JP2010040869A - Crystallization device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallization device that performs crystallization, in which part of irradiation laser light is transmitted through a thin film to be crystallized, with superior uniformity. <P>SOLUTION: There is disclosed the crystallization device, wherein the thin film (amorphous thin film 3) to be crystallized, formed on a substrate 1 with optical transparency, is irradiated with the laser light to crystallize it. The crystallization device includes a substrate stage S for supporting the substrate 1 where the amorphous silicon thin film 3 is formed. The substrate stage S has its surface, for example, made into a mirror plane to have a nearly uniform reflection factor to the whole crystallization region of the amorphous silicon thin film 3. The irradiation laser light has a wavelength in the visible range and is, for example, a higher harmonic of a solid-state laser. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a crystallization apparatus for crystallizing a crystallized thin film such as an amorphous silicon thin film by, for example, a solid laser annealing method.

  A polycrystalline silicon thin film transistor (polysilicon TFT) manufactured over a glass substrate has a structure similar to an SOI structure in a crystalline silicon device, and thus has characteristics similar to those of an SOI device in terms of electrical characteristics. By reducing the thickness of the channel layer (active layer), it is possible to perform a full depletion type operation, and one of them is that the rise voltage difference from the off state to the on state becomes very small.

  In addition, since a light-transmitting substrate (glass substrate) is used, it can be used as a driving element for a display device such as a liquid crystal display, and can be applied to a display panel that is impossible with a crystal semiconductor. Yes. By using a polysilicon TFT having a polycrystalline silicon film as an active layer as a drive element, for example, in a display portion of a mobile phone, display with a definition of about 1/4 VGA can be performed in a region of about 2 inches diagonally. It is possible.

  In the production of polysilicon TFTs, it is essential to form a polycrystalline silicon film, and so far an amorphous silicon thin film, which is a crystallized film, has been polycrystallized (excimer laser annealing) using an excimer laser. Yes.

  In recent years, with the progress of high definition pixels and the development of a new display driving method, there is a demand for a polycrystalline silicon thin film with high crystal uniformity in the array substrate. Under such circumstances, the laser annealing method using an excimer laser, which has been widely used so far, has a limit in the stability of laser oscillation. For example, when irradiating a laser in a pulsed manner, there is an energy variation for each irradiation. For example, it is difficult to dramatically improve the crystal uniformity of the polycrystalline silicon thin film.

  On the other hand, crystallization by a laser annealing method using a solid-state laser or a semiconductor laser has been studied. Solid lasers and semiconductor lasers are extremely stable in laser oscillation, so even when irradiated in pulses, there is little variation in energy input to the amorphous silicon thin film, and the crystal is highly uniform. A silicon thin film can be obtained.

  However, when a crystallization method using laser light in the visible region such as a solid-state laser or a semiconductor laser is employed, the problem is that the absorption coefficient of the amorphous silicon thin film is small. For example, an XeCl type excimer laser device widely used in excimer laser annealing is known to output light having a wavelength of 308 nm. However, absorption by an amorphous silicon (a-Si) thin film is large. In an amorphous silicon thin film having a thickness of about 10 nm, almost 100% of laser light is absorbed.

  On the other hand, in a solid-state laser or a semiconductor laser using a wavelength in the visible region, since the absorption to the amorphous silicon thin film is small, only a part of the irradiated laser light is absorbed by the amorphous silicon thin film. For example, a harmonic (532 nm) of a YAG laser (1064 nm) has an absorption coefficient of only about 1/50, and a typical Si film thickness (50 nm) can be used only about 30%. Usually, since a substrate transparent to 532 nm light is used as the substrate of the display panel, the remaining light that cannot be used passes through the substrate and is irradiated onto the substrate stage that supports the substrate.

