ABOUT MECHANISM OF SURFACE ROUGHNESS DEVELOPMENT ON POLY IMIDE FILMS DURING ANISOTROPIC ETCHING BY FAST ATOMIC OXYGEN

摘要

The problem of polymer films etching polyimide in particular by supersonic beam of atomic oxygen (at a mean velocity about 8 km/s) is of considerable interest for service life evaluation and prediction of polymer materials employed in space at low earth orbit. Fast atomic oxygen and sun"s radiation are known as the main factors which cause intensive polymer surface degradation and etching. The main aim of the paper is to reveal mechanism of carpet-like polyimide film surface topography development under bombardment by fast atomic oxygen beam with energy 2-4 eV and intensity 1E16 atoms/cm~2 at an angle between beam direction and normal to the film surface 30 degrees. Morphology and composition of individual protrusions or "hills" of polyimide carpet-like surface topography were studied by analytical electron microscopy and it was shown that at integral fluence of atomic oxygen 0,5E20 atoms/cm~2 the protrusions have mashroom-shaped structure. They consist of the cylinder "stem" 20-40 nm in diameter and 2 μm in height as well as the "cap" 30-50 nm in diameter and 20-30 nm thick on the top of the "stem". It is determined that the "caps" consist of amorphous diamond-like carbon which has higher resistance to etching by fast atomic oxygen compared to the origin polymer and graphite. An assumption is made that the "stems" etching by oxygen atoms scattered in the carpet-like layer cause the diamond-like "caps" separation and their transformation to dust particles.