KR100252310B1 - Method of manufacturing thin-film transistor - Google Patents

Abstract

PURPOSE: A method for fabricating a thin film transistor is provided to allow the formation of an ohmic contact layer at low temperature and thereby to obtain an excellent ohmic characteristic. CONSTITUTION: In the method, the first metal layer used as source and drain electrodes(203,205) is formed on a transparent insulating substrate(200), and a benzocyclobutene(BCB) layer is then formed on the first metal layer(203,205). The first metal layer(203,205) is made of copper, chromium or titanium, and the BCB layer includes silicon. Next, the first metal layer(203,205) and the BCB layer are treated with heat, so that a silicide layer(207) is formed at an interface between the first metal layer and the BCB layer by diffusion of metal into the BCB layer. The BCB layer is then removed, and a semiconductor layer(208) such as an amorphous silicon layer is formed on the silicide layer(207). Next, a gate insulating layer(209) is formed on the semiconductor layer(208), and the second metal layer used as a gate electrode(210) is formed on the gate insulating layer(209).

Description

Method of manufacturing thin film transistor

The present invention relates to a method of manufacturing a thin film transistor, and more particularly, to a method of forming a silicide by heat-treating a metal and benzocyclobutene and a method of manufacturing a thin film transistor using the silicide formed by the method as an ohmic contact layer.

The liquid crystal display uses an active element such as a thin film transistor as a switching element for driving and controlling each pixel.

A configuration of a general liquid crystal display device having a thin film transistor array will be described with reference to FIG.

The liquid crystal display device is composed of first and second substrates facing each other. The first substrate 100 on which the thin film transistor array is formed is provided with a plurality of data bus lines 123 in the transverse direction and in parallel with the gate bus lines 120 in the longitudinal direction, and includes source / drain electrodes, semiconductor layers, and gates. A thin film transistor composed of electrodes is provided at the intersection of each gate bus line and each data bus line. The gate electrode of the thin film transistor is branched from the gate bus line 10, and the source electrode is branched from the data bus line 123. The pixel electrode 130 is provided in an area formed by the intersection of the gate bus line and the data bus line. The pixel electrode 130 is electrically connected to the drain electrode of the thin film transistor. On the other hand, the second substrate 150 on which the color filter layer 151 and the counter electrode 153 are formed is provided to face the first substrate 100. The liquid crystal 180 is filled between the first substrate and the second substrate, and polarizers 190 and 191 are disposed on outer surfaces of the first substrate and the second substrate.

In the image display of the liquid crystal display having the above configuration, the thin film transistor is connected by the scan signal of the gate bus line and the data signal of the data bus line, and a voltage is applied to the pixel electrode connected to the thin film transistor. This is done by changing.

A schematic configuration of the thin film transistor among the above components will be described with reference to FIG. 2. 2 is a cross sectional view of a case where a staggered thin film transistor having a gate electrode on the upper side and a source / drain electrode on the lower side is used as a switching element of the liquid crystal display device.

Referring to FIG. 2, when the structure of the thin film transistor is described, a source electrode 103 and a drain electrode 105 made of Mo, Ta, Cr, or the like are formed on the transparent glass substrate 100. The drain electrode is connected to the pixel electrode 130 made of a transparent conductive film such as ITO formed on the substrate. An ohmic contact layer 107 of n ⁺ amorphous silicon is formed on the source electrode and the drain electrode, and an amorphous silicon semiconductor layer 108 is formed on the ohmic contact layer and the substrate, and a gate insulating film of silicon nitride is formed on the semiconductor layer. 109 and a gate electrode 110 are formed on the gate insulating film.

The thin film transistor is formed by repeatedly depositing and patterning a film. Hereinafter, a method of manufacturing a staggered thin film transistor will be described with reference to FIG. 3.

First, a first metal layer made of Mo, Ta, Cr, or the like is deposited on the substrate 100 by sputtering. Subsequently, an ohmic contact layer 107 such as n ⁺ amorphous silicon is deposited. The deposited first metal layer and the ohmic contact layer are sequentially patterned to form a source electrode 103 and a drain electrode 105. A source bus line is also formed at the time of forming the source electrode and the drain electrode (Fig. 3A).

Subsequently, the semiconductor layer 108 of amorphous silicon and the gate insulating film 109 of silicon nitride are sequentially deposited by plasma CVD. The gate insulating film 109, the impurity semiconductor layer 108, and the n ⁺ impurity semiconductor layer 107 are patterned sequentially (FIG. 3B).

A gate electrode 110 is formed by depositing and patterning a second metal layer of Cr, Al, or the like on the gate insulating layer 109. A gate bus line is also formed at the time of forming the gate electrode (Fig. 3C).

Through the above processes, the thin film transistor is completed. When the thin film transistor is used as a switching element of a liquid crystal display device, a process of forming a pixel electrode by depositing and patterning a transparent conductive film such as ITO is added. The process of forming the pixel electrode is mainly a source / drain electrode of the thin film transistor. The pixel electrode 130 is electrically connected to the drain electrode 105 to be formed later.

