JPS6024014A - Automatic focusing device - Google Patents

Abstract

PURPOSE:To enable high precision detection even with respect to an object to be measured whose reflectance varies greatly, by controlling two sets of analogue signals so as to make their difference zero without use of any divider. CONSTITUTION:Light reflected from an object to be measured 6 is detected by a position sensor 7. An object lens 3 has its main face in the same plane with reference plane 2, and has the focal length of (h). Two sets of outputs i1 and i2 as detected by the sensor 7 are supplied to an amplifier 10 and a variable gain amplifier 11, respectively. The outputs A1 and A2 from the amplifiers 10 and 11 are supplied to the subtractor 12. A subtracted output D from the subtractor 12 is inputted to an integrater 14 through a switch 13. The integrater 14 integrates the output D and supplies its output I to a driving control circuit 18. A lens barrel 1 is raised and lowered by the circuit 18, and the light emitted by the light source 4 and reflected from the object to be measured 6 varies its position on the sensor 7. Such a loop is repeated until the output D of the subtractor 12 is made zero through the amplifiers 10 and 11.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical field to which the invention pertains] The present invention relates to an automatic distance adjustment device that controls a distance between an object to be measured and a reference plane to be a constant distance.

[Prior art and its problems] Recently, light exposure, X-ray exposure, electron beam exposure, and various other exposure methods have been developed as technologies for forming fine patterns on samples such as semiconductor wafers and masks. In such fields, it is necessary to determine the distance between the sample (object to be measured) and the main surface (reference surface) of the objective lens with high precision. In order to focus the lens by controlling the distance between the object to be measured and the substrate surface at a constant distance, a conventional position sensor is used that shines light onto the object from an angle and generates a two-phase analog signal based on the position of the reflected light. It is detected by etc. Then, by adding and subtracting the above two analog signals, the subtracted output is normalized by the addition output using a divider, and the position of the reflected light, that is, the distance between the object to be measured and the reference surface is detected. was.

However, this type of method has the following problems. That is, when the intensity of the reflected light reflected from the object to be measured changes, the accuracy of the detected position is greatly affected by the accuracy of the divider.

Since the divider is constructed using a non-linear section, it is easily affected by temperature, component parts, etc., and it is extremely difficult to improve its accuracy. For this reason, conventionally it has not been possible to determine the distance between the object to be measured and the reference plane with high precision.

[Object of the Invention] An object of the present invention is to provide an automatic distance adjustment device that can detect the distance between an object to be measured and a reference surface without using a divider, and can control the distance with high precision. It's about doing.

[Summary of the Invention] The gist of the present invention is to shine light obliquely onto an object to be measured, and detect the reflected light with a detector such as a position sensor, so that the distance between the object to be measured and a reference plane matches a desired value. Adjust the variable gain amplifier so that the detection output becomes zero when The reason is that K was adjusted to match the desired value.

That is, the present invention provides an automatic distance adjustment device that adjusts the distance between an object to be measured and a reference surface to a constant distance, and includes a light irradiation means that irradiates the object to be measured obliquely, and a light irradiation means that moves in pair with the reference surface. a reflected light detection means for detecting the reflected light from the object to be measured as two sets of analog signals according to the position of the reflected light; and two sets of detection outputs obtained by the reflected light detection means. an amplification means for amplifying each of the two outputs and making at least one variable the degree of amplification; a subtraction means for calculating the difference between each pair of outputs obtained by the amplification means; a moving means for moving the object to be measured or the reference surface and varying the distance thereof so that the subtraction output becomes zero, and when the distance between the object to be measured and the reference surface is a constant distance, the first The degree of amplification by the amplification means is set in advance so that the subtraction output by the subtraction means becomes zero.
) [Effects of the Invention] According to the present invention, the distance between the object to be measured and the reference plane can be detected without using a divider, and thereby the distance can be controlled with high precision. Furthermore, since the difference between the two analog signals is controlled to zero, the detection accuracy does not deteriorate even for objects to be measured whose reflectance changes greatly.

[Embodiment of the Invention] FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention. In the figure, 1 is a lens barrel 1, and an objective lens 3 is attached to the lower surface (reference surface) 2 of this lens barrel l. 4 is a light source made of LFiD. The light from the light source 4 is irradiated onto the object to be measured 6 through the slit 5. The light reflected from the object to be measured 6 due to this light irradiation is detected by the position sensor 7. The position sensor 7 outputs two sets of analog signals corresponding to the incident position of light, and is attached to the optical lens barrel 1 in parallel to the direction of incidence of light from the light source 4 to the object to be measured 6.

