JP2008066356A - Method and apparatus for laser annealing - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and an apparatus for laser annealing y which the absorption of a laser beam can be improved and an influence of film thickness be also reduced when a semiconductor film is subject to laser annealing by using the wavelength conversion light of solid laser. <P>SOLUTION: A p-polarized laser beam 4 of which electric field vector is parallel to the incident surface of a semiconductor film 1a is produced, and it is given to the semiconductor film at an incident angle θ where the absorption of the laser beam exceeds 50%. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a laser annealing method and apparatus for annealing a semiconductor film using a laser beam.

Laser annealing is treatment for improving crystallinity by irradiating a semiconductor film formed over an insulating substrate with a laser beam. A quartz substrate or a glass substrate is used as the insulating substrate. A glass substrate is suitable for a large-area substrate as compared with a quartz substrate, and a substrate size of 600 mm × 720 mm has already been put into practical use.
The semiconductor film is generally a silicon film (Si), and an amorphous film (amorphous Si: a-Si) or a polycrystalline film (polycrystalline Si: p-Si) is a target for laser annealing.

In the field of semiconductors and liquid crystals, laser annealing is used as a means for polycrystallizing amorphous Si (a-Si) formed on a glass substrate.
Conventionally, an excimer laser has been mainly used as the laser for laser annealing. The excimer laser has the advantage that the silicon film (Si) has high absorptivity because it emits ultraviolet light, and the productivity is high because it has a large output.
However, excimer lasers are expensive, have a short lifetime, and are not easily maintainable. In recent years, laser annealing using wavelength-converted light (visible light) of solid lasers such as YAG, YLF, and YVO4 has been proposed as an alternative laser beam. (For example, Patent Documents 1 to 3).
Further, in polycrystalline Si (p-Si) and crystalline Si devices, attention has been paid that the wavelength-converted light of a solid-state laser can be used for processes such as impurity activation.

  The method of Patent Document 1 aims to uniformize the energy distribution of a laser beam having high coherence. As shown in FIG. 6, the laser beam is irradiated in a first direction perpendicular to the traveling direction of the laser beam. The laser beam is split into two laser beams 51 and 52 having polarization directions that are independent from each other, and the two laser beams are combined into one at or near the irradiation surface 53, perpendicular to the traveling direction of the laser beam, and The laser beam is divided into a plurality of laser beams having different optical path lengths in a second direction perpendicular to the one direction, and the plurality of laser beams are combined into one at or near the irradiation surface 53. Is.

The apparatus of Patent Document 2 aims to be able to generate a semiconductor film with good characteristics. As shown in FIG. 7, a laser having a laser oscillator 62 that outputs laser light that can activate or crystallize a semiconductor film 61 of a substrate. An optical system 63 and a substrate support structure for supporting the substrate are provided, and the intersection angle between the optical axis of the laser beam 64 on the irradiation surface of the substrate and the orthogonal axis of the irradiation surface of the substrate is set to a predetermined value δ. It is characterized by doing.
The predetermined value δ is a range in which the laser light reflected on the substrate surface and the laser light reflected on the back surface of the substrate do not interfere with each other, and preferably 10 degrees or more and 30 degrees or less.

  The method of Patent Document 3 aims to improve the energy utilization efficiency in the laser annealing treatment of the amorphous silicon film. As shown in FIG. 8, the laser beam 72 oscillated from the solid-state laser oscillation device 71 is wavelength-converted. A method of manufacturing a semiconductor device in which a laser annealing process is performed on an amorphous silicon film 75 using a second harmonic 74 obtained by passing through a conversion crystal 73, the second harmonic 74 obtained by wavelength conversion; The mixed silicon wave combined with the fundamental wave 72 that has passed through the wavelength conversion crystal without being subjected to wavelength conversion is irradiated onto the amorphous silicon film 75.

