JPS6262074B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a semiconductor device for detecting an incident position that can output a current or the like that includes information regarding the incident position of light or a particle beam, and more specifically, a semiconductor device for detecting a one-dimensional incident position of a light or particle beam. The present invention relates to a semiconductor device for detecting an incident position suitable for extracting information.

2. Description of the Related Art A semiconductor device for detecting an incident position that can output a current or the like that includes information regarding the incident position of light or particles is known.

First, this semiconductor device for detecting an incident position will be briefly explained.

FIG. 1 is a plan view of a semiconductor device capable of outputting one-dimensional information on the incident position of light, etc., and FIG. 2 is a schematic cross-sectional view.

The semiconductor substrate 5 of this semiconductor device may be of any conductivity type.

A conductive layer 4 having a conductivity type different from that of the semiconductor substrate 5 is formed on one surface of the semiconductor substrate 5 (the upper surface in FIG. 2). This layer 4 has a uniform thickness so that the sheet resistance is kept uniform.
The surface of this incident surface conductive layer 4 is the light receiving surface 1 of this device.
form.

Both ends 4a and 4b of the entrance surface conductive layer 4 are doped with impurities at a particularly high concentration, and metal layers 2a and 3a are formed on their respective upper surfaces. This metal layer 2
a, 3a and the portion doped with impurities at a high concentration form a first position signal electrode 2 and a second position signal electrode 3, respectively.

This semiconductor substrate 5 is provided on the bottom surface of the semiconductor substrate 5.
The bottom conductive layer 6 is doped with impurities of the same conductivity type and at a high concentration. This bottom conductive layer 6
A metal layer is provided on the surface of the electrode 7, and the incident light amount signal electrode 7 is formed by this metal layer.

A lead wire 8 is connected to the first and second position signal electrodes 2 and 3 and the incident light amount signal electrode 7.
a, 8b and 8c are connected to each other.

The operation of the semiconductor device with the above configuration is as follows.

First, a power supply is connected to apply an equal reverse bias voltage between the incident light amount signal electrode 7 and the first and second signal electrodes 2 and 3. In this state, when light is incident on any position on the light-receiving surface 1 of the device, an electromotive force is generated at the PN junction formed by the substrate 5 and the conductive layer 4 near the point of incidence.

Due to this electromotive force, a photocurrent flows from the light amount electrode 7 to the first position signal electrode 2 and from the light amount signal electrode 7 to the second position signal electrode 3. If the polarity of the bias voltage is reversed, the current flows in the opposite direction to the above-mentioned direction. In any case, the ratio between the magnitude of the power flowing through the first position signal electrode 2 and the magnitude of the current flowing through the second position signal electrode 3 is determined by the electrical resistance of the layer 4 between the first position signal electrode 2 and the light incident point. It is proportional to the reciprocal of the ratio of the electrical resistances of the incident surface conductive layer 4 between the two-position signal electrode 3 and the light incident point. From this, the magnitude of the current flowing through the first position signal electrode 2 is I ₁ , the magnitude of the power flowing through the second position signal electrode 3 is I ² , and the first position signal electrode 2 is the coordinate 1, and the second position signal Coordinates of electrode 3 -
In the one-dimensional coordinate set to 1, the point of incidence of the light can be found by performing an analog calculation of (I ₁ −I ₂ )/(I ₁ +I ₂ ).

If the semiconductor device for detecting the incident position of the type described above is miniaturized and applied to a distance meter of a camera, etc., there is a problem that the resistance between the position signal electrodes becomes low and the semiconductor device cannot be used.

In the above application, it is strongly required that the resistance between the position signal electrodes be 200 kΩ or more under certain conditions. The reason is as follows.

Thermal noise current of the semiconductor device is inversely proportional to the square root of the electrical resistance between the two position signal electrodes. That is, when the electrical resistance between the electrodes is small, the thermal noise current becomes large. Therefore, if the resistance between the electrodes is small, the photocurrent for weak incident light will be buried in the thermal noise current, making it difficult to detect the position of the light incident point.

The output currents from the two position signal electrodes of the semiconductor device are usually amplified by separate operational amplifiers. The input offset voltages of the two operational amplifiers do not exactly match. If the electrical resistance between the two position electrodes is small, a current will flow due to the difference between the two input offset voltages. When the incident light is weak and the photocurrent is small, the ratio of the currents sent out by the two position electrodes will deviate greatly from the original ratio of currents caused by the incident light.

