KR20080075099A - Semiconductor pressure sensor - Google Patents

Abstract

This invention provides a semiconductor pressure sensor which can solve a problem that, when the pressure of a pressure medium containing a corrosive substance such as exhaust gas is measured with a semiconductor pressure sensor, an aluminum electrode, an aluminum wire, and an input/output terminal are attacked by a corrosive gas, thereby improving the corrosion resistance of a sensor chip, and, at the same time, can particularly improve the corrosion resistance of a part as a pressure-sensitive part. The corrosion of an electrode is prevented by providing titanium tungsten layer and a gold layer on an aluminum electrode as a corrosion site. The corrosion of a connection wire by a corrosive substance can be prevented by using a gold wire as the connection wire. The corrosion of an input/output terminal can be prevented by plating the input/output terminal with gold.

Description

Semiconductor Pressure Sensor {SEMICONDUCTOR PRESSURE SENSOR}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mounting structure of a semiconductor pressure sensor that improves corrosion resistance to corrosive gas in a semiconductor pressure sensor using a semiconductor strain gauge.

BACKGROUND ART A semiconductor pressure sensor using a semiconductor strain gauge has been conventionally used for measuring intake pressure for automobiles. In recent years, in order to improve the cleanliness of exhaust gas, the adoption of EGR for refluxing the exhaust gas to the intake side has been expanded. In particular, for diesel, the reflux rate of the EGR is in an enlarged direction. As described above, since the semiconductor pressure sensor for measuring the pressure on the intake side is changed to an environment exposed to the exhaust gas by EGR, resistance to the exhaust gas is required.

In addition, in diesel engines, DPF (Diesel Particulate Filter) is being used to reduce particulate matter (PM). However, in order to detect clogging of the filter, it is necessary to detect pressure before and after the filter. In this case, the pressure reducing part of the pressure sensor needs to be resistant to the exhaust gas.

In the conventional semiconductor pressure sensor, as shown in FIG. 3 of Patent Document 1, aluminum is usually used for a chip electrode of a semiconductor strain gauge. Aluminum electrodes are susceptible to corrosion and require countermeasures when used in a corrosive environment.

In patent document 1, the countermeasure is taken by the Ti film | membrane and Pd film | membrane in order to prevent corrosion of an aluminum electrode. This is particularly aimed at improving the corrosion resistance of aluminum electrodes against humidity and moisture, and is not sufficiently resistant to corrosion by nitrate ions by nitrogen oxides contained in the exhaust gas.

[Patent Document 1]

Publication No. 10-153508

Conventional semiconductor pressure sensors are bonded between an aluminum electrode of a bonding pad portion, which is an electrical input / output of a semiconductor strain gauge chip, and an external input / output terminal portion (normally nickel plated terminal) for inputting / outputting a signal of the gauge and the aluminum electrode / external input / output terminal. We use aluminum wire to say. In this mounting structure, when used for a long time in an environment containing exhaust gas, there is a problem that the aluminum wire is corroded by nitrate ions generated from nitrogen oxide contained in the exhaust gas.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor pressure sensor having sufficiently high corrosion resistance even under an exhaust gas environment in view of the problems of the prior art. Other objects of the present invention will be apparent from the following description of the embodiments.

The present invention for achieving the above object is a pressure detecting device for measuring the pressure of a gas containing a corrosive component such as exhaust gas, on the surface of the semiconductor chip, the wire bonding pad to be an electrical input / output unit and the characteristic probe pad The entire front surface is coated with a corrosion resistant material such as silicon nitride (SiN), and the pad bonding portion for wire bonding and the probe pad portion for checking properties are provided on the aluminum electrode with an adhesion secured / diffusion prevention layer. It is characterized in that the gold coating on the surface of the adhesion secured / diffusion prevention layer.

The adhesion securing / diffusion prevention layer is characterized in that the titanium / tungsten (TiW), titanium nitride (TiN) or nickel (Ni) is installed by sputtering, vapor deposition, plating.

The adhesion securing / diffusion prevention layer is configured to overhang the silicon nitride with a layer thickness of about 0.25 μm.

In addition, the electrical input / output unit of the semiconductor chip is connected to an external input / output terminal with a gold wire, and the surface of the external input / output terminal is characterized by being coated with gold. The thickness of the gold coating is characterized in that more than 0.5μm.

Moreover, the semiconductor chip is anodic-bonded to glass, and the temperature which anodic-bonds is bonded at 320 degrees C or less, It is characterized by the above-mentioned.

