JPS61139061A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To eliminate optical, physical and electrical various crosstalks by forming isolation regions consisting of insulating layers among each photodiode. CONSTITUTION:Carriers generated in a photodiode on the left side are collected to a P-N junction section 14, and detected as optical signals. Likewise, carriers generated in a photodiode on the right side are collected to a P-N junction section 15, and detected as optical signals. Since both photodiodes are isolated completely by an isolation region 16 composed of an insulating layer at that time, carriers generated in the photodiode such as one on the left side do not mix with the P-N junction section 15 on the right side, thus remarkably reducing optical and physical crosstalks. Currents do not flow between both photodiodes through the insulating layer, thus markedly minimizing electrical crosstalks.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a semiconductor photodetection device that detects light irradiation.

(Prior Art) A photodiode array in which a plurality of photodiodes are arranged in an array on the same substrate is used for position detection, spectroscopic measurement, and the like.

In such a photodiode array type semiconductor photodetecting device, various problems arise when the degree of integration of the photodiodes is increased in order to improve the resolution of the incident position of incident light.

The first problem is optical crosstalk, in which light incident between adjacent photodiodes causes mutual interference between the elements.

Optical crosstalk will be explained with reference to FIG.

FIG. 8 is a cross-sectional view of the device illustrating optical crosstalk in a photodiode array type semiconductor photodetection device.

Optical crosstalk occurs when light with a small absorption coefficient reaches a deep part of a semiconductor device far from the PN junction, generates electron-hole pairs inside, and these carriers diffuse into adjacent photodiodes in the same array. It happens by reaching .

For example, this is the case when carriers generated in a deep part of the eight layers 10 below the P+ region 12 reach the P+ region 13.

Second, there is a physical losstalk called blooming.

This physical losstalk will be explained with reference to FIG.

Physical crosstalk occurs when the charge accumulated in the depletion layer shown by the broken line in the figure becomes saturated due to strong light irradiation, and then diffuses within the device and reaches the adjacent photodiode.

This is the case, for example, when carriers generated in the depletion layer formed in the eight layers 10 below the P+ region 12 reach the P+ region 13.

These crosstalks blur the position boundaries at the position sensor and the adjacent boundaries at the analysis sensor.

blurring the distinction between two signal peaks.

In recent years, image sensors that combine a photodiode array and a self-scanning circuit (shift register) for continuous signal output have become widely used.

FIG. 10 is a sectional view showing one element of such an image sensor.

P channel MO3FET using such N substrate 1
An equivalent circuit of the image sensor structure is shown in FIG.

In the P-channel MOS FET structure using the N-substrate 1, the PN junction in the source 2 region is used as a light-receiving surface.

When a negative pulse voltage is applied to the gate electrode 4, a P channel is generated on the silicon surface under the gate electrode 4, and at this time, charge is supplied from the drain 3, making the diffusion junction of the source 2 equal to the voltage of the drain 3. Charge this diode.

When the voltage of the gate electrode 4 is turned off and the channel is closed,
The potential (accumulated charge) of the source 2 is maintained as it is.

When the carriers are excited by the incident light in this state, the accumulated charges are discharged into the carriers, and the potential of the source 2 decreases. Next, when the scanning pulse is applied again through the gate 4, the charged charge relative to the discharged charge flows into the source 2,
Detected by external circuit. Repeat this operation below.

□ In such a photodiode array, the potential potential of each element in the array is always different. When the potential potential of a photodiode at a certain point becomes high due to the scanning pulse of the shift register, a phenomenon occurs in which current flows into an adjacent photodiode with a low potential potential. This is electrical losstalk and is particularly likely to occur when the distance between the photodiodes becomes short or when a high resistance substrate is used.

Electrical losstalk makes accurate optical signal measurements and weak light measurements difficult.

These optical, physical, and electrical losstalks will be collectively referred to as crosstalk hereinafter.

Conventionally, a countermeasure against such losstalk has been taken, as shown in FIG. 12, by forming a reflective film such as aluminum between adjacent elements to prevent light from entering between the elements.

However, in this method, if the device is incorporated into a package with a glass window, for example, the light reflected by the reflective film 5 will be further diffusely reflected by the glass window, and mutual interference of signals will become more intense.

Furthermore, it has no effect on electrical losstalk.

As another method, as shown in FIG. 13, a method has been reported in which photodiodes are separated by a P+ layer 6 formed by diffusion.

However, in this method, although the elements are separated to some extent, all carriers generated by light incident near the separation region are absorbed by the P+ type separation region 6, resulting in a decrease in signal amount.

Furthermore, when the separation region P+ layer is provided adjacent to the photodiode, the interaction between the separation P+ layer and the photodiode 2 becomes stronger, and the signal charges accumulated in the photodiode easily flow to the separation P+ layer, resulting in electrical problems. Lostalk increases.

The separation region must have a depth of at least 5 μm, but when it is formed by diffusion, not only the depthwise diffusion but also the same degree of lateral diffusion occur simultaneously.

