JPH1078351A - Thermal infrared sensor and image sensor - Google Patents

Abstract

(57) [Summary] [PROBLEMS] A light receiving portion can be floated from a silicon substrate, and the light receiving portion can be thinned to reduce a heat capacity.
In addition, a thermal infrared sensor and an image sensor with high sensitivity are provided. SOLUTION: A light receiving portion 4 having a Schottky barrier diode 3 is formed in a cross-linked structure on a silicon substrate 1 with a certain gap, and the Schottky barrier diode 3 is composed of a thin film semiconductor 10 and the thin film semiconductor 10 Having a metal or metal silicide thin film 11 formed thereon,
A thin-film conductor 9 was formed below the thin-film semiconductor 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal infrared sensor and an image sensor capable of detecting infrared light with high sensitivity.

[0002]

2. Description of the Related Art Conventionally, a thermal infrared sensor detects infrared rays based on the following principle. That is, infrared rays emitted from the observation target substance are made incident on the light receiving section of the thermal infrared sensor, and the temperature of the light receiving section is changed by the incident infrared rays. The temperature change of the light receiving portion differs depending on the type of the sensor, but is electrically read out by a change in electric resistance, power generation amount, and the like. For this reason, the incident intensity of infrared rays can be detected as an electric signal.

As such a thermal infrared sensor, a PN junction type using a PN junction formed by diffusing an impurity into a silicon substrate or a Schottky junction type using a Schottky junction between a silicon substrate and a metal film (Japanese Patent Laid-Open No. 5-4006
No. 4).

In such a thermal infrared sensor, the light receiving portion is provided with a heat insulating structure with respect to the substrate in order to improve the sensitivity by increasing the temperature change of the light receiving portion even when the infrared light is weakly incident. desirable.

As such a heat insulating structure, a substrate immediately below a light receiving portion is removed by etching to separate the substrate from the light receiving portion.
And a second structure in which the light receiving section is supported by the substrate with a bridge structure and floated from the substrate (not known).

[0006]

However, in a thermal infrared sensor using a conventional Schottky barrier diode, a metal film is usually formed on a single-crystal silicon substrate. Like the structure plan 1,
It is extremely difficult to etch away the substrate directly below the light receiving section.

Therefore, in order to adopt the second structure proposal, it is difficult to form a crosslinked structure with a single crystal, and a crosslinked structure is formed with polycrystalline silicon, and a metal film is formed on the polycrystalline silicon. In this case, a Schottky barrier diode is formed, which causes the following problems.

That is, when the resistance of the polycrystalline silicon forming the Schottky barrier diode is low, that is, when the impurity in the crystal is added at a high concentration (when the impurity concentration is 10 ¹⁹ cm ⁻³ or more). In other words, polycrystalline silicon is in a degenerate state, and a Schottky barrier cannot be formed at the interface with the metal or metal silicide film, and the thermal infrared sensor loses sensitivity to temperature.

FIG. 10 shows the change in the rate of change in temperature resistance β of the thermal infrared sensor with respect to the impurity concentration of polycrystalline silicon.
As shown in (1), the impurity concentration tends to increase as the impurity concentration decreases. The rate of change in temperature resistance β is obtained by Expression 1.

[0010]

(Equation 1) When a constant voltage is applied to the thermal infrared sensor, I ₁ is a current flowing through the Schottky barrier diode at the element temperature T ₁ , and I ₂ is a current flowing through the Schottky barrier diode at the element temperature T ₂ .

In order to realize a highly sensitive thermal infrared sensor, it is necessary to use polycrystalline silicon having a low impurity concentration, that is, a high resistance.

However, when the polycrystalline silicon has a high resistance,
There is a problem that the output of the thermal infrared sensor is blurred due to a temperature change because the high resistance enters the thermal infrared sensor in series.

When a thermal infrared sensor is formed on polycrystalline silicon as described above, the characteristics are greatly affected by the impurity concentration of the polycrystalline silicon, and it is difficult to realize a highly sensitive thermal infrared sensor.

In addition, since the infrared detection sensitivity of the light receiving portion of the thermal infrared sensor becomes higher as the heat capacity becomes smaller, it is desirable to make the polycrystalline silicon layer thinner. However, if the impurity concentration of the polycrystalline silicon is low, the impurity diffusion of the guard ring formed around the Schottky barrier diode is deeply diffused. At this time, if the polycrystalline silicon layer is thin, the guard ring diffusion layer reaches the bottom of the polycrystalline silicon layer, and the electrical characteristics of the thermal infrared sensor cannot be read. Therefore, there is a problem that the polycrystalline silicon layer cannot be made thin, and the heat capacity of the light receiving section cannot be reduced.

