JPH0762605B2 - Semiconductor optical position detector - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a semiconductor optical position detector that detects a spot-shaped optical position projected on a light receiving surface.

[Technical Background of the Invention and Problems Therefor] As a conventional semiconductor optical position detector, there is, for example, one shown in FIG. 2 (Japanese Patent Laid-Open No. 55-87007).

The semiconductor optical position detector chip is an n-type Si substrate with high specific resistance.
A p-type layer 32 is formed on the main surface of 31 to form a light detection surface by a pn junction, and an n ⁺ layer 33 serving as a contact layer is formed on the entire back surface. The chip is formed in a rectangular shape in plan view.

When the n-type is the first conductivity type, the opposite p-type is the second conductivity type.

Electrodes 34 and 35 are formed on the p-type layer 32 at two positions separated by an interval length 1 along two opposite sides of the chip main surface.

The electrode 34 is grounded via a resistor 36a for current-voltage exchange,
A buffer amplifier 37a is connected to a connection point between the electrode 34 and the resistor 36a. Since the value of the photocurrent I ₁ is small, it is converted into a voltage and then amplified by the buffer amplifier 37a.

On the other electrode 35 side as well, a resistor 36b for current / voltage conversion and a buffer amplifier 37b are connected in the same manner as above.

On the other hand, the n ⁺ layer 33 on the back surface has an electrode on all or part of
38 is attached, and the electrode 38 is connected via a resistor 39 to a positive voltage + V power source.

The pn junction on the light detection surface is reverse biased by the above positive voltage + V.

Now the pn junction is fully reverse biased by the positive voltage + V,
The thickness of the p-type layer 32 is smaller than the diffusion length of minority carriers.

As shown in FIG. 2, in the x coordinate on the light receiving surface where the positions of the electrodes 34 and 35 are x = −l / 2 and x = 1/2 respectively, the spot is located at the position of x = x _0. Assuming that a light beam is projected, the photocurrents I ₁ and I ₂ are expressed by the following equations.

I ₁ = I ₀ (1 / 2−x ₀ / l) (1) I ₂ = I ₀ (1/2 + x ₀ / l) (2) Here, I ₀ is generated by the projected light and is taken out. The total photocurrent.

Projection of light by performing the calculation of x ₀ / l = (1/2) · (I ₂ −I ₁ ) / (I ₁ + I ₂ ) ... (3) from both equations (1) and (2) above. The position x = x ₀ is determined.

By the way, a reverse biased pn junction has a leak current due to the physical properties of the semiconductor, and this leak current exponentially increases with temperature, and increases as the area of the junction surface increases.

However, since the area of the light detection surface of the semiconductor optical position detector is formed to be relatively large, the value of the above leakage current cannot be ignored especially at high temperatures. If the leak current value per unit length is J ₀ , this leak current
Under the influence of J _0, the equation (3) is expressed as the following equation.

x ₀ / l = (1/2) ・ [(I ₂ −I ₁ ) / (I ₁ + I ₂ )] ・ (1 + J ₀ l / I ₀ ) ... (4) Therefore, in the conventional semiconductor optical position detector If so, the leak current J ₀ and the intensity of the projected light (the value of I _{0 in} the equation (4)) are affected, and the leak current component included in the leak currents J ₀ and I ₀ becomes an error, and the light position is detected. There was a problem that the accuracy was lowered.

[Object of the Invention] The present invention has been made based on the above circumstances, and provides a semiconductor optical position detector capable of accurately detecting an optical position without being affected by a leak current and the intensity of projected light. The purpose is to

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention forms two electrically isolated island regions of the first conductivity type on a main surface of a semiconductor substrate, and one island region is formed in one island region. A second conductivity type layer that forms a bonding layer with the first conductivity type of the island-shaped region is provided, and electrodes are respectively attached to two spaced apart positions of the second conductivity type layer to form an optical position detecting element, and the other. A leak current compensating element having the same structure as the above-mentioned optical position detecting element and having a light-shielding film coated on its light receiving surface is formed in the island-shaped region, and the leak current compensating element is changed from the current output of the optical position detecting element by subtracting means. By subtracting the leak current output of, the influence of the leak current and the intensity of the projected light does not appear in the detection of the light position.

[Embodiment of the Invention] An embodiment of the present invention will be described below with reference to FIG.

First, in FIG. 1, reference numeral 1 denotes a Si semiconductor substrate, and as the semiconductor substrate 1, an epitaxial substrate in which a phosphorus (P) -doped high specific resistance n-type epitaxial layer is formed on a p-type substrate 2 is used. Has been. The main surface of the p-type substrate 2 is (11
1) Those with a face are used.

At a required portion of the epitaxial layer, p type impurities are selectively diffused to form ap ⁺ dispersion diffusion region 4, and the epitaxial layer is separated by the p ⁺ isolation diffusion region 4 to form a main surface of the semiconductor substrate 1. n-type island area (hereinafter called island)
3a and 3b are formed.

Reference numeral 5 is an n ⁺ buried layer, which is formed by doping antimony (Sb) or arsenic (As) before the growth of the epitaxial layer.

On the island 3a, p-type regions 6 and 7 are diffused and formed at two positions separated by a required distance, and these two p-type regions 6 and 7 are formed.
In between, the p-type layer 8 is formed by ion implantation of boron (B). A photodetection surface is formed by a pn junction between the p-type layer 8 and the n-type epitaxial layer having a high specific resistance which constitutes the island 3a.

Then, the Al electrodes 9 and 10 are attached to the p-type regions 6 and 7, respectively, to form the optical position detecting element 11.

A resistance 12 for current-voltage conversion is connected to the electrode 9 and the resistance 12
Is connected between the inverting input terminal (-) and the output terminal of the differential amplifier 13.