Under such circumstances, in laser annealing apparatuses using harmonics of a solid-state laser, measures are taken such as preventing damage to the substrate stage that supports the substrate (see, for example, Patent Document 1). Patent Document 1 includes a laser emitting device that emits a processing laser beam (second harmonic of a solid-state laser) and a plate in which a layer made of a damage-resistant material is formed on the surface of a plate body made of stone. A laser irradiation apparatus is disclosed. In the invention described in Patent Document 1, a layer made of a damage-resistant material is formed on the surface of the substrate stage, so that it is difficult to be damaged by the irradiation of the processing laser beam.
JP 2006-140230 A

  By the way, in the laser annealing method using the above-described solid state laser or semiconductor laser, the laser light that has not been absorbed by the amorphous silicon thin film passes through the substrate, is reflected by the surface of the substrate stage that supports the substrate, and is again applied to the substrate. It passes through and enters the amorphous silicon thin film, and a part of it is absorbed by the amorphous silicon thin film. At this time, if the reflectivity of the surface of the substrate stage differs depending on the location, the intensity of the reflected energy is different accordingly. As a result, there is a difference in the total amount of energy absorbed by the amorphous silicon thin film, which may be affected by the crystal uniformity of the polycrystalline silicon thin film.

  Specifically, the substrate stage surface pattern, vacuum suction holes and grooves for fixing the substrate, and lift pin holes for mounting or unloading the substrate on the substrate stage, etc. The reflectivity varies depending on the location of the stage, and these structures are reflected in the crystallinity of the polycrystalline silicon thin film, resulting in a loss of crystal uniformity. For example, the surface of the substrate stage is not necessarily uniform, and this non-uniformity appears as a pattern, and the uniformity of crystallinity deteriorates on the order of the size corresponding to the pattern.

  The present invention has been proposed in view of the above problems, and in crystallization in which part of the irradiated laser light is transmitted through the thin film to be crystallized, the total absorption including reflection from the substrate stage is absorbed. An object of the present invention is to provide a crystallization apparatus that can make the amount of energy uniform and can perform crystallization with excellent uniformity.

  In order to achieve the above-described object, the crystallization apparatus of the present invention is a crystallization apparatus that performs crystallization by irradiating a crystallized thin film formed on a light-transmitting substrate with laser light. And a substrate stage that supports the substrate on which the thin film to be crystallized is formed, and the substrate stage has a substantially uniform reflectivity in the entire crystallization region of the thin film to be crystallized.

  As described above, when the crystallized thin film formed on the light-transmitting substrate is irradiated with laser light, part of the laser light is transmitted through the substrate and irradiated onto the substrate stage that supports the substrate. In the present invention, since the reflectance of the substrate stage is made uniform, the total amount of energy absorbed by the thin film to be crystallized out of the energy of the irradiated laser light is made uniform, and uniform crystallization is realized. The

  According to the crystallization apparatus of the present invention, since the reflectance of the substrate stage surface is uniform over the entire crystallization region of the crystallized thin film, a part of the irradiated laser light is transmitted through the crystallized thin film. In crystallization, the total amount of energy absorbed including the reflection from the substrate stage can be made uniform, and crystallization with excellent uniformity can be performed.

  Hereinafter, embodiments of a crystallization apparatus to which the present invention is applied will be described in detail with reference to the drawings.

  First, a crystallization process (a method for producing a polycrystalline silicon thin film) by the crystallization apparatus of the present invention will be described. In this embodiment, the thin film to be crystallized is an amorphous silicon thin film, and crystallization is performed by a solid laser annealing method using harmonics of a solid laser.

  In the crystallization process of an amorphous silicon thin film by a solid laser annealing method, first, as shown in FIG. 1A, an undercoat film 2 that prevents diffusion of impurities by a PE-CVD method or the like on a substrate 1 such as a glass substrate. And an amorphous silicon thin film 3 to be an active semiconductor layer is deposited thereon.

