JPH063128A - Optical type surface shape measuring apparatus - Google Patents

Abstract

PURPOSE:To achieve simultaneous measurement of shapes of the inside and outside of a surface at a superhigh speed by providing an optical heterodyne interfering function and a confocal microscope function within one optical device. CONSTITUTION:Probe light of an acoustooptical element 12 is admitted into a beam splitter 13 and a part thereof is reflected to be detected with a photodetector 14. The other transmission light is condensed with an objective lens 15 to scan over the surface of an object 16 to be measured. The reflected light on the object 16 to be measured travels reversely to be detected with a photodetector 17. Reflected light signals to be detected with the photodetectors 14 and 17 are beat signals with a frequency difference of a double beam light. A control light beat signal 145 is emitted from the photodetector 14 and a reflected light beat signal 175 is emitted from the photodetector 17 to detect a phase difference with a phase comparator 18. The detection covers a optical heterodyne interference. A shape computing section 19 for the outside of surfaces computes a phase difference data to measure the shape of the outside of the surface. The probe light transmitted through the splitter 13 travels reversely through the element 12 and reflected almost entirely with the splitter 11. Thus, the intensity of the reflected light is detected with a photodetector 21 and a confocal detection is performed to compute changes with a shape computing section 22 for the inside of surfaces thereby measuring the shape of the inside of the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an out-of-plane and in-plane shape measuring apparatus using laser beam scanning.

[0002]

2. Description of the Related Art An out-of-plane height of a surface of an object to be measured which has been precisely processed is measured with an accuracy of 1 nm, and an in-plane shape is measured to be 10 nm.
The need for accurate measurement is increasing. A method using optical interference is often used for measuring out-of-plane shapes such as surface roughness, and optical heterodyne interferometry is effective for highly accurate measurement of minute height changes. In this method, two laser beams having different frequencies are made to interfere with each other to create a beat signal having a difference frequency, and a phase change of the beat signal is detected with a resolution of about 1/500 wavelength to measure a change in the height direction of the surface. . Among the optical heterodyne interferometry methods, the differential method of driving an acousto-optic device with an electric signal of two frequency components to generate two-beam light having different frequencies and detecting a phase change between the two-beam light is the present application. The inventor has described in detail in Japanese Patent Publication No. 3-44243, "Surface shape measuring apparatus by optical heterodyne interferometry".

For measuring the in-plane shape of the surface, a method is widely used in which a laser beam focused on a minute spot is scanned to detect a change in intensity of reflected light from the object to be measured. Among them, the laser scanning confocal microscope is used in many fields because it can provide in-plane resolution higher than that of an ordinary microscope.
This is to detect the reflected light from the object to be measured through a pinhole or the like (confocal detection), and it is possible to improve the in-plane resolution by cutting the scattered light that becomes noise. Further, since the confocal microscope detects the reflected light intensity from the focal position of the spot light that irradiates the object to be measured, it is possible to measure the height change that changes in the focal direction. At this time, the in-plane and out-of-plane three-dimensional shapes can be measured by moving the object to be measured in the optical axis direction with a pulse stage or the like and processing the reflected light intensity data detected at each moving position.

[0004]

The laser scanning confocal microscope described above can measure in-plane and out-of-plane shapes, but it is necessary to move an object to be measured on a mechanical stage in order to measure the out-of-plane shape. . Further, the resolution of the out-of-plane shape measurement is about 0.1 μm because the depth of focus of the spot light irradiated on the surface of the object to be measured is relatively large. Therefore, the laser scanning confocal microscope cannot measure minute changes in the out-of-plane shape of about 10 nm. Optical heterodyne interference can measure out-of-plane shape changes of about several nm, but conversely cannot measure in-plane shape. As described above, there is no measuring device for simultaneously measuring the in-plane shape and the out-of-plane shape of an object to be measured, which has an out-of-plane shape change of about several nm and an in-plane shape change of about μm. Separate measuring devices were used. An object of the present invention is to solve the above problems and to realize a measuring device having a novel configuration for measuring in-plane and out-of-plane shapes with one measuring device.

