JPH09243449A - Infrared ray detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a light reception part vacuum-airtight and reduce a size and a cost by placing an infrared ray receiving window on a front of the light reception part with a gap and adhering the window airtightly to a substrate with an adhesive face completely surrounding the light reception part to make the gap vacuum. SOLUTION: Before an infrared ray receiving window 4 and a silicon substrate 1 are adhered to each other, solder 5 is placed on a side of the window 4, it is subjected to thermal treatment in a hydrogen atmosphere to remove an oxide film of the solder 5, and at the same time, the solder 5 is pasted to a metallized layer 5 on a side of a light receiving face. Subsequently, temperature is lowered until the solder 5 is solidified, the solder 5 of the window 4 and the metallized layer 7 of the substrate 1 are aligned in position, they are subjected to thermal treatment in a vacuum, and the window 4 is adhered to the substrate 1 by the solder 5 with a gap 3 provided to completely surround an infrared ray receiving part 2 on a front of the thermal-type receiving part 2 formed on the substrate 1. Since the oxide film of the solder 5 is removed in the hydrogen atmosphere before adhesion, they can be adhered without using soldering flux, while, since they are airtightly adhered in a vacuum, the gap 3 can be made vacuum-airtightly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared detector, and more particularly to a bolometer type, thermopile type and pyroelectric type infrared detector which requires a light receiving portion to be vacuum-tight.

[0002]

2. Description of the Related Art Recently, optical devices using infrared rays have been actively used and used for nighttime monitoring and temperature measurement. With the expansion of this application, the development of an inexpensive infrared detector using a bolometer, thermopile, or pyroelectric thermal detector has been demanded. For example, as described in JP-A-2-196929 and JP-A-4-500437, a bolometer type infrared detector in which each pixel of the detector is floated in a hollow structure with a bridge structure, SPIE Proceeding Vol. 2269Inf
rare Technology XX, (199
4) pages 450 to 459, a thermopile type detector, or a pyroelectric type detector described in Japanese Patent Laid-Open No. 7-243908 discloses an array of infrared detecting pixels on a silicon substrate. It is an infrared detection element formed, and it becomes possible to detect infrared rays as an image by this element. These thermal detectors do not require element cooling compared to quantum infrared image detectors,
It has an advantage that it can be provided as a low-cost infrared detector.

However, the thermal detector converts incident infrared light absorbed by the light receiving portion into a change in temperature of the light receiving portion and detects this as a signal. Therefore, it is highly sensitive to increase the thermal insulation of the light receiving portion. Needed to get detector. In the prior art, in order to obtain high thermal insulation, a method of arranging the entire substrate forming the detection element in a vacuum package has been adopted. As a vacuum package, for example, as shown in FIG. 7, a stem (base) 15 made of ceramic is used.
The infrared detecting element 20 is adhered to, the cap 16 having the infrared receiving window 4 attached thereto is placed on the front surface of the detecting element 20, and airtightly adheres to the stem 15. The inside of the cap 16 is evacuated through the exhaust pipe 17 attached to the cap 16, and the end surface of the exhaust pipe 17 is sealed to finally obtain a vacuum package. The signal of the detection element 20 is the wire bond 18
Is connected to the wiring pad of the device and the signal pin 19 penetrating the stem 15 to be taken out of the package.

In the method of maintaining the thermal insulation of the detection element by such a vacuum package, it is difficult to reduce the size of the detector because the size of the entire detector is determined by the vacuum package no matter how small the detection element may be. Needless to say. In addition, the mounting process of the detection element using the vacuum package is not only complicated, but also requires expensive parts such as a ceramic stem and a large light receiving window, which is not necessarily a low-cost detector.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in order to solve the above problems, and it is possible to obtain vacuum airtightness for attaining thermal insulation of a light receiving portion, and to be small in size and low in cost. The purpose is to obtain an infrared detector.

[0006]

An infrared detector according to the present invention is a bolometer type, thermopile type, and pyroelectric type infrared detector in which a light receiving portion is formed on a silicon substrate. Is disposed with a gap on the front surface of the light receiving window, the light receiving window is airtightly adhered to the substrate with an adhesive surface that completely surrounds the light receiving portion, and the gap is evacuated.

