Semiconductor device manufacturing: process – Making device or circuit responsive to nonelectrical signal – Responsive to electromagnetic radiation
Reexamination Certificate
2001-03-29
2003-07-29
Elms, Richard (Department: 2824)
Semiconductor device manufacturing: process
Making device or circuit responsive to nonelectrical signal
Responsive to electromagnetic radiation
C438S482000, C438S619000, C438S760000
Reexamination Certificate
active
06599771
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATIONS
The subject application is related to subject matter disclosed in Japanese Patent Application No. H12-95812 filed on Mar. 30, 2000 in Japan to which the subject application claims priority under Paris Convention and which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal type infrared sensor and a method of manufacturing the same. More specially, the present invention relates to a thermal type infrared sensor to detect an infrared signal incident from outside, and a thermal type infrared sensor and method of manufacturing the same which manufacturing is easy, accuracy is high and a SOI substrate is unnecessary.
2. Related Background Art
An infrared sensor can detect objects regardless of day and night, and has a feature in which permeability of an infrared ray for smoke and fog is higher than that of a visible light. Furthermore, because it is possible to obtain temperature information of objects, the infrared sensor is widely used as a surveillance camera and a fire-detecting camera.
As an example of thermal infrared sensor to detect the incident infrared ray, a thermal infrared sensor structure having a pn junction to a detecting portion will be described hereinafter.
The pn junction type of the infrared sensor uses a principle that temperature of the pn junction changes by absorption of the infrared ray, and height of diffusion potential barrier and the number of carriers of the pn junction change by the temperature change.
More specifically, surface of the sensor is provided with an infrared absorber of which temperature changes by irradiation of the infrared ray. The temperature change is, for example, transmitted to a transistor circuit including the pn junction in order to allow a band structure of the pn junction to change. The change of the band structure is read out by voltage change in low current operation. By such a method, the irradiated infrared ray is monitored, and shape of a measuring object and its surface temperature can be detected.
Next, an example of a conventional pn junction type of the infrared sensor will be described by using drawings.
FIG.
1
and
FIG. 2
are drawings showing schematic configuration showing an example of a conventional pn junction type of the infrared sensor.
FIG. 1
is a plane view, and
FIG. 2
is a cross sectional view of an A-A′ line.
In these drawings, numeral
1
denotes a substrate, numeral
2
denotes a detecting portion, numeral
4
denotes a support leg, and numeral
7
denotes a processing circuit section. The substrate under the detecting portion
2
and the support leg
4
is removed by a micro machining and an etching technology in order to form a void. The detecting portion
2
is supported at midair by the support leg
4
extending from the substrate
1
.
The detecting portion
2
is formed so that an insulating substrate
12
and insulating films
23
and
32
overlap a detecting layer
21
, and an infrared absorption layer
22
is provided on top of the insulated film
32
. The infrared ray irradiated to the detecting portion
2
is absorbed by the infrared absorption layer
22
. As a result, temperature of the detecting portion
2
goes up. The temperature change is converted into an electric signal by the detecting layer
21
, in order to detect the infrared ray. The electric signal converted by the detecting portion
2
is led to the processing circuit section
7
. The processing circuit section
7
carries out signal processing in order to perform conversion to an output signal.
In such a conventional structure, in order to improve detecting sensitivity, adiathermancy between the detecting portion
2
and the substrate
1
is important. That is, it is necessary to minimize heat slipping from the detecting portion
2
to the substrate
1
. Because of this, the detecting portion
2
is separated from the substrate
1
by the void
6
, and a contact point for the substrate
1
is only the support leg
4
. The support leg
4
is formed by a material that thermal conductance is low, and it is necessary to restrict the thermal conductance to the substrate by fabricating the support leg
4
thinly and longly by using a micro machining technology, in order to reduce the thermal conductance to the substrate
1
.
As a method of forming the void
6
necessary to thermally separate the detecting portion
2
from the substrate
1
, an anisotropic etching is used. As an example of etching solutions, there are a potassium hydroxide (KOH) solution and a tetramethylammonium hydroxide (TMAH). The void
6
is fabricated by infusing an etching hole made by the micro machining technology with the above-mentioned etching solution. When fabricating the void
6
, it is necessary that the detecting layer
21
be wholly overlapped by the insulating substrate
12
and the insulating films
23
and
32
. If the detecting layer
21
contacts the etching hole
51
and the silicon substrate
11
, not only the silicon substrate
11
but also the detecting layer
21
are etched when carrying out the anisotropic etching.
In order to easily realize the structure to wholly overlap the above-mentioned detecting portion
2
by the insulating film, there is a method of using a SOI (Silicon-On-Insulator) substrate that the insulating film and a single crystal silicon film are formed on the substrate in order. In the above-mentioned structure, the insulating film plays a role of the insulating substrate
12
, and the detecting layer
21
is formed in the SOI portion. After forming the detecting layer
21
, the insulating films
23
and
32
are formed on side and top of the detecting portion.
However, in case of using the SOI substrate, thickness of the single crystal silicon substrate and the insulating film has to be determine to take sensitivity of the infrared ray, the anisotropic etching step and so on into account. For example, the structure of a proposed example, i.e. Part of SPIE Conference on Infrared Technology and Applications XXV, vol3698, pp556-564, 1999, uses the pn junction formed to transverse direction. In this example, the single crystal silicon layer has to be thickened in order to enlarge junction area. When the film thickness of the insulating film becomes thick, thermal capacity of the detecting portion increases and high-speed performance of the detecting portion is damaged. On the other hand, when the film thickness of the insulating film becomes thin, the insulating film does not function as an etching block for the detecting layer when carrying out the anisotropic etching.
However, in order to form the detecting portion and the processing circuit on the same SOI substrate, the thicknesses of the single crystal silicon and the insulating layer has to be the same as that of the detecting portion. Therefore, the structure of the semiconductor elements included in the processing circuit section is restricted. For example, in case of using a MOSFET in the processing circuit section, it becomes difficult to avoid influence such as a substrate floating effect or a short channel effect.
Furthermore, because the SOI substrate is more expensive than the silicon substrate, the SOI substrate is also a drawback even in a total cost.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a thermal type infrared sensor and a method of manufacturing the same which form a structure that a detecting portion is thermally separated from a substrate without using an expensive substrate such as a SOI substrate and without an etching step, and have a structure capable of arbitrarily designing thicknesses of a single crystal silicon and an insulating film of the detecting portion and the processing circuit section without being restricted to the structure of the substrate. Therefore, it is possible to reduce cost for manufacturing a thermal infrared sensor of pn junction type, thereby improving characteristics of the detecting portion and the processing circuit section.
In order to achieve the foreg
Iida Yoshinori
Mashio Naoya
Shigenaka Keitaro
Elms Richard
Luhrs Michael K.
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