of FIG. It is known that there is an effect of obtaining high linearity. Therefore, in the present invention, a sensor chip is formed by forming a waveform diaphragm on a silicon wafer by a semiconductor process technique.

That is, in the illustrated embodiment, a thin-film corrugated diaphragm 4 is formed on the upper surface side of the silicon wafer 1 by using low-resistance polysilicon doped with an impurity element to impart conductivity to the silicon wafer 1. The corrugated diaphragm 4 has a shape in which a plurality of corrugated rings 4b concentrically arranged are formed in the outer peripheral region of the corrugated diaphragm 4 as a movable electrode portion 4a using a circular flat zone at the center.
b, the wave depth h is set to be at least 5 times or more the gap length g between the thin film fixed electrode 2a and the movable electrode portion 4a, and the pitch p between the waves is set to 1 to 2 times the wave depth h. Further, a glass wafer 2 is provided on the outer peripheral corner of the corrugated diaphragm 4.
A groove-shaped dust trap 4c is formed at a position directly below the through hole 2b.

The circular thin film fixed electrode 2a formed on the lower surface side of the glass wafer 2 opposite to the movable electrode portion 4a has a valley of a corrugated ring whose outer peripheral edge is aligned with the innermost perimeter of the corrugated diaphragm 4. The outer diameter is set so as to face the portion 4b-1. The reason why the waveform diaphragm 4 is formed in the above-described shape is as follows. That is, there is a possibility that dust 7 such as dust may enter the inside of the sensor chip from the outside through the through hole 2b during assembling the sensor, for example, by wire bonding the through hole 2b on the upper surface side of the glass wafer 2. If a dust trap 4c is formed at one corner of the diaphragm 4 so as to face directly below the through hole 2b as in the embodiment, the dust 7 entering the sensor chip will settle in the dust trap 4c and be formed in the groove. There is no danger that it will be adsorbed to the bottom and move toward the center of the diaphragm to hinder its displacement or obstruct ventilation. The dust trap c is formed simultaneously with the formation of the waveform diaphragm 4 as described later.

Regarding the shape of the corrugated ring 4b, if the corrugated pitch p is too narrow, the wall surface of the corrugated diaphragm 4 grows when the corrugated diaphragm 4 is formed by the CVD method or the like, and the valleys may be buried or the thickness unevenness may increase. In addition, dry etching from the back side of the silicon wafer 1a becomes difficult. On the other hand, if the pitch p is too wide, the stress absorption effect is reduced, or the size of the diaphragm becomes large.

Further, as shown in FIG. 2, the thin film fixed electrode 2a formed on the lower surface of the glass wafer 2 is arranged such that the outer peripheral edge thereof faces the valley portion 4b-1 of the corrugated ring arranged on the innermost side of the thin film diaphragm 4. When the thin film fixed electrode 2a is formed, even if the burr 2a-1 is formed so as to hang down at the periphery thereof at the time of forming the thin film fixed electrode 2a, the burr 2a-1 forms a small gap (gap between the fixed and movable electrodes). (Even if it is large, it is about 1 to 2 μm). A problem such as contact with the movable electrode 4a formed in the flat zone at the center of the diaphragm 4 opposed to each other can be prevented, and the product yield is improved.

Next, a manufacturing process of the sensor chip having the above configuration will be described with reference to FIG. (1) First, in step (a), a silicon wafer (bulk material) 1
Al on the top surface side of a, there is a shallow recess 1b corresponding to the inter-electrode gap of the capacitive sensor and SiO ₂ as a mask is formed by plasma etching. (2) In the step (b), a plurality of corrugated grooves 1e concentrically arranged in the recess 1a and a groove 1f for forming the dust trap 4c (see FIG. 3) are dug by etching.

(3) In the step (c), the surface of the silicon wafer 1a is thermally oxidized by a thermal oxidation furnace or the like, and silicon oxide (Si)
O ₂ ) The film 6 is formed. (4) In step (d), a low-resistance phosphorus-doped polysilicon film 5 is formed on the surface of the silicon wafer 1a as a gas for epitaxial growth of, for example, SiH ₄ + PH ₃ by CVD.

