KR100478757B1 - A method for crystallizing of an amorphous Si - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for crystallizing silicon, and more particularly, to a method for forming a thick polysilicon layer (600 Pa or more) using a low cost laser beam device.

In the method of forming polysilicon according to the present invention, amorphous silicon is divided and deposited several times, and the crystallization process is performed for each deposition process.

In this way, a low-cost laser beam device can be used, and a thick polysilicon layer can be obtained using the laser beam device, thereby making it possible to manufacture a switching device having improved operating characteristics with cost reduction.

Description

A method for crystallizing of an amorphous Si}

The present invention relates to a method of forming a thick polysilicon layer (500 kPa or more) using sequential lateral solidification (hereinafter referred to as "SLS").

In general, silicon may be classified into amorphous silicon and crystalline silicon according to a crystalline state.

Amorphous silicon can be deposited at a low temperature to form a thin film, and is mainly used in switching devices of liquid crystal panels using glass having a low melting point as a substrate.

However, the amorphous silicon thin film has difficulty in deteriorating electrical characteristics and reliability of the liquid crystal panel driving device and increasing the display device large area.

Commercialization of large-area, high-definition and panel image driving circuits, integrated laptop computers, and wall-mounted TV LCDs has excellent electrical characteristics (e.g. high field effect mobility (30㎠ / VS) and high frequency operating characteristics). And low leakage current pixel driving devices, which require the application of high quality poly crystalline silicon.

In particular, the electrical properties of the polycrystalline silicon thin film are greatly influenced by the grain size. In other words, the field effect mobility increases as the grain size increases.

Therefore, the method of single crystallization of silicon has become a big issue in consideration of this point, and recently, the sequential lateral solidification (SLS) (continuous sequential) of producing large single crystal silicon by inducing lateral growth of silicon crystals using an energy source as a laser. The aspect of solidification has been proposed in international patents "WO 97/45827" and Korean published patents "2001-004129".

The SLS technology takes advantage of the fact that silicon grain grows in the direction perpendicular to the interface between the liquid silicon and the solid silicon, and appropriately controls the size of the laser energy and the shift of the irradiation range of the laser beam. By growing the silicon grain by a predetermined length, the amorphous silicon thin film is crystallized.

SLS equipment for realizing this SLS technology is as shown in Figure 1 below.

The SLS device 32 includes a laser generator 36 for generating a laser beam 34, a focusing lens 40 for focusing a laser beam emitted through the laser generator, and a laser beam on a substrate 44. The mask 38 for irradiating and dividing the light, and the reduction lens 42 positioned at the lower portion of the mask 38 to reduce the laser beam 34 passing through the mask at a constant ratio.

The laser beam generator 36 emits an unprocessed laser beam from a light source, passes through an attenuator (not shown) to adjust the energy of the laser beam, and the laser beam 34 through the focusing lens 40. ).

The X-Y stage 46 to which the substrate 44 on which the amorphous silicon thin film is deposited is fixed is positioned at a position corresponding to the mask 38.

In this case, in order to crystallize all the regions of the substrate 44, a method of gradually expanding the crystal regions by moving the X-Y stage 46 minutely is used.

In the above-described configuration, the mask 38 is divided into a transmission region A for passing the laser beam and a blocking region B for absorbing the laser beam.

FIG. 1 illustrates a general SLS crystallization apparatus as an example for clarity. In general, the SLS crystallization apparatus varies in price depending on the energy density of a laser beam generated, and is more expensive for generating a laser beam having a higher energy density. .

Generally, high density energy generating equipment is used to obtain a thick polysilicon layer in one process.

Hereinafter, a method of crystallizing amorphous silicon using an SLS crystallization apparatus for generating a high density laser beam will be described.

2A to 2D are cross-sectional views sequentially illustrating a polysilicon crystallization process according to a conventional process sequence.

As shown in FIG. 2A, a buffer layer 12 which is an insulating film is formed on the substrate 10. As shown in FIG.

