JP2001296181A - Spectrograph - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a compact and high-resolution spectrograph. SOLUTION: In the spectrograph 10, where light 1 that enters through an incidence slit 11, enters a photodetector 15 via a collimate mirror 12, a dispersion-type spectral element 13, and a camera mirror 14, the camera mirror 14 having a longer focal point distance than that of the collimate mirror 12 is used, and at the same time, plane mirrors 16 and 17 for folding are provided in the image forming light path of the camera mirror 14, so the light is made to travel via the plane mirrors 16 and 17, and incident on the photodetector 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spectroscope incorporated in, for example, an optical system of a microscopic Raman spectrophotometer.

[0002]

2. Description of the Related Art Conventionally, as one method of measuring the temperature of a sample made of a semiconductor crystal such as a silicon wafer,
There is a method in which a sample Raman spectrophotometer is used to measure the temperature of a sample based on the peak position of a Raman spectrum obtained when a sample is irradiated with laser light. This is based on the fact that Stokes light generated when a sample as an object is irradiated with a laser beam having a wavelength λ has a strongest peak (Raman shift) at a wavelength λ + Δλ.

In the above-mentioned micro-Raman microspectrophotometer, it is necessary to use a high-resolution spectroscope because the shift amount of the peak position of the Raman spectrum is extremely small and the Raman spectrum is sensitive to a temperature change. FIG.
FIG. 3 schematically shows a configuration of a conventional spectroscope 41. In this figure, reference numeral 41 denotes a Raman light guide as an external light guide,
42 is an entrance slit, 43 is a collimating mirror consisting of a concave mirror, 44 is a diffraction grating having a large number of grooves and a large diffraction angle, rotating 45 about a rotation axis 44a perpendicular to the paper surface, 45 is a camera mirror consisting of a concave mirror, 46 Is a photodetector composed of a Si array detector in the visible light region.

In the spectroscope having the above-described configuration, light 51 from the outside is transmitted through the entrance slit 42 to the collimator mirror 43.
Incident on. Light 52 incident on the collimating mirror 43
Is converted into a parallel light beam 53 by a collimating mirror 43,
The light is incident on the diffraction grating 44 rotating around the center 4a at an incident angle. The diffraction grating 44 splits the light 53 incident at a certain incident angle into a plane orthogonal to a notch (not shown) parallel to the rotation axis 44a. The light 54 split by the diffraction grating 44 is condensed by a camera mirror 45 and is detected by a photodetector 46.
Incident on.

When the diffraction grating 44 is rotated, the incident angle of the light 53 changes in accordance with the rotation angle, and the center of the light 55 which is split and condensed on the light receiving surface of the photodetector 46 is changed. The wavelength changes. Therefore, the spectrum at each wavelength of the light 55 can be obtained by measuring the intensity of the light 55 received by the photodetector 46 while rotating the diffraction grating 44.

[0006]

However, in the above-mentioned conventional spectroscope, the resolution as the spectroscope depends on the focal length of the camera mirror 45 (dimension L in FIG. 4).
Further, it is necessary to set the collimating mirror 43 to a length corresponding to the focal length of the camera mirror 45. Therefore, the physical distance (dimension L in FIG. 4) of the spectroscope main body is inevitably increased, and the spectroscope main body has to be enlarged.

The collimating mirror 43 and the camera mirror 4
Since the optical paths of the collimating mirror 43 and the camera mirror 45 are used in the imaging optical paths of the collimator mirror 43 and the camera mirror 45, the optical paths of the collimating mirror 43 and the camera mirror 45 are used because the optical paths of the collimating mirror 5 and the camera mirror 45 are used to reduce the size of the spectroscope. In addition, it is necessary to interpose the same number of plane mirrors, which complicates the configuration, complicates optical adjustment, and reduces the measurement accuracy of the entire spectroscope due to reflection loss.

The present invention has been made in consideration of the above-mentioned matters, and an object of the present invention is to provide a compact and high-resolution spectroscope.

[0009]

In order to achieve the above object, according to the present invention, light incident through an entrance slit is incident on a photodetector via a collimator mirror, a dispersion type spectroscopic element, and a camera mirror. In the spectroscope, the focal length of the camera mirror is longer than that of the collimator mirror, and a folding plane mirror is provided in the imaging optical path of the camera mirror so that light passing through the plane mirror is incident on the photodetector. I have to.

In the above-mentioned spectroscope, for example, when two folding plane mirrors are provided in the imaging optical path of the camera mirror, the imaging optical path length of the camera mirror is about ３ of that when the folding plane mirror is not provided. become. Therefore, when a high-resolution spectroscope is configured using a high-dispersion diffraction grating and a camera mirror with a long focal length, it is not necessary to increase the physical distance, and a compact and high-resolution spectroscope can be obtained.

