JP3214024B2 - Thin film transistor and manufacturing method thereof - Google Patents

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 and the like and a method for manufacturing the same.

[0002]

2. Description of the Related Art A conventional thin film transistor and a method of manufacturing the same include forming a first polycrystalline silicon layer to be a source / drain region and a channel layer on a glass substrate and forming the first polycrystalline silicon layer on the surface of the film by a thermal oxidation method or the like. A first silicon dioxide layer serving as a gate insulating film is formed. Next, as shown in FIG. 2A, after forming a gate electrode and a second polycrystalline silicon layer to be a wiring film in the same layer as the gate electrode, phosphorus is diffused into the second polycrystalline silicon layer. As a result, the resistance value of the film is reduced , and the film has metallic properties. In the LSI industry in which active elements are formed on a single crystal silicon substrate, a refractory metal silicide film has been used to reduce the wiring resistance of the film. Next, using the gate electrode as a mask to form source and drain regions, impurity ions are implanted into regions of the first polycrystalline silicon layer to be source and drain. Next, as shown in FIG. 2B, a third silicon dioxide layer serving as an interlayer insulating film is formed by a chemical vapor deposition method, a sputtering method, or the like to improve the film quality of the third silicon dioxide layer. Activating impurity ions introduced into the source and drain regions
For that, annealing at a temperature of about 1000 ° C.. next,
In order to form a wiring drawn from the source and drain regions and the gate electrode, a contact hole has been 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 prior art, since the wiring film of the same layer as the gate electrode is formed only of the second polycrystalline silicon layer in which phosphorus is diffused, The wiring resistance of the wiring film is relatively high. Therefore, in an active matrix element using a thin film transistor, since the wiring film is used as a scanning line, the wiring resistance of the film is high, and left and right unevenness and flicker of the screen occur, and the display characteristics are not improved.

Normally, phosphorus is introduced by thermal diffusion in order to reduce the resistance of the second polycrystalline silicon layer as much as possible. However, when the thickness of the second polycrystalline silicon layer is 5000 °,
The limit is to reduce the film resistance to 15Ω / □. In order to realize a larger and higher definition liquid crystal display panel in the future, it is necessary to lower the wiring resistance of the scanning line. For that purpose, a scanning line is provided 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 called L
It 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 the refractory metal silicide are formed, and impurity ions are implanted into the first layer using the two-layer structure film as a mask. After the source and drain regions are formed by implantation into the polycrystalline silicon layer, a third silicon dioxide layer serving as an interlayer insulating film is deposited by a vapor deposition method or a sputtering method. 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 caused 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 polycrystalline silicon layer and a refractory metal silicide layer. become. When a crack occurs in the wiring film, not only does the film resistance not decrease to the physical property value of the film itself, but also a variation in resistance occurs between the wirings, and when a display element or the like using a liquid crystal is formed, display unevenness or flicker occurs. And so on.

In order to solve the above problems, a gate electrode and a scanning line having a two-layer structure of the second polycrystalline silicon layer and the refractory metal silicide layer are formed.
After the surface and side surfaces of the layer structure film are wet-oxidized to form a thermal oxide film, a third silicon dioxide layer serving as an interlayer insulating film is deposited by a vapor deposition method or a sputtering method. Cracks do not occur in the layer or the two-layer structure film of the 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 the variation in the resistance value.

[0007]

According to the present invention, there is provided a thin film transistor formed on a substrate, comprising: a gate electrode; a wiring layer formed of the same layer as the gate electrode; a polycrystalline silicon layer; It is composed of a laminated film with a refractory metal silicide layer formed using a target having a content of 2.3 to 3.0 , and cracks of the refractory metal silicide layer occur on the surface and side surfaces of the laminated film. It is characterized in that a thermally oxidized film having a different thickness is formed.

According to the present invention, a gate electrode of a thin film transistor formed on a substrate and a wiring layer formed of the same layer as the gate electrode are constituted by a laminated film of a polycrystalline silicon layer and a refractory metal silicide layer. A method for manufacturing a thin film transistor, wherein after forming the polycrystalline silicon layer, the content of silicon with respect to metal 1 is 2.3 on the polycrystalline silicon layer.
Stacking the refractory metal silicide layer using a target of 3.0 to form a stacked film; patterning the stacked film to form the gate electrode and the wiring layer; Forming a thermal oxide film with a thickness that does not cause cracking of the refractory metal silicide layer on the surface and side surfaces of the metal oxide film.

