KR20080084449A - Thin film transistor, the fabricating method of thin film transistor, organic light emitting display device and the fabricating method of organic light emitting display device - Google Patents

Abstract

A thin film transistor, a fabricating method thereof, an organic light emitting display device, and a fabricating method thereof are provided to crystallize amorphous silicon into polycrystalline silicon by directly radiating laser beams with narrow width and long length on the silicon without using a mask. A thin film transistor includes a substrate(300), a semiconductor layer(320), a gate electrode(328), a gate insulating film(330), and a source/drain electrode(352). The substrate has a buffer layer(310). The semiconductor layer is formed on the substrate and has a grain boundary in parallel with a crystal growth direction. A roughness of an upper surface of the semiconductor layer is less than 15nm. The gate electrode is formed corresponding to one region of the semiconductor layer. The gate insulating film insulates the semiconductor layer and the gate electrode from each other. The source/drain electrode is connected to the semiconductor layer.

Description

Thin film transistor, manufacturing method of thin film transistor, organic light emitting display device having same and manufacturing method thereof {Thin Film Transistor, The Fabricating Method Of Thin Film Transistor, Organic Light Emitting Display Device and The Fabricating Method of Organic Light Emitting Display Device}

1 is a view showing the size of the crystal grains according to the energy density of the laser beam in a single irradiation of the laser beam,

2a to 2c is a view of a conventional laser crystallization method,

3 is a view showing a laser irradiation apparatus used in the silicon crystallization method of the present invention,

4A is a plan view of amorphous silicon to which a laser beam is irradiated using the laser irradiation apparatus of FIG. 3A,

4b is a photograph of crystallized amorphous silicon,

4C is a graph of the surface roughness of a polycrystalline silicon layer crystallized according to the present invention,

5 is a view of a thin film transistor according to the present invention,

6 is a view of an organic light emitting display device according to the present invention.

The present invention is crystallized by directly irradiating a laser having a predetermined width and a predetermined length on the amorphous silicon layer, there is a grain boundary located in a direction parallel to the crystal growth direction without using a mask, and has a polycrystalline excellent surface roughness A method of crystallizing silicon, a method of manufacturing a thin film transistor using the same, and an organic light emitting display device using the same.

In general, the polycrystalline silicon layer is widely used as a semiconductor layer for thin film transistors because of its advantages in that it can be applied to high field effect mobility, high speed operation circuits, and CMOS circuits. The thin film transistor using the polycrystalline silicon layer is mainly used in the active element of the active matrix liquid crystal display device (AMLCD) and the switching element and the driving element of the organic light emitting element (OLED).

The method of crystallizing the amorphous silicon layer into a polycrystalline silicon layer may include solid phase crystallization, metal induced crystallization, metal induced lateral crystallization, and excimer laser crystallization. Laser Crystallization), and SLS (Sequential Lateral Solidification).

Among them, the crystallization method using a laser is called low-temperature polycrystalline silicon (LTPS; Low Temperature Polysilicone) because it can be crystallized at low temperature.

Excimer laser (ELA) method is a method for manufacturing a TFT using such low-temperature polycrystalline silicon. The excimer laser method has an advantage that the glass substrate is not damaged at all because melting and crystallization of amorphous silicon is performed in a short time of 30 to 200 ns. The actual time it takes is only a few hundred ns per pulse and is a technology that can be used at room temperature. It does not use only a single pulse, it is 15 to 30 cm and the width is about 0.2 to 3 mm. The beam profile of the laser, the number of pulses, the initial substrate temperature, the deposition conditions and the method of deposition of the amorphous silicon film are key variables that affect the final crystallinity.

Hereinafter, the crystallization method of silicon according to the conventional excimer laser heat treatment process (ELA) will be described in more detail.

1 is a graph showing the size of particles of amorphous silicon for each laser energy density.

As shown in FIG. 1, crystallization of amorphous silicon may be classified into regions I, II, and III according to the intensity of laser energy.

