KR101013720B1 - Method of crystallization and method of fabricating thin film transistor using thereof - Google Patents

Abstract

The crystallization method of the present invention is to improve the crystallization rate and device characteristics by applying an alternating magnetic field and using a metal as a catalyst, the method comprising: providing a thin film to be used for crystallization; Depositing a transition metal on the thin film; Providing a crystallization apparatus having a winding type induction coil for inducing alternating magnetic fields and a heating plate for heating the thin film; And crystallizing by applying an alternating current applied to the induction coil of the crystallizing apparatus while applying the induced magnetic field to the thin film.

Catalytic Crystallization, Alternating Magnetic Field, Metal Catalyst, Leakage Current

Description

Crystallization method and manufacturing method of thin film transistor using the same {METHOD OF CRYSTALLIZATION AND METHOD OF FABRICATING THIN FILM TRANSISTOR USING THEREOF}

1A to 1D are exemplary views sequentially illustrating a process of crystallizing a silicon thin film according to the present invention.

2 is an exemplary diagram schematically showing a system used for alternating magnetic field crystallization of the present invention.

3 is a plan view schematically illustrating a structure of a general liquid crystal display panel.

4A to 4I are exemplary views sequentially illustrating a method of manufacturing a liquid crystal display device using a silicon thin film crystallized according to the crystallization method of the present invention.

5 is a graph showing the characteristics of a thin film transistor manufactured according to the present invention.

** Explanation of symbols for main parts of drawings **

110,210: array substrate 111: buffer layer

124,324: amorphous silicon thin film 124A, 324N, 324P: polycrystalline silicon thin film

170: metal 250: graphite heating plate

260: induction coil

The present invention relates to a method for manufacturing a liquid crystal display device, and more particularly, to a method for manufacturing a polycrystalline silicon thin film transistor liquid crystal display device having an improved crystallization method.

Recently, with increasing interest in information display and increasing demand for using a portable information carrier, a lightweight flat panel display (FPD), which replaces a conventional display device, a cathode ray tube (CRT), is used. The research and commercialization of Korea is focused on. In particular, the liquid crystal display (LCD) of the flat panel display device is an image representing the image using the optical anisotropy of the liquid crystal, is excellent in resolution, color display and image quality, and is actively applied to notebooks or desktop monitors have.

The active matrix (AM) method, which is a driving method mainly used in the liquid crystal display device, is a method of driving the liquid crystal of the pixel portion by using an amorphous silicon thin film transistor (TFT) as a switching element. .

Amorphous silicon thin film transistor technology was established in 1979 by LeComber et al., UK, and commercialized as a 3 "liquid crystal portable television in 1986. Recently, a large area thin film transistor liquid crystal display device of 50" or more has been developed.

However, the amorphous silicon thin film transistor is a peripheral circuit such as a CMOS (Complementary Metal Oxide Semiconductor) that requires high-speed operation of 1 MHz or more with a field effect mobility (<1 cm ² / Vsec) of electrons as carriers. There is a limit to use.

Accordingly, studies are being actively conducted to simultaneously integrate the pixel portion and the driving circuit portion on a glass substrate using a polycrystalline silicon thin film transistor having a greater field effect mobility than the amorphous silicon thin film transistor.

Polycrystalline silicon thin film transistor technology has been applied to small modules such as camcorders since the development of liquid crystal color television in 1982. Since it can realize low photosensitivity and high field effect mobility compared to amorphous silicon thin film transistors, ) And the driving circuit can be manufactured directly on the same substrate.

This integration eliminates the need for an additional process of connecting a driver integrated circuit (driver IC) and a pixel array, which has been conventionally required, thereby greatly improving productivity and reliability. As described above, the excellent characteristics of the polycrystalline silicon thin film As a result, it is possible to fabricate smaller and superior thin film transistors.

That is, the increase in mobility may improve the operating frequency of the driving circuit unit that determines the number of driving pixels, thereby facilitating high definition of the display device, and also distorting the transmission signal by reducing the charging time of the signal voltage of the pixel unit. This decreases the image quality can be expected.

