JP4417613B2 - Method and apparatus for crystallizing semiconductor thin film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a crystallization method and a crystallization apparatus for a semiconductor thin film used as an active layer of a pixel display transistor and a drive circuit transistor in a liquid crystal display device, an organic electroluminescence (OELD) display device, and the like.
[0002]
[Prior art]
Liquid crystal display devices and OELD display devices in which drive circuits are formed by polysilicon TFTs on a glass substrate have been put into practical use. As a method for forming a polysilicon film which is an active layer of a polysilicon TFT, a so-called excimer laser annealing method is widely used in which an amorphous silicon film formed on a glass substrate is irradiated with excimer laser light to be melted and crystallized. ing.
[0003]
FIG. 6 shows the principle of excimer laser annealing. The amorphous silicon film 22 formed on the glass substrate 21 is irradiated with pulsed excimer laser light to be melted and crystallized. The irradiation position on the substrate is changed for each pulse of excimer laser light to crystallize the entire surface of the film. At this time, if the energy of the excimer laser light becomes excessive, the film becomes amorphous instead of polysilicon. This is because crystals grow from nuclei remaining at the interface between the glass substrate 21 and the amorphous silicon 22 during the excimer laser annealing growth. When the film is completely melted by irradiation with excessive energy, when the film is rapidly cooled, it solidifies before nucleation and does not become crystalline.
[0004]
On the other hand, in order to increase the particle size of polysilicon and improve the carrier mobility in the film, research on a method for completely melting the film is underway. FIG. 7 is a principle diagram for explaining this type of method. Excimer laser light having such an energy that silicon is completely melted is irradiated through a mask 23 onto a film partially crystallized in advance. At this time, the irradiation edge of the laser beam becomes steep, and a crystal grows in the lateral direction with the boundary between the melted portion and the unmelted portion of the film as a nucleus. By irradiating the excimer laser irradiation area in the horizontal direction for each pulse, the particle size is increased and the entire surface of the film is crystallized.
[0005]
[Problems to be solved by the invention]
Such a crystallization method was studied and known as a crystallization method for SOI devices in the 1980s. When this method is applied on a glass substrate, it is difficult to crystallize the entire surface of the substrate. The reason will be described below. In the crystallization method of FIG. 7 in which the film is completely melted, the film is irradiated with pattern light obtained by condensing excimer laser light with a lens having a shallow depth of focus through a mask in the middle of the optical path. The reason is that in such a crystallization method that performs complete melting, the growth length per pulse is about 2 μm or less, so the edge position of the laser beam that forms the solid-liquid interface is controlled with high precision. It is necessary to do.
[0006]
However, the plate thickness of a normal glass substrate has a wave of about several tens of μm. Even if the glass substrate is attracted by increasing the flatness of the substrate stage, the focus is shifted due to the undulation of the thickness of the glass substrate and the pattern light is blurred. To deal with the undulations, it is easy to use autofocus. However, in order to increase the accuracy of autofocus, the irradiation area per pulse of the laser beam must be reduced, and the entire surface of the glass substrate must be reduced. Since it takes time to irradiate the laser beam, the productivity is significantly reduced. Further, if the waviness of the glass plate thickness is removed by polishing or the like, the manufacturing cost increases accordingly.
[0007]
As described above, it is difficult to crystallize the entire surface of the glass substrate with high productivity by the conventional method.
[0008]
This invention is made | formed in view of such a point, The objective is to provide the crystallization method and crystallization apparatus of the semiconductor thin film which can crystallize a semiconductor thin film with high quality.
[0009]
[Means for Solving the Problems]
According to one aspect of the present invention, an energy beam that has passed through a slit of a mask is condensed by a projection lens on a semiconductor thin film formed on a glass substrate whose thickness varies in a direction orthogonal to the sweep direction. A method for crystallizing a semiconductor thin film, wherein the semiconductor thin film is irradiated and melted and crystallized around the irradiation position,
There is provided a method for crystallizing a semiconductor thin film, characterized in that the mask is arranged so that the longitudinal direction of the energy beam that has passed through the slit of the mask is substantially parallel to the sweep direction when the glass substrate is formed. .
[0010]
In the present invention, since the mask is arranged so that the longitudinal direction of the energy beam that has passed through the slit of the mask is substantially parallel to the sweep direction when the glass substrate is molded, the glass substrate The projection lens can be focused over the entire surface.
[0011]
Further , according to one aspect of the present invention , an energy beam that has passed through a plurality of slits of a mask is applied to a semiconductor thin film formed on a glass substrate whose thickness varies in a direction orthogonal to the sweep direction by a projection lens. In the method for crystallizing a semiconductor thin film in which the semiconductor thin film around the irradiation position is melted and crystallized by condensing and irradiating,
A method for crystallizing a semiconductor thin film, characterized in that the mask is arranged so that the longitudinal directions of the plurality of energy beams that have passed through the plurality of slits of the mask are substantially parallel to the sweep direction when the glass substrate is formed. Is provided .