We solved this problem by using an N-type silicon semiconductor substrate.
The distance between two position signal electrodes is 2 mm, and the width of the light receiving surface is 1 mm.
Further explanation will be given using an example of a semiconductor device for detecting an incident position in mm.

In order to make the electrical resistance of the P-type conductive layer obtained by implanting boron ions into the N-type conductive silicon substrate to 200 kΩ or more, the amount of boron implanted should be 4×10 ¹¹ /cm ² or less. There must be. Therefore, the impurity concentration for setting the conductor layer thickness to 1 μm must be 4×10 ¹⁵ /cm ³ . It is difficult to realize a uniform high resistance layer using such a low concentration of impurities for the following reasons.

First, due to non-uniform impurity concentration in the substrate, a uniform electrical resistance layer cannot be obtained even if boron is uniformly implanted. For example, the average impurity concentration of the substrate is 4×
When there is a variation of 20% at 10 ¹⁴ /cm ³ , a variation of 1% occurs in the boron concentration. This causes a 1% variation in electrical resistance. This variation in electrical resistance may cause an unsatisfactory result as a position signal, depending on the distribution on the light-receiving surface or the point of incidence of the light.

Next, a non-uniform inversion layer is formed in the P-type conductive layer, making it impossible to obtain a uniform electrically resistive layer. That is, a silicon oxide layer is usually provided on the surface of the P-type conductive layer in order to protect the P-type conductive layer and to prevent reflection of incident light. At this time, if the impurity concentration of the P-type conductive layer is low, an inversion layer is formed on the surface of the P-type conductive layer. Furthermore, when dirt adheres to the surface of the oxidized layer, an inversion layer corresponding to the pattern of the dirt is formed. This inversion layer acts as a higher resistance layer in the P-type conductive layer, so that the non-uniformity of electrical resistance corresponding to the dirt pattern on the surface of the oxidized layer will eventually occur in the P-type conductive layer. will occur.

An object of the present invention is to increase the resistance between two position signal electrodes without lowering the concentration of impurities of different conductivity formed on a semiconductor substrate, so that even when weak light is incident, the incident point of the light can be improved. An object of the present invention is to provide a semiconductor device for detecting an incident position, which is capable of detecting the position of an incident position.

In order to achieve the above object, a semiconductor device for detecting an incident position according to the present invention includes a semiconductor substrate of one conductivity type;
a pair of position signal electrodes provided parallel to each other along the short sides of a rectangular entrance surface of the semiconductor substrate; an entrance surface conductive layer formed with a conductive layer different from the conductive layer having a uniform impurity concentration and having a narrow uniform width so as to be divided at equal intervals in the direction and connecting the pair of position signal electrodes with high resistance; and a highly concentrated bottom conductive layer of the same conductivity type as the semiconductor substrate formed on a surface opposite to the rectangular incident surface of the semiconductor substrate, and an incident light amount signal electrode connected to the bottom conductive layer. ing.

Note that according to the above configuration, a considerable portion of the entrance surface is not covered with the entrance surface conductive layer. However, if the distance between the conductive layers on the incident surface is shorter than the diffusion length of the fractional carrier,
Fractional carriers generated on the substrate by the incidence of light reach the entrance surface conductive layer, so there is no problem at all in detecting light incident on the portion not covered by the entrance surface conductive layer. With this configuration, the resistance of the two position signal electrodes can be increased, and the object of the present invention can be completely achieved.

The semiconductor device for detecting an incident position according to the present invention will be described in more detail below with reference to the drawings.

FIG. 3 is a schematic plan view of a semiconductor device for detecting an incident position according to an embodiment of the present invention, and FIG. 4 is a schematic cross-sectional view. The semiconductor substrate 11 contains phosphorus as an impurity.
It is an N-type semiconductor doped with 10 ¹³ /cm ³ and approximately 250 μm thick. The first and second position signal electrodes 12 and 13 are made of boron 4x from one surface of the semiconductor substrate 11.
A highly concentrated P-type conductive layer is doped with 10 ¹¹ /cm ² , and aluminum is deposited on the surface to a thickness of 0.8 μm. First and second lead wires 14 and 15 are connected to each position signal electrode 12 and 13 by wire bonding.
A P-type conductive layer 16 is formed on the incident surface side of the semiconductor substrate 11 . This P-type conductive layer 16 is a core portion 1 that connects the midpoints of the electrodes 12 and 13 in a straight line.
6a, and a plurality of branch portions 16b, 16c, . . . , 16n that perpendicularly intersect the main portion 16a. The other surface (bottom surface) of the semiconductor substrate 11 is doped with phosphorus to form a bottom conductive layer 17 which is a highly concentrated N-type conductive layer, and gold is deposited on the surface to form an incident light amount signal electrode 18. And the third lead wire is connected.

The width of the semiconductor substrate 11 is 1 mm, and the distance between the two electrodes 12 and 13 is 2 mm. The width of the P-type conductive layer is the same as that of the main portion 16a and the branch portions 16b, 16c...16n.
Both are 100 μm, adjacent branch parts 16b and 16c
...16n interval is 100μm, branch portion 16b,1
The length of 6c...16n is 900 μm. The distance between the branch portions of 100 μm is smaller than the diffusion length of the fractional carrier in the semiconductor substrate 11 of 300 μm.

Position signal electrode 13 and electrode 1 of the above-described embodiment device
When the electrical resistance was measured between 4 and 4, a high resistance of 250 kΩ was obtained.

When a conductive layer was formed on the entire incident surface of the semiconductor substrate 11 of this example device under the same conditions, the voltage between the electrodes could not exceed 50 kΩ.

The embodiment illustrated above has been described in detail, but in the embodiment, the branch conductive layers 16b, 16c
. . . By removing 16n and arranging a large number of conductive layers having the same shape as the basic portion 16a in parallel at equal intervals so as to reach the position signal electrodes at both ends, the same effect could be obtained.

As explained in detail above, in the device according to the present invention, the resistance between the position signal electrodes can be increased.
It becomes possible to calculate position with a small optical input signal, and many applications are expected.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a semiconductor device capable of outputting one-dimensional information on the incident position of light, etc., and FIG. 2 is a schematic cross-sectional view. FIG. 3 is a plan view of an embodiment of the semiconductor device for detecting an incident position according to the present invention, and FIG. 4 is a schematic cross-sectional view. 1... Light receiving surface, 2... First position signal electrode, 2
a, 3a...Metal layer, 3...Second position signal electrode,
4... Entrance surface conductor layer, 4a, 4b... Doped portion, 5... Semiconductor substrate, 6... Bottom conductor layer, 7...
...Incident light amount signal electrode, 11...Semiconductor substrate, 12
...First position signal electrode, 13...Second position signal electrode, 14...First lead wire, 15...Second lead wire, 16...Incidence surface conductive layer (P-type conductive layer),
16a...Basic conductive layer, 16b, 16b to 16n
... Branch conductive layer, 17 ... Bottom conductive layer (P-type conductive layer), 18 ... Light quantity signal electrode, 19 ... Third lead wire.

Claims (1)

[Scope of Claims] 1. A semiconductor substrate of one conductivity type, a pair of position signal electrodes provided parallel to each other along the short side of a rectangular incident surface of the semiconductor substrate, and the pair of position signal electrodes. The conductive layer has a uniform impurity concentration and has a uniform impurity concentration such that the rectangular incident surface of the semiconductor substrate is divided at equal intervals in a direction parallel to or perpendicular to the pair of position signal electrodes. an entrance surface conductive layer of different conductivity types and formed to have a narrow and uniform width; and a highly concentrated bottom conductive layer of the same conductivity type as the semiconductor substrate formed on a surface opposite to the rectangular entrance surface of the semiconductor substrate. . A semiconductor device for detecting an incident position, comprising an incident light amount signal electrode connected to the bottom conductive layer. 2. The incident surface conductive layer is comprised of a main conductive layer that directly connects the pair of position signal electrodes, and a plurality of branch conductive layers that are connected at right angles to the main conductive layer. The semiconductor device for detecting an incident position according to item 1. 3. The semiconductor device for detecting an incident position according to claim 1, wherein the width of the semiconductor substrate divided by the incident surface conductive layer is equal to or less than the mean free path of the fractional carrier in the semiconductor substrate.