JP2013011592A - Scanning type detection measuring device and measuring method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a scanning type detection measuring device that can suppress the occurrence of unevenness in a detected light quantity while employing a simple structure.SOLUTION: A scanning type detection measuring device includes a light-emitting element for emitting a laser beam, a scanning optical system for scanning the laser beam supplied from the light-emitting element while irradiating a sample therewith, a detection optical system for detecting the light generated from the sample, and a reflection optical element that is provided between the light-emitting element and the scanning optical system and reflects a part of the laser beam toward the light-emitting element.

Description

  The present invention relates to a scanning detection and measurement apparatus and a measurement method.

  The scanning detection and measurement device moves the height of the objective lens up and down while scanning the laser beam in the XY direction, and measures the detected light quantity at each point on the XY plane, thereby measuring the surface shape of the sample and the optical quality of the transparent sample. It is a measuring device for calculating a typical film thickness. In particular, by using a confocal optical system, vertical and horizontal detection resolution can be improved.

The scanning detection and measurement apparatus has a problem that unevenness in detected light amount appears on the screen. For example, when an object with a constant reflectance is measured and imaged with a scanning detection and measurement device, the detected two-dimensional or three-dimensional light amount distribution should be a flat surface with uniform brightness in the screen. The brightness is not uniform and uneven brightness appears on the screen. This is because the laser beam, which was originally one optical path, is branched into multiple parts by parallel plates or multilayer films on the optical path, and the optical path length difference between the multiple optical paths is increased by scanning these laser lights in the XY direction. Change, thereby changing the interference state between the light beams passing through the plurality of optical paths.
In order to solve the problem of the detected light amount unevenness, conventionally, a high-frequency signal is superimposed (intensity modulated) on the injection current of the laser light source to reduce the coherence of the laser light, thereby suppressing the detected light amount unevenness (for example, Patent Documents). 1).

JP 2005-55538 A

However, when high frequency superposition is applied to the laser light, electromagnetic noise is generated, so that it is necessary to take another noise countermeasure. In particular, in the case of a short wavelength semiconductor laser, the high frequency superposition power for reducing the coherence is increased, so that countermeasures against electromagnetic wave noise are required.
In addition, if a pulsation laser whose on / off of laser light is switched at several hundred MHz is used, high-frequency superposition is unnecessary, but there is a problem that a laser diode is expensive.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a scanning detection and measurement apparatus that can suppress the occurrence of unevenness in detected light amount while adopting a simple configuration.

  The scanning detection and measurement apparatus of the present invention includes a light emitting element that emits laser light, a scanning optical system that irradiates the specimen while scanning the laser light supplied from the light emitting element, and detection that detects light generated from the specimen. An optical system; and a reflective optical element that is provided between the light emitting element and the scanning optical system and reflects part of the laser light toward the light emitting element.

It is good also as a structure which has the rocking | fluctuation mechanism which rocks | fluctuates the said reflection optical element with respect to the optical axis of the said laser beam.
The reflective optical element may be provided immediately after the collimator lens that converts the laser light emitted from the light emitting element into a parallel light beam. The reflective optical element is preferably disposed on the light exit side of the collimator lens, and the distance between the reflective optical element and the collimator lens is preferably 100 mm or less. A configuration in which no other optical element is interposed between the reflective optical element and the collimator lens may be employed. The reflective optical element is preferably provided between the collimator lens and the detection optical system.
The reflective optical element may be made of glass or quartz.
If the detection optical system is a confocal optical system, a scanning detection and measurement apparatus with high detection resolution can be configured.

  The measurement method of the present invention is a measurement method for irradiating a specimen while scanning with a laser beam supplied from a light emitting element, and detecting light generated from the specimen, and is a method for detecting one of the laser lights emitted from the light emitting element. The portion is returned to the light emitting element, and the coherence of light emitted from the light emitting element is reduced by broadening the spectrum of the laser light.