The region I is a partial melting region, in which laser energy is irradiated to the amorphous silicon layer at an intensity such that only the surface of the amorphous silicon layer is melted, and in the first region, after the irradiation, Partial melting of the surface is achieved and small crystal grains are formed on the surface of the silicon layer through a solidification process.

Region II is a near-complete melting region, in which the laser energy is irradiated to the extent that the amorphous silicon layer is almost melted. Although crystal grains grown compared to one region can be obtained, it is difficult to obtain uniform crystal grains. Here, the region II is considerably narrower than the region I.

The region III is a complete melting region, which is a region in which laser energy is irradiated to the extent that all the amorphous silicon layers are melted by increasing the laser energy intensity than the region II, and solidification is performed after all the amorphous silicon layers are melted. Uniform homogeneous nucleation is possible, and after irradiation, a crystalline silicon layer made of fine uniform crystal grains is formed.

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

However, it is difficult to provide a reliable thin film transistor element because a plurality of crystal grain boundaries of polycrystalline silicon act as an obstacle to current flow, and an insulating film is destroyed by collision current and deterioration due to collision between electrons in the plurality of crystal grains. In order to solve this problem, SLS (sequential LAteral Solidification) technology using the fact that the silicon crystal grains grow in the direction perpendicular to the interface at the interface between the liquid and solid silicon in order to improve this problem. Has been proposed to form single crystal silicon.

The SLS method is a semiconductor layer for forming a driving circuit portion of a TFT-LCD or an organic light emitting display device (OLED) as a novel method of improving the mobility of the excimer laser annealing method to improve the mobility of TFTs using low-temperature polycrystalline silicon. It can be used to prepare a polycrystalline silicon film.

The SLS method can produce a low temperature polycrystalline silicon TFT having excellent crystallinity and uniformity on a glass substrate. Particularly, the silicon at this time exhibits a single crystal level of crystallinity rather than a polycrystalline state. Briefly, this method first passes a part of the laser beam using a patterned mask.

At this time, the amorphous silicon sample is placed on the stage moving very finely, about 5-10 nm / shot. The partially passed laser beam repeats melting the silicon very thinly. In other words, once several melting and solidification cycles within hundreds of ns can theoretically produce infinite single crystal silicon. In this regard, the crystallization method using a laser has attracted the most attention in the low temperature crystallization process because it has the advantage of minimizing damage to the lower substrate.

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

The irradiator used in the SLS process concentrates the beam in a narrow area using a mask, so that an amorphous silicon layer stacked on a large area substrate cannot be changed to polycrystalline at the same time. Therefore, after changing the irradiation position of the substrate, the substrate on which the amorphous silicon layer is laminated is mounted on the steer, and then irradiated to a predetermined area, and then irradiated to the entire area of the substrate by moving the substrate to irradiate the next area. To be done.

As the laser used in the SLS method, 308 nm XeCl or 248 nm KrF is mainly used as an excimer laser.

Hereinafter, a method of crystallizing conventional silicon using a general SLS irradiation apparatus will be described with reference to FIGS. 2A to 2C.

2A to 2C are diagrams illustrating the step of crystallizing amorphous silicon by a general SLS crystallization method.

Referring to FIG. 2A, a laser beam having a predetermined beam width w1 is first irradiated to an amorphous silicon layer to completely melt the first laser irradiated amorphous silicon (a-si). When cooling is started after the irradiation of the laser beam, crystallization occurs preferentially at the interface between amorphous silicon and molten silicon to form the seed 110. At this time, due to the latent solidification heat generated when the seed 110 is formed, a temperature gradient is formed in which the temperature gradually decreases from the interface between the amorphous silicon and the molten silicon toward the molten silicon. Since the heat flux flows toward the center of the molten silicon layer, the polycrystalline silicon grains are laterally grown until the molten silicon is completely solidified. The polycrystalline silicon generates a boundary between adjacently growing grains, that is, a grain boundary. The grain boundary generated in the same direction as the growth direction of the grains is referred to as a "secondary grain boundary (120)". In addition, since the polycrystalline silicon grains grow at both interfaces of the molten silicon at the same time, the growth of the grains in the center portion of the molten silicon is stopped, and grain boundaries are generated between the growing grains facing each other. The grain boundary generated in the direction perpendicular to the growth direction of the grain is referred to as "primary grain boundary 130".

Next, referring to FIG. 2B, when the second laser irradiation is performed on the region A including the interface between the polycrystalline silicon region and the amorphous silicon on which the crystal grains are formed, the amorphous silicon and the polycrystalline silicon are melted and then cooled. As a result, atoms are attached to the preformed polycrystalline silicon crystal grains which are not dissolved, thereby increasing the length of the crystal grains. Unlike FIG. 2B, by including the “primary grain boundary 130” in the laser irradiation region A in the second order, a polycrystalline silicon layer having a desired grain size can be formed.

However, since the "primary grain boundary" and the "secondary grain boundary" formed by the SLS crystallization method affect the electrical properties of the thin film transistor, the thin film transistor using the polycrystalline silicon having the grain boundary has a characteristic variation.

In addition, when the crystallization is controlled by adjusting the moving range of the irradiated laser beam to less than 1/2 of the laser beam width to remove the “primary grain boundary”, as shown in FIG. 2C, the grains continue to grow. As these collide or divide, new grain boundaries are formed. The new grain boundaries are irregularly formed, resulting in uneven grain boundaries as a whole. Such non-uniformity of the grain boundary affects the electrical properties of the thin film transistor, causing problems in the characteristics of the thin film transistor, and the electric field is concentrated on the protrusion due to the non-uniform primary grain boundary causing defects And there is a problem of generating the Mura phenomenon.

In addition, there is a disadvantage in that the process is complicated and expensive in terms of using a mask.

In order to solve the problems of the conventional silicon crystallization method as described above, the present invention improves device performance by forming amorphous silicon as polycrystalline silicon using a narrower laser irradiation range of laser, and having large grains and no projections on the surface. The purpose of the present invention is to provide a method for crystallizing silicon that can be used to secure a margin of a process or equipment.

The present invention is a substrate on which a buffer layer is formed; A semiconductor layer disposed on the substrate and having a grain boundary parallel to a crystal growth direction, the semiconductor layer comprising a polycrystalline silicon layer having a top surface roughness of 15 nm or less; A gate electrode formed to correspond to one region of the semiconductor layer; A gate insulating film for insulating the semiconductor layer from the gate electrode; And a source / drain electrode connected to the semiconductor layer, and a method of manufacturing the same. Also disclosed is an organic light emitting display device having the thin film transistor.

Hereinafter, with reference to the accompanying drawings will be described in detail the silicon crystallization method of the present invention.

3 is a view showing a laser irradiation apparatus used in the silicon crystallization method of the present invention, Figure 4a is a view showing a process of crystallization with the laser device of FIG.

3 and 4A, unlike the SLS, the silicon crystallization method of the present invention performs crystallization by directly irradiating a laser onto an amorphous silicon layer without using a mask through a laser irradiation apparatus. This crystallization method is called a directional crystallization method.

First, referring to FIG. 3, the laser is irradiated at 600 to 1000w, and provides a pulsed laser for a long time. In this case, the laser is one of KrF or XeF. The laser is characterized by narrowing the width and length of the laser beam without a mask, and irradiating it in the form of a pulse, and its irradiation interval pitch is very small. In addition, since the upper area of the irradiated laser beam is larger than the irradiated area, the side is steeply inclined.

Referring to FIG. 4A, a laser beam irradiated onto amorphous silicon is optimized to melt and solidify amorphous silicon, and has a length of 365 nm to 1100 nm and a width d1 of 5 μm to 20 μm. In the ELA, a laser having a beam width of 400 mu m is used. Therefore, the laser used in the directional crystallization method is a thinner and longer laser beam.

