A nozzle assembly used for performing gas cluster ion beam (GCIB) etch processing of various materials is described. In particular, the nozzle assembly includes two or more conical nozzles that are aligned such that they are both used to generate the same GCIB. The first conical nozzle may include the throat that initially forms the GCIB and the second nozzle may form a larger conical cavity that may be appended to the first conical nozzle. A transition region may be disposed between the two conical nozzles that may substantially cylindrical and slightly larger than the largest diameter of the first conical nozzle.