JPH04338675A - Image sensor - Google Patents

Abstract

PURPOSE:To reduce a temperature rise of an image area circuit and to improve an S/N by reducing a thickness of a board of a boundary region between an image area circuit region and a peripheral circuit region. CONSTITUTION:A substrate is reduced in thickness in a boundary region between a region of an image area circuit 2 of a semiconductor chip and a region of a peripheral circuit 4. The chip on an image area board 6, a peripheral part board 7, which are not reduced in thickness is 400-700 microns thick. The thickness of a thinned region 8 is about 50-100 microns as a value for satisfying influence to electric characteristics and conditions such as heat insulation, a mechanical strength. The wider the region 8 is, the more its heat insulating effect increases, but from the width of a connecting circuit region of a connector of the circuit 2 and the circuit 4, the width of thin film region is about 100-200 microns. Since the longer length of the thin film region increases more the heat insulating effect, it is thinned up to both ends of the semiconductor substrate.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image sensor.

0002

2. Description of the Related Art Conventionally, a CCD image sensor having the structure shown in FIG. 2 has been proposed.
page). This image sensor has a semiconductor substrate 1 with a constant thickness.
An image area circuit 2 comprising a photodiode and a vertical CCD register, a peripheral circuit 4 comprising a horizontal CCD register and an amplifier 3 on the same substrate, and a connection circuit 5 having a vertical dummy CCD register are arranged on the surface of the circuit. There is.

Signal charges generated by photodiodes in the image area circuit are transferred to an amplifier on the same substrate via a vertical CCD register and a horizontal CCD register. Since the signal charge is weak, it is converted into a low impedance output in the on-board amplifier formed on the same board and having a high impedance input and a low impedance output.

0004

In an image sensor, the optimum operating temperature, allowable operating temperature range, and amount of heat generated differ among the image area circuit, peripheral circuit, and connection circuit. The dark current of the photodiode that makes up the image area circuit increases at high temperatures, resulting in characteristic deterioration such as an increase in noise and a decrease in dynamic range. In a Schottky CCD image sensor whose purpose is to detect infrared rays (e.g., IEEE Transactions on Electron Devices, 1990, Vol. 37, No. 3, pp. 629-634), dark current is generated unless the photodiode is cooled to a low temperature of about 77 Kelvin. Due to the increase, it becomes impossible to operate. In addition, image sensors are used to improve the S/N, even for high-sensitivity image sensors intended to detect weak light and image sensors for astronomical observation with slow frame rates.
In particular, cooling of the image area circuit is required. As described above, in an image sensor, it is necessary to keep the image area circuit at a low temperature.

[0005] Peripheral circuits, especially horizontal CCDs that perform high-speed transfer operations, have the problem of transfer loss at low temperatures (for example, refer to IEICE technical research report published July 17, 1984). (Vol. 84, No. 82, pp. 29-35), operation at extremely low temperatures must be avoided. The operating temperature is preferably 80 Kelvin or higher. By the way, regarding heat generation, peripheral circuits to which a large amount of power is supplied have the highest heat generation. This is mainly due to the high driving frequency of the horizontal CCD and the large amount of power supplied to the low impedance output amplifier on the same board. Conventional image sensors have had a problem in that the temperature of the image area circuit including the photodiode increases due to heat generation in the peripheral circuits.

[0006]

Means for Solving the Problems The present invention provides an image sensor having an image area circuit, a peripheral circuit, and a connection circuit formed on the same substrate, in which the substrate thickness of the boundary area between the image area circuit area and the peripheral circuit area is is becoming thinner.

[0007]

[Function] The thinned substrate part in the boundary area between the light receiving area and the peripheral amplifier part has a small cross-sectional area, so heat conduction is low.
Therefore, heat flow from the peripheral circuits to the image area circuit is suppressed.

[0008]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a semiconductor chip showing a CCD image sensor according to a first embodiment of the present invention. The difference from the conventional example shown in FIG. 2 is that the semiconductor substrate is thinned in the boundary area between the image area circuit area and the peripheral circuit area of the semiconductor chip. A silicon substrate mainly used as a semiconductor substrate has a film thickness of about 400 to 700 microns. The semiconductor chips in the image area substrate 6 and the peripheral substrate 7, which have not been thinned, have this thickness. The thickness of the thinned region 8 is typically about 50 to 100 microns, which satisfies the conditions for influence on electrical properties, heat insulation, and mechanical strength. The wider the thin film region 8 is, the better the insulation effect will be, but the width of the thin film region is 100 to 200 mm, based on the width of the connection circuit region where the image area circuit 2 and the peripheral circuit 4 are connected on the semiconductor substrate.
It is on the order of microns. The longer the length of the thin film region, the greater the heat insulating effect, so the film is made thinner to both ends of the semiconductor substrate.

FIGS. 3 and 4 respectively show the second embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view taken along orthogonal planes of a semiconductor chip showing a CCD image sensor according to an embodiment of the present invention. There are two differences from the conventional example shown in FIG. 2: the boundary area between the image area circuit 2 of the semiconductor chip and the horizontal CCD register constituting the peripheral circuit 4, and the boundary area between the horizontal CCD register and the amplifier 3 on the same substrate. The fact that the substrate is thinner and that Figure 4
As shown in , the film is thinned to the vicinity of both ends of the semiconductor substrate 1, and a thick film peripheral portion 9 of approximately 1 mm is left as an area where the film is not thinned near both ends in order to maintain the mechanical strength of the semiconductor substrate. It is a point. The thickness of each of the thinned region 8 and the non-thinned region is the first
This is the same as in the embodiment. In this example, horizontal CCD
The width of the boundary area between the register and the peripheral circuit 4 is approximately 1 mm.

[0011]

As explained above, the present invention suppresses heat conduction by providing a thin film region at the boundary between the image area circuit and the peripheral circuit, thereby reducing the temperature rise of the image area circuit and improving the image sensor. The S/N, dynamic range, and uniformity of in-plane characteristics can be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of an embodiment of an image sensor of the present invention.

FIG. 2 is a schematic cross-sectional view of a conventional image sensor.

FIG. 3 is a schematic cross-sectional view of a second embodiment of the image sensor of the present invention.

FIG. 4 is a cross-sectional view of a semiconductor substrate of a second embodiment taken in a direction perpendicular to FIG. 3;

[Explanation of symbols]

1 Semiconductor substrate 2 Image area circuit 3 Amplifier on the same board 4 Peripheral circuit 5 Connection circuit 6 Image area board 7 Peripheral board 8 Thin film area

Claims (1)

[Claims] 1. In an image sensor in which an image area circuit, a peripheral circuit, and a connection circuit are formed on the same substrate, the substrate thickness in a boundary region between the image area circuit region and the peripheral circuit region is thinned. An image sensor featuring: