JPH0697101A - Fabrication of thin film transistor - Google Patents

Abstract

PURPOSE:To fabricate a TFT element having improved electric characteristics and reliability efficiently by performing a step for heat treating an amorphous semiconductor thin film with optical energy prior to formation of gate dielectric film and crystalizing the amorphous semiconductor thin film in an atmospheric gas having low thermal conductivity which allows removal of impurities from the film surface. CONSTITUTION:TFT elements are formed on a substrate 1 at least the surface thereof is composed of a dielectric material. The fabrication method comprises a step for heat treating an amorphous semiconductor thin film 2 with optical energy prior to formation of a gate dielectric film 7 thus crystalizing the thin film 2 and the step is carried out in an atmospheric gas having low thermal conductivity which allows removal of impurities from the surface of the thin film 2. For example, an a-Si film 2 is deposited on an insulating substrate 1 which is then transferred into halogen gas atmosphere 4. The substrate 1 is then irradiated with ArF excimer laser beam 5 from above with the temperature of the substrate 1 being sustained at 150 deg.C in order to remove impurities from the surface of the film 2 and to crystalize the a-Si film 2 thus obtaining poly-Si 6.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for efficiently manufacturing a high performance thin film transistor (TFT) element. In particular, it is intended to improve the performance of the device and improve the manufacturing efficiency.

[0002]

2. Description of the Related Art In recent years, there has been an increasing demand for a liquid crystal display having a large area and a high speed driving element. The display substrate for increasing the area is preferably an inexpensive glass substrate, and it is preferable to use the active matrix method for speeding up the driving element. To realize the active matrix method, a thin film transistor (hereinafter,
It is abbreviated as TFT. ) Must be formed. In the conventional technology, a TFT formed on a glass substrate at a process temperature without damage is mainly a TF having an a-Si active layer.
However, recently, by annealing the a-Si with a pulsed laser having a short wavelength, it is possible to obtain a poly-Si TFT capable of driving at a higher speed. For example, in JP-A-62-36854,
A-S on a glass substrate or a thermally oxidized Si wafer
After i is formed, it is crystallized by laser annealing. In the annealing by the pulsed laser, the melting and solidification time of the irradiated film is very short on the order of nsec, so that the film rapidly solidifies from the molten state and the crystal grain size in the film becomes several hundreds nm, and it is possible to make it larger than that. Therefore, there is a limit to the electric properties of the thin film such as mobility. Therefore, there has been a demand for a method of increasing the crystal grain size by lengthening the melt-solidification time of the irradiated film by some method. On the other hand, T
In the case of forming FT, substances such as alkali metal and heavy metal, which pose a problem on the electrical characteristics and reliability of the TFT, may exist at the interface between the gate insulating film and the semiconductor thin film, and the impurities are removed. Will be required. In the prior art, if the step of cleaning the polycrystalline silicon surface before the gate insulating film deposition is not included, the polycrystalline silicon /
Impurities are likely to be present at the interface of the gate insulating film, and even if laser irradiation for improving the interface characteristics is performed, the impurities diffuse near the interface, which may cause a decrease in the TFT characteristic requirements. Even if surface cleaning is performed by wet cleaning or the like, wet cleaning using a chemical solution is inconvenient due to an increase in the amount of chemicals due to an increase in the area of the substrate, the difficulty of waste liquid treatment, and the demand for automation of the process. Dry cleaning is an alternative technology. However, until now, plasma and ions have been used, but the controllability is not sufficient, and there are problems of damage and secondary pollution. Therefore, development of a low-damage surface cleaning method has been required.

[0003]

An object of the present invention is to provide a method for efficiently manufacturing a thin film transistor (TFT) element having improved electrical characteristics and reliability.

[0004]

According to the present invention, in order to solve the above-mentioned problems of the prior art, an amorphous semiconductor thin film formed on an insulating substrate is heated in a gas atmosphere having a low thermal conductivity (k), preferably the thermal conductivity (k). The amorphous semiconductor thin film is melted and solidified by laser annealing with a pulsed laser in a low gas whose k) is 0.01 (W · m ⁻¹ · K ⁻¹ , value at 0 ° C.) or less. The conduction of heat generated in the process can be deteriorated and the temperature change in the thin film can be made gentle, and as a result, the crystal grain size in the thin film after annealing can be made larger than that of the conventional one. The thermal conductivity (k) of the atmosphere gas at the time of annealing is 0.01 or less, and
Moreover, when present at the interface between the gate insulating film and the semiconductor thin film, alkali metal or heavy metal particles (eg Fe, Cu, Ni, C, etc.) which pose a problem in the electrical characteristics and reliability of the TFT.
If a substance capable of removing (r, Mg, Al, Na, Ca) from the film surface is used, crystallization of the thin film and cleaning of the film surface can be performed at the same time, which simplifies the manufacturing process. In addition, the electrical characteristics of the TFT are improved, and the cleaning degree of the semiconductor / gate insulating film interface is also improved, so that the reliability of the device is also improved. Examples of such an atmosphere gas include chlorine gas and freon gas as shown in Table 1 below. The values in Table 1 are values at 0 ° C.

