Low temperature growth of silicon nitride by electron cyclotron resonance plasma enhanced chemical vapour deposition

Silicon nitride (a-SiN) is extensively used as the gate insulator layer in thin films transistors (TFTs) for active matrix liquid crystal displays. Such displays are currently produced on thin, glass substrates; plastic substrates offer a cheaper and more robust alternative, but have maximum process temperatures below 150 degreesC. The deposition of a-SiN by rf plasma enhanced chemical vapour deposition (PECVD) requires the production of SiNxHy radicals in the plasma. However, as N-2 is very stable, a gas mixture of SiH4 with NH3 is required for this to take place, which yields a hydrogen-rich material. High substrate temperatures (similar to 300 degreesC) are therefore required to drive out the excess hydrogen. In electron cyclotron resonance (ECR)-PECVD, a highly ionised plasma (similar to 10(16) m(-3)) with very low ion energies (similar to 10 eV) can be produced. This allows the dissociation of N-2 into atomic N, and hence a gas phase reaction can take place directly with SiH4, which results in a material with a lower hydrogen content than is obtained with NH:, gas. Energy for further PI removal is provided by the bombardment of He ions, allowing a reduction in the deposition temperature to 80 degreesC. In this way a-SiN has been produced with a resistivity of 3 x 10(14) Ohm cm and an average breakdown strength of 4.5 MV cm(-1). (C) 2001 Elsevier Science B.V. All rights reserved.