JPH10111178A - Thermal infrared ray sensor and image sensor using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To raise sensitivity of a sensor and flatten its structure, relating to a thermal infrared ray sensor of micro-bridge structure. SOLUTION: Relating to a thermal infrared ray sensor 10 of a bridge structure where an infrared ray detecting part 10A is supported on a semiconductor substrate 1, an aluminum film (reflection film) is formed below a platinum silicide film 16 (infrared ray absorbing film) through a polycrystal silicon film 14 of a specified film thickness, with the infrared ray absorbing film separated from the reflection film with a specified interval (d). The specified interval (d) is decided according to the following equation: d=(2N-1)×λ/(4n) (n is refraction factor of film formed between infrared ray absorbing film and reflection film, λ is infrared ray wavelength to be detected, N is positive integer).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a thermal infrared sensor, and more particularly to a thermal infrared sensor having a microbridge structure.

[0002]

2. Description of the Related Art An infrared ray radiated from an object to be observed is received by an infrared ray receiving section, and a physical property value of the infrared ray receiving section which changes according to the intensity of the received infrared ray is detected. An infrared sensor for detecting the height is known. Such an infrared sensor has a quantum infrared sensor that utilizes the characteristic that electrons excited when receiving infrared energy exceed a predetermined energy band, and a thermal infrared sensor that utilizes a temperature change of an element caused by infrared irradiation. Type infrared sensors.

[0003] Of these, the quantum infrared sensor must be provided with cooling means for cooling the elements constituting the sensor section to such a degree that the excitation of electrons by heat can be neglected. In particular, many quantum infrared sensors are used. Such an image sensor or the like requires a large apparatus as a whole and is expensive. On the other hand, the thermal infrared sensor has an advantage that it does not require the above-described cooling means, is suitable for miniaturization, and can be inexpensive. However, on the other hand, this thermal infrared sensor has a disadvantage that the sensitivity of detecting infrared rays is lower than that of the quantum infrared sensor.

In order to compensate for such a disadvantage of the thermal infrared sensor, a thermal infrared sensor 100 having a microbridge structure as shown in FIG. 10 has been conventionally proposed. In view of the fact that the sensor sensitivity increases as the physical property value (for example, the resistance value) of the infrared light receiving unit 100A changes responsively according to the intensity of the incident infrared light, the thermal infrared sensor 100 having the microbridge structure takes the infrared light receiving unit 100A and base 100B
(Semiconductor substrate 10 covered with silicon oxide film 101A)
In order to reduce the thermal conductance between (1) and (1), the cavity S is provided by the leg 100C.

In the thermal infrared sensor 100 having a microbridge structure, a reflection film 100D is provided on a base 100B immediately below the infrared light receiving portion 100A so as to further improve the sensor sensitivity. Again, the infrared light receiving unit 100A efficiently absorbs the light to increase the sensor sensitivity.
It is publicly known from Japanese Patent Publication No. 7-509057.

In the thermal infrared sensor 100 having such a microbridge structure, the distance d between the infrared absorbing film 106 (FIG. 10) and the reflecting film 100D in the infrared light receiving portion 100A is determined by the following relational expression (1). ), The height of the cavity S is determined so as to satisfy the condition shown in FIG. d = (2N−1) × λ / 4 (1) (where, λ is the center wavelength of the infrared ray to be detected, and N is a positive integer) By satisfying the relational expression (1), the infrared ray receiving unit 100A After the infrared rays that have passed through and reached the reflection film 100D are reflected by the reflection film 100D, the infrared absorption film 10D
6, the sensor sensitivity is improved (the effect of the optical cavity).

In FIG. 1, reference numerals 107A and 107B denote wirings for electrically detecting a temperature change of the polycrystalline silicon film 104 as a resistor of the bolometer. In the figure, 10
Reference numerals 2 and 108 are silicon nitride films functioning as protective films of the thermal infrared sensor 100.

[0008]

However, the thermal infrared sensor 100 provided with the reflection film 100D still has the following disadvantages.

That is, in the thermal infrared sensor 100 provided with the reflection film 100D, the space between the lower surface of the infrared light receiving portion 100A and the upper surface of the reflection film 100D is set as described above.
Although it must be separated by a predetermined distance d, if the infrared wavelength λ detected by the thermal infrared sensor 100 is 8 μm
Assuming that the center wavelength λ ₁ is 10 μm, the predetermined interval d is about 2.5 μm.

When the infrared light receiving portion 100A is formed at a distance of about 2.5 μm from the upper surface of the reflection film 100D, the leg portion 100C must be strengthened. However, in the field of semiconductor manufacturing technology in which miniaturization has advanced in recent years, the height of 2.5 μm is much higher than the height of other elements. However, if the leg 100C is thick,
The thermal conductance between the infrared receiving section 100A and the base 100B increases, and the sensor sensitivity of the thermal infrared sensor 100 decreases.

To increase the sensitivity of the sensor, the leg 100C
Is smaller, the above-mentioned predetermined distance d cannot always be maintained accurately, and the effect of the optical cavity cannot be obtained. In particular, when an image sensor is configured by arranging a plurality of thermal infrared sensors 100 in a linear or planar manner, the predetermined interval d varies among the individual thermal infrared sensors 100. As a result, the sensitivities of the individual sensors fluctuate, and it becomes impossible to accurately recognize an image.

When the predetermined distance d is increased, the base 100B of the thermal infrared sensor 100 and the infrared light receiving portion 10
There is also a problem that a step difference from 0A becomes large, a focus shift occurs during an exposure process in a manufacturing process of the thermal infrared sensor 100, and fine photolithography cannot be performed.
The present invention has been made in view of such circumstances, and in a thermal infrared sensor having a microbridge structure in which a reflective film is formed, while increasing the sensor sensitivity, the structure is flattened, and the thermal infrared sensor of each thermal infrared sensor is formed. An object of the present invention is to provide a thermal infrared sensor in which sensitivity does not vary and an image sensor in which the thermal infrared sensor is highly integrated.

