JPH0427481B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an edge position detection device, and is useful for optically detecting the peripheral edge position of a plate-like object over a relatively wide range in industrial measurement.

When transferring wafers between manufacturing equipment in the semiconductor manufacturing process, the orientation flats, which are cutouts on the wafer periphery, are aligned at the same angle, and when positioning the wafer at a predetermined position, the edges of the orientation flats are aligned. An edge position detection device that detects the shape becomes necessary. FIG. 1 is a principle diagram showing this type of edge position detection device according to the prior art. In the figure, 1 is a charge-coupled device image sensor (hereinafter referred to as
2 is a CCD image sensor drive circuit, which oscillates the clock.
The CCD image sensor 1 is driven by controlling the register and phototransfer gate within the CCD image sensor 1. 3 is a reading processing circuit;
4 is a counting circuit, and 5 is a light source.

In such an edge position detection device, the peripheral edge position x of the plate-shaped body 6 can be known as the count number N from the shift pulse shown in FIG. 2a to the rise of the output waveform of the CCD image sensor 1 shown in FIG. 2b. . That is, the peripheral edge position x is determined from N counted by the counting circuit 4.

However, in such an edge position detection device,
In order to drive the CCD image sensor 1, complex peripheral circuits such as a clock oscillation circuit and a timing controller are required, and since the CCD image sensor 1 is composed of many small photoelectric conversion elements, the resolution is It depends on the size of the photoelectric conversion element, and has the disadvantage that the structure and manufacturing become complicated, especially in order to obtain high resolution over a wide range, and the price rises.

Further, an example in which an electrode is provided at one end of a PN junction type photocurrent conversion element is shown in Japanese Patent Laid-Open No. 11761/1983.

Although this method has a wide range of uses, as will be described later, nonlinearity such as the influence of the square of position appears in the output, and it is necessary to convert the output.

SUMMARY OF THE INVENTION In view of the above drawbacks of the prior art, it is an object of the present invention to provide an edge position detection device capable of detecting the peripheral position of a plate-like object over a relatively wide range economically and with a simple peripheral circuit. The technical idea of the present invention, which achieves this object, is based on the fact that a photocurrent conversion element is used as a position detection element, and the electrodes for signal extraction are provided at both ends of the element, and the sum of the currents generated in both electrodes is output. It is something.

Embodiments of the present invention will be described in detail below based on the drawings. Note that parts that are the same as those in the prior art are given the same numbers and redundant explanations will be omitted. As shown in FIG. 3, it is biased by a bias power supply 9.
Current extraction electrodes a and b are arranged at both ends of the light incident surface of the PN junction type photocurrent conversion element 7, and the sum of the currents generated in both electrodes a and b is sent out as an output signal e. It's becoming like that. This output signal e is amplified by a current amplifier circuit 8, which is a current measuring section, and is sent out as an output voltage _e0 . At this time, the current amplification circuit 8 can most simply be composed of one operational amplifier. The light source 5 is positioned above the photocurrent conversion element 7 and irradiates the light incident surface of the photocurrent conversion element 7 with light of uniform illuminance. At this time, the plate-like body 6 is positioned between the photocurrent conversion element 7 and the light source 5.

In such an edge position detection device, the output voltage e ₀ is
As shown in FIG. 4, it is proportional to the position x of the peripheral edge of the plate-like body 6. Therefore, the peripheral edge position x can be determined by measuring the output voltage e ₀ . The reason why the output voltage e ₀ is proportional to the peripheral edge position x at this time is as follows. That is, as shown in FIG. 5, if the photovoltaic current generated per unit area that is generated by light incident on the peripheral edge position x of the photocurrent conversion element 7 at a minute length d _x and flows toward the electrode side is I, then The output current dI ₀ taken out from the electrode is expressed as follows.

dI ₀ = Id _x …(1) Therefore, the photovoltaic current I generated per unit area
is constant regardless of the peripheral edge position x, both electrodes a and b
The output current I ₀ that is obtained by integrating the sum of the output currents dI ₀ from the receiving part of electrode a to the edge position x is I ₀ = I x (2), and the current is proportional to the edge position x. Become.

Incidentally, the PN junction type photocurrent conversion element is itself a diode, and has a high surface resistance because the light incident surface is formed thin in order to improve the efficiency of light incident on the PN junction. Therefore,
The current I _i generated by the incident light is divided into the photovoltaic current I flowing through the surface resistance up to electrode a and electrode b, and the current Id flowing short-circuited by the diode, and the photovoltaic current begins to flow. It is considered that only I comes out of the photocurrent conversion element.