Despite the advantages of polycrystalline silicon thin film transistors, high-temperature processes using expensive quartz substrates are required for manufacturing, so the application field is limited to small-area high-resolution liquid crystal displays, and low-temperature processes using low-cost glass substrates are amorphous. Compared to silicon thin film transistors, it is limiting the application of large area liquid crystal display devices.

On the other hand, as a method of manufacturing the polycrystalline silicon thin film transistors as described above, there are largely a method of directly depositing (as-deposition) a polycrystalline silicon thin film on a substrate and a method of depositing an amorphous silicon thin film on a substrate and then crystallizing by heat treatment. In particular, in order to use a low cost glass substrate, a low temperature process is required, and a method for improving the field effect mobility of a thin film transistor is required for use in an element of a driving circuit unit.

In this case, the solid phase crystallization (SPC) method, which is generally used to fabricate a polycrystalline silicon thin film, can obtain a uniform polycrystalline silicon thin film even with a relatively simple process, but the heat treatment temperature is higher than 600 ° C. and the heat treatment time In addition, it has a disadvantage that it is difficult to use a glass substrate as long as several tens of hours.

In addition, the polycrystalline silicon thin film obtained by the solid-phase crystallization method has a relatively large grain (grain) of the order of several micrometers level, but there is a disadvantage that many defects are formed in the grain. The defect is known to adversely affect the performance of the thin film transistor after the grain boundary region.

Recently, various crystallization methods have been studied to fabricate polycrystalline silicon thin film transistors at low temperature, and a method currently emerging is a crystallization method using an excimer laser (EL).                         

In the case of the excimer laser crystallization, there is almost no crystal defect seen in the polycrystalline silicon thin film crystallized by the solid-state crystallization method, so that an excellent electrical characteristic can be obtained. There is a problem of poor uniformity.

In addition, there is a method of metal induced crystallization (MIC), etc. In the case of the metal induced crystallization, the crystallization temperature of silicon is reduced by using a metal layer, but leakage current (leakage current) in the device characteristics is caused by contamination of the metal. It has a big disadvantage.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a crystallization method having a uniform crystallization characteristic without deterioration of device characteristics by improving the crystallization method and a method of manufacturing a thin film transistor using the same.

Another object of the present invention is to provide a crystallization method which increases the crystallization rate using a metal catalyst and reduces the leakage current and a method of manufacturing the thin film transistor using the same.

Further objects and features of the present invention will be described in the configuration and claims of the invention which will be described later.

In order to achieve the above object, the crystallization method of the present invention comprises the steps of providing a thin film to be used for crystallization; Depositing a transition metal on the thin film; Providing a crystallization apparatus having a winding type induction coil for inducing alternating magnetic fields and a heating plate for heating the thin film; And crystallizing by applying an alternating current applied to the induction coil of the crystallizing apparatus while applying the induced magnetic field to the thin film.

At this time, the thin film may be composed of amorphous silicon, the transition metal may be composed of nickel.

In addition, the method of manufacturing a liquid crystal display device using the crystallization method of the present invention comprises the steps of providing a substrate; Depositing an amorphous silicon thin film on the substrate; Depositing a transition metal on the amorphous silicon thin film; Providing a crystallization apparatus having a winding type induction coil for inducing an alternating magnetic field and a heating plate for heating the amorphous silicon thin film; Applying an alternating current to the induction coil of the crystallization apparatus and subjecting the induced magnetic field to the amorphous silicon thin film to perform heat treatment on the amorphous silicon thin film; Patterning the crystallized silicon thin film to form an active pattern; Forming a gate insulating film on the entire surface of the substrate; Forming a gate electrode on the active pattern having the gate insulating film interposed therebetween; Implanting impurity ions into the active pattern using the gate electrode as a mask to form a source region and a drain region; Forming an interlayer insulating film having contact holes formed on the substrate; And forming a source electrode connected to the source region through the contact hole and a drain electrode connected to the drain region through the contact hole.

At this time, the nickel may be added to about 10 ¹³ ~ 10 ¹⁴ atoms / cm ² and heat-treated.

The method may further include forming a buffer layer on the substrate before depositing the amorphous silicon.

Hereinafter, the present invention will be described in detail.

