Elimination of notching and ARDE by simultaneous modulation of source and wafer RF

Summary form only given. Notch formation and aspect ratio dependent etching (ARDE) are becoming serious problems in the over-etching of line and space structures in poly-Si on SiO/sub 2/. Experimental results for Cl/sub 2/ plasma etching of poly-Si and C/sub 2/H/sub 2/F/sub 4/ in SiO/sub 2/ in a helicon etch tool are presented which are modeled by differential charging and ion assisted etching. It is shown that modulation of the 13.56 MHz RF source can eliminate both of these effects in the absence of RF wafer bias but fails in the presence of CW wafer bias. It is also shown that simultaneous source and wafer modulation eliminates both notch formation and ARDE. On/off modulation with a 50% duty cycle and period ranging from 0 to 200 /spl mu/s are investigated and optimum notch and ARDE reduction are found at 40 to 200 /spl mu/s.