JPH05218422A - Thin film transistor and manufacture thereof - Google Patents

Abstract

PURPOSE:To drop the resistance of wiring film of the gate electrode of the thin film transistor, formed on a glass substrate, and the wiring film of the same layer without generation of cracks. CONSTITUTION:When the wiring resistance of the wiring film on the same layer as the gate electrode 105 of a thin film transistor is dropped using a high melting point metal silicide, a thermally oxidized film 107 is grown after the above-mentioned film has been patterned, and the generation of cracks on the metal silicide film 106 is suppressed. It is desirable that a wet oxide film is deposited when a thermally oxidized film 107 is formed taking into consideration of the reliability of the thin film transistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor for driving a liquid crystal display device and a method for manufacturing the thin film transistor.

[0002]

2. Description of the Related Art A conventional thin film transistor and its manufacturing method are as follows. A first polycrystalline silicon layer to be a source, a drain region and a channel layer is formed on a glass substrate and a thermal oxidation method is applied to the surface of the film. A first silicon dioxide layer to be a gate insulating film is formed by the above method. Next, as shown in FIG. 2A, after forming a gate electrode or a second polycrystalline silicon layer to be a wiring film in the same layer as the gate electrode, the second polycrystalline silicon layer is formed on the second polycrystalline silicon layer. By diffusing phosphorus, the resistance value of the film is lowered to give it a metallic property. In the LSI industry in which active elements are formed on a single crystal silicon substrate, a refractory metal silicide film is used when it is desired to reduce the wiring resistance of the film. Next, using the gate electrode as a mask to form the source and drain regions, impurity ions are implanted into the regions of the first polycrystalline silicon layer to be the source and drain. Next, as shown in FIG. 2B, a third silicon dioxide layer to be an interlayer insulating film is formed by a chemical vapor deposition method, a sputtering method or the like to improve the quality of the third silicon dioxide layer. In order to activate the impurity ions introduced into the source and drain regions, they are annealed at a temperature of about 1000.degree. Next, in order to form a lead wiring from the source and drain regions and the gate electrode, a contact hole is opened in the third silicon dioxide film and an aluminum film formed by a sputtering method or the like. Has been used as a wiring film.

[0003]

However, in the above conventional technique, the wiring film in the same layer as the gate electrode is formed only by the second polycrystalline silicon layer in which phosphorus is diffused. The wiring resistance of the wiring film is relatively high. Therefore, in the active matrix element using the thin film transistor, since the wiring film is used as a scanning line, the wiring resistance of the film is high, unevenness on the left and right of the screen and flicker occur, and the display characteristics are not improved.

Usually, phosphorus is introduced by thermal diffusion in order to reduce the resistance of the second polycrystalline silicon layer as much as possible. When the thickness of the second polycrystalline silicon layer is 5000 Å,
The film resistance is limited to 15Ω / □. In order to increase the size and increase the definition of the liquid crystal display panel in the future, it is necessary to reduce the wiring resistance of the scanning line. To that end, a scan line is formed from the second polycrystalline silicon layer,
There is a method of changing to a two-layer structure in which a second polycrystalline silicon layer and a refractory metal silicide layer are deposited. Such a method is
Used in the SI process when heat resistance is required and low wiring resistance is required.

Here, a gate electrode and a scanning line having a two-layer structure of the second polycrystalline silicon layer and a refractory metal silicide are formed, and impurity ions are used as a mask by using the two-layer structure film as a mask. After implanting into the polycrystalline silicon layer to form the source and drain regions, a third silicon dioxide layer serving as an interlayer insulating film is deposited by vapor phase epitaxy or sputtering to form a high-quality polycrystalline silicon layer and Cracks occurred in the high melting point metal silicide film of the two-layer structure film of the melting point metal silicide layer. The cracks were generated by changing the film used as the gate electrode and the scanning line from a conventional polycrystalline silicon film in which phosphorus was diffused to a two-layer structure film of a polycrystalline silicon layer and a refractory metal silicide layer. become. When a crack occurs in the wiring film, not only the film resistance does not decrease to the physical property value of the film itself, but also the resistance varies between wirings, and when a display element using liquid crystal is used, display unevenness and flicker may occur. Cause.

Therefore, in order to solve the above-mentioned problems, after forming a gate electrode and a scanning line having a two-layer structure of the second polycrystalline silicon layer and the refractory metal silicide layer, the above-mentioned 2
When the surface and side surfaces of the layered structure film are wet-oxidized to form a thermal oxide film, and then a third silicon dioxide layer serving as an interlayer insulating film is deposited by vapor phase epitaxy or sputtering, the second polycrystalline silicon is formed. No cracks occur in the layer or the two-layer structure film of refractory metal. By doing so, the wiring film resistance can be reduced to the resistance value of the wiring film itself, and the object is to eliminate variations in the resistance value.

