JP2005201756A - Method and apparatus for measuring strain of thin film crystal layer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for measuring a strain of a thin film crystal layer in a sample having the strained thin film crystal layer and a support layer for supporting the thin film crystal layer. <P>SOLUTION: The apparatus for measuring the strain of the thin film crystal layer is provided with excitation light sources 1-5 for generating visible light and ultraviolet light as excitation light along a common optical axis. A stage 12 is provided in a microscope chamber 7 and supports the sample 11. Projection optical systems 8, 9, 10 project the excitation light onto the sample 11 supported on the stage 12. A spectral means is provided in a spectroscope 18, and diffracts Raman scattering light from the sample 11. A calculation means calculates states of the strain and the support layer from an output from the spectral means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for measuring strain of a thin film crystal layer by Raman spectroscopy.

It is known that distortion occurs in thin film semiconductor crystals formed on semiconductor crystals having different crystal lattice sizes. A strained silicon is known as such a thin film semiconductor.
The strained silicon is obtained by forming a silicon-germanium crystal layer having a thickness of 20 to 500 nm on a normal silicon substrate and further growing a pure silicon crystal layer having a thickness of 10 to 30 nm on the silicon-germanium crystal layer.
Germanium and silicon have different atomic sizes, and the lattice spacing of a pure silicon crystal formed on a silicon-germanium crystal in which two kinds of atoms are regularly arranged is distorted. This strain has the property of increasing the conduction velocity of charges (electrons / holes) in the crystal by a factor of two, so that there is a possibility that a high-speed semiconductor element can be made using strained silicon.
In addition, the gallium-arsenic semiconductor known as a high-speed semiconductor has an advantage that there is no concern about toxicity, and has attracted attention. And research and development related to this is going on actively.

However, the attempt to obtain the data of the strained silicon layer simultaneously with the measurement of the silicon-germanium layer by the conventional visible light performed in the above-described research and development, the Raman scattered light of the strained silicon and the silicon-germanium layer There is a problem that separation of measurement results of Raman scattered light is not easy.
The object of the present invention is to make it possible to clearly distinguish Raman scattering of a strained silicon layer from Raman scattering of a support layer, and to measure data such as strain of the strained silicon layer and composition of the support layer. The object is to provide a method for measuring the strain of a thin film crystal layer.
Still another object of the present invention is to provide an apparatus capable of carrying out the method.

In order to achieve the above object, a method for measuring strain of a thin film crystal layer according to claim 1 according to the present invention comprises:
In a method of measuring strain of a thin film crystal layer in a sample having a thin film crystal layer and a support layer that supports the thin film crystal layer,
An excitation step of irradiating visible light and ultraviolet light as excitation light from the thin film crystal layer side;
A detection step of detecting each Raman scattered light by each excitation light;
The method includes an estimation step of estimating the distortion of the thin film crystal layer from the wavelength shift of the Raman scattered light of the ultraviolet light and estimating the state of the support layer from the wavelength and wavelength shift of the Raman scattered light of the visible light.

The method for measuring the strain of the thin film crystal layer according to claim 2 according to the present invention is the method for measuring the strain of the thin film crystal layer according to claim 1,
The support layer is a silicon-germanium crystal, the thin film crystal layer is a strained silicon, and the strained silicon is a support in which a silicon-germanium crystal layer having a thickness of 20 to 500 nm is formed on a normal silicon substrate. A pure silicon crystal layer having a thickness of 10 to 30 nm formed on the layer.
The method for measuring strain of a thin film crystal layer according to claim 3 according to the present invention is the method for measuring strain of a thin film crystal layer according to claim 1 or 2,
The excitation light of the ultraviolet light is preferably in the range of 350 to 370 nm, and most preferably 364 nm.
A method for measuring strain of a thin film crystal layer according to claim 4 according to the present invention is the method for measuring strain of a thin film crystal layer according to claim 1 or 2,
The ultraviolet excitation light is one selected from an argon ion laser (364 nm, 351 nm), a YAG laser third harmonic (355 nm), and a krypton ion laser (351 nm).

An apparatus for measuring strain of a thin film crystal layer according to claim 5 according to the present invention comprises:
An apparatus for measuring strain of the thin film crystal layer in a sample having a thin film crystal layer having strain and a support layer that supports the thin film crystal layer,
An excitation light source capable of generating visible light and ultraviolet light as excitation light on a common optical axis;
A stage for supporting the sample;
A projection optical system that projects the excitation light onto the sample supported by the stage;
Spectroscopic means for spectroscopically analyzing each Raman scattering from the sample,
It comprises calculation means for calculating the strain and the state of the support layer from the output of the spectroscopic means.

According to the method of claim 1, by irradiating visible light and ultraviolet light as excitation light in the excitation step, it is possible to acquire information on the layer having surface distortion by ultraviolet light and information on the support layer by visible light. .
The method according to claim 2 is a pure silicon crystal layer having a thickness of 10 to 30 nm formed on a support layer in which a silicon-germanium crystal layer having a thickness of 20 to 500 nm is formed on a normal silicon substrate. Measurement of sample distortion and the like becomes possible.

According to the method for measuring strain of a thin film crystal layer according to claim 3 of the present invention, the excitation light of the ultraviolet light is preferably in the range of 350 to 370 nm, and most preferably 364 nm. As a result of the experiment, good results were not obtained with excitation at 325 nm. Good results have been obtained with excitation at 351, 355 and 364 nm.
When excited by ultraviolet light in a region less than 350 nm, the intensity of Raman scattered light is weak and the time required for measurement becomes long. As a result, the S / N ratio becomes small, and it is considered that good measurement results cannot be obtained.
In the case of excitation with ultraviolet light in a region exceeding 370 nm, it is considered that good measurement results cannot be obtained as a result of the excitation light reaching the silicon-germanium crystal layer.

According to the method for measuring strain of a thin film crystal layer according to claim 4 according to the present invention, in the method for measuring strain of a thin film crystal layer according to claim 1 or 2, the ultraviolet light is easily obtained as excitation light. Any one selected from an argon ion laser (364 nm, 351 nm), a YAG laser third harmonic (355 nm), and a krypton ion laser (351 nm) can be used.
According to the fifth aspect of the present invention, the above-described measuring method can be reliably implemented.

The best mode of the method and apparatus of the present invention will be described below.
The strained silicon is obtained by forming a silicon-germanium crystal layer having a thickness of 20 to 500 nm on a normal silicon substrate and further growing a pure silicon crystal layer having a thickness of 10 to 30 nm on the silicon-germanium crystal layer.
Germanium and silicon have different atomic sizes, and the lattice spacing of a pure silicon crystal formed on a silicon-germanium crystal in which two kinds of atoms are regularly arranged is distorted.

Since the Raman spectrum of a crystal is strained in the crystal, the wave number position where it appears shifts, and the amount of shift correlates with the degree of strain, so this measurement knows the strain state of the strained silicon crystal and This is an effective means for evaluating the quality of semiconductor materials.
The Raman spectrum is the wave number of the sample that emits a series of light slightly scattered from the irradiation wavelength as scattered light due to interference with sample molecules and crystal lattice vibrations when the sample is irradiated with light of a certain wavelength. Although it is a difference spectrum, the wave number difference spectrum obtained does not change even if the wave value of the irradiation light changes, that is, irradiation with ultraviolet light or infrared light.

The selection of the wavelength of light to be irradiated when measuring the Raman spectrum of an extremely thin strained silicon crystal layer of 10 to 30 nm is important. Visible light of 400 nm or more passes through the outermost strained silicon layer and reaches the silicon-germanium layer below it, so that excitation light of this wavelength cannot be used for the measurement of the Raman spectrum of the outermost layer.
The present inventor has found that light of 364 nm Ar + laser is optimal for measurement of a strained silicon crystal layer having a thickness of 10 to 30 nm. An example of the measurement result is shown in FIG. An intensity of about 100 times the Raman spectrum when irradiated with a helium-cadmium ion laser (325 nm) is obtained.

FIG. 1 is a block diagram of an apparatus for carrying out a method for measuring strain of a thin film crystal layer by Raman spectroscopy according to the present invention. The excitation light source unit is a light source that generates visible light and ultraviolet light as excitation light on a common optical axis. As the visible light source 1, an argon ion laser that emits visible light of 515 nm is used. The ultraviolet light source 2 is an argon ion laser that emits ultraviolet light of 364 nm.
These visible and ultraviolet light paths are provided with filters 24 and 25 that transmit only the main wavelength light oscillated by the respective lasers and shutters 26 and 27 that are opened and closed at the time of measurement. Temperature rise is prevented.
Visible light passes through the dichroic mirror 3 and is reflected by the mirror 5. The ultraviolet light is reflected by the mirror 4 and the dichroic mirror 3 and takes the same optical path as visible light.

