KR100761345B1 - Method of manufacturing a crystalloid silicone - Google Patents

Abstract

According to the present invention, there is provided a method of manufacturing a semiconductor device, comprising: providing an insulating substrate; Forming an amorphous silicon layer on the insulating substrate; Forming a capping layer made of an insulating material on the amorphous silicon layer; And a step of crystallizing the amorphous silicon layer under the capping layer into a crystalline silicon layer by irradiating the entire melting region energy on the capping layer. Firstly, the method of manufacturing a crystalline silicon layer includes: The capillary film can increase the size of the laser beam and widen the lateral growth region. Secondly, since the coagulation time is prolonged by the thermal insulation power of the capping film, it is possible to prevent the rising phenomenon between the crystal grains. Third, Foreign substances in the atmosphere are prevented from flowing into the silicon layer during the crystallization process, thereby improving the device characteristics of the silicon layer.

Description

[0001] The present invention relates to a method of manufacturing a crystalloid silicone,             

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing a crystallization curve of silicon according to laser energy density. FIG.

FIG. 2 is a schematic cross-sectional view of a laser annealing step during the manufacturing process of crystalline silicon according to the conventional SLS crystallization technique. FIG.

FIGS. 3A to 3C are plan views respectively showing the crystallization mechanism of silicon in a laser annealing process by a general SLS crystallization technique. FIG.

4 is a plan view of a crystalline silicon layer including a small grain region between side growth regions;

FIG. 5A is an enlarged view of a partial region of a general crystalline silicon, and FIG. 5B is a cross-sectional view showing a section cut along the cutting line A-A in FIG. 5A.

6 is a corresponding sectional view of a laser heat treatment step in the process of producing crystalline silicon according to an embodiment of the present invention.

7A to 7C are schematic plan views showing the crystallization mechanism of silicon in the laser annealing process by the SLS crystallization technique according to the present invention.

8A and 8B are cross-sectional views sequentially showing the steps of completing the crystalline silicon layer and removing the capping film in the crystallization process according to the present invention.

Description of the Related Art

100: insulating substrate 106: capping film

116: crystalline silicon layer

117: grain boundary

The present invention relates to a method for producing crystalline silicon, and more particularly, to a method for producing crystalline silicon using a sequential lateral solidification (hereinafter abbreviated as SLS) crystallization technique.

Recently, liquid crystal display devices are attracting attention as next generation advanced display devices with low power consumption, good portability, and high technology value.

The liquid crystal display device has a structure in which a liquid crystal is injected between an array substrate including a thin film transistor (TFT) and a color filter substrate, and a visual effect is obtained by using a refractive index difference of light according to anisotropy of the liquid crystal Means an image display device using a non-light emitting element.

In the field of flat panel displays, active matrix liquid crystal displays (AMLCDs) are the mainstream. In the AMLCD, a thin film transistor (TFT) is used as a switching element that changes the transmittance of a pixel by controlling the voltage applied to one pixel of the liquid crystal.

Such a thin film transistor semiconductor device has a high electric field effect mobility and a low photocurrent so that polycrystalline silicon is mainly used for a liquid crystal display device integrated with a driving circuit or for a display in which light is frequently exposed.

The manufacturing method of the polycrystalline silicon can be divided into a low-temperature process and a high-temperature process according to a process temperature. In the high-temperature process, a temperature condition higher than the deformation temperature of the insulating substrate is required near a process temperature of 1000 ° C., A polycrystalline silicon thin film formed by the high temperature process has a disadvantage that the device application characteristics are lower than that of the polycrystalline silicon by a low temperature process due to a high surface crystallinity such as a surface roughness and a fine crystal grain at the time of film formation A technique for crystallizing amorphous silicon capable of low temperature deposition to form polycrystalline silicon has been researched / developed.

The low-temperature process may be classified into laser annealing, metal induced crystallization, and the like.

In the dual laser heat treatment process, a pulse laser beam is irradiated onto a substrate. According to the pulse laser beam, melting and coagulation are repeated in 10 to 10 ² nanosecond units As the process proceeds, the damage to the lower insulating substrate can be minimized, and thus the most attention is paid to the low temperature crystallization process.

Hereinafter, a silicon crystallization process according to a laser annealing process will be described with reference to the drawings.