The thermal oxide film is formed by wet oxidation.

The high-melting-point metal silicide is molybdenum silicide, and the thermal oxidation of the laminated film is performed at a temperature of 800 ° C. or more to form the thermal oxide film.

[0011]

[0012]

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described in detail based on embodiments.

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 by the second polycrystalline silicon layer to a thickness of 5000.degree. Even when a third silicon dioxide layer serving as an interlayer insulating film for insulating a wiring film is deposited to a thickness of about 1 μm or more by a chemical vapor deposition method or a sputtering method, cracks are formed in the second polycrystalline silicon layer. It did not occur. However, to reduce the wiring resistance,
When a polycrystalline silicon layer and a refractory metal silicide layer are used in a two-layer structure in a wiring film composed 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. Cracks have occurred in the refractory metal silicide film when deposited at 3000 ° or more by vapor phase growth or sputtering. 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 display quality of a liquid crystal display element using a thin film transistor formed on a glass substrate, left and right unevenness occurs on a screen, and there are problems such as noticeable flicker.
By depositing the refractory metal silicide film, the wiring resistance of the film is reduced.

As shown in FIG. 1A, in order to eliminate cracks generated in the refractory metal silicide film, as shown in FIG.
After patterning a two-layer structure film of a second polycrystalline silicon layer serving as a gate electrode and a scanning line and a 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. The ion implantation into the first polycrystalline silicon layer for forming the source and drain regions of the thin film transistor can be performed before or after the oxidation step shown in FIG. There is no change in 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
02 and 103 are both formed of the first polycrystalline silicon layer. 104, a gate oxide film;
Reference numeral 6 denotes a polysilicon portion and a refractory metal silicide portion of the gate electrode and the scanning line, respectively. For the formation of the refractory metal silicide film, it is desirable to form the refractory metal silicide film by a sputtering method because the composition can be easily controlled and a high-purity target can be obtained, so that there are few impurities. 107 is
A thermal oxide film is formed on the exposed portions of the polysilicon film and the refractory metal silicide film. Reference numeral 108 denotes a third silicon dioxide film deposited by a chemical vapor deposition method or a sputtering method.

The refractory metal silicide includes molybdenum silicide, tungsten silicide, tantalum silicide, titanium silicide and the like. When molybdenum silicide and tungsten silicide are oxidized at a high temperature, a silicon oxide film tends to grow without growing a metal oxide film. Among them, the molybdenum silicide thermal oxide film is formed by molybdenum oxide sublimating at 790 ° C.
If oxidized at a temperature of 800 ° C. or more, only silicon oxide is formed. At this time, the silicon oxide film becomes a silicon dioxide film,
107 is 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 ℃, when the contact holes are opened above 106 in FIG. Can be etched.

As shown in FIG. 1B, in order to prevent cracking of the refractory metal silicide film which occurs when an interlayer insulating film is formed, the second polycrystalline silicon layer serving as a gate electrode and a scanning line is connected to a high polycrystalline silicon layer. The surface and side surfaces 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 thickness of the molybdenum silicide and the thickness of the second silicon dioxide is shown in the hatched region in FIG. If there is, no crack occurs in the molybdenum silicide film. The manner in which cracks in the molybdenum silicide film occur is a function of only the thickness of the molybdenum silicide layer and depends on the thickness of the polycrystalline silicon layer even in a two-layer structure film of a polycrystalline silicon layer and a molybdenum silicide layer. do not do.

FIG. 3 shows that the composition of the sputter target is such that the content of silicon with respect to molybdenum 1 is 2.3 to 3.0.
And the pressure during sputtering is 0.1 Pa
FIG. 2 shows a relationship diagram when a film is formed within a range of from 2.0 Pa to 2.0 Pa. Reference numeral 301 denotes a boundary line for determining whether or not cracks occur in the molybdenum silicide film, and reference numeral 302 denotes a region in which no crack occurs in the film. If a different sputtering apparatus is used, the boundary line 301 may fluctuate. However, when a thin film transistor is formed over a glass substrate such as a quartz substrate, the boundary line always exists and is formed. As the thickness of the thermal oxide film increases, cracks may not be generated. However, if an in-line type sputtering apparatus is used for sputtering of molybdenum silicide, the same relationship diagram as FIG. 3 can be obtained.