(5) In the state shown in FIG. 4D in which the phosphorus-doped polysilicon film 5 formed on the surface of the silicon wafer 1a is fixed in the step (e), the substrate is heated to a temperature of about 1000 ° C. An annealing treatment is performed to relax the residual stress generated at the time of film formation together with the activation of the dopant. (6) In the next step (f), the silicon wafer 1a is
The lower surface area of the multiplex waveform portion excluding the central flat zone and the outer peripheral edge portion of the polysilicon film 5 is RIE from the back side.
(Reactive ion etching), a ring-shaped deep groove 1c is dug by a dry etching method such as plasma etching to release the multiple grooves of the polysilicon film 5 from the silicon wafer 1a. In this case, the silicon oxide film 6 formed in the step (c) functions as an etch stop layer.

Incidentally, the annealing treatment described in the step (e) is as follows.
It may be performed after the back surface side of the diaphragm is deeply etched. (7) Further, step (f) The silicon wafer 1a is wet-etched with hydrofluoric acid or the like to remove the silicon oxide film 5 exposed on the lower surface side of the polysilicon film 5. If the silicon oxide film is left as it is, the diaphragm may be distorted due to a difference in thermal expansion coefficient or the like. This allows
On the upper surface side of the silicon wafer 1a, a thin-film corrugated diaphragm 4 having a movable electrode portion 4a, multiple corrugated rings 4b, and a dust trap 4c is formed.

(8) In the next step (g), the glass wafer 2 on which the fixed electrode 2a and the through hole 2b are formed in another step is superimposed on the upper surface of the diaphragm block manufactured through the above step, and the anode Join. (9) In the last step (h), metallized layers 2c and 2d of Au, Al, etc. are formed from the upper surface side of the glass wafer 2 by using a sputtering device or the like to complete through holes and bonding pads.

[Embodiment 2] Next, with respect to the corrugated diaphragm formed on the silicon wafer by the manufacturing method of Embodiment 1, the processing accuracy of the diameter size is increased, and furthermore, the diaphragm is formed on the silicon wafer as an etch stop layer for the diaphragm. A manufacturing method corresponding to claims 8 and 9 of the present invention in which the deposited silicon oxide film is completely removed to suppress distortion due to a difference in linear expansion coefficient from silicon will be described with reference to FIG.

In this embodiment, the manufacturing steps (a) to
As shown in FIG. 4C, the concave portion 1b, multiple corrugated grooves 1e, and the concave groove 1f for dust trapping are etched on the upper surface side of the silicon wafer 1a in the same manner as in the method of FIG. After the formation, in a subsequent step (d), the silicon oxide film 6 formed in the other region except the multiple waveform groove region X of the silicon wafer 1a is removed. The removal of the silicon oxide film 6 is performed by an etching method using masking by a photo process. This allows
The silicon oxide film 6 is processed with high precision on the order of submicrons.

Next, in step (e), a polysilicon film 5 is formed with a uniform thickness over the entire surface of the silicon wafer 1a by the CVD method. An enlarged cross-sectional view of the portions A and B shown in the figure in this state is shown in FIG. In the subsequent step (f), as in the manufacturing method described with reference to FIG. 4, the silicon oxide film 6 is used as an etch stop layer to dry-etch the ring-shaped deep groove 1c from the lower surface side of the silicon wafer 1a. An enlarged sectional view in this state is shown in FIG. Thereafter, in step (g), the polysilicon film 5 is immersed in an etching solution such as hydrofluoric acid.
Is removed by wet etching.

According to this manufacturing method, the silicon wafer 1
The inner and outer diameters (the inner and outer peripheral edges of the corrugated ring forming region) of the corrugated diaphragm 4 released from a do not depend on the processing accuracy of the silicon wafer by the dry etching method, and function as an etching stop layer. Photolithography for processing the silicon oxide film 5 formed on the upper surface of the silicon wafer (Processing for removing a part of the silicon oxide film formed on the upper surface of the silicon wafer is generally performed using masking by a photo process. The processing accuracy is on the order of submicrons and is higher than dry etching).
As a result, the waveform diaphragm 4 is formed with high processing accuracy, and stable sensitivity can be secured.

By leaving the silicon oxide film 6 only in the area where the diaphragm ring is formed as described above, the silicon wafer 1a is etched from the back side to dig a deep groove 1c, and then the silicon wafer 1a is etched. If the silicon oxide film 6 remaining on the back surface is treated by wet etching such as hydrofluoric acid, the silicon oxide film 6 will be completely removed.
Also, the effect of suppressing the occurrence of distortion due to the difference in linear expansion coefficient from the above can be obtained.

