JPS592192B2 - handoutaiatsuriyokuhenkansouchi - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a semiconductor pressure transducer in which a strain resistance element is provided on a semiconductor substrate.

By applying semiconductor planar technology, a part of the silicon alloy and germanium semiconductor substrate is used as a strain plate.
This has led to the development of semiconductor pressure transducers in which a plurality of strain resistance elements are diffused. This type of strain resistance element can directly apply semiconductor bipolar integrated circuit technology, so it is smaller and has higher performance than conventional strain gauges attached to metal or strain gauge types. Moreover, the transducer can be integrated by incorporating a power supply stabilization circuit, an amplifier circuit, and an adjustment circuit. Therefore, as this type of semiconductor pressure transducer, one having a configuration as shown in the cross-sectional view in FIG. 1, for example, is generally used.

The semiconductor pressure transducer shown in FIG. 1 applies pressure using fluid, and is composed of a pressure transducer element 1 and a casing 2.
The pressure transducer element 1 is composed of a pressure transducer main body 3 that receives and responds to fluid pressure P, and a support body 4 for fixing the main body 3. Further, the semiconductor pressure transducer main body 3 has a thin wall portion 5 at the center of one side of the n-type silicon single crystal plate, and this serves as a pressure receiving membrane that receives fluid pressure. A plurality of P-type diffusion resistance layers 6 are provided on the other surface of the pressure-receiving film 5 in accordance with the crystal orientation, and pressure is detected by changes in the piezoresistance. According to the distortion of the pressure-receiving film 5 due to the pressure P, the detection circuit is constructed by forming a half-bridge or full-bridge circuit of these diffusion layers 6 by utilizing the anisotropy of the change in the diffusion resistance value. I can do it. In FIG. 1, the metal layer 8 provided on the insulating film T serves as an internal connection 9 between the diffused resistance layers 6 or an electrode lead terminal 9a to the outside. The silicon pressure transducer configured in this way can be operated as a pressure gauge in various pressure ranges by changing the thickness of the pressure-receiving membrane 5, but the characteristics as a pressure gauge, namely pressure sensitivity, linearity, Breakage strength is pressure receiving membrane 5
depends on thinning technology. Usually, chemical etching or electrolytic etching is used to thin the pressure receiving film 5 of a silicon single crystal plate. Even if one of these methods is adopted, unless the structure is such that only the pressure-receiving membrane 5 in the thin wall part is effectively subjected to the strain force by the fluid pressure P, and the thick part in the peripheral part is not deformed, the measuring instrument will not work properly. High accuracy cannot be expected.

For example, if the diameter of the pressure-receiving membrane is a, the thickness of the pressure-receiving membrane 5 is h, and the fluid pressure is P, then the change value ΔR of the diffusion resistance R with respect to the pressure P has the following relationship.

Let us now assume that the thickness of the thick part around the diameter a of the pressure-receiving membrane 5 is H, and upon receiving the fluid pressure, the thick part will also be strained with a diameter of a + △a, and △
Assuming that the resistance changes by R', equation (1) becomes,
This will be affected by this amount, and inaccuracies will be introduced into the pressure characteristics.

Roughly analogizing, if H = 2h, it is considered that the influence of ΔR due to the deformation of the thick portion will be affected by only one, and if H = 3.3h, it will be reduced to 1/10. It has been experimentally found that H≧3.3h or more is required in order to sufficiently compensate for the nonlinearity of the characteristics with the circuit. On the other hand, single-crystal silicon has extremely high rigidity, and processing techniques such as mechanical polishing cannot achieve high precision comparable to IC technology.

