FR2780504A1 - PRESSURE SENSOR AND MANUFACTURING METHOD THEREOF - Google Patents

Abstract

A pressure sensor comprising a silicon chip (4) fixed to the surface of a metal diaphragm (2a) via a layer of glass (5) and the sensor output of which is not influenced by a bubble formed inside the glass layer. After the silicon chip (4) is fixed, the bubble formed in the glass layer is inspected to determine its size. If the bubble is within predetermined acceptable manufacturing tolerances, the configuration is assembled with a housing (1).

Description

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  The present invention relates generally to pressure sensors, and more particularly to a method of

  manufacture of a semiconductor pressure sensor.

  Japanese patent publication No. Hei 7-11461 describes a pressure sensor comprising a detection body in which a silicon chip is bonded to the surface of a metal pressure receiving diaphragm via a layer of glass and is then assembled in a housing. More particularly, as indicated in FIG. 4a, the silicon chip 4 comprising diffused gauges 3a to 3d is bonded to the surface of the diaphragm 2a of the metal detection body 2 via a layer of glass 5 so that the deformation of the diaphragm 2a caused by the pressure is transmitted to the silicon chip 4 via the glass layer 5. This transmitted pressure brings the values of

  resistance of the diffused gauges 3 to vary.

  The diffused gauges 3 are connected in order to form a bridge circuit from which an electrical signal corresponding to the pressure is supplied at the output. The pressure sensor designed as described has a metal diaphragm, so that its reliability is high even under conditions of high pressure. As a result, the sensor can be used as a high pressure sensor such as a

fuel pressure.

  However, in the manufacture of the pressure sensor described above, while the glass paste is printed on the surface of the diaphragm 2a, the silicon chip 4 is mounted on it and the two components are sintered, a bubble such as bubble 6 in Figure 4b can be formed, and can bite into the glass layer 5 when the diaphragm 2a, for example, is not completely flat. The bubble 6 generated inside the glass layer 5 can be caused by a drop in the temperature characteristic of the sensor, the inability of the glass layer 5 to transmit the deformation of the diaphragm 2a correctly to the chip. of silicon 4, or a dilation / contraction of the bubble 6 due to

a variation in temperature.

  Therefore, it is an object of the present invention to overcome the above mentioned limitations by providing an improved pressure sensor as well as a manufacturing method.

of it. -

  According to a first embodiment of the present invention, a pressure sensor is manufactured by bonding a silicon chip to a surface of a metal diaphragm inside a detection body via a layer of glass. Next, the glass layer is inspected to determine whether a bubble is present in it and, if so, its size, after the chip is glued to the

  diaphragm. A detection body which passes the inspection below

  above is determined to be good, and is assembled in the housing. As a result, it is possible to manufacture a pressure sensor whose sensor output is not influenced by the

  presence of a bubble in the glass layer.

  According to a second embodiment of the invention, a bubble in the glass layer under the diffused gauges of the sensor is inspected during the above glass layer inspection. As the influence of the bubble appears directly on the diffused gauge when a bubble exists in the glass layer under the diffused gauge, the inspection can be carried out

  effectively by inspecting this part.

  When the diffused gauges include central gauges and lateral gauges, it is preferable to inspect the part under the central gauges because the influence of the bubble in the layer of glass under the central gauge is particularly important. Likewise, when the size of the bubble is less than 200 µm, the influence of the bubble on the accuracy of the sensor will be minimal, and thus a layer of glass having a bubble with a size of less than 200 µm is

considered acceptable.

  Note that the bubble inspection described above can be conducted using an infrared microscope or alternatively

  by means of ultrasonic inspection.

  FIG. 1 is a sectional view showing the structure of a pressure sensor according to a first embodiment of the invention,

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  Figure 2 is an enlarged partial perspective view showing a top portion of a detection body of Figure 1, Figure 3 is a flow diagram showing a method of manufacturing the pressure sensor shown in Figure 1, Figures 4A - 4B are explanatory diagrams concerning the operation of a pressure sensor using a metal diaphragm, FIG. 5 is a diagram making it possible to explain various bubble generation locations, FIG. 6 is a table representing the characteristics of sensitivity and of sensor temperature at the bubble generation locations indicated in FIG. 5 in comparison with the case where no bubble is generated, FIG. 7 is a graph representing the relation of the sensitivity of the sensor with the dimension of the bubble when there is a bubble at bubble location A, and Figure 8 is a graph representing the relationship of the sensitivity characteristics. lity in temperature of the sensor with the bubble size when there is a bubble at the bubble location A. Figure 1 is a sectional view showing the structure of a pressure sensor according to a first embodiment of the present invention. The pressure sensor is used to measure fluid pressures on the order of MPa, such as fluid pressures in systems

  fuel injection and vehicle brakes.

  As shown in Figure 1, the sensor includes a housing 1 constructed from a metal with good corrosion resistance and which is capable of being welded (for example, grade SUS 430). The housing has a screw la which is screwed and fixed to a part to be detected, by

example, a fuel line.

  A detection body 2 is made from a metal having a low coefficient of thermal expansion, such as covar, whose coefficient of linear thermal expansion is close to that of silicon. The detection body has a pressure introduction orifice 2b and a thin diaphragm 2a is created at the end of it. The body

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  2 is pressed into an interior section

  hollow housing 1 and is assembled in housing 1.

  A silicon sensor chip 4 is stuck on the surface

  upper part of a diaphragm 2a of the detection body 2, that is to say

  say on a face on the opposite side with respect to the pressure introduction side, via a layer of glass 5 made of a glass with low melting point. A signal processing circuit board 7 for processing electrical signals from the silicon chip 4 is disposed around the tip portion of the sensing body 2, as shown in Figure 1, and includes a laminated ceramic substrate 7a, a circuit chip 7b and a rod 7c. The silicon chip 4 is electrically connected to the circuit board

  signal processing 7 by wires 8.

  The rod 7c in the signal processing circuit board 7 is connected to a connector terminal 10a of a set of terminals 10 by means, for example, of electrical welding, and the set of terminals 10 and a housing connector 11 are crimped with a crimping section lb of the housing 1 by

  via an O-ring 12.

  The upper surface of the detection body 2 and the laminated ceramic substrate 7 are coated with a material of

  coating 9 such as a silicon gel.

  FIG. 2 is a perspective view in enlarged section showing the end part of the detection body 2. The silicon chip 4 on which diffused gauges 3 are formed is bonded to the diaphragm 2a of the detection body 2 via of the glass layer 5. The silicon chip 4 is constructed using a silicon substrate

  monocrystalline type N whose plane orientation is (110).

  Although this is not clearly indicated in FIG. 2, the diffused gauges 3 include central gauges 3a and 3b and lateral gauges 3c and 3d similar to those shown in FIG. 5. The diffused gauges 3a to 3d are connected by aluminum wires (not shown) to build a bridge circuit. In addition, the diffused gauges are electrically connected to the signal processing circuit board 7 by the wire 8, and thus provide at the output electrical signals, corresponding to the displacement of the diaphragm 2a, to the

  signal processing circuit board 7.

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  Next, with reference to Figure 3, a method of manufacturing the pressure sensor described above will be explained. After the detection body 2 in which the pressure introduction orifice 2b and the diaphragm 2a have been formed is prepared, at 100 and 110, the surface of the body is then treated by means of cleaning treatments using acid and decarbonation, after which, in 120, an oxidation treatment is carried out. These treatments are identical to

  those described in Japanese reference JP-B-7-11461.

  Then, in 130, glass paste is printed on the surface of the diaphragm 2a and, in 140, is calcined at around 400 C in order to form the glass layer 5. Then, in 150, the calcined glass layer 5 is mounted on silicon chip 4

  and is sintered at around 500 C in order to stick the chip 4.

  Then, at 160, the glass layer 5 is inspected to determine if bubbles are present therein. As infrared rays are transmitted more or less through silicon, the bubble can be observed by observing the glass layer 5 from the silicon chip 4 using an infrared microscope. It is determined whether or not there is a bubble which has a dimension greater than 200 μm in the glass layer 5 under the central gauges 3a, 3b, in the present embodiment. When a bubble of 200 µm or more is found, the detection body 2 is not routed to the next step. Even if the detection body 2 has a bubble, the detection body 2 is conveyed to the next step when the dimension thereof is less than pm. Then, in 170, the detection body 2, having been evaluated and approved in the above inspection step, is assembled in the housing 1, and the pressure sensor indicated in FIG. 1 is completed by making the connection by wire and others

assembly steps.

  It should be appreciated that, while the bubble inspection has been conducted through the infrared microscope in the embodiment described above, the inspection may also be performed using ultrasonic inspection. Ultrasonic inspection is performed by placing a sample in water and applying ultrasonic waves to observe the internal structure of the sample based on its reflection wave characteristics. Furthermore, although the inspection of the bubble in the glass layer 5 under the central gauges 3a and 3b has been presented in the embodiment described above, the inspection can be carried out in the glass layer 5 under the side gauges 3c, 3d in the same way. In addition, when a silicon chip with in-plane orientation (100) is used as the silicon chip 4, the configuration of the central and side gauges disappears, so that bubble inspection in the layer of glass under each gauge

is conducted in this case.