The buffer layer 12 is formed of one selected from a silicon insulating material including a silicon nitride film (SiN _X ) and a silicon oxide film (SiO ₂ ).

The buffer layer 12 serves to prevent the alkali-based material present on the surface of the substrate from being locally eluted and diffused into the silicon layer by the heat while irradiating the laser beam to the amorphous silicon.

Next, an amorphous preceding film (amorphous silicon layer: a-Si: H) 14 is formed on the buffer layer 12.

The amorphous preceding film 14 is generally deposited on the substrate 10 by using chemical vapor deposition (CVD), which contains a large amount of hydrogen (H) in the thin film.

Since the hydrogen leaves the thin film by heat, it is necessary to first heat-treat the amorphous preceding film 14 to undergo a dehydrogenation process.

This is because if the hydrogen is not removed in advance, the surface of the crystal thin film becomes very rough and its electrical characteristics are poor.

At this time, the thickness of the amorphous preceding film is formed to be thicker than 500Å.

As shown in FIG. 2B, the aforementioned mask 38 is placed on top of the amorphous silicon layer where the dehydrogenation process is completed.

The laser beam irradiated in an arbitrary shape through the mask 38 composed of the transmission region A and the blocking region B partially melts the amorphous silicon, so that the amorphous silicon layer 14 is melted region C. And the non-melting zone (D).

In this case, the laser beam has a high energy density of 1 J / cm 2 per one shot, and an expensive laser beam generator is used for this purpose.

As shown in FIG. 2C, the portion irradiated with the laser beam is rapidly cooled while the grains 60a are formed into the inside of the molten region starting from the boundary between the melting region C and the non-melting region D. 60b) is lateral growth.

Accordingly, the first grain region E and the second grain region F are formed in the molten region C. FIG.

At this time, if the width of the transmissive region (A in FIG. 2B) of the mask is twice or less than the maximum growth length of the grain, the grains 60a and 60b formed in the respective grain regions E and F grow while bumping each other. Will stop.

On the other hand, if the width of the transmissive region (A in FIG. 2B) is greater than twice the maximum growth path of the grain, crystallization will proceed while there is a nucleation region (not shown) between the grain regions. (At this time, the maximum growth path of grain means the maximum length of grain belonging to each grain area.)

In the former case, when the shape of the crystallization is observed in plan view, it is as shown in FIG. 2D.

That is, a partial polysilicon crystal region composed of the first grain region E and the second grain region F is formed in each melting region C. As shown in FIG.

Next, as shown in FIG. 2E, after partially crystallizing, the mask is continuously moved on the X axis (the same as the stage 46 in FIG. 1 is moved on the -X axis).

At this time, the movement distance D of the mask moves smaller than or equal to the length of each of the grains 60a and 60b belonging to the first grain area E. FIG.

When crystallization is performed by irradiating a laser (generally an excimer laser) in such a state, crystallization proceeds while the amorphous silicon layer corresponding to the transmission region A of the mask 38 is completely melted and then cooled.

As a result, not only a new crystal region G is formed, but also grains of the first grain region E are further grown.

If the crystallization proceeds little by little by moving the mask in the above-described manner, as shown in FIG. 2F, a polysilicon layer composed of grains 60a grown to a desired length can be obtained.

However, in the related art, an expensive laser beam device is used to obtain a thick polysilicon layer using a lateral growth method, which is a great burden in terms of cost.

In addition, the thicker the amorphous preceding film, the greater the probability that a defect occurs in the crystal layer during the crystallization process, which causes a decrease in operating characteristics of the device.

SUMMARY OF THE INVENTION The present invention has been proposed to solve this problem, and aims to fabricate a switching device having improved operating characteristics while reducing costs by forming a polysilicon layer having a desired thickness using a low-cost laser beam device.

