JPS6316230A - Semiconductor light position detector - Google Patents

Abstract

PURPOSE:To accurately detect a light position by subtracting a leak current component from the current output of a light position detecting element and extracting only a real photocurrent. CONSTITUTION:On the main surface of a semiconductor substrate 1, n type island areas 3a and 3b are formed. The pn junction of a leak current compensating element 21 is also biased reversely with a voltage which is almost VCC/2, but a photodetection surface is covered with a light shield film 19, so only leak currents are led out of its electrodes 9a and 10b. The leak currents flow to primary-side transistors(TR) 23 and 26 in current mirror circuits 22 and 25 and the same leak currents also flow to secondary-side TRs 24 and 25. The collectors of the TRs 24 and 27 are connected to electrodes 9 and 10 of a light position detecting element 11, so the leak currents flowing to the TRs 24 and 27 are subtracted from output currents I1 and I2 of the element 11. Consequently, only the real photocurrent is led out of the element 11 as a current for the projection position arithmetic of light. The projection position of the light is therefore detected with accuracy without any error.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The 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, there is one shown in FIG. 2, for example (Japanese Patent Laid-Open No. 55-87007).

The chip of the semiconductor device detector has a p-type layer 32 formed on the main surface of a high resistivity n-type Si substrate 31 to constitute a photodetecting surface by a pn junction, and an n+ layer 33 serving as a contact layer on the back surface. It is formed all over. 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 7 amplifier 37a is connected to the connection point between the electrode 34 and the resistor 36a. Since the amount of photocurrent 11 is minute, it is converted into voltage and then amplified by buffer amplifier 37a.

On the other electrode 35 side, a resistor 36b1 for lightning current to positive conversion and a buffer amplifier 37b are connected in the same manner as described above.

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

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

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

Then, as shown in Fig. 2, at the X coordinate on the light receiving surface such that the positions of each electrode 34 and 35 are x = -1/2 and X = intersection/2, a spot is placed at the position x = x□. Assuming that light of 1+ is projected, the photocurrents 1+ and 12 are expressed by the following equations.

It=Io (1/2-Xo/1)”・
<1) I2 = 1o (1/2+xo/sentence)
-(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) ・ (12-It)/ (1+ +12)
...By performing the calculation in (3), the light projection position 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 value of the above-mentioned leakage current cannot be ignored, especially at high temperatures. When the value of leakage current per unit length is Jo, the above equation (3) is expressed as the following equation under the influence of this leakage current Jo.

Xo /l= (1/2) ・((12-11)/(I
I +12>)・(1+Jol/Io)...
(4) For this reason, in conventional semiconductor device detectors, the leakage current JO and the leakage contained in one port 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 current component causes an error, which reduces the accuracy of detecting the optical position.

[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] In order to achieve the above object, the present invention forms two electrically isolated island-like regions of the first conductivity type on the main surface of a semiconductor substrate, and one island-like region has a A second conductivity type layer forming a bonding layer with the first conductivity type of the island region is provided, and electrodes are attached to two positions of the second conductivity type layer separated by 1 ift to form an optical position detection element, A leakage current compensation element having the same structure as the optical position detection element described above and having a light-shielding film coated on its light receiving surface is formed in the other island-shaped region, and the leakage current compensation element is calculated from the current output of the optical position detection element by a subtraction means. By subtracting the leakage current output of the element, 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 p-type substrate 2 is formed with a phosphorus (P)-doped high resistivity n-type epitaxial layer. It is being The main surface of the p-type substrate 2 is (1
11) Those with 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 4, and the epitaxial layer is separated by this p+ isolation diffusion region 4 to form an n-type impurity on the main surface of the semiconductor substrate 1. Island-like 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). High resistivity n constituting the island 3a
A photodetecting surface is formed by a pn junction between the type epitaxial layer and the p-type layer 8.

An additional A pole 9.10 is attached to each P shadow region 6.7 to form the 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 connected to the other electrodes 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.

Reference numeral 16 denotes an n+ contact diffusion region, and a wiring layer 7 is connected to the n''' contact diffusion region 16. Each island 3a, 3b is connected to the wiring layer 17 and the n+
Positive power supply voltage +VCC via the contact diffusion region 16
has been added.

Since +Vcc/2 voltage 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 Vcc-(Vcc/2).
It is reverse biased with a voltage of =Vcc/2.

Reference numeral 18 denotes an oxide film which is formed to have a thickness of about 1000 angstroms 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 the ion implantation of the p-type layer 8, and is then formed to be as thin as iooo angstroms.

On the other hand, the other islands 3b include p shadow areas 6a, 7a,
An element having the same structure as the optical position detection element 11 is formed by the p-type layer 8a and the electrodes 9a and 10a, and a light shielding film is coated on the light-receiving surface (the part above the light-detecting surface). A current compensation element 21 is built in. For example, an A-shiro film is used as one light-shielding film.

The electrode 9a of the leakage current compensation element 21 is connected to the collector of the primary transistor 23 in the current mirror circuit 22, and the collector t 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 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 is connected to the collector of the secondary side transistor 27. It is connected to another electrode 10.

The leakage current output of the leakage current compensating element flows through the primary side transistors 23.26 of each current mirror circuit 22.25, and the same leakage current output also 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 action will be explained.

The pn junction of the optical position detection element 11 is reverse biased with a voltage of cc/2. Electric 1fl! When a spot of light is projected onto a position between 9 and 10, currents 1+ and 12 are taken out from each electrode 9 and 10, respectively.

At this time, a leakage current based on the semiconductor material M, etc. flows through the above p-n junction, and the (In) per unit length is Jo
Then, Jo A/2 flows out from each electrode 9 and 10, and this is included in the above-mentioned currents 1+ and +2 as an error factor.

On the other hand, the pn junction of the leakage current compensation element 21 is also
It is reverse biased with a voltage of C/2, but since the light receiving surface is covered with the light shielding film 19, the 6 voltages @A9a, 'io
Only the leakage current Jol/2 is taken out from a.

The leakage current JOi/2 flows through each primary side transistor 23.26 in the current mirror circuit 22.25, and the same leakage current JOi/2 also flows through each secondary side transistor 24.27 accordingly.

Since the collector of each secondary side transistor 24.27 is connected to each electrode 9.10 of the optical position detection element 11, from the output voltage ML I 1 , I2 of the optical position detection element 11,
The leakage current JO (1/2) flowing through each of the above secondary side transistors 24 and 27 is subtracted, and only the true photocurrent is extracted from the optical position detection element 11 as a current for calculating the light projection position. be done.

Therefore, the projection position of the light is determined by the above (
3) The light position is detected with high accuracy by calculation according to the equation.

Note that the actual calculation is converted into voltage and sent to the differential amplifier 13.
15 is used.

[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 the drawing]

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-like regions, 8.8a: P-type layer forming a pn junction with the n-type island region, 9.10.9a, 10a: electrode, 11: optical position detection element, 19 2 m optical film, 21: Leak current auxiliary 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.