JPS6342863B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a photodiode array, and more particularly to a photodiode array having a structure that prevents an increase in leakage current that occurs when exposed to ultraviolet light.

Continuous exposure of a conventional photodiode array to ultraviolet light without a protective structure results in a continuous increase in leakage current and shortens the life of the photodiode array.

Photodiode arrays are beginning to be used as spectral detectors in analytical instruments such as spectrophotometers. However, in conventional detectors, leakage current reduces or limits the sensitivity of the device. In other words, there are drawbacks such as the increase in leakage current due to ultraviolet irradiation, which shortens the life of the detector, reduces the sensitivity of the analyzer, and limits the use of the detector in operating conditions where the intensity of ultraviolet light is low. Ta. In particular, the use of photodiode arrays in highly sensitive spectrophotometers with a spectral range that includes ultraviolet frequencies and other devices in which radiation at ultraviolet frequencies is applied is limited.

Leakage current in a photodiode increases when it is exposed to ultraviolet radiation. This increase occurs primarily at the edges of the diffusion region where the depletion region intersects the silicon surface. Therefore, by shielding the ends of the diffusion region with a material that is opaque to (does not transmit) ultraviolet rays, it is possible to prevent the leakage current from increasing.

In one method of forming a light shield, a diffusion region is formed using conventional techniques, and a UV shield is formed on the edge of the diffusion region. A light shield is formed to overlap and protect the ends.

FIG. 1 is a cross-sectional view of a conventional photodiode array. In the illustrated photodiode array, leakage current increases when the photodiode array is irradiated with ultraviolet light. A series of plurality of diffusion regions 11 are formed in the substrate 12 . Diffusion region 11 has a conductivity type opposite to that of substrate 12 . The location of the diffusion region 11 is determined by a series of oxide layers 13. Although other materials may be used to define the location of diffusion region 11, silicon oxide is commonly used. An oxide layer 16 is formed on the surface of the photodiode array to form an electrically insulating layer. A depletion region 14 is formed at the boundary between the substrate 12 and the diffusion region 11. It has been found that when irradiated with ultraviolet rays, an increase in leakage current mainly occurs at the end portion 15 of the diffusion region 11 where the depletion region 14 intersects with the oxide layer 13. And this increase mainly occurs for light rays with wavelengths below 2800 Å. Therefore, the end 15 of the diffusion region 11
That is, it is necessary to shield a portion of the array into which high-energy photons are incident. Generally, ultraviolet rays
Transmits to a depth of about 100 Å, while the diffusion region is 0.1
Since the depth is on the order of ~1.0 μm, only the depletion region extending within 100 Å of the surface of the photodiode array is shielded.

FIG. 2 is a cross-sectional view of a photodiode array with a light shield. In the figure, the diffusion region 21
A layer of UV opaque material is formed on the end 25 of the UV light shield 27 to form a UV shield 27 . For example, aluminum is suitable as this material layer. This is because aluminum is opaque to ultraviolet light and is widely used in semiconductor manufacturing technology. Therefore, in conventional manufacturing techniques, it is only necessary to add the steps of determining where to form the aluminum light shield and forming it. In particular, since the integrated circuit manufacturing process includes locating and forming aluminum connections, this process can be used to form aluminum light shields. Note that it is necessary to ensure that the light shield 27 covers the end portion 25.

According to an embodiment of the invention, a UV-impermeable shield is used to locate the diffusion region and protect said edge against UV radiation. This embodiment has the advantage of self-aligning the light shield and the end of the diffusion region. Since the overlapping portion reduces the photosensitive area of the array, the present invention provides a wider photosensitive area.
In this case, the material selected for the light shield must be impervious to UV radiation and have physical properties that are compatible with (or withstand) the diffusion process to create the diffusion region. In particular, the material must be able to withstand the high temperatures during the diffusion process. Materials and structures used as such light shields include polysilicon layers formed on silicon oxide layers. This is because these materials withstand diffusion processes and are already used in MOS circuits formed on the same chip, requiring no additional steps. The present invention will be explained in detail below using the drawings.

FIG. 3 is a cross-sectional view of a photodiode array according to an embodiment of the invention, illustrating a structure with the characteristics described above. In the figure, approximately
A 0.5 μm thick oxide layer 33 is formed, and a polysilicon layer 37 is formed on this oxide layer 33. and polysilicon layer 37 and oxide layer 3
3 is removed from the region required to diffuse impurities. Since oxide layer 33 is insensitive to impurity diffusion, diffusion regions are formed only in the regions exposed by the removal of polysilicon layer 37 and oxide layer 33. An isolated diode is defined by the oxide layer 33 since it completely surrounds the area where the diffusion takes place. The ends 35 of the diffusion regions 31 are shielded by the polysilicon layer 37, since the impurities diffuse into the substrate 32 not only downwardly but also somewhat laterally. Diffusion area 31
Since the polysilicon light shield 37 is formed in self-alignment with the polysilicon light shield 37, a larger light sensitive area can be obtained compared to the structure in which the light shield overlaps over the edge of the diffusion region described above in connection with FIG. can.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a conventional photodiode array, FIG. 2 is a sectional view of a photodiode array having a light shield, and FIG. 3 is a sectional view of a photodiode array formed by a manufacturing method according to an embodiment of the present invention. 11, 21, 31: diffusion region, 12, 22, 3
2: Substrate, 13, 23, 16, 26, 36: Oxide layer, 15, 25, 35: End of depletion region, 2
7: Light shield, 33: Gate oxide layer, 37:
polysilicon layer.

Claims (1)

[Claims] 1 an oxide layer on a semiconductor material layer of a first conductivity type,
forming a polysilicon layer that is opaque to ultraviolet light on the oxide layer; removing the oxide layer and the polysilicon layer at a plurality of predetermined locations; and supplying impurities to the removed locations. forming a plurality of diodes by forming a plurality of regions of a second conductivity type opposite the first conductivity type in the semiconductor material; After the formation of the diode, the film is left as an ultraviolet shielding film, and when forming the region, the region is self-aligned with the polysilicon layer so that all edges of the region on the surface of the semiconductor material are covered with the polysilicon layer. None. A method of manufacturing a photodiode array, wherein the polysilicon layer, which is opaque to ultraviolet light, prevents ultraviolet light from being irradiated to the end portion.