Accordingly, the present invention is to provide a thermal infrared sensor and an image sensor which can float a light receiving portion above a silicon substrate, and can reduce the heat capacity by thinning the light receiving portion, and have high sensitivity. It is an issue.

[0016]

In order to achieve the above object, according to the first aspect of the present invention, a light receiving section having a Schottky barrier diode is formed in a cross-linked structure with a certain gap on a silicon substrate. Wherein the Schottky barrier diode has a thin film semiconductor, a metal or metal silicide thin film formed on the thin film semiconductor, and a thermal infrared sensor in which a thin film conductor is formed below the thin film semiconductor. It is characterized by having done.

According to a second aspect of the present invention, in addition to the configuration of the first aspect, the thin film conductor is made of a high impurity concentration thin film silicon semiconductor.

According to a third aspect of the present invention, in addition to the configuration of the second aspect, the thin film semiconductor has an impurity concentration of 10 ¹⁶ to 10 ^18.
cm ^-3 , the impurity concentration of the thin film conductor is 10 ¹⁹ -1
0 ²² cm ^-3 .

The invention described in claim 4 is the first to third aspects of the present invention.
In addition to the configuration of any one of the above, the thickness of the thin film semiconductor is 0.1 μm to 0.5 μm.

The invention described in claim 5 is the invention according to claims 1 to 4
In addition to the configuration described in any one of the above, a contact portion for establishing electrical connection with the thin-film conductor is formed by diffusing an impurity into the thin-film semiconductor and connected to the thin-film conductor. It is characterized by the following.

[0021] The invention according to claim 6 is the invention according to claims 1 to 5.
In addition to the configuration described in any one of the above, the thin film semiconductor is polycrystalline silicon.

The invention according to claim 7 is the invention according to claims 1 to 5
In addition to the configuration described in any one of the above, the thin film semiconductor is amorphous silicon.

[0023] The invention described in claim 8 is the invention according to claims 1 to 7.
In addition to the constitution described in any one of the above, the thin film conductor is made of polycrystalline silicon.

According to the ninth aspect of the present invention, there are provided the first to seventh aspects.
In addition to the configuration of any one of the above, the thin film conductor is amorphous silicon.

According to a tenth aspect of the present invention, a large number of thermal infrared sensors according to any one of the first to ninth aspects are arranged, and a signal from each thermal infrared sensor is used to control each of the objects to be observed. An image sensor for measuring the intensity of infrared light from a position is provided.

[0026]

Embodiments of the present invention will be described below.

1 to 8 show an embodiment of the present invention.

First, the structure will be described. In FIG. 1, reference numeral 1 denotes a silicon substrate, on which a Ti reflection film 2 as an infrared reflection film is provided below a light receiving section 4 having a Schottky barrier diode 3. It is located at the location. Then, a silicon nitride film 6 is formed on the silicon substrate 1 and the Ti reflection film 2, and a silicon nitride film is formed on the nitride film 6 so that the light receiving portion 4 is lifted off the silicon substrate 1. 7 are formed in a crosslinked structure, and a gap C is formed between the silicon nitride film 6 and the silicon nitride film 6.

The light receiving portion 4 formed on this cross-linked structure
On the silicon nitride film 7, a thin film conductor 9 made of polycrystalline silicon is formed, and on the upper side thereof, a thin film semiconductor 10 also made of polycrystalline silicon is formed. This thin film semiconductor 1
0 is formed with a low impurity concentration and high resistance, while the thin film conductor 9 is formed with a high impurity concentration and low resistance. Then, a metal silicide film 11 constituting the Schottky barrier diode 3 with the semiconductor 10 is formed on the thin film semiconductor 10. Further, a silicon oxide film 12 is formed so as to cover the thin film semiconductor 10 other than the metal silicide film 11.

A guard ring 13 is formed on the thin film semiconductor 10 below the silicon oxide film 12 so as to correspond to a peripheral portion of the metal silicide film 11, and a contact portion 15 is formed outside the guard ring 13. Are formed by thermal diffusion of As ⁺ .

The contact portion 15 and the guard ring 13 are connected to a Ti wiring layer 16 via a contact hole 12a formed in the silicon oxide film 12, respectively. The Ti wiring layer 16 and the silicon substrate 1 are connected via a contact hole 6a formed in the silicon nitride film 6.

Further, the entire crosslinked structure of these is covered with a silicon nitride film 17 as a surface protective film and an infrared absorbing film.

Next, the manufacturing process of the thermal infrared sensor having such a structure will be described.

