KR100669714B1 - A method for preparing thin film transistorTFT having polycrystalline Si, a thin film transistor prepared by the method and a flat pannel display with the thin film transistor - Google Patents

Abstract

The present invention comprises the steps of forming an amorphous silicon film on an insulating substrate; Crystallizing the amorphous silicon film by a crystallization method using a laser to form a polycrystalline silicon film; And a method of manufacturing a thin film transistor, the thin film transistor manufactured according to the present invention, and a flat panel display device having the same.

According to the thin film transistor manufacturing method of the present invention, it is possible to obtain a thin film transistor employing a polycrystalline silicon film in which the surface roughness of the polycrystalline silicon film is highly improved and the silicon crystal is not substantially damaged.

Description

A method for preparing thin film transistor (TFT) having polycrystalline Si, a thin film transistor prepared by the method and a flat pannel display with the thin film transistor}

1 is a cross-sectional structural view of an embodiment of a thin film transistor manufactured according to the method of manufacturing a thin film transistor of the present invention.

2 is an Atomic Force Microscope (AFM) photograph of the surface of a polycrystalline silicon film crystallized by laser annealing.

3 is an AFM photograph of the surface of a polycrystalline silicon film crystallized by laser annealing followed by oxygen plasma etching.

4 is an AFM image of the surface of a polycrystalline silicon film crystallized by laser annealing followed by oxygen plasma etching and then etched with a buffered oxide etchant (hereinafter also referred to as "BOE").

FIG. 5A is a graph showing the surface roughness of the surface of the polycrystalline silicon film formed by laser annealing and then performing oxygen plasma etching under various conditions in comparison with the surface roughness of the surface of the polycrystalline silicon film crystallized by laser annealing.

FIG. 5B is a graph showing the crystallinity of the polycrystalline silicon film formed by laser annealing and then performing oxygen plasma etching under various conditions in comparison with the crystallinity of the polycrystalline silicon film crystallized by laser annealing.

6 is a graph showing the surface roughness of the surface of the polycrystalline silicon film formed by laser annealing, followed by oxygen plasma etching, and then performing BOE etching under various conditions, compared with the surface roughness of the surface of the polycrystalline silicon film crystallized by laser annealing. .

<Short description of drawing symbols>

1 ... insulating substrate 2 ... buffer layer

3 ... gate insulating film 4 ... interlayer insulating film

12 ... semiconductor active layer 13 ... gate electrode

14 Source electrode 15 Drain electrode

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor employing a polycrystalline Si film, a thin film transistor manufactured according to the present invention, and a flat panel display device having the same. More specifically, the surface roughness is greatly improved, and the surface roughness improving process is performed. Among the silicon crystals, a method of manufacturing a thin film transistor employing a polycrystalline silicon film that is substantially intact, and a thin film transistor manufactured accordingly, and a flat panel display device having the same.

Conventional low temperature polycrystalline silicon is obtained by crystallizing amorphous silicon at low temperature, and is widely used as a channel layer of a thin film transistor. The low temperature polycrystalline silicon film used as the channel layer of the thin film transistor can be obtained by crystallizing the amorphous silicon film using various crystallization methods.

Among the crystallization methods of the amorphous silicon film, the crystallization method using a laser is widely used because it has relatively little thermal effect on an insulating substrate such as a glass substrate and can form polycrystalline silicon having superior physical properties as compared to the solid phase crystallization method. It is becoming.

However, in the crystallization method using a laser, the density difference generated as the silicon liquid phase changes into a solid phase becomes uneven, so that surface projections are generated in a portion where the crystallization is relatively slow, resulting in poor surface roughness of the polycrystalline silicon film. Has disadvantages. The protrusions formed on the surface of the polycrystalline silicon film formed by the low temperature crystallization method using a laser have a height of 1/2 to 2 times the thickness of the polycrystalline silicon film.

