243S2009-09-soln

243S2009-09-soln - N.CHEUNG,Sp 2009 EE243 Homework#9...

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N.CHEUNG,Sp 2009 EE243 Homework #9 Solutions Problem 1 (i) Low pd product Gas density is low and inter-electrode spacing is small Electron hits electrodes before they have a chance to ionize gas. Higher applied voltage (i.e., higher E-field) is needed to initiate plasma. High pd product Higher gas pressure. Many collisions but electrons do not acquire high enough energy to overcome threshold for ionization. High applied voltage is required. Problem 2 (a) d= 2.5 mm C = 1 pF/cm 2 J=1mA/cm 2 V=1000V From C= Q/V , Q = 10 -9 Coulombs/cm 2 J= Q/t , t = 10 -6 sec (b) A typical RF frequency ( f =1/t) > 1 MHz can create a net surface charge transfer =0 at steady state . Problem 3 (i) Large loading effect will reduce the fluorine radicals in the plasma. This effectively reduces the F/C ratio and gives lower etching rate. (ii) SiO 2 is considered to be an oxygen source when etched. When oxygen is present in the gas mixture, the C concentration will be lowered. The effective F/C ratio will increase and the tendency for polymerization to occur is reduced. Another thoery (Coburn et al) states that CF
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243S2009-09-soln - N.CHEUNG,Sp 2009 EE243 Homework#9...

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