Therefore, it is difficult to control the width of the P+ isolation region to 10 μm or less. Furthermore, when the depletion layer, which has spread beyond the two layers on the light-receiving surface, reaches the P+ layer 6 in the separation region, the withstand voltage drops significantly.
About m is necessary.

As a result, the spacing between adjacent photodiodes is 50 μm.
That's all. This imposes a limit on resolution.

As described above, forming a separation region of sufficient P between adjacent photodiodes is effective in preventing crosstalk, but it may cause signal ambiguity such as an increase in leakage current, a decrease in withstand voltage, and signal leakage. increases, and the characteristics of the device continue to deteriorate.

As described above, in the conventional technology, there is no effective method for dealing with various types of crosstalk, and an accurate countermeasure is desired.

(Object of the Invention) An object of the present invention is to provide a semiconductor photodetection device that achieves high resolution performance and high position resolution performance by significantly reducing the various types of crosstalk of a photodiode array type semiconductor device. It is in.

(Structure of the Invention) In order to achieve the above object, a semiconductor photodetection device according to the present invention is a semiconductor photodetection device in which a plurality of photodiodes each having a junction for photodetection are arranged in an array on the same semiconductor substrate. , a plurality of mutually separated photodiodes having a second conductivity type formed in the semiconductor substrate having a first conductivity type; and a plurality of photodiodes formed in the semiconductor substrate so as to isolate the plurality of photodiodes from each other; It is constructed by providing an isolation area made of an insulating material.

That is, the device according to the present invention is characterized in that crosstalk is eliminated by forming isolation regions made of an insulator between adjacent photodiodes.

(Example) Hereinafter, the present invention will be described in more detail with reference to the drawings and the like.

FIG. 1 is a diagram showing a first embodiment of a semiconductor photodetection device according to the present invention, in which FIG. 1A is a sectional view and FIG. 1B is a plan view.

A light-receiving surface (P+ region) 12 and a light-receiving surface (P+ region) 13 are formed on the N-type silicon substrate 1o, and each region has a PN junction 14.15 between it and the N-type silicon substrate 1o.
is formed.

Groove-like isolation region 16 separating each PN junction 14.15
．． 16.16 is formed, and a silicon dioxide film 1 is formed on the surface of the groove.
1 is formed.

17 and 18 form a back electrode and a front electrode, respectively.

The carriers generated in the photodiode on the left side of the figure are P
The light is collected at the N junction 14 and detected as an optical signal. Similarly, the carriers generated in the right photodiode are P
The light is collected at the N junction 15 and detected as an optical signal.

At this time, since the two photodiodes are completely separated by the isolation region 16 made of an insulating layer, for example, carriers generated in the left photodiode are transferred to the right PN junction 1.
5, and the optical and physical losstalk is significantly reduced.

Furthermore, since current does not flow between the two photodiodes through the insulating layer, electrical losstalk is significantly reduced.

Furthermore, since the separation region is formed by plasma etching, the width can be reduced to 2 μm or less. Therefore, the spacing between photodiodes can be reduced, and the resolution performance and decomposition performance of the photodiode array can be improved.

Next, the manufacturing process of the embodiment device having the above structure will be explained with reference to FIG. 2.

(A) Silicon dioxide H1i! is formed on the N-type silicon substrate 10 by thermal oxidation. ll is grown to about 1 μm.

(B) The silicon dioxide film in the portion that will become the isolation region is removed by photo-etching, and then a portion of the N-type silicon substrate is removed by about 5 μm using plasma etching.

(C) A silicon dioxide film is grown to a thickness of about 0.5 μm by thermal oxidation again.

(D) Next, the silicon dioxide film on the part that will become the light-receiving surface is removed by photo-etching, a P-type head region 12 is formed by a diffusion method, and then the silicon dioxide film is reduced to a thickness of about 0.2 μm by thermal oxidation.
Make it grow.

Thereafter, predetermined electrode wiring is performed using a gold film made of aluminum or the like, and the process is completed.

Through the above steps, adjacent photodiodes are separated by isolation regions made of an insulator, and operate as described above. However, some problems remain with the device according to this embodiment.

As shown in Figure 3, the separation area 1 is very small.
Optical loss talk caused by carriers generated at a depth deeper than 6.6 is a problem.

FIG. 4 is a sectional view and a circuit diagram showing a second embodiment of the semiconductor photodetection device according to the present invention.

In this embodiment, an N-type region 10 is formed on a P-type silicon substrate 20 by an epitaxial growth method.
A separation region 16 and a light receiving surface 12 are formed therein.

As shown in the figure, a reverse bias is applied between the P type substrate 20 and the N type region 10.

Therefore, carriers generated within the P-type substrate 20 do not diffuse into the N-type region 10, but are all collected on the electrode 19 on the back surface.
All optical crosstalk caused by carriers generated deep in the crystal can be removed.

FIG. 5 is a sectional view showing a third embodiment of the semiconductor photodetection device according to the present invention.