Therefore, even if the current I _i generated by the light incident on the minute length _d It changes depending on the size of resistance.

Therefore, when the output current I _a is taken out only from the electrode a in FIG. 5, the situation is as follows.

When only the vicinity of electrode a receives light, the surface resistance is small and most of the current I _i generated by the incident light becomes photovoltaic current I, which is the output current I _a from electrode a.
It comes out as. However, as the light-receiving surface expands toward electrode b, the distance of the expanded light-receiving surface portion to electrode a becomes longer, and the surface resistance increases.
In the light-receiving surface area spread out in this way, a portion of the current I _i generated by light incidence becomes a current Id flowing through the equivalent resistance of the diode because the surface resistance up to the electrode a is large, and part of the current I _i flows through the electrode. The photovoltaic current I toward a decreases. Therefore, when output current I _a is extracted only from electrode a, as the light-receiving surface widens from electrode a to electrode b, a component increases in proportion to the peripheral edge position x due to the widening of the light-receiving surface; The photovoltaic current I in the expanded light-receiving surface portion decreases with the distance to the electrode a, resulting in an output current I _a having a component that decreases in proportion to the square of the peripheral edge position x. Become.

The same can be said for the case where the output current I _b is taken out only from electrode b in Fig. 5, and when the light receiving surface becomes wider from electrode a to electrode b, the width of the light receiving surface increases in proportion to the peripheral edge position increasing components and
2 of the peripheral edge position x due to the photovoltaic current I of the expanded light-receiving surface portion increasing with the distance to the electrode b.
The output current I _b has a component that increases proportionally to the power
is obtained.

On the other hand, when the outputs from both electrodes a and b in FIG. 5 are added together and taken out as an output current I ₀ , the following is considered to be the case. In a portion of the light-receiving surface near electrode a, most of the photovoltaic current I flows out to the electrode side where the surface resistance is low, and a part flows out to the electrode b side where the surface resistance is high. On the other hand, in the light-receiving surface portion close to electrode b, most of the photovoltaic current I flows out to the electrode b side where the surface resistance is low, and a part flows out to the electrode a side where the surface resistance is high. Further, at the center of the light-receiving surface, approximately the same amount of photovoltaic current I flows out to both the electrode a side and the electrode b side, both of which have approximately equal surface resistances. Therefore, by adding the outputs from both electrodes a and b, the output current is
When I ₀ is taken out, the area with large surface resistance is reduced compared to when the output current is taken out only from one electrode, and the photovoltaic current I generated between electrodes a and b is
Since the magnitude fluctuation of is small and symmetrical, there is no component proportional to the square of the edge position x, and the nonlinearity between the output current I ₀ and the edge position x is reduced.

As described above in detail with the embodiments, according to the present invention, by using a PN junction type photocurrent conversion element having two current extraction electrodes at both ends, a simple peripheral circuit is used and the cost is low. The peripheral edge position of the plate-shaped body can be detected with high accuracy over a wide range. Further, since there is no dead zone on the photocurrent conversion element and continuous position signals can be obtained, differential and integral signals can also be easily extracted.

[Brief explanation of drawings]

Fig. 1 is a principle diagram showing an edge position detection device according to the prior art, Fig. 2 a and b are signal waveform diagrams for explaining the detection method, and Fig. 3 is a basic configuration showing an embodiment of the present invention. Fig. 4 is a characteristic diagram showing an example of the output of the PN junction type photocurrent conversion element used in the embodiment of the present invention, and Fig. 5 is a principle diagram for explaining that the output of the above embodiment is linear. It is. In the drawing, 5 is a light source, 6 is a plate-shaped body, and 7 is a photoelectric conversion element.

Claims (1)

[Claims] 1. A PN junction photocurrent conversion element having a rectangular shape with a long side in the direction of detecting the edge position and having a light incident surface with uniform surface internal resistance, and the edge position of the light incident surface of the photocurrent conversion element. two current extraction electrodes provided at both ends in the direction of detecting the position, a bias power supply applied to the surface opposite to the light incident surface of the photocurrent conversion element, and the two current extraction electrodes. A current measurement unit that outputs the sum of the generated currents as an output signal and a plate-shaped body whose position is to be detected above the light incidence surface of the photocurrent conversion element are sandwiched between the current measurement unit and the plate-shaped body whose position is to be detected. 1. An edge position detection device comprising: a light source that emits uniform light;