[0007]

In a thin film transistor formed on a glass substrate, a gate electrode and a wiring film composed of the same layer as the gate electrode layer are deposited by a polycrystalline silicon layer and a refractory metal silicide layer. When doing so, on the surface and side surface of the two-layer structure film of the polycrystalline silicon layer and the refractory metal silicide layer,
It is characterized in that a thermal oxide film is formed.

In a thin film transistor formed on a glass substrate, when a film composed of a gate electrode and the electrode layer is used as a wiring film and the film is deposited with polycrystalline silicon and refractory metal silicide, (a) thin film transistor Of the gate electrode material or a wiring film of the same layer as the gate electrode material, and (b) Next, molybdenum silicide, titanium silicide, tantalum silicide, tungsten silicide, etc. The step of depositing the refractory metal silicide film of (c), the step of photolithography the two-layer structure film of the polycrystalline silicon layer and the refractory metal silicide layer at once, and (d) It is characterized in that it comprises a step of thermally oxidizing a two-layer structure film comprising the polycrystalline silicon layer and the refractory metal silicide layer.

The deposition of the refractory metal silicide film is
It is characterized in that a silicide target is sputtered.

The above-mentioned oxidation of the two-layer structure film composed of the polycrystalline silicon film and the refractory metal silicide film is a wet oxidation.

In the wet oxidation according to the fourth aspect, oxygen gas containing water vapor is introduced into an annealing furnace to form a surface of a two-layer structure film composed of the polycrystalline silicon layer and the refractory metal silicide layer. And a thermal oxide film is formed on the side surface.

When molybdenum silicide is deposited as the refractory metal silicide film, the temperature of wet oxidation according to claim 5 is set to 800 ° C. or higher to form a silicon dioxide film on the surface and side surfaces of the two-layer structure film. It is characterized by

[0013]

EXAMPLES The present invention will be described in detail below based on examples.

As shown in FIG. 2, when a gate electrode or a wiring film composed of the same layer as the gate electrode is formed on the glass substrate with a thickness of 5000 Å as the second polycrystalline silicon layer, Even if a third silicon dioxide layer serving as an interlayer insulating film for insulating the wiring film is deposited to a thickness of about 1 μm or more by a chemical vapor deposition method or a sputtering method, a crack is generated in the second polycrystalline silicon layer. It never happened. However, in order to reduce the wiring resistance,
When a polycrystalline silicon layer and a refractory metal silicide layer are used as a two-layer structure in a wiring film formed of the same layer as the gate electrode and the gate electrode, the third silicon dioxide layer serving as an interlayer insulating film is chemically formed. A crack is generated in the refractory metal silicide film when deposited by 3000 Å or more by the vapor deposition method or the sputtering method. Here, considering that the thin film transistor is used as an active matrix element, the wiring film in the same layer as the gate electrode becomes a scanning line. When the wiring resistance of the scanning line is high, in the display quality of a liquid crystal display device using a thin film transistor formed on a glass substrate, there are problems such as left and right unevenness on the screen, and flicker is noticeable.
By depositing the refractory metal silicide film, the wiring resistance of the film is reduced.

In order to eliminate the cracks generated in the refractory metal silicide film, as shown in FIG.
After patterning the two-layer structure film of the second polycrystalline silicon layer to be the gate electrode and the scanning line and the refractory metal silicide layer,
The surface and side surfaces of the two-layer structure film are thermally oxidized as shown in FIG. 1B, and then a second silicon dioxide film to be an interlayer insulating film is deposited as shown in FIG. 1C. Ion implantation into the first polycrystalline silicon layer for forming the source and drain regions of the thin film transistor may be performed before or after the oxidation step of FIG. 1 (b). It does not change the characteristics.

In FIG. 1, 101 is a glass substrate containing quartz, 102 is a source and drain region of a thin film transistor, and 103 is a channel region. 1
Both 02 and 103 are formed of the first polycrystalline silicon layer. 104 is a gate oxide film,
Reference numeral 6 denotes a gate electrode, a polysilicon portion of a scanning line, and a refractory metal silicide portion, respectively. In order to form the refractory metal silicide film, it is desirable to form the refractory metal silicide film by the sputtering method because it is easy to control the composition and the impurities are few because a high-purity target is obtained. 107 is
A thermal oxide film is formed on the exposed portions of the polysilicon film and the refractory metal silicide film, and 108 is a third silicon dioxide film deposited by a chemical vapor deposition method or a sputtering method.