[Table 1] Generally, in the crystallization process, it is important to control the light absorptance of the film with respect to the wavelength and the control of heat transfer in the film when the light energy having the wavelength becomes heat energy. Crystallization of the a-Si: H film requires a wavelength of 400 nm or less, and pulse irradiation is convenient for reducing thermal damage to the substrate. Further, a wavelength of 400 nm or less is required to activate halogen. Considering the above matters, the excimer laser is preferable because it satisfies all the conditions, but as the light energy, in addition to the above laser light, for example, a low pressure Hg lamp, a deuterium lamp and the like can be mentioned. If the low-pressure Hg lamp or the deuterium lamp described here is irradiated in a pulsed manner with a shutter or the like, an effect similar to that of a pulsed laser can be expected in the crystallization process.

An embodiment of the present invention will be described below with reference to the drawings. 1 (a) to 1 (f) show each step of the manufacturing process of the polycrystalline silicon TFT element according to the present invention, and FIG.
(A) to (c) of FIG. 3 are diagrams schematically showing the concept of removing impurities on amorphous silicon and crystallization of amorphous silicon in the present invention. Example 1 (1) First, plasma C was applied on an insulating substrate 1 that had been organically cleaned.
An a-Si film 2 having a film thickness of 1000 Å was deposited by the VD method. The deposition conditions are a substrate temperature of 250 ° C. and a vacuum degree of 1 × 10 ⁻⁵ t.
orr [see FIG. 1 (a)]. (2) Next, the substrate 1 is moved to a halogen gas atmosphere (5N purity chlorine gas, 20 torr, 50 sccm) 4 [see FIG. 1 (b)]. (3) And keeping the substrate in the above atmosphere at 150 ° C.
Arf excimer laser (wavelength 19
3 nm, half width 10 nsec) 5 laser power 550
Impurities on the film were removed and amorphous silicon was crystallized under the irradiation conditions of mJ / cm ² and 20 shots. As a result, polycrystalline silicon 6 was obtained [see FIG. 1 (c)]. (4) Next, the substrate temperature is set to 450 ° C. and the atmospheric pressure C is applied to the substrate 1.
A gate insulating film 7 having a film thickness of 1500 Å was deposited by the VD method [see FIG. 1 (d)]. (5) Further, the substrate 1 is kept at room temperature and the degree of vacuum is 1 × 10 ^−5.
The interface characteristics between the polycrystalline silicon 6 and the gate insulating film 7 were improved by irradiating the Arf excimer laser in the state of torr [see FIG. 1 (e)]. (6) Finally, according to a known technique, MOSTF is performed through source / drain contact formation, impurity introduction, activation, gate electrode, source / drain electrode formation, and interlayer insulating film formation.
As a result of forming the T element, good electric characteristics and high reliability could be obtained [see FIG. 1 (f)].

[0006]

[Effects] (1) Since amorphous silicon is the starting film, the deposition temperature (substrate temperature) is set to that of polycrystalline silicon (up to 600).
Since the temperature can be lower than 300.degree. C.) (300.degree. C. to RT), the degree of freedom in substrate selection is improved. (2) By simultaneously performing the heat treatment of the amorphous semiconductor thin film and the removal of impurities on the thin film in the same system, the number of process steps can be reduced and an element with improved reliability can be provided. (3) Thermal conductivity (k) is 0.01 (W · m ⁻¹ · K ⁻¹ ,
By using an atmosphere gas in the range of (value at 0 ° C.) or less, the crystal grain size can be increased and an element with improved electronic characteristics can be obtained. (4) A halogen gas is selected as an atmospheric gas, and laser energy is applied to this gas to activate it, whereby impurities such as metal particles on the film surface are efficiently removed.

[Brief description of drawings]

1A to 1F are manufacturing processes (1) to (6) of a polycrystalline silicon TFT element according to a first embodiment.
It is a figure which shows typically the structure of the element of each process of.

2 (a) to 2 (c) are diagrams schematically showing the concept of removing impurities on amorphous silicon and crystallization of the amorphous silicon according to the present invention.

[Explanation of symbols]

 1 Insulating Substrate 2 Amorphous Silicon 3 Impurity Layer 3'Impurity 4 Atmospheric Gas 5 Laser Light 6 Polycrystalline Silicon 7 Gate Insulating Film 8 Gate Electrode 9 Interlayer Insulating Film 10 Source / Drain Electrode 11 Halogen Molecules 11 ′ Halogen Compound 11 ″ Active Halogenated halogen

Claims (5)

[Claims] 1. A method of forming a thin film transistor (TFT) element on a substrate having at least a surface of an insulating material, the method comprising heat-treating an amorphous semiconductor thin film using light energy before forming a gate insulating film. A method of manufacturing a thin film transistor element (TFT), which comprises the step of crystallizing the step of: and performing the step in an atmosphere gas of low thermal conductivity capable of removing impurities from the film surface of the thin film. 2. A thin film transistor element (TF) characterized in that the thermal conductivity (k) of an atmospheric gas when heat treating the amorphous semiconductor thin film according to claim 1 is in the following range.
Manufacturing method of T). k ≦ 0.01 (W · m ⁻¹ · K ⁻¹ , value at 0 ° C) 3. A method of manufacturing a thin film transistor element (TFT), wherein the atmosphere gas according to claim 1 or 2 is a gas containing halogen. 4. The heat treatment using light energy is 400
The method for manufacturing a thin film transistor element (TFT) according to claim 1, wherein the method is performed with light having a wavelength of nm or less. 5. The method of manufacturing a thin film transistor element (TFT) according to claim 1, wherein the heat treatment using light energy is annealing by an excimer laser.