Coating with the adhesion securing / diffusion preventing layer provided on the wire bonding pad and the property checking probe pad portion and the gold of the surface thereof is carried out after the semiconductor chip is anodic bonded to glass.

Further, in order to prevent breakage of the adhesion secured / diffusion prevention layer due to vibration application during the gold coating, a part of the aluminum part of the lower portion to be wire-bonded of the aluminum electrode is removed.

According to the present invention, since the pad bonding portion for wire bonding and the probe pad portion for checking properties are provided with an adhesion securing / diffusion prevention layer on the aluminum wiring, the diffusion of gold coating coated on the outermost surface to the aluminum electrode is prevented. prevent. In addition, since the electrical input / output part of the semiconductor chip is connected to an external input / output terminal with a gold wire, gold has the smallest ionization tendency among metal elements, thereby preventing corrosion from corrosive substances.

1 is a front view and a cross-sectional view of a pressure sensor submodule according to a first embodiment of the present invention;

FIG. 2 is an enlarged cross-sectional view of the main portion of the pressure sensor submodule of FIG. 1. FIG.

3 is a cross-sectional view of a pressure sensor in which the pressure sensor submodule of FIG. 1 is mounted on a housing;

Figure 4 shows a differential pressure sensor structure to which two pressure sensor submodules of the present invention are applied, 4a is a side cross-sectional view, 4b is a plan view, 4c is a front cross-sectional view,

5 is an enlarged cross-sectional view of the main portion of the pressure sensor submodule according to the second embodiment.

※ Explanation of code for main part of drawing

1: Diaphragm Part 2: Sensor Chip

3: aluminum electrode 4: silicon nitride

5: tight adhesion / diffusion prevention layer (titanium tungsten layer)

6 gold electrode 7 glass substrate

8: case 9: adhesive

10: terminal 11: base material

12: nickel plating 13: gold plating

14 gold wire 15 gel

16: probe pad for characteristic check

20: submodule 21: connector

22: pressure inlet 23: housing

24 connector terminal 25 epoxy resin

31,32: pressure introduction part 33: circuit board

In a preferred embodiment of the present invention, first, the entire surface of the semiconductor strain gauge other than the wire bonding pad and the characteristic verification probe pad, which are electrical inputs and outputs of the semiconductor chip surface, is coated with a corrosion resistant material such as silicon nitride (SiN). . The wire bonding pad portion and the probe pad portion are provided with adhesion securing / diffusion preventing layers on the aluminum wirings, and the outermost surfaces thereof are coated with gold.

The adhesion secured / diffusion prevention layer provided on the aluminum wiring is provided with titanium tungsten (TiW), titanium nitride (TiN) or nickel (Ni) by sputtering, vapor deposition and plating. As a result, diffusion of the gold coating coated on the outermost surface to the aluminum electrode can be prevented.

In the electrical input / output unit of the semiconductor chip, a gold wire is connected between an external input / output terminal for performing electrical input / output of the semiconductor chip, and the external input / output terminal surface is coated with a gold coating by plating or the like.

The gold coating on the outermost surface of the wire bonding pad portion and the characteristic verification probe pad portion, which is an electrical input / output portion on the surface of the semiconductor chip, is formed by sputtering, plating or sputtering and plating. The thickness of the coated gold is 0.5 micrometers or more to ensure corrosion resistance.

In mounting the semiconductor strain gauge as the semiconductor pressure sensor, the semiconductor chip is required for handling. In the case of the absolute pressure sensor, the anode is bonded to the glass substrate to form a vacuum chamber. However, when the gold coating is performed before the anode bonding, the anode bonding temperature is bonded at 320 ° C or lower. When bonding at a high temperature or higher, a crack enters the aluminum electrode, the adhesion securing / diffusion preventing layer, and the line securing coefficient / diffusion preventing layer of each layer of the gold coating, and the gold diffuses into the aluminum. .

In the case where the semiconductor chip and the glass are first anodic bonded, thereafter, a wire bonding pad serving as an electrical input / output unit on the surface of the semiconductor chip and a probe pad portion for checking characteristics are provided, and a gold diffusion coating layer is provided. Is carried out. This prevents the occurrence of cracks in ensuring adhesion / diffusion prevention by application of temperature at the time of anode bonding.

In addition, by locally removing the aluminum electrode from the wire bonded portion, it is possible to prevent breakage of the adhesion securing / diffusion preventing layer due to the application of vibration during gold wire bonding when the wire bonding is applied.