[0012]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a semiconductor thin film crystallization method and a crystallization apparatus according to the present invention will be described in detail with reference to the drawings.
[0013]
The present inventor measured the variation in the thickness of the glass substrate in order to deal with the focus error caused by the variation in the thickness of the glass substrate. FIG. 1 shows the deviation of the typical glass plate thickness from the target plate thickness in μm. As shown in the figure, the variation in the plate thickness of the glass is distributed in a pleat shape, and it can be seen that the plate thickness is uniform toward one direction of the plate.
[0014]
As a result of investigating a large number of glasses, it was found that this distribution is unique to the manufacturing process of large thin glass sheets.
[0015]
FIG. 2 is a diagram showing a manufacturing process of a large thin glass sheet. In the manufacturing process of the large thin glass, the molten glass 1 is poured out from the furnace 2 and formed into a plate shape (FIG. 2A). Subsequently, the glass 1 formed into a plate shape is placed between the rollers 3. In some cases (FIG. 2B).
[0016]
Hereinafter, the manufacturing method of thin glass is demonstrated using this figure. First, the molten glass 1 is poured out from the furnace 2 and formed into a plate shape (FIG. 2A). Next, the glass 1 formed into a plate shape is rolled and formed between rollers 3 (FIG. 2B).
[0017]
In both the case of FIG. 2A and FIG. 2B, the glass is swept in the same direction (the direction of arrow A in the figure). For this reason, when the glass is poured out of the furnace 2, due to the influence of a subtle shape change at the end of the furnace 2 or the influence of a subtle change of the rolling roller 3, in the direction B perpendicular to the sweep direction, FIG. As shown in c), the plate thickness varies.
[0018]
On the other hand, with respect to the direction A parallel to the sweep direction of the glass 1, there is no large fluctuation at a short distance of about one glass, and the plate thickness is substantially uniform.
[0019]
In the present embodiment, the laser light is irradiated in consideration of such a fluctuation direction of the thickness of the glass substrate.
[0020]
(First embodiment)
FIG. 3 is a schematic block diagram showing a first embodiment of a semiconductor thin film crystallization apparatus according to the present invention. The crystallization apparatus of FIG. 3 includes a stage 11 that can be moved in a two-dimensional (XY) direction, a glass substrate 1 that is vacuum-sucked on the stage 11, a stage movement control unit 12 that controls the movement of the stage 11, and an excimer laser. A laser light source 13 that radiates light, a refractive optical system 14 that refracts excimer laser light, a mask 16 in which a slit 15 is formed, a lens 17 that condenses the laser light that has passed through the slit 15 of the mask 16, and a lens And a focus adjustment unit 18 that performs 17 focus adjustments. The focal depth of the lens 17 is about 5 μm in order to obtain a resolution of about 1 μm.
[0021]
Although the surface accuracy of the stage 11 is finished within ± 1 μm, the glass substrate 1 adsorbed on the stage 11 has uneven thickness as described above, so the height from the surface of the stage 11 is not uniform. .
[0022]
The slits 15 formed in the mask 16 are elongated as shown in FIG. This embodiment is characterized in that the longitudinal direction of the slit 15 is arranged substantially parallel to the sweep direction (direction X in FIG. 3) when the glass substrate 1 is formed. By arrange | positioning in this way, focus can be adjusted over the full length of the laser beam irradiated to the glass substrate 1. FIG.
[0023]
The laser light source 13 transmits laser light in a pulse shape at a constant frequency. The stage movement control unit 12 moves the stage 11 at a constant speed in a direction substantially orthogonal to the longitudinal direction of the laser light that has passed through the slit 15. At this time, the focus adjusting unit 18 measures the distance between the surface of the glass substrate 1 and the projection lens 17 and adjusts the distance between the stage 11 and the projection lens 17 so as to keep the distance constant.
[0024]
Since the plate thickness of the glass substrate 1 is substantially constant over the entire length of the laser beam irradiated at one time, the focus is not shifted over the entire length of the laser beam even if the irradiation area of the laser beam is increased.
[0025]
On the other hand, if the irradiation direction of the laser beam is not controlled with respect to the sweep direction at the time of forming the glass, the height of the glass substrate 1 varies within the irradiation area of the laser beam irradiated at one time. It becomes impossible to focus on the entire length of the laser beam. For this reason, when the longitudinal direction of the slit 15 is arranged in a direction substantially orthogonal to the sweep direction when the glass substrate 1 is formed as shown in FIG. 4, the irradiation area of the laser light has to be reduced. However, if the irradiation area of the laser beam is reduced, it takes time to irradiate the entire surface of the glass substrate 1 with the laser beam, and the productivity is significantly reduced.
[0026]
As described above, in the present embodiment, the elongated slit 15 is formed in the mask 16, the longitudinal direction of the slit 15 is arranged in a direction substantially parallel to the sweep direction when the glass substrate 1 is formed, and the stage 11 is made of glass. Since the substrate 1 is moved substantially at right angles to the sweep direction when the substrate 1 is formed, the laser light can be focused on the entire surface of the glass substrate 1 without being affected by the unevenness of the glass substrate 1. Therefore, the irradiation area of the laser beam can be increased and productivity can be improved.
[0027]
In the first embodiment, the example in which the polysilicon film is formed using the mask 16 having the elongated slit 15 has been described. However, if the slit 15 has a different aspect ratio of the area irradiated at one time, the slit 15 The shape is not particularly limited. For example, FIG. 5 shows an example using a mask 16 in which V-shaped slits 15 are arranged in a line for the purpose of controlling the position of crystal grains. In the case of FIG. 5, the direction in which the plurality of slits 15 are arranged is arranged in a direction substantially parallel to the sweep direction when the glass substrate 1 is formed, and the stage 11 is moved substantially perpendicular to the sweep direction when the glass substrate 1 is formed. Let Thereby, like the first embodiment, it is not affected by the unevenness of the glass substrate 1, and the productivity can be improved.
[0028]
【The invention's effect】
As described above in detail, according to the present invention, since the mask is arranged so that the longitudinal direction of the energy beam that has passed through the slit of the mask is substantially parallel to the sweep direction when the glass substrate is formed, Even if the substrate is uneven, the projection lens can be focused over the entire surface of the glass substrate without being affected by the unevenness. Therefore, the irradiation area of the projection lens can be set large, and the semiconductor thin film can be efficiently crystallized in a short time, so that productivity is improved.
[Brief description of the drawings]
FIG. 1 is a diagram showing a deviation of a typical glass plate thickness from a target plate thickness.
FIG. 2 is a diagram showing a manufacturing process of a large thin glass sheet.
FIG. 3 is a schematic block diagram showing a first embodiment of a semiconductor thin film crystallization apparatus according to the present invention.
FIG. 4 is a block diagram showing an example in which the longitudinal direction of the slit is arranged in a direction substantially perpendicular to the sweep direction when the glass substrate is formed.
FIG. 5 is a diagram showing an example using a mask in which V-shaped slits are arranged in a line for the purpose of controlling the position of crystal grains.
FIG. 6 is a principle diagram of excimer laser annealing.
FIG. 7 is a principle diagram illustrating a method for completely melting a film in order to increase the particle size of polysilicon and improve carrier mobility in the film.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass 2 Furnace 3 Roller 11 Stage 12 Stage movement control part 13 Laser light source 14 Refractive optical system 15 Slit 16 Mask 17 Lens 18 Focus adjustment part

Claims (4)

The semiconductor thin film formed on the glass substrate whose thickness varies in the direction perpendicular to the sweep direction is irradiated with the energy beam that has passed through the slit of the mask condensed by the projection lens, and the semiconductor thin film around the irradiation position A method for crystallizing a semiconductor thin film by melting and crystallizing
A method of crystallizing a semiconductor thin film, characterized in that the mask is arranged so that the longitudinal direction of the energy beam that has passed through the slit of the mask is substantially parallel to the sweep direction when the glass substrate is formed. The semiconductor thin film formed on the glass substrate whose thickness varies in the direction orthogonal to the sweep direction is irradiated with the energy beam that has passed through the slits of the mask and condensed by the projection lens. In the semiconductor thin film crystallization method, the semiconductor thin film is melted and crystallized.
A method for crystallizing a semiconductor thin film, characterized in that the mask is arranged so that the longitudinal directions of the plurality of energy beams that have passed through the plurality of slits of the mask are substantially parallel to the sweep direction when the glass substrate is formed. . Moving the glass substrate by a predetermined distance in a direction substantially perpendicular to a sweeping direction at the time of forming the glass substrate;
Adjusting the focus of the projection lens at each moving position;
3. The semiconductor thin film crystal according to claim 1, further comprising: condensing an energy beam that has passed through the mask after the focus adjustment by the projection lens to melt the semiconductor thin film. 4. Method. The energy beam is an excimer laser beam;
4. The semiconductor thin film crystallization method according to claim 1, wherein the semiconductor thin film made of amorphous silicon is irradiated with the excimer laser beam to form a polysilicon film.

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