JPS5945087B2 - Photoelectric element sensitivity correction circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a circuit that detects a difference in light intensity and controls the setting position of a device, a component, etc. The present invention relates to a circuit that corrects sensitivity differences between photoelectric elements when the same amount of light is incident.

For example, when aligning a pattern mask on a wafer surface in a semiconductor pattern manufacturing process, positioning is performed with extremely high accuracy on the order of microns.

Generally, photodetection technology is applied to this type of positioning, in which a photoelectric element is placed close to the positioning part of the device, and a light source guided through a glass fiber or the like is applied to the positioning body using a transmission or reflection method. This is done by detecting the amount of light obtained through the However, this type of photoelectric element has sensitivity variations due to manufacturing reasons, and in order to perform highly accurate positioning, sensitivity correction is required so that the sensitivity between each photoelectric element is constant.

First, a conventional method for minimizing variations in sensitivity between photoelectric elements is to measure the sensitivities of a large number of photoelectric elements under the same conditions and select the photoelectric element with the most matching sensitivity.

However, with this method, when considering sensitivity drift due to changes in ambient temperature, changes over time, etc., each characteristic changes significantly, and highly accurate positioning is still not possible. In addition, as a means to solve this problem, for example, one of the load resistors connected to the two photoelectric elements is replaced with a potentiometer, and this is adjusted so that the apparent sensitivity matches that of the other photodetector. There are possible ways.

However, in this case, the control of the drive system is not only complicated due to the intervention of mechanical elements, but also lacks reliability and precision.
The drawback is that it is slow and cannot be automated. In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to improve the positioning accuracy and reliability of a photoelectric element, automate control, and simplify the sensitivity correction circuit of the photoelectric element.

The present invention is based on a method of providing a correction circuit in the photoelectric element described above, and detects the difference in sensitivity between a plurality of photoelectric elements under the same conditions as a voltage signal, converts it into a digital signal, and converts the difference in sensitivity into a digital signal. The above purpose is achieved by storing the information as information, further converting the stored content into an analog voltage signal, and applying feedback correction to any one of the plurality of photoelectric elements as an error signal to match the sensitivity with the other photoelectric elements. This has been achieved.

The present invention will be described in detail below with reference to the accompanying drawings.

The figure is an example of the implementation of the present invention, and is a sensitivity correction circuit diagram of a photoelectric element when two photoelectric elements are used. In the figure, 1
, 2 is a photodiode, which is a photoelectric element, arranged close to a positioning body (not shown), which receives detection light 3 guided by a glass fiber (not shown), etc.
It performs photoelectric conversion. 4 and 5 are operational amplifiers 0P1,
0P2 is a current-to-voltage conversion circuit composed of resistors Rl and R2 having the same resistance value R; 6 is a voltage differential circuit composed of an operational amplifier 0P3 and resistors R3, R4, R5, and R6 each having the same value; 7 is a voltage differential circuit composed of resistors R3, R4, R5, and R6 each having the same resistance value; An analog-digital converter (hereinafter abbreviated as A/D converter) converts the analog output voltage of the voltage differential circuit 6 into a digital signal, 8 is a correction start signal 1
1 is activated and stores the output of the A/D converter as sensitivity error information; 9 is a digital-to-analog converter (hereinafter referred to as D/A converter) that converts the digital output signal of the storage circuit 8 again into an analog output voltage; converter), 1
0 is the operational amplifier 0P4 and resistors R7 and R, each having the same value.
8, R9, and RlO, and a resistor Rll with a resistance value R. A correction signal output from this voltage-to-current converter circuit 10 is connected to the cathode side of the photodiode 1 described above. It has been entered.

In the circuit connected and configured as shown? To explain the operation differently, when correcting the sensitivity of the photodiodes, first, the same amount of detection light 3 is projected onto the photodiodes 1 and 2.

Therefore, the photodiodes 1 and 2 convert the detection light 3 into a current 11,
Convert to 12. The currents 11 and 12 should have the same value because selected photodiodes 1 and 2 are used, but as mentioned above, there is a difference in sensitivity due to element deterioration, changes over time, etc. As such, the subsequent correction circuit operates. That is, the currents 11 and 12 obtained from the photodiodes 1 and 2 are converted to a voltage V by the current-to-voltage conversion circuits 4 and 5 in which the resistance values of the subsequent resistors Rl and R2 are both R.
,,Convert to 2.

The relationship between currents 11 and 12 and voltages 1 and 2 at that time is as shown in the following equation. 1=11・R, V2−12・R The above voltage 1 output from the current-voltage conversion circuits 4 and 5,
By inputting the voltage V2 into the voltage differential circuit 6 at the next stage, a differential voltage V3 is obtained at its output.

