JPH10214869A - Method for evaluating crystallized thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To evaluate a crystallized thin film non-destructively and on the spot of a crystallization process by applying light for measuring the transmission factor of a specific wavelength on a crystallized crystallization thin film and measuring the transmission of the crystallized thin film. SOLUTION: In a crystallization process for forming a crystallized Si thin film by applying an energy beam 7 for crystallization to an amorphous Si thin film 6 on a light transmission substrate 5, a beam 8 for measuring a transmission factor with a wavelength of 380-650nm is applied to the crystallized Si thin film 9 to measure the transmission factor of the crystallized Si thin film. Then, the transmission factor applying the energy beam 7 for crystallization, namely the transmission factor of the beam 8 in the state of the amorphous Si thin film 6, is measured by a photo detector 10 and then the energy beam 7 for crystallization is applied to the amorphous Si thin film 6, thus measuring the transmission factor of the beam 8 for measuring the transmission factor of a part that turns to the crystallized Si thin film 9 with the photo detector 10 and both values are compared, thus detecting the change in the transmission factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a crystallized thin film used in a manufacturing process of a thin film transistor, an image sensor, an SRAM, etc. for a liquid crystal display device.

[0002]

2. Description of the Related Art In recent years, a liquid crystal display device has been increasing in size and definition more and more, and it is indispensable to improve the performance of a thin film transistor as a driving element.

At present, the mainstream of thin film transistors used in liquid crystal display devices is amorphous Si thin film transistors, but they are shifting to polycrystalline Si thin film transistors which have advantages such as improvement in element performance and incorporation of a substrate.

[0004] As the polycrystalline thin film forming technology,
Compared with the conventional high-temperature forming technique in which usable substrates are limited to quartz substrates, low-temperature (about 600 ° C. or lower) forming techniques that can use inexpensive low-strain-point glass substrates have been actively developed. In particular, excimer laser annealing, which has a small thermal damage to a substrate and melts and crystallizes an amorphous thin film to obtain a high-quality polycrystalline thin film, is a technique which is most practically used.

FIG. 5 is a schematic diagram illustrating an example of a process of crystallizing an amorphous Si thin film by excimer laser annealing. Reference numeral 1 denotes an amorphous Si thin film formed on a transparent substrate 2; Reference numerals 3b, 3c, and 3d denote crystallized thin films irradiated with the excimer laser beam 4 and changed from the region of the amorphous Si thin film 1. As shown in FIG. 5, first, an excimer laser beam 4 is irradiated once (one pulse) on the amorphous Si thin film 1 formed on the light transmitting substrate 2. The Si in the irradiated area undergoes a melt-solidification process of about 100 ns to form a crystallized Si thin film area, that is, a crystallized thin film 3.
a. Next, the excimer laser beam 4 is moved once relative to the amorphous Si thin film 1 on the translucent substrate 2 so as to overlap a part of the previous irradiation area, and then irradiated once. At this point, the newly crystallized Si
A thin film region, that is, a crystallized thin film 3b is formed. Thereafter, by repeating the same procedure, regions of the crystallized Si thin film, that is, crystallized thin films 3c and 3d are formed.

The crystallized thin films 3a, 3b, 3c and 3d obtained by such excimer laser annealing may be caused by instability factors such as variations in the thickness of the amorphous Si thin film 1 and variations in the pulse of the excimer laser beam 4. Therefore, in order to obtain a stable crystallized thin film, it is important to establish an appropriate evaluation method for the crystallized thin film.

In general, as a method for evaluating a crystallized thin film,
Raman spectroscopy, X-ray diffraction, direct observation with a transmission electron microscope, and the like are used.

However, all of these methods require expensive equipment and require a long time for evaluation and analysis, and thus cannot be said to be simple methods.