  According to the present invention, the temperature of the light emitting element is raised by deliberately returning a part of the laser light toward the light emitting element by the reflective optical element. Then, the spectral width of the laser beam can be broadened by using the effect of the temperature increase and the effect of forming the external resonator, and the coherence of the laser beam can be reduced. Therefore, according to the scanning detection and measurement apparatus and measurement method of the present invention, it is possible to suppress the occurrence of detected light amount unevenness without applying high-frequency superimposition to the laser light.

The figure which shows one Embodiment of a scanning type | mold detection measuring device. FIG. 9 shows a spectrum of laser light output from a light-emitting element. The figure which shows the spectrum of the laser beam when not using a reflective optical element. Explanatory drawing which shows the spectrum change when the angle of a reflective optical element is changed. The figure which shows a spectrum when a high frequency signal is superimposed on a laser beam.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing an embodiment of a scanning detection and measurement apparatus. The scanning detection and measurement apparatus 10 of this embodiment is a confocal microscope that acquires a confocal image by scanning a laser beam, and further forms an image without passing through a pinhole by including a non-confocal optical system. Color non-confocal images can also be acquired. In place of the non-confocal optical system, a laser scanning optical system with a wavelength different from that of the confocal optical system is arranged to perform multi-color measurement or target at a timing different from the detection of the confocal optical system. It can also excite things.

  As shown in FIG. 1, the scanning detection and measurement apparatus 10 includes a confocal optical system 10A, a non-confocal optical system 10B, a control unit 90 that performs operation control and signal processing of the scanning detection and measurement apparatus 10, and It has.

  The confocal optical system 10A includes a first illumination optical system 40 that includes a light emitting element 11 that emits laser light, a scanning optical system 50 that irradiates the specimen 25 while scanning the laser light, and light emitted from the specimen 25. And a first detection optical system 60 that detects through a part of the scanning optical system 50.

The first illumination optical system 40 includes a light emitting element 11, a collimator lens 12, a reflection optical element 36, and a swing mechanism 37.
The light emitting element 11 is a semiconductor laser element that emits, for example, blue-violet laser light or red laser light. The light emitting element 11 is driven by a laser drive circuit (not shown) controlled by the control unit 90. The collimator lens 12 is an optical element that collimates laser light.

  The reflective optical element 36 is an optical element that reflects part of the incident laser light and transmits the other part. As the reflective optical element 36, a transparent plate or block of glass or quartz can be used in addition to a half mirror using a metal film or a dielectric film. The reflective optical element 36 is an optical element provided to control the operating state of the light emitting element 11 by reflecting incident laser light and returning it to the light emitting element 11.

What is necessary is just to select the material of the reflective optical element 36 suitably according to a required reflectance. For example, if a reflectivity of about 5% to 30% is required, a half mirror in which a semi-transmissive film of metal or dielectric is formed on a glass or quartz substrate may be used, and a reflectivity of less than 5% is required. In such a case, a reflective optical element made only of a glass or quartz substrate may be used.
The reflective optical element 36 preferably has a reflective surface smoothed with high precision because the reflected light needs to be accurately incident on a predetermined position on the light emitting element 11.

  The swing mechanism 37 is a member that supports and swings the reflective optical element 36. In the case of this embodiment, the oscillation axis of the reflective optical element 36 is set to an axis orthogonal to the optical axis of the laser light that passes through the reflective optical element 36. As the swing mechanism 37, the angle of the reflective optical element 36 may be manually adjusted, or the reflective optical element 36 may be rotationally driven by a driving device controlled by the control unit 90.

  Next, the scanning optical system 50 includes a first scanning mirror 17, a first pupil relay lens (fθ lens) 18, a second pupil relay lens (fθ lens) 19, a second scanning mirror 20, and a third pupil. A relay lens (fθ lens) 21, a tube lens 22, and an objective lens 24 are provided.

