JPH06201498A - Manufacturing pressure sensor - Google Patents

Abstract

(57) [Summary] [Objective] Mobile ions such as Na ⁺ that enter the passivation film during manufacturing of the pressure sensor are removed from the sensor to reduce drift. In a pressure sensor manufacturing process, a metal film 10 is provided on the passivation film 5 around the cut line 9 for each sensor element 7, and the wafer 8 is heated to a high temperature.
By applying a negative high voltage from the high voltage power source 11 to the metal layer 10, mobile ions such as Na ⁺ in the passivation film 5 are collected in the metal layer 10 and trapped.
Therefore, with the movable ions trapped in the metal layer 10, each sensor element 7 in the wafer 8 is divided from each cut line 9 to separate the metal layers 10, and thereby the passivation film 5 in the sensor element 7 is separated. Mobile ions such as Na ⁺ inside are reduced, and the influence of drift of the sensor output can be reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a pressure sensor for converting pressure into an electric signal by utilizing the piezoresistive effect of a semiconductor such as silicon, and more particularly to surface protection of the pressure sensor when manufacturing the pressure sensor. The present invention relates to a passivation method for reducing mobile ions such as Na ⁺ entering a passivation film used for the purpose of reducing the influence of the mobile ions.

[0002]

2. Description of the Related Art In general, a pressure sensor of this type measures a pressure value by generating strain in a gauge resistance by introducing pressure and converting a resistance change due to a piezoresistive effect of the resistance into an electric signal. It is widely used for various purposes including industrial measurement. As shown in FIGS. 2 (a) and 2 (b), the basic structure of this pressure sensor uses a chip-shaped n-type silicon substrate 1 having a thick portion 2 serving as a fixing portion and a thin diaphragm portion 3. In the thin diaphragm portion 3, a gauge resistor 4 (4 _A to 4 _D ) having a piezoresistive effect formed of a p-type diffusion region is formed.

The silicon substrate 1 is fixed to a supporting member 21 such as a glass tube having a pressure introducing port 22 at the thick portion 2, and when pressure is applied from the introducing port 22, the thin diaphragm portion 3 is formed. Is distorted, which changes the resistance value of the gauge resistor 4. Therefore, if these gauge resistors 4 are incorporated in a bridge circuit and a voltage is applied to the bridge circuit, an output signal corresponding to the pressure, that is, the difference between the pressures P _H and P _{L on} the front and back sides of the thin diaphragm portion 3 is taken out from the bridge circuit. You can

Here, the surface of the silicon substrate 1 on which the gauge resistor 4 is formed is covered with a passivation film 5 made of SiO ₂ or the like, and aluminum (A
The extraction electrode 6 made of 1) or the like is formed, and the connection with the outside is usually made by wire bonding.

By the way, such a pressure sensor is manufactured by a batch process using a film forming or etching technique like an ordinary semiconductor device, and its outline will be described with reference to FIG. For example, as a semiconductor single crystal substrate, n
Using the shaped silicon substrate 1a, the central portion on the back side of the silicon substrate 1a is processed into a circular recess by etching or the like to form the thin diaphragm portion 3 and the thick portion 2 having a reduced thickness, and the diaphragm portion 3 is formed. A p-type diffusion region is selectively formed on the upper surface of the sensor to form a gauge resistor 4 having a piezoresistive effect for each sensor element.

Then, a passivation film 5 made of SiO ₂ or the like is formed on the surface of the silicon substrate 1a on which each gauge resistor 4 is formed, and an extraction electrode 6 is formed which is connected to the gauge resistor 4 through a contact hole which is opened. Then, a wafer including a large number of sensor elements is produced. Thereafter, the wafer is divided by dicing from cut lines to be divided into individual sensor elements, which are fixed to the support member 21, and the extraction electrode 6 is connected to an external terminal. By assembling through the assembling process, the pressure sensor having the illustrated structure is produced.

[0007]

By the way, in the pressure sensor manufactured in this way, mobile ions such as Na ⁺ that enter the passivation film 5 during its manufacture freely move around during use, and therefore, It will cause the sensor output to drift. Therefore, trapping with SiO ₂ or phosphorus glass used as a passivation film has been conventionally performed, but even this method cannot trap mobile ions sufficiently. In particular, there has been a problem that the use of phosphorous glass is restricted due to hysteresis in the pressure sensor which is a mechanical element.

In view of the above points, the present invention has been made to solve the above problems, and its purpose is to:
Na that enters the passivation film during the manufacture of the sensor element
^The purpose is to provide a pressure sensor with less drift by removing mobile ions such as ⁺ from the sensor.

[0009]

In order to achieve the above-mentioned object, the present invention forms a gauge resistor having a piezoresistive effect of the semiconductor on a semiconductor single crystal substrate for each pressure sensor element. A passivation film that protects the surface of the gauge resistance is formed on the upper surface of the gauge resistance.Furthermore, for each pressure sensor element, the element must be divided into individual parts. A metal layer is formed and a wafer is created. Then, this wafer is heated to a high temperature and a high voltage is applied to the metal layer to apply Na ⁺ in the passivation film.
Individual sensor elements are prepared by trapping mobile ions such as in the metal layer, and then dividing the wafer from the cut line to separate the metal layer while the mobile ions are trapped in the metal layer. It is characterized by that.

[0010]

In the present invention, for each sensor element of the wafer, a metal film is provided on the passivation film at a position distant from the sensor element, that is, outside the cut line, and the wafer is heated to a high temperature to form a metal layer on the metal layer. By applying a high voltage, mobile ions in the passivation film are collected and trapped in the metal layer. Therefore, mobile ions such as Na ⁺ that enter the passivation film during the manufacture of the pressure sensor element can be removed from the sensor.