[0005]

In order to achieve the above object, the present invention provides a laser beam emitted from a laser light source, which is transmitted through a first beam splitter and is incident on an acousto-optical element, and a frequency from the acousto-optical element. Generate and scan probe light composed of two different beams of light, and separate the probe light into two directions by a second beam splitter,
A probe light which is reflected by the second beam splitter and travels in one direction is detected by a first light receiver to create a reference light beat signal, and which travels through the second beam splitter to travel. Is focused on a small spot by the objective lens and irradiated onto the surface of the object to be measured whose shape is to be scanned, and part of the intensity of the reflected light from the object is reflected by the second beam splitter. Then, the reflected light beat signal is created by detecting with the second light receiver, and the phase change between the reflected light beat signal and the reference light beat signal is detected by the phase comparator to measure the height of the DUT. With an out-of-plane shape calculation unit for calculating the out-of-plane shape in the direction, the reflected light transmitted through the second beam splitter is reflected by the first beam splitter, and the intensity of a partial range of the reflected light intensity distribution Is detected by the third light receiver Create a Shako intensity signal, reflected light intensity signal plane shape operation portion from the intensity variation calculating a plane shape of the object to be measured is provided for, which measures the out-of-plane shape and plane shape simultaneously. Furthermore, when the out-of-plane shape and the in-plane shape of the object to be measured are separately measured, two beam lights having different frequencies are generated from the acousto-optic element when measuring the out-of-plane shape, and the first and second The out-of-plane shape is measured from the reflected light detected by the light receiver of, and in the case of measuring the in-plane shape, a single beam of a single frequency is generated from the acousto-optic element,
The in-plane shape is measured from the reflected light detected by the third light receiver.

[0006]

When the acousto-optic device is driven by an electric signal having two frequency components fa ± fm, two beam lights having different frequencies are generated. The angle formed between the two beams of light is controlled by the frequency fm. When fm is large, separation into two beams is large, and when fm is small, one beam is substantially formed. Therefore, in the case of the out-of-plane shape measurement, the two-beam light state is set and the phase change between the AC beat signals detected by the first and second photodetectors due to heterodyne interference is detected. In the case of measuring the in-plane shape, two-beam light or one-beam light may be used, and the DC reflected light intensity signal is detected by the third light receiver. Since this intensity detection is a fixed point position for beam scanning and is confocal detection that detects reflected light through a pinhole or the like, the in-plane resolution of measurement is high. In this way, the optical heterodyne interference function and the confocal microscope function are realized by one optical device.

When two-beam light is used for in-plane shape measurement, the reflected light signal is detected by all of the first, second, and third light receivers, and out-of-plane and in-plane shapes can be simultaneously measured. . At this time, since each light receiver is provided in the same optical device, the out-of-plane shape and the in-plane shape can be obtained by one optical device. At this time, various polarization elements are provided and the polarization axes thereof are adjusted to set the intensities of the reflected light incident on the three light receivers to optimum values. Furthermore, when measuring the in-plane and out-of-plane shapes separately, set the shape of the beam emitted from the acousto-optic element according to the type of measurement, and maximize the intensity of the reflected light that enters each light receiver, The intensity of the reflected light incident on the light receiver not used for the measurement is minimized to enhance the efficiency of the reflected light detection and the S / N ratio of the reflected light.