  The first scanning mirror 17 and the second scanning mirror 20 are each composed of a galvanometer mirror. The first scanning mirror 17 rotates around the Y axis in the figure and deflects the laser light in the horizontal direction (X direction in the figure). The second scanning mirror 20 rotates around the X axis in the figure and deflects the laser light in the vertical direction (Y direction in the figure). Two-dimensional scanning of the surface of the specimen 25 is possible by the first scanning mirror 17 and the second scanning mirror 20. The first scanning mirror 17 and the second scanning mirror 20 are rotationally driven by a mirror driving unit (not shown) under the control of the control unit 90.

  The first scanning mirror 17 and the second scanning mirror 20 are disposed at the pupil position and the conjugate position of the objective lens 24 by the first pupil relay lens 18, the second pupil relay lens 19, and the third pupil relay lens 21, respectively. ing. The deflected laser light enters the objective lens 24 through the tube lens 22 and is collected on the sample 25.

Next, the first detection optical system 60 includes the polarization beam splitter 15, a quarter-wave plate 16, a pre-pinhole lens 26, a pinhole (confocal stop) 27, and a photodetector 28. ing.
The polarization beam splitter 15 and the quarter-wave plate 16 are disposed between the first illumination optical system 40 and the scanning optical system 50, and laser light that irradiates the specimen 25 and laser light that has been reflected by the specimen 25. Isolate.

The pre-pinhole lens 26 condenses the light incident from the polarization beam splitter 15 in the pinhole 27.
The photodetector 28 is an element that detects light incident through the pinhole 27, converts the amount of received light into an electrical signal, and outputs the electrical signal. Examples of the photodetector 28 include a configuration including a light receiving element such as a photomultiplier or a photodiode, and a signal processing device that is connected to the light receiving element and converts the amount of received light into an electrical signal. The signal processing device outputs the electrical signal to the control unit 90.

  In the confocal optical system 10A having the above configuration, the laser light emitted from the light emitting element 11 is collimated by the collimator lens 12 and then enters the reflective optical element 36. In the reflection optical element 36, a part of the laser light is reflected and returned to the light emitting element 11, while the laser light transmitted through the reflection optical element 36 enters the polarization beam splitter 15.

The laser light emitted from the first illumination optical system 40 passes through the polarization beam splitter 15, is converted into circularly polarized light by the quarter wavelength plate 16, and then enters the first scanning mirror 17 of the scanning optical system 50.
The laser light incident on the scanning optical system 50 is deflected by the first scanning mirror 17 and the second scanning mirror 20, and is irradiated to a predetermined position on the specimen 25 from the objective lens 24 through the tube lens 22.

  The laser light applied to the specimen 25 is reflected by the surface of the specimen 25 and traces the above optical path in reverse. Specifically, the laser light (reflected laser light) reflected by the specimen 25 is transmitted from the objective lens 24 to the tube lens 22, the third pupil relay lens 21, the second scanning mirror 20, the second pupil relay lens 19, and the first pupil. The light enters the quarter-wave plate 16 through the relay lens and the first scanning mirror 17.

  The reflected laser light incident on the quarter-wave plate 16 is converted from circularly polarized light to linearly polarized light and enters the polarizing beam splitter 15. Since the reflected laser light is linearly polarized light having a vibration direction different from that of the laser light emitted from the first illumination optical system 40, the reflected laser light is reflected by the polarization beam splitter 15 and enters the lens 26 before the pinhole. The reflected laser light condensed by the lens 26 before the pinhole passes through the pinhole disposed at the focal position of the lens 26 before the pinhole and enters the photodetector 28. By installing a pinhole, it becomes a confocal optical system, and the vertical and horizontal resolution can be improved as compared with the case where no pinhole is provided.

  In the photodetector 28, the detected amount of received reflected laser light is converted into an electrical signal and output to the control unit 90. The controller 90 forms a reflectance distribution image of the sample 25 based on the input electrical signal.