Further, in the photoetching method, which is a chemical etching method often used in integrated circuit (IC) technology, high precision can be obtained, but deep etching is difficult, and the depth of etching is at most about 200 μm. This is because the silicon single crystal plate is an extremely stable substance against acids and chemicals. Therefore, to illustrate the corrosion resistance of chemical etching masks used in conventional IC technology,
It will look like the table. The etching solution for the silicon single crystal was HF:HNO3=1:5, which is used in ordinary IC technology. As can be seen from Table 1, when a silicon nitride film is used as a mask, the etching is performed to a depth of, for example, 200 mm.
It is also excellent in that it can be etched down to the μm level. Therefore, we used a silicon substrate with a thickness of about 200 jtm, and
If a silicon nitride (Si3N4) film of about 000A is used as a mask, it is possible to make the thickness h of the pressure receiving surface as thin as possible with respect to the thick portion H around the pressure receiving surface.
However, there are two major practical difficulties here. First, when manufacturing a pressure transducer element for high pressure, it is necessary to increase the thickness h of the pressure receiving membrane, and the peripheral thick part H must also be at least 3.3 times thicker than this. It is a must. In other words, it is necessary to use a very thick silicon substrate and perform deeper etching. In this case, it would be theoretically possible to make the silicon nitride film thicker, but
As a result of experiments, it was found that when a silicon nitride film of 2000λ or more is coated on a silicon substrate, cracks occur in various places due to differences in thermal expansion coefficients. Another difficulty is the difficulty in handling silicon substrates. As is well known, I
The industrial advantage of C technology is that it allows as many devices as possible to be formed on a large silicon substrate, increasing the probability of yield. In this respect, it is desirable to make the silicon substrate as large as possible to increase the yield of the device. In recent IC technology, it has become common to use a material with a diameter of 50 mm as a silicon substrate, and there is a trend toward larger sizes of silicon substrates of 75 mm or more. In this case, as the wafer diameter increases, unless the material thickness is made slightly thicker, the probability of breakage during the process increases.
00 μm or more is required.

Therefore, using the silicon nitride film mentioned above as an etching mask, H
The range of the pressure transducing element that can take /H3.3 or more is 50φ
For wafers, there is only one case where H=300μMlh=90μm, and for other requirements, the diameter of the substrate is 40φ, 30φ
Unless you use something small like this, you won't be able to make it. The present invention has been made to address the above-mentioned points. For example, even when a large silicon substrate of 50φ or more is used, it is possible to form a pressure-receiving film extremely well and to achieve stable and high performance semiconductor pressure. The purpose of the present invention is to provide a conversion device.

That is, the present invention provides a semiconductor substrate having a thinner central portion and a peripheral portion thicker than the central portion, a resistive layer provided on one surface of the thin portion of the substrate, and an electrode connected to the resistive layer. In the semiconductor pressure transducer device, a Teflon film is provided on the resistance layer forming surface in an area larger than the thin part, and a Teflon film is provided in the thick part on the other surface. . By forming a Teflon film on both sides of a semiconductor substrate in this way, it is possible to protect the semiconductor substrate or metal wiring, as well as to protect the semiconductor substrate and the Teflon film due to the difference in coefficient of thermal expansion. It is possible to reduce distortion, and by forming a Teflon film on the thick part on the side where the resistive layer is not provided, it is possible to use a thick semiconductor substrate and to deeply etch this substrate.
Even when using the above large-sized semiconductor substrate, it is possible to form a good pressure-receiving film.

Embodiments of the present invention will be described below with reference to the drawings.

