JP2002365129A - Thermal type infrared detector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To restrain heat conduction in a support leg without imparting a stress onto a conductive material included inside an insulation protecting film. SOLUTION: In this thermal type infrared detector having diaphragm structure comprising a photoreceiving part 7, and the support leg 8 for holding the photoreceiving part in a hollow condition, tapered zones (support leg cut-out ends 23) in each of which at least one portion in a width is thinned gradually from an end part toward the center are provided in longitudinal both end sides of the support leg, a cross-sectional area in a base part area other than the tapered zones is reduced to restrain the heat conduction between the photoreceiving part and the substrate, and the stress is prevented from being concentrated in a boundary area by changing the width gradually.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermal infrared detector and, more particularly, to a support leg structure for supporting a light receiving portion of the thermal infrared detector.

[0002]

2. Description of the Related Art Thermal infrared detectors have received special attention among infrared detectors because they do not require cooling of the detector, operate at room temperature and are inexpensive. Among the thermal infrared detectors, those using a titanium bolometer as a heat-sensitive material will be described with reference to FIG. 5 and FIG. 6 showing a cross section thereof. A diaphragm 9 made up of an insulating film 3, an aluminum wiring (A) 4 a, an aluminum wiring (B) 4 b, and an aluminum wiring (C) is formed on the silicon substrate 1 including the readout circuit 2.
4c and the like, and is present in a form floating above the cavity 5.

As shown in FIG. 6 later, an infrared absorbing film 6 is provided on the surface of the light receiving section 7 to absorb incident infrared rays and correspond to the thermal conductivity indicating the ease with which heat can escape to the substrate side. As a result, the temperature of the light receiving section 7 rises, and the resistance of the titanium bolometer 10 which is one of the heat-sensitive materials provided in the area of the light receiving section 7 is changed. Electrically, the titanium bolometer 10 is composed of a conductive material 10a (corresponding to the titanium bolometer 10 in FIG. 5) contained in the support leg 8, and an aluminum wiring (A) 4
a, an aluminum wiring (B) 4b, an aluminum wiring (C) 4c, and a connection to the underlying readout circuit 2 via contacts (A) 11 and contacts (C) 12, which are electrical contacts between the aluminum wiring and the conductive material 10a. In addition, the signal can be read out.

FIG. 6 is a cross-sectional view from the vicinity of the contact (A) 11 to the vicinity of the contact (C) 12 along the titanium bolometer 10 of FIG. The chip of such a thermal infrared detector is actually used in a vacuum package so that the light receiving section 7 easily rises in temperature. Further, the diaphragm 9 is held on a vacuum cavity, and blocks heat from escaping to the substrate side immediately below the light receiving unit 7, and all heat of the light receiving unit 7 escapes through the support legs 8. Is By minimizing the thermal conductivity Gth as much as possible, a thermal isolation structure having a good thermal isolation state from the substrate side is produced. In the thermal type two-dimensional infrared detector, the thermal isolation structure is arranged in a two-dimensional array on a substrate including a readout scanning circuit.

[0005] In addition to the bolometer type, there are a pyroelectric type and a thermocouple type in addition to the bolometer type. The infrared sensitivity of these thermal type infrared detectors is such that the bolometer type has a resistance temperature coefficient of resistance. It is proportional to the thermoelectric conversion coefficient of the thermoelectric material, such as the pyroelectric coefficient for the pyroelectric type and the Seebeck coefficient for the thermocouple bolometer type. Further, the infrared light receiving sensitivity is proportional to the amount of received light and inversely proportional to the thermal conductivity of the support leg. The conventional example using a titanium bolometer will be described in more detail.

