JPS6131402B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an improvement in a flatness measuring device that measures the flatness of a surface to be measured using optical interference.

Glass substrates for photomasks used in the manufacture of semiconductor devices such as ICs and LSIs are strictly required to have flat surfaces in order to form fine patterns.

Therefore, the light sent out from the laser tube is converted into parallel light through an objective lens, collimator lens, etc.
On the other hand, an optical reference surface such as a half mirror or a prism is provided, and the surface of the glass substrate, that is, the surface to be inspected is brought into close contact with the surface, and the parallel light beam is directed at a predetermined angle of incidence onto the half mirror, etc. When the incident light is made incident, a part of the incident light is reflected by the half mirror, and the other part passes through the half mirror and is reflected by the surface to be measured, and due to the interference of these two reflected lights, the light is placed in the optical path of the reflected light. Since interference fringes are generated on the screen, the flatness of the surface to be inspected is measured by counting the number of interference fringes.

In the flatness measuring device using the above method, an operator generally counts the number of interference fringes projected on the screen, and attempts to automate the flatness measuring device have not yet reached the stage of practical use.

It is easy to automatically detect the flatness of the surface to be inspected by capturing the interference fringes projected on the screen with an imaging camera, and processing and digitizing the image signal sent from the imaging camera. In this case, since the scanning direction of the imaging camera is fixed, the direction in which the unevenness of the surface to be inspected is maximized generally does not coincide with the scanning direction. It does not indicate the maximum value.

Because of these difficulties, it has not been possible to automate the process of inspecting the flatness of the glass substrate of a photomask, etc., which attempts to define the maximum value of the unevenness of the surface to be inspected.

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, an object of the present invention is to provide a flatness measuring device in which the scanning direction when imaging interference fringes is variable.

The flatness measuring device of the present invention is characterized in that the imaging camera is provided with a rotation mechanism, and the flatness measurement circuit is used as a drive control means for the rotation mechanism, and the image signal output from the imaging camera is digitized and the interference a digital processing means for detecting the number of fringes; a storage means for storing the number of the detected interference fringes;
and a control means for controlling these means, and the control means controls the drive control means to drive the rotation mechanism to rotate the imaging camera by a desired angle, and the digital processing means The number of interference fringes detected by the scanning line for each rotation of the imaging camera is stored in the storage means, and the stored number of interference fringes of each scanning line is compared and the maximum value is extracted. This is because it is displayed on the display means.

Embodiments of the flatness measuring instrument of the present invention will be described below with reference to the drawings.

FIG. 1 is a system configuration diagram showing an outline of the flatness measuring device according to the present invention, in which 1 is a laser tube;
2, 3, 4, 6, 8, 10, and 11 are reflecting mirrors, 3 is a filter, 5 is an objective lens, 7 is a collimator lens, and 9 is an optical reference plane, and a half mirror is used here. Further, 12 is a screen, and 13 is a test object such as a glass substrate, the test surface of which is brought into close contact with the optical reference surface. The above is no different from conventional flatness measuring devices.

Furthermore, 22 is a pulse motor provided as a rotation mechanism for rotating the imaging camera, 23 to 27 are circuit blocks constituting a flatness measuring circuit, and 23 is a digital circuit for digitizing the image signal output from the imaging camera. chemical processing equipment, 2
4 is a central processing unit (CPU) which is a control means; 25
is a storage device (memory device), 26 is a display device, 2
7 is a drive control device for the pulse motor 22.

Next, a method of measuring the flatness of a surface to be inspected using the flatness measuring device described above will be explained.

The light emitted from the laser tube 1 passes through a reflector 2, a filter 3, and a reflector 4, is expanded by an objective lens 5, passes through a reflector 6, is made into parallel light by a collimator lens 7, and is reflected by a reflector 8. and enters the half mirror 9 at a predetermined angle of incidence. A part of this incident light is reflected by the half mirror 9, the remaining part passes through the half mirror 9 and is reflected by the test surface of the test object 13, and these two reflected lights are further reflected by the reflecting mirrors 10 and 11. It is projected onto the screen 12. At this time, the above 2
There is a difference in the optical path length of the two reflected lights, and if the test surface is uneven, the path difference will differ depending on the position on the screen. Therefore, due to interference between the two reflected lights, the flatness of the test surface is Interference fringes corresponding to are projected.

The image signal obtained by imaging the interference fringes with the imaging camera 21 is digitized by the digitization processing device 23 to detect the number of interference fringes, for example, the number of dark areas, and the CPU 24 calculates the number of detected dark areas for each scan. Each line is stored in the memory device 25.

When the entire surface of the screen 12 has been scanned, the drive control device 27 is activated by a command signal from the CPU 24 to rotate the pulse motor 22 and, therefore, the imaging camera 21 by a desired angle, for example, 1 degree. Then, as before, the entire screen is scanned and the number of dark areas for each scanning line is stored in the memory device 25.

Repeat these operations to set the imaging camera to 180 degrees.
If the interference fringes are rotated by [degrees], the interference fringes will have been scanned in all directions, so the number of dark areas for each scanning line stored in the memory device 25 is compared and the maximum value is taken out and displayed on the display device 26. By displaying the flatness of the surface to be tested, it is possible to easily know the flatness of the surface to be inspected.

In addition to displaying flatness on the display device, an upper limit value for the number of dark areas is set in advance in the CPU 24, and by comparing with this upper limit value, it is also possible to display a determination of a good product or a defective product.

Furthermore, it is easy to understand that the flatness inspection process can be automated by providing an automatic supply/takeout device for the test object 113 and connecting this to the CPU 24.

As explained above, according to the flatness measuring device of the present invention, by rotating the imaging camera and scanning the interference fringes projected on the screen, it is possible to digitize and detect the correct flatness of the surface to be inspected. As a result, it became possible to automate the flatness detection process.

[Brief explanation of the drawing]

FIG. 1 is a system configuration diagram showing an embodiment of the flatness measuring device of the present invention. 9... Optical reference plane, 12... Screen, 13...
Test object, 21...Imaging camera, 22...Rotation mechanism, 2
3... Digitization processing device, 24... Central processing unit, 25... Storage device, 26... Display device, 27... Drive control device.

Claims (1)

[Claims] 1. An imaging camera that images interference fringes resulting from two reflected lights: the reflected light on the optical reference surface and the reflected light on the detection surface obtained from the scanning line sent out through the optical system, and the image signal from the imaging camera. A flatness measuring device comprising: a flatness measuring circuit that automatically detects and displays flatness, wherein the imaging camera is provided with a rotation mechanism, and the flatness measurement circuit is configured as a drive control means for the rotation mechanism; A digital processing means for digitizing the image signal output from the imaging camera and detecting the number of interference fringes, a storage means for storing the number of the detected interference fringes, and a control means for controlling these means. Configure at least
The control means controls the drive control means to drive the rotation mechanism to rotate the imaging camera by a desired angle, and the scanning line detected by the digital processing means for each rotation of the imaging camera. flatness measurement characterized by storing the number of interference fringes in the storage means, comparing the stored numbers of interference fringes of each scanning line, taking out the maximum value and displaying it on the display means. Device.