The present invention proposes a method of crystallizing a polycrystalline silicon thin film by applying an alternating magnetic field at low temperature (= 500 ° C.) without damaging a glass substrate having poor thermal stability for application to a low temperature polycrystalline silicon thin film transistor.

In this case, the present invention proposes a crystallization method using a metal as a catalyst and applying the alternating magnetic field to improve the crystallization speed and improve device characteristics such as a reduction of leakage current, and a method of manufacturing a thin film transistor using the same.

1A to 1D are exemplary views sequentially illustrating a process of crystallizing a silicon thin film according to the present invention. Although the thin film to be crystallized is illustrated as an example, the present invention is not limited thereto.

First, as shown in FIG. 1A, a buffer layer 111 having a predetermined thickness is formed on the entire surface of the substrate 110 made of a transparent insulating material such as glass.

The buffer layer 111 serves to block impurities such as sodium (natrium) from the glass substrate 110 from penetrating into the upper layer during the process.

Thereafter, as shown in FIG. 1B, amorphous silicon 124 is deposited to a predetermined thickness on the substrate 110 on which the buffer layer 111 is formed.

In general, the amorphous silicon thin film can be deposited by various methods, which will be described below.

Representative methods for depositing an amorphous silicon thin film include a low pressure chemical vapor deposition (LPCVD) method and a plasma enhanced chemical vapor deposition (PECVD) method. In the case of depositing the amorphous silicon thin film by the plasma chemical vapor deposition method, the hydrogen atoms of about 20% are included in the amorphous silicon thin film although there is a slight difference depending on the temperature of the substrate during deposition.

In this case, when the amorphous silicon thin film is deposited by a plasma chemical vapor deposition method, a dehydrogenation process, which is an annealing process for discharging the hydrogen atoms to the outside, may be performed.

Next, as shown in FIG. 1C, a small amount of transition metal 170 is deposited on the silicon thin film 124.

At this time, the transition metal 170 is preferably nickel (Ni), aluminum (Aluminum; Al), ferrum (Fe), cobalt (Co), chromium (chromium), or the like. In this embodiment, nickel metal was used because NiSi ₂ , the last phase of nickel-silicide, which acts as a crystallization nucleus, has the same structure as that of silicon and has a lattice constant of 5.406Å and very similar to that of 5.430Å.

On the other hand, the amount of the nickel 170 deposited is formed in a small amount of 10 ¹³ ~ 10 ¹⁴ atoms / cm ² concentration, because the thicker the residual amount of transition metal in the crystallized material has a bad effect on the material properties .

Subsequently, when heat treatment is performed while applying an alternating magnetic field to the substrate 110 on which a small amount of the nickel 170 element is deposited, the crystallized silicon thin film 124A having uniform crystallization characteristics is formed as shown in FIG. 1D. You can get it.

At this time, since the crystallization proceeds as the alternating magnetic field is applied using the nickel 170 element as a catalyst, the crystallization rate can be increased and the crystallization characteristics are also improved.

By applying alternating magnetic fields, it is possible to form a polycrystalline silicon thin film in a short time at a low temperature of 500 ° C. or lower by selective joule heating and activation of atomic mobility of the amorphous silicon thin film.

2 is an exemplary view schematically showing a system used for alternating magnetic field crystallization of the present invention.

As shown in the figure, the present system for applying an alternating magnetic field has a solenoid induction coil 260 and a specimen (i.e., a glass on which silicon thin films are deposited) for inducing an alternating magnetic field. It is composed of a graphite lower heating plate 250 for heating the substrate (210).

At this time, a frequency of 14 kHz may be used as the AC current.

On the other hand, when an alternating current is applied to the induction coil 260, induction heating is generated by a change in a magnetic field. In the case of ferromagnetic materials, the magnetization is magnetized in one direction. Induction heating is caused by friction of molecules that occur when magnetized in the opposite direction, but Joules heat is generated in most nonmagnetic materials, conducting materials.

The Joule heat is induced by the change of the magnetic field due to the alternating current (induced electromotive force) is formed, the eddy current (eddy current) generated in the conductor by the induced electromotive force is generated by Ohm's Law Done.