[0011]

Embodiments of the present invention will be described with reference to the drawings. 1 to 3 show one embodiment of the present invention. First, FIG. 1 shows an example of the configuration of a spectroscope 10 according to the present invention. In this figure, reference numeral 11 denotes an entrance slit, 12 denotes a collimating mirror composed of a concave mirror, and 13 denotes a dispersion type spectrometer that rotates around a rotation axis 13a. A high-dispersion plane diffraction grating as an element, a camera mirror 14 composed of a concave mirror, a Si array detector (hereinafter simply referred to as an array detector) 15 in the visible region as a photodetector, and 16 and 17 connecting the camera mirror 14 It is a plane mirror arranged so as to face each other in the image light path. Numeral 38 denotes a Raman light guide as an external light guide.

More specifically, in this embodiment, in order to obtain high resolution, a high-dispersion plane diffraction grating 13 and a camera mirror 14 having a long focal length are used. 16 and 17 are provided so as to face each other, and the physical distance between the camera mirror 14 and the array detector 15 is reduced to 1/3. The focal length of the collimating mirror 12 is approximately 1/1 / that of the camera mirror 14.
3 and kept within the above physical distance with a bright optical system. In addition, the high dispersion planar diffraction grating 13
Is fixed to an incident angle using high diffraction angle light close to the diffraction limit, and the array detector 15 is configured to enhance the wavelength resolution characteristics by using a fine pitch and a large number of array elements.

In FIG. 1, reference numerals 18 and 19 denote light-shielding plates which are provided to prevent dispersed light in a wavelength range unnecessary for measurement and stray light in the spectroscope 10 from being incident on the array detector 15. is there.

The operation of the spectroscope 10 having the above structure will be described. The Raman light 1 from the Raman light guiding section 38 passes through the entrance slit 11, and the transmitted light 2 becomes a parallel light beam 3 by the collimating mirror 12, and The light is incident on the dispersion plane diffraction grating 13. Of the parallel light beam 3 incident on the high dispersion planar diffraction grating 13, the light in the Raman shift wavelength region is diffracted into diffracted light 4, and the dispersed image of the incident slit 11 is imaged on the array detector 15 by the camera mirror 14. However, since the plane mirrors 16 and 17 are provided in the image forming optical path of the camera mirror 14, the light exiting the camera mirror 14 passes between the plane mirrors 16 and 17 as indicated by reference numerals 5, 6, and 7. It reciprocates and forms an image at a position approximately one-third of the originally required imaging distance.

In the above embodiment, the camera mirror 14
The two plane mirrors 16 and 17 are provided to face each other in the image forming optical path, and the light exiting the camera mirror 14 is turned back by the plane mirrors 16 and 17, so that the image forming optical path length of the camera mirror 14 is about 1 / 3, and a small and high-resolution spectroscope 10 can be obtained.

In the above-described embodiment, the reason why the plane mirrors for folding are not provided in the image forming optical path of the collimating mirror 12 but the plane mirrors 16 and 17 for folding are provided only in the image forming optical path on the camera mirror 14 side. The explanation is as follows. That is, since the resolution of the spectroscope 10 depends on the focal length of the camera mirror 14, the resolution cannot be reduced so much. Further, when the number of reflection surfaces increases on the collimator mirror 12 before dispersion, the light becomes stronger. Only because it is easily affected by the stray light.

Further, in the above embodiment, since the plane mirrors 16 and 17 are provided so that their reflection surfaces face in parallel with each other, the plane mirrors 16 and 17 are arranged above and below the array detector 15 (in the direction indicated by the symbol Y in FIG. 1). ) The position does not change, and the left and right (the direction indicated by the symbol X in FIG. 1, the direction perpendicular to the paper) are reduced. Therefore, the spectroscope 10 is
When adjusting using a standard array detector provided outside the
By simply removing the plane mirror 16, it is possible to detect and confirm the incidence on the standard array detector.

By the way, in the array detector 15 which electronically performs wavelength scanning, the finer the array pitch of the cells is, the higher the resolution is. However, if the pitch is too small, the sensitivity is low. It becomes expensive as it becomes. On the other hand, in the above embodiment, since the focal length of the camera mirror 14 is about three times that of the collimating mirror 12, the dispersion distance can be increased, and the array detector 15
A cell having a relatively large cell arrangement pitch can be used. However, in this case, since the incident slit image is also enlarged about three times, it is necessary to appropriately select the cell arrangement width and the width of the incident slit 11.

As described above, in the above embodiment, since the incident slit image is enlarged, the light in the height direction of the incident slit 11 is generally not used in many parts. Therefore, as shown in FIG. 2, a cylindrical lens 20 is provided on the light incident side of the array detector 15, and the cylindrical lens 20 forms a reduced image only in the vertical direction of the light beam 21 incident on the array detector 15. Alternatively, the imaging light may be used with high efficiency. By doing so, the light amount can be increased by a factor of 2 to several times.