Further, in the infrared detector of the present invention, the infrared receiving window arranged with a gap in front of the light receiving portion is
It is characterized in that it has a thickness in the range of 0.1 to 1.5 mm and is made of silicon having both sides polished.

Further, in the infrared detector of the present invention, the infrared receiving window arranged with a gap in front of the light receiving portion is
It is characterized in that it has a thickness in the range of 0.1 to 1.5 mm and is made of silicon having both surfaces polished and antireflection films on both surfaces.

Further, in the infrared detector of the present invention, the infrared receiving window arranged with a gap in front of the light receiving portion is
It is characterized in that it is hermetically adhered by solder to the silicon substrate on which the light receiving portion is formed.

Further, the infrared detector of the present invention is characterized in that the gap between the infrared receiving window and the silicon substrate on which the light receiving portion is formed is a vacuum of 1 × 10 ^-2 torr or less.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiment 1 FIG. 1 is a sectional explanatory view of an infrared detector according to Embodiment 1 of the present invention. In the infrared detector according to the first embodiment of the present invention, an infrared receiving window 4 having a void 3 is formed on the silicon substrate 1 with solder 5 on the front surface of a thermal type infrared receiving portion 2 formed on the silicon substrate 1. It is glued. FIG. 2 shows FIG.
Is viewed from above, and the light receiving window 4 is adhered by an adhesive surface 6 that completely surrounds the infrared light receiving portion 2 to make the light receiving portion 2 airtight. The adhesive surface between the light receiving window 4 and the solder 5 of the silicon substrate 1 was coated with a metallization layer 7 in advance in order to improve the wettability of the solder. In addition, the silicon substrate 1
Although the adhesive surface of crosses the wiring 8 for extracting the signal,
In order to prevent damage at the time of adhesion, the silicon oxide film 9 was previously coated as a protective film by a sputtering method on the portion corresponding to the adhesion surface on the silicon substrate side. Next, the space 3 between the light receiving window 4 and the silicon substrate 1 needs to be evacuated,
It depends on the following procedure. First, before bonding the light receiving window 4 and the silicon substrate 1 to each other, solder is placed on the light receiving window side and heat treatment is performed in a hydrogen atmosphere. As a result, the oxide film of the solder is removed, and at the same time, the solder is adhered to the metallized layer on the light receiving surface side. Next, the temperature is lowered until the solder is solidified, the solder of the light receiving window 4 and the metallization of the silicon substrate 1 are aligned, and then heat treatment is performed in vacuum to hermetically bond the light receiving window 4 and the silicon substrate 1. Since the solder oxide film is removed in advance in a hydrogen atmosphere, good adhesion is achieved without using a solder flux. Further, since the airtight bonding is performed in a vacuum, the void 3 is kept in a vacuum. In this way, a light receiving element in which the light receiving section 2 is made airtight is obtained. It should be noted that the pads 10 and the wirings 8 in FIG. 2 are drawn to show the features of the present invention, and that the size and the number are different from those of the first embodiment.

Further, the infrared light receiving section 2 of the first embodiment
As shown in FIG. 3, a thermal insulation gap 21 is formed by the bridge structure 11, and a thermal infrared detection circuit is provided on the bridge 11 and is arrayed on the substrate as shown in FIG. It is arranged in a line. One bridge corresponds to one pixel. The detection circuit includes a bolometer resistor 13 and converts the temperature that changes when the upper part of the bridge absorbs infrared rays into a resistance change of the bolometer, and the wiring 8 arranged on the substrate from the electrodes at both ends of the bolometer via supporting legs of the bridge structure. To detect the signal. In this type of infrared detector, the thermal insulation of the detection circuit is important, and the surroundings of the bridge 11 including the gap 21 are in a vacuum state. It should be noted that this bolometer type light receiving unit is an example of the present invention, and it is obvious that the present invention can also obtain the same effect in a thermopile type or pyroelectric type light receiving unit where thermal insulation is important. .

Since infrared radiation from a human body or a room temperature object has a peak near a wavelength of 10 μm, the infrared receiving window 4 can pass 10 μm infrared rays, germanium, silicon, zinc sulfide, zinc selenide. Any material such as can be used. Among them, silicon can be obtained at a relatively low cost among infrared ray transmissive materials, so low cost can be realized, and since it is the same material as the substrate to be bonded, there is no mismatch in thermal expansion and the bonding of the light receiving window is reliable. It will be highly responsive.