  Next, the non-confocal optical system 10B includes a second illumination optical system 70 that irradiates the specimen 25 with uniform illumination light, and a second detection optical system that detects reflected light from the specimen 25 irradiated with the illumination light. 80. The non-confocal optical system 10B shares the objective lens 24 with the confocal optical system 10A, and branches the optical path by a beam splitter 23 disposed between the objective lens 24 and the tube lens 22.

The second illumination optical system 70 includes a light source 29 that emits white illumination light, a condenser lens 32, a beam splitter 23, and an objective lens 24.
The light source 29 is, for example, a halogen lamp. The condenser lens 32 forms a light source image of the light source 29 at the pupil position of the objective lens 24. The beam splitter 23 is an optical element that reflects the light emitted from the light source 29 and transmits the laser light emitted from the light emitting element 11. The objective lens 24 collects the illumination light incident from the condenser lens 32 via the beam splitter 23 on the surface of the sample 25.

The second detection optical system 80 includes a beam splitter 33, a tube lens 34, and a CCD camera 35.
The beam splitter 33 is disposed on the optical axis of the second illumination optical system 70 and reflects the light reflected by the sample 25 toward the tube lens 34 side. The tube lens 34 condenses incident light on the imaging surface of the CCD camera 35. The CCD camera 35 forms an image of the specimen 25 by detecting incident light.

  In the non-confocal optical system 10 </ b> B having the above configuration, white illumination light emitted from the light source 29 passes through the condenser lens 32 and the beam splitter 33 and enters the beam splitter 23. The illumination light is reflected by the beam splitter 23 and collected on the sample 25 by the objective lens 24.

  The illumination light reflected by the specimen 25 is reflected by the beam splitter 23 through the objective lens 24, is further reflected by the beam splitter 33, enters the tube lens 34, and enters the CCD camera 35 to form an image. Then, the image is picked up by the CCD camera 35 and an observation image (non-confocal image) of the specimen 25 is formed.

  In the scanning detection and measurement apparatus 10 according to the present embodiment described above, the reflective optical element 36 is provided in the first illumination optical system 40, so that a confocal image of the specimen 25 is acquired while suppressing occurrence of detected light amount unevenness. be able to. Hereinafter, such operational effects will be specifically described with reference to FIGS.

  FIG. 2 is a diagram showing a spectrum of laser light output from the light emitting element 11 which is a semiconductor laser element. FIG. 3 is a diagram showing a spectrum of laser light when the reflective optical element 36 is not used. FIG. 4 is an explanatory diagram showing changes in the spectrum of the laser light when the angle of the reflective optical element 36 is changed. FIG. 5 is a diagram showing a spectrum of laser light when high frequency superposition is applied.

  In the scanning detection and measurement apparatus 10 of the present embodiment, laser light having a spectrum shown in FIG. 2 is emitted from the first illumination optical system 40 toward the scanning optical system 50. Specifically, a laser beam having a broad spectrum as a whole is emitted, including the peak P1 having the highest intensity and three peaks P2 to P4 on the longer wavelength side than the peak P1.

  Here, the light emitting element 11 is a semiconductor laser element that emits a laser beam having a substantially single peak P1 as shown in FIG. 3, but a part of the laser beam is reflected by the reflective optical element 36, By intentionally returning to the light emitting element 11, the laser light having the spectrum shown in FIG. 2 can be emitted from the light emitting element 11.

  Specifically, when a part of the laser light reflected by the reflective optical element 36 enters the light emitting element 11, the temperature of the light emitting element 11 rises. As a result, the resonator length is extended by the thermal expansion of the light emitting element 11, so that the laser beams having the peaks P2 to P4 on the long wavelength side are easily emitted. In addition, an external resonator having a long resonator length is formed. As a result, it is possible to obtain a laser beam having a wide spectral width including a plurality of peaks P1 to P4.