In these preferred embodiments of the present invention, since the wire bonding pad portion and the property verification probe pad portion are provided with an adhesion securing / diffusion preventing layer on the aluminum wiring, the diffusion of gold coating on the outermost surface to the aluminum electrode is prevented. do. Without this layer, gold diffuses into aluminum, and the corrosion resistance of the connecting electrode portion in the coating with the desired gold cannot be improved.

In addition, the electrical input / output unit of the semiconductor chip is connected to an external input / output terminal by changing with a gold wire. As a result, gold has the least ionization tendency among the metal elements, so that it is possible to prevent corrosion from corrosive substances.

The gold coating on the outermost surface of the wire bonding pad portion and the property verification probe pad portion can be formed by sputtering, plating or sputtering and plating, and can be produced in a gold bump formation manufacturing process of a semiconductor to be used normally. The thickness of the coated gold is 0.5 micrometers or more to ensure corrosion resistance. In the thickness below this, corrosion advances with a corrosive substance, and the target lifetime cannot be ensured.

When the semiconductor pressure sensor is an absolute pressure sensor, the bonding temperature for bonding the anode to the glass substrate to form a vacuum chamber is bonded below 320 ℃. When the bonding is performed at a higher temperature or more, cracks enter the linear expansion coefficient aberration of each layer in the adhesion securing / diffusion preventing layer, and gold diffuses into aluminum, so that the electrode front surface cannot be coated with gold. For this reason, not only corrosion resistance can be secured but a gold wire bonding cannot be comprised.

After the semiconductor chip and the glass substrate are first anodic bonded, the adhesion between the wire bonding pad and the probe pad portion is secured / diffused and a gold coating is applied to the heating during the anodic bonding. Prevents cracking of the layer to secure / diffuse adhesion and prevent diffusion of gold into the aluminum electrode. This ensures the corrosion resistance of the gold coined electrode.

In addition, the aluminum electrode is locally deleted at the portion to be wire bonded. This prevents breakage of the adhesion securing / diffusion prevention layer due to vibration application during gold wire bonding at the time of load application of wire bonding, and prevents diffusion of gold into the aluminum electrode.

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described in detail with reference to drawings.

(Example 1)

1 is a front view (a) and a cross-sectional view (b) of a semiconductor pressure sensor submodule according to the first embodiment of the present invention. In this embodiment, the hydraulic pressure unit of the pressure sensor is a compact sub-module.

The sensor chip 2 is formed with a diaphragm portion 1 made of silicon with a resistor (not shown) serving as a strain gauge. On the surface of the sensor chip 2, a strain gauge resistor and an aluminum electrode 3 connecting them are formed, and covered with silicon nitride (SiN) 4 to protect the strain gauge resistor and the aluminum electrode from a corrosive environment. Lost

The wire bonding pad part for outputting the signal from a strain gauge normally exposes an aluminum electrode, and outputs the signal to the outside with an aluminum wire or a gold wire in this part.

After the wire bonding pad part of the present embodiment has provided the titanium tungsten (TiW) adhesion securing / diffusion preventing layer (hereinafter titanium tungsten layer) 5 on the aluminum electrode 3, the gold electrode 6 by gold plating is provided. It consists. The thickness of gold plating is 0.5 micrometer or more.

As the adhesion securing / diffusion preventing layer, titanium nitride (TiN) or nickel (Ni) other than titanium / tungsten (TiW) can be used. In addition to the sputtering layer, the adhesion securing / diffusion preventing layer can be provided by vapor deposition and plating. Thereby, corrosion by the corrosion component, such as nitric acid produced | generated by nitrogen oxide (Nox) and water which generate | occur | produce when used under environment, such as exhaust gas, is prevented.

Similarly, after the titanium tungsten layer 5 is provided on the aluminum electrode, the probe pad 16 for characteristic confirmation constitutes a gold electrode by gold plating, and probes this gold electrode to confirm a characteristic. Accordingly, compared with the case where the aluminum electrode is exposed as in the related art, when used in an environment such as exhaust gas, corrosion by the corrosion component can be prevented.

The sensor chip 2 is bonded to the glass substrate 7 by an anodic bonding and mounted. In the case where the titanium tungsten layer 5 and the gold electrode 6 are provided on the sensor chip 2 first, and then the glass substrate 7 and the sensor chip 2 are anodic-bonded, high temperature is applied at the time of anodic bonding. Apply by joining.