FIG. 1 is a graph of crystallization curve of silicon according to laser energy density. Laser crystallization region is classified according to the size of crystal grains.

As shown, the first region on the graph is a partial melting regime, which melts only the surface of the silicon layer to form small grains G.

The second region is a near-complete melting regime and can form coarser grains than the first region due to lateral growth, but it is difficult to obtain uniform crystal grains.

The third region is a complete melting regime, which is formed as fine crystal grains by homogeneous nucleation after melting the entire amorphous silicon layer.

That is, in the process of manufacturing the polycrystalline silicon using the laser annealing process, the number of times of irradiation of the laser beam and the overlap ratio are controlled to uniformly form coarse crystal grains using the energy density of the second region.

However, since a plurality of crystal grains of polycrystalline silicon act as obstacles to current flow, it is difficult to provide a reliable thin film transistor element. In a plurality of crystal grains, an insulating film is broken by impact current and deterioration caused by collision between electrons, A technology for forming single crystal silicon by SLS crystallization technology using the fact that silicon crystal grains are grown in the direction perpendicular to the interface at the interface between liquid silicon and solid phase silicon in order to solve such a problem Robert S. Sposilli, MA Crowder, and James S. Im, Mat. Res. Soc. Symp., Proc. Vol. 452, 956-957, 1997).

In the SLS crystallization technique, the amorphous silicon can be crystallized to a single crystal level by appropriately adjusting the laser energy size, the irradiation range of the laser beam, and the translation distance thereof, and growing the silicon crystal grains laterally by a predetermined length.

2 is a schematic cross-sectional view of a laser annealing step in the process of manufacturing crystalline silicon according to the conventional SLS crystallization technique.

A buffer layer 12 and an amorphous silicon layer 14 are sequentially formed on an insulating substrate 1 and then a mask having an open region II on a substrate on which the amorphous silicon layer 14 is formed The laser annealing process is performed.

Although not shown in the drawings, a lens for collecting a laser beam is disposed on the mask 16, and a lens for concentrating the complete melting energy density is provided between the mask 16 and the substrate 1.

Hereinafter, FIGS. 3A to 3C are plan views illustrating the crystallization mechanism of silicon in the laser annealing process using a general SLS crystallization technique.

First, a first laser shot is irradiated onto a partial region of the amorphous silicon layer 14 to completely melt the amorphous silicon layer 14 irradiated with the first laser shot.

At this stage, in the first and second peripheral portions Ia and Ib on both sides of the region L corresponding to the first laser beam size, the partial melting (the first region in FIG. 1) A small grain 18 is formed by energy so that a part of the small grain 18 acts as a seed of the completely melted silicon layer and grows laterally in the direction of the arrow in the "L" region to form the first grain 20 (Fig. 3A).

Next, a second laser shot is added so as to overlap with the small crystal grain (18 in Fig. 3A) (second peripheral portion Ib in the figure) to form a silicon layer of a region LL corresponding to the beam size of the second laser shot The first crystal grains 20 adjacent to the molten silicon layer 15 act as seeds and the lateral growth proceeds in the direction of the arrows indicated in the "LL" region, The second crystal grains 22 having a single crystal level are formed.

Through the repetition of this process, a N-type laser shot is performed to form a single crystal level grain by artificially expanding the lateral growth.

However, in the case where the open region of the mask is large or the laser heat treatment energy is high, an unexpected small grain region can be formed between the side growth regions even in the SLS crystallization process.

4 is a plan view of a crystalline silicon layer including a small grain region between side growth regions.

In the above SLS crystallization method, if the mask open region (for example, the region "II" in FIG. 2) is widened, the lateral growth region by one laser shot can be enlarged and the throughput can be increased .

Of course, this phenomenon does not occur when the mask is small, but when the mask open area is made too small, the production amount is lost.

On the other hand, the laser irradiation proceeds in a pulsed manner. Since melting and solidification are repeated in nano-second units, when the mask open region is large or the energy is small, crystallization occurs in a state where side growth is not sufficiently performed due to short coagulation time, As shown in the figure, the crystallization is completed in a state where the side growth regions III do not meet each other and an unexpected small grain formation region IV is formed between the side growth regions III.

FIG. 5A is an enlarged view of a partial region of general crystalline silicon, and FIG. 5B is a cross-sectional view showing a section cut along the cutting line A-A of FIG. 5A.

