JPH0578950B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a pressure sensing device formed on a semiconductor substrate.

[Conventional technology]

Pressure sensing devices using semiconductors have been proposed in the past, but these devices utilize the strain resistance effect of semiconductor devices such as silicon. That is, 400~
A resistor is formed by a PN junction on a silicon substrate with a thickness of about 600 μm, and the portion of the semiconductor substrate where this resistor is formed is etched until it becomes a thin film of about 20 to 50 μm. Usually, this semiconductor substrate is fixed to a device case using low melting point glass or the like, and a hole is formed in the etched portion to obtain a reference pressure, thereby constructing a pressure sensing device.

With this configuration, the thinly processed portion of the semiconductor substrate is easily deformed by pressure, and pressure is detected by detecting a change in resistance value due to this deformation strain.

[Problem that the invention seeks to solve]

In the conventional semiconductor pressure sensing device described above, the semiconductor substrate is fixed to the device case to form a hole for obtaining the reference pressure. However, because the thermal expansion coefficients of the silicon substrate and the device case are different, Thermal strain occurs in the pressure sensing part due to temperature changes,
This makes it impossible to accurately detect the desired pressure, leading to pressure detection errors.

Additionally, in the past, nitric acid (HNO ₃ ),
Because the treatment is carried out for a long time (4 to 6 hours) using a mixture of hydrofluoric acid (HF), hydrazine (N ₂ H ₂ ), and water (H ₂ O), the thickness of the thin film is This must be controlled by adjusting the concentration, temperature, processing time, etc. of the mixed liquid, which is extremely difficult to control, and there is also the problem that variations occur in the thickness of the thin film, which causes pressure detection errors.

[Means for solving problems]

An object of the present invention is to be able to form a thin film of a pressure sensing part by controlling the thickness of the pressure sensing part with high precision according to the working pressure range;
Furthermore, it is an object of the present invention to provide a method for manufacturing a semiconductor pressure sensing device that can prevent thermal strain from occurring in the thin film and perform highly accurate pressure sensing.

A method for manufacturing a semiconductor pressure sensing device according to the present invention includes the steps of selectively forming a semiconductor region of an opposite conductivity type as a first electrode on a semiconductor substrate of one conductivity type, and excluding a central portion of the semiconductor region. forming a first insulating film from a peripheral portion to the semiconductor substrate; forming a second insulating film covering the central portion of the semiconductor region and extending over the first insulating film; forming a conductive layer as a second electrode covering the entire surface of the second insulating film and extending over the first insulating film; and forming a conductive layer on a part of the conductive layer. forming an opening reaching an insulating film; and removing the second insulating film through the opening by a stylus method to create a space between the conductor layer, the semiconductor region, and the first insulating film. and a step of sealing the opening formed in the conductor film with a third insulating film.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIGS. 1a and 1b are a plan view and a sectional view taken along the line BB of a semiconductor pressure sensing device manufactured by a manufacturing method according to an embodiment of the present invention.First, the structure of the device will be explained.

As shown in the figure, an N-type well 3 is formed on a semiconductor substrate 1.
In this N-type well 3, a square P ⁺ -type conductive layer 15 with a side of about 1 mm is formed as a first electrode in a region defined by a silicon oxide film 5 as a field insulating film. There is. In addition, a platinum thin film 9, which is a second electrode, is formed between this P ⁺ type conductive layer 15 and a void 21 and insulated by an acid-resistant silicon nitride film 6, and the first electrode 15 and the second electrode are insulated. The electrode 9 constitutes a capacitor.

In addition, CVD silicon oxide film 11, low concentration PSG
depositing a film 13 and a CVD silicon nitride film 14;
The structure is such that the opening 20 formed in the platinum thin film 9 is sealed and the void 21 is sealed.

FIGS. 2a to 2f are cross-sectional views for explaining the manufacturing method of the pressure sensing device in the order of steps. In addition, this example also explains the formation process of the MOS transistor that constitutes the peripheral circuit for pressure calculation, and S ₁
indicates the MOS transistor area, and _S2 indicates the pressure sensing device area.

