JP2920702B2 - Semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light receiving section on the front side of a semiconductor substrate, which allows light to enter from the back side of the semiconductor substrate.
The present invention relates to a photodetector (hereinafter, referred to as a back-illuminated light-detecting element) that detects light transmitted through a semiconductor substrate by a light-receiving unit on the front surface, and particularly to an improvement in a cooling structure of the back-illuminated photodetector.

[0002]

2. Description of the Related Art An example of a back illuminated light detecting element is a Schottky infrared detecting element (hereinafter abbreviated as a Schottky element). FIG. 3 shows the structure of a conventional Schottky device. In FIG. 3, a Schottky photodiode (light receiving portion) 102 having sensitivity to infrared rays having a wavelength of 3 to 5 μm is formed on the surface of a Si substrate 101. The incident light enters the light receiving unit 102 from the direction of arrow i. The incident light i is transmitted without being absorbed by the Si substrate 101 (indicated by an arrow j), and is absorbed and photoelectrically converted by the light receiving unit 102, but not all of the incident light i is photoelectrically converted. Although a part of the light is transmitted without being absorbed by the light receiving portion 102, the insulating film 1 such as SiO ₂ is formed on the light receiving portion 102.
The light is reflected by the Al reflecting film 114 formed through the light-receiving portion 13 (indicated by an arrow k), reaches the light receiving portion 102 again, and is photoelectrically converted. The photoelectrically converted signal is taken out from a bonding pad 111a formed on the surface of the Si substrate 101.

In order to use such a Schottky device for various purposes, first, an Si substrate 10 is used.
1 is fixed to the package 103, and the signal is
3 It is necessary to take it out. Further, the Schottky element uses a Schottky barrier generated when a semiconductor and a metal are brought into contact with each other to photoelectrically convert infrared light having a small photon energy. Since the / N ratio cannot be obtained, the package 103 must be cooled.

Hereinafter, a conventional packaging structure and a cooling structure of a Schottky device will be specifically described with reference to FIG. In FIG. 3, the package 103 has an opening at the top and a bottom with a window slightly smaller than the opening at the bottom. The Si substrate 101 of the Schottky element is bonded on its back side with an adhesive. It is fixed to the bottom surface of the package 103 (adhesion surface 112).

The signal photoelectrically converted by the light receiving section 102 is formed at the bonding pad 111a on the Si substrate 101 side. In order to send this signal to the package 103 side, the wire 105
Side pad 111b. The pad 111b and the lead 106 of the package 103 are connected inside the package 103, and a signal can be taken out from the lead 106 to the outside.

In order to cool the package 103, an opening above the package 103 is closed by a lid 104, and a cold head 107 is arranged so as to contact the outside of the lid 104.

As described above, a Schottky device is
From the principle of operation, a good S / N ratio can be obtained when the material is cooled to about 77K, but in general, when the substance is cooled to about 77K in the atmosphere, moisture in the atmosphere solidifies, It adheres to the material surface. Therefore, FIG.
A semiconductor device using a Schottky element as shown in (1) is usually held in a vacuum container.

[0008]

However, the conventional cooling structure described above has the following problems. That is, in the conventional structure, as shown by the arrow A in FIG. 3, the Schottky-type element is cooled along the route of the cold head 107, the lid 104, the package 103, and the Si substrate 101. In addition, since the package 103 and the Si substrate 101 are in contact only with the bonding surface 112, the cooling efficiency is very poor.

If the cooling efficiency is poor, In using a sensor (photodetector), the time required to cool the sensor increases. 2. When the sensor generates heat (for example, when there is a large amount of incident light), a sufficient S / N ratio cannot be obtained until the heat cools down (the Schottky element must be sufficiently cooled). And a sufficient S / N ratio cannot be obtained in principle).

FIG. 3 shows an example of a point sensor in which a single light receiving portion is formed. However, in the case of an image sensor in which a large number of light receiving portions are arranged on the surface of a semiconductor substrate, the image sensor is provided on an adhesive surface with a package. The light receiving portion in the near peripheral portion is cooled quickly, and the cooling of the light receiving portion in the central portion far from the bonding surface is delayed, so that the cooling state differs depending on the light receiving portion.
When starting to use the sensor, it is possible to make the cooling state uniform to some extent by taking a long cooling time, but if a large amount of light is incident during use and the element generates heat, the position of the light receiving section As a result, the temperature varies, and the detection accuracy is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has as its object to provide a semiconductor device having a structure capable of efficiently cooling a back illuminated photodetector.

