JPS638506A - Semiconductor optical position detector - Google Patents

Abstract

PURPOSE:To detect accurately an optical position unaffected by intensities of leakage current and irradiated light, by taking out real optical electrical current only with a leakage current part subtracted from an electric output of an optical position detecting element. CONSTITUTION:A pn-joint of an optical position detecting element 11 is biased reversedly by a Vcc/2 voltage. When a beam of light of a spot-form is irradiated on to a certain position between electrodes 9, 10, currents I1, I2 are taken out from each electrode 9, 10 respectively. If an unit of the leakage current is defined as J0 at this moment, each amount of J0l/2 flows out from each electrode 9, 10. On the other hand, as a light-receiving surface of a leakage compensating element 21 is covered by a light-screening surface 19, only the leakage current J0l/2 is taken out from each electrode 9a, 9b. Leak currents How to transistors 23, 26 and 24, 27 of current mirror circuits 22, 25 respectively. As a result, a leakage current part becomes to be subtracted from the output current I1, I2 of the optical position detecting element 11 and a real beam of optical electrical current only is taken out from the element 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a semiconductor device detector that detects the position of a spot of light projected onto a light receiving surface.

[Technical background of the invention and its problems] As a conventional semiconductor device detector, for example, there is one as shown in FIG.
Fi).

The semiconductor device detector chip has a p-type layer 32 formed on the main surface of a high resistivity n-type 3i substrate 31 to constitute a photodetecting surface by a pn junction, and a contact layer 1m on the back side.
A layer 33 is formed over the entire surface. The chip is formed into a rectangular shape when viewed from above.

Note that if the n-type is the first conductivity type, the p-type, which is the opposite conductivity type, is the second conductivity type.

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

The electrode 34 is grounded via a resistor 36a for current/voltage exchange, and a buffer amplifier 37a is connected to the connection point between the electrode 34 and the resistor 36a. Since the value of the photocurrent 11 is minute, it is converted into a voltage and amplified by the buffer amplifier 37a.

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

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

The pn junction on the photodetection surface is reverse biased by the positive voltage element V mentioned above.

It is now assumed that the pn junction is sufficiently reverse biased by the positive voltage element V, and that the thickness of the p-type layer 32 is smaller than the diffusion length of minority carriers.

Then, as shown in Figure 2, at the X coordinate on the light receiving surface such that the positions of each ffl pole 34.35 are x = -1/2 and X = i/2, a spot is placed at the position x = xO. Assuming that light of 1+ is projected, the photocurrents 1+ and +2 are expressed by the following equations.

It = Io (1/2-XO/u) −(
I12 = IQ (1/2+Xo/l)
.=(2) where IO is the total photocurrent generated and extracted by the projected light.

From both formulas (1) and <2) above, xO/吏= (1/2) ・ (I2 − 1+ )/ (II +12
) ... By performing the calculation in (3), the 1Ω irradiation position of the light X=XO is determined.

By the way, a leakage current exists in a reverse biased pn junction based on the physical properties of the semiconductor, and this leakage current increases exponentially with temperature, and increases as the area of the junction surface increases.

However, since the area of the photodetection surface of a semiconductor device detector is formed to be relatively large, the above-mentioned leakage current value becomes unacceptable, especially at high temperatures. If the value of leakage current per unit length is JO, the above equation (3) is expressed as follows under the influence of this leakage current JO.

Xo /1= (1/2) ・((+2-1+)/
(II +12 >) ・ (1+Jo l/Io
)...(4) Therefore, in the conventional semiconductor device detector, the leakage current Jo and I0 are affected by the leakage current Jo and the intensity of the projected light (the value of IO in equation (4)). There is a problem in that the included leakage current causes an error and the detection accuracy of the optical position decreases.

[Object of the Invention] The present invention has been made based on the above circumstances, and it is an object of the present invention to provide a semiconductor device detector that can accurately detect a light position without being affected by leakage current or the intensity of projected light. With the goal.

[Summary of the Invention 1] In order to achieve the above object, the present invention includes 21 electrically isolated island regions of a first conductivity type on the main surface of a semiconductor substrate.
1! A second conductivity type layer forming a J-diameter layer with the first conductivity type of the island region is provided in one of the letter regions, and a second conductivity type layer is provided at two separated positions of the second conductivity type layer. Electrodes are attached to each to form an optical position detection element, and a leakage current compensation element having the same structure as the above optical position detection element and having a light-shielding film coated on its light receiving surface is formed in the other island-shaped area, and subtraction is performed. By subtracting the leakage current output of the leakage current compensating element from the current output of the optical position detection element by the means, the influence of the leakage current and the intensity of the projected light does not appear on the detection of the optical position.

[Embodiments of the invention] Embodiments of the present invention will be described below with reference to FIG.

First, to explain the structure, in FIG. 1, 1 is a 3i semiconductor substrate, and the semiconductor substrate 1 is an epitaxial substrate in which a phosphorus (P)-doped high resistivity "1-type pitaxial layer" is formed on a p-type substrate 2. The main surface of the p-type substrate 2 is (
111) Those having surfaces are used.

A p-type impurity is selectively diffused into a required portion of the epitaxial layer to form a p+ isolation diffusion region M4, and the epitaxial layer is separated by this p+ isolation diffusion region M4 to form an n-type impurity on the main surface of the semiconductor substrate 1. Island-shaped regions (hereinafter referred to as islands) 3a and 3b are formed.

