JPS63237480A - Manufacture of semiconductor pressure sensor - Google Patents

Abstract

PURPOSE:To decrease the irregularity of characteristics, and reduce the manufacturing cost, by isolating electrically and completely a piezo resistance layer from a first substrate with an insulating layer to stabilize the characteristics even at a high temperature, and forming a piezo resistance layer of single crystal on a diaphgram. CONSTITUTION:From the rear side of a second single crystal silicon substrate 4, an etching applying an anisotropic etching liquid whose main components are, for example, ethylene-diamine, pyrocatechol and water is performed to eliminate the second single crystal silicon substrate 4. In this process, the etching selectively progresses for an N-type conductivity region, and a piezo resistance layer 6, in which boron is diffused with high concentration, and a silicon nitride film 7 are left almost without being subjected to the etching. In this manner, a piezo resistance layer 6 of single crystal is formed on the silicon nitride film 7 as an insulating film serving as a diaphgram. A surface protecting film 9 and a wiring layer 10 composed of Al and the like are formed to constitute a semiconductor pressure sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method of manufacturing a semiconductor pressure sensor, and more particularly, to a method of manufacturing a semiconductor pressure sensor having a single crystal piezoresistive layer on an insulating film.

(Prior art) A diaphragm is formed by thinning a portion of a single crystal silicon substrate by utilizing the fact that the resistance value changes due to the piezoresistance effect when mechanical stress is applied. A semiconductor pressure sensor is used that measures pressure by forming a piezoresistive layer in the epitaxial layer by diffusion, deforming the piezoresistive layer by the pressure applied to the diaphragm, and detecting changes in resistance due to the piezoresistance effect. It is being

(Problems to be Solved by the Invention) However, according to the above-mentioned conventional semiconductor pressure sensor,
Electrical isolation between the single crystal silicon substrate and the piezoresistive layer is achieved by a P/N junction formed within the single crystal silicon substrate, and when such a sensor is used at high temperatures,
There has been a problem in that leakage current increases at the PN junction, making stable measurement difficult.

Furthermore, in a semiconductor pressure sensor as shown in Fig. 5,
Piezoresistive layer 10 formed on silicon oxide film 100
1 is formed into an island shape by etching polycrystalline silicon, which is normally formed by CVD or vapor deposition, into a desired shape by photolithography or the like, and the material is polycrystalline. Here, when comparing polycrystalline and single-crystal piezoresistive layers, a single-crystalline piezoresistance layer is preferable because it has higher sensitivity and can reduce variations in output characteristics. Conventionally, therefore, a technology has been proposed in which a single-crystal piezoresistive layer is formed by recrystallizing polycrystalline silicon. It is difficult to do so, and there arises the problem that the cost of recrystallization is high.

Furthermore, it has been difficult to inspect whether there is a defect in the airtightness of the reference pressure chamber provided in a conventional semiconductor pressure sensor.

(Objective of the Invention) The object of the invention is to solve the above-mentioned problems, and to form a single-crystal piezoresistive layer that can be completely electrically isolated from the substrate even at high temperatures and has small variations in characteristics at a relatively low cost. Another object of the present invention is to provide a method for manufacturing a semiconductor pressure sensor that can guarantee the airtightness of a reference pressure chamber and, more particularly, can easily detect poor airtightness of the reference pressure chamber.

(Means for Solving the Problems) The present invention has been made to achieve the above object, and includes a step of forming a recess on the main surface of a first substrate, and a step of forming a recess on the main surface of a semiconductor single crystal substrate. forming a piezoresistive layer by introducing impurities, and subsequently forming an insulating layer on the main surface; and forming the first layer in an inert gas atmosphere.
By joining the main surface of the substrate and the main surface of the semiconductor single crystal substrate, the same inert gas is injected into the space formed by the first substrate recess and the insulating layer which becomes the diaphragm of the semiconductor single crystal substrate. and etching from the other surface side of the semiconductor single crystal substrate,
The gist of the present invention is to provide a method for manufacturing a semiconductor pressure sensor, comprising the steps of forming the insulating layer serving as a diaphragm and a piezoresistive layer above the main surface of the first substrate.