When wet etching is performed in step (g) in FIG. 5, the silicon oxide film 6 is completely removed as shown in the enlarged sectional view (l), and the deep groove 1 is formed.
At the inner and outer peripheral edges of c, a slit-shaped gap is left locally at the boundary between the polysilicon film 5 and the silicon wafer 1a as a trace of removal of the silicon oxide film. By the way, when the diaphragm block is pulled out from the wet etching solution and dried, if the etching solution remains in the slit-like gap, a sticking phenomenon due to surface tension called stiction may occur.

Therefore, in the present invention, the etching solution entering the slit-like gap is replaced with ethanol having good wettability at normal temperature and normal pressure, and further replaced with liquid carbon dioxide having a small surface tension under high pressure environment and dried. Thus, the occurrence of the stiction is prevented. [Embodiment 3] Next, the construction of a third embodiment of the present invention, in which a reinforcing beam is formed on the movable electrode portion of the corrugated diaphragm, and a method of manufacturing the same will be described with reference to FIGS.

That is, in the sensor chip shown in FIGS. 6A to 6C, the movable electrode portion 4a of the corrugated diaphragm 4 formed by forming a film on the upper surface side of the wafer of the diaphragm block 1 by using polysilicon as a diaphragm structural material. A rib-shaped reinforcing beam 4a-1 which protrudes in a cross shape is integrally formed on the back side, and the wafer material on the back side of the movable electrode portion 4a is removed.

Here, the reinforcing beam 4a-1 has its end connected to the corrugated ring 4b located at the innermost periphery of the corrugated diaphragm 4. With this structure, the bending rigidity of the movable electrode portion 4a increases, and the movable electrode portion itself does not bend and deform even when a measurement pressure is applied from the back surface side of the diaphragm 4, and is parallel to the fixed electrode 2a while maintaining the flat plate shape. Go to As a result, the capacitance between the fixed electrode and the movable electrode changes linearly with respect to the measurement pressure. Moreover, as compared with the movable electrode portion 4a of the embodiment shown in FIG. 1, the weight of the movable electrode portion is reduced by the amount corresponding to the removal of the wafer material on the back surface side. It can be kept small. In the illustrated example, the reinforcing frame 4a-1 is used.
Is a cross shape, but is not limited to this. The reinforcing frame 4a-1 may be formed in a lattice shape or a honeycomb shape.

Next, the above-mentioned movable electrode portion 4a with a reinforcing beam is provided.
7 will be described with reference to FIG. First, in the step (a), a concave portion 1b is formed on the upper surface of the silicon wafer 1a in the same manner as the manufacturing process described with reference to FIG. 4, and then in the next step (b), multiple undulating grooves 1e,
When the concave groove 1f serving as a dust trap is formed by plasma etching, a slit-shaped concave groove 1g is engraved in a cross shape in a flat zone region at the center where a movable electrode is to be formed. The groove width of the concave groove 1g is set to be twice or less the film thickness including the silicon oxide film 6 and the polysilicon film 5 to be formed later.

Subsequently, in step (c), a silicon oxide film 6 is formed on the upper surface of the wafer, and in step (d), the silicon oxide film 6 is formed.
Low-resistance phosphorus-doped polysilicon film 5
The film is formed by a method. In this film forming step, the polysilicon film 5 fills the above-described slit-shaped concave groove 1g, and a portion C in the drawing has a rib-like shape on the back side of the movable electrode portion as shown in the enlarged sectional view (i). Beams are formed simultaneously. In addition, in the state where the polysilicon film 5 is formed, an annealing process is performed as necessary to reduce internal stress.

Next, in the step (e), etching is performed from the back side of the silicon wafer 1a by a reactive ion etching, a plasma etching method or the like, and the silicon oxide film 5 is used as an etch stop layer to remove the polysilicon film 5 excluding the peripheral portion of the wafer. A deep groove 1c is dug in the lower surface area, and in step (f), the silicon oxide film 6 remaining on the lower surface of the polysilicon film 5 is removed by wet etching with hydrofluoric acid or the like to form a corrugated diaphragm 4 released from the wafer. I do. Thus, the reinforcing beam 4a-1 shown in FIG. 6 is formed on the back surface of the movable electrode portion 4a of the corrugated diaphragm 4.

Thereafter, similar to the manufacturing process of FIG.
In step (g), the diaphragm block 1 produced through the above steps and the glass wafer 2 are overlapped and anodically bonded. In the subsequent step (h), through holes and bonding pads are formed in the glass wafer 2 to assemble the sensor chip. Is completed.

