JP2616952B2 - Semiconductor pressure sensor - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor pressure sensor, and more particularly to laser trimming (circuit adjustment) of a diaphragm type semiconductor chip constituting a semiconductor pressure sensor.

[Conventional technology]

A diaphragm-type semiconductor pressure sensor (for example, a silicon pressure sensor) is a pressure sensor using a so-called piezoresistance effect in which the resistance value of a resistance element changes due to a stress caused by deformation of a diaphragm. , Is being widely used in fields such as industrial measurement, medical care, and automobiles. A conventional example of this type of pressure sensor is the monthly magazine “Sensor Technology” (May 1985 issue, Information Research Committee of the publisher).
On pages 32 to 35, and JP-A-62-7217.
There is one disclosed in Japanese Patent Publication No. 8 and the like.

FIG. 4 illustrates an absolute pressure sensor as a first conventional example of the semiconductor pressure sensor.

In FIG. 4, reference numeral 1 'denotes a silicon chip, on which a diaphragm 1'a is formed by performing a concave process on the back surface. The diaphragm 1'a is provided with a strain gauge (not shown) based on diffusion resistance. The silicon chip 1 'is bonded to the pedestal 2 (for example, Pyrex glass # 7740) whose thermal expansion coefficient matches or approximates that of the silicon chip by anodic bonding. The pedestal 2 is formed with a passage 2a for introducing the measured pressure. Silicon chip 1 '
Is fixedly supported on the pedestal 2 such that the pressure sensing surface of the diaphragm faces the opening of the passage 2a.

Reference numeral 5 denotes a base having a pressure introduction hole 5a to be measured. The pedestal 2 with the silicon chip 1 ′ is joined to the upper surface of the base 5 by soldering via the metallization layer 3. The metallized layer 3 has a first layer made of an adhesive layer of Ti or Cr, Ni-Cr or the like having a high bonding strength with the material of the pedestal 2, and a second layer formed of Ni or W, which prevents interlayer diffusion of the multilayer structure material. The third layer is composed of a diffusion prevention layer of Mo, Pt or the like, and the third layer is composed of three layers of a surface oxidation protection layer of Au or Pt for protecting the surface from oxidation. A pressure introducing pipe 6 is provided on the lower surface of the base 5.
Are joined using a brazing agent (for example, silver brazing or copper brazing). Further, four lead pins 7 for obtaining electrical connection with the outside on a semicircle from the center of the base 5 are sealed with hermetic seal glass 8.

Reference numeral 9 denotes a metal cap which is joined to the base 5 by projection welding. The inside of the cap is maintained at a reference pressure (for example, vacuum pressure) to form a reference pressure chamber 11. The pedestal 2 with the silicon chip 1 ′ is arranged in the reference pressure chamber 11.

Such a pressure sensor introduces a measured pressure to the pressure detection surface of the diaphragm 1a via the pipe 6, the pressure introduction hole 5a, and the pressure introduction passage 2a. The diaphragm 1a is deformed by the differential pressure between the reference pressure and the measured pressure, and the output of the strain gauge at that time is sent to an external hybrid IC (amplifier circuit, temperature compensation circuit) via the lead wire 10 and the lead pin 7, The measured pressure is detected. This pressure sensor is an absolute pressure sensor if the reference pressure is a vacuum pressure.

Even if these types of semiconductor pressure sensors are manufactured with the same design, circuit characteristics may vary. And circuit trimming (characteristic adjustment) is performed in this manner.

Recently, due to advances in semiconductor technology, in addition to forming a diaphragm with a strain gauge on a silicon chip, an amplifier circuit and a temperature compensation circuit, which were conventionally externally mounted, have been practically integrated with a diaphragm-type silicon chip. Have been.

By the way, when such a silicon chip integrated with a diaphragm, an amplification circuit, and a temperature compensation circuit is used as an absolute pressure sensor, the circuit formed on the silicon chip is trimmed in the atmosphere in the same manner as a relative pressure sensor. The following problems occur. That is, if the circuit is trimmed at atmospheric pressure and then incorporated into the pressure sensor cap under the reference pressure (vacuum pressure), the atmosphere is applied to the pressure sensing surface side of the diaphragm, and the counter pressure sensing surface side It becomes vacuum pressure. As a result, the diaphragm is slightly deformed before the sensor detects the pressure to be measured, causing a shift in the output, and the precision of the circuit characteristics is reduced even if the trimming is performed.
Conventionally, sufficient consideration has not been given to such a problem.