Formation of such protrusions is inevitable in the crystallization step of crystallizing the amorphous silicon film into the polycrystalline silicon film by the laser crystallization method, which causes various defects in subsequent steps. For example, when the gate insulating film and the gate electrode metal material are deposited on the polycrystalline silicon film, the gate insulating film and the gate electrode metal material are deposited along the surface protrusions of the polycrystalline silicon. It has projections similar to the surface projections of the silicon film.

As described above, in the gate insulating layer having the protrusion, the breakdown voltage may be lowered and the leakage current may increase due to the protrusion. In addition, if the metal material for the gate electrode on which the protrusion is formed is hillocked due to poor surface roughness of the metal material for the gate electrode, the device material is degraded. In addition, such protrusions may cause nonuniformity in the etching process and the exposure process, resulting in deterioration of the reliability of the device.

One method for improving the surface roughness of the polycrystalline silicon film is a method of repeatedly performing wet oxidation and HF treatment. This method repeats the process of removing the oxide film formed on the surface of the polycrystalline silicon film by oxidizing the surface of the polycrystalline silicon film using ozone water in a spin type wet station and then HF treatment in the same equipment. This is how to remove the protrusions.

Since the method performs several surface oxidation and HF treatment processes, the polycrystalline silicon film other than the protrusions is also lost, and thus only the desired protrusions cannot be selectively removed, and process reliability is lowered.

On the other hand, the wet etching process including the HF treatment process, as described above, in addition to the problem that the selective etching is difficult, there are problems such as long etching time and incidental contamination due to the etching solution. In order to solve this problem, research on a dry etching process has been actively conducted recently.

This dry etching process has been applied to a variety of thin film transistor manufacturing. As a specific example thereof, Korean Patent No. 0365414 discloses removing an amorphous carbon film used as a protective film in manufacturing a thin film transistor using oxygen plasma etching. According to the patent, the amorphous carbon film is not only made of carbon but not silicon and does not contain a crystal. The amorphous carbon film is used as a protective film in the manufacture of a thin film transistor, and is removed using an etching process after removing the protrusion on the surface of the polycrystalline silicon film below. do.

However, the oxygen plasma etching process of the patent is not intended to improve the surface properties of the amorphous carbon film but to completely remove the amorphous carbon film, and when applied to the surface of the polycrystalline silicon film, there is a problem such as silicon crystal damage. May occur, which ultimately results in a degradation of the thin film transistor. Accordingly, there is a need to develop an etching process that minimizes the silicon crystal damage of the polycrystalline silicon film after etching while improving the surface roughness of the polycrystalline silicon film by maintaining the advantages of the oxygen plasma etching process to the maximum.

SUMMARY OF THE INVENTION The present invention has been made in an effort to provide a method of manufacturing a thin film transistor capable of minimizing damage to a silicon crystal while improving the surface roughness of the polycrystalline silicon film as described above. As a result, a thin film transistor having an improved reliability due to improved surface roughness and an easy thickness reduction of an insulating film and a flat panel display device having the same can be obtained.

In order to solve the problem of the present invention, the first aspect of the present invention,

Forming an amorphous silicon film on the insulating substrate;

Crystallizing the amorphous silicon film by a crystallization method using a laser to form a polycrystalline silicon film; And

It provides a method of manufacturing a polycrystalline silicon thin film transistor comprising the step of oxygen plasma etching the surface of the polycrystalline silicon film.

The polycrystalline silicon thin film transistor may further include a wet etching step after plasma etching.

The oxygen plasma etching step of the polycrystalline silicon thin film transistor manufacturing method may be performed by setting an internal pressure of 0.3 to 7 Pa in a chamber in which oxygen plasma etching is performed.

In order to solve the other problem of the present invention, the second aspect of the present invention provides a thin film transistor manufactured according to the polycrystalline silicon thin film transistor manufacturing method.

In order to solve the another object of the present invention, a third aspect of the present invention provides a flat panel display device having a thin film transistor manufactured according to the polycrystalline silicon thin film transistor manufacturing method.