[0006] As disclosed in Japanese Patent Application Laid-Open No. 9-203659, "Bolometer type infrared detector", a titanium bolometer infrared detector using metallic titanium as a bolometer material which is a kind of thermoelectric conversion material is used in a normal silicon IC line. Manufacturable, relatively high temperature resolution,
There is an advantage that the yield of non-defective products is also high. In the thermal infrared detector of the titanium bolometer, in order to increase the absorptivity of infrared rays, in the area of the light receiving section 7, the metal titanium The bolometer 10 is provided as a mirror for infrared rays in a zigzag pattern (see FIG. 5), and the infrared absorbing film 6 made of an ultra-thin titanium nitride metal film having a thickness of about 150 ° is opposed to the upper side of the cross section of the diaphragm 9 (see FIG. 6). ), An infrared resonance cavity 18 (oval in FIG. 6) for absorbing infrared light is formed between the two. As shown in the cross-sectional view of FIG. 6, such an infrared absorbing mechanism has a length of the resonance cavity 18 of about 1 μm or more, and inevitably increases the thickness of the diaphragm of the light receiving section 7. Since the thickness of the leg 8 is also increased, the thermal conductivity of the supporting leg 8 is increased, which is slightly disadvantageous for obtaining high sensitivity.

Normally, the conductive material 10a is covered with an insulating protective film such as a third silicon oxide film 15, a fourth silicon oxide film 16 or the like to protect the conductive material 10a from damage during the manufacturing process. In order to reduce the thermal conductivity of the support legs 8 as much as possible, a photoresist method and a selective etching method are used.
It is composed of a conductive material width 20 that can be used in the production line and a support leg width 21 that has a minimum necessary margin in the production line.

In this case, as shown in FIG. 6B which shows a sectional view of the supporting leg at a sectional position 19 of the supporting leg in the sectional view along the titanium bolometer of FIG. 6A, the conductive material is located near the bottom of the rectangle. Since 10a is located, the fourth silicon oxide film 16, which is an insulating protective film thereabove, is cut off by, for example, half dry etching as shown in FIG. There are ways to reduce the degree.

[0009]

However, this etching is usually performed by using anisotropic dry etching, and the boundary between the above-mentioned support leg cut-out region 22 in the support leg 8 and the non-cut-out region outside the support leg 8 (see FIG. 1). Since a steep step is generated in the insulating protective film at the cut end 23) of the supporting leg, a large mechanical stress is generated at this boundary, and the conductive material 10a encapsulated in the insulating protective film.
Micro cracks are easily formed in This causes a problem of increasing defective pixels accompanied by an increase in resistance and deteriorating the yield of non-defective products.

The present invention has been made in view of the above problems, and a main object thereof is to suppress heat conduction in a supporting leg without applying stress to a conductive material included in an insulating protective film. It is an object of the present invention to provide a thermal-type infrared detector that can be used.

[0011]

In order to achieve the above object, a thermal infrared detector according to the present invention is a thermal infrared detector having a diaphragm structure comprising an infrared receiving section and supporting legs for holding the infrared receiving section in a hollow state. In the infrared detector, a tapered region having a gradually decreasing cross-sectional area from the end to the center is provided at both ends in the longitudinal direction of the support leg.

Further, the thermal infrared detector of the present invention is directed to a thermal infrared detector having a diaphragm structure comprising an infrared receiving portion and a supporting leg for holding the infrared receiving portion in a hollow direction. Are provided with tapered regions in which at least a part of the width gradually decreases from the end toward the center.

In the present invention, only the width of the upper end side of the support leg may be gradually reduced, and the cross section of the support leg may have a convex shape. And a width of the insulating protection film on the conductive material may be gradually reduced.

Further, the thermal infrared detector of the present invention is directed to a thermal infrared detector having a diaphragm structure comprising an infrared receiving portion and a supporting leg for holding the infrared receiving portion in a hollow, wherein the supporting leg has a longitudinal direction. Are provided with tapered regions whose thickness gradually decreases from the end to the center.

In the present invention, the support leg is formed so as to include a conductive material by upper and lower insulating protective films, and the thickness of the insulating protective film on the conductive material is limited in a region excluding the end portion. The infrared light receiving portion may be formed to be thinner than the insulating protective film.

In the present invention, the cross section of the tapered region in the longitudinal direction of the support leg may form a curved line, and the width or the film thickness may smoothly change even at the end of the tapered region. it can.

