JPH05335337A - Manufacture of thin-film transistor - Google Patents

Abstract

PURPOSE:To provide a simple process for a high-quality thin-film transistor in which metallic contaminant is eliminated at the interface between insulating layers and semiconductor layers. CONSTITUTION:A polycrystalline silicon film is formed on a glass substrate in an annealing chamber 1. Immediately before a gate insulator of silicon oxide is formed on the polycrystalline silicon film, the glass substrate is transferred to a cleaning chamber 2, where metallic impurities on the polycrystalline silicon film are removed in the form of chloride by applying ArF excimer laser in a high-purity chlorine gas atmosphere from a laser source 4.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming a thin film transistor on an insulating substrate, and more particularly to a method of manufacturing a highly reliable and high performance thin film transistor.

[0002]

2. Description of the Related Art In recent years, the area of liquid crystal displays has been increasing, and the drive system thereof is also shifting to the active matrix system. An inexpensive glass substrate is preferable as the display substrate for increasing the area, and a large number of thin film transistors must be formed on the substrate in the active matrix system.

Japanese Unexamined Patent Publication (Kokai) No. 62-119974 discloses a CVD method and a plasma method in which a gate insulating film can be formed at a lower temperature in order to form a thin film transistor having good characteristics at a process temperature without damaging a glass substrate. CV
After being formed by the D method, the photo CVD method, the plasma anodic oxidation method, or the like, the active layer is irradiated without irradiating the whole or a part of the transistor region with a laser beam without overheating the substrate such as a base glass substrate. Attempts to improve the characteristics of the interface between (polycrystalline silicon) and the insulating film.

[0004]

However, in the above-mentioned prior art, the laser light irradiation is performed after the gate insulating film is formed, and the interface between the insulating film and the semiconductor thin film has a problem in electrical characteristics and reliability of the thin film transistor. There may be a problematic substance such as an alkali metal or heavy metal. Even if surface cleaning is performed by wet cleaning before forming an insulating film, wet cleaning using a solution is not recommended due to an increase in the amount of chemicals used due to an increase in the substrate area, the difficulty of waste liquid treatment, and the demand for automation of the process. There are inconveniences.

As an alternative technique to wet cleaning,
There is a dry cleaning method. Up to now, this dry cleaning has been performed by using plasma or ion irradiation, but it cannot be said that the controllability is sufficient, and furthermore, there are problems of damage and secondary contamination.

The present invention is intended to solve the above problems, and an object thereof is to remove a substance such as a metal or a heavy metal from an interface between an insulating film and a semiconductor thin film, and to provide a thin film transistor having highly reliable thin film transistor characteristics. It is to provide a method for manufacturing a thin film transistor that can be obtained.

[0007]

The present invention has found that the above object can be achieved by performing optical cleaning by ultraviolet irradiation, which is a cleaning method without substrate damage, on the surface of a semiconductor thin film immediately before forming an insulating film. It was made based on that.

That is, in the invention described in claim 1 of the present invention, in forming a thin film transistor having a semiconductor thin film formed on a substrate of which at least the surface is an insulating material as an active layer, a gate insulating film is formed on the semiconductor thin film. Immediately before forming the film, light energy is used to remove impurities on the semiconductor thin film.

Further, the invention according to claim 2 is characterized in that, when the impurities on the semiconductor thin film are metal impurities, a halogen gas is used as an atmosphere gas for removing the metal impurities.

Further, in the invention described in claim 3, as light energy for removing impurities on the semiconductor thin film,
It is characterized by using ultraviolet rays having a wavelength of 400 nm or less.

Fe, C may be used as metal fine particles which are problematic in terms of electrical characteristics and reliability of thin film transistor (TFT) characteristics.
u, Ni, Cr, Mg, Al, Na, Ca and the like. When performing light cleaning to remove these,
A halogen gas is suitable as the atmosphere gas, and chlorine (Cl ₂ ) gas is particularly preferable. Chlorine is photodissociated as shown in [Chemical Formula 1] by irradiation with light having a wavelength of 400 nm or less.

[0012]

[Chemical 1]

The light source is a light pressure mercury lamp, ArF or KrF.
Excimer laser is suitable, and a high-output excimer laser is suitable for improving productivity. The above metal fine particles react with photoexcited chlorine radicals and are removed from the surface as volatile chlorides.

Therefore, if the gate insulating film is formed after the impurities are removed and then the heat treatment is performed by the ultraviolet laser, the ratio of impurity diffusion during the heat treatment is small, and a more stable and highly reliable thin film transistor can be manufactured. Become.

[0015]

When the semiconductor thin film is irradiated with light energy in, for example, a halogen gas atmosphere, Fe on the semiconductor thin film,
Impurities such as Cu are removed from the surface of the semiconductor thin film as volatile halides.

