JP4532787B2 - Condenser microphone and pressure sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a condenser-type microphone or pressure sensor having a vibration film created using a micromachining technique.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, a capacitor type microphone that changes a capacitor capacity according to the sound pressure of a received sound wave and converts the change in the capacitor capacity into an electric signal is known. As such a condenser-type microphone, a microphone having a structure as shown in FIG. 1 is known, and a pressure sensor of the microphone is manufactured by using a micromachining technique.
[0003]
A condenser microphone (pressure sensor) 100 shown in FIG. 1 includes a vibration film 201, a vibration film support part 202, a back plate 301, an exhaust hole 302, and a support part 303. The vibration film 201 is a conductive flat plate having a thickness on the order of microns, and the vibration film 201 and the back plate 301 constitute parallel plate electrodes. The sound wave incident on the vibration film 201 vibrates the vibration film 201 and changes the capacitance of the capacitor formed by the vibration film 201 and the back plate 301.
[0004]
The vibration film 201 is manufactured using a micromachining technique and is cut out by etching a silicon substrate. By using a silicon substrate, it is possible to form a vibration film with high mechanical strength. In addition, by forming each component from a silicon substrate of the same material, the thermal expansion coefficient of each component can be made the same, and unlike the case where a condenser microphone is configured by combining different materials, the temperature change It is difficult to cause distortion. Further, by using a silicon substrate, various silicon electronic circuits can be formed on the substrate.
[0005]
Hereinafter, a conventional manufacturing method of the condenser microphone (pressure sensor) 100 will be described with reference to FIG.
In step 201, an etch stop layer 220 is formed on the vibration film substrate 210 as shown in FIG. The etch stop layer 220 is a portion that becomes the vibration film 201 of the capacitor type microphone (pressure sensor) 100 as shown in FIG. 5D, and an etching amount of the silicon substrate for stably forming the vibration film 201. (Reference: Erin Steinsland et al., “Boron etch stop in TMAH solution”, Sensors and Actuators, A54 (1996), 728-732 (Elin Steinsland et al. ., “Boron etch-stop in TMAH”, Sensors and Actuators, A54 (1996), 728-732).
[0006]
In step 202, the back plate substrate oxide films 330 and 620 are formed on the back plate substrate 310, and the vibration film substrate oxide film 230 is formed on the surface of the vibration film substrate 210 opposite to the surface on which the etch stop layer 220 is formed.
In step 203, as shown in FIG. 5C, the etch stop layer 220 and the back plate substrate oxide film 620 are connected using a technique such as anodic connection to form the bonded substrate 700. By forming the bonding substrate 700, a fine parallel plate electrode can be easily formed with high accuracy.
[0007]
In step 204, the vibration film substrate oxide film 230 and the back plate substrate oxide film 330 are subjected to mask formation processing, and as shown in FIG. 5D, the vibration film substrate oxide film mask 231 and the back plate substrate oxide film mask 331 are formed. Form.
In step 205, the diaphragm 201 and the back plate 301 are formed by etching with an alkaline etchant using the diaphragm substrate oxide mask 231 and the back plate substrate oxide mask 331 as shown in FIG.
[0008]
In step 206, hydrofluoric acid is used to etch portions of the vibration film substrate oxide film mask 231, the back plate substrate oxide film mask 331, and the back plate substrate oxide film 620 except for the support portion 303 shown in FIG. Electrodes are formed to obtain a condenser microphone (pressure sensor) 100.
[0009]
As described above, in the conventional condenser microphone or pressure sensor, the vibration film substrate 210 on which the etch stop layer 220 to be the vibration film 201 is formed and the back plate substrate 310 are bonded to form the bonded substrate 700, and this bonding is performed. After the etching masks 231 and 331 are formed on both surfaces of the substrate 700, the bonding substrate 700 is etched with an alkaline etching solution to form the microphone vibration film 201 and the back plate 301.
[0010]
Here, it is essential to use a silicon thermal oxide film in order to obtain a high-quality etching mask resistant to an alkaline etching solution. The silicon thermal oxide film is usually formed by thermally oxidizing a silicon substrate at a temperature of 900 ° C. or higher in an oxygen atmosphere.
[0011]
[Problems to be solved by the invention]
However, in the conventional method of manufacturing a condenser microphone or pressure sensor, the concentration of boron doped for forming the etch stop layer is lower in the oxide film than in the silicon (etch stop layer), so the etch stop layer is formed. It is known that when the above heat treatment is performed on the bonded substrate, boron diffuses from the etch stop layer to the oxide film.
