JP2003289052A - Crystallizing method of semiconductor and laser irradiation device used for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallizing method of semiconductor having a large crystal grain size and performing crystallization treatment in a short period of time and, to provide a laser irradiation device that is simple in constituting of an optical system for laser condensing. <P>SOLUTION: The crystallizing method of semiconductor comprises a step for performing laser annealing by irradiating a laser beam L3 on an amorphous semiconductor film and crystallizing the amorphous semiconductor film 22. Laser beams L1 uneven in intensity distribution are emitted from a plurality of laser emitting devices 11a-11e. The intensity distribution of each laser beam L1 is uniformized and synthesized after traveling through a homogenizer 12. The amorphous semiconductor film 22 is irradiated by condensing the uniformized and synthesized laser L3 using a condensing lens 15 and the like, and a polycrystal semiconductor film having a crystal grain size of 1 μm or larger is formed. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor crystallization method and a laser irradiation apparatus used therefor, and more particularly to a crystallization method for a large semiconductor substrate and a laser irradiation apparatus used therefor.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for liquid crystal displays as display means for personal computers, personal digital assistants, televisions and the like. The thin film transistors forming the drive circuit, control circuit, etc. of the liquid crystal display are formed of polycrystalline silicon (particularly low temperature polysilicon).

Polycrystalline silicon formed on a large-sized substrate for a liquid crystal display is generally formed by growing an amorphous silicon film on the substrate by a CVD method and melting and recrystallizing the amorphous silicon film. To be done. For this melting / recrystallization, laser annealing is used which can be kept at a relatively low temperature except for the amorphous silicon film to be melted / recrystallized and which is suitable for manufacturing a three-dimensional integrated circuit. Examples of the laser used for this laser annealing include an excimer laser and the like.

In laser annealing using an excimer laser, a laser beam is shaped into a top hat shape shown in FIG. 6A by an optical system called a homogenizer, and the amorphous silicon is irradiated with the laser beam. When amorphous silicon is irradiated with a top hat-shaped beam, the grain size of crystallized silicon becomes about several hundreds nm. Here, the horizontal axis in FIG. 6A indicates the length in the optical axis direction and / or the direction perpendicular to the optical axis, and the vertical axis indicates the energy intensity.

Specifically, as shown in FIG. 7, a laser beam emitted from a laser emission device (not shown) is incident on a first orthogonal cylindrical lens array 71 having a focal length f ₁ . Each beam group that has passed through the focal plane spreads again and is incident on the second orthogonal cylindrical lens array 72 having the focal length f ₂ . Each cylindrical lens array 71, 72 has a predetermined distance a (f ₁ <a <f ₁ + f ₂ ).
Are separated from each other. Next, each beam group L2 after passing through the lens array 72 is refracted by the condenser lens 73 having the focal length f _f and converges on the focal plane (substrate) 74 within the range of the distance D / 2 from the optical axis O. Overlap. That is, all the beam groups L2 are overlapped within the area of the vertical width (or the horizontal width) D, and the laser beam has a uniform energy distribution.

Here, since the excimer laser has a high average output of about 100 to 300 W (pulse energy per pulse is about 0.5 to 1.5 J) at the maximum, laser emission for laser annealing is performed. One device is sufficient, and it is not necessary to narrow the beam so much that the beam size is, for example, 30 (width) (width).
0 mm, vertical width 0.2 to 0.4 mm (200 to 400 μ
m) becomes larger (beam irradiation area becomes wider). For this reason, for example, when laser annealing a large substrate of 600 mm × 720 mm, the time required for the processing can be short (for example, about 3 minutes).

However, in the conventional laser annealing using the excimer laser, the grain size of the crystallized silicon obtained is about several hundred nm at most. In order to obtain crystallized silicon having a grain size of more than 1 μm, it is necessary to form a beam having a steep energy gradient with a half width of about 50 μm as shown in FIG. 6B. However, since the conventional excimer laser forms a top hat-shaped beam and it is difficult to obtain the beam shown in FIG. 6B due to its own beam quality, laser annealing is performed by the excimer laser. If this is done, the crystal grain size of the polycrystalline silicon is limited to 1 μm or less, that is, about several hundreds nm. If the crystal grain size of the obtained polycrystalline silicon is small, the electron mobility will be small, and eventually the characteristics of the thin film transistor will be deteriorated.

