JPH0595122A - Manufacture of semiconductor pressure transducer - Google Patents

Abstract

(57) [Summary] (Modified) [Objective] An object of the present invention is to provide a method for manufacturing a semiconductor pressure transducer having a small residual stress and good temperature characteristics and static pressure characteristics. [Structure] Silicon, which is the same material as the pressure-sensitive pellets, is used as a base 6 for fixing the pressure-sensitive pellets, and the bonding surfaces thereof are mirror-polished, and only a thin oxide film 7 is interposed between the polishing bonding surfaces. The pressure-sensitive pellets and the base are directly joined together with the silanol groups formed on the surface of the oxide film. In particular, by using a silicon oxide film, which is the same material as the pressure sensitive pellets or the base, as the oxide film, the pressure sensitive pellets and the base can be bonded to each other without interposing other foreign matter to form a semiconductor pressure converter. To manufacture.

Description

Detailed Description of the Invention

[Object of the Invention]

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor pressure transducer having a structure in which a pressure sensitive pellet having a strain resistance gauge formed on a thin diaphragm surface of a semiconductor crystal is bonded to a base.

[0003]

2. Description of the Related Art As a pressure transducer for detecting fluid pressure,
Those utilizing the piezo effect of semiconductors have been put to practical use. As shown in the basic structure of this type of semiconductor pressure transducer, a thin diaphragm surface 2 sensitive to pressure is formed in the central portion of a semiconductor single crystal substrate 1 made of, for example, silicon (Si), and this thin diaphragm is formed. A diffusion resistance layer 3 having a conductivity type opposite to that of the substrate 1 is formed on one of the surfaces 2, and this serves as a strain resistance gauge. Then, a window portion is provided in the SiO ₂ insulating film 4 provided on the surface of the substrate 1, and the electrode wiring 5 of aluminum or the like for the strain resistance gauge 3 is formed through the window portion. The pressure-sensitive pellets thus formed are
The peripheral thick portion of the substrate 1 is fixed to the base 6 with an adhesive 7 or the like. A pressure introducing hole 8 is provided at the center of the base 6, and the pressure-sensitive pellets are sensitive to the pressure P introduced through the pressure introducing hole 8.

That is, the strain-resisting resistance gauge 3 shows a change in resistance value due to a diaphragm that causes strain by the pressure P,
This change in resistance value is detected by a full bridge circuit or the like including the strain-flexing resistance gauge 3. As a result, even a slight pressure change can be detected with high sensitivity.

As described above, since the semiconductor pressure transducer detects a weak pressure with high sensitivity due to the strain generated in the diaphragm, the residual stress applied to the pressure-sensitive pellet and its temperature change naturally cause a problem. In order to solve this problem, it is necessary to match the thermal expansion of the base 6 and the adhesive 7 with the semiconductor crystal substrate 1 so that the pressure-sensitive pellets fixed to the base 6 are not stressed. Therefore, conventionally, it has been considered to use silicon, which is the same material as the pressure-sensitive pellet, as the base 6. However, as the adhesive 7, for example, a eutectic of gold / silicon or a low melting point solder glass has to be used, so that there is a problem that residual stress due to these materials having a high coefficient of thermal expansion cannot be removed. It was

On the other hand, recently, it has been attempted that the base 6 is made of borosilicate glass and that the pressure-sensitive pellets are joined to the base 6 by heating at a high temperature or applying a voltage without using an adhesive. ing. According to such means, it is possible to match the thermal expansion in a wide temperature range by appropriately selecting the type of glass.

However, this type of semiconductor pressure transducer is often used under static pressure. In this case, in the bonded body of silicon and glass, since the compressibility of the two is different by one digit or more, uneven deformation occurs, and as a result, stress is applied to the pressure sensitive pellet portion. This stress appears as a zero point variation of the bridge circuit, which is a serious problem in using the semiconductor pressure transducer.

[0008]

As described above, in the conventional semiconductor pressure transducer, there is a residual stress or deformation due to the joining state of the base and the pressure-sensitive pellet, which makes it impossible to measure the pressure with high accuracy. was there.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a semiconductor pressure transducer having a small residual stress and excellent temperature characteristics and static pressure characteristics. is there.

[Constitution of Invention]

[0011]

According to the present invention, silicon, which is the same material as the pressure-sensitive pellets, is used as a base for fixing the pressure-sensitive pellets. The pressure-sensitive pellets are directly bonded to the base while only the oxide film is interposed and the silanol groups are formed. In particular, by using a silicon oxide film, which is the same material as the pressure sensitive pellets or the base, as the oxide film, the pressure sensitive pellets and the base can be bonded to each other without interposing other foreign matter to form a semiconductor pressure converter. It is designed to be manufactured.