According to the examination of the present inventors, when the anode is bonded at a high temperature of 320 ° C. or higher, cracks enter the titanium tungsten layer 5, the gold of the gold electrode 6 diffuses into the aluminum electrode 3, and the protective layer of gold disappears. The phenomenon occurred. For this reason, it is necessary to perform anode bonding at the temperature of 320 degrees C or less.

The sensor chip 2 is mounted on the glass substrate 7, and the glass substrate 7 is bonded to the case 8 of the submodule with an adhesive 9. The case 8 is insert molded with a terminal 10 for inputting and outputting a signal of a submodule to the outside. The terminal 10 is coated with a gold plating 13 after the nickel plating 12 is coated on the base material 11. Since the part which becomes the part connected with the sensor chip 2 is exposed to a corrosive environment similarly to the sensor chip 2, the gold plating 13 improves corrosion resistance.

After bonding connection by the gold wire 14, in order to protect the sensor chip 2 and the gold wire 14, the fluorine gel 15 is filled in this embodiment. The whole upper surface of this gel 15 is a pressure receiving part.

FIG. 2 shows an enlarged sectional view of the main part of the pressure sensor submodule of FIG. 1. The titanium tungsten layer 5 provided on the aluminum electrode 3 is provided by sputtering or the like so as to overhang the silicon nitride 4. The layer thickness of the titanium tungsten layer 5 is about 0.25 μm. This makes it difficult for the corrosive substance to reach the aluminum electrode 3 through the interface between the silicon nitride 4 and the titanium tungsten layer 5. In addition, gold plating is applied on the titanium tungsten layer 5 to form a gold electrode 6 covering the whole with gold.

The terminal 10 is coated with a gold plating 13 on the entire surface after nickel plating 12 on the entire surface. By such a structure, even when a corrosive substance comes to these connection parts, since it covers all the parts which the electrical defect may generate | occur | produce by corrosion with the smallest tendency of ionization, corrosion resistance improves.

3 is a cross-sectional view of the pressure sensor in which the pressure sensor submodule is mounted in the housing. The sub-module 20 of the pressure sensor shown in FIG. 1 is a housing 23 having a connector 21 for performing electrical input / output with the outside, a pressure inlet 22 for introducing a pressure of a measurement pressure medium, and an installation portion. It is mounted on

In this embodiment, the terminal 10 and the connector terminal 24 of the submodule 20 are connected by welding. In addition, the submodule 20 is fixed with an epoxy resin 25, and the epoxy resin 25 also serves as an airtight seal for preventing pressure leakage from the pressure introduction portion 22 or the like.

Exhaust gas or the like of the medium under measurement reaches the sensor from the pressure introduction section 22, and the pressure deforms the diaphragm 1 of the sensor chip 2 via the gel 15. By the deformation of the diaphragm 1, the pressure is converted into an electrical signal by the resistance change of the strain gauge (not shown) provided in the diaphragm 1, and the wire bonding 14, the terminal 10, and the connector terminal ( It is drawn out through 24).

Exhaust gas invading from the pressure introduction section 22 also diffuses into the gel 15 and reaches the gauge chip 2. At this time, by protecting the portion that is not the electrical input / output part with silicon nitride 4, the corrosion component is prevented from reaching the lower layer. As for the part which performs electric input / output, the titanium tungsten layer 5 and the gold electrode 6 are coated on the aluminum electrode 3 as mentioned above. Thus, corrosion of the electrode due to the corrosion component is prevented. Bonding wires for inputting and outputting signals from the electrode 3 also use gold wires 14 to prevent corrosion. In addition, the titanium tungsten layer 5 having a layer thickness of about 0.25 μm is configured to overhang with respect to the silicon nitride 4 as shown in FIG. 2, so that the silicon nitride 4 and the gold electrode 6 are separated from the interface. The diffusion of the exhaust gas that enters the aluminum electrode 3 is suppressed. In addition, the surface of the terminal 11 of the submodule is also coated with gold plating 13 to prevent corrosion of the terminal.

Such a mounting structure makes it possible to prevent the sensor from failing due to corrosion in the case of measuring the pressure of the measurement medium containing corrosive substances such as exhaust gas.

4 shows the structure of a differential pressure sensor as an application example of the present invention. This differential pressure sensor uses two pressure sensor sub-modules 20 for absolute pressure measurement, and its output is configured to output a differential pressure signal from two sensor signals on a circuit board.

