AES Study of Chemical Segregation in the Ti-Pt-PZT system for MEMS devices
EMSL Project ID
2355
Abstract
In past investigations between WSU and EMSL, XPS analysis has provided evidence that Pb has diffused to the Ti/Pt interface in a Si/SiO2/Ti/Pt/PZT stack used in a MEMS microengine. Pb diffusion through the thin films may increase residual stresses and poor adhesion. In more recent studies at WSU, evidence of Pb at the Pt/PZT interface suggests that it remains an issue in our processing. Vickers indentation is used in our studies to qualitatively measure adhesion by assessing delamination area in samples subjected to different PZT and Pt annealing temperatures. Delaminations also make it possible to chemically analyze the failed interface without imposing excessive contamination that might result in during a PZT etch. In addition, Ti diffusion through Pt grain boundaries may be detrimental to device reliability. If oxidation of Ti occurs in the grain boundaries of Pt, compressive stresses in the film may cause the Pt to hillock through the PZT causing the device to short. In past studies, the Ti adhesive layer was found completely oxidized, but its diffusion throughout the Pt layer was not monitored. Currently we have EDS, XPS, and AES resources at WSU, but all pose difficulty in obtaining the information that we need. The large interaction volume associated with EDS prevents us to determine the composition of Pb at the surface of the Pt bottom electrode as well as monitoring its depth profile through the thin film. The XPS/AES system that is at our disposal lacks an SEM capable of resolving delaminations enough to achieve proper beam alignment and mapping capabilities which would enable us to study the Ti and Pb lateral segregation at the PZT and Pt interface. . We seek the use of an AES system in conjunction with an SEM that is able to resolve regions around the indents of 1-10 mm, with mapping capabilities on the sub-mm regime (with beam sizes on the order of 50 nm). We are interested in obtaining local chemistry at the Pt/PZT interface and tracking diffusion of Pb and Ti through the Pt bottom electrode as a function of processing conditions. We expect that these results in conjunction with adhesion testing and roughness and grain size collection will provide valuable information between processing structure and properties. We hope that these results we permit us to manipulate processing conditions to generate conditions best suited for device reliability. This information will be reported through publications in peer reviewed journals and presentations at national materials meetings.
Project Details
Project type
Exploratory Research
Start Date
2001-09-25
End Date
2004-09-29
Status
Closed
Released Data Link
Team
Principal Investigator