JPS62194426A - Spectroscope - Google Patents

Abstract

PURPOSE:To dispense with a mechanical movable part or a slit and to enhance reliability, by applying Fourier transformation to an interferogram obtained as the change of an electrical signal with the elapse of time to detect a spectrum. CONSTITUTION:Incident beam 3 passes through an aperture 1 and a lens 11 to be incident to a polarizer P and, for example, is converted to linear polarized beam in the direction forming an angle of 45 deg. with respect to the direction of the electric field acting on a substance M to be transmitted through the substance M. Further, the transmitted beam is incident to a photoelectric converter means 2 through an analyser A selecting only the linear polarized beam in a predetermined direction and a lens 12. The interferogram 2a obtained from the photoelectric converter means 2 is subjected to Fourier transformation in a Fourier transformation part 8 to detect the spectrum of the incident beam 3 and said spectrum is outputted to a display part 9.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a spectroscopic technique, and particularly to a spectroscopic technique that is effective when applied to detecting the end point of a dry etching apparatus used in the manufacture of semiconductor devices.

[Conventional technology]

Regarding the end point detection of dry etching, please refer to "Electronic Materials J.
November 1982 special issue, P146-P1.5 L
It is described in.

The outline of this method is to determine the end point of etching based on the change over time in the intensity of the emission spectrum of a wavelength corresponding to a specific substance in the plasma of a reactive gas.

By the way, the present inventor has studied a spectroscopic technique for observing emission spectrum intensity over time.

Although the following is not a publicly known technique, it is a technique studied by the present inventor, and its outline is as follows.

That is, the optical path is branched for each different wavelength by a diffraction grating that is oscillated so that the dispersion angle of the incident light changes over time, and the branched light is selected by an output slit and then enters the optical sensor. The intensity of light in a predetermined wavelength range can be detected by determining the wavelength range of light transmitted through the output slit by the swing angle of the diffraction grating.

[Problems to be solved by the invention] However, in the spectrometer having the above structure,
Because the structure has a mechanically movable part that oscillates the diffraction grating, operation reliability is relatively low in applications where it is used continuously for long periods of time. Since the amount of incident light is limited, it is necessary to reduce the scanning speed in order to maintain a predetermined sensitivity, which causes various problems such as an increase in the time required for measurement.

An object of the present invention is to provide a spectroscopic technique that has high operational reliability and can obtain highly accurate measurement results in a short time.

The above and other objects and novel features of the present invention include:
It will become clear from the description herein and the accompanying drawings.

[Means for Solving the Problems] A brief overview of typical inventions disclosed in this application is as follows.

That is, an optical rotation optical system configured by interposing a predetermined substance between a polarizer and an analyzer is interposed in the optical path from the light source to the optical-to-electrical conversion means, and light is transmitted from the light source through the optical rotation optical system. The amount of light reaching the electrical conversion means is changed over time by changing the optical rotation angle of the substance over time, and at this time, the ink ferrogram obtained in the optical-to-electrical conversion means is subjected to Fourier transformation. This is how the spectrum is detected.

[Function] According to the above-described means, reliability of the operation is improved because a mechanical movable part or a slit for limiting the amount of light incident on the light-to-electrical conversion means is not required.

Further, a sufficient amount of light can be obtained for the optical-electrical conversion means, and a spectrum can be detected with high precision in a relatively short time.

[Example 1] FIG. 1 is an explanatory diagram showing the main parts of a spectrometer that is an example of the present invention.

For example, in the optical path of incident light 3 from a light source such as a plasma light emitting part of a plasma etching apparatus (not shown), through a circular aperture 1, to the light-to-electrical conversion means 2, there is a space between a polarizer P and an analyzer A. An optical rotation optical system 4 is interposed, which is constructed by interposing a material M made of, for example, an electro-optic crystal.

In this case, the material M is provided with a pair of electrodes 5a in a direction perpendicular to the optical path of the incident light 3 passing through the material M.
and 5b are provided facing each other.

Further, an optical rotation angle driving unit 6 is connected to the electrodes 5a and 5b, and by sweeping the voltage applied to the electrodes 5a and 5b, the optical rotation angle is formed inside the substance M in a direction perpendicular to the optical path of the incident light 3. The electric field is changed periodically, and the angle of optical rotation inside the substance M of the incident light 3, which is linearly polarized in a predetermined direction by passing through the polarizer P, is changed over time. .