  Here, a natural silicon oxide layer 4 is formed on the surface of the amorphous silicon thin film 3 by natural oxidation, on which contaminants and particles 5 exist. Therefore, for example, cleaning with hydrofluoric acid is performed, and the contaminants and particles 5 existing on the surface are removed together with the natural silicon oxide layer 4 as shown in FIG.

  As the treatment liquid used for the cleaning, for example, one kind selected from hydrofluoric acid, a hydrofluoric acid-containing mixed liquid, and an ammonia-containing reducing liquid can be used. In cleaning with the processing liquid, it is preferable to rotate the substrate on which the amorphous silicon thin film 3 is formed, and this makes it possible to realize uniform and rapid processing.

  Thereafter, crystallization is performed by a solid laser annealing method, and the amorphous silicon thin film 3 is crystallized to form a polycrystalline silicon thin film 7 as shown in FIG. In the solid laser annealing method, the amorphous silicon thin film 3 formed on the substrate 1 is crystallized by irradiation with harmonics of a solid laser. At the time of crystallization, the substrate 1 on which the amorphous silicon thin film 3 is formed on the substrate stage S is supported and fixed, and laser light irradiation is performed. The laser light to be irradiated is a harmonic of a solid-state laser (for example, a harmonic of a YAG laser), and laser light having a wavelength of 400 nm to 600 nm (for example, Nd: YAG of 532 nm) is used. If the harmonics of the solid-state laser can be applied to the silicon film recrystallization process, it is possible to reduce the apparatus cost and maintenance cost by replacing it with a high-power short-wavelength excimer laser. In the present embodiment, the case where a solid-state laser is used as a laser source has been described. However, the present invention can be applied to all cases where a laser beam having a visible wavelength region such as a semiconductor laser is used.

  The above is the crystallization process. After the crystallization process, a thin film transistor and a liquid crystal display panel (array substrate) are manufactured by using the formed polycrystalline silicon film 7.

  That is, after patterning a photoresist on the polycrystalline silicon thin film 7, as shown in FIG. 2A, the polycrystalline silicon film is processed into an island shape using a CDE method or the like. Then, high-pressure steam annealing is performed on the polycrystalline silicon thin film 7 without adding oxygen, for example, at 300 ° C., 20 atm for 1 hour, and dangling existing on the surface of the active semiconductor layer, the crystal grain boundary, and the crystal. A hydrogen atom or an oxygen atom is bonded to the bond.

Then, a low concentration implanted into the polycrystalline silicon film using B ₂ H ₆ serving as an acceptor ion doping method or the like for controlling the threshold voltage of the thin film transistor. Next, as shown in FIG. 2B, a gate insulating film 8 is formed by, for example, PE-CVD, and as shown in FIG. 2C, sputtering, photolithography pattern formation by photolithography, RIE method is performed. Thus, the gate electrode 9 is formed.

At the stage of processing, B ₂ H _{6 serving} as an acceptor is divided into a high concentration and PH _{3 serving} as a donor is divided into a high concentration and a low concentration twice, and regions are respectively selected in the polycrystalline silicon film by an ion doping method. inject. As a result, an n-type thin film transistor having an LDD structure composed of a low concentration donor region 10 and a high concentration donor region 11 as shown in FIG. 2D, and a p-type thin film transistor as shown in FIG. A source region and a drain region (high concentration acceptor region 12) can be formed.

  Then, after annealing at 500 ° C. to activate the implanted impurities, an interlayer insulating film 13 is deposited on the entire surface by PE-CVD, a photoresist pattern is formed by photolithography, and then etched to form a contact hole. To the surface of the polycrystalline silicon film 7. Then, wiring 14 and wiring 15 connected to the source and drain electrodes of the thin film transistor are formed by sputtering, photo resist pattern formation by photolithography, and RIE, as shown in FIG. 2 (e) or FIG. 3 (b). Thus, n-type and p-type thin film transistors are completed.

