KR100478758B1 - 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 crystallization method of silicon, and more particularly, to a laser beam mask and a method of forming polysilicon using the same, wherein the laser beam energy irradiated to the amorphous preceding film is divided into a strong portion and a weak portion.

The mask according to the present invention is configured such that the transmission region through which the laser beam is transmitted has different transmittances, so that a laser of higher energy density is irradiated at the center of the transmission region.

In this way, grains grow further toward the center of the silicon layer corresponding to the transmission region.

Therefore, productivity can be improved by reducing the number of shots of the laser incident pulse and the number of stage movements, and the defects of the thin film due to laser incidence can be reduced.

Description

A method for crystallizing of an amorphous Si}

The present invention relates to a method of forming polysilicon at low temperature, and more particularly, to a crystallization method capable of inducing grain lateral growth to lengthen crystal growth length and shortening processing time.

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 liquid crystal display devices has shown excellent electrical characteristics (e.g. high field effect mobility, high frequency operation characteristics and low leakage current). ), Which requires 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. That is, as the grain size increases, the field effect mobility also 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), which manufactures huge single crystal silicon by inducing lateral growth of silicon crystals using an energy source as a laser, has been emerging. Growth crystallization) technology has been proposed.

The SLS technology takes advantage of the fact that the silicon grain grows in the direction perpendicular to the interface at the interface between the liquid silicon and the solid silicon, and by appropriately controlling the intensity of the laser energy band and the shift of the irradiation range of the laser beam. In this case, the amorphous silicon thin film is crystallized by lateral growth of silicon grain by a predetermined length.

SLS equipment for realizing such an SLS technology is as shown in FIG. 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 regions of the substrate 44, a method of enlarging the crystal region by moving the X-Y stage 46 or the mask slightly 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 blocking the laser beam.

A method of crystallizing silicon using the SLS crystallization equipment as described above will be described.

In general, crystalline silicon is formed by forming a buffer layer (not shown) which is an insulating film on the substrate, and using an amorphous predecessor film on the buffer layer. The amorphous preceding film is generally deposited on a substrate using chemical vapor deposition (CVD) or the like, which contains a large amount of hydrogen (H) in the thin film.

Since the hydrogen (H) is characterized by leaving the thin film by heat, it is necessary to undergo a dehydrogenation process by primarily heat treating the amorphous preceding film.

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.

 FIG. 2 is a substrate 54 in which an amorphous silicon 52 film is formed by undergoing dehydrogenation and partially crystallized.

As shown, crystallization using a laser beam cannot be simultaneously performed over the entire area of the substrate 54.

Because the beam width of the laser beam and the size of the mask (38 in FIG. 1) are limited, the crystallization is performed by aligning the single mask (38 in FIG. 1) many times in large areas and repeating the crystallization process each time. Is done.

In this case, if a region crystallized by the reduced area C of the single mask is defined as one block, crystallization in the one block is also performed through multiple laser beam irradiation.

The crystallization process of the amorphous silicon film according to the first conventional example will now be described with reference to FIGS. 3A to 3D. (The conventional example is performed by a scan & step method, and the feature of the first example is the mask. The width of the transmissive area configured in the laser beam is greater than twice the length of the maximum growing grain upon laser beam irradiation.)

3A to 3D are diagrams sequentially illustrating a crystallization process of an amorphous silicon thin film using the SLS device. In this case, crystallization in units of blocks has been described as an example. In addition, three slits are provided in the mask. Assume that it was formed.)

First, as shown in FIG. 3A, a buffer layer 56 is formed on a transparent insulating substrate 52, and an amorphous silicon layer 58 is formed on the buffer layer 56.

The buffer layer 58 is formed of one selected from a silicon insulating material including a silicon nitride film (SiN _X ) and a silicon oxide film (SiO ₂ ).

Since the amorphous silicon layer contains hydrogen, a dehydrogenation process is necessarily performed before crystallization.

The mask 38 is positioned on the substrate 52 on which the dehydrogenation process is performed. As described above, the mask 38 includes a transmission area A and a blocking area B.

When the laser beam is first irradiated from the upper portion of the mask, the irradiated laser beam is divided by a plurality of slits (transmission regions) A formed in the mask to partially dissolve and liquefy the amorphous silicon thin film 58.

Thus, the amorphous silicon thin film 58 is divided into a liquid silicon inverse region E and a solid silicon region F. As shown in FIG.

In this case, the degree of laser energy uses a high melting region (complete melting regime) such that the amorphous silicon thin film is completely melted.

When the fully melted and liquefied silicon is irradiated with laser beam, the silicon grains are laterally grown at the interfaces 60a and 60b of the solid silicon region E and the liquid silicon region F.

