JPH06224467A - Position sensor - Google Patents

Abstract

PURPOSE:To obtain linearity of a luminous point position and high resolution of a luminous point position of a position sensor by forming a resistance layer between surface electrodes of a high concentration impurity diffused layer, and forming its shape of a sawtoothlike pattern in which intervals of adjacent parallel lines are equal. CONSTITUTION:A resistance layer of an impurity diffused layer for connecting between surface electrodes 2 and 3 for detecting a position is formed of a high concentration P<+> type impurity diffused layer 11 to have a sawtoothlike pattern in which intervals L adjacent parallel lines are equal. Thus, since the layer 11 of a light receiving surface has high implanted impurity concentration, its surface is not inverted, and it is not affected by influence of impurity concentration of an N-type semiconductor substrate. Since it can be formed of a thin width and a long length, a high and uniform resistance between the electrodes 2 and 3 is obtained. Thus, a luminous point position linearity and high resolution of a luminous point position of a position sensor can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a still camera, a VTR.
The present invention relates to improvement of an incident light point position detection photodiode (hereinafter referred to as PSD) called a position sensor used for autofocus of a camera or the like.

[0002]

2. Description of the Related Art Various types of autofocus systems for still cameras, VTR cameras, etc. have been commercialized. The principle of triangulation of the distance between the camera and the subject, that is, infrared light emission inside the camera The light intensity distribution of the reflected light point from the subject of the infrared light emitted from the diode is detected by the light receiving element, the position of the reflected light point is detected from the distribution of the light intensity, and the distance between the camera and the subject is measured, Focusing is on a projection distance measurement method in which the result is fed back to perform focusing.

As the light receiving element, there are a two-divided photodiode, a multi-divided photodiode, a PSD and the like.

When using a two-divided photodiode whose light-receiving portion is divided into two as a light-receiving element, the two-divided photodiode is moved to detect the position of the reflection intersection from the object. It is necessary to form an image in the center.

When a multi-divided photodiode is used as the light receiving element, the position of the reflected light spot can be detected with the multi-divided photodiode fixed, but continuous position detection is not possible.

However, when PSD is used, PS
With D fixed, the reflected light spot position can be detected continuously with high linearity and high accuracy. In order to obtain good intersection position linearity in PSD, it is important that the resistance layer of the light receiving portion between the electrodes is uniform, for example, a P ⁺ -type impurity diffusion layer. Further, in order to detect the position of the light spot with PSD with high resolution, it is necessary to improve the signal-to-noise ratio of PSD. That is, the following current reduction is required.

Thermal noise current due to the resistance of the P ⁺ -type impurity diffusion layer of the light receiving portion, noise current of the operational amplifier, current due to the potential difference of the input offset of the operational amplifier, dark current, Schottky noise due to photocurrent.

In order to reduce the currents (1) to (3), the resistance of the P ⁺ -type impurity diffusion layer in the light receiving portion between the electrodes is high,
Usually, it is required to be 200 kΩ or more.

In a low-priced camera, infrared light is emitted only in the central portion of the screen, and a single PSD measures only the subject distance in the central portion. Therefore, when photographing two persons who are far apart, it is necessary to photograph one of them in the center of the screen for autofocusing, then bring the middle part of the two persons to the center of the screen and press the shutter.

In a high-end camera, the screen is divided into three or five divisions, and P is provided for each area.
It adopts a method of autofocusing by SD. In this case, the infrared light is emitted to each region from three or five LEDs. The light reflected from the object in each area is incident on the PSD in each of a plurality of areas such as three or five areas, and the distance to the subject is measured.

FIG. 5 is a plan view of an example of a conventional single PSD, and FIG. 6 is a sectional view thereof. On the surface of the rectangular N-type semiconductor substrate 1, the P ⁺ -type impurity diffusion layer 4 of the light receiving portion is formed by ion implantation over almost the entire surface, and at both ends of the short side, contact with the electrode is secured in another step. for,
Further, surface electrode contacts 5 and 5 are formed by a high concentration P ⁺ -type impurity diffusion layer. The surface is covered with a SiO ₂ film 9, and the surface electrodes 2 and 3 formed by Al vapor deposition for position detection are connected to the surface electrode contacts 5 and 5 through the SiO ₂ film 9. A channel stopper 6 made of an N ⁺ type diffusion layer is formed around the front surface of the N-type semiconductor substrate 1, and a back electrode is provided between the back electrode 8 provided on the back surface of the N-type semiconductor substrate 1 and the substrate. An N ⁺ -type impurity diffusion layer 7 is provided in order to improve the quality. In FIG. 5, the SiO ₂ film 9
Is omitted.

