Low energy silicon etching technologies

Abstract

Low energy Si etching technologies developed in our laboratory are reviewed. In a study on microwave plasma etching in high magnetic field regime, two local maxima in Si etch rate are found in the magnetic fields around Bc=875 G and 2Bc, and the second maximum at 2Bc attains as high as 1500 A/min at 5x10−5 Torr of NF3 with 600 W. The first mode is ascribed to the ECR (Electron Cyclotron Resonance). From a measurement of the microwave field inside the plasma where the phase velocity of microwave changes continuously with the magnetic field centered on 2Bc, the second mode turned out to be the Whistler mode resonance. Next, layer-by-layer etching of Si has been studied by repeating the reaction cycles of fluorine (F) atom adsorption on a cooled Si surface and subsequent Ar+ ion (⋍20eV) irradiation. The digital etch rate first increases and then reaches a plateau region with an increase in ion irradiation time. F atoms produced by a remote discharge of F2/98.8%He allows atomic layer etching of Si(100) in which the amount of physiosorbed fluorine molecules on Si surface controls the etch rate. The etching in the plateau region exhibits no microloading effect because the fluorine coverage is independent of pattern size.