Laser crystallization method

A laser crystallization method includes forming a plurality of first protrusions and depressions on a surface of an amorphous silicon layer, wherein a first protrusion and an adjacent first depression of the plurality of first protrusions and depressions, together, have a first pitch, and irradiating the amorphous silicon layer with a laser beam to form a polycrystalline silicon layer.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority under 35 U.S.C. §119 to Korean Patent Application No. 10-2015-0153920, filed in the Korean Intellectual Property Office on Nov. 3, 2015, the contents of which are incorporated by reference herein in their entirety.

TECHNICAL FIELD

The present invention relates to a laser crystallization method.

DISCUSSION OF THE RELATED ART

In general, methods of crystallizing an amorphous silicon layer into a polycrystalline silicon layer include solid phase crystallization (SPC), metal induced crystallization (MIC), metal induced lateral crystallization (MILC), excimer laser annealing (ELA), etc. In the manufacturing process of an organic light emitting diode (OLED) display or a liquid crystal display (LCD), ELA is used for crystallizing the amorphous silicon layer into the polycrystalline silicon layer by using a laser beam.

However, when an ELA process is used to form grains in the polycrystalline silicon layer, the grains may not be evenly spaced.

SUMMARY

According to an exemplary embodiment of the present invention, a laser crystallization method includes forming a plurality of first protrusions and depressions on a surface of an amorphous silicon layer, wherein a first protrusion and an adjacent first depression of the plurality of first protrusions and depressions, together, have a first pitch, and irradiating the amorphous silicon layer with a laser beam to form a polycrystalline silicon layer.

In an exemplary embodiment of the present invention, the forming of the plurality of first protrusions and depressions includes forming an insulating layer on the amorphous silicon layer, forming a plurality of openings having a first width on the insulating layer, and etching the surface of the amorphous silicon layer using the insulating layer as an etching mask.

In an exemplary embodiment of the present invention, the forming of the plurality of openings includes, pressing the insulating layer with a nanoimprinter having a plurality of second protrusions and depressions to form a plurality of grooves on the insulating layer, wherein a second protrusion and an adjacent second depression of the plurality of second protrusions and depressions, together, have the first pitch, and performing an ashing process to the insulating layer to change the plurality of grooves into the plurality of openings.

In an exemplary embodiment of the present invention, when the wavelength of the laser beam is referred to as λ, the first pitch is in a range from λ−5 nm to λ+5 nm.

In an exemplary embodiment of the present invention, the first protrusions and depressions include a convex portion and a recess portion disposed adjacent to the convex portion, wherein the first pitch is a sum of a width of the convex portion and a width of the adjacent recess portion.

In an exemplary embodiment of the present invention, a grain boundary of the polycrystalline silicon layer is formed at the convex portion of the first protrusions and depressions.

In an exemplary embodiment of the present invention, the first pitch is in a range of about 305 nm to about 312 nm.

In an exemplary embodiment of the present invention, the laser beam has a linear shape of which a length is longer than a width, the first protrusion and the adjacent first depression of the plurality of first protrusions and depressions have a linear shape of which a length is longer than the first pitch, and a direction in which the width of the laser beam is measured is parallel to a direction in which the first pitch is measured.

In an exemplary embodiment of the present invention, a wavelength of the laser beam is an integer multiple of the first pitch.

According to an exemplary embodiment of the present invention, a laser crystallization method includes forming a first convex portion, a first recess portion, and a second convex portion on a first surface of an amorphous silicon layer, wherein the first convex portion is adjacent to the first recess portion, and the first recess portion is adjacent to the second convex portion, and irradiating the amorphous silicon layer with a laser beam to form a polycrystalline silicon layer.

In an exemplary embodiment of the present invention, a first seed is generated in the first recess portion when the amorphous silicon layer is irradiated by the laser beam.

In an exemplary embodiment of the present invention, the first seed is grown into a first grain when the amorphous silicon layer is irradiated by the laser beam, and the first convex portion corresponds to a first boundary of the first grain.

In an exemplary embodiment of the present invention, the second convex portion corresponds to a second boundary of the first grain.

In an exemplary embodiment of the present invention, a first pitch includes a width of the first convex portion and a width of the first recess portion, and a wavelength of the laser beam equals the first pitch.