Examples of the refractory metal silicide include molybdenum silicide, tungsten silicide, tantalum silicide and titanium silicide. When molybdenum silicide and tungsten silicide are oxidized at a high temperature, the silicon oxide film tends to grow without growing the metal oxide film. Among them, in the thermal oxide film of the molybdenum silicide film, since molybdenum oxide sublimes at 790 ° C.,
When oxidized at a temperature of 800 ° C. or higher, only silicon oxide is formed. At this time, the silicon oxide film becomes a silicon dioxide film,
107 becomes a second silicon dioxide film. Therefore, 800
If the second polycrystalline silicon layer and the molybdenum silicide layer are thermally oxidized at a temperature of not less than ° C, 107 and 108 will become a silicon dioxide film when the contact hole is opened above 106 in FIG. It becomes possible to etch with.

In order to prevent cracks in the refractory metal silicide film that occur when the interlayer insulating film is formed, as shown in FIG. Although the surface and the side surface of the two-layer structure film of the melting point metal silicide layer are oxidized, in the case of molybdenum silicide, the relationship between the molybdenum silicide film thickness and the second silicon dioxide film thickness is shown in the shaded area in FIG. If so, the molybdenum silicide film is not cracked. The occurrence of cracks in the molybdenum silicide film is a function only of the film thickness of the molybdenum silicide layer even in the case of the two-layer structure film of the polycrystal silicon layer and the molybdenum silicide layer, and depends on the film thickness of the polycrystal silicon layer. do not do.

FIG. 3 shows that the composition of the sputter target is 1 to molybdenum and the content of silicon is 2.3 to 3.0.
Target is used and the pressure during sputtering is 0.1 Pa.
2 shows a relational diagram in the case of forming a film within a range of from 2.0 Pa to 2.0 Pa. Reference numeral 301 is a boundary line indicating whether or not a crack is generated in the molybdenum silicide film, and 302 is a region where no crack is generated in the film. If a different sputtering apparatus is used, the boundary line 301 may fluctuate, but when a thin film transistor is formed on a glass substrate such as a quartz substrate, the boundary line is always present and formed. As the thickness of the thermal oxide film becomes thicker, there is a point that cracks will not occur. However, if an in-line type sputtering apparatus is used for sputtering molybdenum silicide, the relationship diagram almost the same as that in FIG. 3 can be obtained.

Although the gate electrode and the scanning line are formed not only on the channel portion of the transistor as shown in FIG. 1 but also on the glass substrate, the surface and the side surface are also oxidized here. Then, there is an effect of preventing cracks. Also,
The area of the remaining two-layer structure film of the second polycrystalline silicon layer and the molybdenum silicide layer does not change the way cracks occur. The oxide rate of the second polycrystalline silicon layer is about 1.5 times the oxide rate of the molybdenum silicide layer, but if the total film thickness of the second polycrystalline silicon layer and the molybdenum silicide layer is less than 5000Å. For example, the two-layer structure film is
Even if a wiring film is placed on the oxide film shown in FIG. 1C, the cross-sectional shape of the reverse taper which causes the disconnection does not occur.

Next, the method of forming the thermal oxide film of the two-layer structure film of the second polycrystalline silicon layer and the molybdenum silicide layer which will be the gate electrode and the scanning line is as follows. It is preferable to use the wet oxidation method introduced into the above. FIG. 4 shows a piping diagram of the oxidation system. 401 is a gas pipe, 402
Is a gas flow controller, 403 is a gas valve, 404 is a quartz flask containing pure water, and 405 is pure water.
It is necessary to put an amount of about 8 minutes and keep the temperature of water at 80 ° C or higher. 406 is an anneal furnace, and oxygen gas is allowed to flow from the gas pipe port A and nitrogen gas is allowed to flow from the gas pipe port B.

The annealing furnace has two inlets, a wet oxygen gas inlet and a nitrogen gas inlet, which means that after wet oxidation, the substrate is not removed from the furnace and continuously annealed in a nitrogen atmosphere.
This is because the When the substrate is taken out of the anneal furnace into the atmosphere after the wet oxidation, the moisture in the furnace is condensed and adheres to the substrate. The dew on a part of the substrate causes malfunction of the thin film transistor. It is necessary to anneal under a nitrogen atmosphere at a temperature higher than the temperature of wet oxidation for 30 minutes or more.

