Experimental performance of a large-diameter multipolar microwave plasma disk reactor

Abstract

Microwave electron-cyclotron-resonance (ECR) discharges have demonstrated excellent potential for single-wafer etching and thin-film deposition. An important technical challenge is concerned with controlling uniformity of processing over large surfaces with high processing rates and minimal damage. The ability to scale microwave plasma disk reactor (MPDR) ECR discharges to large diameters is reviewed and the design and experimental performance of two plasma sources with discharge diameters of 20–25 cm is described. These ECR plasma sources make use of a 12- or 14-pole multipolar static magnetic field geometry enclosed in a 36- or 45-cm cylindrical MPDR. Microwave excitation of 200–1000 W is applied either as a single-mode applicator at 915 MHz or with a controlled multimode excitation at 2.45 GHz. The ECR discharge diffuses into a multipolar, magnetically confined processing chamber producing a uniform, low-energy plasma for processing. The processing chamber plasma density is characterized by double-probe measurements. These measurements indicate that plasma densities in excess of 1011 /cm3 are easily achieved with as little as 1000 W and large-diameter excitation produces uniform densities with less than 3% standard deviation over 15–20 cm diam. Experiments with three wafers placed on an 18-cm-diam wafer holder also indicate uniform etching. Using a SF6 /Ar plasma to etch silicon resulted in a standard deviation of 2.9% in etch depth over a 15-cm-diam region on the wafer holder.