John M. White

High mobility amorphous zinc oxynitride semiconductor material for thin film transistors

Zinc oxynitride semiconductor material is produced through a reactive sputtering process in which competition between reactions responsible for the growth of hexagonal zinc oxide (ZnO) and for the growth of cubic zinc nitride (Zn3N2) is promoted. In contrast to processes in which the reaction for either the oxide or the nitride is dominant, the multireaction process yields a substantially amorphous or a highly disordered nanocrystalline film with higher Hall mobility, 47 cm2 V−1 s−1 for the as-deposited film produced at 50 °C and 110 cm2 V−1 s−1 after annealing at 400 °C. In addition, it has been observed that the Hall mobility of the material increases as the carrier concentration decreases in a carrier concentration range where a multicomponent metal oxide semiconductor, indium–gallium–zinc oxide, follows the opposite trend. This indicates that the carrier transports in the single-metal compound and the multimetal compound are probably dominated by different mechanisms. Film stability and thin film tran...

The Latest Plasma-Enhanced Chemical-Vapor Deposition Technology for Large-Size Processing

The thin-film transistor liquid crystal display (TFT-LCD) industry has in recent years demanded ever-larger- area substrate processing capability to keep up with consumer market demands for larger and larger displays. This paper discusses the latest plasma-enhanced chemical-vapor deposition (PECVD) system, the AKT 50 K PECVD, which handles up to 2160 x 2460 mm2 substrates. As substrate size increases, lowering the processing temperature is getting even more important to improve production reliability and cost performance. The most commonly used process temperature for the so-called active layers of amorphous silicon (a-Si) TFTs is approximately 350 degC. In this paper, a newly developed single-chamber low-temperature PECVD active-layers process is discussed. In particular, our low-temperature process maintains film performance at the same level as high-temperature active layers while also maintaining system productivity and throughput.

Large Area PECVD Technology

With ever-increasing growth of the flat panel display and its commercial success in the large area TV market, a high productivity PECVD tool has been essential to meet the requirements of film quality and system throughput. TFT-LCD industry has been scaling up substrate sizes every 2 years in the past 15 years and the increase of the size over the span is about 50 times as shown in Figure 1. Over the period, AKT has been making a significant and unparalleled contribution to the TFT-LCD industry in particular for continuous reduction of cost per area for the display by meeting the scaling rule intact thereby maintaining throughput all over the generations. AKT PECVD systems are capable of processing multiple substrates in a cluster tool for depositing amorphous-Si, doped amorphous-Si, microcrystalline-Si, SiNx, SiON and SiOx films, based on 13.56MHz RF parallel plate reactor. Figure 2 shows the basic schematic of AKT process chamber design and mechanism of depositions and chamber dry cleaning.

Amorphous-silicon thin-film transistor on soda-lime glass

— Amorphous-silicon (a-Si:H) thin-film transistors (TFTs) on soda-lime glass were fabricated by using a diffusion barrier and a low-temperature process at 200°C. The silicon nitride barrier was optimized in terms of diffusion blocking effectiveness, film adhesion, and surface finish. TFTs on soda-lime glass achieved a saturation mobility 0.47 cm2/V-sec, threshold voltage of 0 V, an off-current of 7.7×10−11 A, and a sub-threshold swing of 1.0 V/dec. From diffusion experiments, a 30,000-hour lifetime for the TFT device at 80°C was estimated, and the robustness of the silicon nitride barrier against long-term migration of sodium was demonstrated.

P-74: Low Temperature a-Si TFT on Soda Lime Glass

Replacing the current non-alkali glass with soda lime glass can significantly reduce the cost of the current TFT-LCD module. One key step in manufacturing is to make TFT backplane on soda lime glass substrate. In this work, we demonstrate low temperature a- Si thin film transistor (TFT) at 200°C on soda lime glass. with the use of SiNx barrier to prevent sodium contamination, we show the TFT properties can be improved significantly and achieve TFT of saturation mobility 0.47cm2/Vs, threshold voltage 0V, off current 77×10−11 A, sub-threshold swing 1.0 V/dec. We also show that our TFT device has comparable or better threshold voltage stability as compared to those made in non-alkali glass. Finally, we show the robustness of SiNx barrier against long term sodium migration.