| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Tuesday Sessions |
| Session PS-TuM |
| Session: | Advanced FEOL/Gate Etching |
| Presenter: | Jason Peck, University of Illinois at Urbana-Champaign |
| Authors: | J.A. Peck, University of Illinois at Urbana-Champaign D.N. Ruzic, University of Illinois at Urbana-Champaign |
| Correspondent: | Click to Email |
In this work, laser exposure was coupled with plasma etch processes for local etch rate enhancement (and under some conditions, etch activation). Materials were tested which are most-frequently used in semiconductor devices – namely Si, SiO2, and Cu. A 100 Hz, 7 ns pulse width Q-switched Nd:YAG laser was applied at its 1064, 532, and 266 nm modes. Using the 532 nm line on Si (40 mJ/cm2/pulse) with a radiofrequency inductively-coupled plasma (RF-ICP) source placed upstream, laser etch enhancement effect was 4 Å /s in 50:4 sccm Ar/SF6, and 3 Å /s etch enhancement at 50:8:2 sccm Ar/C4F8/O2. With no O2 flow in a 50:8 sccm Ar/C4F8 chemistry in an RF capacitively-coupled plasma (RF-CCP) source with a measured self-bias of -140 V, etch activation was seen at 0.62± 0.07 W/cm2 (6.2± 0.7 mJ/cm2), with etch rates linearly increasing with laser intensity. The 266 nm line saw etch activation at roughly the same intensity, though etch rate scaling with laser intensity was roughly 6 times higher than 532 nm, corresponding to the drastically-larger absorption depth of 266 nm in Si. No etch enhancement was produced in either chemistry for SiO2 due to its transparency across the UV-VIS-NIR spectrum, even at 266 nm. CFx polymer thinning was observed on both Si and SiO2 at 266 nm but only on Si at 532 nm, indicating a thermally-driven desorption mechanism which relies on heating the material beneath.
It was shown that continuous wave (CW) laser sources of 405, 455, and 520 nm were unable to produce etch enhancement even up to intensities of 200 W/cm2, demonstrating the necessity of rapid heating of the Q-switched Nd:YAG source (~10s of MW/cm2 over 7 ns) to temporarily but drastically increase wafer surface temperature. COMSOL simulations showed that a Si surface over the duration of a 532 nm laser pulse would increase temperature by 2.7° C per mJ/cm2 – a reliably linear rate, even at high intensity. Testing of highly-doped Si wafers revealed a substantial increase in etch enhancement – 1019 and 1021 cm-3 P-doped wafers showed 1.7× and 3.7× higher etch rates over intrinsic Si, respectively. The increased absorption coefficient in these doped wafers confirmed that the etch enhancement mechanism was due to desorption of etch products through thermal heating, rather than through photolytic bond breaking.
Finally, etch tests of 100 nm full-pitch, 100 nm deep trenches showed the ability to tailor etch profile based on wafer orientation. Polarization parallel to the trench line enhanced etching at the top of the features, while perpendicular to the trench line increased trench bottom etch rate.