Thin film transistors on plastic substrates

• US 6,680,485 B1
• Filed: 02/17/1998
• Issued: 01/20/2004
• Est. Priority Date: 03/05/1996
• Status: Expired due to Fees

• Current Assignee: Lawrence Livermore National Security LLC (Government of the United States of America)
• Original Assignee: Regents of the University of California (University of California)
• Inventors: Carey, Paul G., Smith, Patrick M., Sigmon, Thomas W., Aceves, Randy C.
• Primary Examiner(s): TRAN, THIEN F
• Application Number:
  US09/025,006
• Time in Patent Office: 2,163 Days
• Field of Search: 257/57, 257/64, 257/67
• US Class Current: 257/57
• 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 21/02686 Pulsed laser beam
• CPC Class Codes: H01L 21/268 using electromagnetic radiation, e.g. laser radiation
• CPC Class Codes: H01L 27/1214 comprising a plurality of TFTs formed on a non-semiconducting substrate, e.g. driving circuits for AMLCDs
• CPC Class Codes: H01L 27/1285 using control of the annealing or irradiation parameters, e.g. using different scanning direction or intensity for different transistors
• CPC Class Codes: H01L 29/66757 Lateral single gate single channel transistors with non-inverted structure, i.e. the channel layer is formed before the gate
• CPC Class Codes: H01L 29/78603 characterised by the insulating substrate or support H01L29/78657 takes precedence
• CPC Class Codes: H01L 29/78666 with normal-type structure, e.g. with top gate
• CPC Class Codes: H01L 29/78675 with normal-type structure, e.g. with top gate

Abstract

A process for formation of thin film transistors (TFTs) on plastic substrates replaces standard thin film transistor fabrication techniques, and uses sufficiently lower processing temperatures so that inexpensive plastic substrates may be used in place of standard glass, quartz, and silicon wafer-based substrates. The silicon based thin film transistor produced by the process includes a low temperature substrate incapable of withstanding sustained processing temperatures greater than about 250° C., an insulating layer on the substrate, a layer of silicon on the insulating layer having sections of doped silicon, undoped silicon, and poly-silicon, a gate dielectric layer on the layer of silicon, a layer of gate metal on the dielectric layer, a layer of oxide on sections of the layer of silicon and the layer of gate metal, and metal contacts on sections of the layer of silicon and layer of gate metal defining source, gate, and drain contacts, and interconnects.

Claims

1. A thin film transistor, consisting of

a substrate composed of low-temperature plastic,

said low-temperature plastic substrate being not capable of withstanding sustained processing temperatures greater than about 250°

C.

an insulating layer of SiO₂ on the plastic,

a layer of silicon on the insulating SiO₂ layer, said layer of silicon being composed of sections of doped silicon and undoped silicon,

said layer of silicon including sections of poly-silicon,

a gate dielectric layer of SiO₂ on at least a section of the layer of silicon,

a layer of gate metal on at least a section of the gate dielectric layer of SiO₂,

a layer of oxide on sections of said layer of silicon and said layer of gate metal, and

metal contacts on sections of said layer of silicon and said layer of gate metal, defining source, gate, and drain contacts and interconnects.

2. The thin film transistor of claim 1, wherein said undoped silicon is poly-silicon or amorphous silicon.

3. The thin film transistor of claim 1, wherein said low-temperature plastic is selected from the group consisting of PET, E-CTFE, E-TFE, PES, PTFE, FEP, and HDPE.

4. The thin film transistor of claim 1, wherein said layer of gate metal is selected from the group consisting of Al, Cu, Mo, Cr, Ta, W, Ni, Ti, Si, Ti—

Si, Al—

Si, Al—

Cu, Ti—

Al, and silicides.

5. The thin film transistor of claim 1, wherein said metal contacts are composed of metal selected from the group consisting of Al, Cu, Mo, Cr, Ta, W, Ni, Ti, Ti—

Si, Al—

Si, Al—

Cu, Ti—

Al, and suicides.

6. The thin film transistor of claim 1, wherein said sections of doped silicon comprise a dopant selected from the group consisting of phosphorous, boron, and arsenic [PF₅, BF₃, B₂H₆, and AsF₅].

7. A silicon based thin film transistor, consisting of:

a substrate composed of plastic incapable of withstanding processing temperatures greater than 250°

C.,

an insulating layer on the plastic substrate,

a layer of silicon on the insulating layer, said layer of silicon including sections of doped silicon, undoped silicon, and poly-silicon,

a gate dielectric layer on at least a section of the layer of silicon,

a layer of gate metal on at least a section of the gate dielectric layer,

a layer of oxide on sections of said layer of silicon and said layer of gate metal, and

metal contacts on sections of said layer of silicon and said layer of gate metal defining source, gate, and drain contacts, and interconnects.

8. The thin film transistor of claim 7, wherein said undoped silicon is selected from the group of poly-silicon and amorphous silicon.

9. The thin film transistor of claim 7, wherein said insulating layer is composed of material selected from the group consisting of SiO₂, SiN, and polyamide.

10. The thin film transistor of claim 7, wherein said gate dielectric layer is composed of material selected from the group consisting of SiO₂, SiN, and polyamide.

11. The thin film transistor of claim 7, wherein said layer of gate metal is composed of metal selected from the group consisting of Al, Cu, Mo, Cr, Ta, W, Ni, Ti, Si, Ti—

Si, Al—

Si, Al—

Cu, Ti—

Al, and silicides.

12. The thin film transistor of claim 7, wherein said metal contacts are composed of metal selected from the group consisting of Al, Cu, Mo, Cr, Ta, W, Ni, Ti, Ti—

Si, Al—

Si, Al—

Cu, Ti—

Al, and silicides.

13. The thin film transistor of claim 7, wherein said plastic substrate is composed of material selected from the group consisting of PET, E-CTFE, E-TFE, PES, PTFE, FEP, and HDPE.