Therefore, as shown in FIG. 3B, the lateral growth of the silicon grains 61 and 62 proceeds. Lateral growth of grains 61 and 62 occurs perpendicular to the interfaces 60a and 60b.

In general, the length of crystal growth proceeded by a laser beam irradiation process is generally grown to a length of 1 μm to 1.5 μm, and if the beam pattern is larger than twice the grain growth length, as shown in FIG. In the regions where the grains 61 and 62 grown at both interfaces and the grains are adjacent, a plurality of nucleation regions (fine polycrystalline silicon particle regions) H exist.

In the crystallization process through the first laser beam irradiation as described above, a partially crystallized region E is generated in one block by the number of transmission regions (A in FIG. 3A) configured in the mask 38 of FIG. 3A. .

Next, FIG. 3C is a view showing a state in which grains are grown by irradiating a laser beam secondarily.

After the primary laser beam irradiation, the XY stage (46 in FIG. 1) or the mask is moved several micrometers smaller than the lateral growth length of the grain on one side with respect to the nucleation region (H in FIG. 3B), and then again 2 Different laser beam irradiation is performed.

In this case, if the transmission region of the mask is not configured to correspond to the region including the nucleation region, the grain cannot grow longer than the length grown during the first laser beam irradiation.

Therefore, as described above, the laser beam pattern (mask pattern) is smaller than the lateral growth length of the grain, so that the laser beam pattern may be located including the nucleation region (H in FIG. 3A). It should move below 1 μm.

Therefore, the portion of the silicon that hits the secondary irradiated laser beam includes a substantial portion of the crystal region and an amorphous region, which are liquefied and then crystallized again.

At this time, the lateral growth of the grain is formed in the silicon melting region in succession to the silicon grain (62 in FIG. 3A) of the polycrystalline silicon region formed as a result of the primary irradiation.

After the secondary laser beam irradiation, the silicon crystal is formed of the first grain region 66, the nucleation region I, and the new second grain region 70 grown by the primary irradiation.

Therefore, the above-described process may be repeated a number of times to form an amorphous thin film corresponding to one block as the crystalline silicon thin film 72 as shown in FIG. 3D.

In addition, the crystallization process of the block unit may be repeated to form an amorphous thin film having a large area as a crystalline thin film.

4 is a view showing an energy density of a laser beam shaped by a mask, and thus crystallization of amorphous silicon.

As shown, the mask 38 deposits and partially patterns an opaque metal such as chromium (Cr) or aluminum (Al) on top of a transparent substrate 10 such as quartz.

The patterned thin film layer 12 becomes a blocking region B, and a region between the blocking regions B becomes a transmission region A. FIG.

 At this time, the energy density of the laser beam passing through the transmission region A of the mask 38 is the energy of the complete melting region (complete melting), the same for all the transmission region (A).

When the laser beam having such energy is irradiated to the lower silicon thin film through the mask, after reaching the highest temperature after the laser pulse delay time of several tens of ns, it starts to cool, and the liquid silicon region (E) and the solid phase of which the laser beam width is the outer part Crystals 61 and 62 grow toward the center portion at both interfaces 60a and 60b of the silicon region F band.

At this time, the growth of the lateral growth of the grain is limited by the growth of the nucleation region H generated when the temperature of the center portion is subcooled below the melting point.

In addition, due to the limitation of the grain growth length, a crystal layer made of grain having a desired length can be obtained only by repeating a process in which the mask 38 or the stage (46 in FIG. 1) is micro-migrated several times.

Therefore, in order to achieve all the crystallization of the desired area, the total time required for moving the mask 38 or the stage (46 in FIG. 1) occupies a large proportion of the total crystallization process time, which causes a decrease in process yield. .

However, if the time for generating the nucleation region can be delayed, the lateral growth length due to the laser 1 pulse can be increased.

In this way, in order to achieve a nucleation time delay by increasing the temperature, a method of heating the amorphous silicon region corresponding to the entire beam width by increasing the energy density per laser pulse can be considered. There is this tearing-off problem.

The present invention has been devised to solve this problem, and by redesigning the configuration of the mask to change the spatial distribution of the energy density passing through the transmission region of the mask, delaying the nucleation time generated corresponding to the central portion of the transmission region. It is aimed to allow grain to grow as much as the nucleation region.

Polysilicon forming method according to the present invention for achieving the object as described above comprises the steps of depositing amorphous silicon on a substrate to form an amorphous preceding film; Placing a mask consisting of a blocking region and a transmitting region on an upper portion of the amorphous preceding film; Irradiating a primary laser beam onto the mask to completely melt and crystallize the first region of the amorphous silicon layer corresponding to the transmission region; Mapping a second region overlapping the first region and the transmission region on the amorphous silicon layer; Irradiating a secondary laser beam over the mask to completely melt and crystallize the second region of the amorphous silicon layer, wherein the energy density of the laser beam passing through the central portion of the transmission region is Higher than the energy density of the laser beam passing through the periphery.