According to the method for manufacturing a thin film transistor of the present invention, it is possible to obtain a thin film transistor employing a high quality polycrystalline silicon film in which the surface roughness of the polycrystalline silicon film is highly improved but the silicon crystal is not substantially damaged.

Hereinafter, the present invention will be described in more detail.

The method of manufacturing a thin film transistor of the present invention first includes forming an amorphous silicon film on an insulating substrate. The insulating substrate may be, for example, an insulating substrate having an oxide film or a nitride film formed on a glass substrate. The method of forming an amorphous silicon film on an insulating substrate includes, for example, a chemical vapor deposition process. The thickness of the amorphous silicon film formed on the insulating substrate is 400 kPa to 600 kPa, preferably 450 kPa to 550 kPa. This is because when the thickness of the amorphous silicon film is 600 GPa or more, there may be a problem that the surface of the film is severely rough. When the thickness of the amorphous silicon film is less than 400 GPa, there may be a problem that the crystallization for each region is uneven.

Thereafter, the amorphous silicon film formed on the insulating substrate is crystallized by a crystallization method using a laser to form a polycrystalline silicon film. Examples of crystallization methods using lasers include laser annealing such as Excimer Laser Annealing (ELA method). According to the conventional ELA method, irradiating an amorphous silicon film with a pulse laser of 25 ns to 65 ns melts the amorphous silicon and forms silicon crystals in the process of cooling it. On the surface of the polycrystalline silicon film, protrusions are formed around grain boundaries, and silicon oxide may be formed.

Plasma etching is performed on the surface of the polycrystalline silicon film formed therefrom. The gas used for the plasma etching is oxygen or argon gas, or a gas in which argon or fluorine-containing gas such as SF ₆ or CF ₄ is mixed with oxygen. Among these, the gas preferable for the plasma etching of this invention is oxygen. Oxygen plasma etching is suitable for inductively coupled plasma (ICP) method with bias power and is preferably performed at low pressure so that ions can get sufficient energy. In equipment such as sputter, the energy of ions is excessive. When used for surface treatment of polycrystalline silicon films, the silicon crystals are damaged, but such problems do not occur in inductively coupled plasma type dry etching equipment. Oxygen plasma etching of the present invention can be performed with a chamber internal pressure of 0.3 to 7 Pa, preferably 0.7 to 1.3 Pa. In particular, the pressure may be performed at a chamber internal pressure of about 1.3 Pa. When the chamber internal pressure at which oxygen plasma etching is performed is 7 Pa or more, there may be a problem that ions do not obtain sufficient energy and thus do not contribute to surface roughness improvement, and when the chamber internal pressure at which oxygen plasma etching is performed is less than 0.3 Pa, inductive coupling. This is because it is outside the process pressure range of the plasma equipment. Therefore, it is also possible to use lower pressures if it is possible to lower the process pressure of the equipment.

For the surface of the oxygen plasma etched polycrystalline silicon film, wet etching using a buffer oxide etchant may then be further performed to further improve surface roughness. Conventional BOE is a buffer solution containing an acid that acts as an etch and a material that maintains a pH at which the acid can etch. Examples of the BOE include a mixture of NH ₄ F and HF, a mixture of HNO ₃ , HC ₂ H ₃ O ₂ and HF, among which BOE is most suitable for use in the BOE etching of the present invention is NH ₄ F and HF as an aqueous solution, a mixture of water with a molar ratio of NH ₄ F and HF 1: 6 in an aqueous solution of NH ₄ F and HF. BOE etching can be performed preferably for 10 to 120 seconds, more preferably for 30 to 90 seconds. This is because when the BOE etching is performed for 120 seconds or more, a problem may occur that the silicon is etched to damage the surface, and when the BOE etching is performed for less than 10 seconds, the etching effect by the BOE etching solution does not appear.

