JPH0287006A - Apparatus and method of measuring shape of sample - Google Patents

Abstract

PURPOSE:To simply measure the surface unevenness quantity of a sample to a sample sucking reference plane with good accuracy by calculating the shape of a surface to be measured on the basis of detected interference fringe data. CONSTITUTION:The laser beam emitted from a beam source 6 is expanded in luminous flux by an expander 5 and becomes parallel luminous flux by a collimator lens 6 to be incident to a prism 7. A part of the beam incident to the prism is transmitted through the reference plane thereof to be reflected by the reference plane 2' of a sample sucking table 2 and again passes through the prism 7 to go toward a screen 8. The other beam is reflected from the reference plane 7' of the prism 7 to go toward the screen 8 and generates an interference phenomenon along with the beam reflected from the reference plane 2' to project an interference fringe on the screen 8. The projected interference fringe is formed into an image on the imaging surface of a television camera 10 through a lens 9 to be taken out as an image signal. An opera tional processing part 11 analyzes the surface shape of the sample and that of the reference plane from the detected interference fringe to store both of them and detects the positional relation of both of them from the shape of the reference plane common to both of them to operate the difference of the fine shape of the plane.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface profile measuring device and a measuring method for measuring the surface profile of a sample using an interferometer.

[Prior Art] A semiconductor wafer, which is a thin sample, has a combination of overall warpage and inclination as well as local unevenness, and the front and back surfaces of the wafer have a shape that is a combination of these.

In the semiconductor manufacturing process where fine patterns are printed, it is necessary that the amount of unevenness on the wafer surface be within the depth of focus of the exposure equipment when the wafer is suctioned and fixed to the reference plane. It is important to inspect the amount of surface unevenness.

Conventionally, when performing this inspection using an interferometer, it has been necessary to set the wafer suction reference plane in a known positional relationship in advance with respect to the reference plane of the interferometer. In other words, the inclination of the reference plane on which the wafer is suctioned and fixed cannot be determined from only the state of the interference fringes on the wafer surface. Therefore, in order to obtain the amount of unevenness of the convex surface with respect to the suction reference plane, the inclination of the reference plane must be determined. I had to adjust.

In order to improve this point, the applicant of the present application filed a patent application in 1986-15.
In No. 6212, in order to be able to perform measurements regardless of the positional relationship between the reference plane and the sample adsorption reference plane, a technique was developed to provide a means for forming interference fringes on the reference plane and the standard plane, and to perform fringe analysis based on the information on both interference fringes. is suggesting.

However, since this technique also assumes that the wafer suction reference plane is a perfect plane, if this assumption cannot be guaranteed, sufficient effects cannot be expected.

Furthermore, the current increase in diameter of wafers and miniaturization of batten line widths require extremely high precision measurement.

Fringe scanning interferometry (
rring Scanning Interferom
etry) is known. In this method, the optical path length of the reference light is changed during measurement, interference fringes with relatively different reference phases are read into a computer, and the phase distribution is calculated based on the reference reference phase. According to this method, 1/1
Accuracy on the order of 00 wavelengths is possible.

However, this accuracy becomes meaningless unless the accuracy error of the interferometer itself is less than this.

[Problems to be solved by the invention] In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to solve the problem of sample adsorption without being affected by the positional relationship between the reference plane of the interferometer and the sample adsorption reference plane, the accuracy of the sample adsorption reference plane, and the interferometer. It is an object of the present invention to provide an apparatus and a method that can easily and accurately measure the amount of unevenness on a sample surface with respect to a reference plane.

[Structure of the Invention] In order to achieve the above object, the present invention provides a sample adsorption means having a reference plane that is polished with high precision and has a larger area than the measurement sample, and a reference plane on the sample surface and at least the outer periphery of the sample when adsorbing the sample. In part.

