C. S. Chang

Department of Physics, Korea Advanced Institute of Science and Technology (KAIST)
373-1 Kusongdong, Yusongku, Taejon, Korea 305-701
cschang@fusion.kaist.ac.kr

Result of several years of theoretical study at KAIST on Inductively Coupled Plasmas will be reported. Inductively coupled wave propagation into plasma from a planar type of antenna is studied together with self-consistent wave-particle interactions. Using a new periodic boundary technique, a general analytic expression for non-local electrical conductivity has been obtained, which is valid for arbitrary values of electron collisionality and antenna-to-wafer distance. In consideration of non-equilibrium nature of process plasma, effect of non-Maxwellian electron distribution on Bohm sheath condition is studied. It has been shown that the existence of non-Maxellian tail electrons do not change the Bohm speed, but modify the sheath potential. The most significant effect on the sheath is from the negative ions.

Based upon our theoretical investigation, a numerical simulation code has been built. This code adopt a circuit model to include most of the relevant physical phenomena self-consistently, which includes power coupling from RF source to plasma, time dependent sheath, plasma potential, RF bias on the wafer, etc. Surface interaction with wafer material is treated with Monte-Carlo method. A reasonably simple etch profile simulation is included in the code, with resulting ash components fed back into the plasma simulation. Even though the code can handle several different types of gas mixtures with reasonably fast computation speed, lack of reaction coefficients remains to be the main obstacle.

Effect of weak axial magnetic field on ICP plasma source is also investigated. It is found that a proper choice of magnetic field condition can enhance the power coupling significantly. Physical behavior of radical ions and neutrals, negative ions, and C/F ratio as function of external control parameters (ie., mixed gas flow rates, antenna and wafer RF powers, background pressure, etc) will be presented for selected gas mixtures.