JP4901020B2 - Method for manufacturing polysilicon thin film transistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a manufacturing method for reducing impurity contamination such as boron, phosphorus, and aluminum in a manufacturing process of a polysilicon thin film transistor used for a liquid crystal display device or the like.
[0002]
[Prior art]
In general, amorphous silicon is used for a semiconductor layer of a thin film transistor of a liquid crystal display device, but an example in which polysilicon is used for a semiconductor layer of a thin film transistor having high characteristics such as mobility is increasing. However, the polysilicon thin film transistor has a larger characteristic variation due to impurity contamination such as boron in the atmosphere than amorphous silicon, and requires an environment with little impurity contamination and a process for removing impurity contamination. As these general measures, installation of a boron-less air-conditioning filter is used in terms of environment, and a cleaning process is performed immediately before film formation in terms of process.
[0003]
[Problems to be solved by the invention]
However, there is still a need for improvement in the prior art, and it is desired to reduce impurity contamination in the thin film transistor manufacturing process, which is one of the characteristics variation factors of the polysilicon thin film transistor. Higher characteristics and higher yields of thin film transistors can be expected by reducing the incorporation of impurity contamination into the film interface and into the film.
[0004]
In order to solve the above-described conventional problems, the present invention cleans and protects the substrate constituting each thin film transistor and the surface and interface of each film from impurity contamination such as boron which affects the operation of the transistor, and has characteristics and reliability. An object of the present invention is to provide a method of manufacturing a polysilicon thin film transistor having a high yield and a high yield.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, a method of manufacturing a polysilicon thin film transistor according to the present invention includes a step of continuously forming a semiconductor film made of amorphous silicon and its underlying insulating film in the manufacturing process of a polysilicon thin film transistor used in a liquid crystal display device without exposing it to the atmosphere. When the film is formed, oxygen plasma treatment is performed immediately before the formation of the base insulating film, and then the base thin film is formed without being exposed to the atmosphere , and oxygen plasma treatment is performed immediately after the formation of the semiconductor film, A surface oxide film is formed.
[0006]
The oxygen plasma treatment immediately after the formation of the semiconductor film is preferably performed continuously without exposure to the air immediately after the formation of the semiconductor film.
[0008]
Further, it is preferable to perform dehydrogenation treatment and laser crystallization in a state where a surface oxide film is formed by the oxygen plasma treatment.
[0009]
Moreover, it is preferable to perform pattern formation of the semiconductor film in a state where the surface oxide film is formed by the oxygen plasma treatment.
[0010]
Further, it is preferable that the surface oxide film is removed by hydrofluoric acid etching immediately before the gate insulating film is formed in a state where the surface oxide film is formed by the oxygen plasma treatment.
[0011]
The polysilicon thin film transistor is preferably a top gate type.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention removes impurities in the atmosphere attached to the glass substrate surface by performing oxygen plasma treatment immediately before the formation of the underlying insulating film of the semiconductor film in addition to the conventional cleaning process for the glass substrate in the thin film transistor manufacturing process. Then, the undercoat insulating film and the semiconductor film are formed without exposing to the atmosphere, thereby preventing the contamination of impurities into the film interface and the film. In addition, immediately after the formation of a semiconductor film that is susceptible to impurity contamination such as amorphous silicon, an oxygen plasma treatment is performed on the surface of the semiconductor film without exposure to the atmosphere, thereby forming an oxide film on the surface of the semiconductor film. Impurity contamination is prevented from reaching the semiconductor film.
[0013]
The drawings used in the following first and second embodiments correspond to pixel transistors of polysilicon thin film transistors.
[0014]
(Embodiment 1)