 The laser must have an intensity to instantaneously melt the amorphous silicon, so it must be a full melt region energy or a full melt proximity region energy. In this case, the energy density of the laser is preferably 150 to 1000 mJ / cm 2, and has an intensity capable of sufficiently melting the amorphous silicon.

The present invention is to remove the primary grain boundary located in the direction perpendicular to the crystal growth direction that hinders the electrical flow when using the semiconductor layer which is a disadvantage of the SLS crystallization method.

Also, no mask is used for crystallization using the laser. Therefore, the process is simpler than the conventional crystallization method using a laser, bringing the effect of cost reduction.

According to the present invention, after primary laser irradiation, a primary grain boundary may be formed. However, when the laser is irradiated secondly to the region A including the interface between the polycrystalline silicon region where the grains are formed and the amorphous silicon, the amorphous silicon and the polycrystal As the silicon is melted and then cooled, atoms are attached to the preformed polycrystalline grains that are not dissolved by laser irradiation in the second order, thereby increasing the length to one side of the grains. Therefore, only grain boundaries exist in the direction parallel to the crystal growth direction.

At this time, the pitch, which is the moving distance d2 of the laser beam, should be 1 to 3 μm, and the laser in the pulse form should be continuously irradiated. Because the amorphous silicon layer is melted and solidified to form a grain boundary perpendicular to the crystal growth direction as protrusions are formed by the volume difference, the grain boundary must be melted again to grow crystals.

Therefore, considering that the width of the laser beam according to the present invention is 5 to 20 µm, the laser irradiation pitch must be 3 µm or less to be melted again, including grain boundaries perpendicular to the crystallographic direction. In addition, since the laser must be moved, it must have a pitch of 1 μm or more.

 By irradiating the laser onto the amorphous silicon as described above, the size of the crystal grains can be continuously grown laterally to form large crystal grains. In addition, it is possible to prevent the formation of protrusions formed by the difference in volume by repeating melting and solidifying at a narrow pitch interval, so that the appearance of an electric field concentrated on a portion where the roughness of the polycrystalline silicon layer protrudes is 15 nm or less. Can be prevented and the movement of charges can be smoothed.

4B is a graph of the surface roughness of a polycrystalline silicon layer crystallized according to the present invention. In Fig. 4B,? Is a horizontal direction (laser irradiation direction) of the polycrystalline silicon layer, and? Is a roughness in the longitudinal direction of the polycrystalline silicon layer.

Referring to FIG. 4B, the peak and peak difference are 15 nm or less. Therefore, it can be seen that the surface of the polycrystalline silicon crystallized according to the present invention is flat with few protrusions. Therefore, there is no problem that may occur when the device is formed of polycrystalline silicon having protrusions, and thus, a superior device may be produced.

4C is a SEM photograph of crystallized amorphous silicon according to an embodiment of the present invention.

Referring to FIG. 4C, the polycrystalline silicon crystallized according to the present invention has only a grain boundary G formed in a direction parallel to the crystal growth direction and has a very large crystal. As described above, since there is no grain boundary (so-called "primary grain boundary") formed in a direction perpendicular to the crystal growth direction seen in the conventional laser crystallization method, the crystallinity is excellent because it does not affect the electrical properties of the thin film transistor. In addition, it can produce a thin film transistor having good characteristics when used as a device of the thin film transistor.

Therefore, the polycrystalline silicon layer by the direct crystallization method using the laser of the present invention has a large grain, few surface projections, and does not have a grain boundary formed perpendicular to the direction of crystal growth that impedes the flow of current. When used, the current characteristics are very good. In addition, the process is simplified and the cost can be reduced because the process can be performed using only a laser having a small energy.

Example 1

5 is a view showing a method of manufacturing a thin film transistor according to the first embodiment of the present invention.

Referring to FIG. 5, after the buffer layer 310 is formed on the substrate 300, an amorphous silicon layer is formed on the buffer layer 310. The buffer layer 310 prevents the diffusion of impurities in the substrate 300 during the subsequent crystallization of the amorphous silicon layer.