In this case, the resistors R3 to R6 in the voltage differential circuit 6 have the same resistance value, so the differential voltage is V, =V2-V1-
An input differential voltage represented by R(12-11) is obtained.

This differential voltage is converted into a digital signal by the A/D converter 7 at the subsequent stage, and this is stored in the storage circuit 8 as sensitivity error information by the sensitivity correction start signal 11. The digital information of the sensitivity error stored in the storage circuit 8 is converted into an analog voltage V4 by a D/A converter at the next stage. In the old case, the A/D converter 7 and the D/A converter 9 needed to process negative voltage as well. A bipolar offset binary type shall be used. Further, by using a D/A converter e having completely opposite input/output characteristics to that of the A/D converter 7, the following relationship is obtained: V4=,=R(12-11).

Next, the output voltage 4 of the D/A converter 9 is inputted to the voltage-to-current conversion circuit 10 to obtain the current 1 as its output.

Here, resistors R7 and R8 in the voltage-current conversion circuit 10
, R9, and RlO have the same resistance value, and the resistance value of the resistor Rll is R, so the following relationship is obtained. In this way, if the currents 1 and 6 obtained from the voltage-current conversion circuit 10, that is, the current (1, -11), are feedback-shifted to the output current of the photodiode 1, the output current of the photodiode 1
The current obtained is 11+(12-11)=12, which matches the current output from photodiode 2, and the sensitivity of photodiode 1 is corrected with respect to the sensitivity of photodiode 2.

Therefore, prior to positioning control, if correction is made so that the sensitivities of the two diodes 1 and 2 are the same (δ), when the same amount of light is applied to them during positioning control, the difference between the photoelectric elements Positioning errors due to sensitivity mismatch are avoided,
Accurate positioning control can be achieved automatically. In addition to the sensitivity change due to aging and deterioration of the photodiodes 1 and 2, which are optical elements, the sensitivity changes are due to the resolution of the A/D converter and D/A converter that make up the correction circuit of the photodiode, and the temperature of the resistor. Although variations are possible, select A/D converters and D/A converters with resolution (number of bits) that can cover positioning errors (and resistors with temperature coefficients that can ignore the effect on tolerance errors). If this is done, the problem can be solved, and the reliability is still higher than the conventional method, and simplification can be achieved, so there is a big advantage.

Furthermore, it goes without saying that the present invention is not limited to the above embodiments of positioning control, but can be widely applied to control devices based on photoelectric detection using photoelectric elements. In the above embodiment, the case where two photoelectric conversion elements are provided was explained, but the present invention is not limited to this.
For example, by expanding as follows, it can be easily applied even when a plurality of photoelectric conversion elements are provided.

That is, one of the n photoelectric elements under the same conditions is used as a reference photoelectric element (in the above embodiment, photodiode 2
6), and furthermore, the sensitivity difference between adjacent photoelectric elements is expressed as (
(n-1) voltage differential circuits detect (n-1) tortoise pressure signals. Each of these (n-1) voltage signals is converted into a digital signal and written as L, and further this is (n
-1) analog signals and performs feedback correction as an error signal to each of the (n-1) photoelectric elements excluding the reference optical peep element, thereby making the sensitivity of the n photoelectric elements the same. It can be done. According to this, the correction circuit for the photoelectric element is simple, highly reliable, and has the advantage and effect of achieving highly accurate automatic correction.

[Brief explanation of the drawing]

The attached figure is a diagram that does not show an embodiment of a sensitivity correction circuit for a photoelectric element according to the present invention. 1, 2...Photodiode, 3...
Detection light, 4, 5...Current-voltage conversion circuit, 6...
... City pressure differential circuit, 7 ... A/D converter, 8 ... Memory circuit 29 ... D/A converter,
10... Voltage-current conversion circuit, R1 to Rll...
...Resistance, 0P1 to 0P4... operational amplifier.

Claims (1)

[Claims] 1. A sensitivity correction circuit between a plurality of installed photoelectric elements that receive the same amount of light, and a current-voltage conversion circuit of the same number as the number of photoelectric elements that converts the detection current obtained from the plurality of photoelectric elements into voltage; a voltage differential circuit which inputs the output voltage of each of the current-voltage conversion circuits and outputs a difference voltage between the current-voltage conversion circuits; and after converting the output voltage of the voltage differential circuit into a digital signal, It consists of a storage circuit that stores sensitivity error information, and a voltage-current conversion circuit that converts the digital signal stored in the storage circuit into an analog signal and converts it into a differential current of the detected current. A photoelectric device characterized in that the output difference current of the conversion circuit is fed back to any one of the photoelectric devices and corrected so that the sensitivity of the photoelectric device becomes the same as the sensitivity of the other photoelectric devices. Sensitivity correction circuit.