ETCHING PROFILES AND NEUTRAL SHADOWING IN LONG TRENCHES

The neutral flux in the plasma etching of semiconductor wafers or orga nosilicon planarizing layers has been derived analytically for a simpl e model for a long rectangular trench. The neutral molecules obey a Ma xwellian distribution function and mutual collisions are neglected in the trench. Scattering of the neutrals with the sidewalls and trench b ottom is ignored. The two-dimensional flux vector which is given at ea ch point on the etching profile surface is a function of the local asp ect ratio, the lateral ratio, the density (concentration) of the neutr al molecules and their thermal speed. The flux vector reduces to the e xpression previously determined at the center of the trench. Etching p rofiles of the trench are displayed for a photoresist that is etched a nd one that is not by applying the method of characteristics to the ev olution equation of the trench etch profile.