JPH0582553A - Method of annealing thin film transistor - Google Patents

Abstract

PURPOSE:To enhance through-put of annealing and improve yield by a method wherein a channel layer and source.drain regions are annealed at the same time. CONSTITUTION:A semiconductor layer 12 is formed on the top of an ultraviolet ray transmitting substrate 11 in a first process. In succession, an active layer 17, a source.drain 15, and a drain region 16 are provided on a semiconductor layer 12 for the formation of a thin film transistor 18. Thereafter, the semiconductor layer 12 is irradiated with excimer laser rays 30 from the ultraviolet ray transmitting substrate 11 side in a second process to anneal the source region 15, the drain region 16, and the active layer 17 provided to the semiconductor layer 12.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of annealing a thin film transistor.

[0002]

2. Description of the Related Art Recently, it has been proposed to use a thin film transistor in a memory cell portion of a high density SRAM. A silicon film is used for the film forming the channel region of the thin film transistor. The annealing treatment is very important for improving the characteristics of the silicon film.
As an annealing treatment for obtaining a high-performance silicon film, a method of irradiating with an excimer laser beam and annealing is proposed. The excimer laser light is an ultraviolet ray and, because of pulse oscillation, it is possible to heat only the silicon film to a high temperature without damaging the substrate on which the silicon film is formed. Usually, two annealing treatments are required to anneal the junction layer of a thin film transistor formed on a silicon film by irradiation of excimer laser light. That is, before forming the gate, the channel layer is annealed in the first annealing process to eliminate crystal defects such as dislocations and twins, and reduce the carrier trap region.
Next, after forming a gate on the channel layer and forming a source / drain region, a source / drain region is formed by a second annealing process.
The drain region is annealed to activate the impurities.

[0003]

DISCLOSURE OF THE INVENTION As described above,
In order to anneal the junction layer of the thin film transistor by irradiating the excimer laser light, if the channel layer and the source / drain regions are simultaneously annealed,
The gate acts as a mask and the channel layer is not irradiated with the excimer laser light. Therefore, it is necessary to anneal the channel layer and the source / drain regions. Since the annealing process is performed twice as described above, the throughput in the manufacturing process is reduced. In addition, the heating due to the annealing process distorts the semiconductor layer and the substrate to reduce the yield.

An object of the present invention is to provide an annealing treatment method for a thin film transistor, in which the channel layer and the source / drain regions are annealed by a single annealing treatment.

[0005]

The present invention is a method for annealing a thin film transistor, which has been made to achieve the above object. That is, in the first step, a semiconductor layer is formed on the upper surface of the ultraviolet transparent substrate. Then, a thin film transistor in which an active layer and a source / drain region of the thin film transistor are provided in a semiconductor layer is formed. Then, in a second step, the semiconductor layer is irradiated with excimer laser light from the side of the ultraviolet-transparent substrate to anneal the active layer and the source / drain regions provided in the semiconductor layer.

[0006]

In the annealing method for the thin film transistor, the active layer and the source / drain regions of the thin film transistor are formed on the semiconductor layer formed on the upper surface of the ultraviolet transparent substrate, and then the excimer laser is formed on the semiconductor layer from the ultraviolet transparent substrate side. Light is irradiated to anneal the active layer and the source / drain regions. For this reason, the active layer and the source / drain regions are annealed by excimer laser light irradiation in one step.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to an explanatory diagram of an annealing method shown in FIG. First, in the first step, for example, by a low pressure chemical vapor deposition method, silica glass (Si
The semiconductor layer 12 made of silicon (Si) is formed on the upper surface of the ultraviolet-transparent substrate 11 made of O ₂ ). Then, the semiconductor layer 1 is formed by a normal thin film transistor forming method.
A gate electrode 14 made of polycrystalline silicon is formed on the upper surface of 2 through a gate insulating film 13 made of silicon oxide. After that, impurities are ion-implanted into the semiconductor layer 12 by, for example, an ion implantation method to form the source / drain regions 15 and 1.
6 is formed. At this time, a region of the semiconductor layer 12 which is shaded by the gate electrode 14 and in which impurities are not ion-implanted becomes an active layer (channel region) 17. The thin film transistor 18 is configured as described above.

Then, in the second step, the ultraviolet transparent substrate 1
The semiconductor layer 12 is irradiated with excimer laser light 30 from the first side. The irradiated excimer laser light 30 is transmitted through the ultraviolet-transparent substrate 11 and then the source / drain regions 15 and 16 are formed.
Layer 1 in which the active layer (channel region) 17 and the active layer 17 are formed
2 and then converted into heat, the semiconductor layer 1
The source / drain regions 15 and 16 and the active layer (channel region) 17 provided in 2 are annealed. The excimer laser light 30 is, for example, a krypton fluoride (KrF) laser light having a wavelength of 248 nm or a wavelength of 308 n.
m xenon chloride (XeCl) laser light or the like is used.

In this annealing treatment, for example, the semiconductor layer 1
When 2 is formed of an amorphous silicon layer having a thickness of 40 nm, excimer laser light having an energy density of about 180 mJ / cm ² is pulsed. As a result, crystal defects such as twins and dislocations in the active layer (channel region) 17 are eliminated. Therefore, the threshold voltage is reduced, the mobility is increased, and the swing is reduced. Further, the impurities in the source / drain regions 15 and 16 are activated, and the resistance values of the source / drain regions 15 and 16 are lowered.

In the annealing treatment by irradiation with the excimer laser light 30, the heating time is very short because the pulse width of the excimer laser light 30 is several tens of nanoseconds. Therefore, the impurities in the source / drain regions 15 and 16 do not unnecessarily diffuse into the semiconductor layer 12. Therefore, for example, the channel region 17 having a channel length shorter than 0.5 μm can be formed.

[0011]

As described above, according to the present invention,
The semiconductor layer on which the active layer and the source / drain region of the thin film transistor are formed is annealed by irradiating the semiconductor layer with excimer laser light from the side of the ultraviolet transparent substrate, so that the active layer and the source / drain region formed on the semiconductor layer are Annealing is performed by irradiation of excimer laser light in one step. Therefore, the throughput is improved. Further, since the number of times of heating by the annealing treatment is reduced, thermal strain generated in the semiconductor layer is reduced. Therefore, the yield can be improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an annealing treatment method of an example.

[Explanation of symbols]

11 UV Transparent Substrate 12 Semiconductor Layer 15 Source / Drain Region 16 Source / Drain Region 17 Active Layer (Channel Region) 18 Thin Film Transistor 30 Excimer Laser Light

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location H01L 21/268 Z 8617-4M 27/12 8728-4M

Claims (1)

[Claims] 1. A first step of forming a thin film transistor in which an active layer and source / drain regions are provided in the semiconductor layer after forming a semiconductor layer on the upper surface of the ultraviolet transparent substrate, and the ultraviolet transparent substrate side. By irradiating the semiconductor layer with excimer laser light to anneal the active layer and the source / drain regions provided in the semiconductor layer.
A method of annealing a thin film transistor, which comprises the step of.