Thus, as shown in FIGS. 1 to 4 showing the supporting leg portion of the thermal separation structure, the thermal type infrared detector of the present invention gradually has its width or its thickness at the supporting leg cut end 23. The supporting legs are formed so that the cross-sectional area increases gradually, so that a large mechanical stress is not applied to the ends of the supporting legs, and micro-cracks are generated in the conductive material included therein. The heat resistance can be increased in the portion where the width or thickness is small and the outflow of heat from the light receiving portion can be suppressed.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In a preferred embodiment, a thermal infrared detector according to the present invention is a thermal infrared detector having a diaphragm structure comprising a light receiving portion and supporting legs for holding the light receiving portion in a hollow state. In each of the longitudinal ends of the support leg, a tapered region (support leg cut end) whose width or film thickness gradually decreases from the end toward the center, and the cross-sectional area of the base region other than the tapered region is reduced. By doing so, heat conduction between the light receiving portion and the substrate is suppressed, and stress is prevented from being concentrated on the boundary region by gradually changing the width or the film thickness.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

[Embodiment 1] First, a thermal infrared detector according to a first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an enlarged perspective view of a supporting leg portion of the thermal infrared detector according to the first embodiment, and FIG. 2 is a sectional view thereof. In the present embodiment, the thickness of the insulating protective film constituting the support leg of the thermal isolation structure of the thermal infrared detector is made thinner than the thickness of the insulating protective film of the light receiving portion in most of the support leg, and In the end region, the support leg is gradually tapered in the length direction of the support leg.

Hereinafter, a titanium bolometer infrared detector will be described as an example. As shown in FIGS. 1 and 2, the first embodiment is different from the conventional example in that the shape of the support leg cut end 23 shown in FIG. 7 is changed, and the other configuration is exactly the same as that of the conventional example. At the cut end 23 of the support leg, the support leg 8
Are provided such that the thickness of the insulating protective film gradually increases at both ends in the longitudinal direction.

FIG. 2A is a cross-sectional view along the length direction of the support leg 8 and shows the thickness formed on the first insulating protective film, that is, the third silicon oxide film 15 having a thickness of about 1000 °. A second insulating protective film having a thickness of about 1 μm, i.e., a fourth insulating protection film,
After the silicon oxide film 16 is provided, most of the supporting legs 8 (the supporting leg cutout regions 22) are subjected to an isotropic wet etching method such as a buffered hydrofluoric acid solution through openings of a resist mask formed by a photoresist method. For example, about half the thickness of the fourth silicon oxide film 16, that is, about 5500 °
A tapered step is provided at a boundary (support leg cut end 23) between the support leg cut region 22 (thin film portion) and the original thickness portion (thick film portion) outside thereof.

When the etching is performed in this manner, in most of the support leg cutout regions 22, the entire cross-sectional area of the insulating protective film becomes approximately half the cross-sectional area before the insulating protective film is cut off. in this case,
The connection between the thinnest portion of the insulating protective film and the tapered portion can be made completely smooth as shown by the broken line in the sectional view of the supporting leg along the titanium bolometer in FIG. It can be said that it is more desirable to reduce the stress at the support leg cut end 23 which is the boundary of the thin film portion. In addition, as a method of providing the tapered step at the cut-off end 23 of the support leg, dry etching accompanied by side etching of the resist or an isotropic dry etching method is also possible.

The thermal conductivity of the support leg 8 is the sum of the thermal conductivity of the insulating protective film and the thermal conductivity of the titanium metal. In the case of this embodiment, as shown in FIG. 1, the thickness of the support leg 8 is reduced to approximately half the thickness of the light receiving unit 7, and as a result, the cross-sectional area of the insulating protective film is reduced to approximately half. The overall thermal conductivity of the leg 8 was reduced to about 75%, and the sensitivity of the titanium bolometer infrared detector could be improved to about 1.3 times or more.