[0008]

Embodiments of the present invention will be described in detail below with reference to the drawings.
FIG. 1 is a block diagram showing the configuration of the present invention. Reference numeral 10 denotes a laser light source, which is composed of, for example, a He—Ne laser, a semiconductor laser, or the like, and emits laser light 100 having linearly polarized light. 11 is a first beam splitter (hereinafter, the first BS)
Abbreviated)), which is the configuration of the polarization beam splitter that depends on the polarization. By adjusting the linear polarization axis of the laser light 100, almost 100% of the laser light is transmitted by the first BS. 12 is an acousto-optic element (hereinafter abbreviated as AO)
And the first signal source 112 emitting the frequency fm and the frequency f
It is driven by an acousto-optic device driver (hereinafter abbreviated as AO driver) 110 that receives a signal from the second signal source 114 that emits a. Here, the frequency fm is AO1
The beam shape emitted from 2 is controlled, and the frequency fa
Controls the scanning of the beam. When the frequency fm of the signal emitted from the first signal source 112 is low, the AO 12 emits substantially one beam of diffracted light, and when the frequency fm is high, it emits diffracted light separated into two beams. The light beams have different frequencies.

The two-beam or one-beam probe light emitted from the AO 12 has its polarization axis appropriately converted by the ½ wavelength plate 125, and the second beam splitter 13
(Hereinafter abbreviated as second BS). This second BS 13 is a polarization-dependent polarization beam splitter configuration. The second BS 13 reflects a part of the intensity of the incident probe light, and the reflected light is detected by the first light receiver 14. 1/4 of the probe light transmitted through the second BS 13
An object to be measured 16 which is transmitted through the wave plate 135 and is focused on a minute spot by the objective lens 15 to measure out-of-plane and in-plane shapes.
It is irradiated with and is scanned on the surface. The probe light reflected by the DUT 16 travels backward in the original optical path, and the second BS 13
Then, a part of the intensity is reflected and detected by the second light receiver 17. At this time, the 1/4 wavelength plate 135 adjusts the polarization axis so that the intensity of part of the probe light is reflected.

The first light receiver 14 and the second light receiver 17
The reflected light signal detected at is a beat signal having a frequency of 2 fm, which is the frequency difference between the two beam lights. The reference light beat signal 145 is emitted from the first light receiver 14, and the reflected light beat signal 175 is emitted from the second light receiver 17. 1
A phase comparator 8 detects the phase difference between the reference light beat signal 145 and the reflected light beat signal 175. This detection is optical heterodyne interference. Since the phase of the reference light beat signal 145 is constant and the phase of the reflected light beat signal 175 changes according to the optical path difference between the two beam lights with which the DUT 16 is irradiated, the phase difference can be detected by the phase comparator 18. The phase change of the reflected light beat signal 175 is detected. An out-of-plane shape calculation unit 19 calculates the phase data from the phase comparator 18 to change the out-of-plane shape of the DUT 16.

The probe light having a partial intensity that has passed through the second BS 13 travels backwards through the half-wave plate 125 and the AO 12, and is reflected almost entirely by the first BS 11. Reference numeral 20 is a pinhole, 21 is a third light receiver, and the pinhole 20 is directly attached to the surface of the third light receiver 21. With the light receiver having this configuration, the reflected light intensity in a partial range including the central portion in the intensity distribution of the reflected light is detected. Therefore, confocal detection is performed. Further, this light receiving position is a fixed point position for probe light scanning. Therefore, no matter which position on the surface of the object 16 is scanned by the probe light, the reflected light is detected at the fixed position of the third light receiver 21 through the pinhole 20. An in-plane shape calculation unit 22 calculates the change in the reflected light intensity data of the DC component detected by the third light receiver 21 to detect the edge position of the DUT 16 and measures the in-plane shape. .

When simultaneously measuring the in-plane shape and the out-of-plane shape of the object to be measured 16, two light beams having different frequencies are generated from the AO 12 and the reflected light can be detected by all the three light receivers 14, 17, 21. As described above, the polarization axes of various polarizing elements are adjusted. 1 / when measuring only the out-of-plane shape
The first photoreceiver 14 and the second photoreceiver 17 are adjusted by adjusting the polarization axes of the two-wave plate 125 and the quarter-wave plate 135.
Only the reflected light should be incident on it. On the contrary, when measuring only the in-plane shape, the maximum reflected light is made incident on the third light receiver 21. A polarizing element such as a polarizing plate other than the polarizing element shown in the figure may be provided to adjust the polarization separation.

FIG. 2 shows an example of the shape of the DUT 16 when the out-of-plane and in-plane shapes are simultaneously performed. The DUT 16 has a reflectance R
It is composed of a base material portion 25 having s and a dimension portion 26 having a reflectance Rm, and a space between the dimension portion 26 and the base material portion 25 is 0.1 μ in a convex shape.
There is a step h of about m. The two-beam light 27, 28 focused on a minute spot is scanned on the surface of the object to be measured. Two
The distance between the peak intensities of the light beams 27 and 28 is controlled by the AC signal of the frequency fm emitted from the first signal source 112, and the distance between the peak intensities is set to the distance of the beam diameter of each beam. Further, the frequency fa emitted from the second signal source 114 is changed to scan the two beam lights 27 and 28.

FIG. 3 shows an example of detected signal waveforms. Figure 3
The waveform 31 shown in (1) is a waveform of the phase change of the reflected light detected by the second light receiver 17. Since the optical heterodyne interference according to this configuration is a differential type detection that detects the optical path difference between the two beam lights 27 and 28, the detected phase represents the differentiation of the surface of the DUT 16. When the laser light source is a He-Ne laser, the phase of 1 degree is 0.88.
The optical path difference is nm. Therefore, in the step generating portion which is the edge position of the base material portion 25 and the dimension portion 26, the phase changes according to the step. The phase change on the surface of the base material portion 25 and the dimension portion 26 represents the surface roughness on that surface. Here, the positive sign of the phase is a convex surface between the two beam lights 27 and 28, and the negative sign of the phase is a concave surface. The surface topography can be measured by integrating the phase data thus obtained in the out-of-plane shape calculator 19.

A waveform 32 shown in FIG. 3 (2) is a reflected light intensity pattern signal detected by the third light receiver 21 when the two beam lights 27 and 28 are similarly scanned. The surface reflectance of each member is Rm> Rs. Waveform 32 is central part 3 of intensity
The intensity change is modulated at 22, 324. Figure 3 (3)
A waveform 33 shown in is a differential intensity waveform of the reflected light intensity pattern signal 32. Two rising peaks 330, 331
Between the peaks 332 and the two falling peaks 33
The position of peak 337 between 5,336 is detected. The peak positions 332 and 337 are the state where the central portion of the intensity distribution of the two-beam light is irradiated to the edge positions of the base material portion 25 and the dimension portion 26. The in-plane shape calculation unit 22 detects this edge position. 2 between this edge position
The dimension can be measured from the scanning amount of the light beam, and the shape can be measured from the change in the edge position.

When the out-of-plane shape and the in-plane shape are individually measured, the two-beam optical scanning described in FIG. 3 may be used.
In particular, in the in-plane shape measurement, scanning with one light beam may be performed. FIG. 4 shows an example of edge detection when one-beam scanning is performed. The object to be measured is the same as that shown in FIG. Figure 4
The waveform 41 of (1) is the reflected light intensity signal. The rising portion 410 and the falling portion 415 of the waveform monotonically increase and monotonically decrease. A waveform 42 in FIG. 4B is a difference intensity signal waveform obtained by performing a difference process on the waveform 41. Two peak intensity positions 420, 425 are detected. This peak intensity position is a position where the rate of change in reflected light intensity is maximum, and the peak intensity position of the irradiation beam is in a state of being irradiated on the edge portion.

