JPH10335681A - Manufacture of infrared sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the resistance temperature coefficient of a bolometer titanium, by forming an insulating protection film at a specific growing temperature on a titanium thin film which is a bolometer material. SOLUTION: A silicon oxide film 7 is grown on the whole plane and an aluminum wirings 8 and 8' are formed on the silicon oxide film 7 to be electrically connected with a part of a scanning circuit. Bolometer titanium 9 is deposited, for instance, by sputtering, and a pattern of the bolometer is formed by photoresist method and selective etching. Then, a low-temperature growing insulating protection film 12 made of 1 μm thick silicon oxide film is deposited for covering titanium by plasma CVD method at 300 deg.C or below. When the titanium growing temperature becomes higher than 300 deg.C, titanium resistance temperature coefficient becomes lower than the resistance temperature coefficient of titanium exposed before growing the insulating protection film. Therefore, the resistance temperature coefficient of bolometer titanium can be improved by forming the insulating protection film at 300 deg.C or below.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing an infrared sensor, and more particularly to a method for forming an insulating protective film on a bolometer titanium thin film.

[0002]

2. Description of the Related Art Since an infrared image sensor operating at room temperature does not require a cooler, an apparatus equipped with the infrared image sensor is inexpensive, compact, and easy to use, and has been attracting attention from various fields. The principle of operation of this infrared image sensor is that the infrared radiation heat from the object is absorbed, the tire flam of each pixel arranged two-dimensionally increases in temperature, and the two-dimensional distribution of this temperature increase is provided for each pixel. This is converted into an electric signal by the thermoelectric material and is derived as a two-dimensional video signal.

As an example of such a thermal infrared sensor for detecting a temperature rise of a diaphragm, a method of manufacturing an infrared sensor using titanium as a bolometer material is disclosed in, for example, Japanese Patent Application Laid-Open No. 8-105794.

[0004] In particular, this titanium bolometer infrared sensor has the advantage that since the bolometer as a thermoelectric material is made of titanium, it can be manufactured in an integrated manner using a normal silicon IC production line. An advantageous sensor. Such a room-temperature operating infrared image sensor usually has a wavelength of 8 to
It is designed to have a 12 μm band far-infrared light receiving region.

In such a conventional titanium bolometer infrared sensor, as shown in FIG.
A polysilicon sacrificial layer 5 is formed above the scanning circuit 2 formed on one main surface of the semiconductor device. A bolometer 9 made of titanium is formed on the silicon oxide film 7 serving as a lower insulating film of the diaphragm provided thereon by a sputtering method and a photoresist method to form an insulating protective film 10 of the silicon oxide film.
A growth temperature of about 40 using a reaction gas of monosilane and oxygen.
Cover with 0 ° C. normal pressure CVD method. Thereafter, an infrared absorption film 11 made of titanium nitride is formed.

Thereafter, although not particularly shown, a slit-shaped through hole reaching the sacrificial layer 5 is formed, and the internal sacrificial layer 5 is selectively removed through the through hole to form a cavity. As a result, a thermal isolation structure in which the diaphragm floats on the cavity is formed. The higher the thermal conductivity of this thermal separation structure, the higher the infrared absorption of the diaphragm, and the higher the temperature coefficient of titanium, which is a bolometer that converts the temperature change of the diaphragm into a change in resistance, the higher the sensitivity of infrared detection. Will be possible.

In the above-mentioned titanium bolometer infrared sensor,
Since a silicon oxide film, which is a material having a low thermal conductivity, is used as an insulating protective film on a titanium bolometer, it has a feature that the thermal conductivity is lower than using a silicon nitride film or the like.

In FIG. 4, reference numeral 3 denotes a scanning vertical line, 6 denotes a PBSG film, and 8, 8 'denote aluminum wirings.

[0009]

However, in such a conventional titanium bolometer infrared sensor, the temperature coefficient of titanium as a bolometer is as low as about 0.2% / K.
In addition, the infrared absorption rate of the diaphragm also has an infrared absorption dip near the wavelength of 10 μm because the dielectric film under the infrared absorption film made of titanium nitride is made of a silicon oxide film. About 55% on average
And lower. As a result, there is a problem that the infrared detection sensitivity is relatively low.

