KR20060040367A - Method for fabricating liquid crystal display device by using alternating magnetic field crystallization - Google Patents

Abstract

The present invention relates to a polysilicon forming method using a magnetic field crystallization method, the method comprising: preheating a substrate; Forming an amorphous silicon layer on the substrate; Crystallizing by applying a magnetic field to the amorphous silicon layer; It is characterized in that it comprises a step of injecting hydrogen ions while cooling the crystallized silicon layer to obtain a polysilicon homogeneous and lower the threshold voltage, it is possible to improve the productivity.

Magnetic field crystallization, AMFC, hydrogenation treatment

Description

Liquid crystal display device manufacturing method by magnetic field crystallization method {METHOD FOR FABRICATING LIQUID CRYSTAL DISPLAY DEVICE BY USING ALTERNATING MAGNETIC FIELD CRYSTALLIZATION}

1 is a graph showing the threshold voltage of silicon formed by general magnetic field crystallization.

2 is a flow chart showing the magnetic field crystallization step of the present invention.

3 is a perspective view of a magnetic field crystallization apparatus used in the present invention.

4 is a graph showing the relationship between each step and temperature in the magnetic field crystallization process of the present invention.

5A through 5E are flowcharts of a process of manufacturing a liquid crystal display device according to an embodiment of the present invention.

********** Description of the symbols for the main parts of the drawings ************

301: loader area 302, 303, 304: first, second, third preheating area

305, 307: Stabilization area 306: Process area

308,309,310: First 1,2,3 cooling zones

501: substrate 502: buffer layer

503: amorphous silicon 503a: active layer

504: gate insulating layer 505: gate electrode

506: interlayer insulating layer 507S, 507D: source, drain electrode

508: passivation layer 509: pixel electrode

The present invention relates to a method for manufacturing a liquid crystal display device using polysilicon crystallized by a magnetic field crystallization method, and more particularly, to a method for manufacturing a polysilicon liquid crystal display device with a threshold voltage corrected by a magnetic field crystallization method.

Liquid crystal display devices are widely used today because they are light, thin and portable. The liquid crystal display device displays an image by driving pixels arranged in a matrix, and the pixels are formed in the liquid crystal display panel.

The liquid crystal display panel is supported by a liquid crystal display module, and a driving circuit unit for driving unit pixels is formed outside the liquid crystal display panel or outside the screen display portion of the liquid crystal display panel to drive the pixels.

The liquid crystal display panel includes a color filter substrate and a TFT array substrate on which thin film transistors (TFTs), which are switching elements of unit pixels, are bonded to each other, and liquid crystal is filled therebetween.

The TFT array substrate includes a plurality of gate lines and a plurality of data lines perpendicular to the gate lines, and a unit pixel area is defined by the gate lines and the data lines. A TFT, which is a switching element, is formed in the intersection of the gate line and the data line, particularly in the unit pixel area, and the manufacturing process of the TFT is an important part in manufacturing a liquid crystal display device.

The TFT includes an active layer including a channel region, a source region, and a drain region, a source electrode connected to the source region, a drain electrode connected to the drain region, and a gate electrode to turn a channel on and off by applying a voltage to the channel. It is provided.

In particular, the active layer is mainly composed of a semiconductor, usually composed of amorphous silicon.

However, while amorphous silicon is easy to manufacture, there is a problem in manufacturing a liquid crystal display device requiring high-speed operation due to poor electrical mobility. Today, as the demand for liquid crystal display devices having high-speed operation characteristics capable of realizing moving pictures and the like increases, efforts are being made to manufacture TFTs having high electric mobility and stability.

Among them, research is being actively conducted to form TFTs using polysilicon rather than amorphous silicon as an active layer, and the polysilicon has tens of times to hundreds of times more mobility than amorphous silicon.

As a method of forming the polysilicon, a heating method of heating and crystallizing amorphous silicon in a heating furnace, and a laser crystallization method of crystallizing by instantaneously applying a laser to amorphous silicon and the like are used.

The crystallization by the heating method is not suitable for the manufacture of a liquid crystal display device using glass as a substrate because the crystallization temperature is higher than the transition temperature of the glass, the laser crystallization method has the advantage of forming a good quality of polysilicon In other words, expensive laser equipment should be used, and shot marks appearing by irradiating the laser have a disadvantage of forming a stain on the screen.

Crystallization methods that compensate for these shortcomings include metal induced crystallization (MIC) method using a metal catalyst such as nickel and magnetic field crystallization method that promotes crystallization by applying a magnetic field to the crystallized amorphous silicon (Alternating Magnetic Field). crystallization, hereinafter AMFC) was introduced.