Japanese Patent Application Laid-Open No. 2002-190454, “Laser beam processing method, laser irradiation apparatus, and semiconductor device manufacturing method” JP-A-2002-231655, “Laser annealing apparatus” Japanese Patent Application Laid-Open No. 2003-347237, “Method for Manufacturing Semiconductor Device and Apparatus for Manufacturing the Same”

The wavelength of an excimer laser, which has been mainly used as a laser annealing laser, is 308 nm (XeCl) and 248 nm (KrF), which are ultraviolet light, and has a high silicon film (Si) absorbability and absorptance. Was around 40 to 50% with respect to a-Si having a film thickness of 20 to 80 nm.
On the other hand, the wavelength of the solid-state laser for laser annealing uses wavelength-converted light in order to increase the absorptance. Even in this case, visible light, for example, 527 nm (YLF), 532 nm (YAG, YVO ₄ ) And the absorption rate is low (usually less than 20%).
Further, the absorptance of the solid laser is greatly affected by the film thickness, and there is a problem that the absorptance varies from about 15% to about 50% for a-Si having a film thickness of 20 to 80 nm. Therefore, there is a problem that the crystal state of p-Si varies depending on the location due to the non-uniformity of the film thickness when forming the a-Si film.

  The present invention has been made in view of the above-described problems. That is, an object of the present invention is to provide a laser annealing method and apparatus capable of increasing the absorption rate of a laser beam and reducing the influence of the film thickness in laser annealing of a semiconductor film using wavelength conversion light of a solid-state laser. There is to do.

As a result of examining the a-Si and p-Si absorption rates when using visible light from a solid-state laser, when the incident angle is increased, the change in the absorption rate of the laser beam varies between p-polarized light and s-polarized light. I found that it changed a lot.
In particular, in the case of p-polarized light, the absorptance increases as the incident angle increases. When the film thickness is 50 nm or more, it is higher than 50% in both the amorphous film and the polycrystalline film at an incident angle of 40 ° or more. It was found that the absorption rate.
This is presumably because the reflectance of p-polarized light decreases as the Brewster angle (a-Si: 78.4 °, p-Si: 76.3 °) of the semiconductor film is approached.
In addition, as a result of estimating the change in the absorptance with respect to the film thickness at each incident angle, it was found that the amount of change in the absorptance with respect to the film thickness decreases as the incident angle increases, and is almost constant particularly at an incident angle of 80 °.
The present invention is based on such novel findings.

That is, according to the present invention, a laser annealing method of a semiconductor film using a laser beam,
Generating a p-polarized laser beam whose electric field vector is parallel to the semiconductor film;
There is provided a laser annealing method characterized by irradiating the semiconductor film with the p-polarized laser beam at an incident angle θ in which the absorption rate of the laser beam exceeds 50%.

According to a preferred embodiment of the present invention, the laser beam is a solid-state laser beam of YAG, YVO ₄ , YLF or YAG;
The wavelength of the solid state laser beam is 532 nm, 527 nm, or 355 nm.

The incident angle θ is 65 ° or more and 85 ° or less for a semiconductor film having a thickness of 50 nm or more.
The incident angle θ is preferably ± 5 ° or less with respect to the Brewster angle of the semiconductor film.

  The semiconductor film is an amorphous film or a polycrystalline film.

According to the present invention, there is also provided a laser annealing apparatus for a semiconductor film using a laser beam,
A laser generator for generating a p-polarized laser beam having an electric field vector parallel to the semiconductor film;
There is provided a laser annealing apparatus comprising: an irradiation apparatus that irradiates a semiconductor film with the p-polarized laser beam at an incident angle θ with an absorption rate of the laser beam exceeding 50%.

  According to a preferred embodiment of the present invention, the irradiation apparatus includes an irradiation angle adjuster that can variably adjust the incident angle θ.

The laser beam of the laser oscillator is a solid laser beam of YAG, YVO ₄ , YLF or YAG,
The wavelength of the solid-state laser beam is preferably 532 nm, 527 nm, or 355 nm.

  According to the above-described method and apparatus of the present invention, the semiconductor film is irradiated with a p-polarized laser beam having an electric field vector parallel to the semiconductor film at an incident angle θ in which the absorption rate of the laser beam exceeds 50%. The reflectance of p-polarized light can be reduced, and the absorption rate of the laser beam can be increased.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. In addition, the same code | symbol is attached | subjected to the common part in each figure, and the overlapping description is abbreviate | omitted.

FIG. 1 is a configuration diagram of a laser oscillator 10 constituting the laser annealing apparatus of the present invention. Among these, (A) is an external wavelength conversion system, and (B) is an internal wavelength conversion system.
1A and 1B, 5 is a laser solid medium (for example, YAG rod), 6 is a laser diode for exciting the laser medium, and 7 and 8 are reflection mirrors constituting a Fabry-Perot type resonator. With this configuration, the infrared laser beam 2 determined by the solid medium is generated and amplified between the reflection mirrors 7 and 8.
In the figure, reference numeral 9 denotes a wavelength conversion crystal, which has a function of setting the wavelength of the infrared laser beam 2 to 1 / n (n is an integer: 2 or 3). The wavelength conversion crystal 9 is provided outside the reflection mirrors 7 and 8 in (A) and inside the reflection mirrors 7 and 8 in (B).
The wavelength conversion crystal 9 has the function of converting the wavelength and simultaneously aligning the polarization direction thereof. Therefore, with this configuration, the laser beam oscillated (radiated) to the outside becomes the polarized laser beam 3 having a wavelength 1 / n of the infrared laser beam 2.

FIG. 2 is an overall configuration diagram of a laser annealing apparatus according to the present invention. FIG. 2A is a diagram illustrating a first embodiment, and FIG. 2B is a diagram illustrating a second embodiment.
2A and 2B, the laser annealing apparatus of the present invention includes a laser generator 11 and an irradiation device 14.
The laser generator 11 has a function of generating a p-polarized laser beam 4 having an electric field vector parallel to the incident surface of the semiconductor film 1a. In this example, the laser generator 11 includes a laser oscillator 10 and a converter 12.

The laser oscillator 10 may be either the external wavelength conversion method (A) or the internal wavelength conversion method (B) described above. The polarized laser beam 3 of the laser oscillator 10 is a solid laser beam of YAG, YVO ₄ , YLF or YAG, and the wavelength of this solid laser beam is preferably 532 nm, 527 nm, or 355 nm.

  That is, the laser oscillator 10 generates a polarized laser beam 3 in the visible region. In this example, the polarization direction of the polarized laser beam 3, that is, the electric field vector is s-polarized light perpendicular to the incident surface (upper surface in the drawing) of the semiconductor film 1 a formed on the insulating substrate 1. In this figure, s-polarized light is indicated by a vertical arrow.

The conversion device 12 has a function of converting the s-polarized polarized laser beam 3 into a p-polarized laser beam 4 having an electric field vector parallel to the semiconductor film. In this figure, p-polarized light is indicated by a double circle whose center is a black circle.
A λ / 2 plate can be used as the conversion device 12. The λ / 2 plate has an effect of rotating the polarization direction of the incident beam by twice the angle θ formed with the axis of the element.
If the polarized laser beam 3 is p-polarized light, the conversion device 12 can be omitted.

  The irradiation device 14 has a function of irradiating the incident surface of the semiconductor film 1a with the p-polarized laser beam 4 at an incident angle θ in which the absorption rate of the laser beam exceeds 50%. The incident angle θ is preferably 65 ° or more and 85 ° or less with respect to the semiconductor film 1a having a film thickness of 50 nm or more. Further, the incident angle θ is more preferably within a range of ± 5 ° or less with respect to the Brewster angle of the semiconductor film.

  In FIG. 2A, the irradiation device 14 includes a fixed reflection mirror 15a, a condenser lens 15b, a variable reflection mirror 15c, and a mirror tilting device 15d. The fixed reflection mirror 15a and the variable reflection mirror 15c irradiate the laser beam 4 to a desired position on the semiconductor film 1a, and the condenser lens 15b condenses the laser beam. The tilt of the variable reflecting mirror 15c is controlled by the mirror tilting device 15d so that the incident angle θ is adjusted to a desired angle.

