EFFECT OF H-2 ADDITION ON SURFACE-REACTIONS DURING CF4 H-2 PLASMA-ETCHING OF SILICON AND SILICON DIOXIDE FILMS/

In situ multiple internal reflection Fourier transform infrared spectr oscopy and spectroscopic ellipsometry are used to study the surfaces o f Si and SiO2 films during etching with CF4/H-2 plasmas. At sufficient ly low H-2 concentration, a thin fluorocarbon film forms on both Si an d SiO2 surfaces during etching, but Si and SiO2 removal continues desp ite the existence of such a layer. The structure of this film depends on the H, concentration in the feed gas. Above a critical H-2 concentr ation, the fluorocarbon film becomes more crosslinked, fluorine defici ent, and amorphous carbonlike. Formation and subsequent growth of this fluorinated amorphous carbon (alpha-C:F) film stops etching of both S i and SiO2. In the absence of energetic ion bombardment, the critical concentration at which etching is arrested and alpha-C:F growth begins is the same for both Si and SiO2 films indicating that whether this f ilm forms or not is determined by the fluxes of reactive species arriv ing at the surface from the gas phase rather than by the nature of the surface. In particular, H abstraction of F from tile fluorocarbon fil m is shown to be responsible for the formation of fluorine deficient a morphous carbonlike film. In the presence of energetic ion bombardment this critical H-2 concentration is increased but at different amounts for Si and SiO2 films. The film formed 2 on SiO2 is more easily sputt ered than that which forms on Si due to the higher number of C-O bonds in the film formed on SiO2. The difference in the structure of the in hibiting layers formed on Si versus SiO2 enables the selective etching of SiO2 over Si. (C) 1997 American Vacuum Society.