Polysilicon crystallization method according to the present invention for achieving the object as described above comprises the steps of depositing a first amorphous silicon on a substrate; Placing a mask comprising a transmission region and a blocking region on the first amorphous silicon layer; Irradiating a first laser beam onto the mask to completely melt the first region of the first amorphous silicon layer corresponding to the transmission region and to crystallize the first laser beam; Mapping the second region overlapping the first region of the first amorphous silicon layer and the transmission region; Irradiating a secondary laser beam onto the mask to completely melt and crystallize a second region of the first amorphous silicon layer to form a first polysilicon layer; And depositing second amorphous silicon on the first polysilicon layer and irradiating a third laser beam to form a second polysilicon layer continuously grown on the first polysilicon layer.

The first amorphous silicon layer and the second amorphous silicon layer are characterized in that the thickness of 250 ~ 300Å, respectively, the laser beam melting the laser beam (laser beam) is 350mJ / ㎠ ~ 500mJ / ㎠ low energy density Has

After forming the first amorphous silicon layer and the second amorphous silicon layer, a dehydrogenation process is performed.

The polysilicon layer may be formed by repeating the crystallization process several times. The third laser beam may have an energy density such that the second amorphous silicon layer is completely melted and the surface of the first polysilicon layer is melted. The first region may include first and second crystal regions in which crystals grow from both sides toward the inside thereof, and the second region may overlap the second crystal region. The crystal may grow in the thickness direction. The step of matching the second region with the transmission region may be performed by moving the mask.

Hereinafter, a polysilicon crystallization method (SLS crystallization method) according to the present invention will be described in detail with reference to the accompanying drawings.

First Embodiment

The first embodiment of the present invention is characterized by forming a thick polysilicon layer through multiple shots of a laser beam using a low cost laser beam generator.

Hereinafter, a method of forming a polysilicon layer according to the present invention will be described with reference to the drawings.

3A to 3J are cross-sectional views illustrating a method of forming polysilicon according to the present invention in a process sequence.

As shown in FIG. 3A, a buffer layer 102 which is an insulating film is formed on the substrate 100.

The buffer layer 102 is formed of one selected from a silicon insulating material including a silicon nitride film (SiN _X ) and a silicon oxide film (SiO ₂ ).

Next, a first amorphous preceding film (amorphous silicon layer: a-Si: H) 104 is deposited on the buffer layer 102 to a thickness of about 300 mW.

The amorphous preceding film 104 is generally deposited on a substrate using chemical vapor deposition (CVD), which contains a large amount of hydrogen (H) in the thin film.

Since the hydrogen leaves the thin film by heat, it is necessary to first heat-treat the first amorphous preceding film 104 to undergo a dehydrogenation process.

The reason for such a process is as described above.

As shown in FIG. 3B, a mask 150 including a transmission region A and a blocking region B is positioned on the first amorphous preceding film 104 in which the dehydrogenation process is completed.

The laser beam irradiated in an arbitrary shape through the mask 150 partially overlaps the first amorphous preceding film, whereby the first amorphous preceding film 104 has a complete melting region (liquid region) C and a non-melting region ( Solid-state region) (D).

In this case, the laser beam has a low energy density of about 400 mJ / cm 2.

As shown in FIG. 3C, the portion irradiated with the laser beam is rapidly cooled, and grains 120a and 120b are laterally grown, starting from both sides of the melting region C and the non-melting region D, respectively. Will be

Accordingly, the first grain region E and the second grain region F are formed in the molten region C. FIG.

As described above, when the amorphous silicon layer partially crystallized is observed in plan view, as shown in FIG. 3D, the partially molten region C is formed of first grain regions including side-grown grains 120a and 120b. (E) and the second grain area (F).

Next, as shown in FIG. 3E, after partially crystallizing, the mask 200 is moved on the X axis (the same as the stage of FIG. 1 is moved on the -X axis).

At this time, the movement distance D of the mask moves smaller than or equal to the length of the grains belonging to the first grain area E. FIG.

When crystallization is performed by irradiating a laser (generally an excimer laser) in such a state, after the partial crystal region H and the amorphous region I corresponding to the transmission region A of the mask 200 are completely melted, As it cools, crystallization proceeds.

