JPS5925164B2 - Semiconductor photodetector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor photodetection device, and more particularly to a semiconductor detection device in which a plurality of photodetection semiconductor elements are arranged on the same substrate.

Multi-channel detection methods have already been applied to image sensors, position detection, etc., but in recent years, advances in semiconductor technology have made photodetectors themselves more stable and more sensitive. It is intended to be applied to spectroscopic measurements, etc.

In this case, a self-scanning photodiode array with a built-in scanning circuit is considered to be a promising photodetecting device because of its small size, light weight, and high performance. When using such a diode array, mutual interference of signals between the elements that make up the array becomes a problem, but in particular, in instruments such as spectrophotometers, the shape of the wavelength spectral characteristics of the output photocurrent from the detection device is a problem. is one of the important factors that determines the analytical ability of the instrument.

One factor that affects wavelength resolution is the effect caused by blurring of optical signals, so-called blooming, and reducing this blooming is particularly important in optical signal detection elements. Blooming specifically refers to defects such as blurring of position boundaries in position sensors, unclear distinction between two adjacent signal peaks in analysis sensors and resulting misreading of peaks, and defects such as color shift, blurring, and blurring of contours in image sensors. The cause of such blooming in semiconductor array sensors is that light with a small absorption coefficient generates pairs of electrons and holes inside the semiconductor element, and these carriers diffuse into adjacent semiconductor elements in the same array. arises by reaching . Here, the carrier diffusion distance is usually several 10 No. to 100 No.
The blooming effect is said to be on the order of micrometers, and as the element arrangement density is increased and the distance between each element is narrowed to improve separation performance, the effect of blooming becomes greater. Conventionally, in order to prevent such blooming, carriers generated in the n-layer 2 are reduced by reducing the thickness of the n-layer 2 as a light absorption region to the necessary minimum, as shown in FIG. By increasing the impurity concentration of the n-layer 1 as a substrate and shortening the lifetime of the carriers generated here, the impurity concentration is increased by diffusion. Therefore, measures are being taken to reduce the rate at which the light reaches the pn junction. In FIG. 1, 4 is an oxide film, 5 is an antireflection film, and 6 and 7 are electrodes, respectively. Although it is possible to reduce blooming to some extent by such conventional means, it is not possible to actively prevent the diffusion of carriers to adjacent elements, so complete elimination of blooming cannot be achieved. Appropriate measures are desired.

SUMMARY OF THE INVENTION An object of the present invention is to provide a semiconductor photodetection device that can significantly reduce blooming within an array. A feature of the present invention is that blooming is reduced by separately providing each photodetecting semiconductor element in the array in island-like regions separated by p-n junctions provided in a semiconductor substrate.

More specifically, in a semiconductor photodetection device in which an array of a plurality of semiconductor elements having junctions for photodetection is arranged on the same semiconductor substrate, the semiconductor substrate has a first conductivity type; One semiconductor region having a second conductivity type formed within the main surface of this semiconductor substrate and a plurality of other semiconductor regions separated from each other having a first conductivity type formed within the surface of this one semiconductor region. It is characterized by having a plurality of semiconductor elements made of semiconductor regions, and a semiconductor isolation region having a first conductivity type formed in the main surface of the semiconductor substrate so as to isolate the plurality of semiconductor elements from each other. . The present invention will be explained in detail below based on embodiments shown in the drawings.

The structure of the photodiode array according to the embodiment of the present invention, whose main part is shown in cross section in FIG. 2, will be explained according to its manufacturing process.
First, a p-type silicon substrate 11 (specific resistance: 40Ω-Cm) is doped with a surface impurity concentration of 5× by ion implantation and heat treatment.
An n-type layer 12 of 1015cTn-3 is formed to a depth of 3 μm.

