JPH0560562B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to an automatic focusing device, and more particularly to a photomask microscope automatic focusing device.

[Conventional technology]

Conventionally, photomask microscope automatic focusing devices have a split detection optical system that uses a semiconductor laser as a light source, and sequential detection based on electrical signals obtained from reflected semiconductor laser light from the chrome surface or glass surface of the photomask. An autofocus circuit was provided to generate a control signal.

[Problem that the invention seeks to solve]

The conventional photomask microscope automatic focusing device described above uses a semiconductor laser beam as a light source, but the beam diameter of the semiconductor laser beam on the photomask surface is about 5 μm when it is focused, and when it is out of focus, it has a diameter of about 5 μm. Therefore, since it was 10 μm or more, if the semiconductor laser beam is out of focus and is on the boundary line between the chrome surface and the glass surface on the photomask surface, it can be obtained from two detectors using the split detector method. The drawback is that the electrical signal is unstable and the autofocus oscillates.

[Means for solving problems]

The photomask microscope automatic focusing device of the present invention shines a semiconductor laser beam on the boundary line between the chrome surface and the glass surface of the photomask, and converts the signal obtained from the detector into the gain necessary to operate the automatic focusing motor. The present invention is characterized by comprising a hold circuit that forcibly stops the up/down signal of the automatic focusing motor when the gain switching of the width amplifier for amplifying up to .

Therefore, when the semiconductor laser beam is on the boundary line between the chrome surface and the glass surface, the autofocus is prevented from oscillating.

〔Example〕

Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a block diagram of an optical system of an embodiment of the photomask microscope automatic focusing device of the present invention. However, differential amplifiers are also listed.

After passing through a collimator 2, a continuous or pulsed semiconductor laser beam 1 is irradiated from a beam spiriter 3 to an objective lens 4. Then, the reflected semiconductor laser light from the photomask 5 is divided by the splitting mirror 6 so that the amount of the reflected semiconductor laser light hitting the splitting detector 7 and the splitting detector 8 is divided. The difference in light intensity between the reflected semiconductor laser beams hitting the split detector 7 and the split detector 8 is indicated by an electrical signal by a differential amplifier 9, and the position of the microscope focus is automatically adjusted so that the electrical output of the differential amplifier 9 becomes 0. Corrected.

FIG. 2 is a clock diagram of the autofocus circuit.

The reflected semiconductor laser light is irradiated by a split mirror 6 onto split detectors 7 and 8 in accordance with the focal position. When the light is in focus, the divided detectors 7 and 8 receive the same amount of light, but when the light is out of focus, the divided detectors 7 and 8 receive different amounts of light. The amount of light irradiated by the divided detectors 7 and 8 is converted into an electric signal, and the preamplifiers 11a and 1
1b, respectively. The chromium/glass amplifiers 12a and 12b operate when the semiconductor laser beam is on the chrome surface or on the glass surface, respectively.
There are two types of amplifier gain to obtain the appropriate output. The amplifier gain values of the chrome/glass amplifiers 12a and 12b are determined by the amplifier selection circuit 13. The outputs of the chrome/glass amplifiers 12a and 12b are amplified by amplifiers 14a and 14b, respectively, and then a comparator 15 generates an electric signal corresponding to the difference in the amount of light received by the split detectors 7 and 8. Based on the positive and negative signals of this electrical signal, sequentially controlled automatic focusing is performed by the motor drive circuit 17. When the semiconductor laser beam is on the boundary line between the chrome surface and the glass surface, the signal of the amplifier selection circuit 13 becomes unstable, and the amplifier gain values of the chrome/glass amplifiers 12a and 12b are not constant, causing the motor drive circuit of the autofocus motor to become unstable. 17 up/down signals vibrate. Hold circuit 16 is chrome/glass amplifier 1
Only when gain switching between 2a and 12b occurs frequently, the up/down signal of the motor drive circuit 17 is forcibly held to prevent the focal position from moving.

Here, the hold circuit 16 is the chrome amplifier 12
A and glass amplifier 12b are switched at least 3 times.
The signal from the motor drive circuit 17 is forcibly inhibited when the switching occurs twice, and the signal is canceled when the switching between the chrome amplifier 12a and the glass amplifier 12b is not performed for a certain period of time.

〔Effect of the invention〕

As explained above, the present invention has the effect of preventing the autofocus from vibrating when the semiconductor laser beam is on the boundary line between the chrome surface and the glass surface by providing a hold circuit in the autofocus circuit. be.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an optical system of an embodiment of the photomask microscope automatic focusing apparatus of the present invention, and FIG. 2 is a block diagram of the automatic focusing circuit. 1...Laser light, 2...Collimator, 3...Beam spirititter, 4...Objective lens, 5...Photomask, 6...Divided mirror, 7, 8...Divided detector, 9...Differential amplifier, 11a, 11b...
Preamplifier, 12a, 12b...Chrome/glass amplifier, 13...Amplifier selection circuit, 14a, 14
b...Amplifier, 15...Comparator, 16...
Hold circuit, 17...Motor drive circuit.

Claims (1)

[Claims] 1. A split detection optical system that uses a semiconductor laser as a light source, and electrical signals obtained by the reflected semiconductor laser light from the chrome surface of the photomask and the reflected semiconductor laser light from the glass surface. In a photomask microscope automatic focusing device that has an automatic focusing circuit that controls A hold circuit is provided that forcibly stops the up/down signal of the autofocus motor when the gain of the amplifier that amplifies the gain to the gain necessary for the movement is performed more than a predetermined number of times within a minute time. A photomask microscope automatic focusing device characterized by: