JPH10267638A - Method and apparatus for measurement of flatness on surface of object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the flatness on the surface of an object to be inspected surely by a method wherein the surface of the object to be inspected is irradiated with a plurality of laser beams from a plurality of optical fibers arranged in a prescribed state in such a way that the laser beams are converged in one point at the rear of the object to be inspected and the state of the beams reflected on the surface of the object to be inspected is inspected. SOLUTION: A plurality of optical fibers 4 in a light irradiation part 2 are arranged in such a way that laser beams 3 emitted from their beam radiation ends are condensed toward a certain point 7 and that the beam radiation ends become a square state at uniform intervals. The laser beams 2 which are emitted from the beam irradiation part 2 are reflected on a face 1a, to be inspected, at a wafer 1 so as to be incident, as reflected beams 3', on a CCD camera as a photodetector 8. A spreading angle θ is set in such a way that all the reflected beams 3' can be detected. An image which is obtained by the photodetector 8 by irradiating the laser beams 3 from the optical fibers 4 is a regular image when the wafer 1 is flat. When a warpage or an irregularity exists on the wafer 1, the reflected beams 3' are inclines, and the image is distorted.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring the flatness of an object having a surface which easily reflects light, such as a semiconductor wafer, a reticle or a mask used in the process of manufacturing the wafer, and a method for measuring the flatness. Related to the device.

[0002]

2. Description of the Related Art For example, there is a Hartmann wavefront detection method as a technique for measuring the flatness of a wafer. FIG. 8 shows an outline of an apparatus for measuring the flatness of a wafer by using the Hartmann wavefront detection method. In this figure, reference numeral 71 denotes a wafer to be measured, and 72 denotes a laser beam 73 directed toward the wafer 71. A laser light source 74 is a lens for converting the laser light 73 emitted by the laser light source 72 into parallel light. 75
Is a mask provided so as to be orthogonal to the parallel light beam, and a pattern 77 in which a plurality of holes 76 are arranged in a square is formed on the plane of the mask, as shown in FIG. 9A. Reference numeral 78 denotes 45 ° between the wafer 71 and the mask 75 with respect to the optical path.
, A converging lens 79 for condensing light from the direction of the semi-reflecting mirror 78, and 80 a C as a photodetector
It is a CD.

In the apparatus having the above-described structure, the laser light source 7
The laser light 73 emitting the light 2 passes through the lens 74 to become parallel light, and this parallel light passes through the hole 76 of the mask 75,
Further, the light transmitted through the semi-transparent mirror 78 and vertically incident on the surface of the wafer 71, and a part of the light reflected here is transmitted through the semi-transparent mirror 78, but the other light is reflected by the semi-transparent mirror 78,
The light passes through the condenser lens 79 and enters the CCD 80.

When the wafer 71 is flat (flat) as shown by a solid line in FIG. 8, the image obtained by the CCD 80 is the same as the pattern 77 of the mask 75 shown in FIG. But the wafer 71
However, as shown by a virtual line in FIG.
The image obtained at 80, as shown in FIG.
It becomes distorted. Then, by integrating the amount of distortion in the distorted image, the degree of warpage of the wafer 71 can be obtained quantitatively.

[0005]

However, the above-mentioned conventional apparatus has the following disadvantages. That is, as can be understood from FIG. 8, the lenses 74 and 79 are required as the optical system.
The size of 4,79 must be at least as large as or larger than the object 71 to be measured. Therefore, there has been a problem that the apparatus becomes heavy and bulky and expensive. Also, from using the lenses 74 and 79,
There was an error due to spherical aberration.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to reliably measure the flatness of the surface of an object having a light-reflective surface such as a wafer without using a large lens. It is to provide a method and apparatus that can do this.

[0007]

In order to achieve the above object, a method of measuring flatness on the surface of an object according to the present invention comprises a method for measuring the flatness of a plurality of optical fibers arranged in a predetermined state from the surface of an object to be inspected. Irradiating a plurality of laser beams such that they converge at a point behind the object to be inspected,
In this case, the flatness of the surface is measured based on the state of light reflected on the surface of the inspection object.

The apparatus for measuring flatness on the surface of an object according to the present invention comprises a plurality of optical fibers arranged so that light emitted from a light emitting end is converged toward one point; A photodetector for detecting a two-dimensional spread of reflected light generated when the light is incident on the surface of the object to be inspected arranged in an optical path between a plurality of optical fibers, and an output signal of the photodetector. And a data processing device for receiving and specifying a position of each light in the photodetector.

In the method and apparatus for measuring the flatness on the surface of an object according to the present invention, the flatness of a wafer or the like can be measured without using a huge optical element such as a large lens. Therefore, the device can be configured to be small, compact and inexpensive. Further, since no lens is used, no spherical aberration occurs, and no measurement error due to this occurs.

[0010]

Embodiments of the present invention will be described with reference to the drawings. 1 to 4 show a first embodiment. First, in FIGS. 1 and 2, reference numeral 1 denotes a wafer as an object to be measured, and reference numeral 2 denotes a surface 1a to be measured of the wafer 1. This is a light irradiation unit for irradiating the laser light 3 from the oblique direction. As shown in FIG. 3, the light irradiating section 2 is composed of a plurality of optical fibers 4 arranged uniformly in a lattice. Although not shown in detail, the light irradiation unit 2
In the case 2a, there are provided a plurality of guide members which are partitioned and guide the respective optical fibers 4, thereby holding the weak optical fibers 4.

The upper end of each optical fiber 4 is bundled into a multi-core cable 5 and connected to a laser tube 6 as a light source. The angle of each optical fiber 3 is adjusted so that the laser light 3 emitted from each optical fiber 4 converges at a point 7 behind the wafer 1 (on the back side of the surface 1a to be measured), and the distance between adjacent optical fibers 3 is set. Have been.

In other words, the plurality of optical fibers 3 in the light irradiating section 2 are focused so that the laser light 3 emitted from the light emitting ends is directed toward a certain point 7 and the light emitting ends are connected to the same. They are arranged so as to be in a predetermined state (square state in the illustrated example) with uniform intervals. And
The wafer 1 is provided in the optical path connecting the light emitting end of the light irradiating section 2 and the converging point 7 so as to be irradiated with the laser light 3, and is provided with a laser light 3 row (light row). It is arranged so that the width is substantially equal to the size of the wafer 1.

Further, in FIGS. 1 and 2, reference numeral 8 denotes a CCD camera as a photodetector for detecting the light 3 'reflected by the test surface 1a of the wafer 1 when the laser light 3 emitted from the light irradiating section 2 is detected. , Detection elements are arranged in a grid. The CCD camera 8 is preferably provided so that the reflected light 3 ′ is vertically incident.
Although it is necessary to detect all of the reflected light 3 ′ incident on the camera 8, it is necessary to set the spread angle θ of the reflected light 3 ′ as shown in FIG.

In FIG. 1, reference numeral 9 denotes a data processing device such as a computer,
Based on the signal from the CD camera 8, the position on the detection element for each light in each light train received by the CCD camera 8 is specified.

In the apparatus having the above-described configuration, the wafer 1 is arranged as shown in FIGS. 1 and 2, and, as shown in FIG. 3, a plurality of optical fibers 4 arranged in a lattice form When the wafer 3 is irradiated with the light 3, the image obtained by the CCD camera 8 can be a regular image as shown in FIG. The CCD image shown in FIG. 4A has a congruent or similar relationship with the arrangement of the optical fibers 4 shown in FIG.

On the other hand, when the wafer 1 is warped or disturbed in flatness, the reflected light 3 'changes its inclination in accordance with the inclination of the portion of the test surface 1a irradiated with the laser beam 3. Therefore, as shown by reference numeral 11 in FIG.
A part of the CCD image is distorted. The magnitude and position of the distortion correspond to distortion such as warpage in the wafer 1 and directly correspond to the degree of inclination of a portion on the test surface 1a irradiated with the laser beam 3. That is, this CCD
The image shows the distribution of the inclination of the test surface 1a. By integrating such a signal, for example, it is possible to obtain the height distribution of the test surface 1a, that is, the degree of warpage or flatness.

In the above-described first embodiment, unlike the related art, since a lens having a size equal to or larger than that of the wafer 1 is not used in the optical system, the apparatus can be made small, compact, and inexpensive. Further, since no lens is used, no spherical aberration occurs, and no measurement error due to this occurs.

