JP3556576B2 - Manufacturing method of capacitive pressure sensor - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for manufacturing a capacitive pressure sensor.
[0002]
[Prior art]
In a capacitive pressure sensor, a fixed electrode formed on a base and a movable electrode formed on a diaphragm are arranged to face each other to form a capacitance, and a change in pressure is detected by a change in the capacitance. In addition, sapphire may be used for a diaphragm or a base because of its excellent corrosion resistance and the like.
[0003]
FIG. 3A is a plan view showing a general capacitive pressure sensor, and FIG. 3B is a sectional view taken along line AA ′. As shown in these figures, the pressure sensor 110 includes a base 101 provided with a fixed electrode 101a in a concave portion, a diaphragm 102 provided with a movable electrode 102a, a reference electrode 102b, and pads 102c, 102d, and 102e. It is composed of lead wires 103a and 103b connected to the pad and formed by solder, and the lead wire from the pad 102c is hidden. The reference electrode 102b is used to obtain a reference capacitance. The pad 102f is a dummy, and a lead wire made of solder is not taken out.
[0004]
In the pressure sensor 110 configured as described above, the diaphragm 102 bends in accordance with the pressure difference between the outside of the sensor and the capacitance chamber, and the capacitance changes due to the change in the distance between the movable electrode 102a and the fixed electrode 101a. Measured.
[0005]
Here, a conventional manufacturing process of the pressure sensor 110 will be described.
First, two sapphire wafers are prepared, a base is formed on one wafer, and a diaphragm is formed on the other wafer. That is, one sapphire wafer is machined, laser-processed or ultrasonic-processed to open through holes for forming the lead wires 103a, 103b and the like for each sensor chip, and then dry-etched for each sensor chip. After forming a concave portion for each sensor chip, the fixed electrode 101a is formed by vapor deposition or the like. As a result, a plurality of fixed electrodes are formed on the sapphire wafer.
[0006]
On the other hand, a plurality of movable electrodes 102a, reference electrodes 102b, and pads 102c to 102f are formed on another sapphire wafer by vapor deposition or the like for each sensor chip.
Thereafter, the two wafers are aligned so that each fixed electrode 101a and movable electrode 102a face each other, and then directly bonded under a predetermined heating atmosphere. After the direct bonding, the sapphire wafer on the base 101 side is turned to the upper surface, and then granular solid solder is placed in the through hole, melted by heating, and the lead wire 103a is melted by the molten solder flowing into the through hole. , 103b are formed and connected to the pads 2d, 2f. Finally, dicing the sapphire wafer completes the sensor chip.
[0007]
Through the above steps, a sapphire capacitive pressure sensor excellent in corrosion resistance can be easily mass-produced conventionally.
[0008]
[Problems to be solved by the invention]
However, what is called a micro pressure sensor tends to be made thinner in order to improve the measurement sensitivity (for example, about 50 μm), and has a problem that the diaphragm is easily bent at the time of manufacturing. Was. On the other hand, in order to increase the capacitance, the area of each electrode (the fixed electrode 101a and the movable electrode 102a) tends to be large and the interval between the electrodes tends to be narrow (several μm). Therefore, even if the diaphragm is slightly bent, the electrodes are short-circuited to each other, which causes a decrease in the yield of the sensor. If the deflection is slight, it is possible to correct the measurement result at the signal processing stage.However, in the state where the deflection occurs, the point of zero pressure has already been shifted, so when the diaphragm receives pressure, There is a problem in that there is no allowance for bending and the range of measurable pressure is narrowed. Further, in such a sensor, the point at which the pressure is zero shifts due to the aging of the degree of bending, and the quality deteriorates.
[0009]
An object of the present invention is to solve such a problem, and an object of the present invention is to provide a method of manufacturing a capacitive pressure sensor that can easily suppress deflection of a diaphragm generated during manufacturing.
[0010]
[Means for Solving the Problems]
In order to achieve such an object, a method for manufacturing a capacitive pressure sensor according to the present invention includes a pressure-receiving diaphragm having a movable electrode formed thereon, a fixed electrode formed and a base joined to the diaphragm. Wherein the temperature of the first wafer on which the plurality of movable electrodes are formed is higher than the temperature of the second wafer on which the plurality of fixed electrodes are formed, and then the first and second The two wafers are joined, and these joined wafers are cut.