This is because, in the cross-sectional shape of the support leg 8 having the above-described dimensions, the thermal conductivity of the insulating protective film having a large cross-sectional area before cutting the support leg and a small thermal conductivity, and the thermal conductivity of the insulating protective film having a small cross-sectional area are small. The result is that the thermal conductivity of titanium, which is a conductive material having a high conductivity, is about the same as that of titanium, and the cross-sectional area of the insulating protective film is almost halved after the support leg is cut. When viewed in the longitudinal direction of the support leg 8, the thickness of the protective film gradually increases at the boundary where the thickness of both ends of the thin film region changes, and the stress is reduced because the thickness is not a steep step. Since micro cracks are also suppressed from entering the conductive material 10a, the problem of an increase in defective pixels due to an increase in resistance, which has conventionally occurred, can be solved.

[Embodiment 2] Next, a thermal infrared detector according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 3 is an enlarged perspective view of a supporting leg portion of the thermal infrared detector according to the second embodiment, and FIG. 4 is a sectional view thereof.

The second embodiment is characterized in that the shape of the support leg 8 of the conventional example shown in FIG. 7 is changed, and the other points are exactly the same as those of the conventional example. This is the same as the first embodiment. More specifically, in the second embodiment, both shoulders are removed by selective etching in the width direction of the support leg 8 so that the cross section of the support leg 8 becomes convex, and the support leg cut end 23 is formed.
In this case, the width of the upper end of the convex shape is gradually increased in the longitudinal direction of the support leg 8.

FIGS. 4 (a), 4 (b) and 4 (c) show a front view, a side view and a side view X1, X2 in the length direction of the support leg 8 each having a width of about 2 μm. , X3, each of which is formed of a titanium insulating film having a thickness of about 1000 ° and a width of about 1 μm formed on a first insulating protective film, ie, a third silicon oxide film 15 having a thickness of about 1000 °. After a second insulating protective film, that is, a fourth silicon oxide film 16 having a thickness of about 1 μm is provided on the fine wire of the conductive material 10a,
A convex sectional shape is formed by using a photoresist method and an anisotropic dry etching method. For example, up to about ４ of the fourth silicon oxide film 16, that is, about 75
At 00 °, both sides of the support leg are cut away by about 0.7 μm for one shoulder width, and a tapered widened portion is provided at the cut end 23 of the support leg.

In most of the support leg cutout area 22, the entire cross-sectional area of the insulating protective film is about half of the cross-sectional area before the insulating protective film is cut off. In this case, the region where the insulating protective film thickness is most narrowed and the tapered portion are connected at a certain angle. On the other hand, it can be said that it is more desirable to adopt a smooth connection method as shown by the dashed line in the figure in order to reduce the stress at the widened portion. This can be achieved by fine adjustment of the photoresist mask pattern.

As shown in FIG. 4, the width of the upper part of the first insulating protective film 13 is narrowed in most of the supporting legs, and the cross-sectional area of the insulating protective film is reduced to about half, so that the thermal conductivity is reduced. Can be reduced to about three-quarters of the value, and the sensitivity can be improved to about four-thirds. When viewed in the longitudinal direction of the support leg, the width of the upper portion of the first insulating protective film gradually increases at both ends of the cut region, and there is no rapid change in the cross-sectional area at both ends of the cut region. In addition, no large stress is applied to this boundary, and no microcracks enter the conductive material included in the protective film. Therefore, the number of defective pixels due to an increase in resistance is small, and the yield of non-defective products can be maintained high.

Also, in this embodiment, since the thickness of the support leg 8 is not uniformly reduced as in the first embodiment described above, only the corners are cut off to form a convex shape. Can be suppressed from decreasing even if the diameter becomes smaller.
Note that the cross-sectional shape is not limited to the convex shape, and may be an arbitrary shape such as an L-shape in which only one side is cut or a concave shape in which the center is cut.

Further, in each of the above embodiments, a titanium bolometer thermal infrared detector has been described as an example, but it goes without saying that the present invention can be generally applied to a case where the thickness of the insulating protective film of the supporting leg is sufficiently large. Further, it is needless to say that, when the support leg is thin, the width of the support leg is gradually increased at both ends to reduce the concentration of stress and suppress a resistance increase defect due to microcracks of the conductive material in the support leg.

