STRESSES IN PT PB(ZR,TI)O-3/PT THIN-FILM STACKS FOR INTEGRATED FERROELECTRIC CAPACITORS/

A study of the stresses in a ferroelectric capacitor stack deposited o n an oxidized silicon substrate is presented. The capacitor stack was prepared with sputtered Pt bottom and top electrodes and a ferroelectr ic film of composition PbZrxTi1-xO3 (PZT) with x approximate to 0.5 wh ich was deposited using a modified sol-gel technique. The stresses wer e determined by the changes in the radius of curvature of-the wafer fo llowing the deposition steps, during and after annealing treatments, a nd after etching steps in which the top electrode, the PZT film, and t he bottom electrode were successively removed. The largest stress effe cts are found in the Pt electrodes which are deposited under condition s giving an intrinsic compressive stress. An annealing treatment excee ding 500 degrees C changed the stress of the bottom electrode from app roximate to-750 MPa (compressive) to a large tensile stress (approxima te to 1 GPa). This stress is largely thermal and is caused by the diff erences in thermal-expansion coefficients of the Pt film and the Si su bstrate. The stress of the PZT film is numerically relatively small (b elow approximate to 200 Mpa) and it is found to be of both thermal and intrinsic origin. The deposition and annealing of the top electrode h as a profound influence on the stress of the PZT film as well as on th e electrical properties. The stress behavior of the as-deposited PZT h im shows a poling direction mainly in the plane of the substrate. An a nnealing of the complete capacitor stack changes the poling direction of the ferroelectric film to be perpendicular to the substrate. This e xplains the observed electrical switching properties of as-prepared as well as annealed ferroelectric capacitors. (C) 1995 American Institut e of Physics.