JPH01106342A - Photo-detecting head chip - Google Patents

Abstract

PURPOSE:To reduce the error of a photo-detecting output due to light scattering by covering a part of the photo-nonsensitive band part formed on a substrate surface and the photo-sensitive band part adjoining to the photo-sensitive band part with a shielding film with a small reflection factor. CONSTITUTION:Instead of the shielding film with a high reflection factor composed of gold, aluminum, etc., for example, the shielding film composed of the material with the low reflection factor of light is formed. As the suitable material, molybdenum, carbon, etc., are effective, the film may be formed by a sputtering means, etc., so that the film thickness can be 0.1-2mum. For example, rectangular light receiving elements 30-1-30-4 are provided two by two horizontally and longitudinally and in parallel, a shielding film 30, excluding light receiving element parts 30-1-30-4, is formed continuously to a photo- nonsensitive band part 32.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to the structure of a photodetection cell, and in particular to a servo-based photometry system suitable for detecting light projected onto the cell in sections with high resolution. The present invention relates to photodetection cells used in applications such as photodetection cells.

(Prior Art and its Problems) Conventionally, for example, in compact discs (CDs), optical disc players, etc., various servo systems have been employed in order to correctly extract signals from optical discs in which signal bit strings are formed concentrically. Examples of such servo systems include a focus servo system that automatically focuses an objective lens on a blurred light spot incident on an optical disk, and a tracking servo system that correctly positions this light spot on a signal bit string. There are systems, etc., but in principle, a photodetector is used to determine the position or state of the reflected light of the light spot incident on the optical disc, and a plurality of independent light receiving elements that provide a photodetection signal depending on the amount of incident light are used. A photodetection head chip is constructed by arranging it in a pattern according to the voltage, and the servo is performed by knowing the voltage distribution generated there.

Therefore, in devices aiming for higher density recording, it is necessary to further reduce the signal bit string, bit interval, etc., and accordingly, it is necessary to further reduce the diameter of the light spot, the dimensions and shape of the independent light receiving element, and the adjacent spacing. However, for that purpose,
Efforts have been made to provide high resolution without degrading the separation characteristics between independent light-receiving elements.

FIG. 4 is a plan view of a conventional photodetection head chip 10, and the following description will be made with reference to the same figure.

For example, this photodetecting head chip 10 has - wafers 1
By forming a p-type or n-type region on 1, four rectangular light-receiving elements 12-1 to 12-4, which are photosensitive zones, are formed side by side. is configured to be a light dead zone 13 that does not sense light, but in reality, at the boundary where the light dead zone 13 and the sensitive zones 12-1 to 12-4 touch, there is broad light reception in the range of 0 to 5μ. This creates a sensitive zone, which poses a problem when increasing resolution.

FIG. 5 is an explanatory diagram showing the light receiving sensitivity near the boundary between the light dead zone and the light sensitive zone of the conventional photodetection head chip shown in FIG. 4, where the horizontal axis represents the position in the x direction and the vertical axis represents the The light-receiving sensitivity corresponding to

As is clear from the figure, the light-receiving sensitivity curve 15 of the light-receiving element (for example, 12-27) due to the incoming light 14 shows a broad attenuation characteristic, and does not have the ideal square characteristic, 16, which improves the resolution. In order to achieve this, it was necessary to make the light receiving sensitivity curve 15 as close to the square characteristic 16 as possible.

Figure 6(a) shows two of the other conventional photodetection head chips.
0, and the figure (b) is a sectional view taken along the line II in the figure (a). In this example, the photodetection head chip 10
For example, aluminum,
A light-insensitive zone 13 is sandwiched between the light-sensitive zones 12-1 to 12-4, and a shielding film 1121 made of a material such as gold that does not transmit light.
And it is formed by a thin film forming means such as sputtering so as to cover part of the photosensitive zones 12-1 to 12-4. FIG. 7 is an explanatory diagram for explaining the light receiving sensitivity near the boundary between the light dead zone and the light sensitive zone of the other conventional photodetection head chip shown in FIG.

As shown in the figure, the formation of the shielding film 21 should give the attenuation characteristic of the light sensitivity curve an ideal square characteristic 16, but in reality it becomes a broad curve 22, which is not satisfactory. However, this was not necessarily a sufficient measure to improve resolution.

