JP2014190894A - Infrared sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an infrared sensor capable of maintaining high sensitivity and reducing deterioration of an infrared absorption film.SOLUTION: An infrared sensor includes: a substrate; a cavity that is formed inside the substrate; an absorption film absorption layer 9 that is in a membrane region corresponding to the cavity and in which a base material formed on the upper part of a heat sensitive element is a first organic material; and an absorption film protective layer 10 that is formed on the absorption film absorption layer and is a second organic material for coating the absorption film absorption layer. In a direction orthogonal to the lamination direction of the absorption film absorption layer and absorption film protective layer, the end part of the absorption film protective layer is formed inside the membrane region.

Description

  The present invention relates to an infrared sensor.

  Infrared sensors have been developed as temperature sensors and various applied sensors that use displacement as heat, and are used as small and inexpensive sensors. In recent years, the use of thin film and MEMS technology has led to further miniaturization and higher sensitivity, and since it has become possible to detect minute amounts of heat that cannot be detected in the past, further diversification of applications has progressed. It has come to be applied to response gas sensors and human sensors using arrays.

  As a method for sensing infrared rays and converting them into signals, for example, a thermopile using the Seebeck effect, or a platinum resistor or thermistor using a resistance change depending on the temperature of the material can be used. In both methods, the sensitivity to infrared rays has increased by minimizing the heat capacity, and it has become possible to measure the temperature of a substance in a non-contact manner and detect minute temperature changes. In order to achieve this, it is necessary to capture a very small amount of heat instantaneously without diffusing, and in each high-sensitivity infrared sensor, many sensors having an infrared absorption film that absorbs infrared rays have been seen.

  As an infrared absorbing film, a gold black film is generally known, and the infrared absorption efficiency is almost 100%, which is effective as a material. However, since this material is almost a powder, the mechanical property of the absorbing film itself Since there is no strength and it breaks easily after formation, a thin film type sensor with a membrane region must be formed after forming a cavity corresponding to the membrane region where the strength will be weakest, and patterning to the desired size Therefore, there is a problem that the structure of the essential membrane region is destroyed by passing through the photolithography process and the process of peeling the photolithography, the yield is lowered, and the cost is increased.

  Since an organic film itself has an infrared absorption effect, a method of using an organic substance as an infrared absorption film is effective. Since it is lighter than the metal blackening film, the yield of structures in the membrane region is improved. However, considering various uses of infrared sensors in recent years, the infrared absorbing film is the outermost layer of the sensor element, and thus characteristics and environmental resistance depending on the use application must be taken into consideration.

  In order to improve the infrared absorption characteristics of the organic substance absorption film, it is possible to improve the absorption effect by adding a filler that absorbs infrared rays and forming it thick, or by utilizing the cavity effect due to the porous structure for infrared absorption. An absorption effect equivalent to that of the black film can be obtained. However, in the application of infrared sensors that have been diversified in recent years, for example, when it is desired to be used as a sensor that requires high-speed response, forming a thick absorption film causes an increase in the heat capacity of the membrane region, resulting in a deterioration in response speed. End up. In addition, when using the cavity effect due to the porous structure, the absorption film itself can be formed thin. However, when used for a gas sensor or the like, for example, the sensor element cannot be hermetically sealed. There may be a problem that the sensor sensitivity gradually decreases.

Japanese Patent No. 3928856 JP 09-288010 A

  In order to solve the above problem, there is a method of forming a metal porous film which is an inorganic substance as disclosed in, for example, Japanese Patent No. 3928856. Since the porous film increases the infrared absorption efficiency by the cavity effect, it has a highly efficient infrared absorption effect. In addition, since the porous film formed by this method is an inorganic film, it is highly resistant to thin film processes, and it is possible to form an absorption film structure before forming a cavity corresponding to the membrane area. The improvement in the yield of the object can be ensured, and the resulting sensor can be manufactured at low cost.

  A combination with a porous SiO 2 film and an organic film is also considered effective as disclosed in JP 09-288010 A. Although the porous silica and the organic film itself are not as much as gold black or carbon black, they can be expected to have an infrared absorption effect, and a sufficient infrared absorption effect can be obtained by forming them thick. These two materials are also highly productive because of their high resistance to thin film processes.

  In patent document 1, the infrared absorption effect by a metal porous is utilized. Although the absorption effect is high, since a metal material having a high density is used, even if it is made of a porous material, it is heavier than the main structure of the membrane region. It is desirable that the absorption film be formed inside the membrane region as much as possible in order not to diffuse the received infrared heat, so the strength of the membrane region is necessary to hold the heavy metal porous membrane, and as a result, the membrane region There is a concern that the thickness of the protective film present inside increases and the heat capacity increases. In addition, etching a micron-order metal film from the surface is greatly affected by surface wettability, so there is a concern about variations in the process. If the etching solution does not penetrate to the bottom surface of the absorption film, infrared rays are reflected on the bottom surface, and there is a concern that the difficulty of process stability becomes relatively high. Further, when considered as a sensor element, the metal or other porous film is formed on the outermost surface of the element, so that there is a problem that it cannot be used depending on the sensor use environment due to poisoning or corrosion.

  In Patent Document 2, an organic material that absorbs infrared rays is used, and by adding a filler having a high infrared absorption effect, sensor sensitivity is improved, and by selecting a material having process resistance, improvement in sensor characteristics and productivity is expected. It is. However, the infrared transmission characteristics of organic materials vary depending on the material, and the degree of difficulty varies depending on the organic material used as the base material for the dispersion process and photolithographic process of fillers such as carbon, which have a high absorption effect. In order to cope with environmental resistance, it is necessary to develop an optimal organic material and absorption film forming process under each usage condition. Furthermore, it is not preferable that the organic material is made porous so that the infrared absorption effect can be obtained most, because if the absorption film is in the outermost layer, excess moisture and environmental gas are adsorbed.

  The above problem can be solved by forming a protective layer on the outermost layer, but the protective layer itself also contributes to the heat capacity of the entire sensor.For example, a material having a high infrared absorption effect is used, or the protective layer is used in the membrane region. If it is formed to the outside, the amount of heat absorbed by the protective layer escapes to the substrate before it is transmitted to the heat sensitive film, resulting in a problem that the output sensitivity of the sensor deteriorates.

  In order to solve the above problems, an object of the present invention is to provide an infrared sensor capable of maintaining high sensitivity and reducing deterioration of the infrared absorption film.

  In order to achieve the above object, according to the present invention, a substrate, a cavity formed inside the substrate, and a base material formed on an upper part of a thermal element formed in a membrane region corresponding to the cavity are first organic. An absorption film absorption layer that is a material, and an absorption film protection layer that is a second organic material that is formed on the absorption film absorption layer and covers the absorption film absorption layer. In the direction orthogonal to the stacking direction of the protective layer, an infrared sensor in which an end portion of the absorbing film protective layer is formed inside the membrane region is used.

  Since the end portion of the absorption film protective layer, which is the second organic material covering the absorption film absorption layer, is formed inside the membrane region, it is possible to reduce deterioration of the absorption film absorption layer and absorb The sensitivity can be increased as compared with the case where the membrane protective layer exists outside the membrane region.

  In the present invention, the absorption film protective layer may have an infrared transmission characteristic equal to or higher than that of the absorption film absorption layer, and the infrared reflection characteristic in the laminated structure of the absorption film protection layer and the absorption film absorption layer is: It is good also as being equivalent or less with respect to each infrared reflection characteristic of an absorption film protective layer and an absorption film absorption layer.

  In the present invention, the absorption film protective layer may be formed so as to trace the shape of the absorption film absorption layer.

  In the present invention, the first organic material may be cured by a crosslinking reaction and may be a photosensitive organic material.

  The present invention provides a thermal element formed on a substrate, an absorption film absorption layer in which a base material formed on the thermal element is a first organic material, and an absorption film absorption layer. An infrared sensor characterized by having an absorption film protective layer that is a second organic material covering the film absorption layer, and the absorption film protection layer has an infrared transmission characteristic equal to or higher than that of the absorption film absorption layer It is also good.

  ADVANTAGE OF THE INVENTION According to this invention, it is possible to provide the infrared sensor which can maintain high sensitivity and can reduce deterioration of an infrared rays absorption film.

It is an infrared sensor top view of this embodiment. It is an infrared sensor sectional view of this embodiment. It is sectional drawing of the comparative example 1 (no absorption film). It is sectional drawing of the comparative example 2 (generally gold-black film | membrane absorption film with a favorable output). 10 is a cross-sectional view of Comparative Example 3. FIG. It is an absorption film effect element output comparison. It is a figure which shows the FTIR transmittance | permeability of an infrared rays absorption film. It is a figure which shows the FTIR transmittance | permeability of an infrared rays absorption film. It is a figure which shows the FTIR transmittance | permeability of the laminated structure of the infrared rays absorption film 1st and an infrared rays absorption film. It is a figure which shows the FTIR reflectance of an infrared rays absorption film. It is a figure which shows the FTIR reflectance of an infrared rays absorption film. It is a figure which shows the FTIR reflectance of the laminated structure of an infrared absorption film and an infrared absorption film. It is a block diagram of the comparative examples 4 and 6. FIG. It is a block diagram of the comparative examples 5 and 7. FIG. It is Example 2 top view. It is Example 3 top view. It is a measurement bridge block diagram. It is a device output comparison. It is a membrane type infrared sensor element manufacturing flow. Process tolerance and yield comparison.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, this invention is not limited to the following embodiment. The constituent elements described below include those that can be easily assumed by those skilled in the art and those that are substantially the same. Furthermore, the constituent elements described below can be appropriately combined.

  FIG. 1 is a plan view showing a basic configuration of a thin film thermistor element (20-1, 20-2) having a thermal element of the present embodiment. FIG. 2 is a cross-sectional view of the thin film thermistor element (20-1, 20-2) shown in FIG. 1 cut along the line AA ′.

  The thin film thermistor elements (20-1, 20-2) include a substrate 1, an insulating film 2, two pairs of extraction electrodes (3A, 3B), a thermistor thin film (4A, 4B), a protective film 6, an extraction electrode (3A, 3B) A pair of extraction electrodes (3A, 3B) formed of electrodes PAD (5A, 5B) formed on the exposed portion and formed at a predetermined interval, and on these extraction electrodes (3A, 3B) And the thermistor thin film (4A, 4B) formed between the extraction electrodes (3A, 3B). The thermal element refers to two pairs of extraction electrodes (3A, 3B) and thermistor thin films (4A, 4B).

  The substrate 1 has a first main surface 1A and a second main surface 1B which is the back surface thereof, and an insulating film 2 is formed on at least the first main surface 1A. The material of the substrate 1 is not particularly limited as long as it has a suitable mechanical strength and is suitable for fine processing such as etching. For example, a silicon (Si) single crystal substrate, A sapphire single crystal substrate, a ceramic substrate, a quartz substrate, a glass substrate, or the like is preferable. The insulating film 2 is not particularly limited as long as it has an appropriate mechanical strength and can be easily formed by a known thin film process. A membrane or the like is preferred.

  Further, in the substrate 1, cavities (corresponding to positions where the thermistor thin films (4A, 4B) are arranged are arranged at positions where the thin film thermistor elements (20-1, 20-2) are arranged. 7A, 7B) are formed. The cavity (7A, 7B) has a concave portion inside the substrate from the second main surface 1B side toward the first main surface 1A side. It is preferable that the insulating film 2 is completely exposed in the recess, but if the heat capacity does not increase greatly, there may be a removal residue. The heat capacity refers to a ratio of heat energy generated when a material absorbs an energy source such as infrared rays having a predetermined frequency. That is, if the weight of the material increases (for example, the film thickness increases), the heat capacity increases, and the heat generation rate decreases for the same energy.

