Methods to fabricate thin film transistors and circuits

• US 6,225,149 B1
• Filed: 05/03/1999
• Issued: 05/01/2001
• Est. Priority Date: 05/03/1999
• Status: Active Grant

• Current Assignee: McGill University
• Original Assignee: Feng Yuan Gan, Ishiang Shih
• Inventors: Shih, Ishiang, Gan, Feng Yuan
• Primary Examiner(s): Elms, Richard
• Assistant Examiner(s): Wilson, Christian D.
• Application Number:
  US09/303,743
• Time in Patent Office: 729 Days
• Field of Search: 438/151, 438/492, 438/497, 438/500
• US Class Current: 438/151
• CPC Class Codes: H01L 29/66765 Lateral single gate single channel transistors with inverted structure, i.e. the channel layer is formed after the gate
• CPC Class Codes: H01L 29/78609 for preventing leakage current H01L29/78618 takes precedence

Abstract

A method for fabricating a thin film field effect transistor is described in this invention. The active layer of the thin film transistor (TFT) is formed by a low cost chemical bath deposition method. The fabrication procedure includes deposition of a metal layer on an insulating substrate, patterning of the metal layer to form a metal gate, formation of the di-electric layer, deposition of the active layer and formation of source and drain contacts.

Claims

1. A low cost method for fabricating a plurality of thin film field effect transitors and circuits with high mobility on a substrate, the method comprising the steps of;

depositing and patterning a first metal layer to form at least one gate electrode;

forming a thin dielectric layer on each of said gate electrodes;

preparing a chemical deposition bath and controlling temperature of said chemical deposition bath;

depositing a first semiconductor layer by a chemical bath deposition method in said chemical deposition bath;

patterning and etching said first semiconductor layer to form at least one active channel;

depositing and patterning a second metal layer to form a drain and a source for each of said thin film transistors; and

heat treating at an elevated temperature either in vacuum or in an inert atmosphere.

2. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, wherein electronic quality of said first semiconductor layer is controlled by adjusting the chemical composition and temperature of said chemical deposition bath.

3. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, wherein electronic quality of said first semiconductor layer is controlled by adjusting the temperature of said chemical deposition bath to a value in the rage from 15°

C. to 95°

C.

4. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, wherein electronic quality of said first semiconductor layer is further controlled by adjusting the pH value of said chemical deposition bath to a range from 10 to 13.

5. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, wherein material of said first semiconductor layer is selected from a group comprising of CdS, CdSe, ZnS, ZnSe and CdTe.

6. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, wherein said thin dielectric layer on said gate electrode is selected from a group comprising of Ta₂O₅, TaO_x and Al₂O₃, and formed by an anodization method.

7. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, wherein said thin dielectric layer on said gate electrode is selected from a group comprising of SiO₂, SiN_x, Si₃N₄, TiO₂, Ta₂O₅, TaO_x and Al₂O₃, and formed by a chemical vapour deposition method.

8. A low cost method for fabricating thin film field effect transistors and circuits with high mobility on a substrate in claim 1, further comprising a step of passivating surfaces of said thin film transistors and circuits by applying a passivation layer, materials of said passivation layer being selected from a group comprising of SiO₂, SiN_x, Si₃N₄, Al₂O₃ and polyimide.