Further, when the sample is not placed, means for forming interference fringes on the back surface of the sample when the sample is placed and a reference plane corresponding to the outer periphery of the sample, interference fringe detection means for detecting the interference fringes, An interference fringe analysis means for calculating the shape of the surface to be measured based on each piece of interference fringe information, a means for detecting the positional relationship between the two from reference plane information common to both, and a reference for the back surface of the sample from the surface shape of the front surface of the sample. The method is characterized by comprising means for calculating differences in fine shapes of planes.

Further, forming interference fringes on a reference plane of the sample adsorption means having a reference plane having a larger area than the measurement sample;
a step of detecting the interference fringes, a step of analyzing and storing the shape of the reference plane from the detected interference fringes, a step of adsorbing the sample to the sample adsorption means, and a step of forming interference fringes on the sample surface and the reference plane. a step of detecting the interference fringes; a step of analyzing and storing the shapes of the sample surface and the reference plane from the detected interference fringes; and a step of detecting the positional relationship between the two from the shape of the reference plane common to both. It is characterized by a step that examines differences in minute shapes on a plane.

The present invention will be described in detail.

FIG. 2 shows the cross-sectional shape of the sample suction table, and its surface is slightly convex. Since the sample suction table is originally finished with high precision, extremely minute plane errors can cause problems with the accuracy of the reference plane when the sample is suctioned. .

Therefore, first, we measured the surface shape of the reference plane 2'' with the sample not adsorbed to the reference plane (Fig. 2), and then measured the surface shape of the sample surface and the reference plane with the sample adsorbed (Fig. 3). Then, based on the surface shape of the common part of both, they are superimposed and the difference a between the sample surface and the reference plane is calculated.
can be obtained. This value is closer to the amount of unevenness G (FIG. 5) when the sample is adsorbed onto a completely flat surface, as shown in FIG. 5, compared to the value measured by the conventional device.

[Embodiments of the invention] Hereinafter, one embodiment of the present invention will be described based on the drawings.

FIG. 1 is a basic layout diagram of an optical system when the present invention is applied to a grazing incidence interferometer.

1 is a sample, specifically a wafer. Reference numeral 2 denotes a sample suction table having a reference plane 2- having an area larger than that of the sample 1, and 3 a piezo element which changes the distance between the reference plane 7- and the surface to be measured to change the phase of the reference light.

4 to 8 are optical systems that form interference fringes by oblique incidence interference method.

4 is a reference light source, which uses a )-1e-Ne laser device. The luminous flux emitted from the light m4 is expanded into a luminous flux of a necessary size by an expander 5, and is converted into a parallel luminous flux by a collimator lens 6 arranged so that the expander 5 is located at the front focal position.

7 is a prism having a reference plane 7' that generates interference fringes of the surface of the sample to be measured and the reference plane 2', and 8 is a screen on which an image of the interference fringes is formed.

The interference fringes on the screen 8 are imaged onto the imaging surface of the television camera 10 via the lens 9. Although this embodiment uses a method in which interference fringes are once projected onto the screen 8 and the screen image is conveyed by a television camera, a method may also be used in which the screen 8 is removed and an aerial image is directly photographed by a television camera.

Reference numeral 11 denotes an arithmetic processing unit that processes image data via a television camera and analyzes the surface to be measured.

12 is a monitor that displays images taken by a television camera and analysis results. Also, ]3 is a printing means.

The operation of the above embodiment will be explained below.

The sample suction table 2 is moved to a predetermined measurement position without placing the sample 1 on the reference plane 2-.

The laser beam emitted from the light source 4 is expanded by the expander 5, becomes a parallel beam by the collimator lens 5, and enters the prism 7. A portion of the light incident on the prism 7 passes through the reference plane, is reflected by the reference plane 2- of the sample suction table 2, passes through the prism 7 again, and heads toward the screen 8.

The light incident on the prism 7 is reflected by the reference plane and directed toward the screen 8, causes an interference phenomenon with the light reflected from the reference plane 2-, and is projected onto the screen 8. The interference fringes projected onto the screen 8 are imaged on the imaging surface of the television camera 10 via the lens 9 and taken out as a video signal. The video signal is sent to the arithmetic processing unit]1, where it is analyzed and stored.