The polysilicon crystallized by the MIC has the advantage that the crystallization can be achieved at a low temperature below the glass transition temperature, but the metal catalyst elements remaining after crystallization act as impurities in the crystalline to deteriorate the electrical properties of the polysilicon. have.

On the other hand, polysilicon crystallized by AMFC has excellent homogeneity because of the formation of homogeneous crystalline silicon, while having a threshold voltage shifted to a negative value and a high saturation current voltage of 40 volts or more. There is a problem in that it is difficult to apply to a liquid crystal display device using a driving voltage of 20 volts.

1 shows the V-I curve of a TFT formed by AMFC crystallization.

The first curve 101 of FIG. 1 shows when the drain voltage Vd of the thin film transistor is -10V, and the second curve 102 shows when the drain voltage is -0.1V.

In general, as the threshold voltage, a gate voltage for operating a thin film transistor having a drain current of 10 ⁻⁸ A and a drain voltage of −0.1 V is used. Referring to FIG. 1, it can be seen that the threshold voltage is about −18 volts. have. In general, the lower the threshold voltage, the more controllable a driving device can be manufactured. In addition, since the driving voltage of the liquid crystal display device is usually set between 5 and 20 volts, a polysilicon that can be used in the manufacture of the device is required only when a saturation current voltage (Vs) is formed therebetween. do. However, referring to FIG. 1, a thin film transistor using AMFC-crystallized silicon has a problem that the threshold voltage is moved to a negative value and the saturation current voltage (Vs) reaches about 40 volts, which makes it difficult to apply to the device.

Therefore, an object of the present invention is to form polysilicon having a threshold voltage corrected so that the polysilicon crystallized by AMFC is configured to operate a thin film transistor while operating within a normal driving voltage range. In particular, in forming a thin film transistor using polysilicon formed by AMFC, an object of the present invention is to improve characteristics of a driving device without adding additional process equipment or adding a process.

Therefore, the polysilicon forming method according to the magnetic field crystallization method of the present invention comprises the steps of preheating the substrate; Forming an amorphous silicon layer on the substrate; Crystallizing by applying a magnetic field to the amorphous silicon layer; Injecting hydrogen ions while cooling the crystallized silicon layer.

In addition, the thin film transistor manufacturing method including the polysilicon forming method comprises the steps of forming an amorphous silicon layer on a substrate; Crystallizing by applying a magnetic field to the amorphous silicon layer; Implanting hydrogen ions while cooling the crystallized silicon layer; Patterning the crystallized silicon layer to form an active layer; Forming a gate insulating layer on the active layer; Forming a gate electrode on the gate insulating layer; Forming source and drain electrodes connected to the source and drain regions of the active layer, respectively; And forming a pixel electrode connected to the drain electrode.

Polysilicon has an excellent electric mobility compared to amorphous silicon, and thus is suitable for the manufacture of driving devices requiring high speed operation. Therefore, as the demand for driving devices that operate at high speed to implement moving pictures increases, studies of thin film transistors using polysilicon are active. Among them, the crystallization method by the magnetic field crystallization method has an advantage that polysilicon having homogeneous characteristics can be formed at low temperature, but there is a problem that the threshold voltage of the thin film transistor using the crystallized silicon layer is large.

The present invention provides a method for improving the interfacial properties of polysilicon formed by the magnetic field crystallization method, and aims to lower the threshold voltage of the polysilicon thin film transistor formed by the method.

For this purpose, hydrogen ions are blown into the magnetic field crystallized polysilicon to improve the interfacial properties of the crystallized polysilicon.

In addition, the hydrogenation treatment is not performed separately from polysilicon formation, and the hydrogenation treatment is performed only by blowing hydrogen ions in the process of cooling the polysilicon formed by magnetic field crystallization.

The hydrogenation treatment removes the dangling bonds by combining dangling bonds, which may be non-covalent electron pairs, formed in the lattice of hydrogen ions and polysilicon, in particular, at the interface of polysilicon, thereby removing the dangling bonds. It is a process to stabilize.

The hydrogenation process is usually carried out in a separate process, in particular, stopping the crystallization process in a vacuum environment for the hydrogenation process, injecting hydrogen ions into the chamber where the process is carried out, temperature and pressure for the hydrogenation treatment Hydrogenation is performed through the step of controlling the internal environment.

However, the present invention is characterized in that the crystallization process is subjected to a hydrotreatment at the same time as the magnetic field crystallization process proceeds.