First, a silicon oxide film (not shown) with a thickness of about 8000 Å is formed on the semiconductor substrate 1, and windows are selectively opened in this silicon oxide film by photolithography. Thereafter, boron and phosphorus are selectively introduced into the semiconductor substrate 1 by ion implantation, a silicon nitride film (not shown) is deposited to a thickness of 1000 Å, and windows are selectively opened in this silicon oxide film by photolithography. Then, a second boron ion implantation is performed, and then
The semiconductor substrate 1 is oxidized using the LOCOS method to form a silicon oxide film 5 as a field insulating film as shown in FIG. As a result, the semiconductor substrate 1 has a P type well 2, an N type well 3, and a P ⁺ type conductive layer 4.
are formed simultaneously. Furthermore, a third boron ion is selectively implanted by photolithography, and heat treatment is performed to form a P ⁺ type conductive layer 15 as a first electrode in the pressure sensing device region _S2 .

Next, as shown in Figure b, a silicon oxide film (not shown) of about 100 Å is formed on the semiconductor substrate 1, and then an acid-resistant silicon nitride film of about 1000 Å is deposited at room temperature, and this is patterned by photolithography. After that, a dry etching method is used to selectively leave the silicon nitride film 6. Furthermore, after this, a weakly acidic CVD silicon oxide film is deposited to a thickness of about 1.0 μm, and patterned by photolithography so as to cover the P ⁺ type conductive layer 15 to form a CVD silicon oxide film 7.

Next, as shown in figure c, the MOS transistor area is
A case oxide film 10 of the MOS transistor configured in _S1 is formed, and then a polysilicon film is formed.
After depositing about 2000 Å, a polysilicon film 8 is selectively formed by photolithography. Then, a platinum thin film 9 of about 3000 Å is formed by sputtering, and then heat treated at 500 to 600° C. to convert the platinum thin film 9 formed on the polysilicon film 8 into platinum silicide. Thereafter, a CVD silicon oxide film (not shown) is used to cover the platinum thin film 9 as the second electrode in the pressure sensing device area _S2 , and a mixed solution of nitric acid and hydrochloric acid is used to cover the exposed platinum thin film 9. remove,
As a result, a platinum silicide film 9a serving as the gate electrode of the MOS transistor is formed.

Next, as shown in FIG. d, a silicon nitride film 10 is formed.
The silicon nitride film 10 deposited on the platinum thin film 9 is patterned. Then, a CVD silicon oxide film (not shown) is deposited and selectively opened, and using this CVD silicon oxide film as a mask, the platinum thin film 9 is selectively opened using a mixed solution of nitric acid and hydrochloric acid. Division 20 is established.

In addition, the MOS transistor area _S1 includes P type,
A P-type source/drain region 22 and an N-type source/drain region 23 each doped with an N-type impurity are formed to constitute a P-channel MOS transistor and an N-channel MOS transistor, respectively.

Next, as shown in Figure e, an ultrasonic etching bath containing buffered hydrofluoric acid etching solution was used.
The above as a mask deposited on the platinum thin film 9
The CVD silicon oxide film 7 formed under the CVD silicon oxide film and the platinum thin film 9 is removed by etching through the opening 20 to form a void 21. After that, a CVD silicon oxide film is deposited and selectively etched using photolithography to perform CVD
A silicon oxide film 11 is formed to a thickness of about 1.0 μm. At this time, the opening 20 of the platinum thin film 9 is sealed and the air is
Seal 21.

After that, a contact part is opened in the CVD silicon oxide film 11, and then a 1.5 μm thick aluminum thin film is formed.
The aluminum electrode 1 is deposited by sputtering and then selectively removed.
2.

Next, as shown in figure f, the low concentration PSG film 13 and
A CVD silicon nitride film 14 is deposited, and then windows are selectively opened using photolithography to complete the pressure sensing device.