In this case, in order to eliminate the effects of vibrations, air fluctuations, etc., reliability can be further increased by using known processing methods such as canceling or averaging abnormal values.

In this example, high-precision interference fringe measurement is performed by applying a voltage to the piezo element 3 to change the phase of the reference plane and obtaining a plurality of image data, which is described in many documents. (For example, AI) pl, Opt, '13. P269
3).

Thereafter, the sample suction table 2 is moved to the sample delivery position by a drive means (not shown), and the sample 1 is placed on the reference plane 2- of the sample suction table.
, and after forced vacuum adsorption, move to an indeterminate position again. After the movement, the interference fringes are similarly analyzed to obtain information on the reference plane 2- and the irregularities on the sample surface.

The information is aligned based on the reference plane information common to the two types of information obtained in this way, and the difference between the two is calculated to obtain the amount of unevenness on the sample surface.

This result is displayed on the monitor 12 and printed on the printing means 13.

[Effects of the Invention] As explained above, according to the present invention, after the planar measurement of the sample adsorption reference plane is performed, the unevenness of the surface of the sample adsorbed to the reference surface is measured, and the adsorption reference is determined from the surface shape of the sample. Since the shape of the surface is removed, highly accurate measurement can be performed without being affected by minute plane errors of the suction reference plane.

Similarly, errors inherent in the interferometer will also be removed.

Furthermore, highly accurate measurements can be stably performed without being affected by thermal deformation of the device due to temperature changes in the environment in which the device is used or wear of the suction reference plane due to long-term use.

Furthermore, by using a sample reference plane with a larger area than the sample and obtaining measurement results for the outer circumference of the sample, the exact amount of inclination of the sample reference plane with respect to the reference plane of the interferometer can be determined. There is no need to match.

[Brief explanation of the drawing]

FIG. 1 is a basic layout diagram of an optical system when the present invention is applied to a grazing incidence interferometer, and FIGS. 2 to 4 are diagrams illustrating the present invention in detail. 1...Sample 2...Sample suction table 2'...Reference plane 3...Piezo element 4...)-1e-Ne laser

Claims (5)

[Claims] (1) A sample adsorption means having a reference plane that is polished with high precision and has a larger area than the measurement sample, and when the sample is adsorbed, no sample is placed on the sample surface or at least a part of the reference plane around the sample periphery. Sometimes, means for forming interference fringes on the back surface of the sample when the sample is placed and a reference plane corresponding to the outer periphery of the sample; interference fringe detection means for detecting the interference fringes; an interference fringe analysis means for calculating the shape of the sample, a means for detecting the positional relationship between the two from reference plane information common to both, and a means for calculating the difference in the fine shape of the reference plane on the back surface of the sample from the surface shape of the sample surface. A sample shape measuring device comprising: means. (2) A sample shape measuring device characterized in that the interference fringe detection means for detecting interference fringes in the first term is a two-dimensional image sensor. (3) A sample shape measuring device characterized in that the interference fringe analysis means in item 1 is based on fringe scanning interferometry. (4) forming interference fringes on the reference plane of the sample adsorption means having a reference plane with a larger area than the measurement sample; detecting the interference fringes; and analyzing the shape of the reference plane from the detected interference fringes. storing the sample, adsorbing the sample to the sample adsorption means, forming interference fringes on the sample surface and the reference plane, detecting the interference fringes, and detecting the sample surface and the reference plane from the detected interference fringes. a step of analyzing and storing the shape of the sample, a step of detecting the positional relationship between the two from the shape of a reference plane common to both, and a step of calculating the difference in the fine shape of the reference plane on the back side of the sample from the surface shape of the sample front surface. A sample shape measurement method characterized by comprising steps. (5) A sample shape measuring method, characterized in that the step of analyzing the shape from interference fringes in item 4 is based on fringe scanning interferometry.