Developmental Study of Highly-Uniform Large-Diameter ECR Plasma Reactor

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The purpose of this research is to develop a large diameter electron cyclotron resonance (ECR) plasma source for high-speed processing of 12 inch wafers. We have constructed a multi-annular (MA) antenna which consists of a concentric array of annular slits for microwave irradiation and of permanent magnets for multi-ring cusp magnetic field. The microwave at 2.45 GHz is fed via coaxial line and is distributed into the annular slits to encounter the ECR layr located 5 mm beyond the exit of the slits. Charged particles drift in azimuthal direction in the multi-ring cusp field. This leads to azimuthally symmetric plasma production. The microwave propagates from the slit to the ECR layr from high magnetic field side as R-waves. It is noted that the plasma is not produced inside the slits because the loss rate of charged particles is large due to proximity of slit walls.The plasma source using this MA antenna has produced a plasma of 30 cm in diameter with density n = 2*10^<11>cm^<-3> for Ar gas pressure 5*10^<-4> Torr. We measured plasma parameters by changing the number of the slits to find that the uniformity of the plasma is best for one slit at the outermost location. The uniformity is *10% for 30 cm diameter plasma with n = (8-10)*10^<10>cm^<-3> at 10 cm from the MA antenna. This result is consistent with a numerical calculation of the equation of continuity assuming an initial source profile determined by the slits.The MA antenna has been improved to AMA (adjustable MA) antenna, which has two annular slits at r =140 and 90 mm. Each slit is driven by a magnetron independently. This means that the radial profile of microwave power input is adjustable by simply changing the outputs of two magnetrons. By using AMA antenna, we have achieved plasma production with higher density, higher uniformity at shorter distance from the antenna.