LINE DOSE DEPENDENCE OF SILICON AND GALLIUM ARSENIDE REMOVAL BY A FOCUSED GALLIUM ION BEAM

Abstract
Silicon and gallium arsenide wafers were machined by area-scanning them with a focused gallium ionbeam having a focused spot diameter of 0.25µm and a spot current of 0.71A/cm². With fast scanning removal (low line dose), a shallow and uniform hole is machined. In slow scanning removal, an increase in sputtering yield and a redeposition of sputtered atoms at the sidewall of the machined hole were observed at the line dose of higher than 2.5x10¹⁷/cm² for silicon, and 6.25x10¹⁶/cm² for gallium arsenide. This increase in yield may be attributed to several factors characterized by focused ionbeam sputter etching. First, since the machined hole lies very close to the bombardment area, the incident angular dependence and side ward sputtering phenomena cause an increase in the effective sputtering yield (Shape Effect). Second, a very high line dose (~10¹⁷/cm²) causes an increase in the dislocation density as well as amorphousizing of the target material (High Line Dose Effect). Third, the incident gallium forms an alloy with the target material, which lowers the bonding energy of the target material.