Paper PS1-WeA3
How Electron Density and Collision Rate Reflect the Properties of Chamber Wall and Substrate in IC Manufacturing

Wednesday, October 17, 2007, 2:20 pm, Room 606

Chemically active plasmas as every process plasma interact with the driven electrode and chamber wall. The wall and the electrode is heated and material as byproducts and material from the substrate condense preferably at the chamber wall. Without any additional influence, the parameters of the plasma reach an equilibrium, depending on the external parameters of the discharge as RF power. On the other hand the often used assumption that neutrals in a plasma have room temperature is quite questionable. Hence the indirect heating of the gas by the RF power was really underestimated despite this is one of the major reason of the so-called first wafer effect. There are two reason for the gas heating; the collision with fast ions in the boundary sheathes and the heating of chamber wall without proper 'thermal grounding' and a subsequent heating of the gas by the now hot surface of these chamber parts. Some authors have shown a significant increase of the gas temperature up to 1000 K in a RF plasma. The heat transmission resistances depends on the material, surface roughness, cleanliness and contact pressure. We will start at the experimental example of an increase of the surface temperature of the driven electrode at a 300 mm semiconductor production chamber with dual frequency excitation and the characterization of varying the torque of screws used for mounting. The temperature increase is characterized by the decrease of the electron collision rate. The collision rate, provided by the Self Excited Electron Resonance Spectroscopy, depends via the ohmic heating on the density of the neutrals and so finally on the gas temperature. Furthermore we will provide a qualitative discussion of the temperature effects, in particular resulting in a higher weight of stochastic heating mechanisms. The second example is the interaction of of an substrate, here a 300 mm wafer covered by mainly a polymer mask, an the plasma, in particular the electron collision rate. The interaction of plasma physical mechanisms as electron heating the plasma chemistry is analysed in the same way as indicated above.