JP4186669B2 - Pressure sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor pressure sensor that detects a pressure by forming a plurality of strain gauges in a bridge shape on a diaphragm portion of a semiconductor substrate and outputting the pressure received by the diaphragm portion as an electrical signal.
[0002]
[Prior art]
Conventionally, this type of semiconductor pressure sensor includes a semiconductor substrate having, for example, a thin diaphragm portion and a thick support portion formed around the outer periphery of the diaphragm portion, and the diaphragm portion includes a piezoresistor. A strain gauge consisting of elements is formed, strain is generated in the strain gauge by the pressure received by the diaphragm section, and the change in resistance value due to the piezoresistance effect of the strain gauge is taken out as a voltage change in the bridge circuit to detect the pressure value There is known a sensor provided with a sensor element (see Patent Document 1).
[0003]
In such a pressure sensor, the sensor element and a glass pedestal (glass substrate) provided with a pressure introduction hole for transmitting pressure to the diaphragm are joined by an anodic bonding method, and the glass pedestal is made of metal. A structure in which the base plate is fixed via a low-melting glass is common. Further, in order to improve the bonding strength between the sensor element and the glass pedestal by anodic bonding, an aluminum (Al) layer is formed on the bonding surface of the sensor element with the glass pedestal, One that increases the bonding strength has been proposed (see Patent Document 2).
[0004]
[Patent Document 1]
Japanese Patent Laid-Open No. 10-38726 [Patent Document 2]
JP 2001-284603 A
[Problems to be solved by the invention]
Such a pressure sensor is used for high-pressure measurement by forming the aluminum layer on the support portion of the sensor element and obtaining a strong bond with the glass pedestal. Since the step of forming the aluminum layer is required, the manufacturing process is complicated, and the manufacturing cost of the pressure sensor is increased.
[0006]
The present invention pays attention to the above-mentioned problems, and provides a pressure sensor capable of measuring high pressure and simplifying the manufacturing process.
[0007]
[Means for Solving the Problems]
In order to solve the above-mentioned problem, the present invention provides a semiconductor substrate in which an opening portion and a thin diaphragm portion are formed along with an etching process from the (100) plane, as in the pressure sensor according to claim 1. A pressure sensor disposed on a glass substrate having an introduction hole and bonding the semiconductor substrate and the glass substrate by an anodic bonding method, wherein the width of the bonding surface of the semiconductor substrate to the glass substrate is A When the length from the approximate center of the diaphragm portion to the end of the opening portion is B, the ratio A / B of A and B is 0.2 ≦ A / B ≦ 0.5. The curved surface portion is formed on the inner wall in the vicinity of the bonding surface of the semiconductor substrate .
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
[0010]
The structure of the pressure sensor will be described with reference to FIGS. Reference numeral 1 denotes an n-type semiconductor substrate made of single crystal silicon obtained by cutting a silicon wafer (not shown) having an axial orientation <100> into a square having a side of 2.2 mm. The semiconductor substrate 1 is formed from the (100) plane. The diaphragm portion 2 is formed thin by the etching process, and the support portion 3 is formed integrally with the periphery of the diaphragm portion 2. In the case of this embodiment, the thickness of the diaphragm portion 2 is set to 60 to 100 μm, and the size of the diaphragm portion 2 is set to a square having a side of 1.3 mm. Four strain gauges 4 (4a, 4b, 4c, 4d) made of piezoresistive elements are provided on the support part 3 side in the diaphragm part 2.
[0011]
These strain gauges 4a to 4d are electrically connected by a plurality of lead portions 5 made of a low resistance body, and a bridge circuit 6 is constituted by each lead portion 5 and the strain gauges 4a to 4d. Reference numeral 7 denotes a thermal oxide film made of silicon dioxide (SiO ↓ 2) formed on the surface of the semiconductor substrate 1 by a thermal oxidation method. Reference numeral 8 denotes a thermal oxide film 7 due to external contamination such as moisture or sodium (Na). This is a silicon nitride film for protecting the film.
[0012]
In the thermal oxide film 7 and the silicon nitride film 8, contact holes 10 are formed in portions corresponding to the joint portions 9 (9a, 9b, 9c, 9d) between the lead portions 5, and this contact. An electrode portion 11 made of a conductive material such as aluminum is formed at a location where the hole 10 is formed, and the bonding pad portion 12 is configured by extending the electrode portion 11 outward.