According to this configuration, the capacitance change due to deformation when the second electrode 9 is subjected to pressure is detected, and this is sent as an electric signal to the peripheral circuit for pressure calculation, where the difference between the reference capacitance and the detected capacitance is detected. Pressure can be detected by detecting and performing calculations. At this time, by simultaneously detecting the gas expansion rate of the air 21 due to temperature changes, capacity changes due to temperature changes can be excluded.
Only pure pressure changes can be detected.

Incidentally, according to the pressure sensing device manufactured according to this example, it is possible to detect external pressures of 0 to 1.0 kg/cm ² with high accuracy.

Further, according to this embodiment, the P ⁺ type conductive layer 15 formed on the semiconductor substrate 1 is used as the first electrode, and the platinum thin film 9 is used as the second electrode, forming a variable capacitance structure sandwiching the air 21. The thickness of the platinum thin film 9 can be easily and accurately and uniformly formed by sputtering according to the working pressure range, and pressure detection accuracy and sensitivity can be improved.

Furthermore, since the cavity 21 for obtaining the reference pressure is formed on the same semiconductor substrate 21, it can be easily assembled into an assembly case or the like. Furthermore, since a change in capacitance is used for pressure detection here, there is no substrate distortion due to a difference in thermal expansion between the case and the substrate due to a temperature change, and detection accuracy can be maintained at a high level.

In addition, in the manufacturing method of this embodiment, since the pressure sensing device and the MOS transistors of the pressure calculation peripheral circuit are configured on the same semiconductor substrate 1, the circuit wiring between them can be shortened, and the wiring capacitance and wiring can be reduced. The resistance can be reduced and the detection signal will not be adversely affected.

Here, by appropriately changing the thickness of the platinum thin film and the area of the void, it is possible to detect pressure in an arbitrary range.

〔Effect of the invention〕

As explained above, the pressure sensing device manufactured according to the present invention has a variable pressure sensing device in which a conductive layer formed on a semiconductor substrate is used as a first electrode, and a thin metal film placed opposite to this with an air gap is used as a second electrode. Since it has a capacitive structure, there is no detection error due to the difference in thermal expansion coefficient with the case, etc., and the metal thin film can be formed with a highly accurate film thickness by sputtering method etc.
This makes it possible to improve pressure detection accuracy and sensitivity, and to freely set the detection pressure range over a wide range.

Further, according to the method of the present invention, it can be manufactured without requiring special steps, and a low-cost semiconductor pressure sensing device can be easily obtained.

[Brief explanation of drawings]

Figures 1a and 1b are a plan view and a sectional view taken along line BB of a device manufactured by the method of an embodiment of the present invention;
FIGS. 2a to 2f are cross-sectional views showing the present manufacturing method in the order of steps. 1... Semiconductor substrate, 2... P-type well, 3...
N type well, 4...P ⁺ type conductive layer, 5... silicon oxide film, 6... silicon nitride film, 7, 11...
CVD silicon oxide film, 8...polysilicon film,
9...Platinum thin film (second electrode), 10...Silicon oxide film, 12...Aluminum electrode, 13...
Low concentration PSG film, 14...CVD silicon nitride film,
15...P ⁺ type conductive layer (first electrode), 20...opening, 21...empty area, _S1 ...MOS transistor region, _S2 ...pressure sensing device region.

Claims (1)

[Claims] 1. A step of selectively forming a semiconductor region of an opposite conductivity type as a first electrode on a semiconductor substrate of one conductivity type, and a step of forming a first insulating film from a peripheral part of the semiconductor region excluding a central part to the semiconductor substrate. forming a second insulating film that covers the central portion of the semiconductor region and extends on the first insulating film; and a step of forming a second insulating film that covers the entire surface of the second insulating film. a step of forming a conductive layer as a second electrode extending on the first insulating film; a step of forming an opening reaching the second insulating film in a part of the conductive layer; a step of removing the second insulating film through the opening by an engraving method to create a space between the conductive layer, the semiconductor region, and the first insulating film; and sealing the opening by closing the opening with a third insulating film.