As a result, the crystal region may be expanded, and the grain 120 of the first grain region E may be further grown.

By repeating the above process, as shown in FIG. 3F, the polysilicon layer 122 including the side-grown grains 120 may be formed.

Next, as shown in FIG. 3G, a second amorphous preceding film 124 of about 300 GPa is formed on the entire surface of the substrate 100 on which the crystallized polysilicon layer 122 is formed.

The second amorphous preceding film 124 also undergoes a dehydrogenation process.

As shown in FIG. 3H, the mask 200 including the transmission region A and the blocking region B is positioned on the second amorphous preceding film 124 and irradiated with a laser beam.

In this case, the laser beam has a low energy density of about 400 mJ / cm 2, but when the thickness of the amorphous silicon layer is about 300 μs, the laser beam is sufficient to completely melt it.

When the laser beam is irradiated, the amorphous silicon region of the portion corresponding to the transmission region A of the mask 200 and the surface of the lower portion of the crystalline silicon layer are completely melted so that the amorphous silicon layer is inferior to the molten region C. It becomes the melting region D.

As shown in FIG. 3I, the melting region undergoes crystallization while undergoing a metal cooling process, and crystallization proceeds continuously in the lower crystal layer during the crystallization.

In this process, defects that existed in the crystal layer can be eliminated because the surface of the already crystallized layer is melted and recrystallized.

When the crystallization process as described above is repeated, a thick polysilicon layer 126 may be formed as shown in FIG. 3J.

The above-described process illustrates a crystallization process using multiple shots in which crystallization is performed by irradiating a laser beam several times.

Hereinafter, the second embodiment describes a crystallization process of proceeding crystallization according to the present invention by irradiating two laser beams.

Second Embodiment

The same process as in the first embodiment will be omitted and explained.

4A to 4H are diagrams showing a polysilicon forming method according to a second embodiment of the present invention in order of process. (For convenience, a plane and a cross section are mixed.)

As shown in FIG. 4A, a buffer layer 202 is formed on the substrate 200, and a first amorphous preceding film 204 having undergone a dehydrogenation process is formed on the buffer layer 202 to a thickness of 300 GPa. .

As shown in FIG. 4B, a mask 200 including a transmissive portion A and a blocking portion B is positioned on the first amorphous preceding film 204.

At this time, the width of the transmissive portion (A) of the mask is configured to be greater than or equal to the width of the blocking portion (B).

The first laser beam is irradiated to the upper portion of the mask 200, and as shown in FIG. 4C, the first amorphous preceding film 204 has a melting region C1, C2, C3,, and a non-melting region ( D) consists of.

As described above, the molten regions C1, C2, C3, ... are regions corresponding to the transmissive portions of the mask, and each of the first grain region E and the second grain composed of the laterally grown grains 220a and 220b. It consists of an area F.

As shown in FIG. 4D, the transmissive portion A of the mask 200 is configured to correspond to the upper portion of the non-melted region D. As shown in FIG.

In this case, since the non-melting region D is a portion corresponding to the blocking portion B of the mask 300 in the previous process, the non-melting region D has a width smaller than or equal to the width of the transmission portion A of the mask 300.

As described above, when the mask 300 is positioned and then irradiated with a laser beam to the upper portion of the mask 300, the crystal regions (for example, C1 and C2) of both sides formed through the primary laser beam irradiation process are formed. In the crystal region C1 on one side, the grains 120b belonging to the second grain region F are continuously grown. In the crystal region C2 on the other side, the grains 120B belonging to the first grain region E are grown. The growth is continued and the growth is stopped at the portion corresponding to the central portion of the transmission region A. FIG.

At this time, as described, the laser beam has a low energy density of about 400 mJ / cm 2.

The polysilicon layer 222 may be formed through the two-shot laser beam process as described above.