FIG. 5 shows a specific example of the configuration of the optical system of the surface profile measuring apparatus according to the present invention. The laser light emitted from the laser light source 10 passes through the first BS 11, is converted into a sheet beam having a spread in a plane parallel to the paper surface by the combination of the cylindrical lens 50 and the convex lens 51, and is irradiated on the AO 12. A probe light corresponding to the frequency fm is generated from the AO 12 as described above. The probe light emitted from the AO 12 passes through the half-wave plate 125, the convex lens 52, and the cylindrical lens 53, and is converted into a circular beam again.
The probe light traveling as divergent light is 2 at the second BS 13.
Divided into directions. The reflected light having a partial intensity is condensed by the convex lens 54 and detected by the first light receiver 14.
The transmitted light is collimated by the convex lens 55, passes through the quarter-wave plate 135, is condensed by the objective lens 15, and is measured 16
The surface is scanned while being irradiated. Part of the intensity of the reflected light from the DUT 16 is reflected by the second BS, and the light receiver 1
Detected at 7. The reflected light transmitted through the second BS 13 is reflected by the first BS 11, is condensed by the convex lens 56, and is detected by the third light receiver 21 having a pinhole attached. The above-described optical system enables simultaneous measurement of the in-plane and out-of-plane shapes described above.

[0018]

As described above, according to the present invention, the optical heterodyne interference function and the confocal scanning microscope function are provided in the same optical device, so that the out-of-plane shape is 1 nm accurate and the in-plane shape is 10 nm.
It is possible to measure simultaneously with nm accuracy. Since the intensity distribution of the two-beam light emitted from the acousto-optic device can be freely controlled, the state of the two-beam light can be set according to the measurement purpose, and a wide range of measurements can be performed. Since the data processing of the reflected light intensity signal may be simple processing, real-time measurement is possible with the arithmetic processing unit having a simple configuration. Further, since the two beam lights that irradiate the object surface follow substantially the same optical path, stable measurement is possible without being affected by disturbance, and it is suitable for in-line measurement on a production line.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating the configuration and operation of the present invention.

FIG. 2 is a diagram showing an example of an object to be measured.

FIG. 3 is a waveform diagram of a detection signal when performing out-of-plane shape measurement by phase detection of reflected light and in-plane shape measurement by intensity detection when scanning two beams of light.

FIG. 4 is a signal waveform diagram when performing a difference processing between a reflected light intensity signal detected when performing in-plane shape measurement when performing scanning with one beam of light.

FIG. 5 is a diagram showing an example of a configuration of an optical system.

[Explanation of symbols]

 10 Laser Light Source 11 First Beam Splitter 12 Acousto-Optical Element 13 Second Beam Splitter 18 Phase Comparator 19 Out-of-Plane Shape Calculator 20 Pinhole 22 In-Plane Shape Calculator 25 Base Material 26 Dimensions

Claims (2)

[Claims] 1. A laser beam emitted from a laser light source is transmitted through a first beam splitter and is incident on an acousto-optical element, and the acousto-optical element generates probe light composed of two-beam light with different frequencies to perform scanning. The second beam splitter separates the probe light into two directions, and the probe light reflected by the second beam splitter and traveling in one direction is detected by the first light receiver to detect the reference light beat. A signal is created, and the probe light that passes through the second beam splitter and travels is focused on a minute spot by an objective lens to irradiate and scan the surface of the object to be measured whose shape is to be measured. Part of the intensity of the reflected light from the object is reflected by the second beam splitter and detected by the second light receiver to create a reflected light beat signal, and the reflected light beat signal and the reference light beat signal are generated. The out-of-plane shape calculator for calculating the out-of-plane shape in the height direction of the DUT by detecting the phase change between the signals with the phase comparator, and the reflected light transmitted through the second beam splitter. The light is reflected by the first beam splitter, the intensity of a partial range of the reflected light intensity distribution is detected by the third light receiver, and a reflected light intensity signal is created. An optical surface profile measuring apparatus, which is provided with an in-plane profile calculation unit for calculating an in-plane profile of an object to measure an out-of-plane profile and an in-plane profile simultaneously. 2. When measuring the out-of-plane shape and the in-plane shape of the object to be measured separately, and when measuring the out-of-plane shape, two beam lights with different frequencies are generated from the acousto-optic element,
The out-of-plane shape is measured from the reflected light detected by the first and second light receivers, and when the in-plane shape is measured, the acousto-optical element generates a single beam of the single frequency, An optical surface profile measuring device characterized by measuring an in-plane profile from reflected light detected by a light receiver.