Mask-edge effects at low ion implantation energies for cluster covered silicon

Clusters of independently tailored areal density and size distribution were grown on semiconductor surfaces by molecular beam epitaxy and were used su bsequently as masks for selective ion beam modification. Field emission sca nning electron microscopy shows sharp interfaces between the amorphous area exposed to ion beams and areas of crystalline silicon covered by clusters. Partial etching of the substrate leads to narrow trenches around the initi al cluster site, suggesting significantly enhanced etching near the amorpho us-crystalline interface. The results are explained on the basis of a sligh t density variation in the substrate near the cluster periphery due to a br eak in symmetry of the recoil atom incorporation. Computer simulations were carried out to further characterize these results, using a program based o n the well-established TRIM code to model atomic collision cascades in a ma trix. The resulting density distributions correlate well with the experimen tally observed wet etching patterns, strongly suggesting a relation between cluster-masking related density variations in the amorphized silicon and t he etching rate. (C) 1999 Elsevier Science B.V. All rights reserved.