[0011]
Further, the present invention includes the following configuration as another aspect. That is, a first reference point is provided on the first wafer, a plurality of movable electrodes are laid out on the first wafer based on the first reference point, and a second reference point is provided on the second wafer. And laying out a plurality of fixed electrodes on a second wafer based on the second reference point, wherein the layout includes a movable electrode on the first wafer that has thermally expanded, and a layout on the second wafer. This is performed so as to prevent displacement during bonding with the fixed electrode. The wafer is made of sapphire, silicon, glass or diamond. Further, the temperature difference between the first and second wafers is set to 50 ° C. or more and 150 ° C. or less.
[0012]
Therefore, with this configuration, the present invention can prevent the diaphragm that has been thermally expanded from contracting after joining, so that the diaphragm is prevented from bending. In addition, by laying out the movable electrode and the fixed electrode in consideration of thermal expansion, it is possible to prevent a positional shift occurring at the time of bonding.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is an explanatory diagram for explaining a method of manufacturing a capacitive pressure sensor according to one embodiment of the present invention. As shown in the figure, the manufacturing method according to the present embodiment includes a wafer holding mechanism 3 having a heater 3a, a temperature control means 5 for controlling a heat generation temperature of the heater 3a, and a wafer holding mechanism having a heater 4a. 4 and temperature control means 6 for controlling the temperature of heat generated by the heater 4a. Each of the wafer holding mechanisms 3 and 4 includes an electrostatic chuck, a vacuum chuck, and the like, and can temporarily fix and hold the placed wafers 1 and 2 and, at the same time, moves the placed wafers and attaches them to each other. Can be
[0014]
The wafer holding mechanisms 3 and 4 include heaters 3a and 4a and temperature sensors 3b and 4b, and can control the temperature of the wafers 1 and 2 to a desired temperature by causing the heaters 3a and 4a to generate heat. That is, the temperature controllers 5 and 6 increase the temperature of the wafers 3a and 4a by energizing the heaters 3a and 4a, measure the temperatures of the wafers 1 and 2 using the temperature sensors 3b and 4b, and obtain the desired temperature. Then, the power supply to the heaters 3a and 4a is cut off. By this repetition, the temperature control means 5 and 6 control the temperature of the wafers 1 and 2 to be a temperature desired by the user.
[0015]
Here, the manufacturing procedure according to the present embodiment will be described.
First, as shown in FIG. 1A, the sapphire wafer 1 on the base side is placed on the wafer holding mechanism 3 and the sapphire wafer 2 on the diaphragm side is placed on the wafer holding mechanism 4. Then, the movable electrode 2a and the fixed electrode 1a formed in advance on both wafers by the conventional method are opposed to each other and then directly joined. Direct bonding is performed only by overlapping mirror-polished wafers 1 and 2 by an intermolecular force, and can be firmly bonded by heating.
[0016]
In the case of direct bonding, the heat generation of the heaters 3a and 4a is adjusted by the temperature control means 5 and 6, and the temperature of the wafer 2 on the diaphragm side is higher than the temperature of the wafer 1 on the base side (however, the temperature difference is 50 ° C.). (150 ° C. or less). The reason why the temperature difference is set to 150 ° C. or less is to prevent the bonded wafer from being broken by heat shock, and the temperature difference is set to 50 ° C. or more by sufficiently expanding the wafer 2 on the diaphragm side. That's why. Alternatively, the temperature difference between the two wafers may be increased to several hundred degrees, and then the temperature difference between the two wafers may be controlled as described above. Alternatively, the temperature of the wafer 2 may be kept at room temperature without heating the wafer 1. May be controlled.
[0017]
As a result, the wafer 2 is directly bonded to the wafer 1 in a thermally expanded state, and after being removed from the wafer holding mechanism, the expanded wafer 2 contracts. As shown in FIG. Is bonded to the wafer 1 while maintaining a slight tension. Therefore, it is possible to prevent the wafer 2 from being bent. Thereafter, if the directly bonded wafer is diced, the pressure sensor 10 is completed.
[0018]
Next, the layout of the movable electrode and the fixed electrode will be described. In the present invention, since the temperature of the wafer 2 on the diaphragm side is higher than that of the wafer 1 on the base side, the wafer 2 slightly expands more thermally than the wafer 1. Therefore, when a plurality of electrodes are laid out on each wafer, if the electrodes are laid out at the same interval, the positions of the electrodes may be shifted when they are bonded. Therefore, such a problem can be solved by laying out the electrodes in consideration of thermal expansion.
[0019]
FIG. 2A is a plan view showing a wafer on which a plurality of movable electrodes and reference electrodes are formed, and FIG. 2B is a plan view showing a wafer on which a plurality of recesses and fixed electrodes are formed. The wafer 1 has a plurality of fixed electrodes 1a formed on the front side of the figure, and the wafer 2 has a plurality of movable electrodes 2a formed on the back side of the figure.