On the silicon substrate 1 on which the read-out circuit has been formed by a normal semiconductor process, a Ti reflection film 2 is grown to 0.5 μm as an infrared reflection film. Subsequently, the Ti reflection film 2 other than the light receiving section 4 is etched by dry etching. Next, a silicon nitride film 6 is formed to a thickness of 0.1 μm, and a spin-on glass 20 (hereinafter referred to as “SOG film 2”) is formed thereon.
0 ") and fired (see FIG. 2).

Next, the resist 21 is patterned.
The SOG film 20 other than the light receiving section 4 is etched by a dry etching method (see FIG. 3).

Then, an SOG film 20 is further applied to the periphery of the SOG film 20 shown in FIG. 3 and baked, so that the step on the sensor surface is reduced, and subsequently, patterning is performed by a dry etching method. (See FIG. 4). Note that the above-described gap C is formed by removing the SOG film 20 formed here later.

Next, a silicon nitride film 7 is formed to a thickness of 0.3 μm and patterned, and then a resistivity of 1 × 10 ⁻³ Ωc
m (impurity concentration: 1 × 10 ²⁰ cm ^-3) of N-type polycrystalline thin film conductor 9 which is a silicon to 0.5μm formed by a CVD method, resistivity 1 × 10 ⁴ Ωcm (impurity concentration on this:
A thin film semiconductor 10 of 1 × 10 ¹⁸ cm ⁻³ ), which is N-type polycrystalline silicon, is formed to a thickness of 0.3 μm by a CVD method. Furthermore,
A silicon oxide film 12 is grown by 0.1 μm on the surface of polycrystalline silicon 1 by thermal oxidation (see FIG. 5).

Thereafter, B.sup. ^{+ Is} implanted into the guard ring 13 by ion implantation at 5 × 10 ¹⁵ cm ⁻² around the region where the Schottky barrier diode 3 is formed on the thin film semiconductor 10.
To form The guard ring 13 makes contact with the Schottky barrier diode 3. Furthermore, Similarly, the As ⁺ 3 × 10 ¹⁵ cm ^-2 implanted into N ⁺ region by ion implantation in order to contact the thin film conductor 9, by thermal diffusion of 1 hour at 900 ° C., The contact part 15 is formed. Thereafter, the area other than the area where the Schottky barrier diode 3 is to be formed is covered with a resist (not shown), and the exposed silicon oxide film 12 is removed by wet etching. Subsequently, a platinum metal silicide film 11 serving as a metal electrode of the Schottky barrier diode 3
Is formed to a thickness of 0.01 μm. The metal silicide film 11 is removed except for the light receiving section 4 by lift-off by removing the resist (see FIG. 6).

Thereafter, after patterning with a resist not shown, a contact hole 6a for making contact between the silicon substrate 1 and the Schottky barrier diode 3 is formed in the silicon nitride film 6 by dry etching, and the silicon nitride film is formed. 6, the periphery of the light receiving unit 4 other than the region supporting the light receiving unit 4 is etched. Next, after removing the resist, the resist is patterned again, and the silicon oxide film 12 on the thin-film semiconductor 10 is patterned by dry etching to form a contact hole 12a. Then, the Ti wiring layer 16 is grown by 0.5 μm and patterned so as to be continuous between the contact holes 6a and 12a (see FIG. 7).

Next, a silicon nitride film 17 is formed to a thickness of 0.3 μm as a surface protective film and an infrared absorbing film, and is patterned (see FIG. 8).

Then, the area other than the light receiving section 4 formation area is covered with a resist (not shown), and wet etching is performed.
The SOG film 20 under the silicon nitride film 7 is removed through the opening formed on the side of the bridge structure, and the gap C is formed there. Complete (see FIG. 1).

In such a thermal infrared sensor,
A gap C is provided below the light receiving section 4 to form a bridge structure,
By reducing the thickness of the light receiving section 4, the heat capacity can be reduced, and high sensitivity can be achieved.

That is, in the present invention, a cross-linked structure can be easily formed by using the polycrystalline low-resistance thin-film conductor 9 and the high-resistance thin-film semiconductor 10. Moreover, with such a double structure, a highly sensitive Schottky barrier can be formed between the high-resistance thin-film semiconductor 10 and the metal silicide film 11. Even if the high-resistance thin-film semiconductor 10 is formed in this manner, the resistance that enters the Schottky barrier diode 3 in series is reduced by providing the low-resistance thin-film conductor 9 below the thin-film semiconductor 10. A high-sensitivity thermal infrared sensor can be realized.