[0013]

In order to achieve the above object, according to the first aspect of the present invention, there is provided a heat sink having a bridge structure in which at least an infrared ray receiving section having an infrared ray absorbing film is supported by legs on a semiconductor substrate. Type infrared sensor,
A reflection film is formed below the infrared absorption film via one or more films having a predetermined thickness, and the infrared absorption film and the reflection film are separated by a predetermined distance.

Further, in the invention according to claim 2, the predetermined interval is defined as: d = (2N-1) × λ / (4n) (d is a predetermined interval, and n is a distance between the infrared absorbing film and the reflecting film. The refractive index of the formed film, λ is the wavelength of the infrared light to be detected, N
Is a positive integer).

Further, in the invention according to a third aspect, a diode is formed in the infrared receiving section. Further, the invention according to claim 4 is characterized in that the infrared absorbing film is formed of a metal film, and a polycrystalline silicon film or an amorphous silicon film is formed between the metal film and the reflection film, thereby forming the metal film. A Schottky barrier diode is formed on a bonding surface between a film and the polycrystalline silicon film or the amorphous silicon film.

In the invention according to claim 5, the metal film is a silicide film. According to a sixth aspect of the present invention, the reflective film is used as an electrode for electrically reading out a change in physical properties according to a change in temperature of the infrared light receiving section. According to a seventh aspect of the present invention, a polycrystalline silicon film or an amorphous silicon film serving as a resistor of a bolometer is formed between the infrared absorption film and the reflection film.

The invention according to claim 8 uses the infrared absorption film and the reflection film as electrodes for electrically reading out a change in physical properties according to a temperature change of the infrared light receiving section. is there. Further, the invention according to claim 9 is characterized in that the infrared light receiving section is formed of a silicon oxide film, a silicon nitride film,
This is covered with at least one of the silicon oxynitride films.

The invention according to claim 10 is the first invention.
An image sensor is constituted by arranging a plurality of thermal infrared sensors according to any one of claims to 9 in a linear or planar manner.

(Function) According to the first aspect of the present invention, since one or more films are provided between the reflection film and the infrared absorption film, the reflection film is integrated with the infrared light receiving portion. It is easy to keep the distance between the reflection film and the infrared absorption film constant, and it is easy to achieve an optical cavity. At this time, the cavity of the microbridge structure may have a minimum size necessary for reducing the thermal conductance.

According to the second aspect of the present invention, the predetermined distance can be reduced by increasing the refractive index of the film formed between the infrared absorbing film and the reflecting film, thereby achieving an optical cavity. In doing so, it is possible to reduce the thickness of the infrared light receiving section. As described above, when the infrared light receiving portion is thin and small, the legs can be made thinner, the thermal conductance of the infrared light receiving portion can be reduced, and the sensor sensitivity can be improved.

According to the third aspect of the present invention, in a thermal infrared sensor in which a diode is formed in an infrared light receiving section, sensor sensitivity can be easily improved by an optical cavity. According to the invention of claim 4, the predetermined interval can be freely set to a desired value by adjusting the thickness of the polycrystalline silicon film or the amorphous silicon film constituting the Schottky barrier diode.

According to the fifth aspect of the present invention, a change in physical properties according to a temperature change of the infrared light receiving section can be detected with high accuracy by the Schottky barrier diode using the silicide film. Also, according to the invention of claim 6, it is possible to output an electric signal representing a change in physical properties according to a temperature change of the infrared light receiving section with high accuracy.

According to the seventh aspect of the present invention, the polycrystalline silicon film whose resistance value changes according to the temperature change of the infrared light receiving portion is used as a film for determining a film thickness for achieving an optical cavity. Can also be used,
A highly accurate thermal infrared sensor can be provided. Further, according to the invention of claim 8, it is possible to output an electric signal representing a change in physical properties according to a temperature change of the infrared light receiving section with high accuracy.

According to the ninth aspect of the present invention, the strength of the infrared ray receiving section can be improved, and the durability thereof can be improved. In addition, the etching selectivity when forming the cavity of the microbridge structure can be appropriately determined. Further, according to the tenth aspect of the present invention, an image sensor having a large number of highly sensitive thermal infrared sensors is achieved.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION

(First Embodiment) Hereinafter, a first embodiment of the present invention will be described with reference to the accompanying drawings. The first embodiment corresponds to claims 1 to 6, claim 9, and claim 10.

First, the structure of the thermal infrared sensor 10 will be described with reference to FIG. FIG. 1 is a cross-sectional view schematically showing the structure of a thermal infrared sensor 10 having a microbridge structure. As shown in FIG. 1, the thermal infrared sensor 10 includes an infrared receiver 10 </ b> A on a base 10 </ b> B and a leg 1.
It has a bridge structure supported by OC.

Further, a Schottky barrier diode (hereinafter abbreviated as "SBD") for detecting a change in physical properties of the infrared light receiving portion 10A is formed in the infrared light receiving portion 10A. The SBD changes the value of the reverse saturation current according to the temperature change when the temperature of the infrared light receiving unit 10A changes according to the intensity of the infrared light incident on the infrared light receiving unit 10A. . Thus, this S
The intensity of the incident infrared ray can be obtained by detecting the value of the reverse saturation current of the BD.