  Thereafter, the entire surface is covered with a silicon nitride film serving as a passivation film by PE-CVD, photoresist patterning is performed, and contact holes are opened by etching by CDE. Finally, after applying and patterning the photosensitive transparent resin film, a transparent pixel electrode made of ITO is formed by sputtering, photoresist patterning, and etching. The liquid crystal display panel array substrate is thus completed.

  In the array substrate of the liquid crystal display panel manufactured through the above steps, the characteristics (crystallinity) of the polycrystalline silicon thin film crystallized by the crystallization process affects the characteristics of the thin film transistor, thereby realizing uniform display. Therefore, it is preferable to use isotropic and uniform polycrystalline silicon for the thin film transistor.

  Here, in order to improve the crystal uniformity of the polycrystalline silicon thin film, it is necessary to make the energy that the laser light transmitted through the substrate 1 and reflected by the substrate stage S is absorbed again by the amorphous silicon thin film 3 uniform. For example, as shown in FIG. 4, the irradiated laser light L is absorbed by the amorphous silicon thin film 3 and contributes to crystallization, but a part of the laser light L passes through the substrate 1 and the surface of the substrate stage S. And is incident on the amorphous silicon thin film 3 again, and its energy contributes to crystallization. In the crystallization in which a part of the irradiated laser beam L passes through the amorphous silicon thin film 3, it is necessary to make the total amount of energy absorbed including the reflection from the substrate stage S uniform.

  Even if the surface of the substrate stage S is a flat surface having no structure, it has a certain pattern and is shaded as shown in an enlarged view in the circle of FIG. This difference in shading leads to a difference in reflectivity and a difference in crystallinity occurs on the order of the size corresponding to the pattern. Alternatively, suction holes H and grooves G for vacuum suction of the substrate 1 are formed on the surface of the substrate stage S. If these adsorption holes H and grooves G are present in the crystallization region, it also leads to a difference in reflectivity and hinders uniform crystallization.

  Therefore, in the present invention, for example, the surface of the substrate stage S is mirror-finished to make the reflectance in the laser light irradiation region (crystallization region) uniform. The laser irradiation area of the substrate stage S is a flat surface having no structure, the surface is a mirror surface, and the reflectance of the surface of the laser irradiation area of the substrate stage S is uniform as a whole. That is, the reflectance in the entire crystallization region of the amorphous silicon thin film 3 which is a thin film to be crystallized is substantially uniform.

  The surface of the substrate stage S is not limited to the mirror surface, and may have a structure in which light is uniformly scattered, for example. Alternatively, the surface of the substrate stage S may absorb light. In addition, since heat is generated by laser irradiation, the material of the substrate stage S is preferably metal or ceramic.

  On the other hand, the suction holes H and the grooves G for vacuum-sucking the substrate 1 are preferably formed at positions deviating from the panel region (crystallization region) of the substrate 1. By forming these suction holes H and grooves G at positions outside the panel region, crystallization is not affected. For example, when manufacturing an array substrate of a liquid crystal display panel, as shown in FIG. 6, a plurality of (4 × 4 = 16 in this case) array substrates are separately formed from one substrate 1. A region corresponding to each array substrate is a panel region 21. The suction hole H is formed at a position away from the panel region 21 of the substrate 1. In order to enable the adsorption of the substrate 1 and make the reflectance of the surface of the substrate stage S uniform, for example, a porous material can be used for the substrate stage S, whereby the substrate 1 is spread over the entire surface of the substrate stage S. It becomes possible to hold by adsorption.

  Further, when installing the substrate 1 on the substrate stage S, or when installing a mechanism for lifting the substrate 1 when the substrate 1 is unloaded from the substrate stage S, the panel region (crystallization region) of the substrate 1 is also used. It is preferable to form it at a position away from it. By installing the mechanism outside the laser irradiation area of the substrate stage S, it is possible to have the same functionality as a conventional crystallization apparatus without affecting crystallization.