[0013]
As shown in FIG. 4, the semiconductor pressure sensor having such a configuration is configured by applying a power supply voltage Vcc via a bonding wire 13 connected by wire bonding to a bonding pad 12 serving as the bonding portions 9a and 9b of the bridge circuit 6. The strain caused by the pressure difference between the front and back surfaces of the diaphragm portion 2 is taken out as an output voltage Vo corresponding to the change of each strain gauge 4 from the bonding pad 12 serving as the joint portions 9c and 9d of the bridge circuit 6 through the bonding wire 13. Is.
[0014]
On the other hand, on the back surface side of the semiconductor substrate 1, a glass pedestal 20 is provided that is bonded to the bonding surface 3 a of the support portion 3 in the semiconductor substrate 1 by anodic bonding. The glass pedestal 20 is made of, for example, aluminoborosilicate glass, and has a square shape with a side length of 2.2 mm substantially the same as the semiconductor substrate 1. In the semiconductor substrate 1, a pressure introducing hole 20 a is formed in a substantially center corresponding to the diaphragm portion 2 of the semiconductor substrate 1 by a cutting method, a sandblast method, an ultrasonic method, or the like.
[0015]
Next, the structure of the pressure sensor will be described in more detail with reference to FIGS.
[0016]
The pressure sensor is an n-type semiconductor substrate 1 with a side length L1 of 2.2 mm and a thickness W1 of 150 to 220 μm, and alkali etching such as potassium hydroxide (KOH) so as to leave the support 3. A thin diaphragm portion 2 having a thickness W2 of 80 to 120 μm and a length L2 of one side of the diaphragm portion 2 of 1.2 to 1.3 mm is formed by anisotropic etching that is immersed in a liquid for a predetermined time. In this case, the semiconductor substrate 1 is approximately the center P in the width direction of the semiconductor substrate 1 and the length L2 of one side is 1.2 to 1.3 mm with respect to the approximately center P in the width direction of the diaphragm portion 2. By setting the width L3 of the opening to 1.33 mm and performing anisotropic etching so that the diaphragm portion 2 is obtained, the width (length in the width direction) of the joint surface 3a with the glass pedestal 20 of the support portion 3 is obtained. S) L4 (A) can be set to 0.44 mm (3 decimal places are rounded off) (FIG. 5A). The thickness W1 of the semiconductor substrate 1 is desirably 135 to 215 μm in consideration of the bonding strength with the glass pedestal 20 and the variation in the output characteristics of the pressure sensor.
[0017]
The semiconductor substrate 1 includes a corner portion 15 (see FIG. 5A) formed on the etching surface side of the semiconductor substrate 1 corresponding to the boundary portion 14 between the diaphragm portion 2 and the support portion 3, and a glass pedestal of the support portion 3. The process of removing the inner wall 16 in the vicinity of the joint surface 3a with the 20 is performed. In the semiconductor substrate 1, the corner portion 15 is rounded to form the curved surface portion 17 by isotropic etching using a plasma etching method using a mixed gas of sulfur hexafluoride and hydrogen, and the bonding surface 3 a of the support portion 3 is formed. A curved surface portion 18 is formed on the adjacent inner wall 16 (see FIGS. 2, 3 and 5B). In addition, the thickness W2 of the diaphragm part 2 after the above-mentioned isotropic etching is 60 to 100 μm.
[0018]
The semiconductor substrate 1 is put into an oxidation furnace, and a thermal oxide film 7 is formed on the front and back surfaces.
[0019]
Although not shown in FIGS. 5A and 5B, during the anisotropic or isotropic etching, a thermal oxide film 7 and a silicon nitride film 8 are formed on the surface of the semiconductor substrate 1 and the back surface of the support portion 3. The thermal oxide film 7 and the silicon nitride film 8 are removed after the isotropic etching.