Specifically, the thermal infrared sensor 10 is configured as follows. A read circuit (not shown) for transmitting an output signal of the thermal infrared sensor 10 to the outside is formed on the silicon substrate 1, and a silicon oxide film 2 is formed so as to cover the surface of the read circuit. . A silicon oxide film 12 is formed in a bridge shape on the upper surface of the silicon substrate 1 on which the silicon oxide film 2 is formed, and an aluminum film 13 functioning as a reflection film is formed on the upper surface of the central portion.
Are formed.

On the upper surface of the aluminum film 13, the aluminum film 13
A polycrystalline silicon film 14 having substantially the same planar shape as that described above is formed with a predetermined thickness d. Platinum silicide film 16 is formed substantially at the center of the upper surface of polycrystalline silicon film 14. The platinum silicide film 16 has a thickness of about 1 nm to 10 nm.

In the polycrystalline silicon film 14, a guard ring 14G into which a p-type impurity is introduced and a p-type diffusion layer formed integrally therewith so as to surround a junction surface with the platinum silicide film 16. 14A is provided. Further, an n-type diffusion layer 14 is formed in a region outside the guard ring 14G.
B is provided. The n-type diffusion layer 14B is formed at a depth in contact with the aluminum film 13 formed below the polycrystalline silicon film 14.

A silicon oxide film 15 is formed on the surface of the polycrystalline silicon film 14, and the titanium films 17A and 17A are formed through contact holes formed in the silicon oxide film 15.
17B is electrically connected to the p-type diffusion layer 14A and the n-type diffusion layer 14B. At this time, the titanium film 17B is further electrically connected to the aluminum film 13 via the n-type diffusion layer 14B.

On the other hand, the titanium films 17A and 17B are electrically connected to a readout circuit (not shown) formed on the silicon substrate 1 side, and the SBD changes according to a temperature change of the infrared light receiving portion 10A. Is sent to a readout circuit (not shown) on the silicon substrate 1. The above-described aluminum film 13 is electrically connected to the titanium film 17A via the n-type diffusion layer 14B, and is also used as an electrode for outputting a reverse saturation current of the SBD. As described above, when the aluminum film 13 is used as the electrode, a change in the reverse saturation current of the SBD can be accurately detected.

The polycrystalline silicon film 14, platinum silicide film 16, and aluminum film 13 are covered with silicon oxide films 12, 18 as protective films. In the thermal infrared sensor 10 configured as described above, the SBD formed between the polycrystalline silicon film 14 and the platinum silicide film 16 moves in the opposite direction with the temperature change of the infrared light receiving unit 10A as described above. The saturation current changes, and the intensity of the infrared ray is detected by detecting the reverse saturation current.

On the other hand, the platinum silicide film 16 constituting the SBD is also used as an infrared absorbing film in the infrared receiving section 10A. As described above, the platinum silicide film 16 has a thickness of 1 nm to
The film is formed to have a thickness of about 10 nm (10 ° to 100 °). The reason why the film thickness is set to such a value is that if the film thickness is more than that, the infrared light incident on the infrared light receiving unit 10A is reflected. In contrast, when the platinum silicide film 16 is thinned as described above, on the contrary, infrared rays may be transmitted through the platinum silicide film 16. However, the aluminum film 13 reflects the infrared rays to reach the platinum silicide film 16 again. Therefore, the absorptivity of infrared rays does not decrease.

In the thermal infrared sensor 10 of the present embodiment, the distance d between the aluminum film 13 and the platinum silicide film 16 is the thickness of the polycrystalline silicon film 14 formed between them. The thickness d of the polycrystalline silicon film 14 is such that when the infrared light transmitted through the platinum silicide film 16 provided as the infrared absorbing film is reflected by the aluminum film 13, the reflected infrared light and the platinum Between the infrared light incident on the silicide film 16,
In order to obtain the effect of the optical cavity, it is determined based on the following relational expression (2).

D = (2N−1) × λ / (4n) (2) where n is formed between the infrared absorbing film (mainly the platinum silicide film 16) and the reflecting film (aluminum film 13). The refractive index of the film (in this case, the polycrystalline silicon film 14), N is a positive integer, and λ is the center wavelength of the wavelength range of the infrared light to be detected. By the way, when the wavelength range of infrared rays detected by the thermal infrared sensor 10 is 8 μm to 13 μm, the center wavelength λ is 10 μm.
Therefore, when only the polycrystalline silicon film 14 is formed between the platinum silicide film 16 and the aluminum film 13 as described above (the refractive index n of the polycrystalline silicon is substantially “3.
4 ”) and“ N ”are“ 1 ”, the value of“ d ₁ (= d) ”is about 0.7 μm.

FIG. 2 is a graph showing the relationship between the thickness of the polycrystalline silicon film 14 and the infrared absorption under the above conditions. As shown in this graph, when the wavelength range of the infrared light to be detected is 8 μm to 13 μm, and when the thickness d of the polycrystalline silicon film 14 is 0.7 μm, the infrared absorption becomes about 0.63. It was confirmed by experiments that infrared rays were most efficiently absorbed.

As shown in the above relational expression (2), a desired film thickness d for achieving an optical cavity is obtained.
Can be made smaller as the refractive index "n" of the film formed between the infrared absorbing film (platinum silicide film 16) and the reflecting film (aluminum film 13) becomes larger. When a plurality of films are formed between the infrared absorbing film (here, the platinum silicide film 16) and the reflecting film (the aluminum film 13), the value obtained by adding the respective film thicknesses is expressed by the above relational expression. It is only necessary to satisfy (2).

The aluminum film (reflection film) 13 reflects the infrared light transmitted through the infrared light receiving portion 10A as described above and absorbs the infrared light into the platinum silicide film 16 (infrared absorption film) of the infrared light receiving portion 10A. Infrared receiver 10
The height h1 of the cavity S provided between the lower surface of A and the silicon substrate 1 (substrate) is sufficient if the minimum necessary height for reducing the thermal conductance between the infrared receiving unit 10A and the silicon substrate 1 is sufficient. Therefore, a conventional thermal infrared sensor having a bridge structure (for example, the thermal infrared sensor 10 shown in FIG. 10).
0) can be lower than the height of the cavity S.