[0012]
The above matters
(1) Edited by Toru Hara, VLSI process data handbook, 1982, Science Forum, pages 204-206,
(2) Hisai Yanai, Atsushi Nagata, Integrated Circuit Engineering (1), 1980, Corona, page 76,
(3) Earl. Bee. Fair and Jay. Sea. Sea. Tsai, “Theory and direct measurement of boron segregation in S _i O ₂ during dry, near dry and wet O ₂ oxidation”, J. Electrochem. Soc. 125, No. 12, pp. 2050-2058, 1978, December (RBFair and JCCTsai, “Theory and Direct Measurement of Boron Segregation in SiO ₂ during Dry, Near Dry, and Wet O ₂ Oxidation”, J. Electrochem. Soc. ., 125, No. 12, 2050-2058, Dec 1978),
(4) Jay. W. Colby and L. Yeah. Katz, “Segregation of boron at the Si—S _i O ₂ interface as a function of temperature and orientation”, J. Electrochem. Soc. Vol. 123, No. 3, pp. 409-412, 1976, March (JW Colby and LEKatz, “Boron Segregation at Si-SiO ₂ Interface as a Function of Temperature and Orientation”, J. Electrochem. Soc., 123, No. 3 , 409-412, Mar 1976)
Etc. are known from the literature.
[0013]
As a result, the impurity concentration of the etch stop layer decreases, the internal stress of the etch stop layer shifts in the compression direction, and the vibration membrane is buckled by the internal compressive stress (reference: Cleopatra Cubs et al., "Microphysical study on the mechanical structure realized in p + silicon", J. Microelectromechanical Systems, VOL.4, NO.3, 1995 September (Cleopatra Cabuz et al., "Microphysical Investigations on Mechanical Structures Realized in p + Silicon ”, J. Mircroelectromechanical Systems, VOL.4, NO.3, Sep 1995)).
[0014]
As one of countermeasures against such a problem, a method of performing a thermal oxidation process for forming an oxide film for an etching mask before forming an etch stop layer is conceivable. However, when an oxide film is formed in the initial stage, it is necessary to provide a bonding electrode terminal on the back surface of the substrate in order to bond the substrates, and to prevent scratches on the etching mask that occur in the process after the oxide film is formed. There is a problem that this is a major limitation.
[0015]
In order to reduce stray capacitance between parallel plate electrodes and improve performance, it is conceivable to adopt a complicated etching mask structure with different film thicknesses. However, an etch stop layer should be formed at the beginning of the manufacturing process. However, there are problems such as difficulty in design and production.
As described above, in the conventional manufacturing method, the degree of freedom in design is narrowed with respect to the structure of the parallel plate electrode and the circuit that can be mounted.
[0016]
The present invention has been made to solve such a problem, and its purpose is to eliminate restrictions on the manufacturing process, and to expand the degree of freedom in designing the structure of parallel plate electrodes and circuits that can be mounted. It is to provide a microphone or pressure sensor.
[0017]
[Means for Solving the Problems]
In view of the above points, the invention according to claim 1 is the junction of the vibration film substrate having an etch stop layer formed of silicon doped with boron on one surface and the silicon oxide film on one surface. In a condenser microphone or a pressure sensor formed by etching a bonding substrate bonded via the etch stop layer and the bonding film, the bonding film is the same as the etch stop layer. The boron is contained, and the concentration of boron contained in the bonding film is higher than the concentration of boron doped in the etch stop layer.
[0018]
With this configuration, since the same boron- containing layer as the etch stop layer is used as a bonding film with the etch stop layer, boron redistribution becomes a problem even after the etch stop layer is formed and the substrate is bonded. Without this, the substrate can be subjected to high-temperature oxidation / annealing at about 1200 ° C. or less.
Further, since the concentration of boron contained in the bonding film is equal to or higher than the concentration of boron doped in the etch stop layer, redistribution of boron in the etch stop layer due to segregation in the bonding film can be suppressed. .
In addition, with this configuration, since the etch stop layer and the bonding film doped with boron as an impurity are used, a predetermined alkaline etching solution is used for the bonded substrate obtained by bonding the etch stop layer and the back plate substrate. Etching can be performed.
[0021]
The invention according to claim 2, Oite to claim 1, wherein the boron diffusion for etch stop layer formed is carried out at 1200 ° C. or less, followed by heat treatment 900 ° C. or higher, at a temperature below the boron diffusion It has a configuration to be performed.