The surface roughness of the surface of the polycrystalline silicon film after the laser annealing including the ELA annealing and before the oxygen plasma etching treatment is usually 180 kPa to 230 kPa. However, the surface roughness of the surface of the polycrystalline silicon film produced according to the method described above has a range of 100 kPa to 160 kPa.

1 illustrates a cross-sectional structure of a thin film transistor manufactured by surface treatment of a polycrystalline silicon film according to an embodiment of the present invention.

Referring to FIG. 1, a buffer layer 2 is formed on an insulating substrate 1 such as a glass substrate. The gate insulating film 3 is provided on the buffer layer 2, and the gate electrode 13 is formed of a conductive metal film on a predetermined region of the gate insulating film 3. The gate electrode is formed of a conductive metal film such as MoW, Al, Cr, Al / Cu, but is not limited thereto. The region where the gate electrode 13 is formed corresponds to the channel region C1 of the active layer 12. An interlayer insulating film 4 is formed on the gate electrode 13, and the source electrode 14 and the drain electrode 15 are formed in a state where contact holes are formed in the interlayer insulating film 4 and the gate insulating film 3. It is formed on the interlayer insulating film 4.

The thin film transistor manufactured according to the thin film transistor manufacturing method of the present invention can be usefully used in flat panel display devices. The flat panel display includes, for example, a plasma display panel (PDP), a liquid crystal display (LCD), among these, an organic light emitting diode (OLED), and the like. do. Among these, one embodiment of the organic electroluminescent display device includes a light emitting device having a plurality of pixels; At least one pixel is provided in each pixel, and includes an active layer formed of a silicon thin film and having a channel region, a source and a drain region, a gate insulating layer disposed on the active layer and formed of an insulating layer, and the upper portion of the gate insulating layer. A thin film transistor including a gate electrode provided as a conductive layer in a region corresponding to the channel region; And a gate line electrically connected to the gate electrode.

Hereinafter, with reference to the accompanying drawings, it will be described in more detail of the present invention through one embodiment of the present invention. The following examples are intended to illustrate the invention, the invention is not limited thereto.

EXAMPLE

Amorphous Silicon Film Formation Step

First, an insulating substrate on which a SiNx / SiO ₂ buffer layer was formed on a glass substrate was prepared. A 500 nm thick amorphous silicon film was formed on the insulating substrate by chemical vapor deposition.

Polycrystalline Silicon Film Formation Step

The amorphous silicon film was laser annealed with a XeCl laser of 308 nm in a normal pressure and room temperature atmosphere to form a polycrystalline silicon film. The surface roughness of the polycrystalline silicon film formed by laser annealing is referred to the AFM photograph of FIG. 2. According to FIG. 2, the surface of the polycrystalline silicon film formed by laser annealing includes a protrusion, and the surface roughness of the surface of the polycrystalline silicon film is 210 Å (Root Mean Square: RMS).

Oxygen plasma etching step

A polycrystalline silicon film was formed using laser annealing, and then 200 seconds at 200 sccm O ₂ under a pressure of 1.3 Pa and a source power of 2750 W and a bias power of 400 W. Oxygen plasma etching was performed. Refer to the AFM photograph of FIG. 3 for the surface roughness of the surface of the polycrystalline silicon film immediately after the oxygen plasma etching. 3, the surface roughness of the surface of the polycrystalline silicon film after oxygen plasma etching is 160 kPa. From this, it can be confirmed that the surface of the polycrystalline silicon film subjected to oxygen plasma etching after laser annealing has an excellent surface roughness than the surface of the polycrystalline silicon film formed by laser annealing.

BOE etching step

After oxygen plasma etching at room temperature an aqueous solution of NH ₄ F and HF (a mixture of water with a molar ratio of NH ₄ F and HF of 1: 6 being) by the use of an etchant to the buffer oxide wet etching was performed for 60 seconds. Refer to the AFM photograph of FIG. 4 for the surface roughness of the surface of the polycrystalline silicon film immediately after the buffer oxide etchant etching. According to FIG. 4, the surface roughness of the surface of the polycrystalline silicon film after BOE etching is 125 kPa. From this, the surface of the polycrystalline silicon film subjected to oxygen plasma etching and BOE etching after laser annealing has better surface roughness than the surface of the polycrystalline silicon film formed by laser annealing as well as the surface of the polycrystalline silicon film subjected to oxygen plasma etching after laser annealing. You can check it.