  Figure 5 is a diagram showing a top plan view of a silicon chip 4 whose plane orientation is (110). Diffused gauges 3 include central gauges 3a, 3b arranged in the center of a displacement zone which is displaced by pressure (in the zone where a diaphragm 2a exists below) and lateral gauges 3c, 3d arranged at the periphery of it. Among the bubbles 6 generated in a glass layer 5, a bubble at the location below the central gauge is indicated by A, a bubble at the location on the side thereof by B, a bubble at the the location below the lateral gauge by C and a bubble at the location on the side thereof by D. FIG. 6 is a table indicating the sensitivities of the sensor, and the temperature characteristics of the latter, at bubble generation locations A to D, when the bubble size is 500 µm, compared to the case where no bubble

is not generated.

  As shown in Figure 6, the sensitivity and the temperature characteristic are influenced by the existence of the bubble 6. The influence of the bubble is very important when the bubble 6 exists at the location of bubble A under the central gauge . While the above characteristics are influenced more or less also when a bubble exists at the bubble location C under the side gauge, the influence is not as great in comparison to the case where the bubble exists at the bubble location A, because the generation of stress is low at the locations where the side gauges are created compared to the locations where the gauges

plants are created.

  It should be realized that the sensitivity (Vs / 20) of the sensor described above is found from a sensor output voltage Vs when a pressure of 20 MPa is applied to the diaphragm 2a, and that the characteristic in sensitivity temperature is found from a sensitivity S25 at 25 C

  and a sensitivity S120 'at 120 C by (S120 - S25) / S25 / (120 -

  ). Figures 7 and 8 show experimental results when there is a bubble 6 at the bubble location A.

  can see from these graphs that the sensitivity and

  temperature characteristic with respect to sensitivity is not substantially influenced by the bubble

  when the bubble size is below 200 µm.

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Claims (10)

  1. A method of manufacturing a pressure sensor comprising: fixing a silicon chip (4) comprising diffused gauges (3a to 3d) on a diaphragm (2a) of a detection body (2) by l by means of a layer of glass (5), assembling said detection body (2) with a housing (1), inspecting said layer of glass (5) to find a bubble therein after said bonding, and assembling said sensing body (2) with said housing (1) when said bubble is formed in said glass layer (5) and is determined to be within tolerances of predetermined manufacturing.   2. Method according to claim 1, wherein said inspection step comprises inspecting said bubble in said glass layer (5) under said diffused gauges (3a to 3d). 3. Method according to claim 2, wherein said silicon chip (4) is a chip having a plane orientation (110), said diffused gauges (3a-3d) comprise central (3a, 3b) and lateral (3c) gauges. , 3d), and said inspection step includes inspecting said bubble in said   glass layer (5) under said central gauges (3a, 3b).   4. The method of claim 1, wherein said bubble formed in said glass layer (5) is determined to be within predetermined manufacturing tolerances when said bubble has a diameter less than 200 µm.   5. The method of claim 1, wherein said fixing step further comprises: printing a glass paste on a surface of said diaphragm (2a), calcining said glass paste to form said glass layer (5), 9 2780504   mounting said layer of glass (5) on said silicon chip (4), and sintering said silicon chip (4) in order to fix   said layer of glass (5) to said silicon chip (4).   The method of claim 1, wherein said inspecting step comprises inspecting said layer of   glass (5) using an infrared microscope.   7. The method of claim 1, wherein said inspecting step comprises inspecting said layer of   glass (5) using ultrasonic waves.   8. A pressure sensor comprising: a detection body (2) comprising a pressure-sensitive diaphragm (2a), a layer of glass (5) bonded to said diaphragm (2a) and having a characteristic bubble formed therein which found within predetermined manufacturing tolerances, and a silicon chip (4) mounted on said diaphragm (2a)   through said layer of glass (5).   9. The pressure sensor according to claim 8, in which said silicon chip (4) has a plane orientation (110), said silicon chip (4) comprises central (3a, 3b) and lateral (3c) diffused gauges. 3d), and said bubble is   located under said central gauges (3a, 3b).   10. The pressure sensor according to claim 8, wherein said bubble is within predetermined manufacturing tolerances when said bubble has a diameter less than 200 µm.