Therefore, as a laser source for obtaining crystallized silicon having a crystal grain of more than 1 μm, the second harmonic wave (532 nm) of the YAG laser has been attracting attention. The oscillation method may be pulse oscillation or continuous oscillation (hereinafter referred to as CW), but a CW laser can obtain crystallized silicon having a larger grain size.

Laser annealing of amorphous silicon using a CW laser can secure a sufficient time for melting and solidifying the polycrystalline silicon. Therefore, polycrystalline silicon having a crystal grain size of 1 μm or more, particularly preferably crystal grains is preferable. Polycrystalline silicon having a size of 10 μm or more can be obtained. CW
Examples of the laser include those of arc lamp pumping and those of LD pumping (semiconductor laser pumping). However, LD pumping CW lasers are made of polycrystalline silicon obtained by laser annealing rather than arc lamp pumping CW lasers. The crystal grain size is increased, and the quality of polycrystalline silicon is improved.

[0010]

However, when a YAG laser which is an LD-excited CW laser is used for laser annealing, a fundamental wave with a large power (wavelength: 1064n) is used.
m) but the optical second harmonic (wavelength: 532 nm) is used, but the average output of the optical second harmonic is about 10 W at maximum.
Because of its low level, it requires a plurality of laser emission devices for performing laser annealing of amorphous silicon. Here, it is necessary to collect the laser beams emitted from the respective laser emitting devices, but the same number of optical systems as the respective laser emitting devices are required for this condensing.
That is, there is a problem that the device configuration becomes complicated and the device cost is significantly increased as compared with the case where the excimer laser is used.

Since the average output of the YAG laser is low, it is necessary to narrow the beam in order to obtain the energy required for laser annealing, and the beam size is
For example, width (length) 0.4 mm, height 0.02 mm (2
0 μm), which is very small (beam irradiation area is very narrow). Therefore, for example, 600 mm x 720
When laser annealing a large substrate having a size of mm, there is a problem that the time required for the processing is extremely long as compared with the case where an excimer laser is used.

An object of the present invention devised in view of the above circumstances is to provide a method of crystallizing a semiconductor which has a large crystal grain size and can be crystallized in a short time.

On the other hand, another object of the present invention is to provide a laser irradiation apparatus having a simple optical system for condensing a laser.

[0014]

In order to achieve the above object, a semiconductor crystallization method according to the present invention is to crystallize an amorphous semiconductor film by irradiating an amorphous semiconductor film on a substrate with a laser beam to perform laser annealing. In the method, a laser beam having a non-uniform intensity distribution is emitted from each of a plurality of laser emission devices, each laser beam is passed through an optical system such as a homogenizer and a condenser lens, and is homogenized on an amorphous semiconductor film, and By synthesizing, a polycrystalline semiconductor film having a crystal grain size of 1 μm or more is formed.

Further, it is preferable to use a continuous wave laser as the laser beam.

According to the above method, a polycrystalline semiconductor film having a large crystal grain size can be obtained, and crystallization treatment can be performed in a short time.

On the other hand, the laser irradiation apparatus used for crystallizing a semiconductor according to the present invention is a laser irradiation apparatus for irradiating a laser beam on an amorphous semiconductor film on a substrate to perform laser annealing to crystallize the amorphous semiconductor film.
A plurality of laser emitting devices that emit laser beams with non-uniform intensity distribution, a homogenizer that homogenizes and synthesizes the intensity distribution of each laser beam emitted from each laser emitting device, and a homogenized and synthesized beam And a condenser lens for condensing.

Further, a mirror or an optical fiber for guiding the laser beam emitted from each laser emitting device to the homogenizer is provided between each laser emitting device and the homogenizer.

According to the above structure, the laser irradiation device has a simple optical device structure for condensing the laser beams emitted from each of the plurality of laser emission devices.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A preferred embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a schematic diagram of a laser irradiation apparatus according to the first embodiment.

As shown in FIG. 1, the laser irradiation apparatus 10 according to the first embodiment used for crystallizing a semiconductor emits a plurality of laser beams L1 having a non-uniform intensity distribution (5 in FIG. 1). Laser emitting devices 11a to 11e
And a homogenizer 12 for synthesizing and homogenizing the intensity distributions of the laser beams L1 emitted from the laser emitting devices 11a to 11e, and a condenser lens 15 for condensing the synthesized and homogenized beam L3. It is a thing. Here, the homogenizer 12 is composed of a vertical (or horizontal) cylindrical lens array 13 and a condenser lens 14 arranged on the rear side of the lens array 13. Further, the number of laser emitting devices is the same as the number of convex lenses 13a on one surface side (upper surface side in FIG. 1) of the lens array 13.

A mirror 16 as a laser introducing optical system is provided between each laser emitting device 11 and the homogenizer 12.
Are arranged. The laser beam L1 emitted from each laser emission device 11 is guided to the homogenizer 12 by this mirror 16.

The laser beam L1 emitted from each laser emission device 11 has a visible wavelength range (400 to 700 n).
m) or a CW laser in the ultraviolet wavelength range (less than 400 nm), or a visible wavelength range or an ultraviolet wavelength range that has been difficult to apply to laser annealing in the past because of low output (the output is not sufficient with one laser emission device). A pulse laser or the like can be applied, but a CW laser in the visible wavelength range is preferable. C
Examples of the W laser include a YAG laser (optical second harmonic (wavelength: 532 nm), optical third harmonic (wavelength: 355 nm)
nm), optical fourth harmonic (wavelength: 266 nm)), He-
Ne laser (wavelength: 632.8 nm), Ar laser (wavelength: 514.5 nm, 488 nm), He-Cd laser (wavelength: 441.6 nm), etc. are mentioned. Also,
As the pulse laser, for example, an excimer laser (Xe
F laser (wavelength: 308 nm), XeCl laser (wavelength: 351 nm)), metal vapor laser (copper vapor laser (wavelength: 510 nm, 578 nm), gold vapor laser (optical second harmonic (wavelength: 312 nm), optical first) Harmonics (wavelength: 624 nm), manganese vapor laser (wavelength: 53
4 nm)) and the like.

Next, a semiconductor crystallization method according to the present invention will be described using the laser irradiation apparatus of the first embodiment shown in FIG.

First, the laser beam L1 having a non-uniform intensity distribution (convex beam distribution (see FIG. 6B)) is emitted from each of the laser emission devices 11a to 11e, and the mirror 1 is emitted.
The light enters the homogenizer 12 via 6.

By making each laser beam L1 incident on the lens array 13 of the homogenizer 12, each laser beam L1.
1 is divided into a beam group L2 having a uniform intensity distribution in the optical axis direction (or a direction perpendicular to the optical axis) (having a substantially flat beam distribution (see FIG. 6A)). The beam group L2 is
The power is combined by the condenser lens 14 of the homogenizer 12.

The homogenizer 12 irradiates the amorphous laser film (amorphous semiconductor film) 22 on the substrate 21 with the synthetic laser beam L3 homogenized and synthesized through the condenser lens 15. By the irradiation of the synthetic laser beam L3, the amorphous silicon film (for example, a film thickness of about 50 to 100 nm) 22 is laser-annealed, and a polycrystalline silicon film (polycrystalline film having a crystal grain size of 1 μm or more, preferably 10 μm or more A crystalline semiconductor film) is formed.

Here, as the laser beam L1, a laser beam in the ultraviolet wavelength range, for example, an excimer laser, or a laser beam in the visible wavelength range, for example, an optical second harmonic wave is used.
The absorption coefficient for silicon is different by using the G laser.

Specifically, since a laser beam in the ultraviolet wavelength range such as an excimer laser has a shorter wavelength than a laser beam in the visible wavelength range such as a YAG laser using an optical second harmonic, for example, an excimer laser is used. When the amorphous silicon film 52 on the surface of the substrate 51 shown in FIG.
The excimer laser is almost absorbed by the surface of the amorphous silicon film 52. That is, the melting by the excimer laser (region 53 in the figure) is mainly caused by the amorphous silicon film 52.
Of the amorphous silicon film 52, and the melting of the inside of the amorphous silicon film 52 does not proceed so much because it occurs due to heat conduction.

On the other hand, YA using the optical second harmonic
A laser beam in the visible wavelength range such as a G laser has a longer wavelength than a laser beam in the ultraviolet wavelength range such as an excimer laser, and the absorption coefficient of silicon such as the YAG laser is about 1 of the absorption coefficient of the excimer laser. / 10 or less. For example, when the amorphous silicon film 42 on the surface of the substrate 41 shown in FIG. 4 is irradiated with a YAG laser that uses the second harmonic of light, the YAG laser emits the amorphous silicon film 4.
2 to the inside, that is, melting by the YAG laser (region 43 in the drawing) occurs in the entire amorphous silicon film 42. In this way, the amorphous silicon film 4
Since the entire 2 melts, the crystal grain size of the obtained polycrystalline silicon film becomes larger.

Therefore, from the viewpoint of obtaining a polycrystalline silicon film having a large crystal grain size, a laser beam in the visible wavelength range is more preferable than a laser beam in the ultraviolet wavelength range as the laser beam L1, and a pulse laser is also used. A CW laser is more preferable than a CW laser.

A conventional laser irradiation device (see FIG. 7)
In the above, the homogenizer composed of the cylindrical lens arrays 71 and 72 and the condenser lens 73 was used only for making the intensity distribution of the laser beam uniform. On the other hand, the laser irradiation apparatus 10 according to the present embodiment
The homogenizer 12 to each of the laser emission devices 11a-1a.
It is characterized in that it is used for uniforming the intensity distribution of each laser beam L1 emitted from 1e and synthesizing power. Therefore, according to the laser irradiation apparatus 10 of the present embodiment, a polycrystalline semiconductor having a large crystal grain size can be obtained, but the practical output is not sufficient and it cannot be conventionally applied to laser annealing. Even if a laser beam is used, it can be applied to laser annealing.

Furthermore, the laser irradiation apparatus 1 of this embodiment
0 has a plurality of laser emitting devices for laser annealing the amorphous silicon film 22, but an optical system for condensing the laser beam L1 emitted from each of the laser emitting devices 11a to 11e. Is 1
There is only a set of homogenizer 12 and condenser lens 15.
Therefore, as compared with the conventional laser irradiation device that requires the same number of optical systems as the laser emission device, the device configuration is simplified and the increase in device cost can be suppressed.

Further, the laser irradiation device 10 of the present embodiment.
, YAG with a low average output as a laser beam
Even if a CW laser such as a laser is used, the energy required for laser annealing can be obtained without narrowing the beam to a small size by combining and using the powers of a plurality of CW lasers. Therefore, for example, 600 mm x 720 mm
When a large-sized substrate is combined with the power of a plurality of CW lasers and laser-annealed, the time required for the processing is extremely short compared to the case where a single CW laser is used.

Further, when a laser beam having a high coherence such as a YAG laser is incident on the homogenizer 12 as a laser beam, a homogenizing surface (image forming surface)
Interference fringes are generated by overlapping at. When the amorphous silicon film 22 was irradiated with the laser beam having the interference fringes for crystallization, only a polycrystalline silicon film having a small crystal grain size was obtained. However, in the laser irradiation apparatus 10 of the present embodiment, each convex lens 12a of the homogenizer 12 has an independent light source (each laser emission device 11a).
Since the laser beams L1 oscillated (emitted) from (1) to 11e) are respectively incident, interference fringes do not occur even if these laser beams overlap on the homogenized surface. That is, when using a laser beam having a high coherence such as a YAG laser, an optical system (for example, an optical path correction lens) for correcting the coherence, which is conventionally required, is provided in the laser irradiation apparatus 10 of the present embodiment. Exerts a new effect that is unnecessary.

