FTIR analysis of PZT damage during wafer level transfer of thermo-piezoelectric SI3N4 cantilevers on the CMOS-wafer for nano data storage applications

Abstract

Degradation of lead zirconate titanate (PZT) during wafer level bonding of thermo-piezoelectric cantilevers with a CMOS-wafer was investigated. It was found that the polyimide film which serves as a height adjustment during wafer level bonding between cantilevers and the CMOS-wafer caused significant damage in the PZT sensor when polyimide was coated entirely on the PZT capacitor followed by heating to 300 °C for the bonding process. Fourier transform infrared spectroscopy (FTIR) was used to analyze the reaction product that caused PZT capacitor damage. Three different types of samples were analyzed using FTIR: a sample with coated polyimide only, a sample with a PZT capacitor with no polyimide exposed and a sample with a PZT capacitor where the polyimide has been coated, heated and then removed. NH2 or NH3+ peaks from the sample with the polyimide exposed PZT capacitor were found and these peaks were not detected on the sample with the PZT capacitor or on the polyimide coated sample only. These hydrogen ions contained in the NH2 or NH3 stretch during heating can lead to hydrogen atmosphere annealing which can attack PZT significantly. FTIR analysis therefore confirmed that polyimide reacted with the PZT capacitor to damage its piezoelectric properties.