In an exemplary embodiment of the present invention, when a first pitch includes a width of the first convex portion and a width of the first recess portion, a wavelength of the laser beam is 307 nm and the first pitch ranges from 302 nm to 312 nm.

In an exemplary embodiment of the present invention, the laser crystallization method further includes forming a second recess portion adjacent to the second convex portion and forming a third convex portion adjacent to the second recess portion on the first surface of the of the amorphous silicon layer, wherein a second seed is generated in the second recess portion when the amorphous silicon layer is irradiated by the laser beam, wherein a first pitch includes a width of the first convex portion and a width of the first recess portion, and a second pitch which is equal to the first pitch includes a width of the second convex portion and a width of the second recess portion.

In an exemplary embodiment of the present invention, the first and second recess portions are closer to a second surface of the amorphous silicon layer than the first, second and third convex portions, wherein the first and second surfaces of the amorphous silicon layer are opposite with respect to each other.

In an exemplary embodiment of the present invention, when irradiating the amorphous silicon layer with the laser beam, a first temperature of a portion of the amorphous silicon layer corresponding to the first recess portion is lower than a second temperature of a portion of the amorphous silicon layer corresponding to the first convex portion.

According to an exemplary embodiment of the present invention, a laser crystallization method includes forming an amorphous silicon layer on a substrate, forming an insulating layer on the amorphous silicon layer, forming a plurality of first convex portions and a plurality of first recess portions on the insulating layer by pressing a nanoimprinter on the insulating layer, wherein the nanoimprinter has a plurality of second convex portions and a plurality of second recess portions that are equal to the plurality of first convex portions and the plurality of first recess portions, etching the amorphous silicon layer using the insulating layer as an etching mask, wherein a plurality of third recess portions and a plurality of third convex portions remain on the amorphous silicon layer after the etching of the amorphous silicon layer, and irradiating the amorphous silicon layer with a laser beam to form a polycrystalline silicon layer.

In an exemplary embodiment of the present invention, when a first pitch includes a width of a third recess portion of the plurality of third recess portions and a width of a third convex portion of the plurality of third convex portions, the first pitch ranges from 5 nm smaller than a wavelength of the laser beam to 5 nm greater than the wavelength of the laser beam.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments thereof are shown. As those skilled in the art would realize, the disclosed embodiments may be modified in various different ways without departing from the spirit and scope of the present invention.

Like reference numerals may refer to like elements throughout the specification.

In addition, the size and thickness of each element shown in the drawings may be exaggerated for better understanding and ease of description, but the present invention is not limited thereto.

A laser crystallization method, according to an exemplary embodiment of the present invention, will be described with reference to accompanying drawings.

FIG. 1toFIG. 7are cross-sectional views sequentially illustrating a laser crystallization method according to an exemplary embodiment of the present invention.

As shown inFIG. 1, the laser crystallization method according to an exemplary embodiment of the present invention includes forming an amorphous silicon layer20on a substrate10. The amorphous silicon layer20may be formed by a method such as low pressure chemical vapor deposition (LPCVD), atmospheric pressure chemical vapor deposition (APCVD), plasma enhanced chemical vapor deposition (PECVD), sputtering, vacuum evaporation, and the like. Also, an insulating layer30is formed on the amorphous silicon layer20. The insulating layer30may be a photosensitive film.

As shown inFIG. 2, a nanoimprinter40is positioned on the insulating layer30. Second protrusions and depressions41having a pitch P of a nanometer size are formed in the nanoimprinter. The second protrusions and depressions41include a convex portion41aand a recess portion41bdisposed adjacent to the convex portion41a. According to an exemplary embodiment of the present invention, the nanometer size means a size of several hundred nanometers. According to an exemplary embodiment of the present invention, the pitch P may be about 305 nm to about 313 nm.

As shown inFIG. 3, the nanoimprinter40is pressed on the insulating layer30to form a plurality of grooves30ahaving a second width w2of the nanometer size on the insulating layer30. According to an exemplary embodiment of the present invention, the second width w2of the grooves30amay be from about 150 nm to about 160 nm. After being pressed by the insulating layer30, the nanoimprinter40is raised to be separated from the insulating layer30. Accordingly, on the insulating layer30, a recess portion31is formed at the position corresponding to the grooves30aand a convex portion32is formed at a higher position of the insulating layer30than the recess portion31.