(Example) An example embodying the present invention will be described below with reference to the drawings.

FIGS. 1(a) to 1(q) are sectional views for explaining the present invention in detail, and the manufacturing process thereof will be explained in order. In FIG. 1(a), 1 is a first single-crystal silicon substrate with a (100) plane, and 2 is a silicon oxide film (Si o
2). Using this silicon oxide film 2 as a mask, etching is performed using an anisotropic etching solution such as potassium hydroxide (KOH) to form a recess 3 as shown in FIG. The crystal plane is (
110), or may be made of Pyrex glass, sapphire, or the like with a recess formed therein.

On the other hand, as shown in the same figure (C), for example, the specific resistance is 3
~50cm N-type conductivity type with crystal plane (100)
Alternatively, a silicon oxide film 5 is formed in a predetermined region on the main surface of the second single-crystal silicon substrate 4 (110), and P-type impurities such as boron (B) are added to a high concentration using the silicon oxide film 5 as a mask. Inject and diffuse piezoresistive layer 6 <110>
Form in the direction.

Subsequently, after removing the silicon oxide film 5, the same figure (
As shown in d), a silicon nitride film (Si 3
N4>7 is formed, and a BPS 18 is roughly formed on this silicon nitride film 7. Furthermore, at this time, BPSGrI!
The surface of A8 is almost smooth.

Then, as shown in FIG. 2(e), the second single crystal silicon substrate 1 is aligned on the main surface of the first single crystal silicon substrate 1 using, for example, an infrared microscope so that the upper and lower patterns overlap as set. The BPSG film 8 formed on the substrate 4 is placed. At this time, the first and second single crystal silicon substrates 1 and 4 (
Alternatively, the peripheral portions of these wafers are temporarily bonded by melting and bonding them using a laser in helium gas at a predetermined pressure.

After that, about 1ooo' in helium gas at a predetermined pressure.
The BPSG film 8 is melted by heating to a temperature of 1°C, and both the 1st and 2nd single crystal silicon substrates 1 and 4 are bonded together. On this occasion,
Since the bonding between the two is performed in an atmosphere of helium gas at a predetermined pressure, helium gas at a predetermined pressure is filled in the recess 3 serving as a reference pressure chamber. Further, in this embodiment, a weight is placed on the substrate to ensure complete adhesion.

In addition, BPS is used as an adhesive (bonding) layer to bond the two.
Although the G film 8 is used, other low-melting glass or the like may be used, and the bonding between the two is not limited to melt bonding of low-melting glass. For example, the first single-crystal silicon substrate 1 The upper silicon oxide film 2 may be removed and bonding may be performed by so-called anodic bonding (7-no-decker bonding). Alternatively, they may be directly joined in a high-temperature furnace filled with helium gas at a predetermined pressure without temporary bonding. Roughly speaking, the BPSG film 8 for adhesion may not be formed over the entire surface of the silicon nitride film 7, but may be formed partially only on the adhesion portion. Further, the silicon nitride film 7 as an insulating film may be another insulating film such as a silicon oxide film.

Then, as shown in FIG. 4F, the ground surface (back surface) of the first single crystal silicon substrate 1 is covered with wax or the like (not shown), and the ground surface (back surface) of the second single crystal silicon substrate 4 is covered with wax or the like (not shown). ) side, for example, ethylenediamine (260 mfl>,
The second single-crystal silicon substrate 4 is etched away using an anisotropic etching solution mainly composed of pyrocaterol (45Q) and water (120ml). At this time, the etching selectively removes the N-type conductivity region. The piezoresistive layer 6 and the silicon nitride film 7 in which boron is diffused in a high concentration
remains almost unetched. In this way, a single-crystal piezoresistive layer 6 is formed on the silicon oxide film 7 serving as an insulating film serving as a diaphragm. And the same figure (
As shown in g), a surface protection film 9 and a wiring layer 10 made of A, IJ, etc. are formed to constitute a semiconductor pressure sensor.