In FIG. 2B, the irradiation device 14 includes a fixed reflecting mirror 16a, a variable condenser lens 16b, and a lens moving device 16c. The fixed reflection mirror 16a and the variable condensing lens 16b irradiate the laser beam 4 to a desired position on the semiconductor film 1a, and the variable condensing lens 16b condenses the laser beam. Further, the lens moving device 16c controls the position or inclination of the variable condenser lens 16b to adjust the incident angle θ to a desired angle.

In the method of the present invention using the apparatus described above, a p-polarized laser beam 4 having an electric field vector parallel to the incident surface of the semiconductor film 1a is generated, and this p-polarized laser beam 4 is absorbed by the laser beam. The incident surface of the semiconductor film 1a is irradiated at an incident angle θ with a rate exceeding 50%.
The laser beam is a solid laser beam of YAG, YVO ₄ , YLF or YAG, and the wavelength of the solid laser beam may be 532 nm, 527 nm, or 355 nm.
The incident angle θ is preferably 40 ° or more and less than or equal to the Brewster angle of the semiconductor film with respect to the semiconductor film having a thickness of 50 nm or more.
The semiconductor film 1a is preferably an amorphous film (for example, an a-Si film) or a polycrystalline film (for example, a p-Si film).

  FIG. 3 is a comparison diagram of the absorptivity of p-polarized light and s-polarized light, where (A) shows the case of an a-Si film and (B) shows the case of a p-Si film. In each figure, the horizontal axis represents the incident angle, the vertical axis represents the absorptance, Ip represents the p-polarized absorptance, and Is represents the s-polarized absorptivity. In this example, the wavelength of the solid-state laser beam is 532 nm and the thickness of the semiconductor film is 50 nm.

3A and 3B, it is understood that the absorptivity of the a-Si film and the p-Si film when the visible light of the solid-state laser is used is greatly different between the p-polarized light and the s-polarized light.
In particular, in the case of p-polarized light, the absorptance increases as the incident angle increases, and in the case of a film thickness of 50 nm, the a-Si film has a high absorptance of 82% and the p-Si film 77% at an incident angle of 80 °. I understand that.
Accordingly, in laser annealing of a semiconductor film using a laser beam, the incident angle of the p-polarized laser beam is 65 ° or more and 85 ° or less with respect to a semiconductor film having a thickness of 50 nm or more (in the drawing). It can be seen that a high absorptance is obtained in A).
This is presumably because the reflectance of p-polarized light decreases as the Brewster angle (a-Si film: 78.4 °, p-Si film: 76.3 °) is approached.
In relation to the Brewster angle, the incident angle θ is preferably within a range of ± 5 ° or less (B in the figure) with respect to the Brewster angle of the semiconductor film regardless of the film thickness.

4A and 4B are diagrams showing the absorption rate of p-polarized light of solid-state laser beams having different wavelengths. FIG. 4A shows the case of an a-Si film, and FIG. 4B shows the case of a p-Si film. In each figure, the horizontal axis represents the incident angle, the vertical axis represents the absorptance, and each curve in the figure corresponds to the case where the wavelength of the solid laser beam is 527 nm and 355 nm, and the film thickness of the semiconductor film is common to 50 nm. .
4A and 4B, even when the wavelength of the solid-state laser beam is different, in the case of p-polarized light, the absorptance increases as the incident angle increases. When the film thickness is 50 nm, the a- It can be seen that the Si film has a high absorption rate of 82% and the p-Si film 77%.
Therefore, for laser annealing of a semiconductor film using a laser beam, a higher absorption rate can be obtained with a p-polarized laser beam.

  FIG. 5 is a relational diagram between the film thickness and the absorptance in p-polarized light, where (A) shows the case of an a-Si film and (B) shows the case of a p-Si film. Moreover, in each figure, the curve in the figure has shown the case where incident angle (theta) is changed into 0, 40, 60, 70, 80 degrees.