(Means for Solving the Problems) The present invention has been made to solve the above problems, and includes forming a light dead zone portion and a light sensitive zone portion on the same plane on the substrate surface, and reducing the amount of incident light. In a photodetection head chip formed with a plurality of photodetection elements that each give an independent photodetection signal in response to the It is an object of the present invention to provide a photodetecting head chip characterized in that it is covered with a shielding layer having a small shielding ratio.

However, as a result of investigating the cause of the broad attenuation characteristic of the light receiving sensitivity curve, we found that one of the causes was the reflectance of aluminum, gold, etc. formed as the shield 1121 in the vicinity of the light dead zone and the light sensitive zone. It was found that as a result of a thin film with a high polarity reflecting and scattering incident light, a portion of this scattered light enters the light-receiving element, making the attenuation characteristic of the light-receiving sensitivity curve broader.

As a result, the conventional photodetection head chip 20 shown in FIG.
In this structure, instead of the shielding film 21 having a high reflectance made of gold, aluminum, etc., we came up with the idea of forming a shielding film made of a material with a low light reflectance, for example. According to the results of experiments, molybdenum, carbon, etc. are effective as suitable materials, and the film may be formed by sputtering or the like so that the film thickness is 0.1 to 2 μm.

With the above configuration, the light incident on the light dead zone 13 is absorbed by the shielding film with low reflectance, so the scattering of light is controlled.
The photosensitivity curve is close to the ideal square characteristic 16, allowing an optical head chip with high resolution.

FIG. 1(a) is a plan view of a photodetection head chip 30 according to a second embodiment of the present invention, and FIG.
Although this is an F-IF cross-sectional view, the configuration is basically between the photodetection chip head 20 and the path in FIG.

In this example, rectangular light receiving elements 30-1 to 30-
4 are arranged in parallel, two each in the vertical and horizontal directions, and the shielding 1
1132 is formed continuously in the light dead zone 32 except for the light receiving elements 30-1 to 30-4.

FIG. 2 is a plan view of a photodetection head chip AO according to a third embodiment of the present invention, in which n thin square light receiving elements 41 are arranged in parallel in each direction, and the shielding film 13 is Similarly, it is continuous except for the light receiving element section.

The third factor is a plan view of a photodetection head chip 50 according to a fourth embodiment of the present invention, in which the light receiving element 51 has a shape obtained by dividing a circle into four parts at an angle of 90°, and the shielding film 13 is the light receiving element. It is formed continuously except for the part.

(Effects of the Invention) As described above, the photodetection head chip of the present invention uses a light-insensitive zone formed on the substrate surface and a part of the light-sensitive zone adjacent to the light-insensitive zone to be shielded with a low reflectance. Because it was covered with a shielding film,
The light incident on the light dead zone is absorbed by the shielding film, and light scattering is controlled. As a result, errors in the light detection output due to light scattering can be reduced, making it possible to obtain a high-resolution light detection head chip. Become.

[Brief explanation of the drawing]

FIG. 1(a) is a plan view of a photodetection head chip according to a second embodiment of the present invention, and FIG. 1(b') is an I
f-I [cross-sectional view; FIG. 2 is a plan view of a photodetection head chip according to a third embodiment of the present invention; FIG. 3 is a plan view of a photodetection head chip 50 according to a fourth embodiment of the present invention; FIG. 4 is a plan view of a conventional photodetection head chip, FIG. 5 is an explanatory diagram showing the light receiving sensitivity near the boundary between the light dead zone and the photosensitive zone of the conventional photodetection head chip shown in FIG. Figure 6 <a> is a plan view of another conventional photodetection head chip;
) is a sectional view taken along line II in FIG. FIG. 11... Wafer, 13... Light dead zone, 22... Light spot, 20, 30.40.50... Photo detection head chip, 12-1 to 12-4. 30-1 to 30-4゜4
1.51...shielding film. 3 drawings on the seal (/:)) 6 drawings

Claims (1)

[Claims] In a photodetection head chip in which a light dead zone and a light sensitive zone are formed on the same plane on a substrate surface, and a plurality of light receiving element sections are formed to provide independent light detection signals depending on the amount of incident light, A photodetection head chip characterized in that the light dead zone and a part of the light sensitive zone adjacent to the light dead zone are covered with a shielding film having a low reflectance.