As shown in the figure, when the crystallization process as shown in FIGS. 3A to 3C is performed, a change occurs in the structure of the silicon layer 24 due to the crystal grain boundary 24b defined as a boundary between the crystal grains 24a, In particular, the more the intersection points 26 where the crystal grain boundaries 24b meet, the larger the structural change width (FIG. 5A).

Next, as shown in FIG. 5B, it can be seen that the upheaval 28 (protrusion) generated at the intersection between the crystal grain boundaries 24b (26 in FIG. 5A) is generated most seriously.

The surface of the crystalline silicon layer 24 is roughened by the protrusions 28. This makes it impossible to construct a thin film transistor having a high charge mobility and thus the reliability of the thin film transistor is lowered.

In order to solve the above problems, the present invention provides a method of manufacturing crystalline silicon which can reduce the surface roughness while minimizing the grain boundaries of the silicon in forming the crystalline silicon through the laser heat treatment process according to the SLS crystallization technology, And an object thereof is to provide a liquid crystal display device with improved device characteristics.

That is, in the present invention, a capping film having a thermal insulating property is formed on the amorphous silicon layer, and then the laser annealing process is performed to increase the coagulation time by the thermal insulation power of the capping film, And further to protect the silicon layer from foreign substances in the air during the crystallization process by the capping layer.

According to an aspect of the present invention, Forming an amorphous silicon layer on the insulating substrate; Forming a capping layer made of an insulating material on the amorphous silicon layer; And crystallizing the lower amorphous silicon layer into a laterally grown crystalline silicon layer by performing a laser annealing process at a complete melting region energy density on the capping layer. The method comprising the steps of:

The step of forming the crystalline silicon layer further includes removing the capping layer. In the step of removing the capping layer, a solution containing one of hydrofluoric acid (HF) and buffered oxide etchant (BOE) is used And then etching is performed.

It is preferable that the capping film is formed in a thickness range in which the laser energy can be transmitted as it is, and the capping film is preferably formed of any one of a silicon oxide film (SiO ₂ ) and a silicon nitride film (SiN _x ).

In the step of forming the crystalline silicon, a laser annealing process having an energy density of the completely melted region is used. In the laser annealing process, a mask having an open region is further included do.

Hereinafter, preferred embodiments according to the present invention will be described in detail with reference to the drawings.

FIG. 6 is a sectional view corresponding to the laser annealing step in the process for producing crystalline silicon according to the embodiment of the present invention.

An amorphous silicon layer 104 is formed on an insulating substrate 100 having a buffer layer 102 as an upper layer and a capping layer 106 is formed on an upper portion covering the amorphous silicon layer 104 .

A mask 108 having an open area V is disposed on the capping layer 106 at a predetermined interval and the laser annealing process is performed through the mask 108.

The laser annealing process is characterized in that the SLS crystallization technique described above is used.

The capping layer 106 has a thermal insulating property and can be easily removed by an etchant having an etch selectivity between silicon and oxide such as HF or BOE in a subsequent process, It is preferable to select an insulating material which can be used as a gate insulating film without designing additional process conditions.

As the insulating material satisfying the above conditions, a silicon oxide film (SiO ₂ ) or a silicon nitride film (SiN _x ) can be mentioned.

It is very important that the thickness of the capping layer 106 is set within a thickness range that allows the laser energy to be transmitted without absorbing the laser energy so as not to deteriorate the laser annealing efficiency.

The open area V of the mask 108 corresponds to the beam size irradiated to the amorphous silicon layer 104. In the present invention, since the capping layer 106 has thermal insulation, (V) width (V> II (FIG. 2)) can be formed in a wider range than the conventional one.

In the process of forming crystalline silicon by the low-temperature crystallization process, the process proceeds in a nitrogen (N ₂ ) or vacuum chamber. In general, in the SLS crystallization process, the process proceeds in an atmospheric chamber. The surface of the silicon layer tends to be contaminated by foreign matter or oxygen content in the atmosphere. In the present invention, however, the capping layer 106 is formed on the amorphous silicon layer 104 to prevent the silicon layer from being exposed to the atmosphere .

The capping layer 106 is etched in a subsequent process.

7A to 7C are plan views schematically showing the crystallization mechanism of silicon in the laser annealing process by the SLS crystallization technique according to the present invention.