In some cases, the polysilicon is formed by repeating crystallization several times.

An opaque metal pattern is formed on the substrate in the blocking region of the mask, and a second pattern, which is a dielectric material having a higher absorption coefficient than the substrate and a lower absorption coefficient than the metal pattern, is formed in a part of the transmission region.

The metal pattern is formed of aluminum (Al) or chromium (Cr).

The region in which the amorphous silicon is crystallized is composed of a first crystal region and a second crystal region in which crystal grows from the interface between the melt region and the non-melt region on both sides of the melt region.

The laser beam passing through the transmission region of the mask has an energy density of the complete melting region to completely dissolve the amorphous silicon. The step of matching the second area with the transmission area is performed by moving the mask.

According to an aspect of the present invention, a laser beam mask includes: a transparent substrate defined as a transmission region and a blocking region; A first pattern which is an opaque metal pattern formed in the blocking region; A second pattern configured at a periphery of the transmission region, the second pattern having an absorption coefficient higher than that of the substrate and having an absorption coefficient lower than that of the metal pattern, wherein an energy density of the laser beam passing through the central portion of the transmission region is at the periphery of the transmission region; It is higher than the energy density of the laser beam passing through.

The second pattern is composed of a dielectric materal.

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

Example

5 is a diagram illustrating an energy density distribution of a mask manufactured according to the present invention and a laser beam according thereto.

As shown, the laser beam mask M according to the present invention is a transparent substrate 100, such as quartz, and an opaque metal material such as chromium (Cr), aluminum (Al) partially on the substrate 100 Is deposited and patterned to form a first pattern 102.

The first pattern becomes a blocking region B in the mask M. FIG.

Next, a dielectric material having a larger absorption coefficient than the substrate 100 and a smaller absorption coefficient than an opaque metal may correspond to a partial region of the transmission region A, which is an area between the blocking regions B. The second pattern 104 is formed.

Since the second pattern 104 is deposited and patterned on the first pattern 102, the second pattern 104 is formed to cover the entirety of the blocking region B and a part of the transmission region A. FIG.

At this time, the first pattern 102 and the second pattern 104 may be formed in reverse order.

When the laser beam is irradiated to the upper portion of the mask M manufactured as described above, the spatial distribution D of the laser beam energy density passing through the transmission region A is determined by The energy density D1 of the portion corresponding to the center portion is the highest, and the energy density D2 of the portion corresponding to the periphery of the transmission region is adjusted to be lower.

In this case, the energy densities corresponding to D1 and D2 correspond to the energy densities of the complete melting region.

For example, if the energy density of the laser beam required to fully melt amorphous silicon of about 300 mW is between 350 mJ and 500 mJ, the D1 and D2 are determined within this range.

As described above, the amorphous silicon region irradiated with the laser beam having the artificial spatial distribution undergoes a crystallization process different from the conventional one with time.

A description with reference to FIG. 6 is as follows.

6 is a graph showing a crystallization process with respect to time when a laser beam having a spatial distribution according to the present invention is irradiated.

As shown, the amorphous silicon melts completely at the time of th when the laser beam is irradiated.

Referring to the graph G according to the related art, nucleation starts to occur when t1 is cooled from the time of th.

However, looking at the graph (M) according to the laser beam distribution according to the present invention has the effect of delaying the nucleation time from t1 to t2.

This is possible because the phenomenon when a laser pulse with a pulse delay time of several tens of ns is incident is greatly out of balance.

Therefore, the length at which side growth starts after reaching the peak temperature (th) increases from v (t1-th) to v (t2-th) when the moving speed of the resolidification solid phase / liquid interface is v. You can get the result.

This can be used to increase the lateral growth length by one laser pulse.

Therefore, even the same final grain length can reduce the number of pulses of the laser beam, and can reduce the movement of the stage (number of movements of the mask) described in FIG.

The lateral growth crystallization process according to the present invention using a mask fabricated as described above will be described below with reference to the accompanying drawings.

7A and 7B are diagrams sequentially illustrating a lateral growth crystallization process according to the present invention.

First, as shown in FIG. 7A, a buffer layer 302 is formed on a transparent insulating substrate 300, and an amorphous silicon (a-Si: H) layer 304 is formed on the buffer layer.

The buffer layer 302 is formed of one selected from the group of silicon insulating materials including silicon nitride (SiN _X ) and silicon oxide (SiO ₂ ).

Subsequently, a dehydrogenation process for removing hydrogen (H) contained in the amorphous thin film layer is performed.