FIG. 5 shows a second embodiment.
In this embodiment, a condenser lens 12 having a focal point on a light receiving surface of a CCD camera 8 is provided on each light emitting side of a plurality of optical fibers 4, and a magnification changing lens 13 is provided in front of the light receiving surface of the CCD camera 8. Is provided. According to this embodiment, in addition to the effects of the first embodiment, CC
There is an effect that the image magnification of the D camera 8 can be changed, and a clear image of a desired magnification can be obtained.

FIG. 6 shows a third embodiment.
In this embodiment, the optical path of the reflected light 3 'is divided into two, and the magnification of the image in each optical path is made different so that the measurement can be performed simultaneously with different measurement sensitivities.
That is, in FIG. 6, 13A is a lens for adjusting the reflected light 3 'into a parallel light flux, 14 is a semi-transmissive mirror for dividing the parallel reflected light 3' into two, and one of the optical paths A has a magnification changing lens 15A.
And a second CCD camera 8B is provided on the other optical path B via a magnification changing lens 15B having a magnification different from that of the magnification changing lens 15A. Note that the CCD cameras 8A and 8B are
This is the same as the D camera 8.

In general, when the angle θ in FIG. 1 is increased, the distance between the test surface 1a of the wafer 1 and the CCD camera 8 can be shortened. Conversely, when the angle θ is reduced, the distance can be reduced. Can be longer. When the distance between the wafer 1 and the CCD camera 8 increases, the moving amount of the light spot on the CCD camera 8 increases even for the same inclination of the wafer 1, and the measurement sensitivity can be increased. Therefore, the angle θ may be changed. Hereinafter, this will be described as a fourth embodiment.

FIG. 7 shows a fourth embodiment.
In this embodiment, the position of the optical fiber 4 can be moved in parallel, for example, as indicated by reference numeral 4 'in the figure, and the angle of incidence of the reflected light 3' on the CCD camera 8 is changed from? It can be changed to. With this configuration, wafers 1 of different sizes can be measured with all light trains without changing the positions of the wafer 1 and the CCD camera 8.

The present invention is not limited to the above embodiments. For example, the arrangement of the optical fibers 4 may be any as long as it has a two-dimensional spread such as concentric or radial.

The present invention is not applied only to the measurement of the warpage or the flatness of the wafer, but measures the flatness of an object having a surface which easily reflects light. It goes without saying that it can be widely applied to do so.

[0024]

According to the method and apparatus for measuring flatness on the surface of an object of the present invention, it is possible to measure the warpage or flatness on the surface of an object to be measured without using a huge optical element such as a large lens. Can be. Therefore, the device can be configured to be small, compact and inexpensive. Further, since no lens is used, no spherical aberration occurs, and no measurement error due to this occurs.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an overall configuration of an apparatus according to a first embodiment.

FIG. 2 is a view schematically showing a main part of the apparatus.

FIG. 3 is a diagram showing an arrangement of optical fibers in the device.

FIG. 4 is a diagram for explaining the operation of the device.

FIG. 5 is a diagram schematically showing a main part of an apparatus according to a second embodiment.

FIG. 6 is a diagram schematically showing a main part of an apparatus according to a third embodiment.

FIG. 7 is a diagram schematically showing a main part of an apparatus according to a fourth embodiment.

FIG. 8 is a diagram schematically showing a conventional apparatus.

FIG. 9 is a diagram for explaining the operation of the device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Inspection object, 1a ... Surface, 3 ... Laser light, 3 '... Reflection light, 4 ... Optical fiber, 7 ... Condensing point, 8 ... Photodetector, 9
... Data processing device.

Claims (2)

[Claims] 1. A method for irradiating a plurality of laser beams from a plurality of optical fibers arranged in a predetermined state to a surface of an object to be inspected so that they converge at a point behind the object to be inspected. A method for measuring flatness on a surface of an object, wherein the flatness of the surface is measured based on a state of light reflected on the surface of the object to be inspected. 2. A plurality of optical fibers arranged so that light emitted from a light emitting end is converged toward a point, and a test object arranged in an optical path between the one point and the plurality of optical fibers. A photodetector that detects a two-dimensional spread of reflected light generated when the light is incident on the surface of an object, and receives an output signal of the photodetector to specify a position in the photodetector for each light. An apparatus for measuring flatness on a surface of an object, comprising: the data processing apparatus according to (1).