Through the above processes, the first substrate of the thin film transistor and the liquid crystal display is manufactured.

As described above, the deposition and patterning of the film are repeated to form the first substrate of the liquid crystal display including the thin film transistor. The deposition of the ohmic contact layer is generally performed at a high temperature of 300 ° C. or higher. As such, since the deposition temperature is high, when the ohmic contact layer is deposited, a peeling phenomenon occurs in which the metal film is peeled off due to the difference in thermal expansion coefficient between the substrate and the deposited metal film.

Further, in order to obtain a liquid crystal display device having good image quality, excellent on / off characteristics are required. As the ohmic characteristics of the ohmic contact layer are better, excellent on / off characteristics are obtained.

Accordingly, an object of the present invention is to provide a method for manufacturing a thin film transistor capable of forming an ohmic contact layer at a low temperature, and a thin film transistor manufactured by the method.

Still another object of the present invention is to provide a thin film transistor having excellent ohmic characteristics.

1 is a perspective view of a general liquid crystal display device.

2 is a cross-sectional view showing a schematic configuration of a thin film transistor.

3 is a process sectional view showing a conventional method for manufacturing a general thin film transistor.

4 is a process cross-sectional view showing a method of manufacturing a thin film transistor according to an embodiment of the present invention.

5 is a cross-sectional structure diagram of a liquid crystal display device having a pixel electrode connected to a drain electrode of a thin film transistor according to an embodiment of the present invention.

* Explanation of symbols for main parts of the drawings

100,150,200: substrate 103,203: source electrode

105,205: drain electrode 108,208: semiconductor layer

109,209 insulating film 110,210 gate electrode

130,230 pixel electrode 151 color filter

153: counter electrode 190,191; Polarizer

123: data bus line 120: gate bus line

206: BCB film 207: silicide layer

In order to achieve the above object, a method of manufacturing a thin film transistor according to the present invention includes forming a first metal layer serving as a source electrode and a drain electrode on a substrate, and forming a benzocyclobutene (BCB) film on the first metal layer. And heat treating the first metal layer and the benzocyclobutene film to form a silicide layer on the first metal layer, removing the benzocyclobutene film, and forming a semiconductor layer on the silicide layer; And forming a gate insulating film on the semiconductor layer, and forming a second metal layer serving as a gate electrode on the gate insulating film.

As described above, the method of forming the silicide layer used as the ohmic contact layer of the thin film transistor may include forming a metal layer and benzocyclobutene, but contacting each other, and heat treating the metal layer and the benzocyclobutene layer to heat the metal layer and the benzo. Forming a silicide by interfacial reaction of the cyclobutene layer.

During the heat treatment of the benzocyclobutene film and the source / drain electrode, the metal forming the source / drain electrode diffuses into the benzocyclobutene film to form a precipitate having a metal-silicon bond. The layer shows excellent ohmic characteristics. When the metal forming the source / drain is Cu, Cr, or Ti, the heat treatment temperature is 250 ° C., and the longer the heat treatment period is, the more silicide is formed between the metal-silicon bonds and the ohmic characteristics are excellent.

Hereinafter, a method of manufacturing a thin film transistor according to an embodiment of the present invention will be described with reference to FIG.

EXAMPLE

A first metal layer made of Cu, Cr, Ti, or the like is deposited on a transparent insulating substrate 200 such as a glass substrate by sputtering or the like, and then patterned to form a source electrode 203 and a drain electrode 205 ( 4a).

Subsequently, benzocyclobutene (BCB, 206) is coated on the substrate 200 including the source electrode 203 and the drain electrode 205. As a coating method of benzocyclobutene, the spin coating method is used. After coating benzocyclobutene on the substrate, the benzocyclobutene film is subjected to a baking and curing process so that the benzocyclobutene film is well adhered to the first metal layer such as Cu, Cr, Ti, or the like. The baking and curing process is performed in nitrogen gas, but the amount of oxygen in nitrogen is 10 ppm so as not to oxidize the benzocyclobutene membrane (Fig. 4b).

Subsequently, heat treatment is performed at different temperatures and periods depending on the metal forming the first metal layer. If the metal forming the first metal layer is Cu, the heat treatment temperature is annealed at 250 ° C. and the heat treatment period is 17 hours. If the metal forming the first metal layer is Cr, the annealing temperature is 250 ° C., and the annealing period is annealed for 3 hours or more. If the metal forming the first metal layer is Ti, the annealing temperature is 250 ° C., and the annealing period is annealed for 10 hours or more.

By the above heat treatment, a first metal such as Cu, Cr, Ti, or the like diffuses into the benzocyclobutene film. The diffusion of the first metal into the benzocyclobutene membrane and the degree of diffusion to the benzocyclobutene membrane may vary depending on various conditions including annealing temperature and time. Diffusion to the butene membrane occurs.

As the first metals such as Cu, Cr, Ti, etc. diffuse into the benzocyclobutene film, the benzocyclobutene film around the metal / BCB interface has a metal-Si (for example, Cu-Si, Cr-Si, Ti-Si). A precipitate with bonds is produced. Benzocyclobutene is an organic substance composed of oxygen and carbon including silicon, and its molecular structure is as follows.