Similarly to the above, the other electrode 10 is also connected to the resistor 14 for current-voltage conversion, and the resistor 14 is connected between the inverting input terminal (−) and the output terminal of the differential amplifier 15.

A reference voltage + Vcc / 2 is applied to the non-inverting input terminals (+) of both differential amplifiers 13 and 15, respectively.

16 is the n ⁺ contact diffusion region, and the n ⁺ contact diffusion region 16
An Al wiring layer 17 is connected to. Each island 3a,
A positive power supply voltage + Vcc is applied to 3b via the wiring layer 17 and the n ⁺ contact diffusion region 16 described above.

Since + Vcc / 2 voltage appears at each inverting input terminal (−) of the differential amplifiers 13 and 15 due to the principle of virtual short circuit, the pn junction of the optical position detecting element 11 is Vcc− (Vcc / 2) = Vcc / 2. Reverse biased with voltage.

Reference numeral 18 is an oxide film, and the upper surface of the p-type layer 8 is formed thinly to about 1000 angstroms. The oxide film on the upper surface of the p-type layer 8 is selectively removed by etching when the p-type layer 8 is ion-implanted, and then thinned to about 1000 angstroms.

On the other hand, on the other island 3b, p-type regions 6a, 7a and p-type layers are formed.
A leak current compensating element in which an element having the same structure as the optical position detecting element 11 is formed by 8a and the electrodes 9a and 10a, and a light shielding film 19 is attached to the light receiving surface portion (the portion on the light detecting surface). 21 is built in. As the light shielding film 19, for example, Al
Membranes are used.

The electrode 9a in the leak current compensation element 21 is connected to the collector of the primary side transistor 23 in the current mirror circuit 22, and the collector of the secondary side transistor 24 thereof is connected to the electrode 9 of the optical position detection element 11.

Similarly to the above, the other electrode 10a of the leakage current compensating element 21 is connected to the collector of the primary-side transistor 26 in the other current mirror circuit 25, and the collector of the secondary-side transistor 27 of the other electrode 10a is different from that of the optical position detecting element 11. Connected to electrode 10.

Primary side transistor 23 of each current mirror circuit 22, 25,
In 26, the leak current output of the leak current compensation element flows,
Since the same leak current output as this flows in each of the transistors 24 and 27 on the secondary side, each of the electrodes 6 of the optical position detection element 11,
A leak current component is subtracted from each current output from 7.

Thus, each of the current mirror circuits 22 and 25 constitutes a subtracting means for subtracting the leak current component from each output current of the optical position detecting element 11.

In FIG. 1, the resistors 12, 14, the differential amplifiers 13, 15, and the current mirror circuits 22, 25, etc. are shown by element symbols or blocks, but these elements and device circuits are on the same semiconductor substrate. Built into the other part of 1.

Next, the operation will be described.

The pn junction of the optical position detecting element 11 is reverse biased with a voltage of Vcc / 2. When a spot-like light is projected at a certain position between the electrodes 9 and 10, a current I ₁ ,
I ₂ is taken out.

At this time, a leak current based on the physical properties of the semiconductor flows in the above pn junction, and if the value is J ₀ per unit length, Jol / 2 flows out from each electrode 9, 10 and this is the current I ₁ and I ₂ are included as error factors.

On the other hand, the pn junction of the leak current compensating element 21 is also reverse-biased with a voltage of approximately Vcc / 2, but since the light-receiving surface is covered with the light-shielding film 19, the leakage current from each electrode 9a, 10a is Only J ₀ l / 2 is taken out.

The leakage current J ₀ l / 2 is the current mirror circuit 22, 2 respectively.
5 flows into the primary side transistors 23 and 26, and accordingly, the same leak current J ₀ l / 2 also flows into the respective secondary side transistors 24 and 27.

Since the collectors of the respective secondary side transistors 24 and 27 are connected to the respective electrodes 9 and 10 of the optical position detecting element 11, from the output currents I ₁ and I _{2 of} the optical position detecting element 11, The leak current J ₀ l / 2 flowing through the transistors 24 and 27 is subtracted, and only the true photocurrent is taken out from the photo position detection element 11 as a current for calculating the light projection position.

Therefore, the light projection position is calculated by the equation (3) that does not include an error factor, and the light position is accurately detected.

Note that the actual calculation is converted into a voltage and the differential amplifier 13, 15
It is performed by the value amplified by.

[Effects of the Invention] As described above, according to the configuration of the present invention, since the leak current component is subtracted from the current output of the optical position detection element and only the true photocurrent is taken out, it is possible to detect the optical position. There is an advantage that the influence of the leak current and the intensity of the projected light does not appear, and the light position can be detected accurately.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor optical position detector according to the present invention, and FIG. 2 is a sectional view showing a conventional semiconductor optical position detector. 1: semiconductor substrate, 3a, 3b: island-shaped region, 8, 8a: p-type layer forming n-type island-shaped region and pn junction, 9, 10, 9a, 10a: electrode, 11: optical position detection element, 19: Shading film, 21: Leakage current compensator, 22, 25: Current mirror circuit (subtraction means).

Claims (1)

[Claims] 1. A main surface of a semiconductor substrate is formed with two electrically isolated island regions of a first conductivity type, and one island region has a first conductivity type of the island region and a bonding layer. A second conductivity type layer is formed, and electrodes are respectively attached to two spaced apart positions of the second conductivity type layer to form a light position detection element, and the other island-shaped region is formed with the same light position detection element as the light position detection element. Forming a leak current compensation element with a light-shielding film deposited on the light-receiving surface of the structure element,
A semiconductor optical position detector comprising a subtracting means for subtracting a leakage current output of the leakage current compensating element from an output current of the optical position detecting element.