The optical-to-electrical converter 2 is connected to a Fourier transformer 8 via an amplifier 7, and changes over time the amount of incident light 3 that is incident on the optical-to-electrical converter 2 and includes light of a plurality of wavelengths. The spectrum of the incident light 3 is detected by Fourier transforming the ink ferrogram 2a in accordance with the change in the electrical signal, that is, the ink ferrogram 2a, and is output to the display unit 9. There is.

The optical rotation angle drive unit 6 and the Fourier transform unit 8 are connected to a synchronization control unit 10, and perform operations such as synchronizing the voltage sweep start time in the optical rotation angle control unit 6 and the sampling start time in the Fourier transform unit 8. It is said that the structure is

A lens 11 and a lens 12 are provided between the aperture 1 and the optical rotation optical system 4, and between the optical rotation optical system 4 and the optical-to-electric conversion means 2, respectively.

The operation of this embodiment will be explained below.

Incident light 3 whose light source is plasma emission from a dry etching device (not shown) is transmitted through an aperture 1 and a lens 1.
1, enters the polarizer P, becomes linearly polarized light in a direction that forms an angle of 45 degrees with respect to the direction of the electric field acting on the material M, and then is transmitted through the material M, and then is transmitted in a predetermined direction. Analyzer A and lens 1 that select only linearly polarized light
2 and enters the optical-to-electrical conversion means 2.

In this embodiment, the optical rotation angle driving unit 6 sweeps the voltage applied to the electrodes 5a and 5b provided on the material M in a direction perpendicular to the optical path of the incident light 3 passing through the material M. By periodically changing the intensity of the electric field formed at
For example, only the linearly polarized light in the direction forming an angle of 45 degrees with respect to the direction of the electric field acting on the substance M is selected and reaches the incident light 3 in the light-to-electrical conversion means 2.
The amount of light is changed over time, and the electrical signal changes in accordance with the change over time of the amount of incident light 3 including light of a plurality of wavelengths that is incident on the light-to-electricity conversion means 2, that is, the interferogram. 2a is obtained.

In the Fourier transform section 8, the synchronization control section 10
By synchronizing the start time of the sweep of the applied voltage in the optical rotation angle drive unit 6 obtained via the optical rotation angle drive unit 6 with the start time of sampling of the interferogram 2a, the ink ferrogram 2a is Fourier-transformed to obtain the spectrum of the incident light 3. is detected and output to the display section 9.

As described above, according to the first embodiment, the following effects can be obtained.

(1) Since no mechanical movable parts are required, reliability of operation is improved in applications where the device is used continuously for a long period of time.

(2) As a result of the above (1), the structure is simplified, and the spectrometer can be made smaller and lower in price.

(3) Since there is no need for a slit or the like to limit the amount of light incident on the photo-electric conversion means 2, a sufficient amount of light can be obtained for the photo-electric conversion means 2, and the electrodes 5a and By sweeping the voltage applied to 5b and sampling the ink ferrogram 2a in the Fourier transform unit 8 closely, the spectrum of the incident light 3 can be detected with high precision in a relatively short time.

(4), as a result of +11 to (3) above, for example, dry
When detecting the end point of etching using spectroscopic analysis, it is now possible to quickly analyze changes in the intensity of the spectrum of plasma emission, which changes drastically over time. etc. will be improved.

[Embodiment 2] FIG. 2 is an explanatory diagram showing the main parts of a spectrometer which is another embodiment of the present invention.

In the second embodiment, the optical rotation optical system 4a interposed in the optical path of the incident light 3 entering the light-to-electrical conversion means 2 is made of a material M1 interposed between the polarizer P and the analyzer A. The electromagnet 13 is configured such that the change in the angle of rotation in a substance M1 interposed between the polarizer P and the analyzer A is opposed to the substance M1 through the substance M1, and is disposed in the direction of the optical path of the incident light 3. The difference from the first embodiment is that the magnetic field is changed by changing the magnetic field applied from the magnetic field.

That is, by periodically changing the current to the electromagnet 13 by the optical rotation angle driving unit 6a, the intensity of the magnetic field applied to the substance M1 is changed, and by passing through the polarizer P, the light is linearly polarized in a predetermined direction. and electromagnet 13
Incident light 3 transmitted through the material M1 through the cavity 13a of
The optical rotation angle in the substance M1 is changed over time.

As described above, according to the second embodiment, the following effects can be obtained.

(1) Since no mechanically movable parts are required, the multiplicity of operation is improved, for example, in applications where the device is used continuously for a long period of time.

(2) As a result of the above (11), the structure is simplified, and the spectrometer can be made smaller and lower in price.

(3) Since there is no need for a slit or the like to limit the amount of light incident on the light-to-electricity conversion means 2, a sufficient amount of light can be obtained for the light-to-electricity conversion means 2, and the magnet 13 applies a magnetic field to the substance M1. By changing the current from the optical rotation angle drive unit 6a and sampling the interferogram 2a in the Fourier transform unit 8 closely, the spectrum of the incident light 3 can be detected with high precision in a relatively short time.

(4) As a result of (1) to (3) above, it is possible to quickly analyze the intensity change of the plasma emission spectrum, which changes drastically over time, in end point detection using spectroscopic analysis in dry etching, etc. As a result, end point detection is performed accurately, and dimensional accuracy in etching fine patterns is improved.

Although the invention made by the present inventor has been specifically explained above based on Examples, it goes without saying that the present invention is not limited to the Examples and can be modified in various ways without departing from the gist thereof. Nor. For example, Example 2
In this case, it is also possible to adopt a structure in which the incident light 3 is reciprocated inside the substance M1.

Further, the substances M and Ml are not limited to solids, but may be liquids.

Furthermore, concave mirrors or the like may be used instead of lenses 11 and 12.

The above explanation has mainly been about the application of the invention made by the present inventor to the spectroscopic technology used for detecting the end point of dry etching, which is the background field of application, but the invention is not limited to this. For example, it can be widely applied to fields such as physical and chemical measurement technology.

[Effects of the Invention] The effects obtained by typical inventions disclosed in this application are briefly described below.

That is, an optical rotation optical system configured by interposing a predetermined substance between a polarizer and an analyzer is interposed in the optical path of incident light from the light source to the light-to-electrical conversion means, and the optical rotation angle of the substance is interposed. When changing the amount of incident light that enters the optical-to-electrical conversion means through the optical rotation optical system by temporally changing the Since the structure detects the spectrum by Fourier transforming the obtained ink ferrogram, there is no need for mechanical moving parts or slits to limit the amount of light incident on the optical-to-electrical conversion means, improving the multiplicity of operation. At the same time, a sufficient amount of light can be obtained for the optical-to-electrical conversion means, and a spectrum can be detected with high precision in a relatively short time.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the main parts of a spectrometer which is one embodiment of the present invention, and FIG. 2 is an explanatory diagram showing the main parts of a spectrometer which is another embodiment of the invention. DESCRIPTION OF SYMBOLS 1... Aperture, 2... Optical-electric conversion means, 2a
... Ink ferrogram, 3 ... Incident light, 4, 4a
... Optical rotation optical system, 5a, 5b... Electrode, 6.6a.
... Optical rotation angle drive unit, 7... Amplification unit, 8... Fourier transform unit, 9... Display unit, 10... Synchronization control unit, 11
．． 12... Lens, 13... Electromagnet, 13a...
Cavity part, P...Polarizer, A...Analyzer, M, Ml・
··material. 1st Figure 5979 - Cage 2nd figure / Mt. σ - Sai 5II section

Claims (1)

[Claims] 1. In the optical path of incident light from the light source to the optical-to-electrical conversion means,
An optical rotation optical system configured by interposing a predetermined substance is interposed between the polarizer and the analyzer, and by temporally changing the optical rotation angle of the substance, the light passes through the optical rotation optical system.
When changing the amount of incident light incident on the electrical conversion means, the interferogram obtained as a change over time of an electrical signal in the optical-to-electrical conversion means is Fourier-transformed to detect a spectrum. spectrometer. 2. The substance is an electro-optic crystal, and the operation of temporally changing the angle of optical rotation is performed by periodically changing the intensity of an electric field applied in a direction perpendicular to the optical path within the electro-optic crystal. The spectrometer according to claim 1, characterized in that: 3. The direction of linearly polarized light by the polarizer and analyzer is
3. The spectrometer according to claim 2, wherein the spectrometer forms an angle of 45 degrees with respect to the direction of the electric field. 4. Spectroscopy according to claim 1, wherein the operation of temporally changing the optical rotation angle of the substance is performed by periodically changing the intensity of the magnetic field applied to the substance. vessel. 5. The spectrometer according to claim 1, wherein the spectrometer is a spectrometer used for end point detection of a dry etching apparatus.