In this way, according to this embodiment, the silicon nitride film 7 and the BP
The diaphragm composed of the SG film 8 can be formed almost smoothly over the first single crystal silicon substrate 1 above the recess 3 and around the recess 3, so that the surface facing the piezoresistive layer 6 can be formed almost smoothly. Since the recess 3 can be formed in the recess 3, the volume to be etched to form the recess 3 can be made relatively small, and a small semiconductor pressure sensor can be formed. Then, the piezoresistive layer 6, which is originally a single crystal, is formed on the silicon nitride film 7 without any recrystallization.
can be formed, so the sensitivity can be increased compared to a polycrystalline piezoresistive layer, the variation in characteristics is small, and the manufacturing cost can be reduced.

In addition, the semiconductor pressure sensor formed according to this embodiment can completely electrically separate the piezoresistive layer 6 from the first single crystal silicon substrate 1 by the silicon nitride film 7 or the like, and the semiconductor pressure sensor can be easily separated even when used at high temperatures. The characteristics become stable.

In addition, in the structure of conventional semiconductor pressure sensors, semiconductor components and other components are complexly contained within the package, so it is not possible to raise the temperature to a high temperature, and it is not possible to sufficiently exhaust moisture and other gases. The semiconductor pressure sensor of the example is 300
Since airtight sealing is performed in helium gas at a high temperature of ~1200° C., moisture and other gases are sufficiently discharged, and the characteristics are excellently stabilized.

In addition, in the structure of conventional semiconductor pressure sensors, the inside of the package is filled with helium gas when assembled, but in this embodiment, helium gas is filled in the wafer state, so it is possible to manufacture large quantities with the same precision and at low cost. can.

In the semiconductor pressure sensor manufactured in this way, the main surface of the first single crystal silicon substrate 1 and the second single crystal silicon substrate 4 are separated in the helium gas atmosphere.
By joining the main surfaces of the silicon nitride film 7 and the BPSG film 8, which become the diaphragm of the recess 3 of the first single crystal silicon substrate 1 and the second single crystal silicon substrate 4,
Since the space formed by this can be filled with helium gas, the presence or absence of airtightness defects in the recess 3 can be inspected using, for example, the device shown in FIG. 2 (helium leak detector).

That is, the first valve V1 (three-way valve) is installed in the chamber 11.
A vacuum pump 12 is connected via the second valve v2, and a mass spectrometer 13 is connected between the first valve v1 and the second valve v2 through the third valve V3. A vacuum pump 14 is piped through the analyzer 13. Further, one side of the first valve v1 is opened to the atmosphere, and three valves Vl, V2 . A pressure gauge 15 is provided in the middle of the pipe between V3.

Then, during inspection, the semiconductor pressure sensor wafer 16 manufactured as described above is placed into the chamber 11. At this time, the first valve V1 is switched to the atmosphere side, and the third valve V3 is closed. After storing the wafer 16, the first valve V1 is switched to the vacuum system, the second valve V2 is opened, and the chamber 11 is opened by the vacuum pump 12.
The pressure inside is set to a predetermined level, and then the second valve (2) is closed.

On the other hand, when the vacuum pump 14 makes the piping space between the third valve V3 and the vacuum pump 14 at a pressure equal to or lower than the pressure inside the chamber 11, the third valve V3 is opened. The gas is guided to a mass spectrometer 13.

At this time, if helium is not detected by the quality a analyzer 13, it is determined that the airtightness of the reference pressure chamber of this wafer 16 is maintained and that the wafer 16 is a good product. If helium is detected, it is determined that the airtightness of the reference pressure chambers of some of the chips in the wafer 16 is not maintained, and the wafer 16 is determined to be a defective product.

Thereafter, after closing the third valve (3) and switching the first valve (1) to the atmosphere side, the wafer 16 in the chamber 11 is taken out.

In addition, if you want to identify which chip of the wafer 16 that was found to be defective as a result of the above-mentioned inspection is defective, cut the defective wafer into 1/2 (half) and measure it again as described above to determine if it is defective. Repeat this until the chip is identified.