[0055]

As described above, according to the present invention, the following effects can be obtained. (1) A glass wafer having a thin film fixed electrode formed in the center of the lower surface, and a low-resistance thin film diaphragm (polysilicon film) having a movable electrode portion formed on the upper surface of a silicon wafer, and the wafer material on the back side was removed. A capacitive semiconductor sensor comprising an assembly of a diaphragm block and a structure in which the fixed electrode and the movable electrode face each other and are joined by superimposing and joining a diaphragm block and a glass wafer. The circular flat zone of the part is used as a movable electrode part, and a corrugated diaphragm is formed with a plurality of concentrically arranged wavy rings on the outer peripheral area. Extremely high sensitivity and small capacitance, as the wave ring absorbs stress and keeps the spring constant almost constant The quantity semiconductor sensor can be realized at low cost.

(2) In the above structure, the shape of the corrugated diaphragm is set as in claim 2 so that CVD can be performed.
A thin film diaphragm that effectively functions as a waveform diaphragm can be formed by a method or the like. According to the third aspect, the burr generated on the periphery of the fixed electrode at the time of film formation is reliably prevented from interfering with the movable electrode by directly touching the movable electrode, so that the product yield is improved. Practical effects are obtained, such as foreign substances that have entered from the outside through the through-holes opened in the upper surface of the glass wafer can be prevented from moving to the gap between the electrodes and obstructing the sensor function.

(3) Further, the reinforcing electrode is integrally formed on the back surface side of the movable electrode portion of the thin film diaphragm as in claim 6, so that the movable electrode portion has a large mass (coupling with the back surface of the movable electrode portion). The rigidity can be increased without providing the movable electrode part, while maintaining the parallel displacement of the movable electrode part while suppressing the influence of the sensor output fluctuation due to the mounting direction and vibration, etc. Measurement accuracy is further improved.

(4) Further, according to the manufacturing method of the seventh aspect, the thin film of the diaphragm structure material formed on the upper surface of the silicon wafer is subjected to dry etching from the back surface side of the silicon wafer to make the thin film into a diaphragm. When released, the silicon oxide film functions as an etching stop layer, so that a corrugated diaphragm having a uniform thickness and almost no internal stress remains can be formed with a good yield. By using this method in combination, it is possible to stabilize the sensor sensitivity by specifying the diameter size of the waveform diaphragm with higher processing accuracy, and to completely remove the silicon oxide film remaining on the back surface of the diaphragm to increase the linear expansion coefficient of the structural material. It is possible to provide a sensor that exhibits excellent sensor characteristics and excellent effects in manufacturing, such as preventing generation of distortion due to a difference.

[Brief description of the drawings]

FIG. 1 is a configuration sectional view of a capacitance type pressure sensor according to a first embodiment of the present invention.

FIG. 2 is an enlarged view of a main part in FIG.

3 is an external perspective view of the entire sensor chip shown in FIG. 1, (a) is an exploded view, and (b) is an assembled state diagram.

4 (a) to 4 (h) are state diagrams showing the manufacturing process of the sensor chip shown in FIG.

FIGS. 5A to 5H are explanatory diagrams of a manufacturing process of the sensor chip according to the second embodiment of the present invention, wherein FIG. 5A to FIG. A in ~ (g),
Enlarged sectional view of part B

FIGS. 6A and 6B are configuration diagrams of a sensor chip according to a third embodiment of the present invention, wherein FIGS. 6A and 6B are external perspective views as seen from above and below, respectively, and FIG.

FIGS. 7A to 7H are explanatory views of a manufacturing process of the sensor chip shown in FIG. 6, wherein FIGS.
(i) is an enlarged sectional view of part C in (d).

FIG. 8 is a diagram schematically illustrating operating characteristics of a diaphragm in which a waveform diaphragm and a flat diaphragm are compared with each other.

