The present invention comprises a dynamic brake that applies restraining frictional force to a wafer in a wafer holder while the wafer holder is substantially at rest, but releases the restraining force as the processing carousel containing several wafer holders rotates about a central axis of the carousel. This dynamic brake preferably comprises a boot that passes through an opening in the wafer holder to rest on the surface of the wafer in an exclusion zone near the wafer's edge. The exclusion zone is typically no more than about 3mm in extent. The frictional force between the boot and wafer is sufficient to prevent unwanted motion of the wafer in the holder. As the wafer holder rotates about a central axis of the processing carousel, centrifugal forces applied to the brake arising from such rotation cause the boot to pivot upward, releasing the frictional force on the wafer.