Therefore, the airtightness of the reference pressure chamber can be easily inspected online using the helium leak detector, and the airtightness can be guaranteed.

Note that the present invention is not limited to the embodiment described above. For example, in the embodiment described above, the thickness of the diaphragm can be adjusted by adjusting the thickness of the silicon nitride film 7, but the adjustment can be made as shown in FIG. You may also do this. That is,
A polycrystalline silicon layer or a recrystallized single-crystalline silicon layer 17 having an appropriate thermal expansion coefficient is formed on the silicon nitride film 7 of the second single-crystal silicon substrate 4 before bonding, and a BPSG film 8 is formed thereon. The thickness of the diaphragm may be arbitrarily adjusted depending on the thickness of the silicon layer 17.

Furthermore, although the pattern of the piezoresistive layer 6 is formed in advance,
P-type impurities may be diffused throughout the second single-crystal silicon substrate 4 from the main surface side to a predetermined thickness, and a predetermined pattern may be formed after the second single-crystal silicon substrate 4 is etched.

Roughly, in the explanation of the above example, it was omitted for the sake of brevity.
A circuit for processing the output of the semiconductor pressure sensor may be formed within the first single crystal silicon substrate 1. That is, FIG. 4 is a cross-sectional view showing, for example, a MOSFET as a component of the output processing circuit. In the figure, 18 is a P-well region formed in the first single crystal silicon substrate 1, 19. - N+ source diffusion region and drain diffusion region formed in the well region 18, 21 is a field insulating film, 22 and 23 are a source electrode and a train electrode, respectively;
Reference numeral 4 indicates the electrodes 1 to 25, and 25 indicates an insulating film, each of which is formed by a known semiconductor processing technique.

Further, the gas sealed in the recess 3 used in this invention may be an inert gas such as argon other than helium.
In short, any inert gas may be used as long as it does not have an adverse effect on each semiconductor material.

Effects of the Invention As described above, according to the present invention, the piezoresistive layer can be completely electrically separated from the first substrate by the insulating layer, its characteristics can be stabilized even at high temperatures, and there is no possibility of regeneration. Since a single-crystal piezoresistive layer can be formed on the diaphragm without crystallization, variations in characteristics can be reduced and manufacturing costs can be lowered. Therefore, by detecting the inert gas, the airtightness of the reference pressure chamber can be determined and the airtightness can be guaranteed, which is an excellent effect.

[Brief explanation of the drawing]

1(a) to (Q>) are sectional views for explaining the present invention in detail, FIG. 2 is a diagram showing a helium leak detector, FIG. 3 is a diagram for explaining another example, and FIG. 4 is a diagram for explaining a helium leak detector. 5 is a diagram for explaining another example, and FIG. 5 is a diagram for explaining a conventional semiconductor pressure sensor. 1 is a first single-crystal silicon substrate, 3 is a recessed portion, and 4 is a second single-crystal silicon substrate. A crystalline silicon substrate, 6 is a piezoresistive layer, 7 is a silicon nitride film, and 8 is a BPSG film. Patent applicant Nippondenso Co., Ltd. Agent Patent attorney On 1) Hironobu Figure 1

Claims (1)

[Claims] 1. Forming a recess on the main surface of the first substrate and introducing impurities from the main surface of the semiconductor single crystal substrate to form a piezoresistive layer, and then forming a piezoresistive layer on the main surface. and bonding the main surface of the first substrate and the main surface of the semiconductor single crystal substrate in an inert gas atmosphere.
a step of filling the inert gas into a space formed by the first substrate recess and the insulating layer that will become a diaphragm of the semiconductor single crystal substrate; and etching from the other surface side of the semiconductor single crystal substrate. A method for manufacturing a semiconductor pressure sensor, comprising the step of forming the insulating layer serving as a diaphragm and a piezoresistive layer above the main surface of the first substrate. 2. The method of manufacturing a semiconductor pressure sensor according to claim 1, wherein the insulating layer has a substantially smooth surface.