Next, another embodiment of the present invention will be described with reference to the accompanying drawings.

FIG. 2 shows a schematic diagram of a laser irradiation apparatus according to the second embodiment.

As shown in FIG. 2, the laser irradiation apparatus 20 according to the second embodiment used for crystallizing a semiconductor has a homogenizer 32 and a homogenizer 32 while the basic apparatus configuration is the same as that of the laser irradiation apparatus 10. The vertical (or horizontal) cylindrical lens array 13 and the horizontal (or vertical) cylindrical lens array 23, which are arranged at a predetermined distance as shown in FIG. Here, the lens arrays 13 and 23 are arranged so as to be mirror-symmetric with respect to the optical axis direction.

According to the laser irradiation device 20 of this embodiment, the laser beams L1 emitted from the laser emission devices 11a to 11e are perpendicular to the optical axis direction and the optical axis by the lens arrays 13 and 23 of the homogenizer 32. Intensity distribution in different directions becomes uniform, the homogenized beam group L4 is synthesized by the condenser lens 14, and the homogenized and synthesized synthetic laser beam L5 is generated by the condenser lens 1.
The amorphous silicon film (amorphous semiconductor film) 22 on the substrate 21 is irradiated with the light through the film 5.

Also in the laser emission device 20 of this embodiment, the laser irradiation device 10 of the first embodiment described above is used.
The same effect as is obtained.

Further, the laser emitting device 20 of the present embodiment
In the above, since the intensity distribution of the synthesized laser beam L5 is more uniform than the intensity distribution of the synthesized laser beam L3 in the laser irradiation device 10 of the previous embodiment, this synthesized laser beam L5 is applied to the substrate 21. By irradiating the upper amorphous silicon film 22, the irradiated portion can be more uniformly melted. As a result, a polycrystalline semiconductor film having a larger crystal grain size can be obtained as compared with the laser irradiation device 10 of the previous embodiment. Here, each laser beam L by the homogenizer
Whether to make the intensity distribution of 1 uniform in one direction of the optical axis direction (or in the direction perpendicular to the optical axis) or in two directions of the optical axis direction and the direction perpendicular to the optical axis, It is appropriately selected according to the uniformity of the intensity distribution required for the laser beams obtained by the synthesis.

FIG. 3 shows a schematic view of a laser irradiation apparatus according to the third embodiment. Here, the same members as those in FIG. 1 are designated by the same reference numerals.

The laser irradiation apparatus 10 of the first embodiment shown in FIG. 1 is a mirror as a laser introduction optical system for making the laser beams L1 emitted from the laser emission apparatuses 11a to 11e incident on the homogenizer 12. 16 was used.

On the other hand, as shown in FIG. 3, the laser irradiation device 30 according to the third embodiment has the same basic device structure as the laser irradiation device 10 but emits a CW laser. The devices 31a to 31e and the optical fibers 36a to 36e as a laser introduction optical system are provided. Here, a collimator 37 is coupled to the tip of each of the optical fibers 36a to 36e. With this collimator 37, each of the optical fibers 36a to 36e
The laser beam L1 propagating through is collimated and is incident on the homogenizer 12.

Also in the laser emission device 30 of the present embodiment, the laser irradiation device 10 of the first embodiment described above is used.
The same effect as is obtained.

Further, the laser emission device 30 of the present embodiment.
In the above, by using the optical fibers 36a to 36e as the laser introducing optical system between the laser emitting devices 31a to 31e and the homogenizer 12, the laser emitting portions (laser emitting devices 31a to 31e) and the laser irradiation portion (homogenizer 12). , The condenser lens 15, and the substrate 21) can be separately arranged at different places. Therefore, even when there is no space for installing a plurality of laser emission devices in the laser irradiation portion, each laser emission device can be installed at a location distant from the laser irradiation portion to deal with it.

