Degradation of Ferroelectric Capacitors during Metal Etching and Ashing Processes
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Degradation of Ferroelectric Capacitors during Metal Etching and Ashing Processes Chanro Park, O Sung Kwon, Yeo Song Seol, Jin Woong Kim and Hee Koo Yoon Advanced Process-Etch, Memory R & D Div., Hyundai Electronics Industries San 136-1, Ami-ri, Bubal-eup, Ichon-si, Kyongki-do, 467-701, Korea ABSTRACT Polarization degradation due to metal etch and/or photoresist(PR) strip processes has been investigated for Pt/SrBi2Ta2O9(SBT)/Pt ferroelectric capacitors. Interconnect metal line consisting of TiN/Al/Ti/TiN/Ti layers has been patterned by normal photolithography and plasma etch processes. We used two different sources for metal etcher, helicon or electron cyclotron resonance(ECR) source, and stripped the PR with either microwave or helicon source stripper. Polarization degradation was evaluated by measuring switching and non-switching polarization of the ferroelectric capacitors. Neither etch machine nor etch parameters played an important role for determining polarization of the ferroelectric capacitors. Photoresist strip process, however, significantly affected the polarization of the ferroelectric capacitors. Factors affecting polarization of the ferroelectric capacitors were presence of hydrogen and plasma density during the strip process. Hydrogen atoms and protons produced by H2O or NH3 plasma penetrated through the dielectric layer and caused hydrogen induced damage. Thus the hydrogen damage was dependent on strip temperature and time. Photoresist strip with high density plasma results in charging damage to ferroelectric capacitors. It is believed that charges from the plasma are trapped at domain boundaries and interfaces, leading to polarization degradation. Damage free metal etching process for the ferroelectric capacitor was applied for the fabrication of the fully working ferroelectric random access memory. INTRODUCTION Ferroelectric random access memory(FeRAM) has been attracted great attention as a nonvolatile memory, because of its low operation power and high read/write speed[1]. However, there are challenges that should be overcome for the realization of the FeRAM. Fatigue, retention and imprint characteristics should meet the requirement for long term operation[2]. Processes that do not affect to the electrical properties of the ferroelectric capacitor should also be established. Various plasma etching processes, such as capacitor etching, contact etching, and metal etching are required for the fabrication of the FeRAM. Plasma etching can cause damage to the ferroelectric capacitors. Plasma etching damage can lead to deterioration of the electrical properties such as reduction of remnant polarization and increase of leakage current. Plasma etching damage can be recovered by thermal annealing at high temperature. Metal etching damage, however, can not be recovered by annealing process, because annealing temperature is higher than the melting point of the interconnecting Al metal line. Thus it is necessary to etch metal line without damage to the ferroelectric capacitors. In this paper, we investigated
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