GENERATION AND RELIEF OF MECHANICAL STRESSES IN ION-IRRADIATED SIC AND SIO2

We have investigated the generation and relief of mechanical stresses in 6H-SiC and in alpha-quartz during bombardment with 50 keV Ne- and N a-ions at 77 K as a function of the applied ion fluence, by measuring the curvature change of the samples utilising mechanical surface profi ling (MSP). In addition, the irradiation induced damage was depth prof iled by means of Rutherford Backscattering Spectrometry in Channeling geometry (RBS-C). Density alterations could be deduced by combining th e results on surface swelling obtained by MSP with the thickness of th e ion beam modified layer observed with RBS-C. Bombardment with ion fl uences below a critical fluence phi(c), (nucleation regime) results in the accumulation of defect agglomerates and/or small amorphous zones in a still crystalline surrounding. At phi(c), a coherent amorphous la yer has formed, buried at the depth of maximum energy deposition. Furt her irradiation at higher fluences results in the growth of this layer perpendicular to the surface (growth regime). In the nucleation regim e, strong compressive stresses of the order of 1.5-3 GPa are generated by the excess volume of the defect agglomerates. Only small volume sw elling could be detected in this regime. After the amorphous layer ext ends to the surface, slow release of the compressive stresses could be observed, which was completed after application of phi = 3 phi(c), (S iC) and phi = 10 phi(c), (SiO2), respectively. The stress relaxation i s accompanied by strong volume swelling perpendicular to the surface a nd a continuous decrease of the atomic density by up to about 20%. At still higher fluences, further growth of the amorphous layer occurs at reduced, but constant density. (C) 1998 Elsevier Science B.V.