In general, when used as an absolute pressure sensor, a method of performing circuit trimming of a silicon chip under an atmosphere of a reference pressure in advance before applying the cap to the sensor, and thereafter applying the cap. Was adopted.

However, according to such a method, since the cap is applied after trimming, if the reference pressure fluctuates before and after the trimming, a difference occurs between the reference pressure at the time of trimming and the reference pressure in the sensor after the cap is attached, and the circuit characteristic is reduced. Does not always fully satisfy the trimming accuracy of

In order to solve the above problems, in recent years, an exterior case for hermetically sealing the sensor member, the output adjustment resistor, and the operation display element is formed of a light transmitting member. In addition, a method has been proposed in which the operation display element is hermetically sealed and the inside of the case is made to have an absolute pressure, and then the output adjusting resistor is irradiated with laser light through the outer case to perform circuit trimming. FIG. 5 shows an example. In the figure, the same reference numerals as those in FIG. 4 indicate the same parts.

As shown in FIG. 5, the circuit output side of the silicon chip 1 is connected to the lead pin 7 via the Au thin wire 10 (φ30 μm) after mounting the silicon chip 1 and the pedestal 2 on the base 5. Thereafter, a cap 9a, which will be described later, is hermetically attached to the base 5 in an atmosphere set to the reference pressure.

The cap 9a is formed of a material having a good laser transmittance, such as quartz glass, sapphire glass, etc., and the cap 9a is mounted on the base 5 by, for example, anodic bonding or a material similar to the one indicated by reference numeral 3. The reference pressure chamber 11 is formed around the silicon chip 1 and the pedestal 2 by soldering through the metallized layer 13 of the layer.

When laser trimming is performed in such a pressure sensor, as shown by the arrow, the laser is transmitted from the atmosphere via the laser-permeable cap 9a, and is formed on the silicon chip 1 at the reference pressure. The trimming is performed by irradiating the circuit adjustment element (this is referred to as a second conventional example).

[Problems to be solved by the invention]

The second conventional example eliminates the drawbacks of the first conventional example and guarantees highly accurate circuit trimming.

An object of the present invention is to enable high-precision circuit trimming even in an absolute pressure sensor as in the second conventional example, and thus to improve the detection accuracy of the sensor.
It is still another object of the present invention to provide a semiconductor pressure sensor which can be miniaturized and employ various mounting modes for components of the pressure sensor.

[Means for solving the problem]

The above object is achieved by applying the following means if the pressure sensor is taken from a structural point of view.

That is, it has a semiconductor chip on which a diaphragm for detecting pressure, an amplifier circuit, and a temperature compensation circuit are formed, and a passage for introducing a pressure to be measured. A semiconductor pressure sensor comprising a pedestal that opposes and fixedly supports the semiconductor chip, wherein the semiconductor chip surface on the side opposite to the pressure detection surface of the diaphragm is hermetically enclosed with a cap while maintaining a set reference pressure,
In addition, the cap is formed of a material that transmits laser and is formed in a shape that can be directly mounted on the semiconductor chip, and the counter pressure detecting surface of the diaphragm surface, the amplification circuit, and the temperature compensation circuit are formed on the semiconductor chip surface. It is attached so as to surround it.

[Action]

According to the above configuration, the counter pressure detecting surface of the diaphragm type semiconductor chip is maintained at the reference pressure by the cap, so that it can be used as an absolute pressure sensor.

Also, after the cap is attached, the reference pressure of the pressure sensor is kept constant, and after the diaphragm type semiconductor chip is set in this stable reference pressure atmosphere, laser trimming of the circuit adjustment element of this semiconductor chip is performed. Unless there is an accident, the reference pressure does not change before and after trimming. As a result, high-precision and stable circuit trimming becomes possible, and the detection accuracy as an absolute pressure sensor is enhanced.

Further, since the cap for holding the absolute pressure (reference pressure) is directly mounted on the semiconductor chip, the size of the cap can be reduced, and the diaphragm on the semiconductor chip, the amplifying circuit and the temperature compensation circuit ( Since these pressure sensor components are covered from the outside, they are effectively protected. In addition, the diaphragm type semiconductor chip with the cap and the lead terminal collectively cover the semiconductor chip and the lead terminal on the base for mounting the base like a conventional cap (for example, the cap in FIGS. 4 and 5). Since the semiconductor chip and the lead terminal can be independently arranged without being attached in this manner, various mounting forms of the sensor can be adopted.

