Effect of different pulse modes during Cl₂/Ar inductively coupled plasma etching on the characteristics of nanoscale silicon trench formation

The etch characteristics of silicon trenches masked with various SiO₂/Si₃N₄pattern distances were investigated using synchronously and asynchronously pulse modes in addition to the continuous wave (CW) mode for Ar/Cl₂inductively coupled plasmas. By using synchronously and asynchronously pulse modes instead of CW mode, the selectivity between Si and the mask layer was increased by 2 and 10 times, respectively. Also, the etch rate differences between wide and narrow pattern distance patterns (aspect ratio dependent etching, ARDE) was decreased from 35% to 21 and to 8%, respectively. The increased etch selectivity and reduction of ARDE for the synchronously pulsed mode were related to the increased conduction of Cl radicals/byproducts through the high aspect ratio trench, therefore, increased chemisorption/byproduct removal on the silicon trench surface during the pulse-off period. For the asynchronously pulsed mode, the further improved etch selectivity and reduced ARDE were believed to be related to the time separated etch cycle composed of Cl chemical adsorption on the silicon trench surface and the removal of the chemisorbed species by ion bombardment. It is believed that, the asynchronously pulsed plasma etching method can be applicable to various next generation deep nanoscale device fabrication requiring high etch selectivity and low ARDE.