[0033]

As described above, according to the thermal infrared detector of the present invention, by cutting off a part of the supporting leg, the cross-sectional area of the insulating protective film is reduced, so that the thermal conductivity is reduced. Thus, the sensitivity can be improved. In addition, since a steep step does not occur in the insulating protective film at the boundary between the cutout regions of the support legs, a large stress does not occur at this boundary, microcracks do not enter the conductive material included in the protective film, and there are few resistance defects. A two-dimensional thermal infrared detector can be obtained with high yield.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a supporting leg portion of a thermal infrared detector according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a supporting leg portion of the thermal infrared detector according to the first embodiment of the present invention.

FIG. 3 is a perspective view showing a supporting leg portion of a thermal infrared detector according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing a supporting leg portion of a thermal infrared detector according to a second embodiment of the present invention.

FIG. 5 is a perspective view showing a structure of a thermal infrared detector.

FIG. 6 is a sectional view showing a supporting leg portion of a conventional thermal infrared detector.

FIG. 7 is a view showing a supporting leg portion of a conventional thermal infrared detector.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Substrate 2 Readout circuit 3 Insulating film 4a Aluminum wiring (A) 4b Aluminum wiring (B) 4c Aluminum wiring (C) 5 Cavity 6 Infrared absorption layer 7 Light receiving part 8 Support leg 9 Diaphragm 10 Titanium bolometer 10a Conductive material 11 Contact (A 12 Contact (C) 13 Slit 14 Second silicon oxide film 15 Third silicon oxide film 16 Fourth silicon oxide film 17 Slit 18 Resonance cavity 19 Support leg cross-sectional position 20 Conductive material width 21 Support leg width 22 Support leg cut-out area 23 Support leg cut end

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 37/00 H01L 27/14 K F term (Reference) 2G065 AB02 BA11 BA12 BA13 BA14 BA34 CA13 DA18 DA20 2G066 BA04 BA08 BA09 BA55 BB09 CA02 4M118 AA10 AB01 CA20 CA40 CB20 DD02 EA04 EA20 GA10

Claims (7)

[Claims] 1. A thermal infrared detector having a diaphragm structure comprising an infrared receiving section and supporting legs for holding the infrared receiving section in a hollow state, wherein the supporting legs are provided at both ends in the longitudinal direction of the supporting legs, and from the end to the center. A thermal infrared detector comprising a tapered region whose cross-sectional area gradually decreases. 2. A thermal infrared detector having a diaphragm structure comprising an infrared receiving section and a supporting leg for holding the infrared receiving section in a hollow state, wherein the supporting leg is provided at both ends in the longitudinal direction and at the center from the end. A thermal infrared detector comprising a tapered region in which at least part of the width gradually decreases. 3. The thermal infrared detector according to claim 2, wherein only the width at the upper end side of said support leg is gradually reduced, and the cross section of said support leg is convex. 4. The method according to claim 2, wherein the support leg is formed so as to include a conductive material by upper and lower insulating protection films, and the width of the insulating protection film on the conductive material is gradually reduced. Or a thermal infrared detector according to 3. 5. A thermal infrared detector having a diaphragm structure comprising an infrared receiving section and a supporting leg for holding the infrared receiving section in a hollow, wherein the supporting leg is provided at both ends in the longitudinal direction of the supporting leg and at the center from the end. A thermal infrared detector comprising a tapered region whose thickness gradually decreases toward the surface. 6. The support leg is formed so as to enclose a conductive material with upper and lower insulating protective films, and the thickness of the insulating protective film on the conductive material is reduced in a region excluding the end portion. 6. The thermal infrared detector according to claim 5, wherein the thermal infrared detector is formed so as to be thinner than a part of the insulating protective film. 7. The tapered region has a curved cross section in the longitudinal direction of the support leg, and the width or the film thickness changes smoothly even at the end of the tapered region. The thermal infrared detector according to any one of the above.