In order to realize the resistance value of the P ⁺ -type impurity diffusion layer 4 of the PSD shown in FIGS. 5 and 6 of 200 kΩ or more, the P ⁺ -type diffusion layer is provided over almost the entire surface. The amount should be low.
In this case, SiO ₂ on the P ⁺ -type impurity diffusion layer 4 of the light receiving portion
The surface of the P ⁺ -type impurity diffusion layer 4 becomes an N-type inversion layer due to Na ⁺ ions or the like in the film 9, and the resistance of the P ⁺ -type impurity diffusion layer 4 becomes non-uniform. Further, when the impurity implantation amount is low, the resistance of the P ⁺ -type impurity diffusion layer becomes non-uniform due to the non-uniformity of the impurity concentration of the N-type semiconductor substrate. Also,
In order to secure the contact of the surface electrode for position detection, the P ⁺ -type impurity diffusion layers 5 and 5 having a higher concentration than the normal resistance portion are formed on the surface electrode contact portion, which is different from the formation of the P ⁺ -type impurity diffusion layer of the resistance portion. Formed in the process.

In order to solve the above problem, as shown in the plan view of FIG. 7 and the sectional view of FIG.
Between the pair of opposing surface electrodes 2 and 3 for signal detection, which are arranged on the short side of the rectangular light receiving part of the above, a thin and uniform P ⁺ -type impurity diffusion layer 4-1 with a uniform width is formed. And a plurality of P ⁺ -type impurity diffusion layers 4-2 having a uniform width in a fish-bone shape at equal intervals in the vertical direction to the P ⁺ -type impurity diffusion layer 4-1.
There is a structure with. In this case, a high resistance interelectrode resistance can be obtained with a relatively high concentration of impurity implantation so that the above-mentioned problem does not occur. In FIG. 7, Si
The O ₂ film 9 is omitted. Others are the same as the case of FIG. 5 and FIG.

There is also a device provided with an impurity diffusion layer having a rectangular wave pattern as described in Japanese Patent Application No. 2-185648.

FIG. 9 shows a plurality of PSDs, for example, P divided into seven.
FIG. 10 is a plan view of an intermediate electrode type PSD that uses SD and can be used between individual PSDs.
FIG. The same parts as those in FIGS. 5 to 8 are designated by the same reference numerals.

As shown in the figure, a basic resistance part 21 for position detection is provided so as to connect the surface electrodes 20, 20 ...
Are provided with light receiving portion resistance layers 23, 23 ... This light receiving portion resistance layer 2
.. collect the carriers generated in the N-type semiconductor substrate 1. The resistance between the surface electrodes 20, 20 ... Is usually 200 to 400 KΩ or the like from the viewpoint of the SN ratio of PSD.
The light receiving portion resistance layers 23, 23 ...
This is a P ⁺ -type impurity diffusion layer formed by the same diffusion as.
In FIG. 9, the SiO ₂ film 9 is omitted. 22,
22 are surface electrode contacts. The surface electrode 20 is connected if necessary.

[0017]

However, the above-mentioned FIG.
In the PSD having the structure of the fish-bone-shaped impurity diffusion layer as shown in FIG. 8, high resistance cannot be obtained when the distance between the surface electrodes for signal detection is small.

In addition, S having a structure with a rectangular wave pattern
In PD, since the resistance value is not proportional to the incident position of light, the detection error becomes large when the incident spot light is small.

In the conventional intermediate electrode type PSD as shown in FIGS. 9 and 10, in addition to the basic resistance portion 21, P ⁺
Since the resistance of the light receiving portion resistance layers 23, 23 ... Is added by the type impurity diffusion layer, the series resistance becomes large.

When the resistance of the PSD becomes large, the CR of the circuit
There is a problem that the response time becomes slow due to the time constant.

[0021]

In the PSD of the present invention, a resistance layer formed of a high-concentration impurity diffusion layer connecting the position detecting electrodes is formed of a high-concentration impurity diffusion layer, It had a sawtooth pattern with equal intervals. In addition, a plurality of electrodes are provided on the bent portion of the sawtooth pattern and divided into a plurality of regions.

[0022]

With the structure described above, the P-type impurity diffusion layer on the light-receiving surface has a high impurity concentration implanted therein, so that the surface thereof does not undergo N inversion and is not affected by the impurity concentration of the N-type semiconductor substrate. Further, since the width can be made narrow and long, a uniform high resistance between electrodes can be obtained. The high-concentration P-type impurity diffusion layer for securing the contact of the position detection electrode is
Since it can be formed in the same process as the P-type impurity diffusion layer of the light receiving portion, the process is simplified. The series resistance can be selected appropriately, the time constant of the circuit can be shortened, and the response time can be shortened.

[0023]

1 is a plan view of an embodiment of the present invention.
Is a sectional view thereof. It is created as follows. In FIG. 1, the SiO ₂ film 9 is omitted.