At this time, in the case of amorphous silicon, the resistivity is 10 ⁶ to 10 ¹⁰ Ωcm at room temperature, so that Joule heat due to induced electromotive force does not occur.

However, when the temperature of amorphous silicon is increased by external heating, the specific resistance is sharply reduced. The amorphous silicon has a specific resistance of 0.01 to 10Ωcm at 500 ° C. This specific resistance value is close to 0.001 ~ 1Ωcm, the specific resistance value of the graphite 250 in induction heating, and thus Joule heat will be generated by the induced electromotive force.

Therefore, the lower glass substrate 210 may be maintained at a low temperature to suppress the deformation of the substrate and to allow selective Joule heat of the amorphous silicon to promote crystallization of the amorphous silicon.

Meanwhile, as described above, the nickel element deposited on the silicon thin film serves as a crystallization nucleus of amorphous silicon to promote crystallization in the (111) direction, where NiSi ₂ , the last phase of nickel-silicide, has the same structure as silicon. The lattice constant is 5.406Å, which is very similar to the silicon of 5.430 실리콘.

In this case, the silicon thin film crystallized in accordance with an embodiment of the present invention can be used in the fabrication of semiconductor devices such as thin film transistors, solar cells, image sensors, thin film transistors made of the crystallized silicon thin film and a liquid crystal display device having the same. For example, as follows.

In general, in a liquid crystal display device, a thin film transistor is formed in two parts, a pixel part and a peripheral driving circuit part.

3 is a plan view schematically illustrating the structure of a liquid crystal display panel, and illustrates a driving circuit-integrated liquid crystal display panel in which a driving circuit unit is integrated on an array substrate.

As shown in the drawing, the driving circuit-integrated liquid crystal display panel 300 is largely composed of an array substrate 310 and a color filter substrate 320 and a liquid crystal layer formed between the array substrate 310 and the color filter substrate 320. Not shown).

The array substrate 310 includes a pixel portion 315, which is an image display area in which unit pixels are arranged in a matrix form, a gate driving circuit portion 314 and a data driving circuit portion 313 located outside the pixel portion 315. It consists of a driving circuit part.

In this case, although not shown in the drawing, the pixel portion 315 of the array substrate 310 is arranged on the substrate 310 in the vertical and horizontal direction to define a plurality of pixel areas, a plurality of gate lines and data lines, the gate line and A thin film transistor, which is a switching element formed in an intersection region of a data line, and a pixel electrode formed in the pixel region.

The thin film transistor is a switching element that applies and cuts off a signal voltage to a pixel electrode and is a type of field effect transistor (FET) that controls the flow of current by an electric field.

On the other hand, in the driving circuits 313 and 314 of the array substrate 310, the data driving circuit unit 313 is positioned at one long side of the array substrate 310 protruding from the color filter substrate 320. The gate driving circuit unit 314 is positioned at one side of the array substrate 310.                     

In this case, the gate driving circuit unit 314 and the data driving circuit unit 313 use a thin film transistor having a CMOS structure as an inverter to properly output the input signal.

For reference, the CMOS is an integrated circuit having a MOS structure which is used for a thin film transistor of a driving circuit unit requiring high speed signal processing, and requires a transistor of a P channel and an N channel, and the characteristics of speed and density are intermediate between NMOS and PMOS. It shows form.

The gate driving circuit unit 314 and the data driving circuit unit 313 are devices for supplying scan signals and data signals to pixel electrodes through gate lines and data lines, respectively, and are connected to an external signal input terminal (not shown). It controls the external signal input through the external signal input terminal to output to the pixel electrode.

Although not shown in the drawing, a color filter for implementing color and a common electrode that is opposite to the pixel electrode formed on the array substrate 310 are formed in the image display area 115 of the color filter substrate 320.

The array substrate and the color filter substrate configured as described above are provided with a cell gap so as to be uniformly spaced apart by a spacer, and are bonded to each other by a seal pattern formed on the outer side of the image display area to form a unit liquid crystal display. It forms a panel. At this time, the bonding of the two substrates is made through a bonding key formed on the array substrate or the color filter substrate.

