JP4287692B2 - Stress evaluation method for compound thin film of amorphous silicon - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a stress evaluation method for a compound thin film of amorphous silicon , and more particularly, for example, as a semiconductor layer, a resistance layer, a gate insulating film, an interlayer insulating film, a passivation film in a semiconductor device, or an X-ray exposure apparatus. The present invention relates to a stress evaluation method for a compound thin film of amorphous silicon used as a mask constituent material in a charged particle beam exposure apparatus.
[0002]
[Prior art]
Due to the development of semiconductor and metal thin film fabrication technology and microfabrication technology, integrated circuits using single crystal silicon and compound semiconductors, flat panel display devices using amorphous semiconductor thin films, and various sensors are rapidly emerging. Is popular.
[0003]
In the functional devices as 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, insulating properties, and dielectric properties, high adhesion to different materials is required. In addition to the composition of the interface, the adhesion is greatly influenced by the stress of the film. When the stress is large, the film peels off from the base material. In order to prevent this, it is essential to measure and control the stress of the amorphous silicon film or the amorphous silicon compound film for each element.
[0005]
Further, the miniaturization of the semiconductor element as described above is rapidly progressing. In the semiconductor process technology, various exposure technologies have been developed as a technology for manufacturing an element having such a fine pattern. Among them, charged particle beam exposure and X-ray exposure using electrons, ions, and the like are attracting attention as exposure technology based on the sub-μm rule.
[0006]
In such an exposure technique, a mask is used to form a charged particle beam or X-ray. These masks include amorphous materials such as an amorphous silicon thin film, an amorphous silicon nitride thin film, or an amorphous silicon carbide thin film as a mask material or a constituent material of a mask such as a membrane, or as a stress adjusting film. A silicon compound thin film is used.
[0007]
In this case, the amorphous silicon or its compound thin film is often used as a free-standing film. In order to apply amorphous silicon or a compound thin film thereof as such a member, it is indispensable to measure and control the stress of those films.
[0008]
[Non-Patent Document 1]
"Applied physics selection thin film" (pages 127 to 146), published by Jun Kanbara and Hideo Fujiwara, Junkabo 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 for measuring the strain of a crystal lattice by X-ray or electron diffraction or Raman spectroscopy and calculating the stress is disclosed in Non-Patent Document 1, for example. ing. However, silicon and its compound thin films in 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, the stress cannot be measured by the above-described method.
[0010]
On the other hand, as evaluation methods that do not depend on the crystallinity of the film, there are known an evaluation method based on the amount of change in warping of the substrate and a bulge method in which the film is processed into a membrane state and evaluated based on the amount of deformation.
[0011]
However, in the evaluation method in which the change amount of the warp of the substrate is observed, only the average value of the stress of the entire substrate can be evaluated. That is, it is impossible in principle to evaluate a stress in a minute region or an in-plane stress distribution.
[0012]
In addition, in the bulge method, it is possible to evaluate the stress in the submillimeter order region and the stress distribution in the range that can be processed by processing into a membrane membrane shape using micro processing technology, but it is necessary to process the substrate, Nondestructive measurement is impossible. Further, evaluation of a micro area on the order of μm and evaluation of stress distribution by fine area division are impossible.
[0013]
The present invention has been made in view of such circumstances, stress and stress distribution in the small region of the compound thin film of amorphous silicon, nondestructive and readily evaluated amorphous silicon capable of It aims at providing the stress evaluation method of a compound thin film.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, the present invention takes the following measures.
[0015]
That is, the stress evaluation method of the invention of claim 1, Ru method der to evaluate the stress of the hydrogenated amorphous silicon nitride film formed on a substrate. Here, the nitrogen / silicon stoichiometry in the hydrogenated amorphous silicon nitride film is 1.3. Then, using a laser as a light source, measuring the photoluminescence spectrum of the hydrogenated amorphous silicon nitride film, a large photoluminescence intensity due to binding of hydrogen and silicon contained in the hydrogenated amorphous silicon nitride film The correlation between the peak intensity of the photoluminescence and the stress of the hydrogenated amorphous silicon nitride film is grasped, and the stress or the stress distribution of the hydrogenated amorphous silicon nitride film is evaluated using the correlation.
[0016]
Thus, in the stress evaluation method of hydrogenated amorphous silicon nitride film of the invention of claim 1, by taking measures such as described above, the nondestructive spectra in the small region of the film formed on the substrate It is possible to easily measure and detect photoluminescence having high intensity due to the bond between hydrogen and silicon contained in the amorphous silicon nitride film in which the nitrogen / silicon stoichiometry ratio is 1.3 . Then, by using the correlation between the peak intensity of the photoluminescence and hydrogenated amorphous silicon nitride film stress, the stress of the hydrogenated amorphous silicon nitride film can be evaluated with high accuracy. In particular, since the peak value is clear and high in intensity from 2.0 eV to 2.4 eV, the film stress can be evaluated with higher accuracy. Further, it is possible to easily obtain the spectral distribution of the film by scanning the laser as the light source or the substrate of the film to be evaluated.
[0021]
According to a second aspect of the present invention, in the stress evaluation method according to the first aspect, the substrate is single crystal silicon or quartz.
[0022]
When the substrate is made of single crystal silicon or quartz as in the second aspect of the invention described above, the photoluminescence can be produced in any energy region where the photoluminescence spectrum of the hydrogenated amorphous silicon nitride film can be obtained. Since there is nothing, a high S / N ratio can be obtained, and the film stress can be evaluated with higher accuracy.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0024]