When a first metal such as Cu, Cr, Ti, etc. is diffused into the benzocyclobutene having the molecular structure as described above, a precipitate having a metal-Si bond, that is, silicide 207 is formed. The thickness of the silicide formed around the interface between the first metal and the benzocyclobutene can be controlled by varying the annealing temperature and the annealing period for each metal. The temperature and duration of the silicide may be controlled to serve as an ohmic contact layer of the thin film transistor. (Fig. 4c).

After annealing, the remaining silicide and BCB except for silicide having a predetermined thickness are etched and removed. Etching of benzocyclobutene uses an O ₂ + SF ₆ plasma etch. When benzocyclobutene is removed by O ₂ + SF ₆ plasma etching, etching proceeds faster than other plasma etching and no oxide film is formed (FIG. 4D).

Subsequently, a semiconductor layer 208 such as amorphous silicon is deposited by plasma CVD or the like and then patterned (FIG. 4E).

A silicon nitride layer or a silicon oxide layer is deposited on the semiconductor layer and then patterned to form a gate insulating film 209. The gate insulating film may be formed only on the semiconductor layer as in the present embodiment, but may be formed so as to cover the entire surface of the substrate (FIG. 4f).

Subsequently, a second metal layer of Mo, Ta, Cr, or the like is deposited on the gate insulating film. A second metal layer such as Mo, Ta, Cr, etc. is patterned to form the gate electrode 210 (FIG. 4g).

Through the above processes, a source / drain electrode, a silicide layer, a semiconductor layer, a gate insulating film, and a gate electrode are formed to manufacture a staggered thin film transistor.

The pixel electrode 230 of the liquid crystal display is formed by depositing a transparent conductive film such as ITO over the entire surface of the substrate and then patterning it before depositing the first metal layer for forming the source / drain electrodes. As shown, it is formed to be electrically connected to the drain electrode.

Alternatively, as shown in FIG. 5B, after forming the thin film transistor, the pixel electrode 230 is formed to be electrically connected to the drain electrode 205 by depositing and patterning a transparent conductive film such as ITo. A portion of the silicide 207 on the drain electrode is selectively removed for electrical connection between the pixel electrode and the drain electrode.

As described above, the ohmic contact layer of the thin film transistor manufactured using the interfacial reaction during the heat treatment of the metal and the benzocyclobutene is a silicide having a metal-Si bond and has excellent ohmic characteristics and can be formed at a relatively low temperature (250 ° C.). Can be. The ohmic contact layer is formed by an interfacial reaction between a metal and benzocyclobutene, and covers the entire surface of the source / drain electrode, and after formation, a part of the silicide may be selectively removed. The method of forming the silicide ohmic contact layer may be applied to both semiconductor devices requiring an ohmic contact layer for ohmic contact between the electrode and the semiconductor layer in addition to the thin film transistor of the present embodiment.

According to the present invention, by forming a silicide which is an interfacial reactant of a metal / benzocyclobutene produced by heat-treating a metal made of Cu, Cr, Ti, etc. and benzocyclobutene at a temperature of 250 ° C. for a predetermined time, by forming an ohmic contact layer of a thin film transistor A liquid crystal display using a thin film transistor and a thin film transistor having a uniform thickness and excellent ohmic characteristics can be obtained.

Claims (9)

Forming a first metal layer serving as a source electrode and a drain electrode on the substrate; Forming a benzocyclobutene (BCB) film on the first metal layer; Heat treating the first metal layer and the benzocyclobutene film to form a silicide layer on the first metal layer; Removing the benzocyclobutene membrane; Forming a semi-structured layer on the silicide layer; Forming a gate insulating film on the semiconductor layer, and forming a second metal layer serving as a gate electrode on the gate insulating film. The method of claim 1, wherein the first metal layer is chromium (Cr), a heat treatment temperature is 250 ° C., and a heat treatment period is 3 hours or more. The method of claim 1, wherein the first metal layer is titanium (Ti), a heat treatment temperature is 250 ° C., and a heat treatment period is 10 hours or more. The method of claim 1, wherein the first metal layer is copper (Cu), a heat treatment temperature is 250 ° C., and a heat treatment period is 17 hours or longer. The method of manufacturing a thin film transistor according to claim 1, wherein O ₂ + SF ₆ gas is used as an etching gas during etching of the benzocyclobutene (BCB) film. Forming a metal layer and a benzocyclobutene layer so as to be in contact with each other; And heat treating the metal layer and the benzocyclobutene layer to form silicide. The method of claim 6, wherein the metal layer is chromium (Cr), a heat treatment temperature is 250 ° C., and a heat treatment period is 3 hours or more. The method of claim 6, wherein the metal layer is titanium (Ti), a heat treatment temperature is 250 ° C., and a heat treatment period is 10 hours or more. The method of claim 6, wherein the metal layer is copper (Cu), the heat treatment temperature is 250 ° C., and the heat treatment period is 17 hours or more.

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