On the other hand, according to the present invention, the driving circuit-integrated liquid crystal display panel using the polycrystalline silicon thin film having improved crystallization characteristics has the advantages of excellent device characteristics, high image quality, high definition, and low power consumption.

Hereinafter, a CMOS liquid crystal display device using the crystallized silicon thin film manufactured according to the present invention used in the driving circuit integrated liquid crystal display panel configured as described above will be described in detail through the manufacturing process.

4A to 4I are exemplary views sequentially illustrating a method of manufacturing a liquid crystal display device using a silicon thin film crystallized according to the crystallization method of the present invention.

In this case, the thin film transistor formed in the pixel portion may be N type or P type, and both the N type thin film transistor and the P type thin film transistor are formed in the driving circuit to form a CMOS. Only the method of manufacturing an element is shown.

In addition, the left side of the figure shows the method of manufacturing the NMOS which is an N type thin film transistor, and the right side of the figure shows the method of manufacturing the PMOS which is a P type thin film transistor.

First, as shown in FIG. 4A, a buffer layer 311 formed of a silicon oxide film (SiO ₂ ) is formed on a substrate 310 made of a transparent insulating material such as glass.

Next, as shown in FIG. 4B, after depositing amorphous silicon 324 to a predetermined thickness on the substrate 310 on which the buffer layer 311 is formed, a small amount of nickel 370 is formed on the silicon thin film 324. Deposit.

At this time, the amount of the deposited nickel 370 was formed in a small amount at a concentration of 10 ¹³ to 10 ¹⁴ atoms / cm ² , which causes a large amount of transition metal to remain in the crystallized material, thus adversely affecting material properties. Because.

Subsequently, when the heat treatment is performed while applying an alternating magnetic field to the substrate 310 on which the nickel 370 element is deposited, a crystallized silicon thin film having uniform crystallization characteristics can be obtained.

That is, as described above, since the crystallization proceeds while the alternating magnetic field is applied using the nickel 370 element as a catalyst, the crystallization rate can be increased and the crystallization characteristic is also improved.

Next, as shown in FIG. 4C, the crystallized polycrystalline silicon thin film is patterned using a photolithography process to form active patterns 324N and 324P in the NMOS and PMOS regions.

Thereafter, as shown in FIG. 4D, a gate insulating film 315A is deposited on the entire surface of the substrate 310 on which the active layers 324N and 324P are formed.

Next, as shown in FIG. 4E, molybdenum (Mo) and aluminum (Mo) are formed on a predetermined region (that is, a channel forming region of the active layers 324N and 324P) of the substrate 310 on which the gate insulating film 315A is deposited. Gate electrodes 321N and 321P made of Al) or an aluminum alloy or the like are formed.

Next, FIGS. 4F and 4G sequentially perform N doping and P doping to sequentially implant N + ions into N-type thin film transistors (ie, active layers 324N), so that source / drain regions 324N + are respectively implanted. The formed thin film transistor) and the P type thin film transistor are shown.

First, as shown in FIG. 4F, in order to fabricate an N-type thin film transistor, the PMOS region is coated with a material such as photoresist 380, and then implanted with N + ions on the entire surface of the substrate 310.

That is, the NMOS region implants a high concentration of impurity ions into only a predetermined region of the active layer 324N by using the gate electrode 321N as a mask to form a source / drain region 324N + as an ohmic contact layer. To form. In this case, the gate electrode 321N serves as an ion stopper to prevent the dopant from penetrating into the channel region of the active layer 324N.

At this time, the source / drain regions 324N + of the N-type thin film transistor are formed by injecting a Group 5 element such as phosphorus (P) which can donate electrons.

Next, as shown in FIG. 4G, to form a P type thin film transistor, a photoresist 380 pattern covering an N type thin film transistor region is formed.

At this time, the source / drain regions 324P + of the P-type thin film transistor are formed by injecting a group 3 element such as boron (B) which can provide a hole.

Next, as shown in FIG. 4H, a contact hole exposing a portion of the source / drain regions 324N + and 324P + using a photolithography process after depositing an interlayer insulating film 315B on the entire surface of the substrate 310. 390N, 390P).                     