The apparatus of this embodiment uses an N- silicon wafer 21 having a high resistance of 10 Ωcm and manufactured by the CZ method.

Silicon crystals made by the CZ method usually contain 5 to 40
ppm of oxygen is dissolved.

An N-type region 10 is formed on this wafer by an epitaxial method.
After forming 1 to 1 in N2 (nitrogen) gas at 800℃
Heat treatment is carried out for 18 hours in dry oxygen at 1050° C. for 6 hours.

Through this process, minute defects are created in the N-substrate 21 due to the condensation of oxygen.

This is a known method called the internal getter method.

Since these minute defects act as recombination centers, the lifetime of carriers generated within the N − substrate is extremely short, and they all disappear before diffusing into the N region 10 .

The isolation regions in each of the embodiments described in detail above are formed by growing a silicon dioxide film on a plasma etched region. Various modifications can be made to this separation region.

As shown in FIG. 6, a silicon dioxide film 22 can also be deposited on the etched region by CVD or the like.

Further, when the photodiode array according to the present invention and other circuits are simultaneously formed on the same substrate, it is desirable that the substrate be flat.

Therefore, as shown in FIG. 7, a semiconductor material 23 such as polycrystalline silicon is filled.

In this case, the semiconductor material may be a conductive material or an insulating material as long as it can withstand the heat treatment step after forming the isolation region.

Furthermore, it is clear that the semiconductor photodetector according to the present invention can have the same effect even if it is configured with different P-type and N-type elements.

(Effects of the Invention) As described in detail above, the semiconductor photodetection device according to the present invention has a separation region made of an insulating layer between each photodiode, so that various crosstalk such as optical, physical, electrical, etc. can be significantly removed.

Therefore, there is no mutual interference between the photodiodes, and as a result, resolution performance and decomposition performance can be improved.

Further, the width of the separation region can be reduced to 2 μm or less, and an improvement in resolution performance can be expected at the same time.

The semiconductor photodetector according to the present invention can achieve high position resolution performance and high resolution performance by using it as a single unit for position detection and spectrophotometry.

Furthermore, by using the semiconductor photodetection device according to the present invention as an image sensor combined with a self-scanning circuit,
Clear images can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a sectional view and a plan view showing a first embodiment of a semiconductor photodetection device according to the present invention. FIG. 2 is a sectional view showing the manufacturing process of the device of the embodiment. FIG. 3 is a cross-sectional view for explaining problems in the apparatus of the embodiment. FIG. 4 is a sectional view showing a second embodiment of the semiconductor photodetection device according to the present invention. FIG. 5 is a sectional view showing a third embodiment of the semiconductor photodetection device according to the present invention. FIGS. 6 and 7 are cross-sectional views showing modified examples of the insulating region of the semiconductor photodetector. FIG. 8 is a cross-sectional view of a conventional photodiode array type semiconductor photodetecting device showing optical crosstalk. FIG. 9 is a cross-sectional view of a conventional photodiode array type semiconductor photodetecting device showing physical crosstalk. FIG. 10 is a sectional view showing one element of a conventional image sensor. Figure 11 shows the conventional image sensor shown in Figure 10.
FIG. 2 is an equivalent circuit diagram of an image sensor constructed using a P-channel MO3FETIjl substrate. FIG. 12 is a sectional view showing a conventional example in which a reflective film is provided between elements to prevent crosstalk. Figure 13 shows P+ between elements to prevent crosstalk.
FIG. 2 is a cross-sectional view showing a conventional example in which layers are formed. 1... N-type silicon substrate 2... Source region 3.
...Drain region 4...Gate electrode 5...
Reflective film 6...P+separation region 10...
N-type silicon substrate 11... silicon dioxide film 12.13
... Light receiving surface (P+ region) 14.15 ... PN junction 16 ... Separation region 17 ... Back electrode 18
...Surface electrode 20...P-type silicon substrate 21...N-type silicon substrate 22...Silicon dioxide film 23...Polycrystalline silicon layer Patent applicant Hamamatsu Photonics Co., Ltd. Agent Patent attorney Ino B Ju firefly 1 Figure (A) CB) Li 6 Figure fear 9 Figure fθ Figure 1f Figure

Claims (3)

[Claims] (1) In a semiconductor photodetection device in which a plurality of photodiodes each having a junction for photodetection are arranged in an array in the same semiconductor substrate, a second conductivity type photodiode formed in the semiconductor substrate having a first conductivity type; A semiconductor optical device comprising: a plurality of photodiodes separated from each other having conductivity types; and an isolation region made of an insulator formed in the semiconductor substrate to isolate the photodiodes from each other. Detection device. (2) The semiconductor photodetecting device according to claim 1, wherein the semiconductor substrate is a semiconductor wafer of a second conductivity type and a layer of the first conductivity type formed by epitaxial growth. (3) The semiconductor substrate is 10Ω manufactured by CZ method.
2. The semiconductor photodetector according to claim 1, which has a first conductivity type epitaxially grown on a first conductivity type wafer having a high resistance of cm or more.