On the other hand, as one of simple evaluation methods, there is a method of analyzing a spectral reflection spectrum in an ultraviolet region. FIG.
Is a spectral reflection spectrum diagram in the ultraviolet region of a Si thin film crystallized by excimer laser annealing, in which the horizontal axis represents the wavelength of reflected light (nm), the vertical axis represents the reflectance (%) of the crystallized Si thin film, and the dotted line in the figure. Is the reflection characteristic curve of the amorphous Si thin film,
The solid line shows the reflection characteristic curve of the crystallized Si thin film. FIG. 6 shows that as the crystallization of the Si thin film progresses, the reflectance of the band around the wavelength of about 270 nm of the reflected light increases. The crystallized thin film can be evaluated by detecting the change in the reflectance. However, such light having a wavelength in the ultraviolet region is mainly reflected on the surface of the thin film, and is not suitable for evaluating the crystallinity in the depth direction of the thin film. For a method of evaluating a crystallized thin film using a spectral reflection spectrum in the ultraviolet region, see, for example, Japanese Applied Physics VOL. 25, No. 2 (1986
Year) L121 page to L123 page (Japanese)
Journal of Applied Physic
s Vol. 25, No. 2 (1986) pp. L1
21 to L123).

On the other hand, there is a method of analyzing a spectral transmission spectrum. FIG. 7 is a spectral transmission spectrum diagram when the amorphous Si thin film is crystallized by excimer laser annealing. The horizontal axis is the wavelength of transmitted light (nm), the vertical axis is the transmittance of the substrate and the Si thin film (%), In the figure, the dotted line indicates the transmission characteristic curve of the amorphous Si thin film, and the solid line a indicates the laser intensity of 400 mJ /.
The transmission characteristic curve of the crystallized Si thin film when crystallized at cm ² , and the solid line b shows the transmission characteristic curve of the crystallized Si thin film when crystallized at a laser intensity of 250 mJ / cm ² . FIG.
This indicates that the optical absorption edge of the Si thin film to be crystallized shifts to the shorter wavelength side, so that, for example, the transmittance at 400 nm increases as the crystallization proceeds from the amorphous state. This method of analyzing the spectral transmission spectrum is a method suitable for averaging and evaluating the entire thin film in order to detect light transmitted from the surface to the bottom surface of the thin film.

[0011]

However, in both of the conventional methods of analyzing a spectral reflection spectrum and a method of analyzing a spectral transmission spectrum, the conventional methods for evaluating a crystallized thin film separately from the crystallization step. Inspection time is required, and many spectrometers have to be cut into several tens of mm squares as objects to be measured. It was not very suitable as an evaluation method.

According to the present invention, a crystallized thin film is non-destructively and
It is an object of the present invention to provide a method for evaluating a crystallized thin film to be evaluated in-situ in a crystallization step.

[0013]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a method for irradiating an amorphous thin film on a transparent substrate with a crystallization energy beam to form a crystallized thin film. Wavelength of 380 on the crystallized crystallized thin film
This is a method of evaluating a crystallized thin film by measuring the transmittance of the crystallized thin film by irradiating light for transmittance measurement at 650 nm, and cutting the crystallized thin film in-situ in the crystallization step of forming the crystallized thin film. The crystallized thin film can be evaluated in a non-destructive state.

[0014]

DETAILED DESCRIPTION OF THE INVENTION According to the first aspect of the present invention, there is provided a crystallization step of irradiating an amorphous thin film on a light-transmitting substrate with a crystallization energy beam to form a crystallized thin film. At a wavelength of 380 to 650 nm on the crystallized thin film.
This is a method for evaluating the crystallized thin film by measuring the transmittance of the crystallized thin film by irradiating light for measuring the transmittance of the crystallized thin film. Since the transmittance of the crystallized thin film is measured by irradiating the crystallized thin film, the inspection time is not required separately from the crystallization step for the transmittance measurement, and the crystallized thin film is cut. The crystallized thin film can be evaluated in a non-destructive state.

According to a second aspect of the present invention, the energy beam for crystallization of the amorphous thin film has a wavelength of 180 to 320.
2. The method for evaluating a crystallized thin film according to claim 1, wherein the glass substrate is used as a light-transmitting substrate on which an amorphous thin film is formed by using an ultraviolet laser beam having a wavelength of 180 to 320 nm. In this case, since the glass has a low transmittance to ultraviolet light, a photodetector provided behind the light-transmitting substrate does not require a special high light-resistance ultraviolet light shielding filter.