As shown inFIG. 3andFIG. 4, an ashing process is executed on the insulating layer30to entirely etch the insulating layer30. According to an exemplary embodiment of the present invention, when the ashing process is executed on the insulating layer30, the recess portions31corresponding to the grooves30aare completely etched while the convex portions32remain on the insulating layer30with a decreased height. Accordingly, a portion of the convex portions32remain, and the recess portions31corresponding to the grooves30aare removed to form openings4. Each of the plurality of openings4have a first width w1of the nanometer size. In addition, the surface of the amorphous silicon layer20is etched by a dry etching device100using the insulating layer30as an etching mask. Accordingly, recess portions21bare formed on the amorphous silicon layer20.

As shown inFIG. 5, the convex portions32of the insulating layer30are removed to expose the surface of the amorphous silicon layer20. Accordingly, a plurality of first protrusions and depressions21having a pitch P of the nanometer size are formed on the surface of the amorphous silicon layer20.

Each of the first protrusions and depressions21includes a convex portion21aand a recess portion21bthat is lower in height than the convex portion21a. In a first protrusion and depression21, the convex portion21amay be disposed adjacent to the recess portion21b. The pitch P of one of the first protrusions and depressions21is a sum of a width P1of a convex portion21aand a width P2of a recess portion21b. The first protrusions and depressions21are repeated multiple times with the same pitch P on the surface of the amorphous silicon layer20.

As shown inFIG. 6, the amorphous silicon layer20including the plurality of first protrusions and depressions21is irradiated by a laser beam1to generate a temperature gradient deviation inside the amorphous silicon layer20. For example, the temperature of a portion of the amorphous silicon layer20corresponding to a recess portion21bis lower than a temperature of a portion of the amorphous silicon layer20corresponding to a convex portion21a. Accordingly, a seed2is generated at each portion of the amorphous silicon layer20corresponding to the recess portions21b. Thus, the seeds2are generated at equal distances from each other (e.g., the seeds2are generated at a constant interval or uniform spacing) since the recess portions21bare disposed at equal distances from each other.

As described above, since the seeds2are generated with a constant interval, grains3generated from the seeds2may be uniformly spaced in the polycrystalline silicon layer20′ (refer toFIG. 7).

According to an exemplary embodiment of the present invention, the laser beam1may include an excimer laser200.

As shown inFIG. 7, the seeds2are grown to form a polycrystalline silicon layer20′ of which the grains3are formed with the uniform interval. For example, the grains3may be equally spaced apart from each other. In this case, a grain boundary5is formed between adjacent grains3. The grain boundary5is formed at the position of the polycrystalline silicon layer20′ corresponding to the convex portion21aof the first protrusions and depressions21. As described above, the grain boundary5is formed with the constant interval such that the polycrystalline silicon layer20′ may have uniformly spaced grains3.

As described above, by forming the first protrusions and depressions21of the nanometer size in the amorphous silicon layer20to increase the temperature gradient deviation in the amorphous silicon layer20, the uniformity of the polycrystalline silicon layer20′ may be increased.

Also, since the polycrystalline silicon layer having a high grain uniformity may be formed even if a number of irradiations of the amorphous silicon layer20is reduced, a manufacturing cost and a manufacturing time of the polycrystalline silicon layer20′ may be reduced. Thus, the production capacity of the laser crystallization device may be increased.

FIG. 8is a perspective view illustrating a relationship between a laser beam and first protrusions and depressions according to an exemplary embodiment of the present invention.

As shown inFIG. 8, the laser beam1may have a linear shape in which a length direction Y of the laser beam1is longer than a width direction X of the laser beam1. The first protrusions and depressions21formed in the amorphous silicon layer20may have a linear shape in which the length direction Y of the first protrusions and depressions21is longer than a pitch P direction X of the first protrusions and depressions21. Also, the width direction X of the laser beam1may be parallel to the pitch P direction X of the first protrusions and depressions21. In other words, the length of both the laser beam1and the first protrusions and depressions21is measured along the direction Y, and the width of both the laser beam1and the first protrusions and depressions21is measured along the direction X.

