Ž . Thin Solid Films 383 2001 220223 Plasma oxidation of silicon using an electron cyclotron wave Ž . resonance ECWR oxygen plasma D.F. Lai  , J. Robertson, W.I. Milne Cambridge Uni  ersity Engineering Department, Cambridge CB2 1DQ, UK Abstract Ž . A high plasma density system, the electron cyclotron wave resonance ECWR has been used for the room temperature plasma oxidation of silicon. The oxidation efficiency, defined in terms of the ratio of initial growth rate to total anodisation current, is very high. The quality of the oxide as measured by refractive index, infra-red spectra and composition is compared to that of thermally grown silicon dioxide.  2001 Elsevier Science B.V. All rights reserved. Keywords: Plasma oxidation; Silicon dioxide; Electron cyclotron wave resonance 1. Introduction Ž . Active matrix liquid crystal displays AMLCDs re- quire gate insulators formed at low temperatures. Gen- erally, for amorphous silicon thin film transistors used in present AMLCDs, the gate insulator is silicon ni- tride which is formed by plasma deposition below 300°C. Recently, polycrystalline silicon transistors have been introduced for use as pixel switches and display drivers. These use silicon dioxide as the gate insulator. For SiO the choice is between the high quality thermally 2 grown oxide as used in microprocessors, or between various forms of plasma and chemical vapour deposi- tion at lower temperatures. The latter form oxide still with a considerable hydrogen content, which can lead to instabilities. There is also the possibility of the incorporation of impurities at the siliconoxide inter- face, as existing impurities stay at the interface when a deposited oxide is used. On the other hand, a grown oxide will have few impurities at the siliconoxide interface as the interface moves into the silicon as oxidation progresses. However, thermal oxidation has Ž . too large an activation energy 2.3 eV to be a realistic  Corresponding author. Ž . method for use at low temperatures sub-350°C and plasma oxidation must be used. There have been numerous studies of plasma oxidation using the mi- Ž . crowave-powered electron cyclotron resonance ECR sources. These have large magnetic fields and are suit- able for 8  12'' wafers used in microelectronics, but they are difficult to scale up to the 1 m sizes being used in displays and large area electronics. The ECWR has the advantage that it is an RF powered, high plasma density source, and so it could be scaled up for such use. Fig. 1 shows a schematic of the ECWR source used. The ECWR works on the basis of electron heating. A transverse magnetic field provided by a pair of Helmholtz coils modifies the plasma characteristics. By superimposing an electromagnetic wave along the mag- netic field, the electromagnetic wave is split into the right and left circularly polarised components, R wave and L wave, respectively. Because of the magnetic field, the dispersion relations of the R and L waves are different. The L wave experiences a ‘skin effect’ and   does not penetrate into the plasma 1,3,4 . The R wave meanwhile forms a standing wave across the source chamber allowing efficient transfer of energy to elec- trons within the plasma. The electron cyclotron waves are believed to transfer energy into the plasma bulk by 0040-609001$ - see front matter  2001 Elsevier Science B.V. All rights reserved. Ž . PII: S 0 0 4 0 - 6 0 9 0 00 01621-7