In the above-described embodiment, two flat mirrors are used in the image forming optical path of the camera mirror 14 as folding flat mirrors.
The present invention is not limited to this, but the present invention is not limited to this. For example, only the plane mirror 16 may be provided, and the array detector 15 may be provided at the position of the plane mirror 17. In this case, the image forming optical path length of the camera mirror 14 is reduced to about 、, but the focal length of the collimating mirror 12 needs to be approximately の of that of the camera mirror 14. . It is also possible to provide four or more folding mirrors in the imaging optical path of the camera mirror 14, but it is necessary to take into account the required resolution and the like.

FIG. 3 shows an example of a microscopic Raman spectrophotometer 30 incorporating the spectroscope 10 having the above-mentioned configuration. In this figure, reference numeral 31 denotes a laser light source, for example, a wavelength 4965.
The laser beam 32 of Å is emitted. Reference numeral 33 denotes a notch filter provided in front of the laser light source 32, and an optical filter 34 for removing a plasma line included in the laser light 32 is provided between the notch filter 33 and the laser light source 32.
Is interposed. A sample 36 is provided on one side of the notch filter 33 via an objective lens 35.
This sample 36 is a sample holder 37 having a temperature control function.
Is maintained in a predetermined state. A spectroscope 10 is provided on the other side of the notch filter 33 (the side facing the sample 35), and is configured to split the Raman scattered light generated on the surface of the sample 36. In addition, 3
Reference numeral 8 denotes a Raman light guiding unit.

When, for example, the temperature of a silicon wafer is measured using the microscopic Raman spectrophotometer 30 having the above-described configuration, the silicon wafer is held as the sample 36 by the sample holder 37. In that state, the laser light 32 from the laser light source 31
Emits. The laser light 32 is focused on the surface of the silicon wafer 36 via the optical filter 34, the notch filter 33, and the objective lens 35. The irradiation of the laser light 32 generates Raman scattered light in the silicon wafer 36, and the Raman scattered light reaches the Raman light guide section 38 via the notch filter 33, and is further introduced into the spectroscope 10 shown in FIG. The light is received by the array detector 15 and the Raman spectrum is measured.

The Raman spectrum is input to a signal processing device (not shown) such as a computer, and the temperature of the silicon wafer 36 is determined based on the peak position of the Raman spectrum.

The microscopic Raman spectrophotometer 30 having the above-described configuration is
Since the spectroscope 10 is small, the configuration of the entire apparatus is downsized. Since the spectroscope 10 has high resolution, the temperature of the sample 36 such as a wafer can be measured with high accuracy.

As described above, the spectroscope 10 of the present invention exhibits an excellent effect in Raman temperature measurement, but its application is not limited to Raman temperature measurement, and the size is reduced while having high resolution. Needless to say, it may be widely used for various measuring devices that require a spectroscopic unit.

It should be noted that a photodetector using a CCD may be used instead of the array detector 15.

[0027]

As described above, according to the present invention, a small and high-resolution spectroscope for use in the visible region can be obtained, and the spectroscope can be suitably incorporated in various measuring apparatuses having a spectroscopic section. This makes it possible to obtain a spectroscope that contributes to miniaturization of various measurement devices and improvement of measurement accuracy.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of the configuration of a spectroscope of the present invention.

FIG. 2 is a diagram showing an embodiment in the vicinity of an array detector in the spectroscope.

FIG. 3 is a diagram schematically showing a configuration of a micro Raman spectrophotometer incorporating the spectroscope.

FIG. 4 is a diagram for explaining a conventional spectroscope.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Incident light, 10 ... Spectroscope, 11 ... Incident slit, 12
... a collimating mirror, 13 ... a dispersion-type spectroscopic element, 14 ... a camera mirror, 15 ... a photodetector, 16, 17 ... a plane mirror for folding.

 ──────────────────────────────────────────────────続 き Continued on front page F term (reference) 2G020 AA04 CA04 CB03 CB23 CB43 CC04 CC07 CC42 CC63 CD04 CD12 CD24 2G043 AA06 CA05 EA03 FA02 GA04 GA07 GB01 GB02 GB07 HA02 JA04 KA09 LA03 MA03

Claims (1)

[Claims] 1. A spectroscope in which light incident through an entrance slit is incident on a photodetector through a collimating mirror, a dispersive spectroscopic element, and a camera mirror, wherein the camera mirror has a focal length of the collimating mirror. A spectroscope characterized in that a longer mirror is used and a plane mirror for folding is provided in an image forming optical path of a camera mirror, and light passing through the plane mirror is incident on a photodetector.