  A pair of extraction electrodes (3A, 3B) is formed on the insulating film 2, and a thermistor thin film (4A, 4B) is formed on the pair of extraction electrodes (3A, 3B) and between the extraction electrodes (3A, 3B). . Moreover, the protective film 6 for covering the thermistor thin films (4A, 4B) and shielding them from the outside air is formed. The protective film 6 does not need to block the thermistor thin film (4A, 4B) from the outside air, or the absorbing film absorbing layer 9, the infrared reflecting film 8, and the absorbing film protective layer 10 are insulators, and the thermistor thin film ( 4A and 4B) are not essential as long as they are not conductive. As a material of the extraction electrode (3A, 3B), a material having a relatively high melting point that has heat resistance capable of withstanding the film formation process and heat treatment process of the thermistor thin film (4A, 4B) and has an appropriate conductivity. For example, molybdenum (Mo), platinum (Pt), gold (Au), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing two or more of these metals Etc. are suitable. In order to take out an electric signal, the electrodes PAD (5A, 5B) connected to the take-out electrodes (3A, 3B) are formed to be connected to the take-out electrodes (3A, 3B). As a material of the electrode PAD (5A, 5B), a material that can be easily electrically connected such as wire bonding or flip chip bonding, for example, aluminum (Al), Au, or the like is preferable.

  On the thin film thermistor element (20-1), an absorption film absorbing layer 9 for absorbing infrared rays is formed on the protective film 6. The absorption film absorption layer 9 is applied on the entire surface of the first main surface 1A of the substrate 1 by a spin coater, temporarily cured using a baking process, exposed to light and developed by a photolithography process, and patterned into a desired shape. Is done. By adding a pore agent or the like in advance, the absorbent film absorbing layer may be made porous during annealing or baking. The absorption film absorption layer 9 may include a material that absorbs infrared rays as a subcomponent as long as the base material is made of the first organic material and can be patterned into a desired shape. Here, the subcomponent may be less than 50 wt%. Further, the first organic material is not limited to one type, and refers to the entire organic material that is patterned into a desired shape.

  An absorption film protective layer 10 is formed on the absorption film absorption layer 9. The absorption film protective layer 10 is applied onto the entire surface of the first main surface 1A of the substrate 1 by a spin coater, temporarily cured using a baking process, exposed to light and developed by a photolithography process, and patterned into a desired shape. Is done. Here, the step portions which are the upper surface and the side surface of the absorption film absorption layer 9 are covered with the absorption film protection layer 10. That is, it is patterned into a desired shape larger than the shape of the absorption film absorption layer 9 so as to cover the shape of the absorption film absorption layer 9. Further, an organic material having an infrared absorption effect smaller than that of the absorption film absorption layer 9 is selected for the absorption film protection layer 10. The selection of the material, the thickness, and the size of the area is aimed at not impairing the infrared absorption characteristics of the original absorption film absorption layer 9. If the absorption film protective layer 10 is a material having an infrared absorption effect that is more effective than the absorption film absorption layer 9, the combined heat capacity of the absorption film protection layer 10 and the absorption film absorption layer 9 increases. Since the speed decreases, the response speed as a sensor decreases. Further, the amount of heat generated by infrared absorption absorbed by the absorption film protective layer 10 is such that the distance between the absorption film protection layer 10 and the thermistor thin film 4A is longer than the distance between the absorption film absorption layer 9 and the thermistor thin film 4A. The time until transmission to 4A becomes longer, and the response speed as a sensor further decreases. Further, if the absorbent film protective layer 10 is patterned to be smaller than the absorbent film absorbent layer 9 without covering the absorbent film absorbent layer 9, it does not serve as a protective layer against chemical resistance.

  Finally, the second main surface 1B of the substrate 1 is etched to form cavities (7A, 7B). Here, a region corresponding to the cavity (7A, 7B) is defined as a membrane region. The membrane region is a region including a structure existing in the normal direction of the first main surface 1A of the substrate 1 on the cavity (7A, 7B). In this embodiment, the thermal element refers to the sensing element thermal film 4A and the pair of extraction electrodes 3A. However, the present invention is not limited to this, and the sensing element thermal film 4A may be made of a material different from the thermistor thin film. Good. The cavity 7A is formed larger than the laminated structure of the absorption film absorption layer 9 and the absorption film protection layer 10 when viewed in a plane having the first main surface 1A of the substrate as a normal line. Further, since the end portion of the absorption film protection layer 10 exists above the cavity 7A, that is, inside the membrane region, it becomes possible to make it difficult to transfer the heat generated by the infrared absorption to the outside of the cavity 7A. . Therefore, by confining the amount of heat generated by infrared absorption effectively in the laminated structure of the absorption film absorption layer 9 and the absorption film protective layer 10, an effect of realizing a sensor highly sensitive to infrared rays can be obtained. The end portions of the thermistor thin films (4A, 4B) may exist above the corresponding cavities (7A, 7B), that is, inside the membrane region, or may exist outside the cavities (7A, 7B). Good. Further, each end portion of the extraction electrode (3A, 3B) in a direction substantially orthogonal to a straight line connecting the respective centers of the extraction electrode (3A, 3B) exposed portions is an upper portion of the corresponding cavity (7A, 7B), that is, a membrane. It may exist inside the region or outside the cavity (7A, 7B).

(Example)
The manufacturing method of the thin film thermistor element (20-1, 20-2) of this example based on this embodiment will be described. Since the thin film thermistor elements (20-1, 20-2) are used as the infrared sensor 20, the detection side element (20-1), the reference side element (20-2), and the like are respectively associated with the two membrane regions. Are formed adjacent to each other. The detection-side element (20-1) is an element that absorbs infrared rays and detects the amount of generated heat as an electrical signal, and forms a laminated structure of the absorption film absorption layer 9 and the absorption film protection layer 10 of this embodiment. The reference side element (20-2) is formed with an infrared reflecting film 8 for reflecting infrared rays for comparison with the detection side element (20-1). The infrared sensor 20 outputs a difference in change amount of each element due to infrared irradiation as a bridge circuit. That is, since the reference side element (20-2) reflects the infrared rays, the environmental temperature is substantially detected, and the detection side element (20-1) detects the temperature due to the environmental temperature and the infrared absorption. It is possible to determine the amount of change due to infrared rays substantially.

