Effective annealing and crystallization of si film for advanced TFT system
Abstract The effect of the crystallization and activated annealing of Si films using an excimer laser and the new CW blue laser are described and compared with furnace annealing for application in advanced TFTs and for future applications. Pulsed excimer laser annealing (ELA) is currently being used extensively as a low‐temperature poly‐silicon (LTPS) process on glass substrates as its efficiency is high in the ultra‐violet (UV) region for thin Si films with thickness of 40–60 nm. ELA enables extremely low resistivity relating to high crystallinity for both the n‐ and p‐type Si films. On the other hand, CW blue laser diode annealing (BLDA) enables the smooth Si surface to have arbitral crystal grains from micro‐grains to an anisotropic huge grain structure only by controlling its power density. Both annealing techniques are expected to be applied in the future advanced TFT systems.
Advanced Excimer Laser Annealing of Thin Poly Si Films after Solid Phase Grain Growth
Thin silicon films with dendritic large grains can be obtained by Si + or P + implantation and subsequent low temperature annealing of the silicon film. We tried further exposing the films with an excimer laser after the grain growth. As a result, improvement of electronic properties such as high carrier mobility or low resistivity were obtained. By TEM observation, polycrystalline grains with a dendritic structure did not melt after laser annealing and it was found that the improvement of electronic properties were achieved mainly due to the improvement of crystallinity by U-V(Ultra-Violet) reflectance, ESR(Electron Spin Resonance) analysis and TFT characteristics. We are convinced that this advanced laser pulse annealing method is an ideal RTA process in the near future and is expected to be applicable to ULSI processes for inter connects, high density stacked SRAM and for large area electronics on glass such as a contact line sensor or LCD(Liquid Crystal Display).
Principles of Solidification
Solidification, in the sense used in this context, is the process by which a liquid is transformed into a crystalline solid. In crystal growth the solid that forms first is solvent rich as distinct from crystallisation, in which the crystals that are formed are solute rich. It is not always possible to make a clear distinction. Solidification is important as the process employed in the widely used process of casting, in all its forms from large ingots of steel to small crystals of silicon. While in principle it would seem simple to convert a homogeneous liquid into an equally homogeneous perfect crystal, this is extremely difficult, if not impossible to achieve in practice. Thorough understanding requires that the process be studied at various levels, which can be conveniently described as the angstrom level, the micron level and the centimetre level.