281
Mater. Res. Soc. Symp. Proc. Vol. 1426 © 2012 Materials Research Society
DOI: 10.1557/opl.2012.
A Comparative Study on the Activation Behavior of Implanted Boron
and Phosphorus for LTPS Using Solid-Phase Crystallization
Qinglong Li
1
, Tarun Mudgal
1
, Patricia M. Meller
1
, Seth Slavin
1
, Robert G. Manley
2
and Karl D. Hirschman
1
1
Department of Electrical and Microelectronic Engineering, Rochester Institute of Technology,
82 Lomb Memorial Drive, Rochester, NY 14623
2
Science and Technology Division, Corning Incorporated, SP-PR-02, Corning, NY 14831
ABSTRACT
This work presents a study on the activation behavior of high-dose (I > 10
15
cm
-2
) boron
and phosphorus implants for low resistance source and drain regions for thin-film transistors
(TFTs) fabricated using solid-phase crystallization (SPC) of amorphous silicon. Process
variables include factors associated with ion implant and annealing conditions, as well as the
SPC and implant process arrangement. Four-point probe sheet resistance (Rs) measurements
were used as a comprehensive assessment of the electrical properties. Results have identified
similarities and differences in activation behavior that can influence process integration
strategies considering both the SPC approach and TFT fabrication.
INTRODUCTION
Low-temperature polysilicon (LTPS) has emerged as a dominant technology for high
performance TFTs used in mobile LCD and OLED display products. Most of the current LTPS
technology utilizes excimer-laser annealing (ELA) of a-Si [1, 2], however there are challenges in
scaling ELA techniques for backplane manufacturing on large glass panels. Solid-phase
crystallization (SPC) offers an alternative method of forming LTPS without the limitations and
complexity of ELA [3-6]. Recent interest in using LTPS for large-format displays has provided
the motivation to develop process enhancements for improved SPC-LTPS transistor
performance. Ion implantation is typically used for boron and phosphorus dopant introduction in
top-gate LTPS for self-aligned source/drain implants. This work presents an investigation on
SPC-LTPS using boron and phosphorus ion implantation and furnace annealing processes.
EXPERIMENT
Substrate preparation involved the deposition of hydrogenated amorphous silicon (a-Si:H)
using a PECVD process on 150 mm diameter Corning EAGLE XG® display glass wafers with a
100 nm SiN
X
barrier layer and a 250 nm SiO
2
buffer layer. The deposition was performed using
SiH
4
and H
2
at 400 °C, 1 Torr pressure and 30 W RF power. Deposition time was adjusted to
provide silicon film thicknesses (X
Si
) of either 60 nm or 100 nm. A dehydrogenation anneal was
then done at 450 °C for 2 hours at 200 mTorr. The experiments were divided into two parts.
Part-I was designed to investigate the influence of the implant and anneal process arrangement
on the activation of heavily doped boron and phosphorus, and Part-II was a refined experiment to
further the investigation on the influence of the impurity concentration profile within the
deposited silicon layer.
1311