JP2004327843A - Method of evaluating stress of amorphous silicon and its compound thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To evaluate stress and stress distribution in a micro region of amorphous silicon and its compound thin film nondestructively and easily. <P>SOLUTION: In the method of evaluating the stress of an amorphous silicon and its compound thin film 2 on a substrate 1, a laser is employed as a light source and stress of a film, especially stress in a micro region, and stress distribution are evaluated by measuring and analyzing photoluminescence spectrum. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a stress evaluation method for amorphous silicon and its compound thin film, and more particularly, for example, as a semiconductor layer, a resistive layer, a gate insulating film, an interlayer insulating film, a passivation film, or an X-ray exposure in a semiconductor device. The present invention relates to a stress evaluation method for amorphous silicon and its compound thin film used as a mask constituent material in an apparatus and a charged particle beam exposure apparatus.
[0002]
[Prior art]
With the development of semiconductor and metal thin film fabrication technology and microfabrication technology, integrated circuits using single crystal silicon and compound semiconductors, and flat panel display devices and various sensors using amorphous semiconductor thin films are rapidly increasing. It is widespread.
[0003]
In the functional devices described above, for example, an amorphous silicon thin film is widely used as a semiconductor layer or a resistance layer, and an amorphous silicon nitride thin film is widely used as a gate insulating film or an interlayer insulating film.
[0004]
In such applications, in addition to electrical characteristics such as semiconductor characteristics, insulation properties, and dielectric properties, high adhesion to different materials is required. In addition to the interface composition, the adhesion has a great effect on the stress of the film, and when the stress is large, the film is peeled off from the underlying material. To prevent this, it is essential to measure and control the stress of the amorphous silicon film or amorphous silicon compound film for each element.
[0005]
In addition, miniaturization of the semiconductor element as described above is rapidly progressing. In a semiconductor process technology, various exposure technologies have been developed as a manufacturing technology of an element having such a fine pattern. Of these, charged particle beam exposure and X-ray exposure using electrons, ions, and the like have attracted attention as exposure techniques based on the sub μm rule.
[0006]
In such an exposure technique, a mask is used to shape a charged particle beam or X-ray. These masks are made of amorphous silicon thin film, amorphous silicon nitride thin film, amorphous silicon carbide thin film or other amorphous silicon thin film, amorphous silicon nitride thin film, or amorphous silicon carbide thin film as a mask material or a mask constituent material such as a membrane, or as a stress adjusting film. A porous silicon compound thin film is used.
[0007]
In this case, amorphous silicon or its compound thin film is often used as a free-standing film. In order to apply amorphous silicon or its compound thin film as such a member, it is essential to measure and control the stress of those films.
[0008]
[Non-patent document 1]
"Selected Thin Film for Applied Physics" (pages 127-146), written by Kan Kanbara and Hideo Fujiwara, published by Shokabo Co., Ltd. (June 5, 1979)
[0009]
[Problems to be solved by the invention]
As a method for evaluating the stress of a film, for a crystalline film, a method of measuring the strain of a crystal lattice and calculating the stress by X-ray or electron diffraction or Raman spectroscopy is disclosed in, for example, Non-Patent Document 1. ing. However, silicon and its compound thin films that are put into practical use are usually formed by low pressure chemical vapor deposition, thermal chemical vapor deposition, or plasma chemical vapor deposition, and are structurally amorphous films. Since they do not have crystallinity, it is impossible to measure stress by the above-described method.
[0010]
On the other hand, as an evaluation method that does not depend on the crystallinity of the film, an evaluation method based on the amount of change in the warpage of the substrate and a bulge method in which the film is processed into a membrane state and evaluated based on the deformation amount are known.
[0011]
However, the evaluation method for observing the amount of change in the warpage of the substrate can only evaluate the average value of the stress of the entire substrate. That is, evaluation of the stress in the minute region and the stress distribution in the plane is impossible in principle.
[0012]
In addition, in the bulge method, it is possible to evaluate the stress in a sub-millimeter-order region and the stress distribution in the range that can be processed by processing the film into a membrane by using the fine processing technology, but it is necessary to process the substrate. Non-destructive measurement is not possible. Further, it is impossible to evaluate a micro area on the order of μm or to evaluate a stress distribution by dividing the micro area.
[0013]
The present invention has been made in view of such circumstances, and it has been made possible to non-destructively and easily evaluate the stress and stress distribution in a minute region of amorphous silicon and its compound thin film. And a method for evaluating the stress of a compound thin film thereof.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following measures.
