JPS6254477A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To enable the use at a high temperature by forming an electrical insulator portion which electrically isolates the surroundings of the pressure-sensitive element region, and etching from the opposite principal surface of the semiconductor substrate to the insulator portion to form a pressure-receiving portion. CONSTITUTION:N<+> ions are driven into one principal surface of a silicon substrate 1, and N<+> ions are driven also into the other principal surface in the portion except a region 4 in which the pressure-receiving portion is to be formed; this is heat-treated in a N2 atmosphere, forming silicon nitride layers 2, 3. A P-type monocrystalline silicon layer 5 is grown on the upper surface of the second stop layer 2, and N<+> ions are driven, forming a nitride silicon layer 6. A silicon oxide film 7 is formed, the surroundings of each element portion are surrounded with the silicon oxide film 7 and the silicon nitride layer 6, an insulating film 9 is formed on the substrate surface, and a contact hole portion 9A is opened to form a wiring layer 10. Then, the monocrystalline silicon substrate 1 is etched with an alkaline liquid, etching is performed to the second stop layer 2 in the region 4 in which the pressure-receiving portion is to be formed, until etching automatically terminates. With this, the leakage current is prevented, enabling the use in a high-temperature atmosphere.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing a semiconductor pressure sensor that is suitable for mass production and that can be used in a high temperature atmosphere.

[Conventional technology]

Conventionally, as a semiconductor pressure sensor, one is known in which a semiconductor pressure sensitive element (strain gauge) is formed on a semiconductor diaphragm by a method such as diffusion, and a pressure change is detected as a change in resistance value due to a piezoresistive effect. Here, the accuracy of the pressure sensor depends on the parallelism of both sides of the diaphragm and its uniformity.

[Problem that the invention seeks to solve]

However, the conventional pressure sensor described above has the following drawbacks.

That is, industrial mass production is difficult. This is because it is difficult to control the process of manufacturing both surfaces of the diaphragm with good parallelism and uniformity. Generally, a diaphragm is formed by etching a semiconductor substrate to a desired thickness, but the etching rate is extremely difficult to control because it depends on the temperature, agitation state, changes in composition, etc. of the etching solution.

Furthermore, since piezoresistors used as strain gauges are electrically isolated by a Pn junction, it is difficult to use them at high temperatures due to the nature of semiconductors.

In view of the above points, the present invention is capable of accurately controlling the parallelism of the pressure receiving portions to make the thickness of the pressure receiving portions between each chip uniform, and moreover, effectively electrically isolating the periphery of the pressure sensitive element area. An object of the present invention is to provide a method for manufacturing a semiconductor pressure sensor that can be used at high temperatures.

[Means for solving problems]

Therefore, the present invention includes a step of forming an insulating layer inside one main surface of a semiconductor substrate by ion implantation, and a step of forming an insulating layer on the inside of one main surface of a semiconductor substrate, and surrounding at least a pressure-sensitive element region of the semiconductor substrate region on the one main surface above this insulating layer. a step of forming an electrical insulator section for electrically isolating the semiconductor substrate; and a step of etching a region corresponding to the pressure sensitive element region from the opposite main surface of the semiconductor substrate to the insulator layer to form a pressure receiving section. It is characterized by being prepared.

〔Example〕

Next, in order to better understand the present invention, the present invention will be specifically explained using examples shown in the drawings. FIG. 1(A) shows a P-type wheel crystal silicon substrate 1. FIG. FIG. 1(B) shows that N0 ions (nitrogen ions) are accelerated and implanted into the entire surface of one main surface of the silicon substrate 1 so as to be distributed at a predetermined depth. Pressure-receiving forming area 4 where a pressure-receiving part should also be formed on the other main surface.
The silicon nitride layers 2 and 3, which are insulator layers, are formed by implanting N+ ions into the outer portion under the above conditions and then heat-treating preferably at 1200° C. for 2 to 3 hours in an N2 atmosphere. Here, the silicon nitride layer 2 is the second stop layer, and the silicon nitride layer 3 is the first stop layer. This stop layer is uniformly formed inside the single-crystal silicon substrate 1 with great precision, and the surface of the substrate 1 is in a single-crystal state. Subsequently, P-type wheel crystal silicon N5 is epitaxially grown on the upper surface of the second stop layer 2 of the substrate 1, as shown in FIG. 1(C). The film thickness of this silicon N5 can be arbitrarily selected depending on the pressure measurement range of the pressure sensor or the required pressure sensitivity.

