JPS6342762B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a microscope, and more particularly to a microscope equipped with a focus position detection device necessary for automatic focusing.

Highly integrated LSI, valve memory, and image pickup tube face plate are 2
Because of their fine patterns of ~3 μm, high-power microscopes are commonly used for visual inspection of these parts. The depth of focus of a high magnification microscope is 1μ
m or less, and a precise automatic focusing mechanism is required. In particular, automatic inspection equipment requires a mechanism that constantly performs automatic focusing at high speed.

One of the conventional techniques related to such automatic focusing
One will be explained with reference to FIG.

The laser beam 1 is spread by a concave lens 2 as shown by a solid line, reflected by a semi-transparent mirror 3, and condensed by an objective lens 6 to form a minute spot 11 on the sample 4 at a focused point. The reflected light from this surface passes through the objective lens 6 again and is focused on a point 14. However, the number of samples is 4 to 5.
, the reflected light from the sample surface 5 passes through the objective lens 6 and reaches the point 15, as shown by the broken line.
The light is focused on. When the sample surface moves from 4 to 5 in this way, the position of the focal point moves from 14 to 15, so if you move the specimen surface up and down so that the focal point is at position 14, you can move the specimen surface to 4. It can be held in position.

Next, a conventional method for detecting the position of the focal point 14 will be described.

A pinhole plate 8 having pinholes 9 is moved in the vertical direction. On the other hand, a photoelectric element 10 is mounted on the pinhole plate 8, and detects the reflected light that has passed through the pinhole.

In FIG. 2, the horizontal axis x indicates the amount of movement of the pinhole plate 8, and the vertical axis V indicates the output of the photoelectric element 10.

Curves 16 and 17 both have pinhole plate 8 x
It shows the relationship of the photoelectric element output V when moving in the direction. When the sample is at position 4 in FIG. 1, the photoelectric element output V becomes maximum at position 18 of the focal point 14 corresponding to this. On the other hand, when the sample is at position 5, the photoelectric element output V becomes maximum at position 19 of the condensing point 15 corresponding to this. By finding the point where the photoelectric element output V becomes maximum in this way, the position (14 or 15) of the condensing point in FIG. 1 can be found.

However, the above-mentioned conventional technology has the following problems.

Assume that a pattern with high reflectance exists on the sample surface and is moving at high speed in the direction 20 in FIG. Since a pattern with high reflectance passes while the pinhole plate 8 is moving, the relationship between the amount of movement x and the output V of the photoelectric element at this time is as shown in FIG. 3, and the pattern 21 with high reflectance Output 22 is generated when . In this case 22
is larger than the output 23 at the in-focus position 18, so 21 is determined to be the in-focus position.

As described above, in the past, when a pattern with high reflectance existed on the sample surface, the in-focus position could not be detected accurately, and automatic focusing was not possible. The above explanation deals with the case where there is a pattern with a high reflectance on the sample surface, but when there is a pattern with a low reflectance or a pattern with steps, the point where the photoelectric element output is maximum is similarly determined. Automatic focusing was not possible because it could no longer be said to be in focus position. Therefore, conventionally, it has been common to use an air micrometer to detect the height of the top surface of the sample and perform automatic focusing. However, when air was blown onto the sample surface, fine dust was also blown at the same time. In the past, the adhesion of fine dust did not pose a problem, but in industrial fields such as semiconductors, as the initial pattern becomes finer, pattern defects can occur even if such fine dust adheres. Air micrometers are becoming increasingly unusable.

The purpose of the present invention is to eliminate the drawbacks of the prior art described above, and to detect a focus position that enables automatic focusing even when there are patterns with high reflectance, patterns with low reflectance, patterns with steps, etc. on the sample surface. An object of the present invention is to provide a microscope equipped with a device.

The main feature of the present invention is that the reflected light from the sample surfaces 4 and 5 is detected by a second photoelectric element, and the intensity of the laser beam 1 is varied in order to keep this detected value constant. . That is, when the detected value becomes large due to a pattern with a high reflectance, the intensity of the laser beam 1 is reduced to prevent the generation of an output such as 22 shown in FIG. 3.

One feature of the present invention is that as a laser light source,
A semiconductor laser oscillator that responds extremely quickly is used, and the voltage applied to the semiconductor laser oscillator is controlled by the output of the second photoelectric element.

Another feature of the present invention is that a pinhole is provided on the front surface of the second photoelectric element to prevent light reflected from the back surface of the sample from being detected.

An embodiment of the present invention will be described below with reference to the drawings. FIG. 4 is a front view of one embodiment of the present invention.
The laser beam emitted from the semiconductor laser oscillator 24 is condensed by a convex lens 25 as shown by the solid line, and then condensed by a concave lens 26.
Magnify with polarizing beam splitter 27, 1/4
The light passes through the wavelength plate 28, is reflected by the semi-transparent mirror 29, enters the objective lens 30, and forms a laser spot 32 on the sample 31. The reflected light from the sample surface is again collected by the objective lens 30, reflected at 29, passed through 28, and then reflected at 27. Note that 33 is an observation optical system.

FIG. 5 is a plan view of an embodiment of the present invention. 2
The light reflected at 7 is spread by a concave lens 34, split by a beam splitter 35, and reaches a reflected light intensity measuring optical system 36 and a focal position detecting optical system 37. Reference numeral 36 measures the intensity of reflected light from the sample surface, and is comprised of a condenser lens 38, a pinhole plate 39, and a photoelectric element 40. Here, reference numeral 39 is provided to detect only the reflected light from the front surface of the sample without detecting the reflected light from the back surface of the sample. This allows focusing only on the sample surface. On the other hand, numeral 37 detects the focal position of the sample surface, and is composed of a condenser lens 41, a slit plate 42, a bimorph oscillator 43, and a photoelectric element 44.
Here, in order to vibrate the slit plate 42, a bimorph vibrator 43 is used in a cantilevered state. Therefore, when 42 vibrates, 42 is displaced in the left-right direction, so here a slit is used instead of the conventional pinhole.

FIG. 6 shows an embodiment of a control circuit that controls the voltage applied to the semiconductor laser oscillator 24 so that the output of the photoelectric element 40 is always constant.

In FIG. 6, the purpose is to control the output of the photoelectric element 40 to always be _V1 . V ₁ is generated by a constant voltage power supply 45 and a potentiometer 46 . On the other hand, the output of the photoelectric element 40 is amplified by an amplifier 47, and its voltage is set to _V2 . If V ₁ and V ₂ are amplified by the differential amplifier 48 and the output thereof is applied to the semiconductor laser oscillator 24, laser light is generated from the semiconductor laser oscillator 24 so that V ₂ is always equal to V ₁ .

If the above control circuit is used, as described in FIG. The laser beam from the oscillator 24 becomes weaker, and as shown in FIG.
decreases to 49.

The above describes the case where a pattern with high reflectance exists on the sample, but the semiconductor laser oscillator 24 is controlled in the same way when a pattern with low reflectance or a pattern with steps exists, and automatic focus position detection is performed. It becomes possible.

As described above, according to the present invention, a highly versatile automatic focusing device that can replace an air micrometer is provided, so that the defect occurrence rate in the fine pattern forming process is significantly reduced.

[Brief explanation of the drawing]

Figure 1 is a schematic configuration diagram of a conventional automatic focus position detection device, Figure 2 is an explanatory diagram of the detection method in the automatic focus position detection device shown in Figure 1, and Figure 3 explains problems with the conventional detection method. FIG. 4 is a front view showing an embodiment of the automatic focus position detection device according to the present invention.
5 is a plan view of FIG. 4, FIG. 6 is a circuit diagram of an embodiment for controlling the output of a semiconductor laser oscillator, and FIG. 7 is a diagram of a detection signal when the control circuit of FIG. 6 is used. . 24... Semiconductor laser oscillator, 30... Objective lens, 31... Sample, 32... Laser spot, 36... Reflected light intensity measurement optical system, 37... Focus position detection optical system, 39... Pinhole plate, 40
...Photoelectric element, 42...Slit plate, 44...Photoelectric element.

Claims (1)

[Claims] 1 In a microscope that moves a sample having a fine pattern in a plane direction perpendicular to the optical axis of the objective lens and observes the fine pattern on the sample obtained from the objective lens, a laser light source and a laser irradiated from the laser light source are used. an illumination optical system that condenses and illuminates the moving sample through the objective lens; and a branching optical system that branches the reflected light image from the sample surface illuminated by the illumination optical system after passing through the objective lens. ,
a slit diaphragm having a pinhole installed on the optical axis and vibrating in the optical axis direction so as to pass only the reflected optical image from the surface of the sample for one optical image branched by the branching optical system; , a first photoelectric element for detecting a light image that has passed through the pinhole of the slit diaphragm, and a first photoelectric element that detects the light image that has passed through the pinhole of the slit diaphragm; A pinhole plate having a pinhole installed on the optical axis, a second photoelectric element that detects an optical image passing through the pinhole of the pinhole plate, and a detection signal obtained from the second photoelectric element. a control means for controlling the voltage applied to the laser light source based on the control means; and a maximum of the video signal output from the first photoelectric element based on the laser light emitted from the laser light source controlled by the control means. A microscope characterized in that it is equipped with a focusing point control means for positioning a sample at a position showing.