Metalorganic chemical vapor deposition of very thin Pb(Zr,Ti)O-3 thin films at low temperatures for high-density ferroelectric memory applications

The metalorganic chemical vapor deposition of very thin (< 50 nm) Pb(Zr,Ti) O-3 (PZT) thin films was performed for high density (> 32 mega bit) ferroel ectric memory devices. The growth temperatures were set between 450 and 530 degreesC to obtain a smooth surface morphology and prevent damage to the u nderlying reaction barrier layer. The average grain size of a 50-nm-thick f ilm on a Pt electrode was about 34 nm with a size distribution (sigma (2)) of 11 nm. These values are much smaller than the sol-gel-derived PZT films (55 and 25 nm, respectively). Very thin films with a thickness of approxima tely 30 nm were prepared at wafer temperatures ranging from 500 to 525 degr eesC. Even with the very small thickness, the films showed good ferroelectr ic properties with a typical remanent polarization from 10 to 15 muC/cm(2) and an extremely low coercive voltage of 0.3 V. However, the leakage curren t density was rather high resulting in nonsaturating polarization versus vo ltage curves. Even though good ferroelectric properties were obtained, the formation of Pt,Pb, alloys on top of the Pt electrode was consistently obse rved. This precludes the reliable control of film composition and electrica l performance. The adoption of an Ir electrode successfully eliminated inte rmetallic alloy formation and resulted in better and reproducible process c ontrol. A 50-nm-thick PZT film on an Ir/IrO2/SiO2/Si substrate also showed a reasonable ferroelectric performance.