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 3σ variation of silicon etch rate uniformity was 2.3% and for multiple 75 mm wafers with aluminum masks the 3σ 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 μm) trenches and holes were anisotropically etched in silicon and show approximately a 5% lower etch rate than large (>5 μm) features. For the relatively low microwave input power densities used, etch rates ranged from 40 to 140 nm/min as the SF6ratio ranged from 5% to 15%.