Elimination of dehydrogenation step when forming a silicon thin film device by low-temperature laser-annealing

• US 6,080,643 A
• Filed: 02/11/1998
• Issued: 06/27/2000
• Est. Priority Date: 02/14/1997
• Status: Expired due to Fees

• Current Assignee: Sony Corporation (Sony Group Corp.)
• Original Assignee: Sony Corporation (Sony Group Corp.)
• Inventors: Noguchi, Takashi, Kanaya, Yasuhiro, Yagi, Hajime
• Primary Examiner(s): Bowers, Charles
• Assistant Examiner(s): PERT, EVAN T
• Application Number:
  US09/021,826
• Time in Patent Office: 867 Days
• Field of Search: 438/30, 438/142, 438/149, 438/151, 438/166, 438/478, 438/479, 438/482, 438/486, 438/487, 438/308
• US Class Current: 438/487
• CPC Class Codes: H01L 21/02422 Non-crystalline insulating materials, e.g. glass, polymers
• CPC Class Codes: H01L 21/02488 Insulating materials
• CPC Class Codes: H01L 21/02532 Silicon, silicon germanium, germanium
• CPC Class Codes: H01L 21/02592 amorphous
• CPC Class Codes: H01L 21/02631 Physical deposition at reduced pressure, e.g. MBE, sputtering, evaporation
• CPC Class Codes: H01L 21/02675 using laser beams
• CPC Class Codes: H01L 21/02686 Pulsed laser beam
• CPC Class Codes: H01L 21/02691 Scanning of a beam

Abstract

Disclosed is a process of forming a silicon thin film used as an active layer of a thin film transistor, which process is improved for enhancing a quality and a productivity of the silicon thin film. At a physical vapor deposition step, an amorphous silicon thin film is physically formed on a substrate in vacuum. Then, at a laser annealing step, directly after formation of the amorphous silicon thin film without the need of dehydrogenation, a laser light is irradiated to the amorphous silicon thin film, to convert the amorphous silicon thin film into a polycrystalline silicon thin film. After that, the polycrystalline silicon thin film thus converted is processed to form a thin film transistor. In the physical vapor deposition step, an amorphous silicon thin film may be formed by sputtering using a target made from a silicon crystal body or a silicon sintered body. In the sputtering, an amorphous silicon thin film can be formed by sputtering using a target previously mixed with an impurity in a desired concentration. By introducing an impurity in the amorphous silicon thin film at the film formation stage, a threshold characteristic of a thin film transistor can be previously controlled.

Claims

1. A method of fabricating a thin film semiconductor device, comprising:

a physical vapor deposition step of physically forming an amorphous silicon thin film on a substrate in a vacuum of 10^-7 Torr or less wherein said amorphous silicon thin film contains no hydrogen;

a laser annealing step of irradiating laser light on the amorphous silicon thin film directly with the vacuum state maintained continuously after formation of the amorphous silicon thin film without the need of dehydrogenation, thereby converting the amorphous silicon thin film into a polycrystalline silicon thin film;

a step of forming a gate insulating film and a gate electrode;

a step of doping to form the source and drain using the gate as a mask;

a step of patterning the gate insulating film and the silicon thin film;

a step of covering with an insulating film;

a step of making contact holes in the insulating film over the source and drain; and

a step of patterning signal wires on the insulating film.

2. A method of fabricating a thin film semiconductor device according to claim 1, wherein said physical vapor deposition step is a sputtering step of forming an amorphous silicon thin film by sputtering using a target made from a silicon crystal body or a silicon sintered body.

3. A method of fabricating a thin film semiconductor device according to claim 2, wherein said sputtering step is a step of forming an amorphous silicon thin film by sputtering using a target previously mixed with an impurity in a desired concentration, to introduce an impurity in the amorphous silicon thin film at the film formation stage, thereby previously controlling a threshold characteristic of a thin film transistor to be formed from a polycrystalline silicon thin film converted from the amorphous silicon thin film.

4. A method of fabricating a display, comprising:

a step of physically forming an amorphous silicon thin film on a first insulating substrate in vacuum of 10^-7 Torr or less, wherein said amorphous silicon contains no hydrogen;

a step of irradiating laser light on the amorphous silicon thin film directly with the vacuum state maintained continuously after formation of the amorphous silicon thin film without the need of dehydrogenation, thereby converting the amorphous silicon thin film into a polycrystalline silicon thin film;

a step of processing the polycrystalline silicon thin film thus converted, to integrally form thin film transistors comprising;

a step of forming a gate insulating film and a gate electrode;

a step of doping to form the source and drain using the gate as a mask;

a step of patterning the gate insulating film and the silicon thin film;

a step of covering with an insulating film;

a step of making contact holes in the insulating film over the source and drain;

a step of patterning signal wires on the insulating film; and

a step of forming pixel electrodes in a matrix in such a manner as to be connected to the individual thin film transistors;

a step of joining a second insulating substrate previously formed with a counter electrode to the first insulating substrate with a specific gap put therebetween; and

a step of disposing an electro-optic material in the gap.

5. A method of fabricating a display according to claim 4, wherein said step of physically forming is a sputtering step of forming an amorphous silicon thin film by sputtering using a target made from a silicon crystal body or a silicon sintered body.

6. A method of fabricating a display according to claim 5, wherein said sputtering step is a step of forming an amorphous silicon thin film by sputtering using a target previously mixed with an impurity in a desired concentration to introduce an impurity in the amorphous silicon thin film at the film formation stage, thereby previously controlling a threshold characteristic of a thin film transistor to be formed from a polycrystalline silicon thin film converted from the amorphous silicon thin film.