However, if the thickness of the light receiving window is too thin, silicon is not preferable because deformation of the light receiving window becomes large due to a vacuum gap between the light receiving window and the substrate to be bonded. In the first embodiment, the size of the silicon light receiving window 4 is set to 20.
× 20mm, and changing the thickness, the thickness 0.1mm
The maximum amount of deformation at the center of the window is about 0.1 mm, but when it is thinner, the amount of deformation sharply increases. Therefore, the lower limit of the thickness of the silicon light receiving window 4 is preferably 0.1 mm or more. Further, since silicon has some absorption in the vicinity of the wavelength of 10 μm, it is not preferable to make it too thick. In the silicon light receiving window 4 having both surfaces polished according to the first embodiment, the average absorption rate at a wavelength of 8 to 12 μm at a thickness of 1.5 mm was 9.7%. In order to prevent deterioration of sensitivity due to a decrease in infrared transmittance, it is desirable that the average absorptance is 10% or less in the wavelength band of 8 to 12 μm. Therefore, the upper limit of the thickness of the silicon light receiving window 4 is 1. 5 mm
It is preferable that

On the other hand, if silicon is used as it is as the infrared ray receiving window 4, since silicon is a material having a high refractive index characteristic, reflection loss is large, which is not preferable when a detector is required to have high sensitivity. In the first embodiment, both surfaces of silicon are coated with zinc sulfide by a vacuum vapor deposition method having a thickness of 1.1 μm to form an antireflection film. As a result, in the silicon light receiving window having a thickness of 1 mm as shown in FIG. 6, the transmittance at a wavelength of 10 μm was 85%.

The infrared light receiving window 4 may be bonded to the silicon substrate by soldering, glass frit, thermocompression bonding or the like. However, glass frit generally has a high processing temperature, and airtight bonding is performed at a temperature lower than the heat resistant temperature of the light receiving element. It's difficult. Further, in thermocompression bonding, it is difficult to carry out vacuum airtightness due to a step difference on the substrate surface which is slightly generated when the adhesive portion for adhering the light receiving window crosses the wiring 7. On the other hand, bonding with solder is
Needless to say, there is a track record in the mounting process of silicon elements such as memories and logics, and the bonding temperature can be lower than the heat resistant temperature of the element. Since the solder bonding performed in the first embodiment has a bump structure with a thick bonding portion as shown in FIG. 1, only the solder is sufficient for the gap 3 between the light receiving window 4 and the silicon substrate 1. Not only was it possible to obtain a high height, but it was also possible to absorb the level difference due to the wiring on the substrate. Light receiving window 4 and silicon substrate 1
In order to improve the wettability of the solder, the contact portion 6 of the solder of
Three layers of 000Å and 1000 Å of gold were metallized in this order by a sputtering device. The solder used is a lead-tin type, which is initially heat-treated in a hydrogen atmosphere at 350 ° C to remove (reduce) the oxidation of the solder, and then adhere at a temperature of 350 ° C in a vacuum state of 1 × 10 ^-2 torr or less. went. On the silicon substrate side, in order to prevent damage when the solder bonding portion 6 crosses over the wiring, the solder bonding portion 6 was previously coated with silicon oxide having a thickness of 7,000 Å as a protective film.

The degree of vacuum around the light receiving portion of the device is important for obtaining high thermal insulation. The degree of vacuum was detected by the value indicated by a vacuum gauge in the constant temperature layer used when the light receiving window 4 and the silicon substrate 1 were bonded together. In the infrared detector according to the first embodiment, as shown in FIG. 8, when the relative sensitivity when the degree of vacuum is sufficiently increased is set to 1 and the correlation between the degree of vacuum and the sensitivity is observed, 1 × 10 ^−2. There was no significant decrease in sensitivity up to torr, but when the degree of vacuum was worse than that, it rapidly deteriorated.
That is, the degree of vacuum is at least 1 × 10 ⁻² torr.
r or less is desirable.