[0012]

According to the present invention, the silicon oxide film effectively acts as an adhesive layer between the pressure-sensitive pellets and the base to firmly bond the pressure-sensitive pellets and the base. That is, each of the bonding surfaces of the pressure-sensitive pellets and the base, which are mirror-polished, are cleaned,
A thin oxide film is formed on the surface and a silanol group is formed, and both are brought into contact and joined without interposing foreign matter such as dust between them, so that residual stress due to the adhesive, etc. It is possible to obtain a semiconductor pressure transducer having good characteristics and no problems. Further, by making the thickness of the oxide film sufficiently thin, about 1 μm, the static pressure characteristics and temperature characteristics of the semiconductor pressure converter can be made sufficiently high. Therefore, as a semiconductor pressure transducer used for various purposes, a great deal of practical effects can be obtained.

[0013]

EXAMPLES Examples of the present invention will be described below.

According to the present invention, the pressure-sensitive pellets and the base are joined with the silicon oxide film which is the same constituent material as the pressure-sensitive pellets and the base. The details of the reason why they join each other are unknown. However, when the glass and the glass are brought into contact with each other, if the glass surface is sufficiently clean, the coefficient of friction becomes very large, and it is impossible to bond them so strongly that they cannot be separated without breaking the glass. Well known. It is also known that a silicon oxide film is also a kind of glass, and a natural oxide film layer is formed in a short time on a clean surface of silicon. Therefore, it is considered that the same phenomenon as in the glass bonding occurs even in the silicon bonding with the oxide film interposed therebetween. However, in the case of this silicon-to-silicon bond, it is not possible to bond due to the fact that very slight dirt such as oil is present on the surface, the bond surface is not smooth, or there is a slight amount of dust between the bond surfaces. However, the existence of the element makes the joining impossible.

As described above, the oxide film is an essential element for joining silicon, and the oxide film can be formed by a physical vapor deposition method such as a thermal oxidation method, a chemical vapor deposition method or a sputtering method. However, in order to bond silicon, it is necessary that the surface of the bonding surface after the oxide film is formed is a mirror surface. For example, as a result of forming the oxide film by a chemical vapor deposition method with improperly set conditions, the oxide film Bonding between silicon becomes difficult only by the presence of clusters of about 0.2 μm. By the way, in this way, without forming an oxide film positively, silicon is left in clean air such as in a clean room, or it is boiled in an oxidizing liquid such as aqua regia to form a natural oxide film. It is possible to join by just forming. The oxide film may be formed by doping the oxide film with P ₂ O ₅ , B ₂ O ₃ or the like by, for example, a chemical vapor deposition method.

The bonded body of the pressure-sensitive pellet and the base, which are bonded together with the oxide film interposed in this way, shows a high airtightness as it is and a considerably strong adhesive strength. It is possible to significantly increase the bonding strength by performing the heat treatment at. That is, according to the experiments by the present inventors, the bonded body is peeled off only by applying a pressure of about 5 kg / cm ² to the bonded surface of the bonded body, but after the bonded body is heat-treated at 200 ° C. for about 1 hour, , 15kg / cm ²
It was found that peeling did not occur even when the above-mentioned pressure was applied, and the element was broken at a site other than the bonding surface. It is generally known that silanol groups (Si-OH) formed on the surface of glass or an oxide film are dehydrated and condensed at 200 ° C. Considering this, it is considered that the increase in the degree of bonding is a result of the formation of (Si—OSi) bond by dehydration condensation of silanol groups on the surface of the oxide film or the natural oxide film.

Next, a concrete semiconductor pressure converter according to the present invention will be described. The pressure-sensitive pellets can be manufactured by directly using the conventionally known technology. For example, an n-type [111] silicon substrate whose both surfaces are polished is prepared, and a p-type resistance layer is formed by a diffusion method. After that, aluminum vapor-deposited on this substrate is patterned by using a photolithography technique to form a bridge circuit using the p-type resistance layer as a strain resistance gauge. Then, after forming the PSG protective film, the thin diaphragm surface is formed by the etching method. This gives a diameter of 8 mm and a thickness of 150
A pressure-sensitive pellet having a thickness of 400 μm and a size of 10 mm × 10 mm having a thin diaphragm surface of μm is prepared. The sensitivity of this pressure-sensitive pellet is set to a maximum pressure of 4 kg / cm ² .
Further, if the oxide film provided on the bonding surface is previously formed on the wafer by thermal oxidation or the like, it is convenient in the manufacturing process.