When the thermal infrared sensor 10 is formed, the level difference between the silicon substrate 1 and the infrared light receiving portion 10A can be reduced by the amount of the cavity S that can be reduced. In addition, there is no shift in focus, and fine photolithography and the like can be performed.

Further, since the interval between the aluminum film 13 forming the reflection film and the platinum silicide film 16 forming the infrared absorption film can be accurately maintained at a constant value, many thermal infrared sensors such as image sensors are used. In such a device, it is possible to prevent variations in sensor sensitivity between thermal infrared sensors. Next, the thermal infrared sensor 10 having the above structure
3 will be described with reference to FIGS.

(1) A readout circuit (not shown) of the thermal infrared sensor 10 is previously formed on the n-type silicon substrate 1 by a well-known semiconductor manufacturing technique. A silicon oxide film 2 having a thickness of 0.1 μm is formed by a pyro oxidation method. Further, a polycrystalline silicon film 11 is formed on the upper surface by CVD method.
The sacrifice layer 11A is formed by patterning it into a desired shape. (The structure obtained in the steps so far is shown in FIG. 3A.) (2) A silicon oxide film 12 is formed on the upper surface of the silicon substrate 1 on which the sacrificial layer 11A is formed, for example, by a CVD method. The silicon oxide film 1 is formed to a thickness of 0.2 μm and is patterned to cover the entire surface of the sacrificial layer 11A.
Form 2 Next, 30 n is formed by sputtering or vapor deposition so as to cover the upper surface of the silicon oxide film 12.
m aluminum film 13 is formed and patterned.
Match the shape of the infrared light receiving section 10A (FIG. 1) of the thermal infrared sensor 10. (The structure obtained in the steps so far is shown in FIG. 3B.) (3) The polycrystalline silicon film 14 is formed by, for example, a CVD method so as to cover the sacrifice layer 11A having the aluminum film 13 formed on the upper surface.
Is formed to a thickness of 0.5 μm, and is patterned to conform to the shape of the upper surface of the sacrifice layer 11A.

Next, the polycrystalline silicon film 14 is oxidized at a high temperature to form a silicon oxide film having a thickness of 50 nm. In this state, ion implantation of an n-type impurity into the polycrystalline silicon film 14 is performed. A p-type guard ring 14G, a p-type diffusion layer 14A, and an n-type diffusion layer 14B are formed in the polycrystalline silicon film 14 by selectively and sequentially performing ion implantation of p-type impurities. Next, a guard ring 14G, a p-type diffusion layer 14A, and an n-type diffusion layer 14B
Is again oxidized to form a 50-nm-thick silicon oxide film on the surface thereof, and a 0.1-μm-thick silicon oxide film 15 as a whole is formed.
To form (The structure obtained in the steps up to this point is shown in FIG.
It is shown in (c). (4) The silicon oxide film 15 formed on the upper surface of the polycrystalline silicon film 14 is patterned to provide an opening 15A to expose the polycrystalline silicon film 14.

Next, a platinum (Pt) film is deposited on the entire surface of the silicon substrate 1 by a molecular beam epitaxy (MBE) method. At this time, the opening 1
Platinum silicide film 16 is formed only at the interface of polycrystalline silicon film 14 exposed from 5A. When platinum is etched using aqua regia with the platinum film deposited on the entire surface, the opening 15A
The platinum silicide film 16 formed at the more exposed interface of the polycrystalline silicon film 14 remains, and other platinum films are removed. The thickness of the platinum silicide film 16 formed in this case is approximately 1 nm to 10 nm. (The structure obtained in the steps so far is shown in FIG. 4D.) (5) A silicon oxide film 12 is formed to a thickness of 0.1 μm on the entire surface of the silicon substrate 1 on which the platinum silicide film 16 is formed by the CVD method. The silicon oxide film 1
2 is patterned into a desired shape, and a titanium film is deposited on the upper surface thereof to a thickness of 0.2 μm by a CVD method.
This is patterned to form titanium wirings 17A and 17B. (The structure obtained in the steps so far is shown in FIG.
(E). (6) After that, the silicon oxide film 18 is again deposited by the CVD method to a thickness of 0.2 μm (function as a protective film), and then at least the polycrystalline silicon 11 (sacrifice layer 11A) is exposed. The silicon oxide film 18
Is patterned into a desired shape. (The structure obtained in the steps so far is shown in FIG. 4 (f).) (7) As described above, the infrared receiving portion 10A and the leg 10C are covered with the silicon oxide film 18, and the sacrifice layer 11A is formed. In the exposed state, dry etching is performed to remove the polycrystalline silicon film 11 (sacrifice layer) to obtain the structure shown in FIG. The removal of the polycrystalline silicon film 11 is performed by plasma etching using a mixture of a chlorofluorocarbon-based gas (for example, F224) and sulfur hexafluoride (SF ₆ ).

Next, the configuration of the image sensor 20 using the thermal infrared sensor 10 will be described with reference to FIG. Although not shown in the drawing, the thermal infrared sensor 10 having the above configuration is arranged on the silicon substrate 11 in a two-dimensional lattice to form the image sensor 20. As shown in FIG. 5, the image sensor 20 is a MOS image sensor. In actuality, one image sensor 20 includes a large number of thermal infrared sensors 10, 10, 10,... In the horizontal and vertical directions. Hundreds of each are arranged, and these arranged thermal infrared sensors 10 constitute each pixel of the image sensor 20. Note that FIG. 5 shows an example in which a total of four thermal infrared sensors 10a to 10d are arranged in each of two pixels in the horizontal and vertical directions to simplify the description.

