Sub-damage-threshold plasma etching and profile tailoring of Si through laser-stimulated thermal desorption

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A laser-assisted plasma etch process is presented as an alternative to reactive ion etching for Si wafer processing in upcoming integrated circuit technology nodes. Poly-Si films were etched using an upstream 13.56 MHz inductively coupled plasma source while simultaneously being exposed to a pulsed Nd:YAG laser using the 532 nm line, with 100 Hz and 7 ns Gaussian pulse duration. For a fluorocarbon etch recipe of 50:8 sccm Ar:C4F8 with varied O2 flow, a minimum laser intensity for etch onset was necessary to overcome CFx polymer deposition in the absence of substrate bias. This etch onset occurred at 20 ± 3 mJ/cm2/pulse for 0 sccm O2 flow, dropping to 8 ± 2 mJ/cm2/pulse for 1.5 sccm O2. Beyond this onset, the etch rate increased linearly with laser intensity. Secondary ion mass spectroscopy depth profiling data showed that the no-bias 532 nm laser-assisted etch process preserved the distinction between the Si surface and the CFx polymer, with minimal uptake of etch gas residuals (C/F/O) in the Si. On the other hand, RIE showed significant straggle of the Si layer, spreading 3.5 nm through the CFx polymer layer at 1.0 W/cm2 radio-frequency bias and −140 V direct self-bias. comsol modeling of 532 nm incident on 22 nm half-pitch trench features showed strong polarization dependence, with deep-trench heating possible with polarization perpendicular to the trench line. This effect was confirmed in brief laser-assisted SF6 etching of pre-existing 50 nm half-pitch linear trenches.