  On the other hand, when the reflection optical element 36 is not provided, the spectrum of the laser light emitted from the light emitting element 11 does not change, and thus the single peak laser light shown in FIG. 3 is input to the scanning optical system 50. The laser beam input to the scanning optical system 50 is branched into a plurality of laser beams whose optical paths substantially overlap due to internal reflection of the beam splitter 23 and the like disposed at a connection portion between the scanning optical system 50 and the second illumination optical system 70. However, the optical path length difference between the plurality of laser beams is periodically changed by the scanning operation in the scanning optical system 50. When the coherence of the laser light is high, the detected light amount unevenness occurs due to this optical path length difference.

  On the other hand, in the present embodiment, the laser light supplied to the scanning optical system 50 has a wide spectrum width and low coherence as described above, and therefore the optical path length difference of the branched laser light changes. However, it is difficult to interfere, and the occurrence of uneven detection light quantity can be suppressed. Further, since the spectrum of the laser beam according to the present embodiment is similar to the spectrum of the laser beam with high frequency superposition shown in FIG. 5, the same low coherence as in the case of using the laser beam with high frequency superposition is used. It is thought that the effect is obtained.

  As described above, according to the scanning detection and measurement apparatus 10 of the present embodiment, the coherence of the laser light can be reduced by using the reflective optical element 36, thereby suppressing the occurrence of detected light amount unevenness. Therefore, high-frequency superposition is not required, and no countermeasure against electromagnetic noise is required. In addition, since an expensive laser element such as a pulsation laser is not required, a scanning detection and measurement apparatus can be provided at a low cost.

  In the present embodiment, the spectral width of the laser light emitted from the light emitting element 11 can be adjusted by providing the rocking mechanism 37 that rocks the reflective optical element 36. This spectrum width adjustment function will be described below.

  In the scanning detection and measurement apparatus 10 of the present embodiment, when the reflection angle of the laser light on the reflective optical element 36 is changed by operating the swing mechanism 37, the reflected laser light on the emission surface of the light emitting element 11 is changed. The incident position changes.

  Here, the temperature of the light emitting element 11 is highest when the laser beam reflected by the reflective optical element 36 enters the laser emission port of the light emitting element 11, and the temperature of the light emitting element 11 increases as the incident position deviates from the laser emission port. The temperature is lowered. As the temperature of the light emitting element 11 changes in this way, the oscillation wavelength of the light emitting element 11 changes.

  Specifically, when the temperature of the light emitting element 11 is lowered by changing the angle of the laser beam reflected by the reflective optical element 36, the heights of the peaks P1 to P4 change as shown in FIG. Specifically, compared with the spectrum of FIG. 2, the peak P1, which is the main peak, is relatively high, and the peaks P2 to P4 caused by the deviation of the resonator length are relatively low. As a result, the spectral width of the entire laser beam changes narrowly compared to the case shown in FIG. In addition, when the reflected laser beam returns straight to the exit, the effect of the external resonator having a long resonator length is increased, and the effect of expanding the spectrum width is also superimposed.

  The wider the spectral width of the laser light incident on the scanning optical system 50, the lower the coherence, and the less uneven the detected light amount. On the other hand, the resolution decreases as the spectral width increases. Therefore, if the spectral width of the laser light can be adjusted as in the present embodiment, the spectral width can be narrowed within a range in which the detected light amount unevenness does not occur, so that a high-resolution confocal image can be obtained.

  When the light emitting element 11 is a semiconductor laser element that can emit laser beams of a plurality of colors, the angle of the reflective optical element 36 may be varied for each color of the laser light emitted from the light emitting element 11. For example, when the light emitting element 11 can emit blue-violet laser light and red laser light, when the blue-violet laser light is emitted from the light emitting element 11, the laser light reflected by the reflective optical element 36 is emitted from the light emitting element 11. The laser beam may be incident on the laser emission port, and when the red laser beam is emitted, the laser beam reflected by the reflective optical element 36 may be incident on a position shifted from the laser emission port. Such a configuration can also be easily realized by including the swing mechanism 37.

