ANISOTROPIC ETCHING OF SUBMICRON SILICON FEATURES IN A 23 CM DIAMETER MICROWAVE MULTICUSP ELECTRON-CYCLOTRON-RESONANCE PLASMA REACTOR

The performance of a large diameter, 2.45 GHz multicusp electron-cyclotron-resonance (ECR) plasma etching system with regard to etch rate uniformity and submicron pattern definition in silicon is described. Results are compared to earlier work on a similar system operated at 915 MHz. The plasma source utilizes a 23 cm diam discharge and a 12-pole static magnetic field geometry to create multicusp ECR zones in the plasma excitation region. Microwave excitation at 2.45 GHz with power levels up to 600 W is used to excite discharges for etching of single 125 mm diam wafers and multiple 75 mm diam wafers. For single 125 mm wafers with oxide masks the 3-sigma variation of silicon etch rate uniformity was 2.3% and for multiple 75 mm wafers with aluminum masks the 3-sigma variation was 8.1% over a 150 mm diam. Vertical anisotropic etching was obtained both at the center of the wafers and the peripheries. Etch profiles were evaluated as a function of position on the substrate and no substantial positional or orientation effects were observed. Microloading effects appear small for both oxide and aluminum masks. Submicron (0.6-mu-m) trenches and holes were anisotropically etched in silicon and show approximately a 5% lower etch rate than large (> 5-mu-m) features. For the relatively low microwave input power densities used, etch rates ranged from 40 to 140 nm/min as the SF6 ratio ranged from 5% to 15%.