[0016]

EXAMPLES Next, the present invention will be described in more detail by way of examples. Example 1 A schematic structure of a thin film transistor manufacturing apparatus is as shown in FIGS.
Annealing chamber 1, cleaning chamber 2, C
It is composed of a VD chamber 3 and a laser beam irradiation device 4.
The cleaning chamber 2 has a cylinder 7a of high-purity chlorine gas.
However, the CVD chamber 3 is provided with cylinders 7b of silicon oxide film forming material, and the annealing chambers 1 to CVD are connected to each other.
The chamber 3 is connected to the exhaust system 8. Further, the laser light irradiation device 4 includes a laser 4a, a mirror 5 and an optical system 6. 10 is a heater.

Using the above apparatus, a thin film transistor was manufactured by the following steps [see FIGS. 3 (a) to 3 (f)]. (1) First, amorphous silicon 12 (a-Si: H) is formed on a glass substrate 11 that has been organically cleaned by a plasma CVD method.
Was deposited to a film thickness of 1000Å. The deposition conditions are a substrate temperature of 250 ° C. and a vacuum degree of 1 × 10 ⁻⁵ torr [FIG.
(A)]. (2) Next, the glass substrate 11 is set in the annealing chamber 1 and heated at a substrate temperature of 500 ° C. for 1 hour to carry out dehydrogenation. Then, the substrate temperature is room temperature and the degree of vacuum is 1 × 10 ⁻⁵ torr. The ArF excimer laser 14 (wavelength 193 nm, half-value width 10 nsec) was irradiated with a laser power of 350 mJ / cm ² for one shot to obtain polycrystalline silicon 13 [FIG. 3 (b)]. (3) Next, the glass substrate 11 is moved to the cleaning chamber 2, and the ArF excimer laser 14 is irradiated in the 99.999% chlorine gas 15 from the cylinder 7a to perform optical cleaning of the surface of the polycrystalline silicon 13. went. The optical cleaning conditions were as follows: the chamber internal pressure was 20 torr, the gas flow rate was 50 sccm, and the substrate temperature was 150 ° C. and the ArF laser 14 was vertically irradiated. Laser power is 300 mJ / cm
² , the number of shots is 20 [Fig. 3
(C)]. (4) Next, the glass substrate 11 is moved to the CVD chamber 3, and the silicon oxide 1 to be the gate insulating film is formed by the atmospheric pressure CVD method.
6 was deposited at a film thickness of 1500Å at 450 ° C [Fig. 3
(D)]. (5) Move the glass substrate 11 to the annealing chamber 1 again,
The substrate temperature is room temperature and the degree of vacuum is 1 × 10 ⁻⁵ torr.
Was irradiated and heat-treated. The irradiation condition is 350 mJ / cm ² ,
20 shots (FIG. 3 (e)). (6) Next, source / drain contact formation, impurity mixing, impurity activation, and gate electrode 17 are performed by known techniques.
After forming the source / drain electrodes 18 and the interlayer insulating film, a MOS TFT element was formed [Fig.
(F)]. As a result, good TFT characteristics and high reliability could be obtained.

[0018]

As is apparent from the above description, claim 1
In the method of manufacturing a thin film transistor described in (1), the impurities on the semiconductor thin film are removed by using light energy immediately before forming the gate insulating film, so that it is caused by the diffusion of impurities existing at the interface in the heat treatment step for improving the interface characteristics. It is possible to prevent the instability of the TFT characteristics and the deterioration of the reliability. Also, because of the optical process,
There is no damage to the semiconductor thin film and no adverse effect on the interface.
In the method of manufacturing a thin film transistor according to the second aspect of the present invention, by using a halogen gas having a strong activity, it is possible to efficiently remove the metal impurities that are the causative substance of destabilizing the TFT characteristics and lowering the reliability. In the method of manufacturing a thin film transistor according to the third aspect, by using ultraviolet rays having a wavelength of 400 nm or less, the halogen gas is photoexcited and the metal impurities can be reliably removed.

[Brief description of drawings]

FIG. 1 is a schematic explanatory diagram of a thin film transistor manufacturing apparatus used in the present invention.

FIG. 2 is an explanatory diagram showing a flow of a glass substrate in the apparatus shown in FIG.

FIG. 3 is an explanatory view of a thin film transistor manufacturing process showing an embodiment of the present invention.

[Explanation of symbols]

 1 Annealing Room 2 Cleaning Room 3 CVD Room 4 Laser Light Irradiation Device 4a Laser 5 Mirror 6 Optical System 7a, 7b Cylinder 8 Exhaust System 9 TFT Element (Sample) 10 Heater 11 Glass Substrate 12 Amorphous Silicon 13 Polycrystalline Silicon 14 Laser 15 chlorine gas 16 silicon oxide (gate insulating film) 17 gate electrode 18 source / drain electrode

Claims (3)

[Claims] 1. When forming a thin film transistor having a semiconductor thin film as an active layer, which is formed on a substrate having at least a surface made of an insulating material, light energy is used immediately before forming a gate insulating film on the semiconductor thin film. And removing impurities on the semiconductor thin film. 2. The method of manufacturing a thin film transistor according to claim 1, wherein a halogen gas is used as an atmosphere gas for removing metal impurities on the semiconductor thin film. 3. The method of manufacturing a thin film transistor according to claim 1, wherein ultraviolet light having a wavelength of 400 nm or less is used as light energy for removing impurities on the semiconductor thin film.