FIG. 1 is an elevation view showing 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, the stress evaluation method according to the embodiment of the present invention uses a laser as a light source in the stress evaluation of amorphous silicon on the substrate 1 and its compound thin film 2, and measures and analyzes the photoluminescence spectrum. 2 stress, in particular, a stress in a minute region, or a stress distribution.
[0026]
This utilizes the characteristic 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 attributed to the film structure, and other optical physical properties such as optical band gap and electroluminescence, and electrical physical properties such as electrical conductivity have a correlation with stress. There may be.
[0027]
However, in the other physical properties described above, the material of the substrate 1 is limited for evaluation, and it is necessary to form an electrode or the like. Have difficulty.
[0028]
On the other hand, in the photoluminescence measurement using the laser as the light source as described above, the spectrum in a minute region can be easily obtained without destructing the thin film 2 formed on the substrate 1. Further, it is possible to easily obtain the spectral distribution of the thin film 2 by scanning the laser as the light source or the substrate 1 of the film to be evaluated.
[0029]
Then, as a result of examining in detail the relationship between the photoluminescence spectrum measurement in various amorphous silicon-based thin films, the analysis thereof and the stress measured by other methods, for example, as shown in FIG. And found the correlation of stress. That is, it was found that the spectrum intensity or 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 amorphous silicon containing a large amount of hydrogen in the film 2 and its compound thin film, photoluminescence having a higher intensity due to the silicon-hydrogen or nitrogen-hydrogen bond can be obtained. Can be evaluated.
[0032]
This 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 the peak value is clear and high in strength particularly from 2.0 eV to 2.4 eV, the film stress can be evaluated with higher accuracy. It becomes possible.
[0034]
Further, it is more effective when the substrate 1 is single crystal silicon or quartz.
[0035]
That is, when the substrate 1 is a single crystal silicon or quartz substrate, since there is no photoluminescence at all in the energy region where the photoluminescence spectrum of the amorphous silicon and the compound thin film is obtained, a high S / N ratio is obtained. As a result, the stress of the thin film 2 can be evaluated with higher accuracy.
[0036]
Next, a specific example in the case where the stress of the thin film 2 of amorphous silicon and its compound is evaluated by the stress evaluation method as described above will be described.
[0037]
First, a method for producing 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 producing such an evaluation sample, first, a thin film 2 made of silicon nitride is formed on a 4-inch single crystal silicon wafer as a substrate 1 by high-frequency plasma chemical vapor deposition.
[0038]
The high-frequency plasma chemical vapor deposition conditions are as follows.
Source gas: Silane, ammonia, hydrogen.
Ammonia flow rate (variable conditions): 3% to 15% (volume flow rate% relative to total gas flow rate).
Reaction pressure: 133 Pa (1 Torr).
High frequency power: 180 W.
Substrate temperature: 400 ° C.
[0039]
Film thickness: 200 nm.
[0040]
As a result of conducting various analyzes on the thin film 2 obtained under the above conditions, all have a composition close to stoichiometry (nitrogen / silicon = 1.3) and contain 10 to 20 atomic% hydrogen. I understood. Further, X-ray diffraction revealed no peak and was found to be amorphous.
[0041]
Next, photoluminescence spectra of arbitrary four types of silicon nitride films formed under conditions with different ammonia flow rates were evaluated. A 325 nm helium-cadmium laser was used as the laser. The silicon nitride film was irradiated with this laser light through a microscope having a condensing optical system. At the same time, photoluminescence light was energy-resolved 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 is a strong correlation between the stress measured by the warpage of the wafer and the intensity of the photoluminescence peak value (2.1 eV). 2.1 eV corresponds to 585 nm. Furthermore, the results of the production and evaluation with the volume ratio of the flow rate of ammonia with respect to the total flow rate of 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 and quantified from the photoluminescence peak intensity 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, by using the calibration curve A as shown in FIG. 2 as an example, the film stress in the non-destructive and smaller 1 μm diameter region and the 4-inch wafer It is possible to evaluate the stress distribution above.
[0045]
As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, this invention is not limited to this structure. Within the scope of the invented technical idea of the claims, those skilled in the art will be able to conceive various changes and modifications, and these changes and modifications are also within 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, the compound thin film of amorphous silicon was deposited on the substrate, to evaluate the stress based on the results of photoluminescence measured by irradiating a laser it can. Therefore, it is possible to evaluate the stress in the micro area 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 the stress evaluation method according to the embodiment of the present invention. FIG. 2 is evaluated by the stress evaluation method according to the embodiment of the present invention. FIG. 6 is a correlation diagram between the stress and the photoluminescence intensity.
[Explanation of symbols]
1 ... Substrate, 2 ... Thin film, A ... Calibration curve

Claims (2)

In the stress evaluation method of the hydrogenated amorphous silicon nitride film formed on the substrate,
The nitrogen / silicon stoichiometric ratio in the hydrogenated amorphous silicon nitride film is 1.3.
Using a laser as a light source, the photoluminescence spectrum of the hydrogenated amorphous silicon nitride film is measured, and photoluminescence with high intensity due to the bond between hydrogen and silicon contained in the hydrogenated amorphous silicon nitride film is obtained. And detecting the correlation between the peak intensity of the photoluminescence and the stress of the hydrogenated amorphous silicon nitride thin film, and using the correlation, the stress or stress distribution of the hydrogenated amorphous silicon nitride film is determined. Stress evaluation method to be evaluated.   The stress evaluation method according to claim 1, wherein the substrate is single crystal silicon or quartz.

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