[0012]

According to the present invention, there is provided a semiconductor device comprising:
A semiconductor substrate having a light receiving portion formed on one surface thereof, a package for holding the semiconductor substrate, and a closing member for closing the package on the light receiving portion forming surface side of the semiconductor substrate; In order to achieve, between the light receiving portion and the closing member, at least room temperature plastic, that is,
A heat conducting member having a property of being continuously deformed when an external force is applied is enclosed.

[0013]

As described above, the back-illuminated type photodetector has a configuration in which light is incident from the back surface of the semiconductor substrate and light transmitted through the substrate is received. The cooling member cannot be arranged in the area corresponding to the light receiving section of the above).

Accordingly, in the present invention, a heat conductive member is sealed between the light receiving portion forming surface of the back illuminated type photodetector and the lid of the package. As a result, the back-illuminated type photodetector is not only from the peripheral portion of the back surface of the semiconductor substrate,
It will be cooled from the surface in contact with the heat conductive member,
Since the area in contact with the cooling member increases, the cooling efficiency improves.

Therefore, the cool down time (time during which the element is cooled from room temperature to a usable temperature) when using the light detecting element is short, and even if the element generates heat,
Since this heat can be quickly removed, S /
The element can be used with a good N ratio.

Further, since the entire light receiving portion forming area comes into contact with the heat conductive member, even when the light detecting element is an image sensor in which a plurality of light receiving portions are arranged, the cooling state of each light receiving portion is made uniform. It is possible to keep.

Now, in the present invention, the heat conductive member is limited to a plastic member at least at room temperature.
This is to prevent an excessive force from being applied to the light receiving unit when the package is covered with the light receiving unit. When the cooling of the element and the temperature rise to room temperature are repeated, stress is generated due to the difference in the coefficient of thermal expansion between the semiconductor substrate and the heat conductive member. However, the stress is absorbed by the deformation of the heat conductive member. No damage is caused to the light receiving section. As the heat conductive member, grease that is a liquid having a high viscosity and maintains plasticity even at a low temperature is preferably used, and a gas that does not solidify at the cooling temperature of the element or a soft metal such as In can also be used.

[0018]

Next, the present invention will be described more specifically with reference to the drawings. FIG. 1 is a sectional view showing a structure of a semiconductor device according to a first embodiment of the present invention. The structure of the back-illuminated type photodetector itself and the packaging structure are the same as those in FIG. 3 described above, and a light receiving unit 2 composed of a Schottky photodiode is formed on the surface of the Si substrate 1. An Al reflective film 10 is laminated on the insulating film 13 with an insulating film 13 interposed therebetween.

The Si substrate 1 is fixed (adhesive surface 12) to the bottom surface of the package 3 with an adhesive on the back surface side.
Pad 11a on substrate 1 and pad 11 on package 3
b is connected by wire 5 and the photoelectric conversion signal is
The lead 6 is taken out to the outside.
The upper opening of the package 3 is closed by the lid 4, and the cold head 7 is arranged so as to be in contact with the outside of the lid 4.

The above configuration is the same as the configuration of FIG. 3 described above, but in this embodiment, grease 8 is sealed as a heat conductive member between the lid 4 and the light receiving portion forming surface.

The method of assembling the semiconductor device when grease 8 is used as the heat conductive member is as follows. First,
The Si substrate 1 is bonded to the bottom of the package 3 in the same manner as in the related art. Thereafter, grease 8 is applied to the light receiving portion forming surface, and the surface side (the side not in contact with the element) of the grease 8 is piled up so as to be higher than the upper surface 9 of the package 3 (grease 8).
Is extremely high in viscosity and can thus be exaggerated). In this state, if the lid 4 is placed on the package 3, the grease 8 protruding above the upper surface 9 of the package 3
Are crushed by the lid 4 and come into close contact with the lid 4. After that, if the cold head 7 is brought into contact with the outer surface of the lid 4, FIG.
Is obtained.

