Investigation of a nitrided-oxide dielectric for epitaxial lateral overgrowth applications
Abstract
Polyoxide gate dialectic degradation problems were encountered during the process development of a three-dimensional CMOS structure. In prior studies, the gate dialectric degradation was found to occur when the polyoxide was exposed to the oxygen deficient, low pressure silicon rich epitaxial lateral overgrowth (ELO) ambient. The durability of thin polyoxide dielectrics is essential to three-dimensional process, allowing bottom gate control of the vertically stacked PMOS load device. The previous process had approximately a 1000 A minimum thickness limit on the bottom gate dielectric, unacceptable when compared to modern day CMOS technology. This research was directed at developing a durable high quality 100-300 A nitrided polyoxide (NPOX) gate dielectric process. The incorporation and distribution of nitrogen in both ammonia nitrided polyoxide (NPOX) and nitrided silicon dioxide (NOX) dielectric films were studied. The effects of the nitrogen concentration and distribution on the resistance of the NPOX and NOX films to ELO ambient degradation were determined. It was observed that the surface nitrogen concentration had no effect on the durability of the dielectric. However, a bulk nitrogen concentration as low as 8 at% significantly reduced the formation of ELO ambient induced pinholes in 250A dielectric films. After 40 min. of ELO stress the electrical yield was raised from 0%, for polyoxide and silicon dioxide dielectric capacitors, to over 80% for NPOX and NOX dielectric capacitors. Analyses of the failed devices suggest that active pinhole generation still existed, however, the bulk nitrogen concentration dramatically reduced the frequency and speed at which these defects were produced. Fixed oxide charges and interface state densities on the order of $1.2\cdot10\sp{11}$ were observed after $1100\sp\circ$C, 10 min. nitridation with NPOX capacitor yields of 84% after 40 min. of ELO growth ambient stressing. After 60 minutes of nitridation, the surface became resistant to the ELO growth ambient induced surface pitting and roughening.
Degree
Ph.D.
Advisors
Neudeck, Purdue University.
Subject Area
Electrical engineering
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