[0011]

1 is a schematic view for explaining an embodiment of a method for manufacturing a pressure sensor according to the present invention. FIG. 1 (a) is a plan view thereof and FIG. 1 (b) is a diagram for voltage application. The partial cross-sectional view of a metal layer part is shown, respectively. In this embodiment, the central portion on the back side of the n-type silicon substrate 1a is processed into a circular recess by etching or the like to form a thin diaphragm portion 3 and a thick portion 2 with a reduced thickness (see FIG. 2). A p-type diffusion region is selectively formed on the diaphragm portion 3 to form a gauge resistor 4 (4 _A to 4 _D ) having a piezoresistive effect for each sensor element 7. Then, a passivation film 5 made of SiO ₂ or the like is formed on the surface of the silicon substrate 1a on which each gauge resistor 4 is formed, and a lead electrode 6 is formed to electrically connect to the gauge resistor 4 through a contact hole opened. (See FIG. 2), the steps up to the step of forming the wafer 8 including a large number of sensor elements 7 (two in the figure) are basically the same as those in the conventional example described above, but the extraction electrode At the time of formation, each sensor element 7 has a predetermined pattern on the outer periphery of the cut line 9 which is to be divided individually.
a metal layer 10 (10 ₁ to ₁₎ composed of 1 or the like for voltage application.
0 ₄ ) are formed at the same time.

Then, the wafer 8 is heated to, for example, about 400 ° C. (below the boiling point when the electrode 6 and the metal layer 10 are Al).
The high voltage power source 1 is applied to each metal layer 10 while being heated to the high temperature.
1, a negative high voltage of, for example, about 1 KV is applied to trap mobile ions such as Na ⁺ in the passivation film 5 in each metal layer 10, and then the temperature is lowered to room temperature,
The application of the high voltage is stopped. After that, the wafer 8 is divided from the cut line 9 by dicing, and each metal layer 1 is divided.
By separating 0, it is divided into individual sensor elements 7. The process of assembling each sensor element 7 after this division is similar to that of the conventional example, and the description thereof is omitted. Further, in FIG. 1, the same or corresponding parts as those in FIG. 2 are designated by the same reference numerals.

As described above, according to this embodiment, in the process of manufacturing the pressure sensor, the metal film 10 is provided on the passivation film 5 around the cut line 9 for each sensor element 7, and the wafer 8 is heated to a high temperature. (400 ° C or less)
And applying a negative high voltage from the high voltage power source 11 to the metal layer 10 causes the Na ⁺ in the passivation film 5 to rise.
Mobile ions such as are collected in the metal layer 10 and trapped. Therefore, the temperature of the wafer 8 is lowered to room temperature, the application of the high voltage is stopped, and the movable ions are trapped in the metal layer 10, and each sensor element 7 in the wafer 8 is cut from each cut line 9. Divide them into metal layers 1
By separating 0, mobile ions such as Na ⁺ in the passivation film 5 in each sensor element 7 can be reduced. Therefore, the influence of the drift of the sensor output can be reduced.

Although a silicon substrate is used as the semiconductor single crystal substrate in the above embodiment, the present invention is not limited to this, and a substrate having an SOS structure may be used, or a thin diaphragm may be used. The gauge resistance can be modified in many ways, such as by forming an arbitrary number in a predetermined area.

[0015]

As described above, according to the present invention, in the process of manufacturing a pressure sensor, a metal film is formed on each passivation film on the outer periphery of the cut line for dividing each sensor element of the wafer. By providing this wafer and heating the wafer to a high temperature and applying a high voltage to the metal layer, the mobile ions in the passivation film are collected and trapped in the metal layer, so that the passivation film is formed during the production of the pressure sensor. Mobile ions that enter, such as Na ^+, can be removed from within the sensor. Therefore, the effect of the drift of the sensor output can be reduced, and a pressure sensor with less drift can be obtained.

[Brief description of drawings]

1A and 1B are schematic views illustrating an embodiment of a method for manufacturing a pressure sensor according to the present invention, FIG. 1A is a plan view thereof, and FIG. 1B is a partial cross-sectional view of a metal layer portion for voltage application. .

FIG. 2 is a basic configuration diagram of a pressure sensor according to a conventional example,
(a) is the top view, (b) is sectional drawing.

[Explanation of symbols]

1a Silicon substrate 2 Thick part 3 Thin diaphragm part 4 _A to 4 _D Gauge resistance 5 Passivation film 6 Extraction electrode 7 Sensor element 8 Wafer 9 Cut line 10 Metal layer for voltage application 11 High voltage power supply

Claims (1)

[Claims] 1. A gauge resistor having a piezoresistive effect of the semiconductor is formed for each sensor element on a semiconductor single crystal substrate, and a passivation film for protecting the surface is formed on the upper surface of each gauge resistor. Further, for each sensor element, a step of forming a metal layer for voltage application having a predetermined pattern on the passivation film on the periphery outside the cut line where the element is to be divided into individual parts, and creating a wafer, Heating the wafer to a high temperature and applying a high voltage to the metal layer to trap mobile ions such as Na ⁺ in the passivation film in the metal layer; and thereafter trapping mobile ions in the metal layer. And dividing the wafer from the cut line to separate the metal layer in this state to form individual sensor elements. Manufacturing method of the pressure sensor according to symptoms.