Simultaneous Activation and Crystallization by Low-Temperature Microwave Annealing for Improved Quality of Amorphous Silicon Thin-Film Transistors

Abstract

In this study, activation and crystallization in short channel amorphous Si TFTs were demonstrated using a novel microwave annealing (MWA) technique. Both low-temperature MWA and rapid thermal annealing (RTA) were compared to study the dopant activation level. We successfully activated the source/drain region, improved the electronic mobility and suppressed the short-channel effects using low temperature MWA. This can reduce the annealing temperature and processing time below that of solid phase crystallization (SPC). This technique is promising for realizing a high utility rate of AM-LCDs with low cost.The commercial success of active-matrix liquid-crystal displays (AM-LCDs) has attracted much research into the performance improvement of thin-film transistors (TFTs), which function as the pixel switches in AM-LCDs. Various materials have been investigated as candidates for high mobility channels, such as organic semiconductors, 1 amorphous silicon (α-Si), 2 and semi-conducing oxide. 3 Among these candidates, amorphous silicon has attracted much attention because of its wide range of applicability in large area electronics, lower cost and ease of fabrication. 4 Along with finding new materials, it is necessary to develop a low temperature fabrication process capable of producing high performance TFTs (e.g., high carrier mobility and low resistances at source and drain) using glass as a substrate. SPC of α-Si is a method for manufacturing poly-Si films with low cost and excellent uniformity. 5 Although some heatproof glass could accept annealing temperature over 600 • C, 6 it is generally considered to be harsh condition to use glass as the substrate material. In addition, laser annealing, rapid thermal annealing (RTA), and metal-induced crystallization have been also used as annealing techniques for recrystallization and dopant activation in the amorphous or implanted Si layer. While RTA achieves the best results for short durations of processing, the lamp photons are not only heating the Si layer but also stimulate unintended defect formations which cause dopant diffusion. 7 Metal-induced crystallization in the short channels leads to unwanted contaminations of the active regions. 8 Furthermore, MWA were demonstrated to process annealing with lower crystallization temperatures and short dwell times than the SPC process. 9,10 Therefore, the devices with MWA can reduce the impacts of punch-through, DIBL to obtain nano-scaled transistors with good short channel control. 11 In addition, this technique appears to be a promising replacement for RTA for the semiconductor industry. In this study, TFTs on the amorphous-Si films were fabricated using MWA. The MWA process can reduce the crystallization temperature of amorphous Si, lowering the thermal budget of the entire process while enhancing substrate applications. In addition, the shrinkage of the device size may enhance the aperture rate. ExperimentalA 6-in. (100) bulk silicon wafer was used as the starting material. After a 500 nm-thick silicon dioxide (SiO 2 ) laye...

Cutting properties of deposited amorphous silicon in ultra-precision machining

“…Three distinctive (1 1 1), (2 2 0) and (3 1 1) Bragg peaks are commonly observed in thermally [19] and microwave [1] annealed amorphous silicon with the preferred (1 1 1) orientation [1,19] as in figure 1. The integrated intensities (in arbitrary units) of (1 1 1) peak after the annealing at 600 and 700 °C were 438 and 610, respectively, indicating better crystallinity [20] for the film annealed at higher temper ature.…”

“…Amorphous silicon (aSi) films are widely used in thin film transistors (TFTs) for large displays [1]. They are suitable for optical devices, such as optical sensing [2], x-ray imaging [3], both based on TFTs, and wave guides [4], etc.…”

“…aSi films can be deposited by different techniques such as sputter deposition [6], low pressure chemical vapor deposition (LPCVD) [1], and plasma enhanced chemical vapor deposition (PECVD) [7], etc, in which hydrogen content can be controlled. They can be grown at different rates and thicknesses on silicon and non-silicon substrates [8], suitable for different applications [1][2][3][4][5], and potentially mechanically machined into micro lenses and other structures which require the thickness of silicon films in the range of a few micrometers to few tens of micrometers. The mentioned deposition techniques are the standard and cheap processes applied in the semiconductor industry.…”

Effects of Chamber Pressures on the Passivation Layer of Hydrogenated Nano-Crystalline Silicon Mixed-Phase Thin Film by Using Microwave Annealing

“…The effects are ascribed to the details of microwave absorption, which selectively affects Si-H bonds, and thus hydrogen bonds were restructured [31]. Some studies have reported microwave annealing in the thin-film coating technology [32][33][34][35]. The MWA has two major microwave heating processes: ohmic conduction and dielectric polarization losses, mainly influenced by the thickness and conductivity of the thin films; and the other is the dielectric permittivity of the thin film materials [36].…”

High‐Performance Solution‐Processed IGZO Thin‐Film Transistors with Al2O3/BN Composite Dielectrics Fabricated at Low Temperature

“…Furthermore, the portion of Al‐O bonding states in the films fabricated by microwave annealing was very similar to that in the films fabricated by thermal annealing at 400 °C, supporting the contention that high‐quality Al 2 O 3 /BN composite films can be achieved by microwave annealing at room temperature. Whereas thermal annealing provides thermally activated energy by heating conduction for a longer time during the sol‐gel process, microwave annealing supplies electronically excited energy by microwave absorption for a shorter time …”