[0020]
In the semiconductor substrate 1, the thermal oxide film 7 on the surface corresponding to the formation positions of the strain gauges 4 a to 4 d is removed in the diaphragm portion 2, and the inside of the diaphragm portion 2 is formed by thermal diffusion using a p-type semiconductor material such as boron. The strain gauges 4a to 4d are formed at the predetermined positions, and the thermal oxide film 7 is formed again at the portions where the strain gauges 4a to 4d are formed (see FIG. 5C). Since the semiconductor substrate 1 has the strain gauges 4a to 4d in the shape of the bridge circuit 6 shown in FIGS. 1 and 4, for example, the thermal oxide film 7 is removed in a predetermined pattern from both ends of the strain gauges 4a to 4d. A bridge circuit 6 is obtained by forming each lead portion 5 by thermal diffusion using a p-type semiconductor material such as boron having a higher concentration than the strain gauges 4a to 4d.
[0021]
Each joint portion 9a to 9d formed by each lead portion 5 of the semiconductor substrate 1 is formed in a joint portion shape so that the contact hole 10, the electrode portion 11, and the bonding pad 12 can be formed. Then, in the semiconductor substrate 1 on which the bridge circuit 6 is formed, a silicon nitride film 8 is formed on the thermal oxide film 7 on the surface of the semiconductor substrate 1 (see FIG. 5D).
[0022]
In the semiconductor substrate 1, in the diaphragm portion 2, the silicon nitride film 8 corresponding to the formation positions of the joint portions 9 a to 9 d is removed by a plasma etching method or the like, and the portion of the thermal oxide film from which the silicon nitride film 8 is removed 7 is removed using a hydrofluoric acid mixed solution or the like. Accordingly, in the semiconductor substrate 1, contact holes 10 reaching the junctions 9a to 9d from the silicon nitride film 8 through the thermal oxide film 7 are formed (see FIG. 5E). In this case, the thermal oxide film 7 formed on the back side of the semiconductor substrate 1 is removed by removing the thermal oxide film 7.
[0023]
In the semiconductor substrate 1, the electrode part 11 and the bonding pad 12 are formed at a position where the contact hole 10 is formed by means of a conductive member made of aluminum or the like by vapor deposition or sputtering (FIG. 5F).
[0024]
Then, the semiconductor substrate 1 is disposed on the glass pedestal 20, the semiconductor substrate 1 is used as an anode, the glass pedestal 20 is used as a cathode, and the semiconductor substrate 1 is placed on the glass pedestal 20 by an anodic bonding method in which a predetermined DC voltage is applied. The pressure sensor is completed by fixing.
[0025]
The bonding pad 12 is electrically connected to an external circuit (not shown) by a bonding wire 13 as shown in FIG.
[0026]
Such a pressure sensor has high detection accuracy and easy adjustment, so that the linearity in the temperature characteristics of the full-scale voltage (output voltage) of the pressure sensor is best, as shown in FIG. The distance between the approximate center Q of the gauge 4 (4a to 4d) and the approximate center P of the diaphragm part 2 is X, and the distance between the boundary part 14 between the diaphragm part 2 and the support part 3 and the approximate center P of the diaphragm part 2 is R. It is desirable to dispose the strain gauge 4 on the diaphragm portion 2 so that the ratio X / R of X and R is 0.93 to 0.98. This is proposed in Japanese Patent Application No. 2002-285604 by the applicant of the present application.
[0027]
FIG. 7 shows a ratio L4 / L5 between the width L4 of the joint surface 3a of the support portion 3 with the glass pedestal 20 and the length L5 (B) from the approximate center P of the diaphragm portion 2 to the end of the opening, It is a figure which shows the relationship between the joining strength of the semiconductor substrate 1 and the glass pedestal 20, and the hole diameter of the pressure introduction hole 20a of the glass pedestal 20 is 0.8 mm, and the pressure from the pressure introduction hole 20a is the back side of the diaphragm portion The strength when the pressure is applied in the direction in which the semiconductor substrate 1 is peeled off from the glass pedestal 20 is shown. Assuming that the semiconductor substrate 1 having a thickness W1 of 150 μm is used, it is assumed that the pressure sensor has a ratio L4 / L5 of “ 0.5 ” as shown in FIG. Since the fracture strength is substantially constant, it is desirable to use a material having a ratio L4 / L5 in the vicinity. However, when the dimension of the width L4 of the joint surface 3a is increased and the ratio L4 / L5 is brought close to “ 0.5 ”, will be the semiconductor substrate 1 is enlarged, reduced the number of take of the semiconductor substrate 1 from the silicon wafer, leading to up significant production cost.
