Self-Aligned IGZO TFTs with Boron Implanted Source/Drain Regions

Abstract

This study investigates techniques to realize self-aligned Indium-Gallium-Zinc Oxide (IGZO) TFTs that are not subject to gate-source/drain misalignment due to overlay error or process bias. The working source/drain electrodes in IGZO TFTs can be direct metal contact regions to the IGZO, however this typically requires several microns of gate overlap in order to provide ohmic behavior with minimal series resistance and ensure tolerance to overlay error. Boron ion implantation has been demonstrated to successfully dope IGZO, resulting in an estimated electron concentration level n ~ 1019 cm-3. Top-gate co-planar TFTs were fabricated using boron implantation to selectively form IGZO:B n+ regions, with the channel region masked by the gate electrode. A novel lithographic strategy to extend this technique to the more traditional bottom-gate staggered TFT configuration has also been explored which utilizes top-side exposure rather than a back-side through-glass exposure, and would enable self-aligned devices on non-transparent substrates. Details of the self-aligned top-gate TFTs, and the top-side exposure lithographic process will be presented.

48‐2: Invited Paper: Advanced LTPO Technology for CMOS Driving

“…The channel length should be long enough to prevent hydrogen diffusion into the channel area. Recently, new studies have been reported to overcome this problem [10].…”

Performance Improvement of Self-Aligned Coplanar Amorphous Indium–Gallium–Zinc Oxide Thin-Film Transistors by Boron Implantation

“…In this study, we examined the electrical characteristics and stability properties of SA coplanar a-IGZO TFTs by B doping of the n + region using an ion implantation method. Although there have been studies on B implantation in a-IGZO TFTs, ,− we systematically analyzed the effects of the precisely controlled distribution of B in IGZO thin films on the electrical and reliability characteristics of IGZO thin films. Electrical, chemical, and physical characteristics were evaluated to gain insight into the conduction mechanism of B implantation.…”

Interpretation of Donor Activation in Boron and Argon Implanted Self-Aligned Bottom-Gate IGZO TFTs

“…Several techniques have been used to selectively form conductive IGZO regions including the introduction of hydrogen (1,2), plasma exposure (3) and ion implantation (4). We have recently presented an original investigation on the application of boron ion implantation for a self-aligned topgate (SA-TG) IGZO TFT (5). As an extension, the following work provides an interpretation of donor activation induced by ion-implantation of boron ( 11 B + ) and argon ( 40 Ar + ) species as the source/drain treatment applied to SA IGZO devices.…”

“…The bottom-gate staggered electrode configuration was used for this investigation, utilizing the opaque gate electrode as a mask for a through-wafer exposure of positive photoresist. This technique provides a perfectly aligned implant mask and averts charge accumulation on a floating metal top-gate during the ion implant process, which has been suspected of subjecting the gate dielectric to a high electric field and the creation of ionized defects (5). Utilizing an "implant-last" strategy, both boron and argon implanted SA bottom-gate (SA-BG) devices exhibited electrical characteristics consistent with non-SA devices, with minimal impact of added series resistance.…”