JPS61141175A - Semiconductor photodetector - Google Patents

Abstract

PURPOSE:To improve the resolving power and position resolving power by a method wherein the second conductive type mutually isolated multiple photodiodes and isolated regions comprising the first conductive type polycrystalline semiconductor mutually isolating the photodiodes are provided on the first conductive type semiconductor substrate. CONSTITUTION:A silicon dioxide film 11 is grown by thermal oxidation on an N type silicon substrate 10 and then parts of silicon dioxide film 11 to be isolated regions are removed by means of photoetching process further removing a part of N type silicon substrate 10 utilizing plasma etching process. Next the isolated regions are filled with polycrystalline silicons 12 and after forming a P type region 13 by diffusing process removing the silicon dioxide film 11 to be receptive planes by photoetching process, the silicon dioxide film 11 is grown by thermal oxidation for later specified electrode wiring. Through these procedures, the resolving power and position resolving power may be improved suffering no mutual interference between photodiodes since the isolated regions 12 comprising N<+> layer are provided between photodiodes to eliminate various crosstalks such as optical, physical and electrical crosstalks, etc.

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 semiconductor photodetection device 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. 6 is a cross-sectional view of a 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 Nl11O under the P+ region 13 reach the P+ region 14.

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 N layer 10 below the P+ region 13 reach the P+ region 14.

These crosstalks blur the position boundaries at the position sensor and blur the distinction between two adjacent signal peaks at the analysis sensor.

Furthermore, in recent years, image sensors that combine a photodiode array and a self-scanning circuit (shift register) for signal reading have been widely used.

FIG. 8 is a sectional view showing one element of such an image sensor.

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

In the P channel MOSFET structure using 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,
Taken out to external circuit.

Repeat this operation below.

In such a photodiode array, the potential of each element within the array is always different. When the potential of a photodiode at a certain point increases due to the scanning pulse of the shift register, a phenomenon occurs in which current flows into an adjacent photodiode with a lower potential. This is particularly likely to occur when the distance between the photodiodes is shortened due to electrical losstalk, 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, as shown in FIG. 10, in order to deal with such losstalk, a reflection layer 11 such as aluminum is used between adjacent elements.
Measures have been taken to form 51i5 and prevent light from entering between the elements.

However, in this method, when the device is incorporated into a package with a glass window, for example, the light reflected by the reflection 11i5 is further diffusely reflected by the glass window, and mutual interference of signals becomes more intense.

Furthermore, it has no effect on electrical losstalk.

Another possible method is to use a structure in which the photodiodes are separated by a P+ layer 6 formed by diffusion, as shown in FIG.

However, in this method, although the elements are separated for the time being, all carriers generated by light incident near the 1iIl region are absorbed by this P+ type separation region 6, resulting in a decrease in signal amount.

Furthermore, when the separation region P10 layer 6 is provided adjacent to the photodiode, the interaction between the P10 layer and the photodiode 12 becomes stronger, and the signal charge accumulated in the photodiode is transferred to the separation P10 layer. It becomes easier to flow, and electrical losstalk increases.

The depth of the isolation region must be 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 P layer on the light receiving surface, reaches the P+ layer 6 in the separation region, the withstand voltage will drop significantly, so the distance between the light receiving surface and the separation region must be at least about 20 μm.

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

Although forming a P+ isolation region between adjacent photodiodes as described above is effective in preventing crosstalk,
Increase in leakage current, decrease in withstand voltage.

On the contrary, the ambiguity of the signal increases due to signal leakage, etc., and the characteristics of the device only deteriorate.

As shown in FIG. 12, a structure may be considered in which isolation regions 7 made of an insulator or grooves are formed between photodiodes.

This structure structurally isolates the photodiodes and is therefore very effective in eliminating crosstalk.

However, this structure is also not satisfactory in terms of performance related to dark current and reverse breakdown voltage.

The maximum amount of charge that can be stored in a photodiode is determined by the product of junction capacitance and bias voltage.

Since the junction capacitance exhibits a constant value depending on the type of substrate, the maximum amount of charge is determined by the magnitude of the bias voltage.

However, if the bias voltage is too large, the depletion layer may reach the isolation region 7.

The isolation region 7 has poor crystallinity due to damage during formation, and when the depletion layer reaches it, leakage current flows intensely.

Therefore, the bias voltage cannot be increased, and as a result, the maximum amount of charge detected by the photodiode is limited.

Furthermore, the increase in dark current limits the maximum storage time.

As described above, it is difficult to obtain a photodiode array with satisfactory characteristics using the conventional techniques described above.

(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 reducing the various crosstalks of a photodiode array type semiconductor device. be.

(Structure of the Invention) In order to achieve the above object, a semiconductor photodetection device according to the present invention includes 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 of a second conductivity type formed in the semiconductor substrate of 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 configured by providing an isolation region made of a polycrystalline semiconductor having one conductivity type.

(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 cross-sectional view and FIG. 1B is a plan view.

A light-receiving surface (P+ region) 13 and a light-receiving surface (P+ region) 14 are formed on the N-type silicon substrate 10, and each region has a PN junction 15.16 between the N-type silicon substrate 10 and the light-receiving surface (P+ region) 14.
is formed.

Isolation regions 12.12.12 of polycrystalline semiconductor are formed to separate each PN junction 15.16, the top surface of which is covered with a silicon dioxide film 11.

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 15 and detected as an optical signal. Similarly, the carriers generated in the right photodiode are P
The light is collected at the N-junction 16 and detected as an optical signal.

At this time, the two photodiodes are completely separated by the isolation region 12 made of an N+ layer, so that, for example, carriers generated in the left photodiode are transferred to the right PN junction 1.
6, and optical and physical losstalk can be significantly reduced.