In the crystalline silicon manufacturing process according to the present invention, since the capping film is formed on the silicon layer and the laser annealing process is performed, when the laser is irradiated on the silicon layer, the coagulation time of the silicon layer is extended Therefore, even when the laser beam size is longer than the conventional one, it is possible to suppress the formation of small crystal grains occurring between the side growth regions in the crystallization step.

At this stage, in the present invention, since the solidification time can be extended by forming the capping film (106 in Fig. 6), the first laser shot having the beam size increased by + alpha than the conventional one is irradiated, The first crystal grains 110 may be formed by side growth using the small crystal grains 112 surrounding the (L + α) region as seeds after melting the corresponding silicon layers of the (L + α) ).

7B, the second laser shot having the beam size corresponding to the first laser shot is further irradiated so as to overlap with the small crystal grain region (the right small peripheral grain region in the drawing), and the corresponding region LL + α) is melted and the single crystal grain 114 is grown by the side growth method using the first crystal grains 110 crystallized through the step of FIG. 7A as a seed, as shown in FIG. 7C do.

As a result of this repetition, the N-type laser shot proceeds to form a single crystal level by a method of artificially expanding the lateral growth. The crystal grains 114 according to the present invention are formed by a And can be formed in a large size.

This is because the capping film (106 in FIG. 6) covering the upper portion serves to increase the beam size and prevent the molten silicon layer from being easily solidified, I can do it.

FIGS. 8A and 8B are cross-sectional views sequentially illustrating steps of completing the crystalline silicon and removing the capping film in the crystallization process according to the present invention, which are sectional views of the plan view of FIG. 5A.

6, the capping layer 106 is formed as an upper layer of the amorphous silicon layer 104 (see FIG. 6), and the laser heat treatment process is performed to form the capping layer 106 It is possible to obtain the crystalline silicon layer 116 having improved planarization characteristics by suppressing the protrusions generated between the crystal grain boundaries 117 of the crystalline silicon layer 116 formed under the silicon crystal layers 116 and 106.

8B, the capping layer 106 on the crystalline silicon layer 116 is removed.                     

In this step, the capping layer 106 is etched using an etchant such as hydrofluoric acid or BOE to expose the crystalline silicon layer 116.

However, in the present invention, it is also possible to use the capping film as a gate insulating film in a later process.

If the above method is applied, additional deposition may be performed by the thickness of the gate insulating film.

On the other hand, a thin film transistor having improved device characteristics can be formed by applying a top gate type thin film transistor process in which a gate electrode is formed on a semiconductor layer.

The present invention is not limited to the above embodiments, and various modifications may be made without departing from the spirit of the present invention.

As described above, in the present invention, in forming the crystalline silicon by using the SLS crystallization technique capable of providing a single crystal level of crystalline silicon, the capping film is covered on the amorphous silicon layer before the laser heat treatment process, It has the same advantages.

First, the laser beam size can be increased by the thermal insulation power of the capping film, and the lateral growth region can be widened.

Secondly, since the coagulation time is prolonged by the thermal insulation of the capillary cap film, the protrusion phenomenon between the grain boundaries can be prevented.

Thirdly, foreign substances in the atmosphere are prevented from flowing into the silicon layer during the crystallization process by the capping layer, so that the device characteristics of the silicon layer can be improved.

Claims (7)

Providing an insulating substrate; Forming an amorphous silicon layer on the insulating substrate; Forming a capping layer made of an insulating material on the amorphous silicon layer; Crystallizing the lower amorphous silicon layer into a laterally grown crystalline silicon layer by performing a laser annealing process at the entire melting region energy density on the capping layer ≪ / RTI > The method according to claim 1, Wherein the step of forming the crystalline silicon layer further comprises removing the capping film. 3. The method of claim 2, Wherein the capping layer is removed by etching using a solution containing one of hydrofluoric acid (HF) and buffered oxide etchant (BOE). The method according to claim 1, Wherein the capping layer is formed in a thickness range in which the laser energy is transmitted as it is. The method according to claim 1, Wherein the capping film is any one of a silicon oxide film (SiO ₂ ) and a silicon nitride film (SiN _x ). The method according to claim 1, Wherein the forming of the crystalline silicon is performed using a laser annealing process having an energy density of the entire melting region. The method according to claim 6, Wherein the laser annealing process further includes a mask having an open region.

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