Temperature and oxygen concentration effects on anisotropy in chromium hard mask etching for nanoscale fabrication

Abstract

Chromium and its oxides are valuable as functional materials and plasma-etching hard masks in micro- and nanofabrication. While the continuous decrease in feature sizes opens new opportunities for applications of patterned chromium, the demands placed on the patterning process require a new level of mechanistic understanding. In this work, we investigate plasma etching with chlorine/oxygen chemistry using temperature and oxygen concentration as a means to controllably pattern chromium at the nanometer level. Building on our previous studies on blanket film chromium etching, we look here at patterned trenches 15–100 nm wide in 20 and 10 nm thick chromium films. We vary oxygen concentrations from 1.5% to 81% at substrate temperatures of +20 and −50 °C, respectively. Feature and trench profiles are evaluated from high-resolution cross-sectional SEM images. The ternary chromium etch product shows very different profiles as oxygen, temperature, and feature size are varied. We find the highest anisotropy at −50 °C and 50% oxygen concentration. Etch results suggest that the redeposition of nonvolatile intermediate reaction compounds enhances anisotropy at low temperature, whereas re-emission of reactive species causes undercut at the higher etching temperature.

Versatilely tuned vertical silicon nanowire arrays by cryogenic reactive ion etching as a lithium-ion battery anode

“…For the second mask template, we employed a 100 nm thick Cr layer as a hard mask because of its high selectivity in Si deep reactive ion etching (DRIE) 34 . This material was also proven to be able to sustain as a mask during deep physical RIE of ~5 µm high vertical gallium nitride (GaN) nanowires, in which GaN is known as a wide-bandgap semiconductor possessing higher hardness, stiffness (i.e., Young’s modulus of 300–350 GPa), and mechanical stability than Si 33 , 35 – 38 .…”

Etching of iron and iron–chromium alloys using ICP-RIE chlorine plasma

“…Curtis et al [44] studied the evolution of Cr etching by varying the percentage of O 2 in CCl 4 /O 2 mixtures and observed a maximum of chromium etch rate for 50 %O 2 . Staaks et al [45,46] performed etching of Cr by using Cl 2 /O 2 plasma, observing a maximum of etch rate for 20-40 %O 2 . By studying the substrate temperature impact, they showed a strong increase in etch rate, from 5 to 40 nm/min when the substrate temperature increased from -80 o C to 40 o C. This evolution can be due to chemical etching of Cr.…”

Cr and CrOx etching using SF6 and O2 plasma

“…The plasma etching of Cr is currently almost exclusively reserved for chlorine-oxygen-based chemistry by forming chromyl chloride (CrO 2 Cl 2 ) as the final etch product. [29][30][31][32][33][34][35][36][37][38][39][40][41] The consensus is that both chlorine (e.g., Cl 2 plasma) and oxygen radicals (e.g., O 2 plasma) are needed to create the volatile chromyl chloride product. It was demonstrated by Abe et al 29 roughly 45 years ago and a few years later explained by Nakata et al 30 As both O and Cl radicals are needed to remove a Cr atom, possibly allowing any intermediate CrO x Cl y reaction path, the etch rate (ER) shows an optimum for a specific ratio between the supplied Cl 2 and O 2 gas.…”