The operation will be described below with reference to FIG. The SBDs 21 to 24 of the thermal infrared sensors 10a to 10d are shown in FIG.
Is formed on the bonding surface between the platinum silicide film 16 and the polycrystalline silicon film 14 shown in FIG.
1 to 24 are thermally separated from the silicon substrate 1 by a microbridge structure.

The SBD of the thermal infrared sensor 10a
The drain of a p-type MOS transistor (vertical switch) 25 for reading is connected to 21, the gate of the vertical switch 25 is connected to a vertical scanning circuit 31, and the vertical switch 2
The source of No. 5 is connected to the vertical read line 37. The drain of a vertical switch 26 is connected to the SBD 22 of the thermal infrared sensor 10b.
Is connected to the vertical scanning circuit 31, and the source of the vertical switch 26 is connected to the vertical readout line 38.

The SBD 23 of the thermal infrared sensor 10c
Is connected to the drain of the vertical switch 27, the gate of the vertical switch 27 is connected to the vertical scanning circuit 31, and the source of the vertical switch 27 is connected to the vertical readout line 37. Also, the SBD 24 of the thermal infrared sensor 10d
Is connected to the drain of the vertical switch 28, the gate of the vertical switch 28 is connected to the vertical scanning circuit 31, and the source of the vertical switch 28 is connected to the vertical readout line 38.

One end of the vertical read line 37 is connected to the drain of a horizontal output p-type MOS transistor (horizontal switch) 35, the gate of the horizontal switch 35 is connected to the horizontal scanning circuit 32, and the source of the horizontal switch 35 is output. It is connected to terminal 39. On the other hand, the drain of a horizontal output p-type MOS transistor (horizontal switch) 36 is connected to one end of the vertical read line 38, the gate of the horizontal switch 36 is connected to the horizontal scanning circuit 32, and the source of the horizontal switch 36 is an output terminal. 39 is connected. An OP amplifier 34, a feedback resistor 33, and a power supply E are connected between the output terminal 39 and the horizontal switches 35 and 36.

Horizontal scanning circuit 32 and vertical scanning circuit 31
Are each constituted by a shift register or the like, and are each driven by a clock pulse and a start pulse. The horizontal scanning circuit 32 generates drive pulses Φ1 and Φ2, and outputs these to the horizontal switches 35 and 36, respectively. On the other hand, the vertical scanning circuit 31 generates drive pulses Φ11 and Φ12, which are
7 and 28, respectively.

The driving pulses Φ1 and Φ2 output from the horizontal scanning circuit 32 are supplied to the gates of the horizontal switches 35 and 36, respectively, and the ON / OFF timing of the horizontal switches 35 and 36 is controlled. On the other hand, the driving pulses Φ11 and Φ12 output from the vertical scanning circuit 31
5 and 26, respectively, are supplied to the gates of the vertical switches 27 and 28, respectively.
8 is controlled.

By controlling the on / off timing of the horizontal switches 35, 36 and the vertical switches 25, 26, 27, 28 in this manner, each of the thermal infrared sensors 10a to 10a is controlled.
10d and the output terminal 39 conduct at a predetermined timing. Assuming that the voltage at the output terminal 39 is V0 and the voltage of the power supply E is Vp, the current flowing through the SBD 21 flows into the feedback resistor 33 connected in parallel with the OP amplifier 34. As a result,
Since the voltage drop across the feedback resistor 33 becomes equal to V0-Vp, the SBD is measured by measuring the output voltage V0.
Can be measured.

Thus, the current IR represents the amount of infrared rays incident on the thermal infrared sensors 10,. In the image sensor 20 having such a configuration, the pulse signals Φ11 and Φ11 from the vertical scanning circuit 31 and the horizontal scanning circuit 32 are output.
Vertical switches 25, 26, 2 using Φ12, Φ1, Φ2
By turning on and off the horizontal switches 7 and 28 and the horizontal switches 35 and 36, the function as an infrared image sensor is achieved.

FIG. 6 shows a thermal infrared sensor 10 'according to a first modification of the first embodiment. This thermal infrared sensor 10 'is different from the thermal infrared sensor 10 in that a silicon nitride film 19 is further formed on the surface of the infrared light receiving portion 10A' as an infrared absorbing film.
This is different from the thermal infrared sensor 10 described above. As described above, by forming the silicon nitride film 19 in addition to the platinum silicide film 16 as the infrared absorption film, the sensor sensitivity of the thermal infrared sensor 10 'is further improved.

In this case, the infrared light transmitted through the silicon nitride film 19 and the platinum silicide film 16 is reflected by the reflection film (aluminum film 13), and is then absorbed by the platinum silicide film 16 so as to be efficiently absorbed by the polycrystalline silicon. The thickness d of the film 14 is determined. The thickness d of the polycrystalline silicon film is the same as that of the thermal infrared sensor 1 of the first embodiment.
Like the film thickness d at 0, it is determined based on the above-mentioned relational expression (2).

The thermal infrared sensor 1 shown in FIG.
Of the parts 0 ', the same parts as those of the thermal infrared sensor 10 shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 7 shows a thermal infrared sensor 10 ″ according to a second modification of the first embodiment.
In the case of 0 ", the point that the aluminum film 13" is formed outside the protective film (silicon oxide film 12), that is, outside the infrared light receiving portion 10A (the lower part in FIG. 7) is different from the first embodiment described above. different.

As described above, the reflecting film (aluminum film 13 ″) is
By providing the film on the outside of the infrared light receiving portion 10A, not only the film thickness d14 of the polycrystalline silicon film 14 but also the film thickness d12 of the silicon oxide film 12 can be reduced by the infrared absorbing film (in this case, the platinum silicide film 16) and the reflecting film ( In this case, the aluminum film 1
3) can be used to provide an interval d, which increases the degree of freedom in design.

The thermal infrared sensor 1 shown in FIG.
The same reference numerals as those of the thermal infrared sensor 10 described above denote the same parts of the thermal infrared sensor 10, and a description thereof will be omitted. The thermal infrared sensor according to the first and second modifications is described. Needless to say, an image sensor having the same configuration as the image sensor 20 can be obtained by arranging a large number of 10 'and 10 "as shown in FIG.

In the first embodiment, the reflection film (aluminum film 13) and the infrared absorption film (platinum silicide film 1) are used.
6), an example in which the polycrystalline silicon film 14 is formed between the reflective film and the infrared absorption film is obtained. Can be Further, in the first embodiment, the example in which the sacrifice layer 11A is formed of the polycrystalline silicon film 11 has been described. Alternatively, the sacrifice layer may be formed of polyimide or the like.

In the first embodiment, an example in which the Schottky barrier diode is composed of the platinum silicide film 16 and the polycrystalline silicon film 14 has been described.
The same effect can be obtained even if other Schottky barrier diodes such as a gold and n-type polycrystalline silicon film, a tungsten and n-type polycrystalline silicon film, and a platinum and n-type polycrystalline silicon film are formed. The effect is obtained.

Further, a p-type polycrystalline silicon film is used instead of the above-mentioned n-type polycrystalline silicon film, and this p-type polycrystalline silicon film and platinum silicide or another metal are used.
A Schottky barrier diode may be configured. In this case, the guard ring, the respective diffusion layers constituting the pn junction, and the like are formed so as to have conductivity opposite to that of the above embodiment.

In the first embodiment, an example in which a Schottky barrier diode is formed in the infrared light receiving portion 10A has been described. Instead, a pn junction type diode is formed in the polycrystalline silicon film 14. To the infrared receiver 10A
May be formed. In this case, a silicon nitride film or a metal film that efficiently absorbs heat may be formed above the polycrystalline silicon film 14 (on the side where infrared rays are incident), and these may be used as infrared absorption films.

(Second Embodiment) Next, a second embodiment will be described. The thermal infrared sensor 40 according to the second embodiment is a bolometer, and the second embodiment is a bolometer according to the first, second, seventh, ninth, and tenth aspects.
Corresponding to The configuration of the thermal infrared sensor 40 according to the second embodiment will be described with reference to FIG.

As shown in FIG. 8, the thermal infrared sensor 40 has a bridge structure in which an infrared receiving section 40A is supported by a leg 40C above a base body 40B. A polycrystalline silicon film 44 is formed as a resistor of the bolometer. When the temperature of the infrared light receiving portion 40A changes according to the intensity of the infrared light incident on the infrared light receiving portion 40A, the resistance value of the polycrystalline silicon film 44 changes according to the temperature change. Thus,
By applying a predetermined voltage to both ends of the polycrystalline silicon film 44 and detecting the value of the current flowing at that time, the intensity of the incident infrared light can be obtained.

Next, the configuration of the thermal infrared sensor 40 will be specifically described. A read circuit (not shown) for transmitting an output signal generated by the thermal infrared sensor 40 to the outside is formed on the silicon substrate 1, and a silicon oxide film 2 is formed so as to cover the surface of the read circuit. ing. Silicon substrate 1 on which silicon oxide film 2 is formed
A silicon oxide film 42 is formed in a bridge shape on the upper surface of the substrate, and an aluminum film 43 is formed on a lower surface of a central portion thereof.

On the other hand, on the upper surface of the silicon oxide film 42, a polycrystalline silicon film 4 having a substantially same planar shape as the aluminum film 43 is formed.
4 is formed with a predetermined film thickness.
Are formed with n-type diffusion layers 44A and 44B. On the upper surface of the polycrystalline silicon film 44, titanium films 47A and 47B are formed via a silicon oxide film 45, and the titanium films 47A and 47B are formed through contact holes provided in the silicon oxide film 45. Above n
The diffusion layers 44A and 44B are electrically connected.

On the other hand, the titanium films 47A and 47B
Readout circuit formed on silicon substrate 1 side (not shown)
Are electrically connected to each other to send a signal indicating a change in the resistance value of the polycrystalline silicon film 44 to a readout circuit (not shown) on the silicon substrate 1. On the upper surface of the silicon oxide film 45, a metal film 46 made of gold black in which gold is deposited in a state of large particles is formed. This metal film 46 is used as an infrared absorbing film.

A silicon nitride film 48 (protective film) is formed on the entire surface so as to cover the silicon oxide film 42, the polycrystalline silicon film 44, the silicon oxide film 45, and the metal film 46. In this case, the silicon nitride film 48 is also used as an infrared absorbing film. In the thermal infrared sensor 40 configured as described above, the temperature of the infrared light receiving portion 40A changes mainly because the metal film 46 and the silicon nitride film 48 absorb infrared light, and the temperature change causes the polycrystalline silicon film 44 to change. Changes its resistance value (physical properties).

By the way, in the thermal infrared sensor 40 of the present embodiment, the distance d40 between the aluminum film 43 and the metal film 46 is determined by the silicon oxide film 42, the polycrystalline silicon film 44,
It is determined by the thickness of the silicon oxide film 46. Thus, the thickness d40 is such that the infrared light transmitted through the metal film 46 is
When the infrared light reflected by the aluminum film 43 (reflection film) is reflected by the infrared light incident on the metal film 46,
The determination is made in the same manner as in the first embodiment so as to obtain the effect of the optical cavity.