[0015]
That is, in the stress evaluation method according to the first aspect of the present invention, in the stress evaluation of the amorphous silicon and the compound thin film formed on the substrate, a laser is used as a light source, and a photoluminescence spectrum is measured and analyzed to thereby analyze the film. Is evaluated for stress or stress distribution.
[0016]
Therefore, in the stress evaluation method for the amorphous silicon and its compound thin film according to the first aspect of the present invention, by taking the above measures, the spectrum in the minute region of the film formed on the substrate can be non-destructively measured. Can be easily obtained. Further, by scanning a laser as a light source or a substrate of a film to be evaluated, a spectral distribution of the film can be easily obtained.
[0017]
According to a second aspect of the present invention, in the stress evaluation method according to the first aspect, the amorphous silicon and its compound thin film are hydrogenated amorphous silicon and its compound thin film.
[0018]
In the case where the amorphous silicon and its compound thin film are hydrogenated amorphous silicon and its compound thin film as in the second aspect of the present invention, the photoluminescence having high intensity due to the silicon-hydrogen bond is not generated. As a result, the film stress can be evaluated with higher accuracy.
[0019]
According to a third aspect of the present invention, in the stress evaluation method according to the first or second aspect, the amorphous silicon compound thin film is an amorphous silicon nitride thin film or a hydrogenated amorphous silicon nitride thin film.
[0020]
In the case where the amorphous silicon compound thin film is an amorphous silicon nitride thin film or a hydrogenated amorphous silicon nitride thin film as in the third aspect of the present invention, a silicon-nitrogen bond or nitrogen-hydrogen Due to binding. In particular, since it has a clear and high peak value in the range of 2.0 eV to 2.4 eV, it is possible to evaluate the film stress with higher accuracy.
[0021]
According to a fourth aspect of the present invention, in the stress evaluation method according to any one of the first to third aspects, the substrate is made of single crystal silicon or quartz.
[0022]
When the substrate is made of single-crystal silicon or quartz as in the invention of claim 4 described above, photoluminescence does not occur in any of the energy regions where photoluminescence spectra of amorphous silicon and its compound thin film can be obtained. Since there is no S / N ratio, a high S / N ratio can be obtained, and film stress evaluation can be performed with higher accuracy.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0024]
FIG. 1 is an elevation view illustrating an example of amorphous silicon whose stress is evaluated by the stress evaluation method according to the embodiment of the present invention.
[0025]
That is, in the stress evaluation method according to the embodiment of the present invention, in the stress evaluation of the amorphous silicon and its compound thin film 2 on the substrate 1, the film is measured and analyzed by using a laser as a light source and measuring a photoluminescence spectrum. The stress of No. 2, especially the stress or the stress distribution in a minute area, is evaluated.
[0026]
This utilizes the property that amorphous silicon and an amorphous silicon compound can obtain a light emission peak due to strong photoluminescence in an energy region of 1.5 eV to 2.5 eV, that is, a visible light region. Such physical properties are due to the film structure, for example, optical band gap, other optical physical properties such as electroluminescence, and also electrical physical properties such as electrical conductivity, have a correlation with stress. In some cases.
[0027]
However, in the other physical properties described above, the material of the substrate 1 is limited for the evaluation, and it is necessary to form an electrode or the like. Have difficulty.
[0028]
On the other hand, in the measurement of photoluminescence using a laser as a light source as described above, the thin film 2 formed on the substrate 1 can be non-destructively and a spectrum in a minute region can be easily obtained. Further, by scanning the laser light source or the substrate 1 of the film to be evaluated, the spectral distribution of the thin film 2 can be easily obtained.
[0029]
As a result of a detailed study of the relationship between the spectrum measurement of photoluminescence in various amorphous silicon-based thin films, the analysis thereof, and the stress measured by other methods, for example, as shown in FIG. And the stress correlation. That is, it was found that the spectrum intensity or the peak value and the stress showed a strong correlation.
[0030]
Furthermore, the stress evaluation method according to the embodiment of the present invention is particularly effective when the amorphous silicon and its compound thin film are hydrogenated amorphous silicon and its compound thin film.
[0031]
That is, in the case of amorphous silicon containing a large amount of hydrogen in the film 2 and its compound thin film, stronger photoluminescence due to silicon-hydrogen or nitrogen-hydrogen bonds can be obtained, so that the film stress can be increased with higher accuracy. Can be evaluated.
[0032]
It is particularly effective when the amorphous silicon compound thin film is an amorphous silicon nitride thin film or a hydrogenated amorphous silicon nitride thin film.
[0033]
In the case of an amorphous silicon nitride thin film and a hydrogenated amorphous silicon nitride thin film, since a clear and high peak value is obtained particularly at 2.0 eV to 2.4 eV, evaluation of film stress with higher accuracy is required. It becomes possible.