  As shown in FIG. 1 and FIG. 2, a (100) Si substrate having a substrate surface orientation of (100) is prepared as a substrate 1, and Si oxide is formed as an insulating film 2 on the first main surface 1 </ b> A of the substrate 1. A film is formed. In order to form the Si oxide film, for example, a thermal oxidation method or the like may be applied. The film thickness of the insulating film 2 may be adjusted to such an extent that insulation with the substrate 1 is ensured, and for example, about 0.1 μm to 1.0 μm is preferable. In this embodiment, a 0.5 μm silicon dioxide film is formed as the insulating film 2.

  Next, a pair of extraction electrodes (3A, 3B) is formed on the insulating film 2 on the first main surface 1A. In order to form the pair of extraction electrodes (3A, 3B), for example, a metal thin film (3A, 3B) that becomes a pair of extraction electrodes (3A, 3B) of about 150 nm to 600 nm on the insulating film 2 by sputtering or the like. ), An etching mask is formed by a photolithography process, the metal thin film (3A, 3B) is processed into a predetermined electrode shape by dry etching such as reactive ion etching or ion milling, and the extraction electrode (3A, 3B). In order to improve the adhesion between the pair of extraction electrodes (3A, 3B), which are metal thin films, and the insulating film 2, it is preferable to interpose an adhesion layer of titanium (Ti) or the like at about 5 to 10 nm. In this example, a Pt / Ti film was used as the extraction electrode (3A, 3B). Pt was formed to a thickness of 0.1 μm by sputtering, and Ti having good compatibility with silicon dioxide was selected as the adhesion layer. Pt was formed to 100 nm by sputtering. Thereafter, a pair of extraction electrodes (3A, 3B) was formed using dry etching. Here, each end portion of the extraction electrode (3A, 3B) in a direction substantially orthogonal to a straight line connecting the respective centers of the extraction electrode (3A, 3B) exposed portions described later is the corresponding cavity (7A, 7B). It formed so that it might exist in the upper part.

  Next, a composite metal oxide film (4A, 4B) as a thermistor thin film (4A, 4B) is deposited on the extraction electrode (3A, 3B) by sputtering, and the composite metal oxide film (4A, 4B) by wet etching. Is patterned into a predetermined shape. Here, the thermistor thin film (4A, 4B) is patterned in a shape that is continuous with a part on the pair of extraction electrodes (3A, 3B) and a part between the pair of extraction electrodes (3A, 3B). Further, the thermistor thin films (4A, 4B) were patterned so that the end portions existed outside the corresponding cavities (7A, 7B). That is, current generated by applying a voltage between the pair of extraction electrodes (3A, 3B) flows through the thermistor thin film (4A, 4B). In this example, Ar gas is used under sputtering conditions of a substrate temperature of 600 ° C., a film forming pressure of 1.0 Pa, and an RF power of 200 W, and Mn—Co—Ni-based oxide is extracted to 0.4 μm on the electrodes (3A, 3B). Deposited. Next, it was processed into a predetermined shape by wet etching using an aqueous ferric chloride solution, and the Mn—Co—Ni-based oxide film was heat-treated at 600 ° C. for 2 hours in an air atmosphere using a baking furnace.

  A silicon dioxide film is formed as the protective film 6. The protective film 6 may be a film having insulating properties and moisture resistance, such as silicon dioxide or silicon nitride. In this example, silicon dioxide was formed over the entire surface of the substrate with a thickness of 0.4 μm by a TEOS-CVD method using an organometallic material called tetraethoxysilane.

  Next, the absorption film absorption layer 9 was apply | coated by the spin coat on the detection side element (20-1). In this embodiment, the film was formed at a thickness of 1.4 μm at 3000 rpm for 30 seconds. As the material, a commercially available resist in which carbon is contained in a negative photosensitive resin, or a black matrix resist was used. The carbon content was 10 wt%. After pre-curing using a baking process, exposure and development are performed by a photolithography process, and the gap between the electrodes of the pair of extraction electrodes (3A, 3B) is completely completed in a direction orthogonal to the normal line of the main surface 1A of the substrate 1 Patterned to cover.

  Next, the absorbing film protective layer 10 was applied on the detection side element (20-1) by spin coating. In this example, the film was formed with a film thickness of 3.0 μm at 3000 rpm for 30 seconds. The material used was a commercially available polyimide photosensitive resin. After pre-curing using a baking process, exposure and development were performed by a photolithography process, and patterning was performed so as to completely cover the absorption film absorption layer 9 and to have its end portion inside the membrane region. After the patterning, baking was performed at 220 ° C. for 120 minutes for complete curing.

  At this time, as shown in FIG. 15, in the infrared sensor 150, the absorption film absorption layer 9 and the absorption film protection layer 10 are substantially circular or elliptical, and the normal line of the first main surface 1 </ b> A of the substrate 1. As shown in FIG. 16, the infrared sensor 160 includes the absorption film absorption layer 9 and the absorption film, as shown in FIG. 16. As in Example 3 in which the protective layer 10 has a cross shape and is formed in a shape overlapping with a part between the pair of extraction electrodes 3A when viewed from the normal line of the main surface 1A of the substrate 1 Further, by forming the absorption film protective layer 10 so as to cover the entire surface so as to trace the shape of the absorption film absorption layer 9, the heat absorption generated by the film absorption layer 9 other than the thermistor thin film 4A of the amount of heat generated by the infrared rays. It is possible to reduce heat dissipation Ri, the optimal sensitivity. Here, it is preferable that the size of the trace is as close as possible to the absorption film absorption layer 9 at the end of the absorption film protection layer 10 in consideration of a manufacturing margin. Usually, the margin is not less than 1 μm and not more than 10 μm.