  In the above embodiment, the case where the reflective optical element 36 is disposed between the collimator lens 12 and the polarization beam splitter 15 has been described. However, the position of the reflective optical element 36 is not limited to this. In the case of this embodiment, the reflective optical element 36 can be disposed at an arbitrary position on the optical axis of the laser light between the light emitting element 11 and the quarter wavelength plate 16. The reflective optical element 36 is preferably provided between the collimator lens 12 and the first detection optical system 60.

  A preferred arrangement of the reflective optical element 36 is the position shown in FIG. This is because the laser light reflected by the reflective optical element 36 needs to be accurately incident on the laser emission port of the light emitting element 11 or the vicinity thereof, and therefore the reflective optical element 36 is disposed at a position close to the light emitting element 11. If the collimator lens 12 is disposed between the light emitting element 11 and the reflective optical element 36, the laser light reflected by the reflective optical element 36 is condensed on the light emitting element 11 by the collimator lens 12. This is because it can be effectively used for raising the temperature of the light-emitting element 11. In this case, in consideration of the function of the reflective optical element and the size of the device, the position of the reflective optical element 36 is preferably within a range of 100 mm or less from the collimator lens 12.

  In the above embodiment, the case where the spectral width of the laser light is adjusted by changing the angle between the reflective optical element 36 and the laser light has been described. However, the configuration for obtaining a desired spectral width is limited to this. It is not something. For example, the reflectance of the laser light in the reflective optical element 36 may be changed by changing the base material of the reflective optical element 36 or the material of the reflective film. Also in this case, the intensity of the laser beam returned to the light emitting element 11 can be changed, and the spectrum width can be adjusted. If the above configuration is used when the spectral width of the laser light emitted from the first illumination optical system 40 is fixed, it is preferable because the set spectral width hardly changes.

  DESCRIPTION OF SYMBOLS 10 ... Scanning type | mold detection measuring device, 10A ... Confocal optical system, 10B ... Non-confocal optical system, 11 ... Light emitting element, 25 ... Sample, 27 ... Pinhole (confocal stop), 36 ... Reflective optical element, 37 ... Oscillating mechanism 40 ... first illumination optical system 50 ... scanning optical system 60 ... first detection optical system (detection optical system) 70 ... second illumination optical system 80 ... second detection optical system 90 ... control Part

Claims (7)

A light emitting element for emitting laser light;
A scanning optical system for irradiating the specimen while scanning the laser beam supplied from the light emitting element;
A detection optical system for detecting light generated from the specimen;
A reflective optical element that is provided between the light emitting element and the scanning optical system and reflects a part of the laser beam toward the light emitting element;
A scanning detection and measurement apparatus characterized by comprising:   The scanning detection and measurement apparatus according to claim 1, further comprising a swing mechanism that swings the reflective optical element with respect to an optical axis of the laser beam.   The scanning detection and measurement apparatus according to claim 1, wherein the reflection optical element is provided between a collimator lens that converts a laser beam emitted from the light emitting element into a parallel light beam and the detection optical system. .   4. The scanning detection and measurement apparatus according to claim 1, wherein the reflection optical element is provided immediately after a collimator lens that converts a laser beam emitted from the light emitting element into a parallel light beam. 5.   The scanning detection and measurement apparatus according to any one of claims 1 to 4, wherein the reflective optical element is made of glass or quartz.   The scanning detection and measurement apparatus according to any one of claims 1 to 5, wherein the detection optical system is a confocal optical system. A measurement method for irradiating a specimen while scanning with laser light supplied from a light emitting element, and detecting light generated from the specimen,
A measurement method, wherein a part of the laser light emitted from the light emitting element is returned to the light emitting element, and the coherence of the light emitted from the light emitting element is reduced by broadening the spectrum of the laser light.

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