Next, as shown in FIG. 4F, a second amorphous preceding film 224 having a thickness of about 300 GPa is formed on the entire surface of the substrate 200 on which the crystallized polysilicon layer 222 is formed.

The second amorphous preceding film 224 also undergoes a dehydrogenation process.

The laser beam is irradiated after the mask 300 including the transmission region A and the blocking region B is positioned on the second amorphous preceding film 224.

In this case, the laser beam has a low energy density of about 400 mJ / cm 2, but when the thickness of the amorphous silicon layer is about 300 μs, the laser beam is sufficient to completely melt it.

When the laser beam is irradiated, the amorphous silicon region of the portion corresponding to the transmission region A of the mask 300 and the surface of the crystalline silicon layer below are completely melted, so that the amorphous silicon layer is formed in the molten regions C1, C2, C3 ,,,) and the non-melting region D.

As shown in FIG. 4G, the melting region (C1, C2, C3 of FIG. 4F) undergoes a rapid cooling process, and crystallization proceeds, and crystallization is continuously performed in the lower crystal layer 222 during the crystallization. Proceeds.

In this process, defects that existed in the crystal layer may be removed because the surface of the already crystallized layer 222 is melted to recrystallize.

If the above-described crystallization process is further performed as described in the aforementioned 4f, a thick polysilicon layer 226 may be formed as shown in FIG. 4H.

A thick polysilicon layer composed of grains laterally grown by the above-described process can be formed using a low-cost laser beam generator.

Therefore, when the thick polysilicon layer is formed in accordance with the present invention, a thick polysilicon layer with a minimum of defects can be obtained, and thus a switching device having excellent mobility can be produced, and a low-cost laser beam generator is used. This can reduce costs.

1 is a view schematically showing a laser beam generator for forming a lateral growth crystallized polysilicon layer,

2A to 2F are process diagrams illustrating a lateral growth crystallization process of amorphous silicon according to a conventional method,

3A to 3J are process diagrams showing the lateral growth crystallization process of amorphous silicon in the order of the first embodiment of the present invention,

4A through 4H are cross-sectional views showing a process of crystallizing the side growth of amorphous silicon in the order of the second embodiment of the present invention.

<Explanation of symbols for the main parts of the drawings>

100 substrate 102 buffer layer

104: partially melted amorphous silicon layer

Claims (10)

Depositing a first amorphous silicon on the substrate; Placing a mask comprising a transmission region and a blocking region on the first amorphous silicon layer; Irradiating a first laser beam onto the mask to completely melt the first region of the first amorphous silicon layer corresponding to the transmission region and to crystallize the first laser beam; Mapping the second region overlapping the first region of the first amorphous silicon layer and the transmission region; Irradiating a secondary laser beam onto the mask to completely melt and crystallize a second region of the first amorphous silicon layer to form a first polysilicon layer; Depositing a second amorphous silicon on the first polysilicon layer and irradiating a third laser beam to form a second polysilicon layer continuously grown on the first polysilicon layer Polysilicon forming method comprising a. The method of claim 1, Wherein the thicknesses of the first amorphous silicon layer and the second amorphous silicon layer are 250 kPa to 300 kPa, respectively. The method of claim 2, And the first, second and third laser beams each have an energy density of 350 mJ / cm 2 to 500 mJ / cm 2. The method of claim 1, And forming a first amorphous silicon layer and a second amorphous silicon layer, and then performing a dehydrogenation process, respectively. The method of claim 1, Wherein the first and second polysilicon layers are formed by repeating the crystallization process several times. The method of claim 1, And the third laser beam has an energy density such that it completely melts the second amorphous silicon layer and melts the surface of the first polysilicon layer. The method of claim 1, Wherein the first region includes first and second crystal regions in which crystals grow from both sides toward the inside thereof. The method of claim 7, wherein And the second region overlaps the second crystal region. The method of claim 1, The second polysilicon layer is a polysilicon forming method wherein crystals grow in the thickness direction. The method of claim 1, The step of causing the second region to correspond to the transmissive region may be performed by moving the mask.