Hereinafter, the polysilicon crystallization method of the present invention will be described in detail with reference to FIG. 2.

The crystallization method of the present invention uses an alternating magnetic field crystallization method (AMFC) in which crystallization proceeds while applying an alternating magnetic field to amorphous silicon.

Referring to FIG. 2, the substrate on which the amorphous silicon layer is formed is transferred to a loader that starts to preheat. The loader becomes the starting point of the conveyor belt allowing the crystallization process to proceed continuously and starts preheating the substrate to a predetermined temperature.

Subsequently, the substrate is preheated in earnest. The preheating step is to gradually bring the amorphous silicon to a temperature for magnetic field crystallization, and prevents damage to the substrate due to sudden temperature rise.

The preheating step of the substrate may be divided into a plurality of steps according to the preheating temperature.

The preheated substrate then moves to the main chamber where magnetic field crystallization proceeds. Since the magnetic field crystallization process is performed under normal pressure, the magnetic field crystallization process may proceed continuously with the preheating process.

In the magnetic field crystallization process, amorphous silicon is changed to polysilicon while an alternating magnetic field is applied on the heated substrate.

Next, after the crystallization process is performed, the crystallized silicon is gradually cooled to reach room temperature. At this time, the gas containing hydrogen ions is blown into the chamber in which the cooling is performed.

As a result, hydrogen ions implanted in the cooling process are stabilized in combination with defects that can penetrate into the crystallized silicon and form in the crystalline silicon layer. In particular, the hydrogen ions are combined with a dangling bond formed on the surface of the polysilicon to improve the interfacial properties of the polysilicon layer.

Since the dangling bond is reduced at the interface of the polysilicon, when the polysilicon is applied to the channel, electrons moving through the channel layer are not trapped by the dangling bond, thereby lowering the threshold voltage of the thin film transistor.

Subsequently, the substrate on which the polysilicon layer which has undergone the cooling process and the hydrogenation process is formed is stored in a cassette.

The polysilicon layer formed by the above process is supplied to the following process.

Hereinafter, the magnetic field crystallization method of the present invention will be described in more detail with reference to FIGS. 3 and 4.

FIG. 3 is a perspective view of a magnetic field crystallization process chamber in which magnetic field crystallization proceeds, and FIG. 4 is a graph showing the crystallization step performed in the magnetic field crystallization process chamber in detail.

As shown in FIG. 3, the magnetic crystallization process chamber may be divided into a loader region 301, preheating regions 302, 303, 304, stabilization and process regions 305, 306, 307, and cooling regions 308, 309, 310.

In the loader area 301, cassettes transferred through an automatic transport cart are transferred, and the substrates stored in the cassettes are moved to the preheating area one by one. The substrate is moved by a robot arm, and the magnetic field crystallization process chamber is processed at normal pressure, and has a moving means such as a conveyor belt to continuously process the process.

The preheating region may be divided into first, second, and third regions according to the preheating temperature. The first preheating region 302 is a region for heating the substrate at a low temperature, and heats the substrate to about 200 ° C. The process can be seen with reference to the graph of FIG.

Subsequently, the substrate is transferred by the substrate moving means such as the conveyor belt or the like, passing through the second preheating region 303 and preheated to about 500 ° C.

The substrate is also heated to about 600 ° C. while passing through the third preheating region 304 while continuing to move.

The substrate then reaches the process region 306 for magnetic field crystallization, which undergoes a first stabilization step 305 to stabilize the heated substrate before magnetic field crystallization proceeds. In the first stabilization step, the heated substrate is maintained at a constant temperature for a predetermined time.

Subsequently, a high intensity alternating magnetic field is applied to the substrate to proceed with crystallization. In the magnetic field crystallization step 306, the substrate is further heated by an applied magnetic field to promote crystallization.

The substrate passed through the magnetic field crystallization step 306 is transferred to the cooling step through a second stabilization step 307 for stabilizing the crystallized silicon layer while maintaining a constant temperature for a predetermined time. The second stabilization step is also called a buffer step.

The substrate that has passed through the second stabilization step is gradually cooled in the cooling step, and the cooling temperature is cooled to about 600 ° C to 300 ° C.

A valve for injecting gas into the chamber is installed in the cooling area of the process chamber where the cooling step is performed to cool the substrate to inject hydrogen ions. Therefore, as the cooling process proceeds, hydrogen ions are injected to penetrate the crystallized silicon layer.

