JPS5850332B2 - Optical scanning device using a rotating polygon mirror - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device that uses a rotating polygon mirror as a line deflector.

Such an optical scanning device can be used, for example, in a scanning microscope, but the following problem arises.

That is, in a scanning microscope, a rotating polygon mirror is used as a line deflector to perform line scanning of the scanning light, and a frame deflector is used to perform frame scanning on this line scanning light to produce an optically scanned image of the test sample on a monitor scope. When attempting to reproduce an image, if there is an error in the angle between each surface of the rotating polygon mirror and the rotation axis, that is, the inclination angle of each surface, the intervals between the line scanning lines will not be constant, resulting in unevenness and distortion of the reproduced image.

Furthermore, if the density of the line scanning lines changes for each frame, the way the image is distorted also changes, and since images with different shapes appear for each frame, the reproduced image appears to be shaky.

This image fluctuation appears even if the error in the angle of inclination of each surface of the rotating polygonal mirror line deflector is considerably reduced, degrading the quality of the reproduced image.

An object of the present invention is to reliably and easily fix a reproduced image regardless of the magnitude of the tilt angle error when image fluctuation occurs due to the tilt angle error of each surface of the rotating polygonal mirror line deflector mentioned above. The object of the present invention is to provide a simple optical scanning device as described above.

The optical scanning device of the present invention includes a line deflector for performing horizontal line deflection, which has a rotating polygon mirror whose number of surfaces is an integer of the number of line scanning lines, and a line deflector arranged at a distance from the line deflector. a frame deflector for performing vertical frame scanning, an afocal lens system disposed between the line deflector and the frame deflector, and a part of the line scanning light from the line deflector; A photoelectric element that receives light and generates a pulsed signal in synchronization with line scanning, and counts the pulses generated by the photoelectric element, and when the counted value becomes a predetermined integral multiple of the number of surfaces of the rotating polygon mirror, and a counter for driving the frame deflector.

The invention will be explained with reference to the drawings.

FIG. 1 shows an example of a scanning microscope to which the optical scanning device of the present invention is applied.

In FIG. 1, a light source 1 emits a parallel light beam, such as a laser beam.

The line deflector 2 is a rotating polygon mirror that deflects the line in the horizontal direction.

The light beam reflected and deflected by the line deflector 2 is made incident on the frame deflector 5 through the equal-magnification afocal lens systems 3 and 4.

The frame deflector 5 is a vibrating mirror or a rotating polygon mirror (a vibrating mirror in this example), and performs frame scanning in the vertical direction.

By inserting the equal-magnification afocal lens systems 3 and 4 in this way, the line and frame deflectors 2 and 5 can be spaced apart, and the frame deflector 5 can be made smaller, and the deflection can be further reduced. The light beam becomes a parallel light beam, and moreover, it is accurately two-dimensionally deflected.

The light beam reflected by the frame deflector 5 is focused on an image plane T through a lens 6, and raster scans as shown at 8 on an image plane 7.

The scanning raster 8 thus formed on the image plane 7 scans the sample to be inspected through the epi-reflection microscope.

For this purpose, a scanning light spot formed in the image plane 7 is projected via a prism 9, a semi-transparent mirror 10 and an objective lens 11 onto the specimen 12 to be examined.

In this example, the test sample 12 is a semiconductor chip such as an IC or LSI, and semiconductor regions, junctions, connecting conductors, etc. shaped and expanded in this chip are inspected.

This utilizes the well-known phenomenon that a photocurrent or photovoltaic force is generated by irradiating a semiconductor with light.

Since such inspection using a light beam is a non-contact method, it has the advantage of not damaging the sample and allowing accurate inspection.

An illumination light source 13 is provided to observe the sample 12, and the emitted light is directed to the sample 1 through a semi-transparent mirror 10 and an objective lens 11.
Epi-illumination on 2.

The reflected light from the sample surface is passed through the objective lens 11. The light is guided through a semi-transparent mirror 10 and a prism 9 to an eyepiece 14.

Further, an electrical signal generated by irradiating the sample 12 with the scanning spot light is supplied to the monitor scope 16 via the signal processing circuit 15, a visible image is reproduced on the monitor scope, and this image is observed. The sample 12 can be inspected.

In order to drive the monitor scope 16 as described above, in this example, a prism 17 and a photoelectric element 1 are installed between the lenses 3 and 4.
8, a part of the line scanning light from the rotating polygon mirror of the line deflector 2 is incident on the photoelectric element 18 via the prism 17 to generate a pulsed signal synchronized with the line scanning, and this signal is converted into a signal. The signal is supplied to a monitor scope 16 via a processing circuit 15.

In the above-mentioned scanning microscope, if there is an error in the angle of inclination of each surface of the rotating polygon mirror of the line deflector 2, the line scanning line of the scanning raster formed on the image plane 7, and thus the sample plane, will be as shown in FIG. As such, the spacing is not constant, resulting in uneven density.

On the other hand, the monitor scope 1 corresponds to this raster scanning light.
Since the raster line scanning lines written on 6 are at regular intervals as shown in FIG. 3, the circular object shown in FIG. 2 is reproduced distorted as shown in FIG.

If the density of the raster line scan lines changes from frame to frame, the distortion of the reproduced image will also vary from frame to frame.
In the end, images with different shapes are reproduced in each pot frame.

Therefore, images of different shapes that appear one after another are continuously observed on the monitor scope, and the reproduced image appears to be shaky.

This fluctuation in the reproduced image appears even if the tilt angle error of each surface of the rotating polygon mirror of the line deflector is considerably reduced, so it cannot be solved simply by reducing the tilt angle error.

As mentioned above, image fluctuation occurs because an image with a different shape appears in each frame, so in order to eliminate the fluctuation, even if the image is slightly distorted, the image must be distorted to the exact same shape in each frame. All you have to do is make it appear.

Considering this in terms of scanning, it is only necessary to make the density positions of the line scanning light of the scanning raster corresponding to each frame constant.

For example, in Figure 2, if the a-th scanning light is deflected by the A-th point of the rotating polygon mirror of the line deflector, in order for the position of the a-th line scanning light to remain the same in each frame, it is necessary to In both cases, the line polarized light by the A-th surface of the rotating polygon mirror may become the a-th line scanning light.

In other words, the number of line scanning lights for each frame may be made an integral multiple of the number of surfaces of the rotating polygon mirror of the line deflector.

Therefore, in the present invention, pulses synchronized with line scanning from the photoelectric element 18 are counted by a counter 19, and each time the counted value reaches a predetermined integral multiple of the number of surfaces of the rotating polygon mirror, the frame deflector 5 is activated. It is driven so that the position of each scanning line of the scanning raster formed on the image plane 7 is constant for each frame.

Incidentally, a pulsed signal synchronized with this line scanning can be obtained by placing a prism at one end of the scanning surface of the image plane 7 and making each line scanning light incident on the photoelectric element through this prism. Because it is necessary to scan a wider area of the scanning plane than the actually required scanning area, the lens 6
requires a fairly wide angle of view.

It is also possible to generate the light electromagnetically or photoelectrically by providing a magnet or a light emitting element at a position corresponding to each surface of the rotating polygon mirror of the line deflector, but in this case, the structure becomes complicated.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an example of a scanning microscope to which the optical scanning device of the present invention is applied, FIG. 2 is a line diagram showing an example of a scanning raster generated by the optical deflection device of FIG. 1, and FIG. 3 is a diagram showing the scanning raster occurring on the monitor scope of the figure; FIG. 1... Light source, 2... Rotating polygon line deflector, 3.4... Equal magnification afocal lens system, 5... Frame deflector, 7... Image plane, 8... Scanning raster, 11... Objective lens, 12... Sample, 16... Monitor scope, 18 ...Photoelectric element, 19...
...Counter.

Claims (1)

[Claims] 1. A line deflector for performing horizontal line deflection having a rotating polygon mirror whose number of surfaces is an integer of the number of line scanning lines in one frame; and a line deflector separated from the line deflector. a frame deflector for performing frame scanning in the vertical direction, which is arranged to perform frame scanning in the vertical direction; an afocal lens system arranged between the line deflector and the frame deflector; a photoelectric element that receives a portion of the light and generates a pulse-like signal in synchronization with line scanning; and a photoelectric element that counts the pulses generated by the photoelectric element, and each time the counted value becomes equal to the number of line scanning lines, An optical scanning device using a rotating polygon mirror, characterized by comprising a counter that starts a frame deflection operation of a deflector.