On the N-type semiconductor substrate 1 made of N-type and having a specific resistance of about 1000 Ω · cm, boron is selectively implanted at a high concentration from the surface by photoetching and ion implantation, and a uniform light receiving portion is formed. A high-concentration P ⁺ -type impurity diffusion layer 10 having a width is formed. At this time, the P ⁺ -type impurity diffusion layer 10 of the light receiving portion is formed into a sawtooth pattern having a uniform width as shown in the figure by photoetching in order to increase the resistance value between the electrodes. At this time, in order to make the connection of the surface electrode for position detection good, the surface electrode contacts 5 and 5 of the high-concentration P ⁺ -type impurity diffusion layer are simultaneously formed at the planned electrode positions. The intervals L between adjacent parallel straight line portions of the sawtooth pattern are made equal over the entire surface.

Next, in order to secure the contact property of the high-concentration N ⁺ -type channel stopper 6 and the back surface electrode 8 formed after the back surface of the semiconductor substrate, the high-concentration N ⁺ -type impurity diffusion layer 7 is formed on the back surface. Are spread all over the surface at the same time.

Thereafter, front surface electrodes 2 and 3 made of Al for position detection and a back surface electrode 8 made of Au on the back surface of the semiconductor substrate 8 are formed.
Are each formed by vapor deposition.

The back electrode 8 can also be provided as an Al electrode on the front surface of the chip. The formation of the SiO ₂ film 9 and the surface electrodes 2 and 3 is the same as in the case of FIGS.

FIG. 3 is a plan view of another embodiment, and FIG. 4 is a BB 'sectional view thereof. In addition, in FIG.
The SiO ₂ film 9 is omitted.

Boron of high concentration is selectively implanted from the surface of the N-type semiconductor substrate 1 made of silicon having a specific resistance of about 1000 Ω · cm by photoetching and ion implantation, so that the light receiving portion has a narrow and uniform width. A P ⁺ type impurity diffusion layer 11 having a high concentration is formed. At this time, as in the case of FIG. 1, the P ⁺ -type impurity diffusion layer 11 is formed in a sawtooth pattern having a uniform width by the photoetching technique. The interval is, for example, 100 μm.

Next, an N ⁺ type channel stopper 3 and
The high-concentration N ⁺ -type impurity diffusion layer 7 is simultaneously diffused in order to secure the contact property of the back surface electrode 8 with Au.

Thereafter, the front and rear surface electrodes 20, 20 ... And the back surface electrode 8 for detecting the surface position are respectively formed by the vapor deposition technique. Intermediate electrodes 20, 20 ...
Are provided at the bent portions of the sawtooth pattern.

The back electrode 9 may be provided as an Al electrode on the surface of the chip. The N ⁺ type channel stopper 3 and the N ⁺ type diffusion layer 7 on the back surface may be diffused before the boron implantation. SiO ₂ film 9 and surface electrodes 20, 2
The formation of 0 ... Is almost the same as in the case of FIGS. 22 and 22 ... are surface electrode contacts,
Only the required number should be provided.

As compared with the conventional example of FIGS. 9 and 10, the basic resistance portion 21 and the light receiving portion resistance layer 23 are replaced with the P ⁺ -type impurity diffusion layer 11 which is a resistance layer having a sawtooth pattern.

[0034]

As described above, according to the present invention, even when the distance between the electrodes for position detection is small, a relatively high boron implantation amount without causing N reversal and being unaffected by the impurity concentration of the semiconductor substrate. Thus, a P ⁺ -type impurity diffusion layer serving as a resistance layer can be formed, and high resistance and uniform interelectrode resistance can be obtained. Therefore, good linearity of the light spot position and high resolution of the light spot position can be obtained. Also, the process is simplified. The response time can be shortened by adjusting the resistance value.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ of FIG.

FIG. 3 is a plan view of another embodiment.

FIG. 4 is a sectional view taken along line BB ′ of FIG.

FIG. 5 is a plan view of a conventional example.

6 is a cross-sectional view of FIG.

FIG. 7 is a plan view of another conventional example.

8 is a cross-sectional view of FIG.

FIG. 9 is a plan view of another conventional example.

10 is a cross-sectional view taken along the line CC ′ of FIG.

[Explanation of symbols]

1 N-type semiconductor substrate 2, 3, 20 Front surface electrode 4 P ⁺ type impurity diffusion layer 5, 22 Front surface electrode contact 6 Channel stopper 7 N ⁺ type impurity diffusion layer 8 Back surface electrode 11 p ⁺ type impurity diffusion layer

Claims (2)

[Claims] 1. A semiconductor substrate of a first conductivity type, electrodes formed at both ends of the substrate, and an impurity diffusion layer of a second conductivity type having a uniform width for connecting the electrodes to each other. 2. A position sensor, comprising: a resistive layer formed on the surface of the resistance layer, wherein the resistive layer has a sawtooth pattern in which the intervals between adjacent parallel linear portions are equal. 2. An electrode is provided at a plurality of bent portions of a sawtooth pattern and is divided into a plurality of regions.
The described position sensor.