On the other hand, as the base, a silicon disk having an outer diameter of 14 mmφ, an inner diameter of 4 mmφ and a thickness of 3 mm is machined to be prepared, and the surface to be bonded is mirror-polished. This disk is heated at 1200 ° C. in an oxygen atmosphere to form an oxide film of 0.50 μm on the surface. The pressure-sensitive pellets and the base thus obtained were boiled with trichlene, washed with ultrasonic waves of acetone, and then washed with water, replaced with acetone, and cleaned with freon drying to obtain a state in which silanol groups were formed on the oxide film surface. obtain. Then, in a clean room, the surfaces to be joined were brought into contact with each other and lightly pressed to join them. Then, the joined body was put in an oven and heated at 200 ° C. for about 30 minutes.
Although a weight of 5 kg was applied to some of the samples during this heating, an essential difference such as the bonding force due to the presence or absence of this weight could not be detected.

The temperature change of the residual resistance at zero pressure of the semiconductor pressure converter thus obtained, the presence or absence of vacuum leak, and the element breakdown pressure were examined, and they all satisfied the intended specifications. Was confirmed. That is, the temperature change of the residual resistance is 2% in the range of -30 ° C to + 100 ° C.
It was confirmed that there was no leak even if the vacuum degree was 10 ^-9 Torr or less, and the breaking pressure was 10 kg / cm ² or more. Also, put this semiconductor pressure converter in a hydraulic container, and
A static pressure of 40 kg / cm ² was applied, and the difference in the equilibrium point of the resistance bridge from the case of normal pressure was examined, but it was about 0.01% and practically no problem.

On the other hand, the same pressure-sensitive pellets as those described above were used as an example of bonding with a natural oxide film interposed therebetween, and a silicon substrate machined and polished in the same manner as described above as a base was boiled in aqua regia for 1 hour. After that, it was washed with water and dried, and its surface was well wetted with water to form a natural oxide film, which was then contacted in a clean environment.
Also in this case, a considerably strong joined body could be obtained. Further, this joined body was heated in an electric furnace at 400 ° C. for 10 minutes to increase the joining strength. It was confirmed that the semiconductor pressure transducer obtained in this way also showed a very slight change in temperature and static pressure at the bridge equilibrium point and exhibited sufficient characteristics as a pressure sensor.

The present invention is not limited to the above embodiment. For example, as a method of forming an oxide film, a conventionally known technique can be appropriately used, and the film thickness thereof may be determined according to the specifications. Also, the oxide film thickness should be 5 μm or less, which is practically
About 0.6 μm is preferable. In short, the present invention can be variously modified and implemented without departing from the scope of the invention.

[0022]

As described above, according to the present invention, the silicon oxide film effectively acts as an adhesive layer between the pressure-sensitive pellet and the base to firmly bond the pressure-sensitive pellet and the base. It is possible to obtain a semiconductor pressure transducer having good characteristics without problems such as residual stress due to the adhesive. Further, by making the thickness of the oxide film sufficiently thin, about 1 μm, the static pressure characteristics and temperature characteristics of the semiconductor pressure converter can be made sufficiently high.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of a semiconductor pressure converter.

[Explanation of symbols]

1 ... Semiconductor crystal substrate, 2 ... Thin diaphragm surface, 3 ... Strain resistance gauge, 5 ... Electrode wiring, 6 ... Base.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shunji Shiramizu 1 Komukai Toshiba-cho, Sachi-ku, Kawasaki-shi, Kanagawa Stock company Toshiba Research Institute

Claims (3)

[Claims] 1. A semiconductor comprising bonding a pressure-sensitive pellet having a strain-resisting resistance gauge formed on a thin diaphragm surface to a base having a pressure introduction hole for introducing pressure to the thin diaphragm surface of the pressure-sensitive pellet at a central portion thereof. A method of manufacturing a pressure transducer, wherein the base is formed of the same material as the pressure-sensitive pellets, and the surfaces of the base and the pressure-sensitive pellets to be joined are mirror-polished, respectively, And the step of forming an oxide film on at least one of the surfaces to be joined of the pressure-sensitive pellets, the step of forming a silanol group on the surface of the oxide film, the base and the pressure-sensitive pellets directly without any foreign matter A method of manufacturing a semiconductor pressure transducer, comprising: a step of bringing them into contact with each other and joining them. 2. The method for manufacturing a semiconductor pressure converter according to claim 1, wherein the silanol group is formed by a washing treatment with water. 3. The method for manufacturing a semiconductor pressure converter according to claim 1, wherein the oxide film is an oxide of the same material as the pressure sensitive pellet and the base.