The wet oxidation method is superior to the dry oxidation method in the following two points. First, the deposition rate of the silicon dioxide film grown on the molybdenum silicide layer is
It is about 10 times faster than the dry oxidation method, and can be performed faster. Second, in FIG. 3, when the dry oxidation method is adopted, the boundary line 301 indicating whether or not a crack is generated becomes steep. Therefore, if the film thickness of molybdenum silicide is the same, a thicker oxide film is required in the dry oxidation method. When the thickness of the thermal oxide film 107 in FIG.
The gate oxide film also becomes thicker, and the thickness of the first polycrystalline silicon layer 102 and 103 becomes thinner, so that the reliability of the thin film transistor is likely to be impaired.

[0024]

According to the present invention described above, when the metal silicide film is formed in order to reduce the wiring resistance of the gate electrode of the thin film transistor and the wiring film formed in the same layer as the gate electrode, When the silicon dioxide film was deposited on the metal film by the sputtering method or the CVD method, the metal silicide film was cracked. However, the cracks can be eliminated by thermally oxidizing the surface and side surfaces of the two-layer structure film of the polycrystalline silicon layer and the metal silicide layer, and a thin film transistor that operates effectively can be manufactured. Further, when the thermal oxidation method is wet oxidation, even if the oxide film thickness is thin, the metal silicide film can be prevented from cracking, and the reduction in the film thickness of the first polycrystalline silicon layer can be suppressed. It is possible to provide a thin film transistor with a good put.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a process of forming a thin film transistor of the invention.

FIG. 2 is a cross-sectional view of a conventional process for forming a thin film transistor.

FIG. 3 is a diagram showing a relationship between how molybdenum silicide and an oxide film thickness are cracked.

FIG. 4 is a piping diagram of a wet oxidation system.

[Explanation of symbols]

 101 glass or silicon dioxide layer 102 source or drain region 103 channel layer 104 first silicon dioxide film 105 second polycrystalline silicon layer 106 metal silicide layer 107 second silicon dioxide film 108 third silicon dioxide Film 201 Glass or Silicon Dioxide Layer 202 Source or Drain Region 203 Channel Layer 204 First Silicon Dioxide Film 205 Second Polycrystalline Silicon Layer 206 Third Silicon Dioxide Film 301 Boundary Line without Cracks 302 Area where crack does not occur 401 Gas pipe 402 Gas flow rate controller 403 Valve 404 Quartz flask 405 Pure water 406 Anneal furnace

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location H01L 27/12 Z 8728-4M 29/40 A 7738-4M 29/46 T 7738-4M

Claims (6)

[Claims] 1. In a thin film transistor formed on a glass substrate, when a gate electrode and a wiring film composed of the same layer as the gate electrode layer are deposited by a polycrystalline silicon layer and a refractory metal silicide layer, A thin film transistor comprising a thermal oxide film formed on a surface and a side surface of a two-layer structure film of the polycrystalline silicon layer and the refractory metal silicide layer. 2. A thin film transistor formed on a glass substrate, wherein a film composed of a gate electrode and the electrode layer is used as a wiring film, and the film is deposited with polycrystalline silicon and refractory metal silicide. ) A step of depositing a polycrystalline silicon film as a gate electrode material of a thin film transistor or a wiring film of the same layer as the gate electrode material, and (b) Next, molybdenum silicide, titanium silicide, tantalum silicide, tungsten A step of depositing a refractory metal silicide film of silicide or the like; (c) a step of photolithography the two-layer structure film of the polycrystalline silicon layer and the refractory metal silicide layer at a time; 2. A method of manufacturing a thin film transistor, which further comprises the step of thermally oxidizing a two-layer structure film composed of the polycrystalline silicon layer and the refractory metal silicide layer. 3. The deposition of the refractory metal silicide film comprises:
The thin film transistor formed by the manufacturing method according to claim 2, wherein a silicide target is sputtered. 4. The thin film transistor formed by the manufacturing method according to claim 2, wherein the oxidation of the two-layer structure film composed of the polycrystalline silicon film and the refractory metal silicide film is wet oxidation. 5. The wet oxidation according to claim 4, wherein oxygen gas containing water vapor is introduced into an annealing furnace to form a two-layer structure film composed of the polycrystalline silicon layer and the refractory metal silicide layer. A thin film transistor, wherein a thermal oxide film is formed on a surface and a side surface of the thin film transistor. 6. When depositing molybdenum silicide as the refractory metal silicide film, the wet oxidation temperature according to claim 5 is set to 800 ° C. or higher to form a silicon dioxide film on the surface and side surfaces of the two-layer structure film. A thin film transistor, which is characterized by being formed, and a manufacturing method thereof.