With this configuration, boron diffusion for forming the etch stop layer is performed at 1200 ° C. or less, and the subsequent heat treatment is performed at 900 ° C. or more and 1200 ° C. or less, so that an appropriate temperature range for the subsequent heat treatment is ensured and the etch stop is performed. The redistribution of boron in the layer can be suppressed.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a condenser microphone or a pressure sensor according to a first embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 2 is a diagram schematically illustrating a manufacturing process of the condenser microphone or the pressure sensor according to the first embodiment.
[0023]
The condenser microphone (pressure sensor) 100 is formed using a semiconductor substrate such as a silicon substrate, and a thin vibrating membrane is required for sound wave detection in order to improve detection sensitivity. Hereinafter, for convenience of explanation, the semiconductor substrate is limited to a silicon substrate. Usually, an etching technique is used to form the thin vibration film 201, and an etch stop layer 220 having a thickness of several microns is formed on the vibration film substrate 210 in order to control the etching amount.
[0024]
In step 101, an etch stop layer 220 is formed on the vibration film substrate 210 as shown in FIG. The etch stop layer 220 is formed by a solid diffusion method, and a method of thermally diffusing impurities on the silicon substrate to a high concentration. In the thermal diffusion of impurities, heat treatment is performed at a high temperature in order to obtain a high-concentration impurity layer, but heat treatment is performed at a temperature of 1200 ° C. or less in order to prevent thermal deformation of the silicon wafer. In the first embodiment, the case where the etch stop layer is formed using the solid diffusion method will be described. However, other formation methods such as an ion implantation method and a coating method may be used.
[0025]
In step 102, as shown in FIG. 2A, a bonding film 320 is formed on the back plate substrate 310, and the bonding film 320 is formed by a method of applying powder silicon oxide or a method of depositing by a CVD method or the like. It is formed. The oxide film formed by powder silicon oxide, CVD method, or the like used here contains the same impurity as that doped for forming the etch stop layer 220 at a high concentration. The impurity concentration in the bonding film 320 is higher than the impurity concentration in the etch stop layer 220.
[0026]
In step 103, as shown in FIG. 2C, the vibration film substrate 210 and the back plate substrate 310 are bonded to each other through the etch stop layer 220 and the bonding film 320 to form the bonded substrate 400. The bonding can be performed using a bonding technique such as heat welding, anodic bonding, or direct bonding.
In step 104, the back substrate 310 side of the bonding substrate 400 is polished to a desired back plate thickness.
[0027]
In step 105, the bonding substrate 400 is heat-treated in an oxygen atmosphere, thereby forming oxide films 230 and 330 for an etching mask on both surfaces of the bonding substrate 400. The oxide films 230 and 330 for the etching mask are formed so as to have a thickness of about 4000 mm from the silicon etching depth of the vibration film substrate 210.
[0028]
The heat treatment for forming the oxide films 230 and 330 is performed at a temperature equal to or lower than the etch stop layer formation temperature in order to prevent re-diffusion of impurities in the etch stop layer 220. In the first embodiment, the heat treatment temperature for forming the oxide films 230 and 330 is set to 900 ° C. or higher. This heat treatment temperature is set to ensure an appropriate speed for the growth of the oxide films 230 and 330 and to increase the interface charge between the vibration plate substrate 210 and the bonding oxide film 320 in the low temperature treatment ( Reference: edited by Toru Hara et al., VLSI process data handbook, 1982, Science Forum, pages 142-143).
[0029]
In step 106, the oxide films 230 and 330 are processed using a photolithography technique to form a vibration film etching mask 231 and a back plate etching mask 331 as shown in FIG.
In step 107, the bonding substrate 400 is etched using the vibration film etching mask 231 and the back plate etching mask 331 to form the vibration film 201 and the back plate 301 as shown in FIG. At that time, etching can be performed using a predetermined alkaline etching solution such as TMAH (Tetramethyl ammonium hydroxide).
[0030]
In step 108, portions of the vibration film etching mask 231, the back plate etching mask 331, and the bonding film 320 other than the support portion 203 shown in FIG. 1 are etched to form parallel plate electrodes. With the above processing steps, a monolithic condenser microphone or pressure sensor is obtained.
[0031]
FIG. 3 is a diagram showing an impurity profile from the interface between the bonding oxide film and the etch stop layer toward the silicon substrate when the oxide film 6000 膜 is formed on the bonding substrate as described above. In the graph shown in FIG. 3, the vertical axis represents the logarithmic impurity concentration, and the horizontal axis represents the distance from the interface toward the silicon substrate. From FIG. 3, no significant decrease in impurity concentration was observed near the interface (0 μm position), and the impurity profile was almost the same as that before the thermal oxidation treatment.
