JP2557650B2 - Sample shape measuring device - Google Patents

Description

The present invention relates to an apparatus for measuring the shape of a sample such as a film or a wafer by using an interferometer, and more specifically, to increase the surface shape and thickness unevenness of the sample. The present invention relates to a device for measuring and evaluating with accuracy.

[Prior Art] Generally, a thin plate-shaped sample such as a wafer has both a general warp and a partial unevenness, and the front surface and the back surface of the sample have a combined shape.

For the measurement of the surface condition and thickness unevenness of such a sample, there is known a device for measuring and determining a plurality of predetermined points in the sample with a micrometer, a capacitance sensor or the like.

However, the information that can be obtained is insufficient because it only measures the thickness of a predetermined point, and if more detailed data is to be obtained, the number of measurement points must be increased dramatically, resulting in a measurement time Can be long or very expensive.

For this reason, conventionally, the most widely used device for measuring the unevenness of the entire measurement region of a sample is a device that uses 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 with 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 should be set in advance so that the interference fringes on the reference plane have one color. Need to be adjusted.

FIG. 3 is a measurement example of the surface shape obtained by the apparatus.

The upper part of the figure shows the interference fringes on the sample surface 1. The lower part of the figure is a cross section X including the most convex part and the most concave part of the sample surface.
-X 'surface shape.

However, since the lower part of the figure cannot be immediately obtained from the upper part of the figure, the unevenness determination mechanism of the interference fringe determines the unevenness.

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

However, it is very difficult to accurately maintain the positional relationship between the reference plane 2'of the sample loading table 2 and the interferometer (reference plane) such that the interference fringes on the reference plane become one color during operation. is there. From the sensitivity of interference fringes generally required, the influence of vibration and thermal deformation of the device cannot be ignored. Further, when the sample loading table 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 problems of the above-described conventional apparatus, the present invention is directed to the surface shape of the sample to be measured regardless of the variation in the positional relationship between the reference plane of the interferometer and the reference plane (= the back surface of the sample) of the sample loading table. An object of the present invention is to provide an apparatus capable of accurately measuring thickness, thickness unevenness, and the like in a short time with high accuracy.

[Structure of the Invention] In order to achieve the above-mentioned object, the present invention has (1) a reference plane which has an adsorption means for adsorbing a sample and is formed to an accuracy capable of forming an interference fringe beyond the area of the adsorbed sample. A sample mounting table, an interference fringe forming optical system that forms interference fringes on the sample and the reference plane, respectively, and images of the interference fringes of the sample and the reference plane, and based on each imaged interference fringe information of the sample and the reference plane. And an evaluation means for evaluating the sample.

[Embodiment of the Invention] A thickness unevenness measuring apparatus according to an embodiment of the present invention will be described below with reference to the drawings.

 FIG. 1 is a schematic view showing the structure of the above-mentioned apparatus as a whole.

Reference numeral 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 for forcibly adsorbing the sample 1 are formed in the reference plane 2 ′, and the diameter and the arrangement position of the small holes for adsorbing the sample 1 do not cause local deformation in the sample 1 and Are considered to be in perfect contact with the reference plane 2 '.

The reference plane 2'is inclined with respect to the optical flat as shown in FIG. This tilt amount is sufficiently large for the sensitivity of the interference fringes, the change in the positional relationship between the interferometer and the measured surface caused by thermal deformation, and the reproducibility of 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 measurement.

The interference fringes on the reference plane 2'other than the sample surface are straight lines at equal intervals, and accurately represent the inclined state of the sample back surface. Therefore, the unevenness difference C in the vertical direction with respect to the back surface of the sample can be calculated by removing the tilt component of the back surface of the sample from the uneven state obtained from the interference fringes on the front surface of the sample.

Reference numerals 3 to 8 are portions that form interference fringes and are configured by so-called oblique incidence interference method.

A light source 3 uses a He-Ne laser device. Light source 3
The light flux emitted from is expanded by the extender 4 into a light flux of a required size. The collimator lens 5 is arranged so that the extender 4 is located at the front focus position,
The laser light flux is a parallel light flux.

Reference numeral 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 surface.
Reference numeral 8 denotes an image forming lens for forming an interference fringe on the image pickup surface of the television camera 9.

If the TV camera 9 is provided with a zoom function, a sample having a small diameter can be enlarged and measured.

Reference numeral 6 denotes an incident angle adjusting prism that changes the incident angle of the laser light beam. The sensitivity of one stripe can be arbitrarily changed by changing the incident angle of the laser beam. Switch 15,
Drive the pulse motor 16 via the controller 14,
By moving the incident angle adjusting prism 6, the incident angle of the laser beam is adjusted.

The incident angle adjusting prism 6 is also used for converting the video signal into a binarized signal by the image processor 10 and for modulating so as to extract it as a clear signal.

The image processor 10 takes in the image data via the television camera 9 and processes it to analyze the unevenness of the surface to be measured. 11 is a switch panel for setting various measurement modes at the time of measurement. Reference numeral 12 is for printing the analysis result, and reference numeral 13 is a monitor for displaying the analysis result.

The operation of the embodiment having the above configuration will be described below.

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

The laser light flux emitted from the light source 3 is expanded by the expander 4 and becomes a parallel light flux by the collimator lens 5. The laser light that has become a parallel light beam is incident angle adjustment prism 6
The incident angle of the laser light is adjusted by and is incident on the prism 7. The light flux transmitted through the reference surface 7'of the prism and reflected on the surface of the sample 1 and the light flux reflected by the reference surface 7'cause an interference phenomenon.

The light flux that has caused the interference phenomenon is imaged on the imaging surface of the television camera 9 by the imaging lens 8. The video signal thus obtained is sent to the image processor 10 as image data and stored as image data via the A / D unit. The image data is captured twice by modulating the interference fringes as described above.

By calculating, filtering, and projecting these image data, the sample area is recognized, and the interference fringes are discriminated from the binarized image. Data such as the determination of the fringe order is calculated from the interference fringes thus determined, and the unevenness is analyzed.

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

[Effects of the Invention] According to the configuration of the present invention, interference fringes are formed on the sample surface and the reference plane, respectively, and the surface shape, thickness unevenness, and the like of the sample are detected from the relationship between the two interference fringes. Highly accurate measurement can be performed without being affected by changes in the positional relationship between the measurement surface and the like.

[Brief description of drawings]

FIG. 1 is a schematic view showing the structure of the entire apparatus of one embodiment of the present invention, FIG. 2 is a view for explaining the state of a reference plane 2 ', and FIG. 3 is an example of measuring the surface shape obtained by a conventional apparatus. Showing the figure,
FIG. 4 shows an example of measurement by the apparatus of the embodiment. 1: sample to be measured 2: sample loading platform, 2 ': reference plane 6: incident angle adjusting prism, 7: prism 9: TV camera 10: image processor

Claims (3)

(57) [Claims] 1. A sample mounting table having suction means for sucking a sample and having a reference flat surface finished with an accuracy capable of forming interference fringes beyond the area of the sample to be sucked, and the interference fringes on the sample and the reference flat surface, respectively. An interference fringe forming optical system for forming an image, an evaluation means for imaging the interference fringes of the sample and the reference plane, and evaluating the sample based on each interference fringe information of the imaged sample and the reference plane. Sample shape measuring device. 2. The evaluation means according to claim 1, wherein an image processing means for processing an image of the interference fringes of the sample and the reference plane, and an analysis for analyzing the sample on the basis of the information obtained by the image processing means. And a sample shape measuring device. 3. The sample shape measuring apparatus according to claim 1, wherein the reference plane is tilted with respect to an optical flat surface.