Second Embodiment FIG. 5 shows a second embodiment of the present invention. The second embodiment is the same as the first embodiment except the shape of the light receiving window 14, and therefore the same effect can be expected. The light receiving window 14 is formed by making the bonding portion around the light receiving window with the substrate 1 convex. In this case, although the processing cost of the light receiving window 14 increases, the distance between the light receiving window 4 and the silicon substrate 1 is sufficient. Therefore, the present invention can be used even if the light receiving portion has a height. Further, since the thickness of the solder bump is not necessary to obtain the void 3, there is an advantage that the contact area of the solder can be reduced.

[0019]

According to the infrared detector of the present invention, in the bolometer type, thermopile type and pyroelectric type infrared detectors in which the light receiving portion is formed on the silicon substrate, the infrared receiving window is provided in front of the light receiving portion. The light receiving window is an adhesive surface that completely surrounds the light receiving portion, and is fixed by air-tightly adhering to the substrate on which the light receiving portion is formed, and the inside of the air gap is vacuumed. Therefore, there is an effect that a small-sized and low-cost infrared detector can be obtained.

The infrared receiving window has a thickness of 0.1 m.
When silicon is polished on both sides in the range of m to 1.5 mm, there is an effect that a low-cost and highly reliable infrared detector can be obtained.

The infrared receiving window has a thickness of 0.1 m.
When both surfaces are polished in the range of m to 1.5 mm and both surfaces are coated with an antireflection film, a high-performance infrared detector having excellent sensitivity can be obtained.

Further, when the infrared receiving window is airtightly adhered to the substrate on which the light receiving portion is formed by solder, there is an effect that a highly reliable infrared detector can be obtained.

In the infrared detector, when the vacuum degree of the gap between the light receiving window and the substrate on which the light receiving portion is formed is 10 ^-2 torr or less, an infrared detector having excellent sensitivity can be obtained. It is effective.

[Brief description of drawings]

FIG. 1 is a sectional explanatory view showing a structure of an infrared detector according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram of the first embodiment of the infrared detector of the present invention viewed from above (infrared receiving window).

FIG. 3 is a cross-sectional explanatory diagram of a light receiving portion used in the first embodiment of the present invention.

FIG. 4 is an explanatory cross-sectional view showing an arrangement state of light receiving portions of the present invention on a substrate.

FIG. 5 is a cross-sectional explanatory view of an infrared detector using an infrared receiving window having another shape according to the second embodiment of the infrared detector of the present invention.

FIG. 6 is a diagram showing the transmittance of an infrared transmitting window provided with an antireflection film used in the first embodiment of the present invention.

FIG. 7 is an explanatory sectional view showing a conventional example.

FIG. 8 is a diagram showing a correlation between vacuum degree and sensitivity.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Light receiving part 3 Air gap 4 Light receiving window 5 Solder 6 Adhesive surface 7 Metallization layer 8 Wiring 9 Silicon oxide protective film 10 Pad 11 Bridge 12 Antireflection film 13 Bolometer 14 Other light receiving window 15 Stem 16 Cap 17 Exhaust pipe 18 Wire Bond 19 Signal pin 20 Infrared detector 21 Gap

Claims (5)

[Claims] 1. In a bolometer-type, thermopile-type, and pyroelectric-type infrared detector in which a light receiving portion is formed on a silicon substrate, an infrared light receiving window is arranged with a gap in front of the light receiving portion, and An infrared detector characterized in that the light receiving window is an adhesive surface that completely surrounds the light receiving portion, is fixed by air-tightly adhering to the substrate on which the light receiving portion is formed, and the air gap is evacuated. 2. The infrared light receiving window arranged with a gap on the front surface of the light receiving portion is silicon whose both surfaces are polished in a thickness range of 0.1 mm to 1.5 mm. 1. The infrared detector according to 1. 3. An infrared light receiving window arranged with a gap on the front surface of the light receiving portion has a thickness in the range of 0.1 mm to 1.5 mm, both sides of which are polished and an antireflection film is applied to both sides. The infrared detector according to claim 1, which is made of silicon. 4. The infrared light receiving window, which is arranged with a gap on the front surface of the light receiving portion, is airtightly adhered to the silicon substrate on which the light receiving portion is formed by soldering. Infrared detector. 5. The infrared detector according to claim 1, wherein the degree of vacuum of the gap between the infrared light receiving window and the light receiving portion is 1 × 10 ⁻² torr or less.