〔Example〕

An embodiment of the present invention will be described with reference to FIGS. In these drawings, the same reference numerals as those in the conventional example shown in FIGS. 4 and 5 denote the same or common elements.

 FIG. 1 is a longitudinal sectional view showing one embodiment of the present invention.

The semiconductor chip (silicon chip) 1 of this embodiment has a diaphragm 1a formed by forming a concave portion on the back surface of a silicon single crystal, and a strain gauge (diffusion resistor) corresponding to the diaphragm 1a on the surface and an integrated amplifier circuit. -A temperature compensation circuit (with a circuit adjusting element) is formed.

The cap 9b of the present embodiment is formed of a material having laser transmittance, and is characterized in that the cap 9b is directly mounted on the silicon chip 1 by bonding (bonding is performed by anodic bonding or the like). Have. This cap 9b
Is mounted on the silicon chip 1 under a reference pressure atmosphere so as to surround the counter pressure detecting surface side of the diaphragm 1a of the silicon chip 1, the amplification circuit and the temperature compensation circuit. Also in this case, the reference pressure chamber 11 is formed in the cap 9b, and one surface of the diaphragm becomes the reference pressure, and the other surface (pressure detection surface) receives the measured pressure, so that an absolute pressure sensor can be formed.

When the circuit trimming of the silicon chip 1 is performed, the laser is irradiated from the atmosphere to the circuit adjustment element at the reference pressure (in the cap) from the atmosphere via the glass cap 9b. Also in this case, since the laser trimming is performed at the reference pressure after the cap is attached, a situation in which the reference pressure changes before and after the trimming does not occur, and a stable and high-precision semiconductor pressure sensor can be obtained. Can be reduced in size. Further, by reducing the size of the cap 9b, various mounting forms of the sensor can be adopted.

FIGS. 2 and 3 show examples of mounting the semiconductor pressure converter shown in FIG.

FIG. 2 shows the silicon chip 1 and the cap.
The pedestal 2 provided with the base 9b is fixedly housed in a mold case (base) 5 'via an adhesive 15, and then a mold cap 5'a is attached to the mold case 5' in the atmosphere.

FIG. 3 shows a cap 2 on a pedestal 2 with a silicon chip 1.
After mounting the pressure conversion part to which 9b is joined on the base 5, a metal cap 9 is applied in an atmosphere of the atmosphere.

〔The invention's effect〕

As described above, according to the present invention, since laser trimming is performed after the cap is applied and the reference pressure is kept constant,
The trimming adjustment can be performed with high accuracy, and the detection accuracy as an absolute pressure sensor can be improved. In addition, various mounting modes can be adopted for miniaturization of this kind of semiconductor pressure sensor and for components of the pressure sensor.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing an embodiment of the present invention, FIGS. 2 and 3 are sectional views showing a mounting mode thereof, and FIGS. 4 and 5 are longitudinal sectional views showing a conventional example of an absolute pressure sensor. FIG. 1 ... Semiconductor chip, 1a ... Diaphragm, 2 ... Pedestal, 2a ... Measured pressure introduction passage, 5 ... Base, 9a, 9b ...
… Laser permeable cap, 9c …… Cap, 11 …… Standard pressure chamber.

Claims (1)

(57) [Claims] 1. A semiconductor chip having a diaphragm for detecting pressure, an amplifier circuit, and a temperature compensation circuit, and a passage for introducing a pressure to be measured. A semiconductor pressure sensor comprising: a pedestal for fixedly supporting the semiconductor chip with the detection surface opposed to the semiconductor pressure sensor, wherein the semiconductor chip surface on the side opposite to the pressure detection surface of the diaphragm is hermetically sealed with a cap while maintaining a set reference pressure. The enclosure and the cap are formed of a material that transmits laser, and are formed in a shape that can be directly mounted on the semiconductor chip, and a counter pressure detection surface of the diaphragm surface, the amplification circuit, and the temperature compensation are formed on the semiconductor chip surface. A semiconductor pressure sensor which is attached so as to surround a circuit.