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

On the island 3a, there are two p
A shadow region 6.7 is formed diffusely, and these two p shadow regions 6.7 are formed diffusely.
A p-type layer 8 is formed between the layers 7 and 7 by ion implantation of boron (B). n of the specific resistance that constitutes the island 3a
A photodetecting surface is formed by a pn junction between the type epitaxial layer and the p-type layer 8.

An electrode 9.10 of An is attached to each p shadow region 6.7 to constitute an optical position detection element 11.

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

A resistor 14 for current-voltage conversion is also connected to the square electrode 10 in the same manner as described above, and the resistor 14 is connected between the inverting input terminal (-) and the output terminal of the differential amplifier 15.

The non-inverting input terminal (+) of both differential amplifiers 13 and 15 is
A reference voltage +Vcc/2 is applied to each.

16 is an n+ contact diffusion region, and a wiring layer 17 is connected to the n+ contact diffusion region 16. Each island 3a, 3b includes the wiring layer 17 and the n+ contact diffusion region 1ii! 16 through the positive supply voltage +V
CC has been added.

Since +V CC/2' Ml pressure appears at each inverting input terminal (-) of the differential amplifier 13.15 due to the principle of virtual short circuit, the pn junction of the optical position detection element 11 is
cc/2)=Vcc/2.

Reference numeral 18 denotes an oxide film which is formed as thin as about 1000 Å on the upper surface of the p-type layer 8. The oxide film on the upper surface of the p-type layer 8 is selectively etched away during ion implantation of the p-type layer 8, and is then formed to a thickness of about 1000 angstroms.

On the other hand, the other island 3b has p-type regions 1i 5 a,
7a, the O-type layer 3a, and the electrodes 149a and 10a form an element having the same structure as the optical position detection element 11, and a light-shielding film 19 is coated on the light-receiving surface portion (the portion on the light-detecting surface). A leak current compensating element 21 is built in. As one light-shielding film, for example, a helical film is used.

The electrode 9a of the leak current compensation cable 21 is connected to the collector of the primary transistor 23 in the current mirror circuit 22, and the collector of the secondary transistor 24 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 compensation element 21 is connected to the collector of the primary side transistor 26 in the other current mirror circuit 25, and its secondary f
The collector of the f111 transistor 27 is connected to the other electrode 10 of the optical position detection element 11.

The leak current output of the leak current compensation element flows through the primary side transistor 23.26 of each current mirror circuit 22.25, and the same leak current output flows through each secondary side transistor 24.27. Optical position detection element 1
A leakage current is subtracted from each current output from each electrode 6.7.

The current mirror circuits 22 and 25 constitute subtraction means for subtracting the leakage current from each output current of the optical position detection element 11.

In Fig. 1, resistor 12.14, differential amplifier 13.15
, current mirror circuits 22, 25, etc. are each shown using element symbols or blocks, but these elements, device circuits, etc. are fabricated in other parts of the same semiconductor substrate 1.

Next, the effect will be explained.

The pn junction of the optical position detection element 11 is reverse biased with a voltage of Vcc/2. When a spot of light is projected onto a position between the electrodes 9.10, a current 11.12 is extracted from each electrode 9.10.

At this time, a leakage current based on the physical properties of the semiconductor flows through the above pn junction, and if its value is Jo per unit quality, Jo 1/2 flows out from each 'T1 pole 9.10, and this is the above current. 1+, [2 is included as an error factor.

On the other hand, the pn junction of the leakage current compensation element 21 is also
Although it is reverse biased with a voltage of C/2, since the light-receiving surface is covered with a light-shielding film 19, only leakage current Jo/2 is taken out from each electrode 9a, 10a.

The leakage current Jon/2 flows through the primary side transistors 23.26 in the current mirror circuits 22.25, and the same leakage current JO/2 also flows through the respective secondary side transistors 24.27.

Since the collector of each secondary side transistor 24.27 is connected to each electrode 9.10 of the optical position detection element 11, the output current 11, I2 of the optical position detection element 11 is connected to each of the secondary side transistors 24, 27. 24.Leakage current J flowing through 27
o tl/2 is subtracted, and only the true photocurrent is taken out from the optical position detection element 11 as a current for calculating the light projection position.

Therefore, the projection position of the light is determined by the above (
3) The light position is precisely detected by calculation using the equation.

Note that the actual calculation is converted into voltage and sent to the differential amplifier 13.
This is done using a value amplified by 15.

[Effects of the Invention] As explained above, according to the configuration of the present invention, since the leakage current is subtracted from the current output of the optical position detection element and only the true photocurrent is extracted, it is easy to detect the optical position. This has the advantage that the influence of leakage current and the intensity of the projected light disappears, and the light position can be detected with high accuracy.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of a semiconductor device detector according to the present invention, and FIG. 2 is a sectional view showing a conventional semiconductor device detector. 1: Semiconductor substrate, 3a, 3b two island regions, 8.8a: pTF forming n-type island region and ρn junction
3 layers, 9.10.9a, 10a: tilt pole, 11: optical position detection element, 19: light shielding film, 21: leakage current compensation element, 22.25: current mirror circuit (subtraction means).

Claims (1)

[Claims] Two electrically isolated island regions of a first conductivity type are formed on the main surface of the semiconductor substrate, and a second conductivity type bonding layer is formed in one of the island regions and the first conductivity type of the island region. A conductivity type layer is provided and electrodes are attached to two separate positions of the second conductivity type layer to form an optical position detection element, and the other island-shaped area is provided with a light receiving element having the same structure as the optical position detection element. A semiconductor optical position comprising: a leakage current compensating element having a light-shielding film coated on its surface; and subtracting means for subtracting the leakage current output of the leakage current compensating element from the output current of the optical position detecting element. Detector.