The desired film thickness d40 for achieving the optical cavity is determined by the infrared absorption film (metal film 46).
The larger the refractive index “n” of the film formed between the film and the reflective film (aluminum film 43), the smaller the value can be. Thus, the infrared absorbing film (metal film 46)
Is reflected by the reflection film (aluminum film 43) and is again absorbed by the infrared absorption film (metal film 46), so that the height h40 of the cavity S is reduced by the infrared light receiving portion 40A.
The required minimum height for reducing the thermal conductance between the silicon substrate 1 and the silicon substrate 1 is sufficient.

When the thermal infrared sensor 40 is formed, the step between the silicon substrate 1 and the infrared light receiving portion 40A can be reduced by an amount corresponding to the lower cavity S. In addition, there is no shift in focus, and fine photolithography can be performed. The aluminum film 43 and the infrared absorbing film (metal film 4
Since the interval d40 with 6) can be accurately maintained at a constant value, it is possible to prevent variations in sensor sensitivity among the thermal infrared sensors in an apparatus using a large number of thermal infrared sensors such as an image sensor.

It is needless to say that the thermal infrared sensor 40 according to the second embodiment can be an image sensor having the same configuration as the image sensor 20 even when laid out as shown in FIG. is there. In the thermal infrared sensor 40 according to the second embodiment, the reflection film (the aluminum film 4) is used.
The infrared light reflected in 3) is efficiently absorbed by the metal film 46. However, when only the silicon nitride film 48 is used as the infrared absorbing film without providing the metal film 46, the aluminum film 43 (reflection film) is used. The distance between the upper surface of ()) and the lower surface of the silicon nitride film 48 may be determined to a value at which an optical cavity can be obtained.

(Third Embodiment) Next, a third embodiment will be described. The thermal infrared sensor 50 of the third embodiment is also a bolometer, and the third embodiment corresponds to claims 1, 2, and 7 to 10. The configuration of the thermal infrared sensor 50 according to the third embodiment will be described with reference to FIG.

As shown in FIG. 9, the thermal infrared sensor 50 has a bridge structure in which an infrared receiving section 50A is supported by a leg 50C above a base 50B. Then, a polycrystalline silicon film 54 is formed as a resistor of the bolometer in the infrared receiving section 50A. When the temperature of the infrared light receiving portion 50A changes according to the intensity of the infrared light incident on the infrared light receiving portion 50A, the resistance of the polycrystalline silicon film 54 changes according to the temperature change. .

On the upper surface of the polycrystalline silicon film 54, a titanium thin film 56 which functions as an infrared absorbing film and also functions as a bolometer electrode is formed with a thickness of 0.01 μm.

On the other hand, on the lower surface of the polycrystalline silicon film 54,
A titanium film 53 that functions as a reflection film and also functions as an electrode of the bolometer is formed with a thickness of 0.1 μm. And the titanium thin film 56 is made of titanium film 57B.
And the titanium film 53 is electrically connected to the titanium film 57A.

On the other hand, the titanium films 57A and 57B, on the other hand, are electrically connected to a readout circuit (not shown) formed on the silicon substrate 1 side, and change in accordance with a temperature change of the infrared light receiving section 50A. A wiring for sending an output signal representing the resistance value of the crystalline silicon film 54 to a readout circuit (not shown) on the silicon substrate 1 is configured. The thermal infrared sensor 5
The other configuration of 0 is substantially the same as that of the thermal infrared sensor 40 of the above-described second embodiment. Corresponding portions are denoted by the same reference numerals, and a detailed description thereof will be omitted.

The thermal infrared sensor 5 of the third embodiment
0, the distance d between the titanium thin film 56 and the titanium film 53 is d.
50 is the thickness of the polycrystalline silicon film 54 formed between them. Thus, when the infrared light transmitted through the titanium thin film 56 provided as an infrared absorbing film is reflected by the titanium film 53, the reflected infrared light and the infrared light incident on the titanium thin film 56 also have a thickness d50. Is determined based on the relational expression (2) in the same manner as in the first embodiment so that an effect due to the optical cavity can be obtained.

Also in the third embodiment, the height h of the cavity S is
The minimum height 50 required for reducing the thermal conductance between the infrared light receiving portion 50A and the silicon substrate 1 is sufficient. Further, when the thermal infrared sensor 50 is formed, the step between the silicon substrate 1 and the infrared light receiving portion 50A is reduced by the amount that the cavity S can be reduced. And fine photolithography.

Further, since the interval d50 between the titanium film 53 and the infrared absorbing film (metal film 56) constituting the reflecting film can be accurately maintained at a constant value, a large number of thermal infrared sensors such as image sensors are used. In the device, it is possible to prevent variations in sensor sensitivity between the thermal infrared sensors.
In addition, by using the titanium thin film 56 as an infrared absorbing film and an electrode and using the titanium film 53 as a reflecting film and an electrode as described above, it is not necessary to separately form an electrode. A change in the resistance (physical property) of the polycrystalline silicon film 54 in accordance with the temperature change of the infrared light receiving unit 50A having received the light can be electrically detected with high accuracy.

Further, since the titanium thin film 56 also serves as an infrared absorbing film and an electrode and the titanium film 53 also serves as a reflecting film and an electrode, there is no need to separately form an electrode.
In the manufacturing process, a separate process for forming an electrode is not required, and the manufacturing cost can be reduced. Furthermore,
Since there is no need to separately form an electrode, the infrared receiving unit 50A
The weight of the sensor can be reduced to provide a sensor that is strong against impact. In addition, the sensitivity of the sensor can be increased by making the leg 10C thinner by the weight of the infrared receiver 50A.