An embodiment of the present invention will be described with reference to FIGS. First, as shown in FIG. 1 (a), the oxygen glass treatment A is applied to the entire surface of the glass substrate 1 after cleaning in a reduced pressure of a CVD apparatus or the like, so that boron on the surface of the insulating substrate adhering to the substrate is transferred. Remove contaminants.
[0015]
Next, as shown in FIG. 1B, after the oxygen plasma treatment A, an insulator film (undercoat insulating film) 2 corresponding to the base film of the semiconductor film is formed to a thickness of 300 to 700 nm without being exposed to the atmosphere. Then, a film is formed. Subsequently, the amorphous silicon film 3 is formed to a thickness of 300 to 600 nm without being exposed to the atmosphere.
[0016]
Next, as shown in FIG. 1C, the surface oxide film is formed on the amorphous silicon film 3 by performing oxygen plasma treatment B on the entire surface after the amorphous silicon film 3 is formed without being exposed to the atmosphere or exposed to the atmosphere. 4 is formed to a thickness of 10 to 50 nm.
[0017]
Next, as shown in FIG. 1D, the hydrogen content was reduced to 5% or less by performing a dehydrogenation process C, which is a heat treatment at 400 to 500 ° C., with the surface oxide film 4 formed. An amorphous silicon film 5 is formed.
[0018]
Next, as shown in FIG. 1E, the amorphous silicon film 5 on which the surface oxide film 4 is formed is subjected to laser crystallization D with an irradiation intensity of 300 to 400 mJ / cm ² to obtain a polysilicon film. 6 is formed.
[0019]
(Embodiment 2)
Using the intermediate formed in the first embodiment, a top gate type was manufactured as shown in FIGS. First, as shown in FIG. 2A, after the polysilicon film 6 is formed, patterning is performed while the surface oxide film 4 is formed, thereby forming a polysilicon film 6 ′ and a surface oxide film 4 ′.
[0020]
Next, as shown in FIG. 2B, the surface oxide film 4 'is removed by hydrofluoric acid etching immediately before the gate insulating film is formed, and then the gate insulating film 7 is formed immediately using a CVD apparatus or the like. .
[0021]
Thereafter, a gate metal film 8, an interlayer insulating film 9, a source metal film 10, a protective film 11 and the like are formed through several cleaning, film formation, photolithography, and etching processes, and a top gate type polysilicon thin film transistor is manufactured. Is done.
[0022]
【Effect of the invention】
As described above, in the thin film transistor manufacturing method, the surface and interface of the glass substrate / insulator film / semiconductor film / gate insulating film can be cleanly and protected from impurity contamination such as boron which affects the operation of the transistor. Thus, a polysilicon thin film transistor having high characteristics and reliability and high yield can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a manufacturing process until polysilicon formation of a polysilicon thin film transistor in Embodiment 1 of the present invention. FIG. 2 shows a manufacturing process until formation of a top gate type of a polysilicon thin film transistor in Embodiment 2 of the present invention. Sectional view shown
1 Glass substrate 2 Base insulator film 3 Amorphous silicon film 4 Surface oxide film 5 Amorphous silicon film (after dehydrogenation)
6 Polysilicon film 7 Gate insulating film 8 Gate metal film 9 Interlayer insulating film 10 Source metal film 11 Protective film A Oxygen plasma treatment (cleaning purpose)
B Oxygen plasma treatment (for oxide film formation)
C Dehydrogenation treatment D Laser crystallization

Claims (5)

In the manufacturing process of a polysilicon thin film transistor used in a liquid crystal display device, an oxygen plasma treatment is performed immediately before the formation of the underlying insulating film when the amorphous silicon semiconductor film and the underlying insulating film are continuously formed without being exposed to the atmosphere. Then, a method for producing a polysilicon thin film transistor is characterized in that the surface thin film is formed by forming the base thin film without exposing to the atmosphere and performing oxygen plasma treatment immediately after the formation of the semiconductor film. 2. The method according to claim 1, wherein the oxygen plasma treatment immediately after the semiconductor film is formed is continuously performed without being exposed to the air immediately after the semiconductor film is formed . 3. The method according to claim 1, wherein dehydrogenation treatment and laser crystallization are performed in a state where a surface oxide film is formed by oxygen plasma treatment. The method according to claim 1 or 2, wherein the semiconductor film is patterned in a state where a surface oxide film is formed by oxygen plasma treatment.   3. The method according to claim 1, wherein the surface oxide film is removed by hydrofluoric acid etching immediately before forming the gate insulating film in a state where the surface oxide film is formed by oxygen plasma treatment.

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