Integration Challenges of Flash Lamp Annealed LTPS for High Performance CMOS TFTs

Abstract

This work demonstrates a method of producing polycrystalline silicon TFTs using Flash Lamp Annealing (FLA) as a potential industrial counterpart to excimer laser annealing. Material uniformity and low-temperature dopant activation are explored within an investigation on solid-phase epitaxial regrowth for PMOS TFTs. Silicon self-implantation is used to partially amorphize select regions of FLA LTPS material, allowing epitaxial regrowth to incorporate boron into the resulting lattice. This regime is compared with total amorphization, in which epitaxial regrowth cannot occur. The effects of these different methods of recrystallization are demonstrated through transfer characteristics of fabricated transistors. Devices utilizing a partial pre-amorphization of FLA LTPS demonstrated effective hole channel mobilities of 40 - 50 cm2/(Vs) in low drain bias operation. Additionally, self-aligned TFTs using FLA are presented for the first time, with effective hole channel mobilities of 30 - 60 cm2/(Vs) in low drain bias operation using the same treatment.

Flash Lamp Annealed Polycrystalline Silicon TFT Dependence on Surface Morphology and the Back-Channel Material Interface

“…Other research has focused on FLA as a candidate for microsecond dopant activation (5), (6) or material for photovoltaic applications (7), (8). This study builds off previous work in FLA polycrystalline silicon (FLAPS) TFTs that produced high mobility PMOS transistors (9), and was extended towards scalable and self-aligned device structures (10). The best-case devices in these experiments utilized a Si-ion self-implantation step during dopant introduction to aid in activation through epitaxial regrowth.…”

“…mask designed gate-source/drain overlaps), and demonstrates a peak hole mobility of 44.2 cm 2 /(Vs). Adapted from (10).…”

Edge-Directed LTPS Via Flash Lamp Annealing Using a Cr Adhesion Layer for Improved Wettability

“…ELA requires repeated laser pulses of a small and non-continuous laser spot, which must be scanned across the entire area to be crystallized. As the display industry trends towards 10.1149/09807.0131ecst ©The Electrochemical Society ECS Transactions, 98 (7) 131-139 (2020) larger, Gen 10+ substrates, the cost and logistics of this method become increasingly demanding.…”

Flash Lamp Annealed LTPS TFTs with ITO Bottom-Gate Structures

“…FLA (Flash lamp annealing) has been explored as an alternative to ELA LTPS (7), and has the potential to streamline and decrease the cost of fabrication while providing applicable electrical performance. In this method, amorphous silicon is exposed to a single pulse of light emitted from a xenon flash lamp, causing melting and recrystallization in an area of cm 2 rather than nm 2 in less than a millisecond.…”

“…The low wettability of liquid silicon on most low-absorption materials has often resulted in a crystallized material made of randomized voids and pathways, as shown in Figure 1a, with the density of voids proportional to the amount of energy absorbed during the anneal. Nevertheless, FLA has been used to realize functional devices such as shown in Figure 1b (7). Investigations on alternative material morphology are in progress (9).…”