Incidentally, even if the thermal infrared sensor 50 according to the third embodiment is laid out as shown in FIG. 5, it is needless to say that an image sensor having the same configuration as the image sensor 20 can be obtained. is there. Further, in the thermal infrared sensor 50 of the third embodiment described above, an example in which the titanium thin film 56 is used as the infrared absorbing film 56 has been described. An infrared absorbing film may be formed.

In the first to third embodiments, an example in which a polycrystalline silicon film is formed between the infrared absorbing film and the reflecting film has been described. The same function and effect can be obtained in a thermal infrared sensor in which an amorphous silicon film is formed between them.

Further, in each of the thermal infrared sensors 10,... Of the first to third embodiments, an example in which the protective film is formed of a silicon oxide film or a silicon nitride film has been described. A silicon film or the like may be used. Note that the material of the protective film can be appropriately determined according to the material of the sacrificial layer when forming the cavity S, the etchant, and the like.

[0085]

As described above, according to the first to ninth aspects of the present invention, the distance between the reflecting film and the infrared absorbing film is one.
Or, since it is provided via two or more films, it is easy to maintain a desired distance between the reflection film and the infrared absorption film, and the effect of the optical cavity becomes large, thereby increasing the sensor sensitivity. In addition, the structure of the thermal infrared sensor is also flattened, and a focus shift in photolithography is avoided in the manufacturing process. Also, since the distance between the infrared absorption film and the reflection film can be reduced,
When the cavity is achieved, the film thickness of the infrared light receiving section can be reduced, the legs of the bridge structure can be made thinner, the thermal conductance of the infrared light receiving section can be increased, and the sensor sensitivity can be improved. .

According to the tenth aspect of the present invention, the structure of the thermal infrared sensor is flattened while increasing the sensitivity of the sensor, and the sensitivity of the thermal infrared sensor does not vary. Performance is improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a thermal infrared sensor 10 according to a first embodiment.

FIG. 2 shows a polycrystalline silicon film 14 of the thermal infrared sensor 10.
3 is a graph showing the relationship between the thickness of the infrared ray and the infrared absorption.

FIG. 3 is a sectional view showing a manufacturing process of the thermal infrared sensor 10.

FIG. 4 is a cross-sectional view showing a manufacturing process of the thermal infrared sensor 10 performed after the manufacturing process shown in FIG.

FIG. 5 is an image sensor 20 using the infrared sensor 10.
FIG. 3 is a circuit diagram of a data read circuit of FIG.

FIG. 6 is a cross-sectional view illustrating a thermal infrared sensor 10 ′ of a first modification of the first embodiment.

FIG. 7 is a sectional view showing a thermal infrared sensor 10 ″ according to a second modification of the first embodiment.

FIG. 8 is a sectional view showing a thermal infrared sensor 40 according to the second embodiment.

FIG. 9 is a cross-sectional view illustrating a thermal infrared sensor 50 according to a third embodiment.

FIG. 10 is a cross-sectional view showing a conventional thermal infrared sensor 100.

[Explanation of symbols]

 Reference Signs List 1 semiconductor substrate (silicon substrate) 11A sacrificial layer 10, 40, 50 thermal infrared sensor 10A, 40A, 50A infrared light receiving unit 10C, 40C, 50C leg 10D reflective film 13, 43 aluminum film (reflective film) 14, 44, 54 polycrystalline silicon film 16 platinum silicide film (infrared absorbing film) 20 image sensor 46 metal film (infrared absorbing film) 53 titanium film (reflecting film) 56 titanium thin film (infrared absorbing film) S cavity

Claims (10)

[Claims] 1. A thermal infrared sensor having a bridge structure in which at least an infrared ray receiving section having an infrared ray absorbing film on a semiconductor substrate is supported by a leg portion, wherein a predetermined film thickness of 1 or 2 is provided below the infrared ray absorbing film. A thermal infrared sensor, wherein a reflective film is formed via the above film, and the infrared absorbing film and the reflective film are separated by a predetermined distance. 2. The predetermined interval is: d = (2N−1) × λ / (4n) (d is a predetermined interval, n is a refractive index of a film formed between the infrared absorbing film and the reflecting film, and λ Is the wavelength of the infrared light to be detected, N
2. The thermal infrared sensor according to claim 1, wherein the thermal infrared sensor is determined so as to satisfy the following condition. 3. The thermal infrared sensor according to claim 1, wherein a diode is formed in the infrared light receiving section. 4. The infrared absorption film is formed of a metal film, and a polycrystalline silicon film or an amorphous silicon film is formed between the metal film and the reflection film. 4. A Schottky barrier diode is formed on a junction surface with a silicon film or an amorphous silicon film.
The thermal infrared sensor according to any one of the above. 5. The thermal infrared sensor according to claim 4, wherein the metal film is a silicide film. 6. The method according to claim 1, wherein the reflection film is used as an electrode for electrically reading out a change in physical properties according to a change in temperature of the infrared light receiving unit. 2. A thermal infrared sensor according to claim 1. 7. The method according to claim 1, wherein a polycrystalline silicon film or an amorphous silicon film serving as a resistor of the bolometer is formed between the infrared absorption film and the reflection film. The thermal infrared sensor as described in the above. 8. The method according to claim 7, wherein the infrared absorption film and the reflection film are used as electrodes for electrically reading out a change in physical properties according to a temperature change of the infrared light receiving unit. The thermal infrared sensor as described in the above. 9. The infrared light receiving section comprises: a silicon oxide film;
9. The semiconductor device according to claim 1, wherein the semiconductor device is covered with at least one of a silicon nitride film and a silicon oxynitride film.
The thermal infrared sensor according to any one of the above. 10. An image sensor using a thermal infrared sensor, wherein a plurality of thermal infrared sensors according to claim 1 are arranged in a line or in a plane. .