A reactive ion etch study for producing patterned platinum structures

Various high-density DRAM and FRAM technologies currently under investigation utilize high-dielectric constant materials requiring noble metal or refractory metal oxide electrodes. In this paper we describe a study of platinum patterning by reactive ion etching (RIE). Platinum films were etched in a rf diode parallel plate RIE tool with a grounded upper electrode and a 13.56 rf powered lower electrode upon which substrates were processed. The removal characteristics of blanket platinum films and platinum films with a patterned photoresist etch mask were investigated as a function of gas chemistry (Ar, CF4, SF6, and Cl-2), rf power (100 to 680 W), gas pressure (5 to 100 mTorr), total gas flow (5 to 80 sccm), and substrate temperature (21 to 300 degrees C). The platinum etch was characterized in terms of etch rate, amount of redeposited material observed on the photoresist etch sidewalls ('fencing'), and etch scale-up non-uniformity versus small size and feature size. Platinum etch rates from 80 to 1250 Angstrom/minute were observed with corresponding substrate de bias voltages of -500 to -1600 V. A computer program was developed to model the etch process. Computer modeling results were correlated with etched structures to optimize the etch process conditions. Optical emission spectroscopy (OES) was utilized to observe gas phase plasma species for chemical etching determination, and optimized as an optical endpoint monitor. Auger electron spectroscopy (AES) was implemented in chemically analyzing the redeposited 'fence' material. Using selected RIE process conditions, platinum films with a patterned photoresist etch mask were etched resulting in clean, residue-free structures with sidewall angles approximately 29 degrees. Best process to date using a post-RIE cleanup yields sidewall angles approximately 69 degrees.