8 in the figure is a drive control circuit for moving the optical mirror tal in the earthwork direction. The main surface of the objective lens 3 is in the same plane as the reference plane 2, and the focal length of this lens 3 is h.

Two sets of detection output people detected by the position sensor 7! , A2 are respectively supplied to an amplifier 10 consisting of an operational amplifier 10a and a resistor 10b of Rloa, and a variable gain 11 consisting of an operational amplifier 11g and a variable resistor 11b of Rua. The output B1 amplified via the amplifier 10 is supplied to one input terminal of the subtracter 12. Similarly, the amplified output A2 is supplied to the other input terminal of the subtracter 12 via the variable gain amplifier 12. The subtractor 12
The zero subtraction output p is inputted to the integrator 140 input resistor 14a (Rx4a) through the switch 13. The switch 15 is OFF and integrates the output of the subtracter 12 which is the integral amount 14, and supplies the output (2) to the drive control circuit 8.

The lens barrel 1 is moved up and down by a drive circuit, and the light source 4 and the object to be measured 6
The position of the reflected light reflected from the object changes on the physical sensor 7. The above loop is repeated until the output of the subtractor]2 becomes zero via the amplifier]0 and the variable gain amplifier [1]0.The initial setting of the distance between the object to be measured 6 and the reference plane 2 is as follows. It's like that.

The switch 13 is grounded, and the switch 15 is connected to the resistor 14b.

Set it to the 14C side. Adjust the variable power supply 14 a, and integrator 1
4, the drive circuit 8 is moved to set the distance between the object to be measured 6 and the reference plane 2 to h. Amplifier]0, which outputs the position sensor output at the position of the reflected light reflected from the object to be measured 6;
The variable gain amplifier 11 amplifies the signal, and the gain of the variable gain amplifier 11 is adjusted so that the output of the subtracter 12 becomes zero. After adjusting the variable power supply 14d and the variable gain amplifier 11, the switch 13 is connected to the output side of the subtracter 12, and the switch 15 is connected to the resistor 14.
Return to side a, and the initial setting of the distance between the object to be measured 6 and the reference plane 2 is completed.

In FIG. 2, it is assumed that the distance between the object to be measured 6 and the reference plane 2 has changed by Δh. The distance Δ that the reflected light from the object to be measured 6 moves on the position sensor 7 is as follows, assuming that the angle of incidence of the light incident on the object to be measured 6 is θ, △7= , 6h- COS θ Output current of the position sensor 7 11.12, where the amount is the total current of the position sensor 7, L is the detection effective length of the position sensor 7, and l is the spot position of the position sensor 7 before the Δh movement.

Outputs AI and A of the amplifier 10 and variable gain amplifier 11
2 is AI ==-11' R10a A2 knee i2 ・R1,8 The output of the subtractor 12 is D "A2" = '1'10a '2R11aL-
Since A l -凰几1゜a--1R11a is adjusted to zero by the upper IC' initial setting, D is.

The output of the subtractor 2 is integrated by the integrator 14, and the integral output is made so that △l becomes zero.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an embodiment of the present invention, and FIG. 2 is a schematic diagram for explaining the present invention in detail. ··lens. 4...LED (light source), 5...Slit, 6...
...Object to be measured, 7...Position sensor, 8...
Drive control circuit, 10... Amplifier, 1]... Variable gain amplifier, 12... Subtractor, 13... Switch,
14... Integrator, 15... Switch. (7317) Patent attorney Kensuke Chika (and 1 other person) 7

Claims (1)

[Claims] An automatic distance adjusting device that adjusts the distance between the object to be measured and the reference surface to a constant value, comprising: a light irradiation means for emitting light from an oblique angle to the object to be measured; a reflected light detection means for detecting the reflected light from the object to be measured as two sets of signals according to the position of the reflected light, and amplifying each of the two sets of detection outputs obtained by the reflected light detection means, and at least On the one hand, there is an amplification means for amplifying with a variable amplification degree, a subtraction means for calculating the difference between two sets of amplified outputs, an integration means for integrating the output of the subtraction means, and an output of the integration means for the measurement target. a control means for controlling the distance between the object and the reference plane; an initial value setting means for setting the initially set distance between the object to be measured and the reference plane to the initial value of the integrating means; The output of the reflected light detection means is input to the amplification means (f), and the amplification degree of the variable amplification factor of the two amplifiers is adjusted so that the output of the subtraction means becomes zero. An automatic focusing device characterized in that initial focusing is performed by a degree adjustment means.