The silicon layer crystallized in the above process is removed from the dangling bond that can be formed therein, in particular, the interface properties are improved.

Hydrogenation process is usually carried out by injecting hydrogen ions in a state heated to 400 ℃, in the magnetic field crystallization method of the present invention because the cooling process is performed between about 600 ℃ ~ 300 ℃ only hydrogen ion is injected into the chamber without additional heating The hydrogenation treatment can be carried out.

Therefore, the magnetic field crystallization process chamber of the present invention further includes a valve capable of injecting hydrogen ions into the chamber in the cooling zone.

The cooling zone may be divided into first, second and third cooling zones 308, 309 and 310 according to the cooling temperature. Referring to the graph of FIG. 4, the first cooling zone 308 is cooled between about 600 ° C and 500 ° C. The second cooling zone 309 is cooled between 500 ° C. and 300 ° C., and the third cooling zone 310 is cooled between about 300 ° C. and room temperature.

Subsequently, the cooling process is completed, the substrate is loaded back into the cassette by the robot arm and transferred to the next step. Therefore, 311 of FIG. 3 is a conveying area where the cassette is conveyed.

Hereinafter, a method of manufacturing a liquid crystal display device using the crystallization method will be described with reference to FIGS. 5A to 5E.

As shown in FIG. 5A, a buffer layer 502 including a silicon nitride film (SiNx) or a silicon oxide film (SiO 2) is formed on a substrate 501. The buffer layer 502 serves to prevent diffusion of impurities and the like contained in the substrate into the silicon layer in the process of crystallizing the amorphous silicon.

Subsequently, amorphous silicon is deposited on the buffer layer 502 by plasma chemical vapor deposition (PECVD).

Subsequently, the magnetic field crystallization is performed while continuously performing the preheating step, the magnetic field crystallization step, the hydrogenation step, and the cooling step while passing through the process chamber of the present invention, the substrate on which the amorphous silicon layer is formed as described above. The magnetic field crystallization process can be described with reference to FIG. 5B. That is, the crystallization progresses while the amorphous silicon layer on the substrate 501 passes through the chamber region in which the magnetic field generating unit M is formed. The magnetic field crystallization process may be performed by passing a space where a high magnetic field is formed while the substrate is heated.

It is known that the crystallization of the silicon layer is accelerated by the application of the magnetic field, and the induced current is generated in the silicon layer by the magnetic field, and the heating is applied to the amorphous silicon due to the induced current, which promotes crystallization even at low temperatures.

Therefore, when the crystallization proceeds while applying a magnetic field, crystallization can be achieved while lowering the temperature applied directly to the substrate, which is suitable for a method of manufacturing a liquid crystal display device using glass as a substrate.

The magnetic field may be applied to crystallize by heating amorphous silicon in a chamber in which a high magnetic field is formed, or may be crystallized by passing the amorphous silicon crystallized by a scan method through a magnetic field generating device. This embodiment adopts a method in which the substrate is passed through a chamber in which a magnetic field is formed and scanned by the magnetic field to crystallize the process to ensure continuity of the process.

On the other hand, the present invention improves the interfacial properties of the crystallized silicon layer since the magnetic field crystallization is progressed and the hydrogenation treatment is simultaneously performed on the crystallized silicon layer while the substrate is cooled. In addition, the driving device adopting the hydrogenated crystalline silicon layer as a channel has a low threshold voltage, so that the driving device can be used in a wide driving voltage range, and is particularly applicable to a general liquid crystal display device using a driving voltage of 5 to 20 volts. This becomes possible.

After magnetic field crystallization, as shown in FIG. 5C, the crystallized silicon layer is patterned to form the active layer 503a. The active layer 503a may be patterned by a photolithography process.

After the active layer 503a is formed, a gate insulating film 504 composed of a silicon oxide film (SiO ₂ ) or a silicon nitride film (SiNx) is formed on the active layer 503a. The gate insulating film may be formed to have a thickness of about 1000 mW, a single layer of a silicon nitride film or a silicon oxide film, or a plurality of two layers.

The gate insulating layer 504 insulates the gate electrode from the active layer, and the channel is turned on or off by the voltage applied to the gate electrode.

Subsequently, after the gate insulating layer 504 is formed, as shown in FIG. 5C, the gate electrode 505 is formed on the gate insulating layer 504. The gate electrode 505 may be formed of a double layer of aluminum alloy or aluminum alloy and molybdenum. The process of forming the gate electrode 505 may be performed by depositing a metal layer on the gate insulating layer 504 by a sputtering method, and then patterning the metal layer through a photolithography process.