Next, a p + -type isolation region 13 is formed in this n-layer 12 by boron diffusion. In this case, the isolation region 13 corresponds to the number of array elements in the photodiode array, as shown in FIG. 2 and FIG. 3, which will be described later. It is shaped so as to surround the n-type layers 12A, 12B, 120, . . . in a plurality of regions corresponding to the silicon substrate 11 and the n-type layer 12.
diffused to a depth that reaches the junction with the Next, an oxide film is formed to a thickness of about 1 .mu.m over the entire main surface, and the oxide film is selectively removed by photoetching in the portions corresponding to the p+ layer formation portions for photodiode light reception and the MOS transistor formation portions.

After forming a gate oxide film 16 to a thickness of 0.1 μm in a dry oxygen atmosphere, a polycrystalline silicon layer is formed. Further, after removing unnecessary portions of polycrystalline silicon by photoetching, the gate oxide film on the p+ layer formation portion is removed. Next, a p+ layer 14 is formed to a thickness of 1 μm by a boron diffusion method. Through these processes, the source and drain of the MOS transistor are respectively formed. p
The + layer region 14 serves as the source of the MOS transistor and as a guard ring for the p-type layer 15, which will be described later. After that, the oxide film in the light receiving area is removed, and a p-type diffusion layer 15 is formed to a depth of less than 1 μm by boron diffusion.
(15A, 15B, 150...) are formed.

In this case, in order to increase the sensitivity at short wavelengths, the depth of this junction is preferably 0.1 to 0.2 μm. All of the above-mentioned treatments such as ion implantation, diffusion, and photoetching are performed by known methods. Through these treatments, as shown in FIG. 2, an n-type layer 12A,
12B, 12c, ... and p-type layers 15A, 1
5B, 15c, . . . p for photodetection, respectively.
- A plurality of photodiode elements having n-junctions JA, J3, JO, . 12A, 12B, 12c (individually isolated by respective p-n junctions KA, KB, KO, . . . between the 5p+ type isolation layer 13 and the p-type silicon substrate 11) Next, phosphor glass 17 is formed over the entire surface of the photodiode array thus formed by the CVD method, and then the electrodes 18 are opened.

Aluminum is deposited as electrodes, and predetermined wiring portions are formed between these electrodes by photoetching. Note that 19 in the figure indicates a common electrode. The blooming prevention effect during the light detection operation in the photodiode single array of this embodiment configured as described above will be described below.

In the photodiode array, most of the carriers (holes) optically excited in the element n-type layer 12A in the island-like region at the left end in FIG. The current is collected at the n-junction JA and becomes the optical signal current of this photodiode element. Some carriers are n-type layer 12A
and p + type isolation region 13 and p type silicon substrate 11
It is collected at the p-n junction KA between the substrate 11 and the like and disappears. Further, among pairs of electrons and holes that are photoexcited in the substrate region 11, the holes are blocked by the pn junction KA and recombined in the substrate region 11. Some of the electrons generated near the p-n junction KA enter the n-type layer 12A, but these electrons enter the p-n junction J.
It will not be collected in A. As a result, the carriers of photoexcitation that contribute to the photocurrent in the photodiode element in the island-like region on the left end of FIG. The carrier will not mix with the optical signal current of the photodiode element.

This also applies to each of the photodiode elements in the other islands, so that blooming between the components of the photodiode array is significantly reduced. 3 and 4 show an example in which the photodiode array shown in FIG. 2 is configured as a self-scanning photodetector, and FIG. 5 is an equivalent circuit thereof.

In the figure, island-like regions 1 are individually separated by isolated regions
Each photodiode element PA, PB, PO, . . . formed in A, IB, c, . . . is connected to a respective MOS transistor switch QA, QB, QO, .
... are connected to the scanning circuit (shift register) S, and their optical output currents are sequentially read out from the output terminal 0UT in FIG. In the figure, E indicates a power supply and R indicates a load resistance. A sampling signal from the scanning circuit S sequentially turns on the MOS transistor switches QA, QB, QC, . . . , and each photodiode PA, shown in FIG. PB,
PO,... p-n junction JA, JB, JC,...
The charge charged in the capacitor .

