JPH01406A - Sample shape measuring device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is an apparatus for measuring the shape of a sample such as a film or a wafer using an interferometer, and more specifically, a device for measuring the surface shape and thickness unevenness of a sample with high precision. This invention relates to a device for measuring and evaluating.

[Prior Art] Generally, a thin plate-like sample such as a wafer has both overall warpage and local unevenness, and the front and back surfaces of the sample have a shape that is a combination of these.

For measuring the surface condition and thickness unevenness of these samples,
There is known an apparatus that measures and determines a plurality of predetermined points within a sample using a micrometer, a capacitance sensor, or the like.

However, since it only measures the thickness at a predetermined point, the information obtained is insufficient, and in order to obtain more detailed data, the number of measurement points must be increased dramatically, resulting in a longer measurement time. The process becomes long and extremely expensive.

For this reason, conventionally, the most popular device for measuring the unevenness of the entire measurement area of a sample is a device using an interferometer measuring device that uses the wavelength of light as a reference for measurement.

In order to read the interference fringes formed on the sample surface using this device and determine the surface shape and thickness unevenness, the positional relationship between the reference plane of the interferometer and the sample to be measured must be adjusted in advance so that the interference fringes on the reference plane are of one color. need to be adjusted.

FIG. 3 shows an example of surface profile measurements obtained using the device.

The upper part of the figure shows interference fringes on the sample surface 1.

The lower part of the figure shows the surface shape of the cross section xx'', which includes the most convex part and the most concave part of the sample surface.

However, since it is not possible to immediately determine the lower part of the figure from the upper part of the figure, the unevenness is determined by an interference fringe unevenness determination mechanism.

The y-axis represents the amount of unevenness, with the sensitivity of interference fringes as one scale. The back surface of the sample is in close contact with the reference plane 2' where the interference fringes are one color, and form a straight line parallel to the X axis. Therefore, the thickness unevenness of the sample can be determined as dimension C in FIG.

However, it is extremely difficult to maintain the positional relationship between the reference plane 2' of the sample loading stage 2 and the interferometer (reference plane) at a positive value during operation, so that the interference fringes on the reference plane become one color. be. Considering the generally required sensitivity of interference fringes, the effects of vibration and thermal deformation of the device cannot be ignored. Further, when the sample loading stage is moved for sample exchange or the like, it is difficult to accurately reproduce the positional relationship between the reference plane 2' and the interferometer (reference plane).

[Object of the Invention] In view of the above-mentioned problems of the conventional device, the present invention provides a method for determining the surface shape of a sample to be measured regardless of variations in the positional relationship between the reference plane of the interferometer and the reference plane (=back surface of the sample) of the sample loading stage. It is an object of the present invention to provide a device that can measure thickness irregularities, etc. with high accuracy in a short time.

[Structure of the Invention] In order to achieve the above object, the present invention provides a sample loading table having a reference plane and forcibly adsorbing a sample, an interference fringe forming means for forming interference fringes on the sample and the reference plane, and a sample loading table. and interference fringe detection means for detecting interference fringes on the reference plane, and means for performing fringe analysis based on the interference fringe information on the detected sample and the reference plane. It is characterized by being unaffected by changes in the positional relationship between the two.

[Embodiments of the Invention] Hereinafter, a thickness unevenness measuring device according to an embodiment of the present invention will be described based on the drawings.

FIG. 1 is a schematic diagram showing the overall structure of the above device.

1 is a sample to be measured, and 2 is a sample loading table having a reference plane 2- which is one size larger than the sample and finished with high precision.

A large number of small holes are drilled in the reference plane 2- for forcibly adsorbing the sample 1, and the diameters and positions of these small holes for adsorption are determined so that the sample 1 is not deformed locally. It is designed to be in complete contact with the reference plane 2'.

The reference plane 2- is inclined with respect to the optical flat as shown in FIG. This amount of inclination is set sufficiently large to take into account interference fringe sensitivity, changes in the positional relationship between the interferometer and the measured surface caused by thermal deformation, etc., and reproducibility between the interferometer and the measured surface when the sample is replaced. The unevenness of the stripes is uniquely determined. FIG. 4 shows an example of such a measurement.

The interference fringes on the reference plane 2' other than the surface of the sample are equally spaced straight lines, and accurately represent the tilted state of the back surface of the sample. Therefore 1. By removing the oblique component of the back surface of the sample from the uneven state determined from the interference fringes on the front surface of the sample, it is possible to calculate the difference in unevenness C in the vertical direction with respect to the back surface of the sample.

Reference numerals 3 to 8 are parts for forming interference fringes, and the structure is based on the so-called oblique incidence interference method.

3 is a light source, which uses a He-Ne laser device. The luminous flux emitted from the light source 3 is expanded by the extender 4 into a luminous flux of a necessary size. The collimator lens 5 is arranged so that the extender 4 is located at its front focal position, and the laser beam is made into a parallel beam.

7 is a prism for generating interference fringes on the sample to be measured 1 and the reference plane 2', and 7' is a reference plane. 8
is an imaging lens for forming an image of interference fringes on the image carrying plane of the television camera 9.

If the television camera 9 is equipped with a zoom function, it is possible to enlarge and measure a small-diameter sample.

6 is an incident angle adjusting prism that changes the incident angle of the laser beam. - The sensitivity of the fringe can be varied arbitrarily by changing the incident angle of the laser beam. switch 15,
The incident angle of the laser beam is adjusted by driving the pulse motor 16 via the controller 14 and moving the incident angle adjusting prism 6.

The incident angle adjustment prism 6 is also used to modulate the video signal so that it can be extracted as a clear signal when the image signal is converted into a binary signal by the image processing processor 10.

The image processing processor 10 takes in image data via the television camera 9, processes it, and analyzes the uneven state of the surface to be measured. Reference numeral 11 denotes a switch panel for setting various measurement modes during measurement. Reference numeral 12 is for printing the analysis results, and reference numeral 13 is a monitor for displaying the analysis results.

Next, the operation of the embodiment having the above configuration will be explained.

The sample loading table 2 is moved to a predetermined measurement position after the sample 1 is placed on the reference plane 2- by a drive means (not shown) and is forcibly adsorbed.

A laser beam emitted from a light source 3 is expanded by an expander 4 and turned into a parallel beam by a collimator lens 5. The incident angle of the laser beam, which has become a parallel beam, is adjusted by an incident angle adjusting prism 6, and then enters a prism 7. The light beam transmitted through the reference surface 7- of the prism and reflected on the surface of the sample 1 and the light beam reflected on the reference surface 7' cause an interference phenomenon.

The light beam causing the interference ring is imaged by the imaging lens 8 on the image plane of the television camera 9. The image data of the video signal obtained in this way is sent to the image processing processor 10 and stored as image data via the A/D unit. Image data is captured by modulating the interference fringes as described above! Do it twice.

By extracting, filtering, and projecting these image data, the sample area is recognized and interference fringes are determined from the binarized image. From the interference fringes determined in this manner, data such as determining the fringe order is extracted and the uneven state is analyzed.

Based on the analysis result, it is printed out on the printer 12 or the bird's-eye map and contour map are output on the monitor 13.

[Effects of the Invention] According to the present invention, interference fringes are formed and photographed on the sample surface and a reference plane, and are calculated and processed by an image processing device, thereby forming a reference plane of an interferometer and a reference plane of a sample loading stage. Regardless of variations in the positional relationship (=back side of the sample), the surface shape, thickness unevenness, etc. of the sample to be measured can be measured with high precision in a short time.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram showing the overall structure of the device according to an embodiment of the present invention, Fig. 2 is a diagram illustrating the state of the reference plane 2', and Fig. 3 is an example of measuring the surface shape obtained by the conventional device. A diagram showing
FIG. 4 shows an example of measurement using the apparatus of the embodiment. 1: Sample to be measured 2; Sample loading table 2': Reference plane 6: Incident angle adjustment prism 7: Prism 9: Television camera 10; Image processing processor

Claims (1)

[Claims of Claims] 1) A sample loading table having a reference plane and forcibly adsorbing a sample, an interference fringe forming means for forming interference fringes on the sample and the reference plane, and detecting interference fringes on the sample and the reference plane. A sample shape measuring device comprising: interference fringe detection means for detecting interference fringes; and means for performing fringe analysis based on interference fringe information on the detected sample and a reference plane.