The present invention has been made in order to solve the problems of the prior art, and an object of the present invention is to provide a method of manufacturing an infrared sensor capable of improving the temperature coefficient of resistance of bolometer titanium. Is to provide.

Another object of the present invention is to provide a method of manufacturing an infrared sensor capable of improving the infrared absorptivity of the diaphragm.

[0012]

According to the present invention, there is provided a method of manufacturing an infrared sensor, wherein an insulating protective film having a growth temperature of 300 ° C. or less is formed on a titanium thin film as a bolometer material.

Further, a silicon oxide film, a silicon nitride film or a BPSG film is formed as the insulating protective film.

According to the present invention, a silicon oxide film or a silicon nitride film having a growth temperature of 300 ° C. or less is grown as an insulating protective film on the bolometer titanium thin film, and a BPSG film is formed thereon. Is obtained.

The operation of the present invention will be described. By forming the insulating protective film on the bolometer titanium at a temperature of 300 ° C. or less, the temperature coefficient of resistance of titanium is improved. As an insulating protective film on the bolometer titanium, especially a BPSG film of 30
By growing at 0 ° C. or lower, the infrared absorptivity of the diaphragm is also improved.

Further, by growing the insulating protective film on the titanium bolometer at a temperature of 300 ° C. or less and subsequently growing the BPSG film, the infrared absorption of the diaphragm is also improved.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a cross-sectional view of one embodiment of the present invention, and the same parts as those in FIG. 4 are denoted by the same reference numerals. First, a BPSG film 4 is grown on a semiconductor substrate 1 having a scanning circuit 2 on one main surface by a CVD method.
The surface is almost flattened by MP polishing or the like. And
A polysilicon sacrificial layer 5 having a thickness of about 1 μm and a square of about 40 μm is formed thereon at a pitch of 50 μm, and the sacrifice layer and the sacrifice layer are covered with a BPSG film 6.
The membrane is selectively opened.

Subsequently, a silicon oxide film 7 is grown on the entire surface, and aluminum wirings 8, 8 'for electrically connecting to a part of the scanning circuit are formed thereon. After that, thickness 1000
Angstrom bolometer titanium 9 is deposited by, for example, a sputtering method, and a bolometer pattern is formed by a photoresist method and a selective etching method. Subsequently, a low-temperature grown insulating protective film 12 made of a silicon oxide film having a thickness of 1 μm for a titanium cover is deposited at a temperature of 300 ° C. or less by a plasma CVD method.

Subsequently, after sequentially depositing titanium nitride 11 as an infrared absorbing film having a thickness of 100 to 200 angstroms, the polysilicon sacrificial layer 5 is removed from the surface of the insulating protective film by a selective oxide film etching method using a photoresist method. Is formed.

Thereafter, the sacrificial layer polysilicon is removed by selective etching using human azine, TMAH, or the like.
A diaphragm floating in the air is formed, and infrared rays can be detected. As a result, the infrared detection sensitivity became 1.5 times or more that of the related art.

FIG. 2 is a diagram showing the relationship between the growth temperature of the silicon oxide film and the temperature coefficient of resistance of titanium. When the growth temperature is higher than 300 ° C., the resistance temperature coefficient of titanium becomes lower than the resistance temperature coefficient of titanium exposed before growing the insulating protective film. That is, the temperature coefficient of resistance of titanium when a plasma silicon oxide film is grown using a growth temperature of 250 ° C. and a reaction gas of monosilane Si H4 and N 2 O as follows:
Although it is 0.33% / K which is the same as that of the exposed titanium, for example, the temperature coefficient of resistance of titanium in the case of the plasma silicon oxide film grown at 400 ° C. is 0.2% / K, which is about 60% in the case of the exposed titanium. %.

This tendency is almost the same even when the low-growth insulating protective film 12 on the bolometer titanium is changed to a BPSG film. In this case, the infrared absorptance is also about 40
% Increase. However, since the growth rate decreases and the reproducibility of the film quality deteriorates as the growth temperature decreases, the growth is usually performed at 350 ° C. or higher.

FIG. 3 is a sectional view of a second embodiment according to the present invention, and the same parts as those in FIG. 1 are denoted by the same reference numerals.
In this embodiment, a plasma silicon nitride film is formed at a growth temperature of 300 ° C. by using a reaction gas of monosilane and ammonia instead of a plasma silicon oxide film as the low-temperature growth insulating protective film 12 on titanium of the first embodiment. After growing thinly to Å, a BPSG film 13 having a growth temperature of 400 ° C. and a thickness of about 9000 Å is successively deposited by a normal pressure CVD method, and other processes are substantially the same.

The concentrations of B and P in the PBSG membrane were each 1
0% and 5%. In this case, the infrared absorption of the titanium bolometer-type infrared sensor was about 75%. Similarly to the first embodiment, the temperature coefficient of resistance of the bolometer titanium is increased by 50% as compared with the conventional example, and the infrared absorption is also increased by the first factor.
As in the case where the BPSG film was grown as the insulating protective film of the example, the increase was 35%. With these two improvements, the infrared detection sensitivity is improved by about 90% in total.

As a third embodiment, instead of the thin plasma silicon nitride film of the second embodiment, a plasma C
A plasma oxide film is grown at a growth temperature of 250 ° C. by a VD method.
After growing thinly to 2,000 Å, a BPSG film 13 having a thickness of about 9000 Å was deposited by plasma CVD.

Others are almost the same manufacturing process,
In this case, the temperature coefficient of resistance of the bolometer titanium increased only by 30% as compared with the conventional one, and was slightly inferior to that of the first embodiment. However, the infrared absorptance is close to the case where the BPSG film was grown as the insulating protective film of the first embodiment, and increased by about 30%. The two improvement effects improve the infrared detection sensitivity by about 70% in total. is what happened.

[0027]

The first effect of the present invention is that the cover insulating film on boron titanium is formed at a temperature of 50 to 100 ° C. lower than the conventional growth temperature.
By lowering the above, the temperature coefficient of resistance of the bolometer titanium can be increased by 50% as compared with the related art. The reason is that by lowering the growth temperature, titanium deposited by the sputtering method is suppressed from being oxidized or nitrided during the growth of the cover insulating film, and the intrinsic temperature coefficient of resistance of the deposited titanium film can be realized. is there.

The second effect is that, after depositing a thin plasma silicon nitride film or a thin plasma silicon oxide film capable of growing a cover insulating film on a bolometer titanium at a growth temperature of 300 ° C. or lower, a BPSG film is successively deposited. In addition, it is possible to suppress a decrease in the temperature coefficient of resistance of titanium and at the same time improve the infrared absorptance by about 30% or more as compared with the conventional case.

The reason is that the BPSG film occupies most of the insulating protective film on titanium as the dielectric film in the diaphragm. In the case of this BPSG film, compared with the conventional silicon oxide film or plasma silicon nitride film, , Wavelength 10μm
This is because the dip in the absorption rate in the vicinity decreases.

These double effects are synergistic, so that the detection sensitivity of the infrared sensor can be greatly improved as compared with the related art. Further, the BPSG film has an advantage that the thermal conductivity is smaller than the silicon oxide film and smaller than the silicon nitride film, and the thermal conductivity of the diaphragm can be reduced.

[Brief description of the drawings]

FIG. 1 is a sectional view of a first embodiment of the present invention.

FIG. 2 is a graph showing the dependence of the temperature coefficient of titanium resistance on the growth temperature of a cover oxide film.

FIG. 3 is a sectional view of a second embodiment of the present invention.

FIG. 4 is a cross-sectional view of a conventional infrared sensor.

[Explanation of symbols]

 Reference Signs List 1 semiconductor substrate 2 scanning circuit 3 scanning vertical line 4,6,13 BPSG film 5 polysilicon sacrificial layer 7 silicon oxide film 8,8 'aluminum wiring 9 bolometer titanium 10 insulating protective film 11 titanium nitride 12 low temperature growth insulating protective film

Claims (3)

[Claims] 1. A method for manufacturing an infrared sensor, comprising forming an insulating protective film having a growth temperature of 300 ° C. or less on a titanium thin film as a bolometer material. 2. A silicon oxide film as said insulating protective film,
2. The method according to claim 1, wherein a silicon nitride film or a BPSG film is formed. 3. A method of manufacturing an infrared sensor, wherein a silicon oxide film or a silicon nitride film having a growth temperature of 300 ° C. or less is grown as an insulating protective film on a bolometer titanium thin film, and a BPSG film is formed thereon. Method.