Various Methods to Reduce Defect States in Tantalum Oxide Capacitors for DRAM Applications

Abstract

Tantalum oxide has attracted world-wide interest for DRAM (dynamic random access memory) capacitor applications because of its relative high dielectric constant compared to silicon dioxide or nitride. We would like to point out that tantalum oxide behaves very much like a large bandgap n-type semiconductor with 3 main types of donors responsible for leakage current. Native oxygen vacancies are very deep double donors with Ec -Ed = 0.8 eV approximately, where Ec is the bottom of the conduction band and Ed is the energy level of the defect state. Si-O vacancy complexes are relatively shallow single donors with Ec -Ed = 0.2-0.4 eV. C-O vacancy complexes are relatively shallow single donors with Ec -Ed = 0.5-0.6 eV. The key points regarding how to suppress these 3 types of donor defects will be discussed for the purpose of leakage current reduction.