It is needless to say that the embodiments of the present invention are not limited to the above-mentioned embodiments but various other embodiments are possible.

[0049]

In summary, according to the present invention, the following excellent effects are exhibited.

(1) According to the semiconductor crystallization method of the present invention, a polycrystalline semiconductor film having a large crystal grain size can be obtained, and crystallization treatment can be performed in a short time.

(2) According to the laser irradiation apparatus used for crystallization of the semiconductor according to the present invention, the device configuration of the optical system for concentrating the laser beams emitted from each of the plurality of laser emission devices is simplified. Become.

[Brief description of drawings]

FIG. 1 is a schematic diagram of a laser irradiation apparatus according to a first embodiment.

FIG. 2 is a schematic view of a laser irradiation device according to a second embodiment.

FIG. 3 is a schematic diagram of a laser irradiation apparatus according to a third embodiment.

FIG. 4 is a cross-sectional view showing a state where an amorphous silicon film is irradiated with a laser beam in a visible wavelength range.

FIG. 5 is a cross-sectional view showing a state where an amorphous silicon film is irradiated with a laser beam in the ultraviolet wavelength range.

FIG. 6 is a diagram showing an intensity distribution of a laser beam. Figure 6
6A shows the beam distribution after the homogenization, and FIG. 6B shows the beam distribution before the homogenization.

FIG. 7 is a diagram for explaining laser beam homogenization.

[Explanation of symbols]

10, 20, 30 Laser irradiation device 11a-11e, 31a-31e Laser emission device 12, 32 Homogenizer 13, 23 Cylindrical lens array 14 Condenser lens 15 Condensing lens 16 Mirror 21 Substrate 22 Amorphous silicon film (amorphous semiconductor film) 36a- 36e Optical fiber L1 Laser beams L2 and L4 having non-uniform intensity distribution Beam group L3 and L5 having uniform intensity distribution Synthetic laser beam

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takahiko Murayama             3-15 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             In the center (72) Inventor Mikito Ishii             3-15 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             In the center (72) Inventor Kenichiro Nishida             3-15 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             In the center (72) Inventor Miyuki Masaki             3-15 Toyosu, Koto-ku, Tokyo Ishikawajima             Harima Heavy Industries Tokyo Engineering Co., Ltd.             In the center F term (reference) 5F052 AA02 BA11 BB01 BB04 BB07                       DA02                 5F110 AA16 AA28 AA30 BB02 GG02                       GG13 GG16 GG25 PP03 PP04                       PP06 PP07

Claims (4)

[Claims] 1. A method of crystallizing an amorphous semiconductor film by irradiating an amorphous semiconductor film with a laser beam to perform laser annealing, wherein a laser beam having a non-uniform intensity distribution is emitted from each of a plurality of laser emitting devices,
Each laser beam is passed through a homogenizer to homogenize and combine the intensity distribution of each beam, and the homogenized and combined laser beam is focused by a condenser lens etc. to irradiate the amorphous semiconductor film, and the crystal grain size A method of crystallizing a semiconductor, which comprises forming a polycrystalline semiconductor film having a thickness of 1 μm or more. 2. The method for crystallizing a semiconductor according to claim 1, wherein a continuous wave laser is used as the laser beam. 3. A laser irradiation device for irradiating a laser beam on an amorphous semiconductor film on a substrate to perform laser annealing to crystallize the amorphous semiconductor film, wherein a plurality of lasers emit a laser beam having an uneven intensity distribution. An emission device, a homogenizer that synthesizes and homogenizes the intensity distribution of each laser beam emitted from each laser emission device, and a condenser lens that condenses the homogenized and synthesized laser beam. Irradiation device used for crystallization of semiconductors. 4. The semiconductor crystallization according to claim 3, further comprising a mirror or an optical fiber for guiding the laser beam emitted from each laser emitting device to the homogenizer, between each laser emitting device and the homogenizer. Laser irradiation device used.