[0034]
Further, it is more effective when the substrate 1 is made of single crystal silicon or quartz.
[0035]
That is, in the case where the substrate 1 is a single crystal silicon or quartz substrate, in each of the energy regions where the photoluminescence spectra of the amorphous silicon and the compound thin film are obtained, there is no photoluminescence, so that a high S / N ratio is obtained. Thus, the stress of the thin film 2 can be evaluated with higher accuracy.
[0036]
Next, a specific example in which the stress of the thin film 2 of amorphous silicon and its compound is evaluated by the above-described stress evaluation method will be described.
[0037]
First, a method for manufacturing an evaluation sample will be described. Here, an evaluation sample in which a silicon nitride film is formed on the substrate 1 will be described. When manufacturing such an evaluation sample, first, a thin film 2 of silicon nitride is formed on a 4-inch single crystal silicon wafer as the substrate 1 by a high frequency plasma chemical vapor deposition method.
[0038]
The high frequency plasma chemical vapor deposition conditions are as follows.
Source gas: silane, ammonia, hydrogen.
Ammonia flow rate (variable condition): 3% to 15% (volume flow rate relative to total gas flow rate).
Reaction pressure: 133 Pa (1 Torr).
High frequency power: 180W.
Substrate temperature: 400 ° C.
[0039]
Film thickness: 200 nm.
[0040]
Various analyzes were performed on the thin film 2 obtained under the above conditions. As a result, the thin film 2 had a composition close to the stoichiometry (nitrogen / silicon = 1.3) and contained 10 to 20 atomic% of hydrogen. I understood. Also, no peak was observed from X-ray diffraction, and it was found that the substance was amorphous.
[0041]
Next, photoluminescence spectra of four types of silicon nitride films formed under different conditions of ammonia flow rate were evaluated. A 325 nm helium-cadmium laser was used as the laser. The silicon nitride film was irradiated with the laser light through a microscope having a focusing optical system. At the same time, the photoluminescence light was energy-decomposed in the range of 300 nm to 800 nm using a grating to obtain a spectrum. The irradiation area was 5 μm in diameter. The minimum irradiation area can be up to 1 μm in diameter.
[0042]
As a result, as shown in FIG. 2, it was shown that there was a strong correlation between the stress measured by the warpage of the wafer and the intensity of the photoluminescence peak value (2.1 eV). Note that 2.1 eV corresponds to 585 nm. Furthermore, the results of the evaluation made with the volume ratio of the flow rate of ammonia to the total flow rate being 6% and 10% also agree well with the calibration curve A.
[0043]
From these results, it is understood that the film stress can be estimated from the photoluminescence peak intensity and quantified by using the obtained result as a calibration curve.
[0044]
That is, in the stress evaluation method according to the embodiment of the present invention, the use of the calibration curve A as shown in FIG. It is possible to evaluate the stress distribution above.
[0045]
Although the preferred embodiments of the present invention have been described with reference to the accompanying drawings, the present invention is not limited to such configurations. Within the scope of the invented technical concept of the claims, those skilled in the art will be able to conceive various changes and modifications, and those changes and modifications will be described in the technical scope of the present invention. It is understood that it belongs to.
[0046]
【The invention's effect】
As described above in detail, according to the present invention, amorphous silicon and its compound thin film formed on a substrate are evaluated for stress based on the result of photoluminescence measured by irradiating a laser. Can be. Therefore, it is possible to evaluate the stress in the minute region and the distribution of the stress in a non-destructive manner.
[Brief description of the drawings]
FIG. 1 is an elevation view showing an example of amorphous silicon whose stress is evaluated by a stress evaluation method according to an embodiment of the present invention; FIG. 2 is an elevation view illustrating an amorphous silicon evaluated by a stress evaluation method according to an embodiment of the present invention; FIG. 4 is a correlation diagram between the applied stress and the photoluminescence intensity.
[Explanation of symbols]
1: substrate, 2: thin film, A: calibration curve

Claims (4)

In stress evaluation of amorphous silicon and its compound thin film formed on the substrate,
A stress evaluation method that uses a laser as a light source and measures and analyzes the photoluminescence spectrum to evaluate the stress or stress distribution of the film. The stress evaluation method according to claim 1, wherein the amorphous silicon and its compound thin film are hydrogenated amorphous silicon and its compound thin film. The stress evaluation method according to claim 1 or 2, wherein the amorphous silicon compound thin film is an amorphous silicon nitride thin film or a hydrogenated amorphous silicon nitride thin film. The stress evaluation method according to claim 1, wherein the substrate is made of single crystal silicon or quartz.

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