  Furthermore, as a material to be selected, it is preferable that the absorption film protective layer 10 has a greater infrared transmission characteristic than the absorption film absorption layer 9. Further, the infrared protective properties of the absorbing film protective layer 10 and the absorbing film absorbing layer 9 are equal to or lower than the infrared reflecting characteristics of the laminated structure of the absorbing film protective layer 10 and the absorbing film absorbing layer 9. It preferably has reflection characteristics. By selecting in this way, an optimum response speed can be obtained. This will be described below.

  FIG. 7 shows the results of infrared transmittance evaluated by FT-IR, that is, so-called Fourier transform infrared spectroscopy, of the absorbing film absorbing layer 9 and FIG. 8 shows the absorbing film protective layer 10. The horizontal axis of the graph indicates the wavelength of infrared rays (μm), and the vertical axis indicates the transmittance (%). That is, in FIGS. 7 and 8, it can be said that the lower the transmittance, the higher the infrared absorption effect. In this embodiment, since the main component of the absorption film absorption layer 9 and the absorption film protection layer 10 is an organic material, a specific decrease in transmittance can be seen in a specific wavelength region, but as apparent from the figure. Further, it can be seen that the FT-IR transmittance of the absorbing film protective layer 10 is larger than the FT-IR transmittance of the absorbing film absorbing layer 9. That is, it can be seen that the material that does not impede the transmission of the infrared ray to the absorption film absorption layer 9 is selected for the absorption film protection layer 10 with respect to the infrared ray incident from the absorption film protection layer 10 side. This is shown in FIG. FIG. 9 shows the FT-IR transmission characteristics of the second laminated structure of the absorption film absorption layer 9 and the absorption film protective layer 10. However, even if FIG. 7 is compared with FIG. I understand. Accordingly, the absorption film absorbing layer 9 efficiently absorbs infrared rays, and the presence of the absorption film protection layer 10 makes it possible to compare with the case where the absorption film protection layer 10 is assumed to be the absorption film absorption layer 9. Since the increase in heat capacity for infrared rays is reduced, the amount of heat generated by infrared absorption can be transmitted to the thermistor thin film 4 and the response speed is increased.

  The second organic material of the absorption film protective layer 10 can be selected from the types of organic materials according to the environment in which the infrared sensor 20 is used. However, the thermal conductivity of the material differs depending on the type of organic material, and the thermal conductivity. When a material having a high thermal conductivity is used, heat from infrared rays is easily released, so that the output of the infrared sensor 20 may be lower than when a material having low thermal conductivity is used. However, a decrease in the output of the infrared sensor 20 due to the thermal conductivity of the material can be suppressed to a minimum by forming the end of the absorption film protective layer 10 inside the membrane region. In Example 1, a polyimide having a thermal conductivity of 0.2 (W / ° C.) was used, but as Example 4, a silicone resin material having a thermal conductivity of 5.0 (W / ° C.) was used. An infrared sensor 200 having the same thin film manufacturing process conditions as in Example 1 was manufactured. The silicone resin material was formed with a film thickness of 3.0 μm. Further, a material having an infrared transmittance of FT-IR substantially equal to that of the polyimide photosensitive resin of Example 1 was selected.

  10, 11, and 12 show the FT-IR reflection characteristics of the absorption film absorption layer 9, the absorption film protection layer 10, and the laminated structure of the absorption film absorption layer 9 and the absorption film protection layer 10, respectively. The multilayer structure is formed so that the reflectivity of each of the FT-IR in FIGS. 10 and 11 is compared with the reflectivity of the laminate structure in FIG. 12 so that the reflectivity of the laminate structure is smaller than each reflectivity. I understand. Here, since the reflectance of the laminated structure is small, it is possible to reduce the rate at which infrared rays absorbed by the absorption film absorption layer 9 are emitted from the absorption film protection layer 10 to the outside. Therefore, the sensitivity is high. Furthermore, if the absorption film protective layer 10 has a greater infrared transmission characteristic than the absorption film absorption layer 9, it absorbs infrared light more efficiently and is generated by infrared absorption from the absorption film absorption layer 9 close to the thermistor thin film 4. Since the amount of heat can be transmitted to the thermistor thin film 4, the response speed becomes faster.

  Next, the infrared reflective film 8 was formed on the reference element (20-2). The reflective film material was platinum and formed in a desired shape by a lift-off method. The purpose of the infrared reflecting film 8 is to prevent the infrared rays incident into the infrared sensor 20 from being transferred to the heat sensitive film (4-B). Here, it is preferable that the surface of the infrared reflection film 8 projected in the direction perpendicular to the first main surface 1A perpendicular to the substrate 2 covers the entire heat sensitive film (4-B). The ambient temperature can be measured because the heat sensitive film does not react to the incident infrared ray incident from the infrared reflecting film 8 side. Moreover, since the resistance value of the heat sensitive film (4-A) of the sensing element (20-1) changes depending on the infrared rays and the ambient temperature, a difference occurs between the resistance value and the heat sensitive film (4-B), and the difference is detected. Thus, the infrared sensor 20 that detects infrared rays is obtained. Therefore, the material used for the infrared reflecting film 8 is generally a metal material that efficiently reflects infrared rays, and among them, platinum having good infrared reflection efficiency is often selected. Further, even if an infrared reflecting material is used as the infrared reflecting film 8, a slight temperature rise occurs. However, by forming the infrared reflecting film 8 to the outside of the membrane region, the temperature rise of the infrared reflecting film 8 is released to the substrate 1. It is preferable at the point which can do.

  Next, a part of the absorption film protective layer 6 is removed by reactive dry etching to form an extraction electrode (3A, 3B) exposed portion, and an electrode PAD (5A, 5B) is formed on the extraction electrode (3A, 3B) exposed portion. Was formed by the lift-off method. The material of the electrode PAD (5A, 5B) was aluminum (Al). Here, the electrodes PAD (5A, 5B) were formed outside the membrane region.

