Dry Etching Issues in the Integration of Ferroelectric Thin Film Capacitors

Abstract

Dry etching is an area that demands a great deal of attention in the large scale integration of ferroelectric thin film capacitors for nonvolatile random access memory applications. In this review, we discuss some of the issues relating to the etching of the ferroelectric films, patterning of the electrodes, device damage caused by the etch process and post-etch residue problems. An etch process that can provide high etch rates and good etch anisotropy for the current candidate ferroelectrics including Pb(Zr, Ti)O3 and layered structure SrBi2Ta2O9 thin films using environmentally benign gases such as hydrochlorofluorocarbons is presented. The etch mechanism for both of these materials was determined to rely substantially on ion bombardment effects. For example, PZT films were etched anisotropically at rates of up to 60 nm/min using CHCIFCF3 gas under high rf power and low gas pressure conditions. Problems remain with respect to the acrosswafer differential etch rates observed when more than one phase is present in the material (e.g., amorphous/pyrochlore + perovskite phases in PZT). Damage caused by the etch process which can lead to changes in device characteristics, including hysteresis and fatigue properties, and the underlying mechanism that causes the damage are discussed. O2 was found to be a suitable etch gas for etching the conductive oxide electrode material RuO2. However, an anomaly in the etch rate was detected upon introduction of a small amount of fluorine containing gas: addition of 2% of CF3CFH2 gas to the O2 plasma increases the etch rate by a factor of four. This can be taken advantage of in obtaining high etch selectivity between the electrode and ferroelectric layers.

Characterization and elimination of dry etching damaged layer in Pt/Pb(Zr0.53Ti0.47)O3/Pt ferroelectric capacitor

“…Up to now, it is not easy to find out etching process without the etching damage during dry etching process. [2][3][4][5][6] Recently, Torii et al attempted the rf oxygen plasma treatment to reduce the etching damage. However, the etching damage was not completely removed by rf oxygen plasma treatment.…”

Influence of Dry-Etch Patterning of Top Electrode and SrBi[sub 2]Ta[sub 2]O[sub 9] on the Properties of Ferroelectric Capacitors

“…These findings are in agreement with previous works. 10 For largest P/A values, Fig. 6b also compares hysteresis loops measured after RA, with and without patterning SBT: the loop is slightly tilted and the P r is slightly lower if SBT is patterned, which indicates that the recovery of the SBT etch damage is only partial.…”

“…The authors report the observation of smaller crystallites of SBT in the damaged zone by SEM, in agreement with our observation, and also report the identification of crystallographic changes ͑X-ray diffraction, XRD͒ and Bi reduction ͑atomic emission spectroscopy, AES͒ in the same zone. Some other groups have evidenced composition changes too, 10,12 or huge P r degradation when FeCAP size is decreased. 13 Our results ͑see Fig.…”

Processing and Characterization of Piezoelectric Materials and Integration Into Microelectromechanical Systems

“…In RIE, material removal is accomplished by a combination of physical (ion bombardment) and chemical (reaction with the etch gas) processes. In their review of dry etching of ferroelectric thin films, Menk et al (89) indicate that RIE is the preferred dry method due to its high etch rate and good anisotropy. Potential drawbacks include etching-induced damage from the ion bombardment and the accumulation of residue on the film.…”