Subsequently, as shown in FIG. 1(D), N2 ions were implanted into the epitaxial P-type wheel crystal 9937 layer 5 so as to be distributed at a predetermined depth, and heat-treated in a N2 atmosphere. This was done to form silicon nitride N6, which serves as an electrically insulating layer. Therefore, monocrystalline silicon@5A exists on the top of the silicon nitride layer 6, and monocrystalline silicon layer 5B exists on the bottom.

Next, as shown in FIG. 1(E) or FIG. 2, a pressure sensitive element region (for example, a piezoresistive element) 8 and a detection processing circuit for compensating and amplifying the output of the pressure sensitive element are formed on the same substrate. In this case, the portion excluding the circuit component region a (that is, the shaded portion b in FIG. 2) is selectively oxidized by the commonly used LOCO5 method to reach the silicon nitride layer 6 to become an electrical insulator portion. A silicon oxide film 7 was formed so that each element portion was completely surrounded by the silicon oxide film 7 and the silicon nitride layer 6. Note that it is also possible to diffuse impurities to a predetermined concentration into the element part 8 after forming the piezoresistive element part, but if the concentration of the P-type epitaxial N5 or 5A is controlled in advance before the formation of the element part 8, the above-mentioned effect can be achieved. This is desirable because elements with a desired impurity concentration can be formed at the same time during the selective oxidation of the element, which simplifies and makes the element formation process uniform.

Subsequently, an insulating film 9 such as a silicon oxide film or a silicon nitride film is formed on the surface of the substrate, and then a contact hole 9A is formed in the insulating film 9 to form a wiring layer 10 for electrical connection to the piezoresistive element 8. was formed. As a material for this wiring layer 10, /l, or a high melting point metal such as molybdenum silicide, tungsten silicide, molybdenum, or tungsten is used.

Subsequently, a silicon nitride film 11 was formed as a passivation film by plasma CVD, and a contact hole 11A for external extraction was opened. In this way, as a passivation film, a nitride film (S!: +N4 film) is used as in this example.
By using silicon (Si), the thermal expansion coefficient can be matched with that of silicon (Si), making it possible to use it in an even higher temperature atmosphere. In addition, 5io, which has a thermal expansion coefficient similar to that of silicon, is also available.
Other insulating films such as zJI* may be selected.

Next, the single crystal silicon substrate 1 is etched in an alkaline etching solution such as KOH or other silicon etching solution. At this time, the first stop layer 3 prevents the etching from progressing in the area outside the planned pressure receiving part forming area 4, while in the pressure receiving part forming area 4, etching is completed up to the second stop layer 2 and the etching is automatically completed. Etching is performed over the entire surface of the pressure receiving portion forming region 4 with good parallelism. Therefore, as shown in FIG. 1 (F), the pressure receiving part 1 is a diaphragm that moves (deforms) due to the pressure of the object to be detected.
2. And the support part 13 of the pressure receiving part 12 is formed.

Note that the pressure sensor detects the pressure by utilizing the fact that the resistance of the pressure sensing element region 8 changes due to the piezoresistance effect due to the deformation of the pressure receiving portion 12. FIG. 2 is a schematic plan view in the middle of the process of FIG. 1(F), showing an example of a pattern of the selectively oxidized silicon oxide film 7 (slope portion b).

In this embodiment, nitrogen ions were used for ion implantation, but it is of course possible to achieve the same results by using oxygen ions, carbon ions, etc. Alternatively, the first stop layer 3 may be formed by 5i on the surface of the substrate 1 instead of by ion implantation.
nz film, Si3N4 film.