Evaluation Example 1-Evaluation of surface roughness and crystallinity according to the internal pressure of oxygen plasma etching

Oxygen plasma etching was performed on the surface of the polycrystalline silicon film formed by laser annealing to evaluate surface roughness and crystallinity of the polycrystalline silicon film, respectively, and are graphically shown in FIGS. 5A and 5B.

5A is a graph illustrating oxygen plasma etching effects over various plasma etching pressures and times. It can be seen from FIG. 5A that the surface roughness of the polycrystalline silicon film is most improved when oxygen plasma etching is performed at a chamber internal pressure of 1.3 Pa.

5B is a graph showing that the silicon crystals were not substantially damaged even after the oxygen plasma etching of the present invention by measuring the crystallinity of the polycrystalline silicon film. The crystallinity was measured as the fraction of the crystalline peak area from the crystalline peak and the amorphous peak obtained by Raman analysis of the silicon film surface. In Fig. 5B, in particular, the crystallinity of the polycrystalline silicon film formed by laser annealing is substantially the same as the crystallinity of the oxygen-etched polycrystalline silicon film subjected to oxygen plasma etching for 200 seconds at a pressure of 1.3 Pa after laser annealing. In the case of the silicon film, it can be seen that almost no damage to the silicon crystals occurred.

Evaluation Example 2-Evaluation of Surface Roughness According to BOE Etching Time

Oxygen plasma etching was performed on the surface of the polycrystalline silicon film generated by laser annealing at a pressure of 1.3 Pa for 200 seconds, and then BOE etching was performed under various time conditions to evaluate the surface roughness of the surface of the polycrystalline silicon film.

6 is a graph showing surface roughness of the surface of a polycrystalline silicon film according to BOE etching time. When the BOE etching time passes 60 seconds, there is no change in surface roughness. Therefore, the BOE etching time is preferably 60 seconds or less from the viewpoint of reagent and energy saving.

According to the manufacturing method of the thin film transistor of the present invention, it is possible to adopt a polycrystalline silicon film in which the surface roughness of the polycrystalline silicon film formed by crystallizing the amorphous silicon film is substantially undamaged silicon crystals, thereby improving reliability and thickness of the insulating film A thin film transistor having an easy reduction can be obtained. Such thin film transistors may be usefully used in flat panel displays including organic light emitting displays.

Claims (6)

Forming an amorphous silicon film on the insulating substrate; Crystallizing the amorphous silicon film by a crystallization method using a laser to form a polycrystalline silicon film; Oxygen plasma etching the polycrystalline silicon film surface; And A method of manufacturing a thin film transistor comprising wet etching a surface of the oxygen plasma etched polycrystalline silicon film with a buffered oxide etchant (BOE) after the oxygen plasma etching step, wherein the surface roughness of the polycrystalline silicon film is RMS. The manufacturing method of the thin film transistor which is 100 kV-160 kV. delete The method of claim 1, wherein the oxygen plasma etching step is performed using an internal pressure of 0.3 Pa to 7 Pa in a chamber in which oxygen plasma etching is performed. The method of claim 1, wherein the BOE of the wet etching step includes a mixture of NH ₄ F and HF, and the wet etching step is performed for 30 to 90 seconds. A thin film transistor manufactured according to any one of claims 1, 3 and 4, wherein the surface roughness of the polycrystalline silicon film is RMS 100 Hz to 160 Hz. A flat panel display device manufactured according to any one of claims 1, 3, and 4, comprising a thin film transistor having a surface roughness of RMS 100 Hz to 160 Hz.

Images