Abstract

Indium Gallium Zinc Oxide (IGZO) is an amorphous oxide semiconductor (AOS) being used in the display industry for backplane TFTs due to its superior mobility in comparison to hydrogenated amorphous silicon, as well as being compatible with the existing flat-panel manufacturing infrastructure. The ongoing research efforts primarily revolve around making the processing more robust so improved performance can be obtained and with greater consistency. The original proposed studies involved investigations on process options that promote enhanced passivation of defect states, and resistance to hydrogen plasma exposure to enable straightforward device integration schemes. However, during the beginning stages of experimentation there were problems identified that required a redirection of process development efforts. This work specifically focuses on adhesion issues with the sputtered source/drain metal bilayer in bottom gate (BG) TFTs, which has become a more frequent observation in recent process lots, mostly in peripheral (non-device) regions. Apart from the process integration issue this challenge poses, there was also the concern that the reduced electrical performance might be linked to this phenomenon. An initial blanket wafer peeling experiment led to the hypothesis that some organic chemical residue from the positive resist lithography processing contaminated the IGZO surface causing the poor interface between the two layers. Treatment results also suggested that water adsorption may also be an issue on an exposed IGZO surface. The proposed solution was to use an oxygen plasma treatment to remove any organic residue from the IGZO back-channel surface, immediately treat the wafer in HMDS vapor to render the surface hydrophobic, then process the wafers through the S/D lift-off lithography and sputter deposition processes within a short timeframe. The Trion Apollo ICP downstream plasma ash and oxygen RIE processes were investigated and found to promote metal adhesion on blanket wafers, though only the ICP ash treatment was successful at preventing peripheral peeling on device wafers. Unfortunately, these treatments resulted in some compromise in the TFT operation resulting in gate leakage and lower breakdown strength. Further, the device characteristics were affected by trap states indicating some inefficacy of the passivation steps. The challenge that remains is finding an effective treatment that supports metal adhesion while being gentle enough to avoid device degradation. Possible options for further investigation to resolve the metal adhesion issues are discussed, which would enable the return to the original focus areas.

Library of Congress Subject Headings

Thin film transistors--Materials; Indium gallium zinc oxide; Thin film transistors--Quality control

Publication Date

5-2024

Document Type

Thesis

Student Type

Graduate

Degree Name

Microelectronic Engineering (MS)

Department, Program, or Center

Electrical and Microelectronic Engineering, Department of

College

Kate Gleason College of Engineering

Advisor

Karl D. Hirschman

Advisor/Committee Member

Michael Jackson

Advisor/Committee Member

Jing Zhang

Campus

RIT – Main Campus

Plan Codes

MCEE-MS

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