The invention according to claim 3 of the present invention is the method for evaluating a crystallized thin film according to claim 2, wherein the ultraviolet laser beam is an excimer laser beam. When a glass substrate is used as the light-transmitting substrate on which the glass is formed, the glass has a low transmittance for ultraviolet light, so a special high light-resistance ultraviolet light-shielding filter is required for the photodetector provided behind the light-transmitting substrate. And not.

According to a fourth aspect of the present invention, there is provided an irradiation region of an amorphous thin film with a crystallization energy beam,
At least a part of the irradiation area of the light for transmittance measurement irradiated on the crystallized crystallized thin film overlaps, and the light transmitted through the crystallized thin film and the light transmitting substrate is detected to reduce the transmittance of the crystallized thin film. The method for evaluating a crystallized thin film according to claim 1, wherein the irradiation region of the energy beam for crystallization and the irradiation region of the light for transmittance measurement are at least partially overlapped with each other. Since the light for transmittance measurement transmitted through the optical substrate is used, another device is not required for measuring the light for transmittance measurement.

According to a fifth aspect of the present invention, there is provided the crystal according to the first, second, third, or fourth aspect, wherein the amorphous thin film mainly comprises Si (silicon). This is a method for evaluating a thin film.

An embodiment of the method for evaluating a crystallized thin film according to the present invention will be described below with reference to the drawings.

(Embodiment 1) FIG. 1 is an explanatory view of an evaluation process of an evaluation method of a crystallized thin film according to Embodiment 1 of the present invention.
FIG. 2 is a partial plan view of the explanatory view of the evaluation step of FIG. 1, in which a crystallization energy beam 7 composed of an excimer laser and a He-N
A light 8 for transmittance measurement composed of an e-laser beam (wavelength 633 nm) is irradiated along the same optical axis, and the crystallized Si thin film 9 on the light-transmitting substrate 5 changed by the irradiation of the energy beam 7 for crystallization. The same part as the light 8 for transmittance measurement
And the light 8 for transmittance measurement transmitted through the crystallized Si thin film 9 and the translucent substrate 5 is incident on the photodetector 10,
Measure the transmittance.

With such a configuration,
The transmittance before irradiation of the energy beam 7 for crystallization, that is,
The transmittance of the light 8 for transmittance measurement in the state of the amorphous Si thin film 6 is measured by the photodetector 10, and then,
By irradiating the amorphous Si thin film 6 with the energy beam 7 for crystallization, the transmittance of the light 8 for transmittance measurement in the portion that has become the crystallized Si thin film 9 is measured by a photodetector 10 and the values of both are measured. By comparison, the Si before and after crystallization
A change in the transmittance of the thin film can be detected. Where S
As shown in the spectral transmission spectrum diagram of FIG. 7, the transmittance of the i thin film is determined from the transmittance in the amorphous state before irradiation with the energy beam for crystallization 7 to the transmittance in the crystallized state after irradiation. Increase.

(Embodiment 2) FIG. 3 is an explanatory view of an evaluation process of a method for evaluating a crystallized thin film according to Embodiment 2 of the present invention.
FIG. 4 is a partial plan view of the evaluation step explanatory view of FIG. 3, and FIG. 3 and FIG. 4 are different from FIG. 1 and FIG. 2 showing the first embodiment in that a crystallization energy beam composed of an excimer laser is used. By scanning and irradiating the amorphous Si thin film, only the portion that has become the crystallized Si thin film extends in a band shape on the amorphous Si thin film, and the other points are the same. 1 and FIG. 2 are denoted by the same reference numerals, and description thereof is omitted. Numeral 11 denotes a crystallization energy beam composed of an excimer laser for scanning and irradiating the amorphous Si thin film 6 on the translucent substrate 5.
On the i thin film 6, a crystallized Si thin film 12 changed into a band shape is formed. In this case, the energy beam for crystallization 1
Since it is only necessary that the scanning of 1 can be performed relatively, either the translucent substrate 5 or the energy beam 11 for crystallization may be scanned. Further, the photodetector 10 on which the light 8 for transmittance measurement that has passed through the crystallized Si thin film 12 and the light transmitting substrate 5 must be relatively stationary with respect to the light 8 for transmittance measurement.

As in the first embodiment, the transmittance of the Si thin film is measured by detecting the light 8 for transmittance measurement that has passed through the crystallized Si thin film 12 and the translucent substrate 5 with the photodetector 10 as in the first embodiment. Is what you do.

In the first and second embodiments, the irradiation area of the transmittance measuring light 8 at least partially overlaps the irradiation area of the crystallization energy beams 7 and 11 on the amorphous Si thin film 6. Although the irradiation is performed along the same optical axis, the light 8 for transmittance measurement and the energy beams 7 and 11 for crystallization have the same optical axis even if their irradiation areas need to partially overlap. It is not necessary that they have the same cross-sectional shape.

In general, a glass substrate is used as the translucent substrate 5. However, since glass has a low transmittance with respect to ultraviolet light, excimer laser beams of the crystallization energy beams 7, 11 are continuously and repeatedly irradiated. In this case, no special high lightfast ultraviolet light shielding filter is required on the optical path to the photodetector 10.

Further, the cross-sectional shape of the beam is not particularly limited. For example, a beam having a linear cross section (a beam width of one axis is extremely shorter than the beam width of the other axis) may be used.

Although the Si thin film has been described as a crystallized thin film, the same applies to other crystallized thin films, for example, a Ge thin film.

[0028]

As described above, according to the method for evaluating a crystallized thin film of the present invention, the on-site evaluation of the crystallization step is possible, and the post-inspection step is omitted, which is effective for improving the productivity. . In addition, it is possible to evaluate not only the sampling but also the total number, which is effective for improving the yield. Further, since the evaluation is non-destructive, an advantageous effect of improving productivity can be obtained.

[Brief description of the drawings]

FIG. 1 is an explanatory view of an evaluation step of an evaluation method of a crystallized thin film according to a first embodiment of the present invention.

FIG. 2 is a partial plan view of the evaluation step explanatory view of FIG. 1;

FIG. 3 is an explanatory view of an evaluation step of an evaluation method of a crystallized thin film according to the second embodiment of the present invention.

FIG. 4 is a partial plan view of the evaluation step explanatory view of FIG. 3;

FIG. 5 is a schematic process diagram illustrating an example of a crystallization process of an amorphous Si thin film.

FIG. 6 is a spectral reflection spectrum diagram of a Si thin film in an ultraviolet region.

FIG. 7 is a spectral transmission spectrum diagram when an amorphous Si thin film is crystallized by excimer laser annealing.

[Explanation of symbols]

 1,6 Amorphous Si thin film 2,5 Transparent substrate 3a, 3b, 3c, 3d Crystallized thin film 4 Excimer laser beam 7,11 Energy beam for crystallization 8 Light for transmittance measurement 9,12 Crystallized Si Thin film 10 Photodetector

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI H01L 21/336 H01L 29/78 627G

Claims (5)

[Claims] In a crystallization step of irradiating an amorphous thin film on a light-transmitting substrate with a crystallization energy beam to form a crystallized thin film, a wavelength of 380-6 is applied to the crystallized crystallized thin film.
A method for evaluating a crystallized thin film in which the transmittance of the crystallized thin film is measured by irradiating light for measuring the transmittance of 50 nm. 2. The method for evaluating a crystallized thin film according to claim 1, wherein the energy beam for crystallization of the amorphous thin film is an ultraviolet laser beam having a wavelength of 180 to 320 nm. 3. The method according to claim 2, wherein the ultraviolet laser beam is an excimer laser beam. 4. The crystallization energy beam irradiation region on the amorphous thin film and the transmittance measurement light irradiation region irradiated on the crystallized crystallized thin film at least partially overlap each other. The method for evaluating a crystallized thin film according to claim 1, wherein the transmittance of the crystallized thin film is measured by detecting light transmitted through the translucent substrate. 5. The method for evaluating a crystallized thin film according to claim 1, wherein the amorphous thin film mainly comprises Si (silicon).