A 1 z O! It is also possible to form the first stop layer by forming a film or the like and using photolithography. Further, as is clear from the gist of the present invention, even if the P-type silicon is replaced with n-type silicon and the n-type silicon is replaced with P-type silicon in the above embodiments, there is no change in the operation. Further, the stop layer does not necessarily have to be a layer that is not etched with a silicon etching solution, and can serve as a stop layer if the etching rate is much lower than that of the silicon substrate. Further, in the above embodiment, the P-type diffusion layer 8 was provided as a strain gauge, but the diffusion layer 8 may not be provided and other elements may be used to detect the strain deformation of the diaphragm made of silicon.

Next, FIG. 3 shows another embodiment of the present invention.

In this example, instead of forming the thick epitaxial layer 5 as in the previous example, a very thin epitaxial layer is formed, or no epitaxial layer is formed at all. One insulating film that also serves as the external insulating layer 6 is provided inside the silicon substrate.

That is, by performing heat treatment on the P-type wheel crystal silicon substrate 101 after implanting N ions to a predetermined depth from one principal surface and the opposite principal surface, a first silicon nitride layer is formed.
A silicon oxide layer that forms the stop J'W 103 and the second stop layer 102 and selectively oxidizes the silicon substrate region (or including the epitaxial layer) above the second stop layer 102 to reach the second stop layer 102. 104 and a pressure sensitive element region 105 are formed. Note that 106 is an insulating film, 107 is a wiring layer, 108 is a passivation film, and 10
9 is a pressure receiving part, and 110 is a support part of the pressure receiving part 109. The method of forming these is the same as in the previous embodiment.

According to this embodiment, the wall thickness of the pressure receiving portion can be made thinner, and the pressure sensor can be further miniaturized.

〔Effect of the invention〕

As described above, in the method of the present invention, a predetermined stop layer is formed in advance in the semiconductor substrate and this substrate is etched, so the thickness and parallelism of the pressure receiving part are determined by the ion implantation layer. Not only is control extremely easy, but the etching is automatically terminated when the desired thickness of the pressure-receiving portion is reached, making it possible to manufacture a large number of devices with uniform characteristics. Furthermore, in the method using the stop layer of the present invention, even if several wafers with different thicknesses of pressure receiving parts, such as 20μ and 25μ, are mixed, etching can be performed automatically on a large number of wafers with the same etching accuracy. As a result, the same process can be performed, and as a result, a large number of semiconductor dungeon frames can be manufactured with high precision.

Furthermore, since the periphery of the pressure-sensitive element area is completely electrically isolated by the electrical insulator, leakage current from the pressure-sensitive element area can be eliminated, making it possible to use it in a high-temperature atmosphere.

[Brief explanation of the drawing]

FIGS. 1(A) to (F) are cross-sectional views showing the manufacturing process according to an embodiment of the present invention, FIG. 2 is a schematic plan view used to explain the method of the present invention, and FIG. FIG. 1.101... Single crystal silicon substrate, 2,102...
- A silicon nitride layer (second stop layer) forming an insulator layer. 3.103...Silicon nitride layer (first stop layer), 6.
...Silicon nitride layer, 7.104...Silicon oxide film forming the main part of electrical insulator section, 8.105...Pressure sensitive element region, 9,106...Insulating film, 10,107...・・・
Wiring layer, 12, 109...pressure receiving part. (A
(B) (E)
(F) 8 Moisture L God, Be Figure 1

Claims (1)

[Claims] A step of forming an insulating layer inside one principal surface of the semiconductor substrate by ion implantation, and electrically connecting at least the area around the pressure-sensitive element region of the semiconductor substrate region of the one principal surface above the insulating layer. The present invention is characterized by comprising a step of forming a separating electrical insulator portion, and a step of etching a region corresponding to the pressure sensitive element region from the opposite main surface of the semiconductor substrate to the insulator layer to form a pressure receiving portion. A method for manufacturing a semiconductor pressure sensor.