JPH07167708A - Infrared sensor - Google Patents

Abstract

PURPOSE:To provide an infrared sensor having a photodetecting membrane which does not accompany a self destruction from an internal stress, without deteriorating the sensitivity or increasing the area. CONSTITUTION:A beam 1 is formed to have a supporting point within an area of a photodetecting membrane 2. When a supporting part is within the photodetecting membrane, a residual stress is lessened and the sensor is prevented from being broken. The beam may be supported at a rear side of the photodetecting membrane.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an infrared sensor,
In particular, it relates to a thermal infrared sensor that obtains a signal by the heat that has absorbed infrared rays.

[0002]

2. Description of the Related Art In recent years, various techniques have been developed for producing a thermal infrared sensor by utilizing semiconductor fine processing. This thermal infrared sensor has a heat-insulating structure in which the light-receiving membrane is floated from the substrate and supported at four points. For example, Jin-Shown
Shie et al. ("Fabrication of Micro-bolometer on Sil
icon Substrate by Anisotropic Etching Technique, "I
EEE Trans. Digest of Technical Papers, pp627-628)
As shown in FIG. 3, the infrared absorption film 3 on the thin light receiving membrane 32 having a heat insulating structure as shown in FIG.
3, which absorbs infrared rays and converts a temperature rise due to the infrared rays into electric resistance change or electromotive force by a temperature sensitive element 35 such as a thermistor or a pyroelectric material to obtain a signal proportional to the dose of infrared rays to be measured. Is. Conventionally, if the substrate is supported at several places or around the light receiving membrane (see FIGS. 2 and 3), the rate at which the heat received and stored escapes to the substrate increases and the detection sensitivity deteriorates. In addition, this four-point support heat insulating structure is adopted as an efficient method.

[0003]

However, in the above-mentioned four-point support, the light-receiving membrane is supported on the substrate by four beams, but this light-receiving membrane is thinned to improve the sensitivity, and the beam is similarly thin. It is formed. There is a problem that internal stress exists in the film forming the light receiving membrane and the beam, and when the light receiving membrane is processed, very large stress concentration occurs in the beam and the beam is broken. This is a factor that reduces the strength of the infrared sensor. If the beam is lengthened as shown in FIG. 4 so as to relieve the stress concentration, the light receiving membrane has to be made smaller, and the light receiving efficiency is rather lowered, which cannot be solved. On the contrary, if the beam is lengthened while keeping the area of the light receiving membrane as it is, the area of one sensor must be increased, which is not a good solution either. Therefore, an object of the present invention is to provide an infrared sensor having a light receiving membrane that does not self-destruct by internal stress without reducing the sensitivity or increasing the area.

[0004]

In order to solve the above-mentioned problems, the structure of the present invention comprises an infrared ray receiving portion formed of a thin film and including a temperature sensitive element, a beam for adiabatically supporting the light receiving portion, In an infrared sensor including a substrate that supports a beam, a supporting portion of the beam on the side of the light receiving portion is provided at a position inside the light receiving portion. In addition, the configuration of the related invention of the present invention is characterized in that the light receiving portion is above the beam, and the supporting portion is provided on a back surface of the light receiving portion.
Another related configuration is also characterized in that the light receiving portion is rectangular, and the beam is a structure extending on a diagonal line of the rectangle.

[0005]

[Advantageous Effects of the Invention and Effects of the Invention] By locating the supporting portion of the beam on the light receiving portion side inside the light receiving membrane area, the stress applied to the beam is relaxed, and the beam length can be made longer than before, so that the stress is usually concentrated. A large stress concentration does not occur in the supporting portion, and the cause of the fracture is suppressed. Further, for the same reason, stress concentration is alleviated also in the support portion on the substrate side, and the risk of beam breakage is suppressed. Further, since the area of the light receiving membrane can be maintained almost the same as the conventional one, the output of the infrared sensor equivalent to the conventional one can be obtained without lowering the sensitivity.

[0006]

EXAMPLES The present invention will be described below based on specific examples. 1 is a front view (FIG. 1 (a)) of the light receiving membrane 2 which is the infrared light receiving portion of the infrared sensor, and a cross-sectional view of the broken line portion AA shown in the front view (FIG. 1 (b)). , The beam 1 is projected diagonally from the four sides of the surface around the hole of the rectangular cavity formed in the Si substrate, and the supporting portion is provided inside the light receiving membrane 2 and near the temperature sensitive element 5 near the center. It is formed on. Therefore, in this embodiment, the light receiving membrane has a shape in which the slit is along the beam on the diagonal line. In other words, the four sides of the light-receiving membrane have a shape in which wings are spread from the supporting part near the center to receive infrared rays.

