The demand for lower cost per panel in TFT-LCD production is driving the PECVD market to deposition systems that combine high throughput and uptime with high yield. Today it is generally believed that a multichamber system that combines a number of single-panel deposition chambers is the best way to achieve these goals.
For these PECVD systems to be economical, the deposition rate of a-Si:H, SiNx and SiO2 has to be in the 1200–1500 Å/min range. In 13.56 MHz parallel-plate glow discharge systems SiNx and SiO2 deposition rates exceeding 1500 Å/min are commonly achieved, whereas the deposition rate of a-Si:H is limited to 100–200 Å/min due to powder formation. Over the last 5 years significant progress has been made to increase the deposition rate of a-Si:H. Methods include the use of very-high-frequency glow discharge (VHF-GD) and pulsing of the rf discharge. However, substrate sizes never exceeded 100mm×100mm.
We have developed a multichamber PECVD system for TFT-LCD production where VHFGD is used to obtain uniform high deposition rates for (doped) semiconductors and insulators, such as a-Si:H, n+ a-Si:H, SiNx and SiO2 over areas as large as 470mm×370mm. Even at deposition rates well above 1200 Å/min hydrogen in a-Si:H is exclusively bound as monohydride. The optoelectronic properties of the films are at least as good as those of their 13.56 MHz counterparts and thus good-quality TFTs can be obtained. At the same time the number of added particles is low allowing for high production yields.