Finally, as shown in FIG. 4I, source / drain electrodes 322N, 322P, 323N, and 323P are electrically connected to the source / drain regions 324N + and 324P + through the contact holes 390N and 390P. do.

Meanwhile, in the above embodiment, a method of fabricating a liquid crystal display device and a liquid crystal display panel using the silicon thin film crystallized by the present invention is described, but the present invention is not limited thereto and may be applied to devices such as organic EL. Can be.

In particular, it is important for the switching elements of the pixel portion of the liquid crystal display panel configured as described above to suppress the off-state current, that is, the leakage current, and the high field effect mobility of the unit elements of the driving circuit portion.

In this case, the type thin film transistor fabricated using the silicon thin film crystallized according to the present invention exhibits a high leakage current and high on-current characteristics as described above.

5 is a graph showing the characteristics of the thin film transistor fabricated in accordance with the present invention, showing the characteristics of the P-type thin film transistor, for example.

As shown in the figure, the on-current at the drain voltage of 0.1 and 10V is higher in the case of crystallization by adding nickel than in the case of no addition of nickel, and the leakage current (ie, the off current) is crystallized by adding nickel. It can be seen that the case is lower than the case where no nickel is added.

In addition, it can be seen that the threshold voltage is also improved when nickel is added due to the characteristics of the on current and the off current as described above.                     

At this time, the graph shown as filled rectangles shows the result of crystallization without adding nickel to the crystallization of the active layer, and the graph shown as unfilled circles shows 3x10 ¹³ atoms / cm ² deposited with nickel. Shows the result of crystallization.

On the other hand, all of the same alternating magnetic field was applied to crystallize the silicon thin film.

As described above, when the silicon thin film is crystallized by applying an alternating magnetic field in the state where nickel is added, the off current is reduced and the nickel acts as a catalyst to shorten the crystallization time.

Many details are set forth in the foregoing description but should be construed as illustrative of preferred embodiments rather than to limit the scope of the invention. Therefore, the invention should not be defined by the described embodiments, but should be defined by the claims and their equivalents.

As described above, the crystallization method according to the present invention provides an effect of shortening the crystallization time and improving crystallization characteristics by applying crystallization of an alternating magnetic field using a transition metal such as nickel as a catalyst.

In addition, when the thin film transistor is manufactured using the silicon thin film crystallized by the above method, the device characteristics such as low leakage current and high on current are improved.

Claims (7)

Providing a thin film to be used for crystallization; Depositing a transition metal on the thin film; Providing a crystallization apparatus having a winding type induction coil for inducing alternating magnetic fields and a heating plate for heating the thin film; And And crystallizing by applying an alternating current applied to an induction coil of the crystallizer by applying an alternating magnetic field to the thin film. The method of claim 1, wherein the thin film is composed of amorphous silicon. The method of claim 1, wherein the transition metal is made of nickel. 4. The crystallization method according to claim 3, wherein the nickel is crystallized by adding about 10 ¹³ to 10 ¹⁴ atoms / cm ² . Providing a substrate; Depositing an amorphous silicon thin film on the substrate; Depositing a transition metal on the amorphous silicon thin film; Providing a crystallization apparatus having a winding type induction coil for inducing an alternating magnetic field and a heating plate for heating the amorphous silicon thin film; Applying an alternating current to the induction coil of the crystallization apparatus and subjecting the induced magnetic field to the amorphous silicon thin film to perform heat treatment on the amorphous silicon thin film; Patterning the crystallized silicon thin film to form an active pattern; Forming a gate insulating film on the entire surface of the substrate; Forming a gate electrode on the active pattern having the gate insulating film interposed therebetween; Implanting impurity ions into the active pattern using the gate electrode as a mask to form a source region and a drain region; Forming an interlayer insulating film having contact holes formed on the substrate; And Forming a source electrode connected to the source region through the contact hole and a drain electrode connected to the drain region through the contact hole. 6. The method of claim 5, wherein the nickel is added to about 10 ¹³ to 10 ¹⁴ atoms / cm ² and heat treated. The method of claim 5, further comprising forming a buffer layer on the substrate before depositing an amorphous silicon thin film.

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