According to the first embodiment, the cold head 7
Heat flows between the device and the element through the lid 4 and the grease 8. At this time, since the cold head 7 and the lid 4, the lid 4 and the grease, and the grease 8 and the element are in contact with each other in a large area, the heat conduction efficiency is extremely high. In addition, since the grease 8 is a high-viscosity liquid, the grease 8 can be assembled without applying excessive force to the element when the cover 4 is closed.

In the example shown in FIG. 1, the grease 8 is used as the heat conducting member. Instead of the grease 8, a soft metal such as an In column may be introduced between the lid and the element. The In column is not a liquid unlike grease, but is a very soft solid, so that it can be sealed without applying excessive force to the element, and has a large area with respect to both the light receiving portion forming surface and the lid 4. Can be in close contact.

In addition, instead of the grease 8, a gas (for example, He or the like) that does not solidify at the element cooling temperature (cooling to 77K in the case of a Schottky element) may be contained. When gas is confined, gas molecules become a heat transfer medium, improving the cooling efficiency of the element and
There is no need to apply excessive force to the element when assembling.

Heretofore, a structure for cooling a light detecting element (point sensor) having only one light receiving portion in the element has been described. However, the present invention can also be applied to, for example, an image sensor in which a plurality of light receiving units are provided in one light detecting element. FIG. 2 shows an embodiment in that case.

In FIG. 2, since the structure other than the light receiving portion and the Al reflection film is the same as that of FIG. 1, the same members are denoted by the same reference numerals as those in FIG. 1, and duplicate description is omitted. In this embodiment,
A plurality of light receiving portions 2a are arranged at a constant pitch on the surface of the Si substrate 1, and an Al reflecting film 10a is provided on each light receiving portion 2a via an insulating film 13. There are also a plurality of Al reflection films 10a so as to correspond one-to-one with the light receiving portions 2a, and are arranged on each light receiving portion 2a.

The Si substrate 1 is held in a package 3 with a structure similar to that of FIG. 1, and grease 8 is sealed as a heat conductive member between the light receiving portion forming surface and the lid 4 of the package 3. .

When an element having a plurality of light receiving portions as shown in FIG. 2 is to be cooled by a conventional cooling structure, the element is cooled only from the contact surface 12 between the Si substrate 1 and the package 3. The cooling time has a time difference depending on the difference in the distance between the surface 12 and each light receiving unit 2a. However, in this embodiment, since each light receiving portion 2a is uniformly cooled from the direction of arrow i via the grease 8, temperature unevenness between the light receiving portions does not occur.

[0029]

As described above, the semiconductor device of the present invention has the following features.
Since a plastic heat conductive member is sealed between the light receiving part of the back-illuminated type photodetector and the lid of the package,
The cooling efficiency of the element can be improved, the cool down time can be shortened, and an excellent S / N ratio can be secured. In addition, since the heat conducting member is plastic, there is an advantage that the device can be easily assembled without applying excessive force to the element. Further, in the case where the element is an image sensor having a plurality of light receiving sections, it is possible to eliminate temperature unevenness between the respective light receiving sections, and the practical value of the present invention is very large.

[Brief description of the drawings]

FIG. 1 is a sectional view of a semiconductor device according to a first embodiment of the present invention.

FIG. 2 is a sectional view of a semiconductor device according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view of a conventional semiconductor device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor substrate 2, 2a Light receiving part 3 Package 4 Package lid 5 Wire 6 Lead 7 Cold head 8 Grease 9 Top surface of package 10 Al reflection film 11a, 11b Pad 12 Adhesive surface 13 Insulating film

Claims (2)

(57) [Claims] 1. A semiconductor device comprising: a semiconductor substrate having a light receiving portion formed on one surface; a package for holding the semiconductor substrate; and a closing member for closing the package on the light receiving portion forming surface side of the semiconductor substrate. 2. The semiconductor device according to claim 1, wherein a heat conducting member that is plastic at least at room temperature is sealed between the light receiving portion and the closing member. 2. The semiconductor device according to claim 1, wherein a plurality of light receiving sections are arranged on the surface of the semiconductor substrate.