[0032]
FIG. 4 is a profile obtained by measuring the surface displacement of the vibration film manufactured after forming the oxide film 6000 mm on the bonding substrate as described above using a laser displacement meter. In the graph shown in FIG. 4, the vertical axis represents the surface displacement of the diaphragm, and the horizontal axis represents the in-plane distance of the diaphragm. FIG. 4 shows that the profile in the diaphragm is almost flat and no buckling has occurred.
[0033]
As described above, the condenser microphone or pressure sensor according to the first embodiment applies or deposits a layer having an impurity concentration higher than the impurity concentration in the etch stop layer as a bonding film with the etch stop layer. Therefore, it is necessary to form an etch stop layer, which is indispensable for manufacturing a thin vibration film, and to oxidize the substrate at a high temperature within about 1200 ° C. even after the substrates are bonded. An annealing treatment can be performed.
[0034]
In addition, since annealing can be performed, the bonded substrates can be processed such as grinding, polishing, and cleaning.
In addition, since the substrate can be processed after bonding the substrates, it is possible to form the substrate and each layer formed thereon with a desired thickness, and to form a complicated etching mask having different film thicknesses.
[0035]
【The invention's effect】
As described above, according to the present invention, the capacitor microphone or pressure is formed by applying or depositing a layer having an impurity concentration higher than the impurity concentration in the etch stop layer as a bonding film with the etch stop layer. To realize a condenser microphone or pressure sensor that can eliminate restrictions on the manufacturing process of the sensor, and reduce the stray capacitance, etc., and improve the performance by improving the parallel plate electrode structure and the design flexibility of the mounted circuit. Can do.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a condenser microphone or a pressure sensor.
FIG. 2 is a diagram showing an outline of a manufacturing process of the condenser microphone or the pressure sensor according to the first embodiment of the present invention.
FIG. 3 is a diagram showing an impurity profile from the interface between the bonding oxide film and the etch stop layer toward the silicon substrate when an oxide film 6000Å is formed on the bonding substrate according to the first embodiment of the present invention. .
FIG. 4 is a view showing a profile obtained by measuring the surface displacement of a vibration film manufactured after forming an oxide film of 6000 mm on the bonding substrate according to the first embodiment of the present invention using a laser displacement meter; It is.
FIG. 5 is a diagram showing an outline of a manufacturing process of a conventional condenser microphone or pressure sensor.
[Explanation of symbols]
100 condenser microphone (pressure sensor)
201 Vibration membrane 202 Vibration membrane support (substrate)
210 Oscillating film substrate 220 Etch stop layer 230 Oscillating film substrate oxide film 231 Oscillating film etching mask 301 Back plate 302 Exhaust hole 303 Support part 310 Back plate substrate 320 Oxide film 330, 620 containing the same impurities as the etch stop layer Film 331 Back plate etching mask 400, 700 Bonded substrate 500 Substrate on which etch stop layer and oxide film are formed 600 Substrate on which oxide film is formed

Claims (4)

A vibration film substrate having an etch stop layer formed of silicon doped with boron on one surface, and a back plate substrate having a bonding film of a silicon oxide film formed on one surface, the etch stop layer and the Oite a bonded substrate which is bonded via the bonding film condenser microphones be formed by etching,
The bonding film includes boron as in the etch stop layer,
The concentration of boron contained in the bonding film, condenser microphones, characterized in that said at least a concentration of doped boron etch stop layer. A vibration film substrate having an etch stop layer formed of silicon doped with boron on one surface, and a back plate substrate having a bonding film of a silicon oxide film formed on one surface, the etch stop layer and the In a pressure sensor formed by etching a bonded substrate bonded via a bonding film,
The bonding film includes boron as in the etch stop layer,
The pressure sensor according to claim 1, wherein a concentration of boron contained in the bonding film is equal to or higher than a concentration of boron doped in the etch stop layer. 2. The condenser microphone according to claim 1, wherein boron diffusion for forming the etch stop layer is performed at 1200 [deg.] C. or lower, and subsequent heat treatment is performed at 900 [deg.] C. or higher and below the boron diffusion temperature. 3. The pressure sensor according to claim 2, wherein boron diffusion for forming the etch stop layer is performed at 1200 ° C. or lower, and the subsequent heat treatment is performed at 900 ° C. or higher and below the boron diffusion temperature.

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