9A and 9B are configuration diagrams of a conventional capacitance-type pressure sensor, in which FIG. 9A is a cross-sectional view as viewed from the side, and FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diaphragm block 1a Silicon wafer 2 Glass wafer 2a Fixed electrode 2b Through hole 4 Thin film diaphragm 4a Movable electrode part 4a-1 Reinforcement beam 4b Wave ring 4c Dust trap 5 Polysilicon film 6 Silicon oxide film

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2F055 AA40 BB20 CC02 DD05 EE25 FF01 FF11 FF49 GG01 GG15 4M112 AA01 BA07 CA22 CA36 DA03 DA04 DA06 DA14 DA18 EA04 EA06 EA13

Claims (13)

[Claims] 1. A glass wafer having a thin-film fixed electrode formed in the center of the lower surface, and a movable electrode-integrated thin-film diaphragm opposed to the fixed electrode with a small gap formed on the upper surface of the silicon wafer. The thin film diaphragm is composed of a plurality of waveforms concentrically arranged in the outer peripheral area with a circular flat zone at a central portion as a movable electrode portion as a movable electrode portion. An electrostatic capacitance type semiconductor sensor characterized by being a waveform diaphragm formed with a ring. 2. The semiconductor sensor according to claim 1, wherein the outer diameter of the thin film fixed electrode formed on the lower surface of the glass wafer is opposed to the valley of the corrugated ring whose outer peripheral edge is aligned with the innermost periphery of the corrugated diaphragm. A capacitance-type semiconductor sensor characterized in that it is set to perform the following. 3. The semiconductor sensor according to claim 1, wherein a through-hole for leading a lead of the fixed electrode is formed in an outer peripheral portion of the glass wafer, and a concave portion is formed in the outer peripheral portion of the corrugated diaphragm immediately below the through-hole. A capacitance type semiconductor sensor characterized by forming a dust trap. 4. The semiconductor sensor according to claim 1, wherein the corrugated ring of the corrugated diaphragm has a depth of at least five times the gap between the thin-film fixed electrode and the movable electrode.
An electrostatic capacitance type semiconductor sensor, wherein a wave pitch is set to 1 to 2 times a wave depth. 5. The capacitance-type semiconductor sensor according to claim 1, wherein the corrugated diaphragm is formed of polysilicon having conductivity imparted by doping an impurity element as a structural material. 6. The semiconductor sensor according to claim 1, wherein a rib-like reinforcing beam is formed on the back side of the movable electrode formed at the center of the corrugated diaphragm, and the wafer material on the back side of the electrode is removed. A capacitance type semiconductor sensor characterized by the above-mentioned. 7. A concave portion corresponding to a gap between fixed / movable electrodes and a concentric multiple groove corresponding to a corrugated ring of a corrugated diaphragm are formed on the upper surface of a silicon wafer by etching. A diaphragm structure material is formed by stacking, and thereafter, a corrugated diaphragm is formed by removing the wafer material from the lower surface region of the diaphragm by dry etching using the silicon oxide film as an etching stop layer from the lower surface side of the silicon wafer. A method for manufacturing the capacitance-type semiconductor sensor according to claim 1. 8. A method according to claim 7, wherein a silicon oxide film is formed on the entire upper surface of the silicon wafer, and then the silicon oxide film is removed from the remaining region excluding the multiple groove region of the wafer. After the diaphragm structure material is formed, and the silicon oxide film is used as an etching stop layer, the wafer material in the lower surface area of the diaphragm is removed by dry etching from the back surface of the silicon wafer, and the silicon oxide film remaining on the back surface of the diaphragm is wet-etched. A method for manufacturing a capacitance-type semiconductor sensor, comprising: 9. The manufacturing method according to claim 8, wherein the silicon oxide film remaining on the back surface of the diaphragm is removed by wet etching, the etching solution is replaced with ethanol at normal temperature and normal pressure, and liquid carbon dioxide is further formed under a high pressure environment. A method for manufacturing a capacitance-type semiconductor sensor, characterized in that the method is changed to a drying method. 10. The method according to claim 7, wherein the step of forming multiple grooves concentrically arranged on the silicon wafer comprises:
A method for manufacturing a capacitance-type semiconductor sensor, wherein a groove serving as a dust trap is simultaneously formed in a corner portion of an upper surface of a silicon wafer. 11. The method according to claim 7, wherein an annealing process is performed after the formation of the corrugated diaphragm so as to alleviate the internal stress. 12. The manufacturing method according to claim 7, wherein a slit-like groove corresponding to the reinforcing beam according to claim 6 is formed in an electrode forming region on the upper surface of the wafer, and the film is formed when a diaphragm structure material is formed. A method for manufacturing a capacitance-type semiconductor sensor, comprising forming a reinforcing beam for a movable electrode portion by filling a concave groove. 13. The manufacturing method according to claim 12, wherein the groove width of the groove is not more than twice as large as the film thickness of the silicon oxide film and the diaphragm structure material formed on the upper surface of the wafer. A method for manufacturing a capacitance type semiconductor sensor.