Subsequently, the amorphous silicon layer is crystallized into a polycrystalline silicon layer (not shown) by using a directional crystallization method (Thin beam Directional Crystallization) according to the present invention. The thin beam directional crystallization method is a method of directly irradiating an amorphous silicon layer with a beam having a predetermined width and a predetermined length without a mask.

In the present invention, the intensity and area of the laser beam are optimized to melt and solidify the amorphous silicon layer. The optimized laser beam has an energy density of 150 to 1000 mJ / cm 2, an area of 365 to 1100 mm in length and a width of 5 to 20 μm, and the laser has a pitch of 1 to 3 μm to remove the primary grain boundaries. The laser travels a small distance as much as it travels and examines consecutive shots.

In the directional crystallization method, the laser is irradiated without using a mask. When the laser is irradiated to one side of the amorphous silicon layer, the portion is melted and solidified. Then, the laser is irradiated by overlapping a part of the boundary in the second laser irradiation, and the colon is first grown in the laser irradiation progress direction by the laser irradiation unit.

As the shots are repeatedly and continuously irradiated, crystallization is continuously performed, and the pitch interval is continuously set to 1 to 3 μm so that grain boundaries formed in a direction perpendicular to the crystal growth direction existing in the conventional SLS crystallization method are not formed. Irradiate the laser.

Therefore, in the polycrystalline silicon layer crystallized by the directional crystallization method of the present invention, a uniform silicon layer having only grain boundaries located in a direction parallel to the crystal growth direction is formed. In addition, since the grain size is very large, it may have excellent characteristics when used as an electrical device. When the polycrystalline silicon layer is used as a semiconductor layer, the grain boundary is formed to be located in a direction parallel to the direction in which charge flows.

As described above, the semiconductor layer 320 is formed in the thin film transistor formation region by patterning the formed polycrystalline silicon layer. The gate insulating layer 330 is formed on the substrate 300 including the semiconductor layer 320. The gate insulating layer 330 may be formed using a silicon oxide layer (SiO 2), a silicon nitride layer (SiN x), or a stacked structure thereof.

Subsequently, a single layer of an aluminum alloy such as aluminum (Al) or aluminum-neodymium (Al-Nd), or a plurality of aluminum alloys stacked on chromium (Cr) or molybdenum (Mo) alloy on the gate insulating layer 330. The gate electrode metal layer (not shown) is formed.

The gate electrode 328 is formed in a predetermined region corresponding to the semiconductor layer 320 by etching the metal layer for the gate electrode 328. The predetermined region is a region corresponding to the channel region 324 formed in a subsequent process.

Next, a source / drain region 322 is formed by doping a conductive type impurity with the gate electrode 328 as a mask. An impurity doped region located between the source / drain regions 322 serves as the channel region 324. Alternatively, the doping process may proceed by forming a photoresist before forming the gate electrode 328. In addition, in the present invention, the process of forming the gate electrode after forming the semiconductor layer has been described, but the process of forming the gate electrode under the semiconductor layer may be performed before forming the semiconductor layer.

Subsequently, an interlayer insulating layer 340 is formed on the substrate 300 including the gate electrode 328, penetrates the interlayer insulating layer 340 and the gate insulating layer 330, and a part of the source / drain region 322. A contact hole 342 is formed to expose the contact hole. The conductive material is deposited on the substrate 300 including the contact hole 342 and then patterned to form a source / drain electrode 352 connected to the source / drain region 322 through the contact hole 342. Form.

The thin film transistor may have a top gate structure or a bottom gate structure.

Example 2

6 is a diagram of an organic light emitting display device according to a second embodiment of the present invention.

Since the second embodiment includes the thin film transistor according to the first embodiment, a manufacturing process of the thin film transistor is omitted in order to avoid duplication.