[0028]
Therefore, if the length L2 of one side of the diaphragm part 2 is 1.2 to 1.3 mm and the thickness W2 of the diaphragm part 2 is 60 to 100 μm without changing the size of the semiconductor substrate 1, each strain gauge 4 ( 4a to 4d) when the distance between the approximate center Q and the approximate center P of the diaphragm part 2 is X, and the distance between the boundary part 14 between the diaphragm part 2 and the support part 3 and the approximate center P of the diaphragm part 2 is R. In order to set the ratio X / R between X and R of 0.93 to 0.98, the width L3 of the opening is set to 1.33 mm and anisotropic etching is performed, so that the glass pedestal of the support 3 The ratio L4 / L5 of the width L4 of the joint surface 3a to 20 and the length L5 (B) from the approximate center P of the diaphragm portion 2 to the end of the opening is in the range of 0.2 to 0.5. It becomes possible. The length L2 of one side of the diaphragm 2 is a safety factor indicating the relationship between the rated pressure of the pressure sensor and the designed breaking strength of the pressure sensor, the linearity of the full-scale voltage of the output voltage of the pressure sensor, etc. Is set to 1.2 to 1.3 mm.
[0029]
It is apparent from FIG. 7 that the pressure sensor using the ratio L4 / L5 of 0.2 to 0.5 can withstand a high pressure of 2000 kpa or more.
[0030]
Such a pressure sensor includes a semiconductor substrate 1 having an opening and a thin diaphragm portion 2 formed in accordance with an etching process from the (100) plane on a glass pedestal 20 having a pressure introduction hole 20a. The surface 3a and the glass pedestal 20 are joined by an anodic bonding method. The width of the joining surface 3a of the semiconductor substrate 1 with the glass pedestal 20 is L4, from the approximate center P of the diaphragm 2 to the end of the opening. When L5 is L5, the ratio L4 / L5 between L4 and L5 is set to satisfy 0.2 ≦ L4 / L5 ≦ 0.5. Therefore, since a pressure sensor that can withstand high pressure measurement can be obtained only by setting the ratio L4 / L5 without requiring a dedicated process for improving the bonding strength as in the prior art, the manufacturing process is simplified. In addition, the manufacturing cost of the pressure sensor can be reduced with the simplification of the manufacturing process.
[0031]
The pressure sensor forms a curved surface portion 18 on the inner wall 16 in the vicinity of the bonding surface 3 a of the semiconductor substrate 1, and in the peeling direction of the semiconductor substrate 1 due to the pressure introduced from the pressure introduction hole 20 a of the glass pedestal 20. The acting stress, that is, the stress acting on the glass pedestal 20 and the joining surface 3a can be dispersed by the curved surface portion 18, and the joining strength can be further improved.
[0032]
【The invention's effect】
According to the present invention, a semiconductor substrate in which an opening and a thin diaphragm portion are formed in accordance with an etching process from the (100) plane is disposed on a glass substrate having a pressure introducing hole, and the semiconductor substrate and the glass substrate With respect to the pressure sensor formed by joining together by the anodic bonding method, it becomes possible to obtain a pressure sensor capable of measuring high pressure and simplifying the manufacturing process.
[Brief description of the drawings]
FIG. 1 is a plan view showing a pressure sensor according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view taken along line AA in FIG.
3 is a cross-sectional view taken along the line BB in FIG.
FIG. 4 is a diagram showing a circuit configuration of the pressure sensor.
FIG. 5 is a view showing a manufacturing process of the pressure sensor.
FIG. 6 is a view for explaining output characteristics of the pressure sensor.
FIG. 7 is a view for explaining the bonding strength of the pressure sensor.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2 Diaphragm part 3 Support part 3a Joint surface 16 Inner wall 18 Curved surface part 20 Glass base (glass substrate)
20a Pressure introduction hole

Claims (1)

A semiconductor substrate having an opening and a thin diaphragm portion formed by etching from the (100) plane is disposed on a glass substrate having a pressure introducing hole, and the semiconductor substrate and the glass substrate are anodically connected. A pressure sensor joined by law,
A / B ratio A / B where A is the width of the bonding surface of the semiconductor substrate to the glass substrate and B is the length from the approximate center of the diaphragm portion to the end of the opening. But,
0.2 ≦ A / B ≦ 0.5
The pressure sensor is characterized in that a curved surface portion is formed on an inner wall in the vicinity of the bonding surface of the semiconductor substrate .

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