Light from the excitation light source unit supplied through the filter is incident on the microscope chamber 7. The microscope chamber 7 is provided with a strained thin film crystal layer (hereinafter referred to as a sample) and a sample stage for supporting the sample. The laser light introduced into the microscope chamber 7 is reflected by the dichroic mirror 8 and is made to coincide with the optical axis of the sample microscope by the reflecting mirror 9, and is focused on the surface of the sample 11 by the objective lens 10 of the sample microscope. .
The sample is placed on a sample stage 12 that can move back and forth and right and left, and local analysis of any point on the sample surface is possible. For observation of the sample surface, there are provided a small CCD camera 13 and a movable dichroic mirror 14 that is inserted into the optical path only during observation and guides the laser light incident point image to the camera.

The Raman scattered light emitted from the laser beam incident point on the sample 11 is collected by the objective lens 10, travels in the opposite direction to the incident laser beam, passes through the dichroic mirror 8 and is guided outside the microscope chamber 7.
A necessary wave number component is transmitted by the visible / ultraviolet switching filter 15 and enters the spectroscope 18 through the reflecting mirror 16 and the focusing lens 17.
The optical arrangement of the spectroscope 18 is of a normal Zellnie Turner type having a collimator mirror 19 and a camera mirror 20.
A grating 21 whose spectral efficiency is optimized in the visible region and a grating 22 which is optimized in the ultraviolet region are built in, and are switched according to the wavelength of the laser beam to be irradiated. The spectrally scattered Raman scattered light is converted into an electrical signal of a spectrum by a high sensitivity CCD detector 23 equipped with a cooling device using liquid nitrogen and sent to a signal processing system at the next stage.

Using the apparatus, Raman spectra were measured for two samples.
In addition to the sample, a Si substrate corresponding to the substrate itself was prepared and used as a reference. FIG. 2 shows a reference (reference) in visible light excitation and Raman spectrum profiles of Sample 1 and Sample 2. FIG. 3 shows a reference (reference) in ultraviolet light excitation and Raman spectrum profiles of Sample 1 and Sample 2.
In each figure, (1) and (4) are reference Raman spectra, (2) and (3) are Si-Ge Raman spectra, and (5) and (6) are top silicon Raman spectrum profiles, respectively. . The Raman spectrum of each example will be described and discussed later.

First sample top silicon layer having a top silicon thin film formed on a Si-Ge having a thickness as described below on a Si substrate (wafer) 25 nm
Si _(1-x) Ge _x (x = 0.15) 400 nm
Si base 0.75mm

Raman spectrum of Si-Ge layer:
A peak was obtained at a wave number position of 511 cm ⁻¹ by excitation with visible light having a wavelength of 515 nm (see (2) in FIG. 2).
Raman spectrum of top silicon layer:
A peak was obtained at a wave number position of 516 cm ⁻¹ by excitation with ultraviolet light having a wavelength of 364 nm (see (5) in FIG. 3).

Second sample top silicon layer having a top silicon thin film formed on a Si-Ge having a thickness as follows on a Si substrate (wafer) 21 nm
Si _(1-x) Ge _x (x = 0.2) 400 nm
Si base 0.75mm
Raman spectrum of Si-Ge layer:
A peak was obtained at a wavenumber position of 507 cm ⁻¹ by excitation with visible light having a wavelength of 515 nm (see (3) in FIG. 2).
Raman spectrum of top silicon layer:
A peak was obtained at a wave number position of 514 cm ⁻¹ by excitation with ultraviolet light having a wavelength of 364 nm (see (6) in FIG. 3).

  In strained silicon, it is known that in the case of tensile strain, it shifts to the lower wave number side than the unstrained one. It shows that the strained silicon of the sample of Example 2 has a larger tensile strain.

FIG. 2 is a Raman spectrum measured using the above-mentioned apparatus and using an argon ion laser with visible light having a wavelength of 515 nm as an irradiation light source.
Comparing the Raman spectra of the first sample, the second sample, and the reference silicon bulk (corresponding to the base) in excitation with visible light, the spectrum (1) is that of pure silicon, and the lattice vibration of Si—Si is at the wave number position 521 cm ⁻¹ Appears as a large peak. Spectrum (2) and spectrum (3) are the spectra of sample 1 (germanium content 15%) and sample 2 (germanium content 20%), respectively.

