JPH11325846A - Interference measuring method of large diameter plane - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable precise measurement of a large diameter plane, mike a reference plane unnecessary, and simplify the constitution of a measuring apparatus, by dividing a plane to be measured into many fine planes to be measured, and measuring all the fine planes to be measured by the scanning with a transverse shear interferometer. SOLUTION: A laser light outputted from a laser light source 7 is made a parallel light by a collimator lens 8, reflected by a plane 17 to be measured, reflected by the surface and the back of a parallel surface plate 9, and divided into a reference light wave surface A and an object light wave surface. These interfere with each other, and interference fringes are formed, which are detected by a detector 13. The width of an aperture 14 for measurement of a transversal shear interferometer head 4 is (d). The plane 17 is divided into fine planes 18 to be measured which have a width (d). The interferometer head 4 is made to approach the plane 17, and moved along a scanning rail, by every d/2 in the (x) direction and the (y) direction. As a result, the interference fringes are obtained on the whole surface of the plane to be measured. Each of the measurement results of the fine planes 18 is inputted in a control unit 5 and analyzed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a large-diameter plane interference measurement method. The present invention can be used in the semiconductor industry and the optical machine industry.

[0002]

2. Description of the Related Art In the semiconductor industry, for example, 256 Mb
On the other hand, the integration condition of the memory has progressed, and the exposure condition of the mask pattern under the current condition becomes strict with a depth of focus of ± 0.5 μm for a silicon wafer having a diameter of 30 cm, and the precision corresponding thereto It is necessary to measure the shape of the wafer.

When measuring the shape of a plane including this wafer, the optical interferometer is capable of measuring the shape of a plane to be measured such as a mirror surface of an optical component with high accuracy without contact. In addition, since the measurement can be performed on the entire surface at the same time, it is an extremely effective inspection means. Typically, the plane is measured by a Fizeau-interferometer. The Fizeau interferometer can measure the flatness of a mirror surface having a diameter of about 10 cm in a non-contact manner with high accuracy, and several companies in Japan and overseas have already marketed the apparatus.

[0004]

However, when measuring a large plane with such a Fizeau interferometer, a large-diameter high-precision reference plane and a large-diameter high-precision lens are required. Is expensive, and the weight is large and the device is bulky. A conventional method of scanning a small-diameter Fizeau-interferometer and partially measuring a plurality of times while partially overlapping to obtain the entire shape may be considered. The number becomes too large and measurement becomes impossible. In addition, an unnecessary tilt error at the time of scanning causes unnecessary tilt fringes, and as a result, the measurement sensitivity of the fringes changes depending on the location, and the measurement accuracy is deteriorated.

Another conventional method for measuring the flatness of a large area is a grazing incidence interferometer, which can simultaneously measure the entire surface, but has a problem in that the sensitivity is rather low and the apparatus is bulky.

Accordingly, it is desired to develop a measuring technique for a large-diameter plane which can measure a large-diameter plane with high accuracy, does not require a reference plane, and can simplify the configuration of a measuring apparatus. It is rare.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to measure a large-diameter plane with high accuracy, to eliminate the need for a reference plane, and to simplify the configuration of a measuring apparatus. It is an object of the present invention to provide a large-diameter plane interference measurement method that can be used.

[0008]

To cope with this object, a large-diameter plane interference measuring method according to the present invention divides a plane to be measured into a large number of small planes to be measured, and attaches a lateral shear interferometer to the plane to be measured. The method is characterized in that scanning is performed to measure all the minute measurement surfaces by lateral shear interference, and the measurement results of the minute measurement surfaces are connected over the measurement surface.

In addition, the scanning head for a transverse shear interferometer according to the present invention converts a laser light source and laser light emitted from the laser light source into parallel light to pass through a measurement opening to a plane to be measured. An irradiating optical system, a plane-parallel plate that divides the reflected light from the plane to be measured into two parts, and a detector that detects interference fringes of the two-divided reflected lights, and the measurement opening Is provided on the part facing the plane to be measured.
And a scanning device for moving the frame along a guide rail.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the drawings showing one embodiment. In FIG. 1, reference numeral 1 denotes an interference measurement device. The interference measurement device 1 includes a lateral shear interferometer 2 and a scanning device 3. The lateral shear interferometer 2 includes a lateral shear interferometer head 4 and a control device 5. The transverse shear interferometer head 4 includes a laser light source 7, a collimator lens 8, a parallel plane plate 9, an imaging lens 11, a filter 12, and a detector 13 such as a CCD image detector in a frame 6. I have. A measurement opening 14 is formed in the frame 6, and outgoing light and reflected light enter and exit through the measurement opening 14. The transverse shear interferometer head 4 is the scanning rail 1 of the scanning device 3.
5 can be moved. Such an interference measuring device 1
The method for measuring the interference of a large-diameter plane according to the present invention is described below. Although the principle of the plane measurement of the transverse shear interferometry itself is known, the laser light emitted from the laser light source 7 is converted into parallel light by the collimator lens 8 and briefly described here. Is illuminated and reflected under the influence of the plane to be measured 17, reflected by the front and back surfaces of the plane-parallel plate 9, and divided into a reference light wavefront A and an object light wavefront B. This interferes to form an interference fringe representing a shape error, and this interference fringe is detected by the detector 13. Horizontal shear interferometer head 4
The width of the measurement opening 14 is d, the measurement plane 17 is divided into a number of minute measurement surfaces 18 having a width d in the scanning direction, and the horizontal shear interferometer head 4 is moved to the measurement surface 17 of the measurement object 16. In the x direction along the scanning rail 15 to obtain an interference fringe image over the entire surface to be measured.
Next, the lateral shear interferometer head 4 is rotated to generate a shear of Δy in the y direction, and d / 2 in the y direction.
The interference fringe image is obtained for the entire surface of the plane to be measured by moving it one by one. The measurement results of each minute measurement surface 18 are input to the control device 5 and analyzed to analyze the flatness of the measurement surface.