  The infrared reflective film 8 and the electrodes PAD (5A, 5B) are formed after the absorption film absorption layer 9 and the absorption film protection layer 10 are formed. The reason is as follows. First, if the electrode PAD (5A, 5B) is present on the insulating film 2 before the absorption film absorption layer 9 is formed, the metal PAD (5A, 5B) and the base material for the absorption film absorption layer 9 are used. 1 organic material adheres by electrostatic force, and it becomes difficult to form the absorption film absorbing layer 9. Second, if the infrared reflection film 8 and the metal PAD (5A, 5B) are formed before the absorption film protective layer 10 is formed, the absorption film absorption layer is used as an organic solvent used in the photolithography peeling process in each process. 9 materials may not be tolerated.

Finally, an etching mask is formed on the second main surface 1B side of the substrate 1 by a photolithography process, and then the substrate 1 is secondly etched by reactive ion etching such as D-RIE method using a fluoride-based gas. The main surface 1B is deeply drilled perpendicularly to open the cavities (7A, 7B). The D-RIE method mainly suppresses chemical side etching caused by F radicals by depositing a reaction suppression film (fluorocarbon-based polymer) on the sidewall of the cavity (7A, 7B) using C ₄ F ₈ gas. Plasma etching step, and chemical etching of the substrate 1 with F radicals using SF ₆ gas and physical etching of the reaction suppression film with F ions to anisotropically etch the substrate 1 substantially vertically This is a method of deepening the substrate 1 by alternately repeating the plasma etching process.

(Evaluation)
For the infrared sensors of Examples and Comparative Examples shown below, the output voltage corresponding to the amount of infrared for estimating the amount of infrared was measured. As a circuit for obtaining an output voltage, a full bridge circuit including the detection element (20-1) and the reference element (20-2) shown in FIG. 17 was used for the infrared sensor 20 of the example and the infrared sensor of the comparative example. . This will be described below.

  In the full bridge circuit shown in FIG. 17, one end of the first reference resistor R1 and one end of the sensing element (20-1) having the resistor THs are connected, and the other end of the second reference resistor R1 is connected to the reference potential power source. The other end of the sensing element (20-1) having the resistance THs is connected to the Gnd potential, one end of the second reference resistance R2 and one end of the reference element (20-2) having the resistance THr are connected, The other end of the second reference resistor R2 is connected to the reference voltage power source, the other end of the reference element (20-2) having the resistor THr is connected to the Gnd potential, and the sensing element having the first reference resistor R1 and the resistor THs ( The first output voltage is output from the first connection P1 in which one end of each of the reference elements 20-1) and 20-2) is connected to each of the reference element (20-2) having the second reference resistance R2 and the resistance THr. Second connection where one end of each is connected 2 and outputs a second output voltage. Here, it is preferable to equalize the thermal effects other than the amount of heat generated by infrared absorption from the outside with respect to the detection element (20-1) and the reference element (20-2). For detection using such a resistance difference, a half-bridge circuit or a full-bridge circuit is often used, but in this embodiment, a full-bridge circuit may be used for a portion that obtains an output voltage corresponding to the amount of infrared rays. preferable.

  Here, by aligning the shape and composition of the first and second reference resistors (R1, R2), the resistance THs of the sensing element (20-1) and the resistance THr of the reference element (20-2) are externally applied. Thermal effects other than the amount of heat generated by the absorption of infrared rays can be made almost equal.

Output voltage P corresponding to the amount of infrared radiation is obtained at first the first and the output voltage V _P1 second voltage difference or voltage difference between the output voltage V _P2 from the connection point P2 from the connection point P1. The value of the first output voltage V _{P1 at} the first connection point P1 between the resistance THs of the detection element (20-1) and the first reference resistance R1 changes according to the amount of infrared rays. That is, as the resistance THs of the detection element (20-1) receives the infrared rays, the first output voltage V _P1 decreases as the resistance decreases as the temperature increases. While the second output voltage _{V P2} in resistance THr and the second connection point between the second resistor R2 of the reference element (20-2) is almost not undergo the influence of the infrared, the reference element (20-2) The resistance THr shows a change with a slight influence from an infrared ray that cannot be radiated and a change in ambient temperature other than the infrared ray. Therefore, the difference between the first output voltage V _P1 and the second output voltage V _P2 , that is, the difference voltage, that is, the output voltage P indicates the amount of infrared rays in which the influence of the ambient temperature other than infrared rays is reduced. It shows that a sensitivity is so good that P is large. The sensing element (20-1) and the reference element (20-2) are thin film thermistors, and as described above, the infrared temperature of the structure in which the sensing element (20-1) and the reference element (20-2) are arranged adjacent to each other. This is a sensor 20.

As a method for measuring the amount of infrared rays, the reference voltage Vcc (of the reference voltage power supply) when a predetermined infrared ray was applied to the infrared temperature sensor 20 held at a predetermined temperature for the first to third embodiments and the comparative example shown below. The first output voltage V _P1 and the second output voltage V _P2 of the circuit to which the voltage is applied are measured.

Specifically, as a measurement object in which the temperature of the infrared sensor 20 in which two elements of the detection element (20-1) and the reference element (20-2) are arranged adjacent to each other is kept at 25 ° C. and the surface temperature is set to 40 ° C. The potential at each measurement point corresponding to the surface temperature of the flat black body, that is, the first output voltage V _P1 and the second output voltage V _P2, were measured.