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 a glass substrate. Then, there is an effect of preventing cracks. Also,
The manner in which cracks occur does not change depending on the area of the remaining two-layer structure film of the second polycrystalline silicon layer and the molybdenum silicide layer. 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 within 5000 mm. For example, a two-layer film
Even if a wiring film is put on the oxide film shown in FIG. 1 (c) 108, the cross-section does not have a reverse tapered shape to cause disconnection.

Next, a method for forming a thermal oxide film having a two-layer structure film of the second polycrystalline silicon layer and the molybdenum silicide layer, which is to be a gate electrode and a scanning line, comprises: supplying an oxygen gas containing water vapor into a furnace. It is preferable to use a wet oxidation method to be introduced into the substrate. 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 for holding pure water, and 405 is pure water in the flask.
It is necessary to keep the temperature of the water at 80 ° C. or higher by adding an amount of about 8 minutes. Reference numeral 406 denotes an annealing furnace in which oxygen gas flows from the gas pipe port A and nitrogen gas flows from the gas pipe port B.

In the annealing furnace, there are two inlets, a wet oxygen gas inlet and a nitrogen gas inlet. The reason is that after the wet oxidation, the substrate is continuously placed in a nitrogen atmosphere without leaving the substrate outside the furnace.
This is because the When the substrate is drawn out of the annealing furnace into the atmosphere after the wet oxidation, the moisture in the furnace is condensed and adheres to the substrate. When a part of the substrate is exposed, a malfunction of the thin film transistor is caused. The nitrogen atmosphere needs to be annealed at a temperature higher than the wet oxidation temperature 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 growing on the molybdenum silicide layer is:
It is about 10 times faster than dry oxidation. Second, in FIG. 3, when the dry oxidation method is employed, the slope of the boundary line 301 as to whether or not cracks occur becomes steep. Therefore, if the film thickness of molybdenum silicide is the same, the dry oxidation method requires a thicker oxide film. When the thickness of the thermal oxide film 107 is increased in FIG.
The thickness of the gate oxide film is also increased, and the thickness of the first polycrystalline silicon layers 102 and 103 is reduced, which tends to impair the reliability of the thin film transistor.

[0024]

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

[Brief description of the drawings]

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

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

FIG. 3 is a graph showing the relationship between molybdenum silicide and oxide film thickness and how cracks occur.

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 where cracks do not occur 302 Crack-free area 401 Gas pipe 402 Gas flow controller 403 Valve 404 Quartz flask 405 Pure water 406 Anneal furnace

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/3205 H01L 21/336 H01L 29/40 H01L 29/43 G02F 1/1368

Claims (4)

(57) [Claims] 1. A thin film transistor formed on a substrate, or a wiring layer consisting of the gate electrode and the gate electrode in the same layer, and a polycrystalline silicon layer, the content of silicon to the metal 1 2.3
And a high-melting-point metal silicide layer formed by using a target having a thickness of 3.0 mm and having a thickness that does not cause cracking of the high-melting-point metal silicide layer on the surface and side surfaces of the stacked film. A thin film transistor comprising a film. 2. A method for manufacturing a thin film transistor, comprising: a gate electrode of a thin film transistor formed on a substrate; and a wiring layer formed of the same layer as the gate electrode, which is formed by a laminated film of a polycrystalline silicon layer and a refractory metal silicide layer. After forming the polycrystalline silicon layer, on the polycrystalline silicon layer,
Stacking the refractory metal silicide layer using a target having a silicon content of 2.3 to 3.0 with respect to metal 1 to form a stacked film; and patterning the stacked film to form the gate. Forming an electrode and the wiring layer; and forming a thermal oxide film on the surface and side surfaces of the stacked film with a thickness that does not cause cracking of the refractory metal silicide layer. Production method. 3. The method according to claim 2, wherein the thermal oxide film is formed by wet oxidation. 4. The thermal oxide film according to claim 2, wherein the high-melting-point metal silicide is molybdenum silicide, and the laminated film is thermally oxidized at a temperature of 800 ° C. or more to form the thermal oxide film. A method for manufacturing a thin film transistor.