Low-Temperature Deposition of Hydrogenated Amorphous Silicon in an Electron Cyclotron Resonance Reactor for Flexible Displays

Electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) is investigated as a technique for depositing hydrogenated amorphous silicon (a-Si : H) at a temperature of 80°C, which is compatible with the use of transparent, plastic substrates. The ECR-PECVD reactor is described and the principles underlying its operation explained. In particular, the factors controlling the deposition of a-Si : H by this technique are investigated, and it is shown that control of gas phase reactions between silane and hydrogen species is essential. High-quality a-Si : H is deposited in a narrow processing window with a photosensitivity greater than 10⁶. Thin-film transistors (TFTs) fabricated at 125°C incorporating low-temperature a-Si : H as the channel layer have a switching ratio of almost 10⁵. With further optimization of the other material layers, such TFTs could be used for the active matrix transistors in flexible liquid crystal displays on plastic substrates.