  When the output characteristics of the infrared sensors (20, 200) of Example 1 and Example 4 are compared, the second organic material having a thermal conductivity of 0.2 (W / ° C.) is used for the absorbing film protective layer 10. Compared with the sensor output of Example 1, the sensor output of Example 4 using a second organic material having a thermal conductivity of 5.0 (W / ° C.) for the absorbing film protective layer 10 is about 15% lower. It became. This difference in output is due to the difference in the thermal conductivity of the absorption film protective layer 10, but the reason why the output is reduced by only about 15% even when a material having a thermal conductivity of 25 times different is used. It is considered that by forming the end portion of 10 within the membrane region, the amount of heat obtained from the infrared rays could be transferred to the heat sensitive film with almost no escape to the substrate side. That is, the sensitivity is high.

(Comparative Example 1)
In order to compare the effects of the present embodiment, as shown in FIG. 3, the structure other than the absorption film absorption layer 9 and the absorption film protection layer 10 is made the same, and the absorption film absorption layer 9 and the absorption film protection layer 10 are formed. The infrared sensor 30 that was not used was manufactured, and the output was compared with that of Example 1. The result is shown in FIG. Compared with Example 1, the output voltage P decreased by 60% to 40%. By comparing with the state in which the absorption film absorption layer 9 and the absorption film protection layer 10 are not formed, the infrared absorption effect of the absorption film absorption layer 9 and the absorption film protection layer 10 is actually understood.

(Comparative Example 2)
In order to compare the effects of the examples, as shown in FIG. 4, a gold black film generally used as an infrared absorption film with the same structure except for the absorption film absorption layer 9 and the absorption film protection layer 10. And the output of the infrared sensor 40 was compared with Example 1. The gold black film was formed by a low pressure vapor deposition method. The result is shown in FIG. Compared with Example 1, the output voltage P decreased by 17% to 83%. From this result, it can be seen that an output equal to or higher than that of a general absorption black film can be obtained. The film thickness of the gold black film was set to 3 μm at which the output voltage P was maximized, that is, the infrared transmittance evaluated by FT-IR was minimized.

(Comparative Example 3)
In order to compare the effects of this example, as shown in FIG. 5, after the absorption film absorption layer 9 was formed, the absorption film protective layer 10 was formed of the same material as the infrared absorption film absorption layer 9. That is, an infrared sensor 50 in which an infrared absorption film is formed with the infrared transmission characteristics of the absorption film protection layer 10 and the absorption film absorption layer 9 made equal is manufactured, and the output characteristics and heat capacity are increased by the bridge circuit shown in FIG. The response speed with respect to infrared rays, which is one of the concerns, was compared with Example 1. The results are shown in FIG. As a result, since the infrared transmission characteristics are the same for the output voltage P, the results were almost the same, but the overall heat capacity increased, and the amount of heat generated in the absorption film protective layer 10 due to the absorption of incident infrared rays. It takes a long time to reach the thin film thermistor, so that the response speed to infrared light, that is, the response speed of the sensor is deteriorated by about 10%.

(Comparative Example 4)
In order to compare the effects of the present example, as shown in FIG. 13, the absorbing film protective layer 10 was formed to the outside of the membrane region. Also, considering the variety of infrared sensors, in order to compare the characteristics due to the difference in thermal conductivity of the absorption film protective layer 10 as the outermost layer film, a material having a relatively low thermal conductivity, this time the thermal conductivity of 0 .2 (W / m.degree. C.) organic material, specifically polyimide, was used, the other configurations were the same as in Example 1, an infrared sensor 130A was formed, and the output was compared with Example 1. The result is shown in FIG. When the absorption film protective layer 10 is formed outside the membrane region, a part of the heat generated by the infrared absorption from the absorption film protection layer 10 to the substrate 1 escapes, so the output is about 95% of the first embodiment. It was.

(Comparative Example 5)
In order to compare the effects of this example, as shown in FIG. 14, an absorption film protective layer 10 was formed on the entire surface of the device. Since the reference element (20-2) having the infrared reflection film 8 must have a function of reflecting the incident infrared ray, only the area where the detection element heat sensitive film 4B exists is subjected to a photolithography process by the photolithography process. Was removed. Also, considering the variety of infrared sensors, in order to compare the characteristics due to the difference in thermal conductivity of the absorption film protective layer 10 as the outermost layer film, a material having a relatively low thermal conductivity, this time the thermal conductivity of 0 .2 (W / m ° C.) organic material, specifically polyimide, was used, the other configurations were the same as in Example 1, the infrared sensor 140A was formed, and the output was compared with Example 1. The result is shown in FIG. When the absorption film protective layer 10 is formed outside the membrane region, a part of the heat generated by the infrared absorption from the absorption film protection layer 10 to the substrate 1 escapes, so the output is about 93% of the first embodiment. It was.

(Comparative Example 6)
In order to compare the effects of the present example, as shown in FIG. 13, the absorbing film protective layer 10 was formed to the outside of the membrane region. In addition, in consideration of the variety of infrared sensors, a silicone resin having a thermal conductivity of 5.0 (W / m ° C.) is used to compare characteristics due to differences in thermal conductivity of the absorption film protective layer 10 which is the outermost layer film. An infrared sensor 130B was formed using the same material and the other configurations were the same, and the output was compared with that of Example 1. The result is shown in FIG. When the absorption film protective layer 10 is formed to the outside of the membrane region, the phenomenon that part of the heat generated by infrared absorption from the absorption film protection layer 10 to the substrate 1 escapes is the same, but compared with Comparative Example 4. Thus, it is easy to be affected by the thermal conductivity. The output was about 41% of the first embodiment.

(Comparative Example 7)
In order to compare the effects of this example, as shown in FIG. 14, an absorption film protective layer 10 was formed on the entire surface of the device. Since the reference element (20-2) having the infrared reflection film 8 must have a function of reflecting the incident infrared ray, only the area where the detection element heat sensitive film 4B exists is subjected to a photolithography process by the photolithography process. Was removed. In addition, in consideration of the diversity of infrared sensors, water absorption resistance to the polyimides used in Comparative Example 4 and Comparative Example 5 is compared in order to compare characteristics due to differences in thermal conductivity of the protective film 10 serving as the outermost layer film. However, it uses a silicone resin material with high thermal conductivity and thermal conductivity of 5.0 (W / m ° C). Compared to Example 1. The result is shown in FIG. When the absorption film protective layer 10 is formed to the outside of the membrane region, the phenomenon that part of the heat generated by infrared absorption from the absorption film protection layer 10 to the substrate 1 escapes is the same. It turns out that it becomes easy to be influenced by thermal conductivity. The output was about 39% of Example 1.

