Suppression of notching by lowering the bias frequency in electron cyclotron resonance plasma with a divergent magnetic field

Abstract

Etch rate control in a 27 MHz reactive ion etching system for ultralarge scale integrated circuit processing ''Notching,'' which is a kind of local side etching caused by charging of pattern structures, is a serious obstacle to achieving tight critical dimension ͑CD͒ control in fabrication beyond quarter micron devices. Although sidewall protection with increased polymer deposition on the sidewall can reduce notching, it tends to enhance the so-called proximity effect, which is the variation of etched profiles observed when the pattern spacing is varied. Therefore, notching has to be suppressed without extra sidewall protection to achieve tight CD control. To solve this problem, we studied the effects of rf bias frequency for both continuous mode and pulse modulated mode electron cyclotron resonance plasma sources with divergent magnetic fields, and found out that lowering the bias frequency can reduce the notching by itself. We found that the notch depth is markedly decreased by lowering the bias frequency from 13.56 MHz to 400 kHz under most conditions. In continuous mode plasma, however, this improvement becomes minimal when the pressure is decreased to reduce the proximity effect. On the other hand, using a pulsed plasma source having a 100 s cycle and 25%-50% duty, we succeeded in suppressing notching even in cases of 1 mT and lower. Consequently, we have achieved a vertical etched profile with minimal proximity effect.

Time-resolved investigations of pulsed microwave excited plasmas

“…Pulsed dc [1], radio-frequency (RF) [2][3][4] or microwave (MW) [5] excited plasmas are nowadays used to increase the etch rate, selectivity [6,7], uniformity, deposition rates and quality of deposited organic [8,9] or inorganic thin films [10]. Pulsed plasmas can also reduce notching [11], particle formation [12], charge buildup damage and the heat flux to a substrate. Process improvements depend on the right choice of the two parameters pulse frequency and duty cycle.…”

Improvement of high aspect ratio Si etching by optimized oxygen plasma irradiation inserted DRIE

“…(i) When f bias is higher than f pi , V dc is almost half of V pp , because the incident ions cannot follow a potential modulation of the bias electrode [14]. (ii) When f bias is lower than f pi , V dc is less than half of V pp , because the ions can follow the modulation [15]. In this case, the ions are repelled when the electrode potential is positive to the plasma in one RF cycle.…”

Prevention method of a notching caused by surface charging in silicon reactive ion etching

“…Rickard and McNie referred to the minimization of an ARDE by adjusting individual process factors such as gas flow rate, pressure, etc to reduce overetching [9]. Morioka et al disclosed the use of lower frequency plasma to evade surface charging [10]. The increase of ions with low directionality and kinetic energy in low frequency plasma effectively neutralizes the negative potential barrier at the entrance of the trench.…”