511cm ^-1 of the spectrum (2), the peak of 507cm ^-1 spectral (3), Izure also not derived from the top silicon layer having a strain is formed on the outermost surface, the silicon of the support layer - germanium mixed crystal It is by lattice vibration of Si-Si bonds in a peak by the top silicon layer to 516cm ^-1 in the spectrum (2), spectrum (3) in a respective separation sufficient to 514cm ^-1, the small shawl loaders Appears.
Since the thickness of the top silicon layer is thin and 515 nm laser light is easily transmitted, such a measurement result is obtained, and it is not possible to measure only the spectrum of the top silicon layer with visible wavelength light. The spectrum of the Si-Ge layer is obtained.

FIG. 3 is a spectrum obtained by switching the irradiation light source to a 364 nm argon ion laser. The spectra (4), (5), and (6) correspond to the spectra (1), (2), and (3), respectively, and the peak wavenumber positions of the spectra (5) and (6) are 516 cm ⁻¹ , 514 cm ⁻¹ , which is the same as the wave number position of the Schoulder in the spectra (2) and (3).
Spectrum Spectrum (5) is the peak of 507cm ^-1 of 511cm ^-1 and spectrum (3) (2), does not appear in the spectrum (6), indicates that the ultraviolet light irradiation does not penetrate below the outermost layer ing.

  It can be widely used for research and development such as strain measurement of a thin film layer, for example, “stress measurement” of a strained silicon layer, or “quality evaluation” of a product in the semiconductor industry.

1 is a block diagram of an apparatus for carrying out a method for measuring strain of a thin film crystal layer by Raman spectroscopy according to the present invention. FIG. It is a Raman spectrum of the standard sample, the 1st sample, and the 2nd sample which measured the visible light of wavelength 515nm of an argon ion laser as an excitation light source. It is a Raman spectrum of the standard sample, the 1st sample, and the 2nd sample which measured using the ultraviolet light of wavelength 364nm of an argon ion laser as an excitation light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Visible light source 2 Ultraviolet light source 3 Dichroic mirrors 4 and 5 Mirror 7 Microscope room 8 Dichroic mirror 9 Reflective mirror 10 Objective lens 11 Sample 12 Sample stage 13 CCD camera 14 Dichroic mirror 15 Filter 16 Reflecting mirror 17 Focusing lens 18 Spectrometer 19 Collimator mirror 20 Camera mirrors 21 and 22 Grating 23 CCD detector 24 Visible light transmission filter 25 Ultraviolet light transmission filter 26 Visible light shutter 27 Ultraviolet light shutter

Claims (5)

In a method of measuring strain of a thin film crystal layer in a sample having a thin film crystal layer and a support layer that supports the thin film crystal layer,
An excitation step of irradiating visible light and ultraviolet light as excitation light from the thin film crystal layer side;
A detection step of detecting each Raman scattered light by each excitation light;
The thin film crystal layer comprises: an estimation step for estimating distortion of the thin film crystal layer from the wavelength shift of the Raman scattered light of the ultraviolet light, and estimating the state of the support layer from the wavelength and wavelength shift of the Raman scattered light of the visible light. A method of measuring strain.   The support layer is a silicon-germanium crystal, the thin film crystal layer is a strained silicon, and the strained silicon is a support in which a silicon-germanium crystal layer having a thickness of 20 to 500 nm is formed on a normal silicon substrate. The method for measuring strain of a thin film crystal layer according to claim 1, which is a pure silicon crystal layer having a thickness of 10 to 30 nm formed on the layer.   The method for measuring strain of a thin film crystal layer in a sample according to claim 1 or 2, wherein the excitation light of the ultraviolet light is preferably in the range of 350 to 370 nm, and most preferably 364 nm.   The excitation light of the ultraviolet light is any one selected from an argon ion laser (364 nm, 351 nm), a YAG laser third harmonic (355 nm), and a krypton ion laser (351 nm). A method for measuring strain of a thin film crystal layer in a sample. An apparatus for measuring strain of the thin film crystal layer in a sample having a thin film crystal layer having strain and a support layer that supports the thin film crystal layer,
An excitation light source capable of generating visible light and ultraviolet light as excitation light on a common optical axis;
A stage for supporting the sample;
A projection optical system that projects the excitation light onto the sample supported by the stage;
Spectroscopic means for spectroscopically analyzing each Raman scattering from the sample,
An apparatus for measuring the strain of the thin film crystal layer comprising the computing means for computing the strain and the state of the support layer from the output of the spectroscopic means.

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