Further, even if the impurity concentration of the thin film semiconductor 10 is low and the guard ring 13 attempts to diffuse deeply, the output of the Schottky barrier diode 3 flows through the low-resistance thin film conductor 9, so that the low concentration impurity region, That is, the thin film semiconductor 10 can be made thin, and the heat capacity can be reduced as described above.

In the above embodiment, the thin film semiconductor layer 9 and the thin film conductor 10 are both formed of polycrystalline silicon. However, either or both of them may be formed of amorphous silicon instead of polycrystalline silicon. .

FIG. 9 shows another example of the embodiment of the present invention.

That is, a large number of the thermal infrared sensors A of the above embodiment are arranged in a predetermined relationship adjacent to each other vertically and horizontally, and these thermal infrared sensors A are connected to the horizontal shift register 23 and the vertical shift register 24, respectively. I have.

The shift registers 23, 24
By scanning with, the signals are sequentially read from the thermal infrared sensors A, whereby the light intensity of the infrared light from each position of the observation target is measured.

[0049]

As described above, according to the present invention, the heat capacity can be reduced by providing a gap below the light receiving portion to form a bridge structure and making the light receiving portion thinner. And high sensitivity can be achieved.

According to the fifth aspect of the present invention, in addition to the above-mentioned effects, a contact portion is formed on a high-resistance thin-film semiconductor and connected to a low-resistance thin-film conductor to thereby provide a Schottky barrier diode. From the point of view, which is a practically useful effect.

[Brief description of the drawings]

FIG. 1 is a sectional view of a thermal infrared sensor according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a manufacturing step according to the embodiment.

FIG. 3 is a cross-sectional view showing a manufacturing step according to the embodiment, which is a step subsequent to FIG. 2;

FIG. 4 is a cross-sectional view of a step subsequent to FIG. 3 showing a manufacturing step according to the embodiment.

FIG. 5 is a cross-sectional view showing a manufacturing step according to the embodiment, which is a step subsequent to FIG. 4;

FIG. 6 is a cross-sectional view showing a manufacturing step according to the embodiment, which is a step subsequent to FIG. 5;

FIG. 7 is a cross-sectional view showing a manufacturing step according to the embodiment, which is a step subsequent to FIG. 6;

FIG. 8 is a cross-sectional view of a step subsequent to FIG. 7 showing a manufacturing step according to the embodiment.

FIG. 9 is a schematic diagram of an image sensor showing another example of the embodiment of the present invention.

FIG. 10 is a graph showing a relationship between an impurity concentration and a rate of change in resistance temperature.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 3 Schottky barrier diode 4 Light receiving part 9 Thin film conductor 10 Thin film semiconductor 11 Metal silicide film 13 Guard ring 15 Contact part C gap

Claims (10)

[Claims] 1. A light receiving section having a Schottky barrier diode is formed in a cross-linked structure on a silicon substrate with a certain gap, and the Schottky barrier diode includes:
A thermal infrared sensor comprising a thin film semiconductor and a metal or metal silicide thin film formed on the thin film semiconductor, wherein a thin film conductor is formed below the thin film semiconductor. 2. The thin film conductor according to claim 1, wherein the thin film conductor is made of a high impurity concentration thin film silicon semiconductor.
The thermal infrared sensor as described in the above. 3. The method according to claim 1, wherein the impurity concentration of said thin-film semiconductor is 10 ^{16 or} less.
10 ¹⁸ cm ^-3 , the impurity concentration of the thin film conductor is 10
Thermal infrared sensor according to claim 2, characterized in that it is a ¹⁹ to 10 ^{22 cm-3.} 4. The thickness of the thin-film semiconductor is 0.1 μm or more.
The thermal infrared sensor according to claim 1, wherein the thickness of the thermal infrared sensor is 0.5 μm. 5. The thin-film conductor according to claim 5, wherein a contact portion for making an electrical connection with said thin-film conductor is formed by diffusing impurities into said thin-film semiconductor and connected to said thin-film conductor. The thermal infrared sensor according to any one of claims 1 to 4. 6. The thermal infrared sensor according to claim 1, wherein the thin film semiconductor is polycrystalline silicon. 7. The thermal infrared sensor according to claim 1, wherein the thin film semiconductor is amorphous silicon. 8. The thermal infrared sensor according to claim 1, wherein said thin-film conductor is polycrystalline silicon. 9. The thermal infrared sensor according to claim 1, wherein said thin-film conductor is amorphous silicon. 10. A thermal infrared sensor according to claim 1, wherein a large number of thermal infrared sensors are arranged, and a light intensity of infrared light from each position of the observation target is determined by a signal from each thermal infrared sensor. An image sensor characterized by measuring the following.