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

Abstract

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:C 4 F 8 with varied O 2 flow, a minimum laser intensity for etch onset was necessary to overcome CF x polymer deposition in the absence of substrate bias. This etch onset occurred at 20 6 3 mJ/cm 2 /pulse for 0 sccm O 2 flow, dropping to 8 6 2 mJ/cm 2 / pulse for 1.5 sccm O 2. 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 laserassisted etch process preserved the distinction between the Si surface and the CF x 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 CF x polymer layer at 1.0 W/cm 2 radiofrequency bias and À140 V direct self-bias. COMSOL modeling of 532 nm incident on 22 nm halfpitch 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 SF 6 etching of pre-existing 50 nm half-pitch linear trenches.

Emerging laser-assisted vacuum processes for ultra-precision, high-yield manufacturing

“…Peck et al performed a 532 nm laser-assisted plasma etching (LAPE) on a Si wafer to demonstrate the polarization selectivity of lasers with wavelengths much larger than the feature size. 43 Simulation results of a 532 nm plane wave, exposed to the 22 nm half-pitch trench lines with an aspect ratio of 80, indicate that the Si trench structure behaves as a polarization-selective waveguide (Fig. 2a and b).…”