In order to reduce particulate matter (PM) contained in the exhaust gas of diesel engines, installation of diesel particulate filters (DPF) has begun. For clogging detection of this filter, it is necessary to measure the differential pressure before and after the filter. In order to measure the differential pressure of the exhaust gas, it is necessary to improve the corrosion resistance of the hydraulic pressure section in order to protect against corrosion caused by the corrosion component of the exhaust gas.

In this application example, as shown in FIGS. 4A and 4B, the pressure is measured using two pressure sensor submodules 20 for absolute pressure measurement in which a gold electrode, a gold wire, and a gold plated terminal are used, and the circuit board 33 is measured. ) Processes the signal from the pressure sensor submodule 20, and outputs a differential pressure signal.

As shown in Fig. 4C, the pressure before and after the filter is guided to the pressure introduction portions 31 and 32 of the present differential pressure sensor, respectively. Pressure is converted into an electrical signal by the pressure sensor submodule 20 provided in each of the pressure introduction parts. The pressure signal from the submodule 20 is introduced into the substrate 33, and the differential pressure signal processing circuit provided on the circuit board processes and outputs the differential pressure signal from the signal of each pressure sensor submodule 20.

(Example 2)

FIG. 5 is a partially modified embodiment of an enlarged cross-sectional view of a main part of the pressure sensor submodule of FIG. 2.

The gold electrode 6 of the sensor chip 2 and the gold plating 13 of the terminal portion 10 are electrically connected by wire bonding connection by the gold wire 14. By bonding the gold wire 14, corrosion resistance by a corrosive substance is improved. In the application of vibration at the time of bonding of the gold wire 14, in order to prevent the damage of the adhesion securing / diffusion prevention layer 5, the aluminum electrode just under the wire bonding part is deleted locally. This prevents cracks from entering the titanium tungsten layer 5 when a load or vibration due to bonding is applied, thereby preventing the gold of the gold electrode 6 from diffusing into the aluminum electrode 3.

Local deletion of the aluminum electrode can take many forms in addition to FIG. The aluminum electrode may have a structure in which the portion immediately below the wire bonding is removed in advance.

As described in the section of the background art, the aluminum electrode used for the chip electrode of the semiconductor pressure sensor is vulnerable to the corrosive environment, and the countermeasure is required when using the corrosive environment. The present invention proposes a corrosion resistant structure of a semiconductor pressure sensor used in such a corrosive environment, and practical use is expected.

Claims (9)

In the pressure detection device for measuring the pressure of the gas containing a corrosive component such as exhaust gas, On the surface of the semiconductor chip, the entire surface other than the wire bonding pad and the characteristic verification probe pad which become the electrical input / output part is coated with a corrosion resistant material such as silicon nitride (SiN), The wire bonding pad part and the probe probe part for checking characteristics are provided with an adhesion secured / diffusion prevention layer on an aluminum electrode and a gold coating of the surface of the secured adhesion / diffusion prevention layer. The method of claim 1, The adhesion secured / diffused layer is a semiconductor pressure sensor characterized in that the titanium tungsten (TiW), titanium nitride (TiN) or nickel (Ni) is installed by sputtering, vapor deposition, plating. The method according to claim 1 or 2, The adhesion securing / diffusion prevention layer has a layer thickness of about 0.25 μm and is configured to overhang the silicon nitride. The method according to any one of claims 1 to 3, And a gold wire connected between the electrical input and output terminals of the semiconductor chip with an external input and output terminal, and the surface of the external input and output terminal is coated with a gold coating. The method according to any one of claims 1 to 3, The gold coating on the surface of the pad portion for wire bonding and the probe pad for property checking is formed by sputtering, plating, or sputtering and plating. The method of claim 5, The thickness of the gold coating is a semiconductor pressure sensor, characterized in that more than 0.5μm. The method according to any one of claims 1 to 6, The semiconductor chip is anodic bonded to glass, and the temperature at which the anodic bonding is performed is bonded at 320 ° C. or lower. The method according to any one of claims 1 to 6, The semiconductor pressure sensor, wherein the adhesion is secured / diffusion prevention layer provided on the wire bonding pad and the property verification probe pad portion, and the surface is coated with gold on the surface thereof after the semiconductor chip is anodically bonded to glass. The method according to any one of claims 1 to 6, The semiconductor pressure sensor, characterized in that the aluminum portion of the lower portion of the wire bonding of the aluminum electrode is removed in order to prevent breakage of the adhesion secured / diffusion prevention layer due to vibration applied during the gold coating.

Images