Repeat the above steps. In the embodiment of the present invention, as shown in FIG. Since they are individually isolated by the n-junctions KA, KB, KC, . . . , it is possible to significantly reduce the influence of blooming between the individual components when receiving optical signals.

Therefore, when such a photodiode array is applied to, for example, a spectrophotometer and used as a photodetection device, the reduction in blooming increases the wavelength resolution and greatly improves the analytical ability. Particularly when the photodiode array is applied to the self-scanning photodetector shown in FIGS. 3 to 5, each photodiode element PA, PB, PO, . . . Depending on the island-like areas IA, IB, IC,...
・The isolated structure eliminates leakage current from the interface with the scanning circuitry and other adjacent elements, thus extending the charge accumulation time and allowing low-level incident light to be detected. It becomes possible.

Furthermore, in the photodiode array of this embodiment, the MO
S transistor switch QA, QB, QO,...
・p+ formed during diffusion of each source and drain
Since the shaped layer 14 acts as a guard ring for the photodiode, when the depth of the pn junction is made shallow to increase short wavelength sensitivity, dark current can be reduced and bias breakdown voltage can be improved.

Furthermore, if the p-n junction is shallow like this, the resistance of the p-type layer 15 will increase, and there is a risk that charges will be left behind during operation in the charge storage mode, reducing the detection ability. Since the resistance of the p+ type region 14 is small, the diffusion resistance is substantially reduced and such problems can be avoided. Such a structure is particularly effective when a relatively large photodiode light-receiving area is required due to the shape of the spectrometer slit in spectrophotometer applications. In the above embodiments, the photodiode array is of a self-scanning type and includes a MOS transistor switch, but the present invention can of course be constructed as a photodetecting device consisting only of a photodiode array.

Furthermore, the formation of the isolation region is not limited to the method described in the above embodiments. For example, an n-type layer is epitaxially grown on a p+-type silicon substrate, and the p+-type layer is selectively diffused into this layer to form an island. It is also possible to form a shaped region. Further, the device of the present invention can be constructed by starting from an n-type substrate instead of the p-type substrate used in the above embodiments, and forming regions of respective predetermined conductivity types on the main surface of the n-type substrate.

In the above embodiment, the case where the photodiode junction is a p-n junction was explained, but in the present invention, other cases such as a shot junction, a heterojunction, a case where an interfacial inversion layer of SiO2 and S1 is used, etc. are explained. Can be used.

Further, the material of the diode element is not limited to the silicon used in the above embodiments, and compound semiconductors such as GaAs and InP may also be used. As described above, according to the semiconductor photodetecting device of the present invention, the detection ability can be greatly improved by reducing the blurring of optical signals between individual photodetecting elements.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of the main parts of a conventional photodiode array.
FIG. 2 is a sectional view of the main part of the photodiode array used in the embodiment of the present invention, FIGS. 3 and 4 are plan views of the main part of the embodiment of the invention, and FIG. 5 is an equivalent view of the photodiode array of the above embodiment. It is a circuit. 11...p-type silicon substrate, 12A, 12B,
120...n-type layer, 13...p+ type isolation region, 15A, 15B, 150...p-type layer,
JA, JB: Jc... p-n junction (photodetection),
KA, KB, KC... p-n junction (isolated).

Claims (1)

[Claims] 1. In a semiconductor photodetection device in which a plurality of semiconductor elements having junctions for photodetection are arranged on the same semiconductor substrate, a semiconductor substrate having a first conductivity type and one main surface of this semiconductor substrate a first semiconductor region having a second conductivity type formed within the first semiconductor region; and a first semiconductor region having a first conductivity type formed within the first semiconductor region so as to be exposed on one main surface; a plurality of photodiode elements having a plurality of second semiconductor regions; and a semiconductor isolation region having a first conductivity type formed in the main surface of the semiconductor substrate to isolate the plurality of photodiode elements from each other. A semiconductor photodetection device characterized by: