Paper PS2-WeM11
Investigating Fundamental Etch Limits: Molecular Dynamics Simulations of Sub-10 nm Feature Fabrication

Wednesday, October 17, 2007, 11:20 am, Room 607

As semiconductor devices are continually scaled down in size, individual device features are approaching the molecular scale. Fundamental knowledge of the mechanisms of the etch process at very small scales will be necessary to effectively design future etch-enabled pattern transfer schemes. Additionally, it is currently unclear how small features can be made using conventional processing methods. Molecular dynamics (MD) simulations have been carried out to examine the fundamental characteristics of etching very small features on silicon and diamond carbon surfaces. These features are created in simulation through bombardment of surfaces by idealized ion and radical beams (i.e. with perfectly controlled confinement, directionality, and energy). For very small beam diameters (less than 2 nm) a novel mode of hole formation is seen in MD in which the substrate atoms are displaced laterally by the ion beam, but not sputtered. This results in uniform holes with high aspect ratios and the formation of a densified, amorphized region laterally surrounding the hole. Lateral densification occurs from atoms that have been displaced from the hole void region during bombardment. As the beam diameter is increased to ~2 nm and beyond, sputtering is seen with yields comparable to those at steady state on bulk flat surfaces. The effects of redeposition on the side walls of the hole in relation to hole uniformity, achievable aspect ratios, and other feature characteristics are discussed. The effects of ion mass, quality of beam confinement, and the dynamics of ion-surface collisions are also addressed. The addition of chemistry to the inert ions (fluorine and fluorocarbon radicals and ions) is also discussed, and its effects on the hole formation processes are illustrated.