Referring to FIG. 6, after forming the thin film transistor as in Example 1, a protective film 362 is formed over the entire surface of the substrate including the source / drain electrodes 352. Thereafter, a via hole (not shown) is formed on the passivation layer 362 to form a first electrode 372, and a pixel definition layer 382 defining a pixel region on the first electrode 372 is formed. To form an opening in the first electrode.

Next, an organic light emitting layer 392 is formed in the opening of the first electrode, and a second electrode 402 is formed over the entire surface of the substrate to complete the organic light emitting display device.

Although the present invention has been shown and described with reference to the preferred embodiments as described above, it is not limited to the above embodiments and those skilled in the art without departing from the spirit of the present invention. Many variations and modifications will be possible.

      The present invention relates to a method for crystallizing silicon, wherein a laser having a narrow and long beam size without using a mask directly crystallizes amorphous on a silicon as polycrystal, and the crystallized polycrystalline silicon is in a crystal growth direction. It consists only of grain boundaries located in parallel directions, so it does not interfere with the flow of current, so it has excellent characteristics when used as a thin film transistor. In addition, since the grain size is large and the surface projections of the silicon layer are small, there are few electrical defects, which is very excellent when used as an electric element.

Claims (10)

A substrate on which a buffer layer is formed; A semiconductor layer disposed on the substrate and having a grain boundary parallel to a crystal growth direction, the semiconductor layer comprising a polycrystalline silicon layer having a top surface roughness of 15 nm or less; A gate electrode formed to correspond to one region of the semiconductor layer; A gate insulating film for insulating the semiconductor layer from the gate electrode; And And a source / drain electrode connected to the semiconductor layer. The method of claim 1, The plurality of grain boundaries, the grain boundaries are thin film transistors, characterized in that located in a direction parallel to the direction of the current flow. Providing a substrate on which a buffer layer is formed, Forming an amorphous silicon layer on the substrate, Irradiating the amorphous silicon layer with a laser beam having an energy density capable of forming a fully melted region or a fully melted proximity region on one side of the amorphous silicon layer to crystallize a portion of the amorphous silicon layer, The laser beam is moved to overlap with the crystallized portion and irradiated with laser again to crystallize,  The above process is repeated a plurality of times to continuously irradiate a laser to form a polycrystalline silicon layer, And forming the semiconductor layer by patterning the polycrystalline silicon layer. The method of claim 3, wherein The method of manufacturing a thin film transistor, characterized in that the laser beam irradiated on the substrate is emitted in a pulsed manner. The method of claim 3, wherein The laser beam is a method of manufacturing a thin film transistor, characterized in that any one of XeF or KrF. The method of claim 3, wherein The laser beam has an energy density of 150 to 1000mJ / ㎠, a length of 365 to 1100mm and a width of 5 to 20㎛ manufacturing method of a thin film transistor. The method of claim 3, wherein The laser beam is a method of manufacturing a thin film transistor, characterized in that the continuous shot proceeds in a direction perpendicular to the length of the beam to form a crystal. The method of claim 3, wherein The method of manufacturing a thin film transistor, characterized in that no mask is used when irradiating the laser beam. Providing a substrate, A semiconductor layer on the substrate, the semiconductor layer having a grain boundary parallel to the crystal growth direction, the semiconductor layer comprising a polycrystalline silicon layer having a top surface roughness of 15 nm or less; A gate electrode formed to correspond to one region of the semiconductor layer; A gate insulating film for insulating the semiconductor layer from the gate electrode; A source / drain electrode connected to the semiconductor layer; A passivation layer on the source / drain electrode over the entire substrate; A first electrode on the passivation layer and connected to any one of a source / drain electrode; A pixel defining layer exposing a portion of the first electrode and positioned on the substrate; An organic light emitting layer on the exposed first electrode; And An organic light emitting display device, characterized in that the second electrode is located in front of the substrate. The method of claim 9, And a plurality of grain boundaries, wherein the grain boundaries are located in a direction parallel to a direction in which a current flows.

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