  In the crystallization apparatus of the present embodiment having the above-described configuration, since the reflectance of the surface of the substrate stage S is uniform over the entire crystallization region of the amorphous silicon thin film 3, the substrate stage S in the amorphous silicon thin film 3 is changed. The total amount of absorbed energy including the reflection of can be made uniform, and the polycrystalline silicon thin film 7 having excellent uniformity can be formed.

  Hereinafter, specific examples of the present invention will be described based on experimental results.

The laser irradiation area of the substrate stage used in this example is a flat surface having no structure, the surface is a mirror surface, and the reflectance of the substrate stage is uniform over the entire substrate stage surface. A glass substrate having an amorphous silicon thin film formed thereon is placed on this substrate stage, and a solid-state laser having a wavelength of 532 nm in the visible region (second harmonic of YAG laser) is irradiated in pulses at an energy density of 600 mJ / cm ^2. did.

  In the irradiated laser of each pulse, a part of the laser incident from the surface of the amorphous silicon thin film is absorbed, and the others are transmitted through the glass substrate, reflected by the substrate stage, and again transmitted through the glass substrate to form the amorphous silicon thin film. Incident from the back side. Then, as in the case from the surface, a part of the incident laser is absorbed by the amorphous silicon thin film, and the rest escapes above the substrate. As a result, the absorbed energy causes the amorphous silicon thin film to melt and crystallize into a polycrystalline silicon thin film. However, since the reflectivity of the substrate stage is uniform over the entire surface of the substrate stage, the amorphous silicon thin film of the irradiated laser A polycrystalline silicon thin film having a uniform crystal with a uniform amount of total energy absorbed and a good uniformity with a grain size of about 0.4 μm was obtained.

(A)-(c) is a schematic sectional drawing which shows a crystallization process in process order. (A)-(e) is a schematic sectional drawing which shows the preparation process of an n-type thin-film transistor in order of a process. (A)-(b) is a schematic sectional drawing which shows the production process of a p-type thin-film transistor in order of a process. It is a schematic sectional drawing which shows typically the mode of irradiation of a laser beam. It is a top view which shows typically an example of the surface structure of a substrate stage. It is a typical top view which shows the panel area | region of a board | substrate.

Explanation of symbols

1 substrate, 2 undercoat film, 3 amorphous silicon thin film, 4 natural silicon oxide layer, 5 particles, 7 polycrystalline silicon thin film, 8 gate insulating film, 9 gate electrode, 10 low concentration donor region, 11 high concentration donor region, 12 High concentration acceptor region, 13 interlayer insulating film, 14, 15 wiring, 21 panel region, S substrate stage, H adsorption hole, G groove

Claims (10)

A crystallization apparatus for performing crystallization by irradiating a crystallized thin film formed on a light-transmitting substrate with laser light,
A substrate stage for supporting the substrate on which the thin film to be crystallized is formed;
The substrate stage has a substantially uniform reflectivity over the entire crystallization region of the thin film to be crystallized.   The crystallization apparatus according to claim 1, wherein a wavelength region of the laser beam is a visible region.   The crystallization apparatus according to claim 1, wherein the laser beam is a harmonic of a solid-state laser.   2. The crystallization apparatus according to claim 1, wherein the thin film to be crystallized is an amorphous silicon thin film.   The crystallization apparatus according to claim 1, wherein the surface of the substrate stage is mirror-finished.   The crystallization apparatus according to claim 1, wherein the surface of the substrate stage uniformly scatters light.   The crystallization apparatus according to claim 1, wherein the surface of the substrate stage is made of a non-reflective material.   The crystallization apparatus according to any one of claims 1 to 4, wherein a material of a surface of the substrate stage is a metal or a ceramic.   9. The crystallization apparatus according to claim 1, wherein a mechanism for holding the substrate of the substrate stage is installed at a position deviating from the crystallization region.   The crystallization apparatus according to any one of claims 1 to 9, wherein a mechanism for setting or unloading the substrate on the substrate stage is installed at a position out of the crystallization region.

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