When the wavelength of the laser beam1is referred to as λ, a pitch P of the first protrusions and depressions21may have a value between λ−5 nm and λ+5 nm. Accordingly, when the wavelength of the laser beam1is 307 nm, the pitch P of the first protrusions and depressions21may be from about 302 nm to about 312 nm.

FIG. 9is a view illustrating a crystallization state of a polycrystalline silicon layer when a pitch of first protrusions and depressions is the same as a wavelength of a laser beam, according to an exemplary embodiment of the present invention.FIG. 10is a view illustrating a crystallization state of a polycrystalline silicon layer when a pitch of first protrusions and depressions is 302 nm, according to an exemplary embodiment of the present invention.FIG. 11is a view illustrating a crystallization state of a polycrystalline silicon layer when a pitch of first protrusions and depressions is 312 nm, according to an exemplary embodiment of the present invention.FIG. 12is a view illustrating a crystallization state of a polycrystalline silicon layer when a pitch of first protrusions and depressions is 301 nm, according to an exemplary embodiment of the present invention.FIG. 13is a view illustrating a crystallization state of a polycrystalline silicon layer when a pitch of first protrusions and depressions is 313 nm, according to an exemplary embodiment of the present invention.

FIG. 9,FIG. 10,FIG. 11,FIG. 12, andFIG. 13illustrate the crystallization state in the width direction X and a thickness direction Z of the amorphous silicon layer20depending on time passage of 15 ns, 37 ns, 75 ns, 97 ns, and 120 ns. The direction Z, along which a thickness of the amorphous silicon layer20is measured, is orthogonal to the directions X and Y.

As shown inFIG. 9, when the wavelength of the laser beam1is 307 nm and the pitch P of the first protrusions and depressions21is 307 nm, a seed2is generated at a constant position inside the amorphous silicon layer20. For example, the constant positions inside the amorphous silicon layer20may include a plurality of locations of the amorphous silicon layer20which correspond to the recess portions21bof the first protrusions and depressions21. In other words, the seeds2are generated to be uniformly spaced inside the amorphous silicon layer20. The grain3is gradually grown from the seed2, and then the grain3is positioned at the convex portion21aof the first protrusions and depressions21. For example, a grain3grows from a seed2located in an area of the amorphous silicon layer20corresponding to a recess portion21binto two neighboring convex portions21a.

Also, as shown inFIG. 10, when the wavelength of the laser beam1is 307 nm and the pitch P of the first protrusions and depressions21is 302 nm, the seed2is generated at the constant position inside the amorphous silicon layer20. In other words, the seeds2are generated to be uniformly spaced inside the amorphous silicon layer20. Also, as shown inFIG. 11, when the wavelength of the laser beam1is 307 nm and the pitch P of the first protrusions and depressions21is 312 nm, t the seed2is generated at the constant position inside the amorphous silicon layer20. In other words, the seeds2are generated to be uniformly spaced inside the amorphous silicon layer20.

However, as shown inFIG. 12, when the wavelength of the laser beam1is 307 nm and the pitch P of the first protrusions and depressions21is 301 nm, the seed2is randomly generated at several the amorphous silicon layer20that do not correspond to the recess portions21b. Also, as shown inFIG. 13, when the wavelength of the laser beam1is 307 nm and the pitch P of the first protrusions and depressions21is 313 nm, the seed2is randomly generated at several parts of the amorphous silicon layer20that do not correspond to the recess portions21b.

As described above, when the wavelength of the laser beam1is referred to as λ and the pitch P of the first protrusions and depressions21has the value ranging from λ−5 nm to λ+5 nm, the seed may be generated in portions of the amorphous silicon layer20that correspond to the recess portions21bof the first protrusions and depressions21.

Accordingly, the pitch P of the first protrusions and depressions21is selected to have a size that increases a uniformity of the grains3formed in polycrystalline silicon layer20′, and the wavelength of the laser beam1may be selected in consideration of the pitch P to increase the uniformity of grains3formed in the polycrystalline silicon layer20′. For example, when the wavelength of the laser beam1is selected as an integer multiple of the pitch P of the first protrusions and depressions21, the seeds2may be generated at the locations of the amorphous silicon layer20that correspond to the recess portions21bof the first protrusions and depressions21. According to an exemplary embodiment of the present invention, the integer multiple of the pitch P is 1. For example, the pitch P of the first protrusions and depressions21and the wavelength2of the laser beam1may be equal.