Further, since no current flows between the two photodiodes through the highly concentrated N+ layer, electrical losstalk can be similarly reduced.

Furthermore, since the isolation region 12 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.

The periphery of the isolation region 12 is N+ because the phosphorus-doped polycrystalline silicon acts as a diffusion source. Even if a bias voltage is applied to the photodiode to the extent that the depletion layer reaches the isolation region 12, the depletion layer does not spread to the highly doped N+ layer, and as seen in the configuration shown in FIG. Leakage current due to damage is not a problem.

Therefore, the bias voltage applied to the photodiode can be made as large as possible without causing an increase in leakage current, and as a result, the sensitivity of the photodiode can be improved.

Next, refer to FIG. 2 for the manufacturing process of the device of the above embodiment.

and explain.

(A) A silicon dioxide film 11 of about 1 μm is grown on an N-type silicon substrate 10 by thermal oxidation.

(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) The isolation region is filled with polycrystalline silicon 12 by depositing polycrystalline silicon doped with phosphorus or arsenic at a high concentration over the entire surface by CVD.

(D) Next, the silicon dioxide film in the portion that will become the light-receiving surface is removed by photo-etching, a P-type region 13 is formed by a diffusion method, and then the silicon dioxide film is removed by thermal oxidation.
．． Grow 2 μm.

Thereafter, predetermined electrode wiring is performed using a metal film such as aluminum, and the process is completed.

In the semiconductor photodetector device manufactured by the above steps, each junction is separated by the polycrystalline silicon 12 of the separation region as described above. However, this embodiment also has some problems.

As shown in FIG. 3, optical loss talk caused by carriers generated deeper than the polycrystalline silicon 12 in the isolation region becomes 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 second example device, an N-type layer 10 is formed on a P-type silicon substrate 20 by epitaxial growth.

In this N-type region 10, a separation region 12 and a light-receiving surface 1 are provided.
3.

The device of this embodiment is used with a reverse bias applied between the P type substrate 20 and the N type region 10.

Therefore, the carriers ordered in the P-type substrate 20 do not diffuse into the N-type region 10, but are all collected on the electrode 17 on the back surface. Therefore, all optical crosstalk can be eliminated by carriers generated deep in the crystal.

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

This example device is manufactured by the pulling method (CZ method).
A silicon substrate 21 having a high resistance of -10 Ωcm is used.

Silicon crystals produced by the CZ method usually contain 5 to 50p.
PM of oxygen is dissolved.

After forming an N-type region 10 on this substrate by an epitaxial method, heat treatment is performed in nitrogen (N2) gas at 800°C for 1 to 16 hours and in dry oxygen at 1050°C for 18 hours.

This step creates minute defects 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 21 is extremely short, and they are all annihilated before diffusing into the N region 10 .

Therefore, as with the method shown in FIG. 11, all optical crosstalk can be removed.

Various modifications can be made to the embodiments described in detail above.

Similar effects can be obtained even if the P-type and N-type in the above-described embodiments are changed.

(Effects of the Invention) As described in detail above, since the semiconductor photodetection device according to the present invention has a separation region made of an N+ layer between each photodiode, various optical, physical, electrical, etc. Crosstalk can be significantly eliminated.

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

Furthermore, 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.

Further, since a depletion layer does not spread in the highly doped N+ layer, the bias voltage applied to the photodiode can be made as large as possible, and the sensitivity of the photodiode can be improved.

The photodetection device 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. Further, by using the semiconductor photodetection device according to the present invention as an image sensor in combination 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 shows a third embodiment of the semiconductor photodetection device according to the present invention.
FIG. 2 is a cross-sectional view showing one embodiment. FIG. 6 is a cross-sectional view showing optical crosstalk in a conventional photodiode array type semiconductor photodetecting device. FIG. 7 is a cross-sectional view showing physical crosstalk in a conventional photodiode array type semiconductor photodetecting device. FIG. 8 is a sectional view showing one element of a conventional image sensor. FIG. 9 is an equivalent circuit diagram of an image sensor obtained by changing the conventional image sensor shown in FIG. 8 to a P-channel MOS FET structure using an N substrate. FIG. 10 is a sectional view showing a conventional example in which a reflective film is provided between elements to prevent crosstalk. Figure 11 shows P+ between elements to prevent crosstalk.
FIG. 2 is a cross-sectional view showing a conventional example in which layers are formed. FIG. 12 is a sectional view and a plan view showing a conventional example in which isolation regions made of an insulator are formed between elements to prevent crosstalk. 1... N-type silicon substrate 2... Source 113.
...Drain region 4...Gate electrode 5...
Reflection 11! J 6...P+separation area 1
0...N-type silicon substrate 11...Silicon dioxide film 1
2... N+ isolation region 13.14... Light receiving surface (P+ region) 15.16... PN junction 17... Back electrode 18... Surface electrode 20... P type silicon substrate 21. ...N-type silicon substrate patent applicant Hamamatsu Photonics Co., Ltd. agent Patent attorney Jusai Inoro

Claims (3)

[Claims] (1) In a semiconductor photodetection device in which a plurality of photodiodes having junctions for photodetection are arranged in an array in the same semiconductor substrate, a second conductivity type formed in the semiconductor substrate of a first conductivity type is used. A plurality of photodiodes of conductivity types separated from each other, and an isolation region made of a polycrystalline semiconductor having a first conductivity type formed in the semiconductor substrate so as to isolate the plurality of photodiodes from each other. A semiconductor photodetection device characterized by: (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 has a first conductivity type layer having a high resistance value of 10 Ωcm or more that is epitaxially grown on a first conductivity type fabricated by a CZ method. The semiconductor photodetection device described.