[0020]
First, the movable electrodes 2a are formed at equal intervals on the wafer 2 on the diaphragm side. On the other hand, if the wafers 1 on the base side are formed at equal intervals, when the wafers 2 are directly bonded, the fixed electrodes 1a and the movable electrodes 2a of the expanded wafers 2 are displaced. In this case, the layout of the fixed electrode 1a is shifted in advance. That is, the layout of the fixed electrode 1a is adjusted according to the distance from the reference point in the drawing and the coefficient of thermal expansion of the wafer 2, and the positional deviation increases as the distance from the reference point increases. Increase the electrode spacing (horizontal and vertical). When this relationship is expressed by an equation, x1 <x2 <x3 <x4 <x5 <x6 <x7 <x8, and y8 <y7 <y6 <y5 <y4 <y3 <y2 <y1.
[0021]
After that, the wafers 1 and 2 are directly bonded after the reference points in the drawing and other alignment marks (not shown) are made to coincide with each other, and the directly bonded wafers are diced to complete a sensor chip. Note that, instead of increasing the distance between the fixed electrodes laid out on the wafer 1 on the base side as described above, the distance between the movable electrodes 2a laid out on the wafer 2 on the diaphragm side may obviously be reduced. It is. Further, the position at which the reference point is provided is not limited to the position shown in FIG. 2. For example, if the reference point is provided at the center of the wafer, the amount of displacement during layout can be minimized. Further, in the above description, the size of each electrode is not changed without changing the position of the electrode, but the size of each electrode may be changed in consideration of thermal expansion.
[0022]
The case where sapphire is used as the material of the diaphragm and the base has been described above, but the present invention is not limited to this. For example, a single crystal material such as silicon, glass, or diamond may be used. Further, the reference electrode is not an essential component, and may be added as needed. Therefore, the present invention includes a configuration using only the movable electrode and the fixed electrode.
[0023]
【The invention's effect】
As described above, the present invention sets the temperature of the first wafer for forming the pressure receiving diaphragm higher than the temperature of the second wafer for forming the base, In addition, since the second wafer is bonded, the diaphragm that has been thermally expanded after the bonding contracts, so that it is possible to prevent the diaphragm from being bent. In addition, by laying out the movable electrode and the fixed electrode in consideration of thermal expansion, it is possible to prevent a positional shift occurring at the time of bonding.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram for explaining a method of manufacturing a capacitive pressure sensor according to one embodiment of the present invention.
2A is a plan view showing a wafer on which a plurality of movable electrodes and reference electrodes are formed (each electrode is formed on the back surface of the wafer); FIG. FIG. 3 is a plan view showing a wafer (each electrode is formed on the surface of the wafer).
3A is a plan view showing a general capacitive pressure sensor, and FIG. 3B is a cross-sectional view taken along line AA ′.
FIG. 4 is a cross-sectional view showing a pressure sensor (in a state where no pressure is applied) manufactured by a conventional manufacturing method.
[Explanation of symbols]
1, 2, wafer; 3, 4, wafer holding mechanism, 3a, 4a heater, 3b, 4b temperature sensor, 5, 6 temperature control means, 10 pressure sensor.

Claims (4)

In a capacitive pressure sensor having a pressure-receiving diaphragm on which a movable electrode is formed, and a base on which a fixed electrode is formed and joined to the diaphragm,
After the temperature of the first wafer on which the plurality of movable electrodes are formed is higher than the temperature of the second wafer on which the plurality of fixed electrodes are formed, the first and second wafers are joined,
A method for manufacturing a capacitive pressure sensor, characterized by cutting these bonded wafers. In claim 1,
Providing a first reference point on the first wafer, laying out a plurality of movable electrodes on the first wafer based on the first reference point,
Providing a second reference point on the second wafer, laying out a plurality of fixed electrodes on the second wafer based on the second reference point,
Wherein the layout is performed so as to prevent a displacement of the thermally expanded movable electrode on the first wafer and a fixed electrode on the second wafer during bonding. Manufacturing method of sensor. In claim 1,
The method for manufacturing a capacitive pressure sensor, wherein the wafer is made of sapphire, silicon, glass, or diamond. In claim 1,
A method for manufacturing a capacitive pressure sensor, wherein a temperature difference between the first and second wafers is set to 50 ° C. or more and 150 ° C. or less.

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