This light receiving membrane 2 has NiCr on the outermost surface.
An infrared absorbing film 3 which is a well-known thin film having a good infrared absorbing property such as gold or gold black is provided, and the infrared ray incident from above is absorbed and converted into heat, and the temperature sensitive element 5 arranged at the bottom. Then, the temperature change due to this heat is detected electrically. Therefore, to obtain a signal with a small amount of infrared rays,
That is, the light receiving membrane 2 is made thin to improve the detection efficiency. This is because if the heat capacity of the light-receiving membrane is small even with a small amount of infrared light, the temperature of the light-receiving membrane rises, which increases the detection efficiency. On the contrary, if it is too thin, the strength will decrease. Has become. Usually, the beam 1 is formed as a part of the insulating support layer that supports the light receiving membrane (7 in FIG. 1), and Si ₃ N ₄
It is formed of a film or a SiO ₂ film.

The thickness and length of the beam that supports the light receiving membrane are not limited to the rectangular shape of the light receiving membrane or the like, but vary depending on the size of the light receiving membrane to be designed and the like. Cannot be shown. As an example, in the configuration having a beam extending radially from the center as shown in FIG. 1, stress calculation by computer simulation as shown in FIG. 5 is performed at the stage of designing the structure of the light receiving membrane and the beam, and this simulation is performed. As a result, by setting the width and length so that the stress concentration does not exceed the stress limit at which the stress concentration is equal to or lower than the fracture stress value, it is possible to obtain a structure that does not self-destruct. That is, the length and thickness may be appropriate according to FIG. 5, and it is not necessary to limit to a specific position in the light receiving membrane region.

FIG. 5 shows the result of simulating the residual stress of a beam based on the conventional structure using the length of the beam as a parameter. In addition, a means the width of the beam. The length of the conventional beam is about 20 μm, and as the length of the beam becomes longer, the residual stress values of both the supporting portion A on the substrate side of the beam and the central portion B of the beam decrease, and the longer the beam is, the more difficult it is to break. I understand. The area of the light-receiving membrane 2 other than the supporting portion related to the beam is equivalent to the simulation shown in FIG. 4 from the viewpoint of the mechanical structure. Therefore, the simulation result shown in FIG. 5 can be directly used for designing the beam length shown in FIG. The length and thickness of the beam may be selected by looking at the stress value according to the degree of the light receiving membrane.

The structure of the infrared sensor of the embodiment shown in FIG. 1 is different from the conventional one in terms of shape, but the structure such as film formation is almost the same as the conventional one, and the surface micromachining conventionally used. Can be formed by technology.

FIG. 6 is a front view and a sectional view of an embodiment of an infrared sensor in which the light receiving membrane 62 is located above the beam 61 and the supporting portion is formed on the back side of the light receiving membrane 62. There is no slit in the membrane 62, and the entire surface of the light receiving membrane 62 becomes effective. Incidentally, in the case of this structure, the process of forming the light receiving membrane becomes somewhat complicated, but this is also formed by the same well-known surface micromachining technique.

As described above, by forming the beam supporting portion on the light receiving membrane side of the beam supporting the thin film light receiving membrane inside the light receiving membrane region, it is durable against self-destruction due to internal stress and is practically used. An infrared sensor with a long life was obtained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an infrared sensor embodying the present invention.

FIG. 2 is a schematic configuration diagram of an infrared sensor having a conventional configuration.

FIG. 3 is a schematic configuration diagram of a conventional infrared sensor having another configuration.

FIG. 4 is an explanatory view showing a state of a light receiving membrane when a beam is lengthened.

FIG. 5 is a simulation result diagram showing the dependence of residual stress on beam length.

FIG. 6 is a schematic configuration diagram of an infrared sensor showing another embodiment of the present invention.

[Explanation of symbols]

1 Beam 2 Light Receiving Membrane 3 Infrared Absorbing Film 4 Electrode Wiring 5 Temperature Sensing Element 6 Insulating Layer (SiO ₂ Layer) 7 Insulating Layer (Si ₃ N ₄ Layer) 8 Insulating Layer (SiO ₂ Layer) 9 Si Substrate

Claims (3)

[Claims] 1. An infrared sensor comprising an infrared ray receiving portion formed of a thin film and including a temperature sensitive element, a beam that adiabatically supports the light receiving portion, and a substrate that supports the beam. An infrared sensor characterized in that a support portion on the side of the unit is provided at an internal region position of the light receiving unit. 2. The infrared sensor according to claim 1, wherein the light receiving portion is located above the beam, and the supporting portion is provided on a back surface of the light receiving portion. 3. The infrared sensor according to claim 1, wherein the light receiving portion has a rectangular shape, and the beam has a structure extending on a diagonal line of the rectangular shape.