For example, the pressure transducer main body 11 is manufactured by the steps shown in FIGS. 2a to 2e. First, a silicon oxide (SiO2) film 12 is placed on one side of an n-type silicon mold plate 11 with a thickness of 500 [μm].
Then, a silicon nitride (Si2N4) film 13 is formed on the other surface (FIG. 2a). Next, the SiO2 film 12 is selectively removed, and boron B is diffused into the removed portion to form the P-type resistance layer 1.
4 (Figure 2b). And this P type resistance layer 14
evaporate aluminum 15 in order to take out the electrode from the
This aluminum 15 is selectively removed (Fig. 2c)
. After this, the surface on which aluminum 15 was formed and the Si3N
4. A Teflon film 16 was applied to the surface on which the 1°3 film was formed by 12.5°.
When attaching this Teflon film 16 (FIG. 2 d), the pressure transducer body U is first surface treated in, for example, an aminosilane solution, and then heated in air to about 140°C to activate the surface. After that, the Teflon film 16 is brought into close contact with both sides of the substrate and heated in air at about 3500 C to adhere it. Next, a chemical etching window 17 for forming a pressure-receiving film is formed on one side (the side where the P-type resistor layer 14 is not provided) on which the Teflon film 16 is coated in this way, and the other side (the side where the P-type resistor layer 14 is not provided). From the side where the aluminum layer 15 is provided, the wiring window 18 and the adhesive surface 19 for fixing the conversion element body 11 are formed.This step can also be performed by a normal semiconductor photoresist process.However, liquid photoresist Instead of applying a resist, it is better to use a photoresist film with a thickness of about 40 to 60 μm, such as Liston or Fodar. It is pressed and bonded on a hot plate at about 90°C with a pressure of about 40k9/cm2.If this is exposed to ultraviolet light using a mask and developed in a methylene chloride solution, the desired shape can be easily obtained. The resist film can be removed.The Teflon film 1 on the window portion
Gas plasma method is the most effective method for removing No. 6. That is, 500 to 600 in 02 atmosphere of about 1 t0rr.
The Teflon film is etched by a high voltage discharge of about 30 V, and a window 18 can be formed as shown in FIG. 2e. It should be noted here that the plasma etching process also removes the Si3N4 film 13 previously formed on the etched surface of the conversion element at the same time as the Teflon film 16, thereby exposing the silicon surface. It should be noted that deep chemical etching can be performed by using the Teflon film 16 alone without applying the Si3N4 film 13 in advance, but site etching can be reduced by overlapping the Si3N4 film 13 of 2000λ and the Teflon film 16 in the etching window 17, for example. , it is possible to form a pressure-receiving film 20 with sharp edges, and its characteristics are also improved. Further, as in the above embodiment, the Teflon film 16 is also provided on the diffusion resistor 14 side of the conversion element main body 11 because the diffusion layer 14
Although it has the advantage that it is useful for bonding between the Teflon film 16 and the silicon substrate 11 and for protecting metal wiring, the main purpose of the present invention is to reduce the strain caused by the difference in thermal expansion coefficient between the Teflon film 16 and the silicon substrate 11 on both sides. The purpose is to reduce this by coating with a Teflon film 16. In particular, when etching the silicon substrate 11, the success or failure of etching is influenced by the strain applied to the silicon substrate 11. Furthermore, after protecting the side surface of the diffusion layer of the conversion element body u on which the window portion 18 is formed with the Teflon film 16 using, for example, wax, etching processing 5 is performed for about 120 minutes in a solution of, for example, HF:HNO3l:5 ( Figure 2 e).
Etching of the silicon substrate 11 progresses by about 480 ttm, and the thickness of the pressure receiving film 20 can be reduced to 20 μm. As shown in FIG. 3, the conversion element body thus formed is fixed to the support 21 with epoxy adhesive O or low melting point glass using the adhesive portion 19 described above, and pressure conversion can be performed by connecting a predetermined wiring 22 to the ponding terminal 23. Element 30
is completed. The peripheral wall thickness of the pressure transducer body illustrated here is 500 μm, and the thickness of the pressure receiving membrane 20 is 20 μm.
Therefore, H/h is actually 25, and the deterioration of the characteristics due to the deformation of the peripheral thick portion due to pressure is reduced to the extent that it can be ignored. Note that the bonding terminal 23 is fixed to a package plate 24 that fixes the bonding terminal 23, and is connected to a lead 25 via this package plate 24. The pressure transducer element 30 with the pressure transducer main body 11 fixed to the support body 21 in this manner is inserted into the casing specified in the conventional example, and is pressurized with fluid from the pressure receiving surface 20 side. A pressure transducer is thus obtained. Note that the peripheral wall thickness of the pressure transducer main body 11 shown in the above embodiment is 500 [μm].
], and since the thickness of the pressure-receiving membrane 20 is 20 [μm], H/h is actually 25, and the deterioration in resistance caused by the deformation of the peripheral thick portion due to the pressure P can be reduced to a negligible extent.

Further, although a support is required in the above embodiment, it is not necessarily necessary, and the shape of the package plate is not limited to this.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view for explaining the structure of a conventional semiconductor pressure transducer device, FIG. 2 is a process schematic diagram showing the manufacturing process of a semiconductor pressure transducer main body according to the present invention, and FIG.
The figure is a sectional view schematically showing the structure of a semiconductor pressure transducer according to an embodiment of the present invention. 11... Pressure conversion element body, 16...
Teflon membrane, 21...Support, 30...
・Pressure conversion element.

Claims (1)

[Claims] 1. A semiconductor substrate having a thinner central portion and a peripheral portion thicker than the central portion, a resistive layer provided on one surface of the thin portion of the substrate, and an electrode means connected to the resistive layer. In the semiconductor pressure device, a Teflon film is provided on the resistance layer forming surface in an area larger than the thin part, and a Teflon film is provided in the thick part on the other surface. Device.