4 (A) and 4 (B), it can be seen that as the incident angle increases, the amount of change in the absorptance with respect to the film thickness decreases, and becomes substantially constant particularly at an incident angle of 80 °.
Accordingly, the p-polarized light is incident in an incident angle range of 65 ° or more and 85 ° or less (more preferably, a range of ± 5 ° or less with respect to the Brewster angle of the semiconductor film). In addition, the laser absorptance of the p-Si film can be greatly increased, and the laser power can be effectively utilized.
In addition, the throughput of the apparatus can be greatly improved.
Also, by increasing the incident angle, the change in the absorptance with respect to the film thickness of a-Si and p-Si can be reduced, and unevenness of the crystal state due to film thickness non-uniformity during a-Si film formation can be eliminated. Is possible.

  As described above, according to the method and apparatus of the present invention, a semiconductor film is irradiated with a p-polarized laser beam having an electric field vector parallel to the semiconductor film at an incident angle θ where the absorption rate of the laser beam exceeds 50%. Therefore, the reflectance of p-polarized light can be reduced, and the absorption rate of the laser beam can be increased.

  In addition, this invention is not limited to embodiment mentioned above, Of course, a various change can be added in the range which does not deviate from the summary of this invention.

It is a block diagram of the laser oscillator which comprises the laser annealing apparatus of this invention. 1 is an overall configuration diagram of a laser annealing apparatus according to the present invention. It is a comparison figure of the absorption factor of p polarized light and s polarized light. It is a figure which shows the absorption factor of the p polarization | polarized-light of the solid laser beam from which a wavelength differs. It is a related figure of the film thickness and absorption factor in p polarization. It is a schematic diagram of the method of patent document 1. FIG. It is a schematic diagram of the apparatus of patent document 2. FIG. It is a schematic diagram of the method of patent document 3. FIG.

Explanation of symbols

1 insulating substrate, 1a semiconductor film, 2 infrared laser beam, 3 polarized laser beam,
5 Laser solid medium (YAG rod), 6 Laser diode,
・ Reflection mirror, 9 wavelength conversion crystal,
10 laser oscillator, 11 laser generator,
12 conversion device (λ / 2 plate), 14 irradiation device,
15a fixed reflection mirror, 15b condenser lens,
15c variable reflection mirror, 15d mirror tilting device,
16a fixed reflecting mirror, 16b variable condenser lens,
16c Lens moving device

Claims (8)

A laser annealing method of a semiconductor film using a laser beam,
Generating a p-polarized laser beam whose electric field vector is parallel to the semiconductor film;
A laser annealing method, wherein the semiconductor film is irradiated with the p-polarized laser beam at an incident angle θ in which the absorption rate of the laser beam exceeds 50%. The laser beam is a solid laser beam of YAG, YVO ₄ , YLF or YAG,
The laser annealing method according to claim 1, wherein the wavelength of the solid-state laser beam is 532 nm, 527 nm, or 355 nm.   2. The laser annealing method according to claim 1, wherein the incident angle θ is 65 ° or more and 85 ° or less with respect to a semiconductor film having a thickness of 50 nm or more.   The laser annealing method according to claim 1, wherein the incident angle θ is in a range of ± 5 ° or less with respect to the Brewster angle of the semiconductor film.   The laser annealing method according to claim 1, wherein the semiconductor film is an amorphous film or a polycrystalline film. A laser annealing apparatus for a semiconductor film using a laser beam,
A laser generator for generating a p-polarized laser beam having an electric field vector parallel to the semiconductor film;
A laser annealing apparatus comprising: an irradiation apparatus that irradiates the semiconductor film with the p-polarized laser beam at an incident angle θ with an absorption rate of the laser beam exceeding 50%.   The laser annealing apparatus according to claim 6, wherein the irradiation apparatus includes an irradiation angle adjuster capable of variably adjusting the incident angle θ. The laser beam of the laser oscillator is a solid laser beam of YAG, YVO ₄ , YLF or YAG,
The laser annealing apparatus according to claim 6, wherein the wavelength of the solid-state laser beam is 532 nm, 527 nm, or 355 nm.

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