(Comparative Example 8)
In order to compare the effects of the examples, the process resistance in the thin film forming step was compared in the state where the absorption film absorption layer 9 and the absorption film protective layer 10 had the same structure. First, the final step in the thin film formation step, that is, the insulating film 2 was left and the cavity (7A, 7B) was formed on the substrate and then the absorption film absorbing layer 9 was formed. All things were destroyed (Comparative Example 8-1). Next, the protective layer 6 is opened to form an exposed portion of the extraction electrode (3A, 3B), and after the electrode PAD (5A, 5B) is formed on the exposed portion, that is, the protective layer 6 and the insulating film 2 remain, and the substrate The absorption film absorption layer 9 was formed immediately before forming the cavities (7A, 7B) in the electrode, but the electrodes PAD (5A, 5B) are made of metal, and are scattered in islands in the insulating film 2 on the wafer. Therefore, it will be charged with static electricity. The static electricity is firmly adhered to the absorption film absorption layer 9 that is an insulating material, and the absorption film absorption layer 9 after the electrode PAD (5A, 5B) formation remains after the patterning formation of the absorption film absorption layer 9 as well. The electrical signal could not be conducted, and this could not be formed (Comparative Example 8-2). This was the same result in the infrared reflective film process, which is the previous process, due to the close contact with the metal reflective film (Comparative Example 8-3). Finally, just after the formation of the protective film 6, only the absorption film absorption layer 9 was formed in the same thin film formation process as that of the present example, but the organic used for resist removal in the photolithography process in the infrared reflection film formation process after this process. The absorption film was lost with the solvent (Comparative Example 8-4). A series of process steps is shown in FIG.

  The problem of Comparative Example 8-4 was solved by the laminated structure of the absorption film absorption layer 9 and the absorption film protective layer 10. As shown in Comparative Examples 8-1 to 8-3, it is best to form the absorption film absorbing layer 9 before the metal is formed on the outermost surface. The optimum process position for forming the absorption film absorption layer 9 is a state in which the extraction electrodes (3A, 3B) are completely covered with the protective film 6. In this state, the entire surface of the wafer is covered with the protective film 6 and the metal material is not exposed. That is, no local static electricity is generated. However, in the subsequent process, the electrodes PAD (5A, 5b) and the infrared reflecting film 8 are scattered in the form of islands on the insulating film, similarly to the extraction electrodes (3A, 3B). That is, in this embodiment, it is optimal to form the absorption film absorption layer 9 immediately after the formation of the protective film 6. However, the absorbing film absorbing layer 9 alone cannot withstand the subsequent thin film process, for example, the formation of the electrodes PAD (5A, 5B) and the organic solvent used when forming the infrared reflecting film 8, and the oxygen plasma process. This problem can be solved by completely covering the absorption film absorption layer 9 with the absorption film protection layer 10 selected from organic materials having solvent resistance and oxygen plasma resistance. By forming the end portion of the absorption film protective layer 10 inside the membrane region, the sensor output does not deteriorate as shown in the embodiment.

  It can be used for a wide variety of applications as an infrared sensor.

DESCRIPTION OF SYMBOLS 1 Silicon substrate 2 Insulating film 3A Detection element extraction electrode 3B Reference element extraction electrode 4A Detection element thermal film 4B Reference element thermal film 5A Detection element electrode PAD
5B Reference element electrode PAD
6 Protective film 7A Sensing element cavity 7B Reference element cavity 8 Infrared reflective film 9 Absorbing film absorbing layer 10 Absorbing film protective layer 20 Infrared sensor 20-1 Sensing element 20-2 Reference element

Claims (9)

A substrate,
A cavity formed in the substrate;
An absorption film absorption layer in which a base material formed on an upper part of a thermal element formed in a membrane region corresponding to the cavity is a first organic material;
An absorption film protective layer that is formed on the absorption film absorption layer and is a second organic material covering the absorption film absorption layer;
An infrared sensor in which an end portion of the absorption film protective layer is formed inside the membrane region in a direction orthogonal to a stacking direction of the absorption film absorption layer and the absorption film protection layer.   2. The infrared sensor according to claim 1, wherein the absorption film protective layer has infrared transmission characteristics equal to or higher than the absorption film absorption layer.   The infrared reflection characteristic in the laminated structure of the absorption film protective layer and the absorption film absorption layer is equal to or less than the infrared reflection characteristic of each of the absorption film protection layer and the absorption film absorption layer. Or the infrared sensor of 2.   4. The infrared sensor according to claim 1, wherein the absorption film protective layer is formed so as to trace the shape of the absorption film absorption layer. 5.   The infrared sensor according to claim 1, wherein the first organic material is an organic material that is cured by a crosslinking reaction and has photosensitivity.   A heat-sensitive element formed on the substrate; a base material formed on the heat-sensitive element is a first organic material; an absorption film absorption layer formed on the absorption film absorption layer; and the absorption film An absorption film protective layer that is a second organic material that covers the absorption layer, and the absorption film protection layer has an infrared transmission characteristic equal to or greater than that of the absorption film absorption layer. Sensor.   The infrared reflection characteristic in the laminated structure of the absorption film protective layer and the absorption film absorption layer is equal to or less than the infrared reflection characteristic of each of the absorption film protection layer and the absorption film absorption layer. The infrared sensor described in 1.   The infrared sensor according to claim 6 or 7, wherein the absorption film protective layer is formed so as to trace the shape of the absorption film absorption layer.   The infrared sensor according to claim 6, wherein the first organic material is an organic material that is cured by a crosslinking reaction and has photosensitivity.

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