Subsequently, impurities are injected into the active layer 503a by applying the gate electrode 505 as a mask to form a source 503S and a drain region 503D. In order to form the N-type TFT, a group 5 element such as phosphorus may be used as the impurity to be implanted, and in order to form the P-type TFT, a group 3 element such as boron may be used as the impurity to be implanted.

Since the gate electrode 505 acts as a blocking mask for impurity implantation in the source and drain region forming process, a channel layer 503C made of intrinsic polysilicon is formed below the gate electrode 505.

Subsequently, as shown in FIG. 5D, an interlayer insulating layer 506 is formed to cover the gate electrode 505. The interlayer insulating layer 506 may be formed of a silicon oxide film or a silicon nitride film.

Subsequently, a contact hole exposing the source and drain regions 503S and 503D is formed on the interlayer insulating layer 506 and a conductive layer (not shown) such as chromium is coated. Subsequently, the conductive layer is patterned to form a source electrode 507S and a drain electrode 507D.

Next, as shown in FIG. 5E, a passivation layer 508 may be formed on the source and drain electrodes 507S and 507D, which may be composed of an organic film or an inorganic film. BCB (BenzoCycroButen) may be used as the organic layer, and a silicon nitride layer or a silicon oxide layer may be used as the inorganic layer.

Next, a contact hole exposing the drain electrode 507D is formed on the passivation layer 508, and a pixel electrode 509 is formed on the passivation layer 508.

The pixel electrode 509 is formed of indium tin oxide (ITO) or indium zinc oxide (IZO) on the protective layer 509 by a sputtering method and a photolithography process. It can be formed by patterning through.

As described above, since the magnetic field crystallization and the hydrogenation are simultaneously performed in one process, the manufacturing process of the liquid crystal display device according to the exemplary embodiment of the present invention using the method of forming polysilicon has been described. Therefore, the crystallization method of the present invention is not limited to the above embodiments but can be applied to any production method for forming polysilicon by magnetic field crystallization.

By the magnetic field crystallization, the present invention can obtain first homogeneous silicon crystalline. When polysilicon is applied as a driving element of a liquid crystal display device, in particular, as a driving element of a pixel unit, it is necessary to use a uniform driving element having characteristics in order to obtain uniform image quality. Although the uniformity is poor even though the driving speed of the driving device is fast, the image quality may be degraded, such as spots on the screen. Therefore, the liquid crystal display device formed by the present invention has an advantage of having uniform operating characteristics.

Second, a driving device using polysilicon formed by magnetic field crystallization has a high threshold voltage, and thus has limitations in application to liquid crystal display devices. However, the polysilicon which has undergone the hydrophobization treatment process and the magnetic field crystallization according to the present invention has a low threshold voltage, and thus can be used for general purpose liquid crystal display devices.

In addition, the present invention can process the hydroprocessing process and the magnetic field crystallization process in a continuous process can shorten the process and improve the productivity.

Claims (10)

Forming an amorphous silicon layer on the substrate; Crystallizing by applying a magnetic field to the amorphous silicon layer; Implanting hydrogen ions while cooling the crystallized silicon layer; Patterning the crystallized silicon layer to form an active layer; Forming a gate insulating layer on the active layer; Forming a gate electrode on the gate insulating layer; Forming source and drain electrodes connected to the source and drain regions of the active layer, respectively; And forming a pixel electrode connected to the drain electrode. The method of claim 1, wherein the cooling of the crystallized silicon layer is performed at about 300 ° C to 600 ° C. The method of claim 1, wherein the crystallized silicon layer is hydrogenated by hydrogen ions implanted during the cooling process. The method of claim 1, wherein the cooling process and the hydrogen ion implantation process are performed at the same time. 4. A method according to claim 3, wherein the threshold voltage of the silicon layer crystallized by said hydrogenation process is lowered. The method of claim 1, wherein the magnetic field crystallization step and the hydrogen ion implantation step are configured in-line. Preheating the substrate; Forming an amorphous silicon layer on the substrate; Crystallizing by applying a magnetic field to the amorphous silicon layer; And a crystallization method comprising the step of injecting hydrogen ions while cooling the crystallized silicon layer. 8. The method of claim 7, wherein the crystalline silicon is hydrogenated by hydrogen ions injected during cooling. The method of claim 8, wherein the cooling and hydrogenation of the crystallized silicon layer are performed simultaneously. The method of claim 7, wherein the magnetic field crystallization step and the hydrogenation step are configured in-line.

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