[0011]

According to the interference measurement method of the present invention, as compared with the conventional method of scanning a Fizeau interferometer head, a reference surface is unnecessary and the number of stripes increases even when the inclination of the planar shape error is large. This is advantageous in that measurement is not likely to be impossible, and that tilt errors during scanning do not generate unnecessary tilt fringes. Therefore, the measurement sensitivity of the fringes is constant without changing depending on the location, and there is an advantage that the measurement accuracy does not deteriorate. For example, z = x
Consider a case where a plane having a shape error such as 2 + y2 is measured. When this is measured by a conventional method of scanning a Fizeau-interference head, the density of interference fringes gradually increases as the scanning is performed (as x increases), and finally, the resolution exceeds the resolution of the detector (x = xlim). Becomes impossible. Further, even with a small tilt error due to scanning, some stripes may be superimposed and measurement may not be possible before x = xlim. Compared to this, in the present method, the interval between the stripes is constant, so that it is possible to measure any distance. In addition, there is almost no influence of a slight tilt error caused by scanning.

As described above, the method of scanning the shear interferometer according to the present invention and partially measuring the number of times while partially overlapping to obtain the entire shape requires no reference plane and a planar shape error. When the inclination is large, it is difficult for the number of stripes to be too large to be unmeasurable, and the tilt error during scanning does not generate unnecessary tilt stripes, so that the measurement sensitivity of the stripes is constant without changing from place to place. The measurement accuracy does not deteriorate.

Another conventional method for measuring the flatness of a large area is an oblique incidence interferometer, which can measure the entire surface at the same time. However, there is a problem in that the sensitivity is rather low and the apparatus is bulky. If the measurement area is extremely large, measurement cannot be performed. On the other hand, this apparatus requires only a small and light head and a scanning device, and has a simple structure, and can measure even an extremely large area.

In this apparatus, the flatness of a mirror surface having a large area can be measured by scanning a small transverse shear interference head. At this time, since a slight tilt or misalignment error in head scanning hardly affects the interference fringes, the flatness of a mirror surface having an extremely large area can be measured. This is effective for inspecting the flatness of a large area such as a silicon wafer or a magnetic disk with high accuracy.

[Brief description of the drawings]

FIG. 1 is a configuration explanatory view showing an interference measuring apparatus according to the present invention;

FIG. 2 is an explanatory plan view showing a relationship between a plane to be measured and a minute surface to be measured;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Interferometer 2 Lateral shear interferometer 3 Scanning device 4 Lateral shear interferometer head 5 Controller 6 Frame 7 Laser light source 8 Collimator lens 9 Parallel plane plate 11 Imaging lens 12 Filter 13 Detector 14 Measurement Aperture 15 Scanning rail 16 Object to be measured 17 Plane to be measured 18 Small surface to be measured A Reference wavefront B Object wavefront

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[Procedure amendment]

[Submission date] May 6, 1999

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0008

[Correction method] Change

[Correction contents]

[0008]

To cope with this object, a large-diameter plane interference measuring method according to the present invention divides a plane to be measured into a large number of small planes to be measured, and attaches a lateral shear interferometer to the plane to be measured. The method is characterized in that all the micro-measurement surfaces are measured by lateral shear interference while scanning to partially overlap the measurement locations, and the measurement results of the micro-measurement surfaces are connected over the measurement surface.

[Procedure amendment 3]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

Further, the present invention provides a large-diameter plane interference measuring apparatus.
Location includes an optical system for irradiating the measured plane through the measurement opening in the laser light parallel light emitted from the laser light source and a laser light source, reflected light from the measured plane 2
A frame provided with a parallel plane plate to be split, and a detector for detecting interference fringes of the two-divided reflected light, and wherein the measurement opening is provided in a portion facing the plane to be measured; and A horizontal shear interferometer scan head having a scanning device for moving the frame along the guide rail ,
Divide the plane to be measured into many small planes to be measured,
The instrument scans the plane to be measured to partially overlap the measurement points.
While measuring all the micro-measured surfaces by lateral shear interference
The measurement result of the minute measurement target surface is
It is characterized by connecting over .

Claims (3)

[Claims] 1. A micro-measurement method comprising: dividing a plane to be measured into a large number of micro-measurement surfaces; scanning a horizontal shear interferometer on said measurement surface to measure all said micro-measurement surfaces by lateral shear interference; A method for interferometric measurement of a large-diameter plane, characterized in that measurement results on a plane are connected over the plane to be measured. 2. The method for measuring interference of a large-diameter plane according to claim 1, wherein the lateral shear interferometer performs the measurement at every moving distance smaller than the width of the minute surface to be measured in the scanning direction. 3. An optical system for irradiating a laser light source and laser light emitted from said laser light source into parallel light and irradiating a plane to be measured through an opening for measurement, and A parallel plane plate that divides the reflected light into two, and a detector that detects interference fringes of the halved reflected light are attached, and the measurement opening is provided in a portion facing the plane to be measured. A transverse shear interferometer scan head, comprising: a frame; and a scanning device for moving the frame along a guide rail.