The mask M including the transmission region A and the blocking region B is positioned on the amorphous silicon layer 304 subjected to the dehydrogenation process.

As described above, the blocking region B includes a first pattern 306 formed by depositing and patterning an opaque metal such as chromium (Cr) or aluminum (Al), and the blocking region B and the transparent region ( A dielectric pattern is deposited over a portion of A) to form a patterned second pattern 308.

When the laser beam is irradiated to the upper portion of the mask M, the laser beam width passing through the transmission region A of the mask M has different energy densities and melts the amorphous silicon.

In this case, all of the amorphous silicon regions corresponding to the central portion A1 and the peripheral portion A2 of the transmission region A are completely melted, but at this time, the laser is irradiated to the amorphous silicon region corresponding to the central portion A1 of the transmission region A. The energy density of the beam is higher.

The laser beam as described above is irradiated so that the amorphous silicide layer 304 is partially melted and cooled at the same time.

Therefore, as shown in FIG. 7B, grains 312a and 312b grow from both interfaces 310a and 310b of the liquid phase region E and the solid state region F. As shown in FIG.

At this time, the portion corresponding to the center portion (A1 in FIG. 7A) of the mask transmission region has a high temperature, so that the cooling time is delayed and the nucleation time is delayed.

The grains 312a and 312b grown from both sides continue to grow and hit each other to stop growth.

Therefore, a crystal region composed of the first crystal region J1 and the second crystal region J2 can be obtained for each liquid region E. FIG.

As a result, grains grown longer for one pulse of the laser beam can be obtained.

Since the process is the same as the process described in Figures 3c to 3d described above it will be omitted.

Through the process as described above, it is possible to form the lateral growth crystallized polysilicon layer using the mask according to the present invention.

Therefore, when the polysilicon layer is formed using the laser beam mask according to the present invention, grains grown longer with respect to a laser beam of one pulse can be obtained than in the prior art, thereby reducing the number of shots of the laser beam and the number of mask movements. Can be.

Therefore, there is an effect of improving the yield due to shortening the process time.

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

2 is a view showing a substrate that is partially crystallized,

3A to 3C are cross-sectional views illustrating a conventional method of crystallizing lateral growth according to a process sequence;

4 is a view showing an energy density distribution and a crystallized state of a laser beam according to a conventional mask,

5 is a view showing an energy density distribution of a mask according to the present invention, and a laser beam according thereto,

6 is a graph comparing the crystallization process with time according to the present invention,

7A and 7B illustrate a side growth crystallization process according to the present invention.

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

100: transparent substrate 102: opaque first pattern

104: second pattern formed of a dielectric material

Claims (10)

Depositing amorphous silicon on the substrate to form an amorphous preceding film; Placing a mask consisting of a blocking region and a transmitting region on an upper portion of the amorphous preceding film; Irradiating a primary laser beam onto the mask to completely melt and crystallize the first region of the amorphous silicon layer corresponding to the transmission region; Mapping a second region overlapping the first region and the transmission region on the amorphous silicon layer; Irradiating a secondary laser beam on top of the mask to completely melt and crystallize the second region of the amorphous silicon layer, And the energy density of the laser beam passing through the central portion of the transmission region is higher than the energy density of the laser beam passing through the periphery of the transmission region. The method of claim 1, An opaque metal pattern is formed on a substrate in a blocking region of the mask, and a part of the transmission region is formed of a second pattern, which is a dielectric material having a higher absorption coefficient than a substrate and a lower absorption coefficient than a metal pattern. The method of claim 2, The metal pattern is polysilicon forming method of aluminum (Al) or chromium (Cr). The method of claim 1, The method of forming side growth polysilicon further comprising repeating the crystallization process several times. The method of claim 1, And the crystallized region of the amorphous silicon comprises a first crystalline region and a second crystalline region in which crystal grows from the interface between the molten region and the non-melting region on both sides of the molten region to the molten region. The method of claim 1, The laser beam passing through the transmission region has a polysilicon forming method having an energy density of the complete melting region that can completely dissolve the amorphous silicon. 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. The method of claim 1, Forming the amorphous silicon layer, and further comprising the step of performing a dehydrogenation process. A transparent substrate defined by a transmission region and a blocking region; A first pattern which is an opaque metal pattern formed in the blocking region; A second pattern disposed at a periphery of the transmission region, the second pattern having a higher absorption coefficient than the substrate and having a lower absorption coefficient than the metal pattern; And an energy density of the laser beam passing through the center of the transmission region is higher than an energy density of the laser beam passing through the periphery of the transmission region. The method of claim 9, The second pattern is a laser beam mask composed of a dielectric (dielectric materal).