JPH03148836A - Manufacture of thin film transistor - Google Patents

Abstract

PURPOSE:To inhibit the lateral diffusion of an impurity and to form a low- resistance region having little defect by a method wherein source and drain regions are locally melted using an excimer laser, are doped and a heat treatment is also performed simultaneously with the doping. CONSTITUTION:An insulation film 11 is formed on the surface of a semiconductor single crystal substrate 1 with an IC element formed thereon and a polycrystalline silicon layer 12 is grown on the surface of the film 11. Then, a gate oxide film 4 and a polycrystalline silicon layer 13, which is used as a gate electrode, are formed. Irradiated with an excimer laser 8 in an atmosphere containing P-type impurity gas 7, the layer 12 is melted and an impurity is introduced in source and drain regions 14a and 14b. Moreover, when the gas 7 is introduced in the silicon layer 13 simultaneously with the irradiation of the laser 8, the gate electrode 15 can be formed simultaneously with the introduction of the gas 7. The depth of the layer 12 which is melted by the laser is small, the lateral diffusion of the impurity is inhibited and a low- resistance region having little defect can be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a thin film transistor using polycrystalline silicon, and more particularly to a thin film transistor using laser doping technology.

[Summary of the invention]

The present invention is a method of forming a source region and a drain region of a thin film transistor by a self-line method, and forming a junction by a laser doping technique. first,
A gate oxide film and a polycrystalline silicon gate region are formed on it, and using this gate region as a mask, an excimer laser, which is a short wavelength pulsed laser, is irradiated in an atmosphere of a gas containing boron trifluoride. This is a method of manufacturing a thin film transistor including a step of forming a source region and a drain region. Even though the thickness of the source region and drain N region of the thin film transistor is less than 500 angstroms, it is possible to form low resistance regions with few defects.

(Prior art) A method has been proposed for forming shallow junctions on a semiconductor single crystal substrate using a so-called laser doping technique, in which impurities are introduced by irradiating a laser, particularly an excimer laser, which is a short-wavelength pulsed laser. For example, C.I.L.D.
(Gas Immersion Laser Dopi
There was a method for manufacturing P-channel MOSFETs called n1) (IEEE I!electron Dev
ice letters, V.

1.9 No. 10. 1988, pp. 542-544).

An outline of the manufacturing method is shown in FIGS. 2a to 2C. First, as shown in FIG. 2a, a band oxide film 2a and a nitride film 2b for insulation isolation are formed on the surface of a semiconductor single crystal substrate 1. Formed in a predetermined area. Next, as shown in FIG. 2, after forming a field oxide film 3, a gate oxide film 4 is formed.
Furthermore, a gate electrode 5 of polycrystalline silicon is formed. The polycrystalline silicon including the side surfaces of the gate electrode is oxidized to form a silicon oxide film sidewall 6 (this sidewall is made to have a thickness commensurate with the lateral diffusion distance when introducing impurities). Next, as shown in FIG. While irradiating with the XeCl excimer laser 8,
P-type impurities are introduced into source region 9a and drain region 9b.

A shallow junction can be formed by introducing impurities using this excimer laser. However, when a single-crystal silicon substrate is used as the substrate, there is a risk that defects are likely to occur at shallow junctions or at the boundary between the field oxide film and the junction.

In recent years, in order to increase the capacity of memory devices, an insulating film is provided on an IC element on which a thin film transistor has already been formed as a load resistor for a memory circuit, and a P-channel MOSFET or the like is formed on the surface of the insulating film. A memory device having a structure forming a so-called stacked thin film transistor (hereinafter referred to as stacked TET) has been proposed.

(Problems to be Solved by the Invention) In order to form the source and drain regions of the stacked TPT, it is necessary to have as few defects as possible near the junction and to minimize movement of the junction that affects the channel length. When impurities are implanted using the ion implantation method described above, heat treatment is required to activate and recrystallize the amorphous implanted region, and lamp annealing or the like is required for this purpose.

However, in order to realize a stacked TPT with a short channel length of submicron or less, it is necessary to
In order to avoid the effects of heat on the device, it was necessary to apply local radiant energy at low temperatures for a short period of time and to improve the crystallinity near the junction.

[Means for solving R problem]

In the method for manufacturing a thin film transistor according to the present invention, an excimer laser, which is a short-wavelength pulsed laser, is used to locally melt and dope the source and drain regions, and heat treatment is also performed at the same time, thereby minimizing lateral diffusion. Stacked TPT can be realized.

[Effect]

In the method for manufacturing a thin film transistor according to the present invention, when the source NNi and drain regions are irradiated with a short wavelength pulsed laser, the film thickness of the polycrystalline silicon in the source and drain regions is 500 angstroms or less, and the laser irradiation melts the polycrystalline silicon. The depth is approximately 40
Since the thickness is 0 angstrom, defects caused by recrystallization are less likely to occur, and movement of the junction can be kept to 500 angstrom or less.

〔Example〕

Embodiments of the present invention will be described with reference to FIGS. 1-ah and 1-s.

As shown in FIG. 1a, an insulating film 11 is formed on the surface of a semiconductor single crystal substrate 1 (not shown) on which IC elements such as memories have been formed. This insulator 1111 is an interlayer insulating film for separating and wiring the IC elements below, and is usually used for Sing.
Use a membrane. Next, approximately 400 angstroms of polycrystalline silicon Li12 is grown on the surface of the insulating mill by CVD or the like. Next, a gate oxide 114 and polycrystalline silicon 13 to become a gate electrode are formed to form a polycrystalline silicon pattern having a width corresponding to a predetermined channel length. Next, as shown in Figure 1, in an atmosphere of a P-type impurity gas such as boron trifluoride,
1 of excimer laser 8 is irradiated. Polycrystalline silicon layer 12 is melted by irradiation with excimer laser 8, and impurities are introduced into the melt regions of source region 14a and drain region 14b. Since the impurity-introduced region is recrystallized by a predetermined scanning time of the excimer laser, defects at the junction are less likely to occur, and the source region 1 with low resistance is formed.
4a and a drain region 14b can be formed. Since the depth of the junction is limited by the thickness of the polycrystalline silicon film 12, the influence of changes in laser power and pulse width is smaller than in laser doping of a single crystal substrate.

If an impurity gas is simultaneously introduced into the polycrystalline silicon 13 of the gate to form the gate electrode 15, the source, drain, and gate can be formed by one laser doping.

Although the embodiments of the present invention have been described using P-type impurity gas, N-type impurity gas may also be used.

[Effects of the Invention] According to the method for manufacturing a thin film transistor according to the present invention, since the film thickness of the source region and the drain region is set to 500 angstroms or less, the lateral diffusion of impurities is suppressed to the film thickness or less, and the generation of defects is prevented. Since it is possible to form a source region and a drain region with a small amount of low resistance, it is possible to realize a fiII film transistor with a small leakage current.

[Brief explanation of the drawing]

1A and 1A are process diagrams for manufacturing the thin film transistor of the present invention, and FIGS. 2A to 2C are conventional MOS
It is a process diagram of manufacturing FET.

Claims (1)

[Claims] A gate region is formed on the surface of a polycrystalline silicon layer on an insulating film, and the source region and drain region are irradiated with a short wavelength pulsed laser in an atmosphere of impurity gas, using the gate region as a mask for impurity introduction. A method for manufacturing a thin film transistor, including a step of forming it.