Paper PS-ThP14
Characteristics of SiO₂ Etching with Ar/C₄F₈/CHF₃/O₂ Gas Mixture in 60 MHz/2 MHz Dual Frequency Capacitive Coupled Plasmas

Thursday, November 3, 2011, 6:00 pm, Room East Exhibit Hall

As the size of the semiconductor device is drastically scaled down to nano-scale, the etching technology of high aspect ratio contact (HARC) is increasingly important. To etch the nano patterned HARC, the multi-layer resist (MLR) structure conventionally composed of a PR, SiON layer, and amorphous carbon layer has been developed because it is difficult to etch HARC directly using a photoresist mask only. However, even though the etching of HARC tends to show higher etch selectivity and proper etch profile with MLR structures, for the next-generation nano-scale dynamic random access memory devices, the etching of nano-scale SiO₂ HARC using fluorocarbon plasmas is becoming more and more important.

Nanoscale SiO₂ contact holes were etched by using C₄F₈/CHF₃/O₂/Ar gas mixtures in dual-frequency capacitive coupled plasmas (DF-CCPs) where 60 MHz source power is applied to the top electrode while 2 MHz bias power is applied to the bottom electrode. we added CHF₃ and O₂ gases to control the etch rate and improve the etch selectivity. Proper additive gas ratios are needed to get the high etch selectivity and maintain CD size. We measured radical intensity, etch rate and SiO₂ surface by using optical emission spectroscopy(OES), X-ray photoelectron spectroscopy(XPS), field emission scanning electron microscopy(FE-SEM) respectively.

In this study, we confirm that the etch rate and etch selectivity are varied as a function of CHF₃/O₂ gas ratios. The SiO₂ and amorphous carbon layer(ACL) etch rate are increased with increasing the HF power due to the improvement of gas dissociation. But as increasing the HF power, etch selectivity is saturated. In this study, Highest etch selectivity of about 6 is obtained at HF power 300 W, LF power 500 W, Ar/C₄F₈/CHF₃/O₂ = 150/20/25/5 sccm, process pressure of 20 mTorr.