Defect state D (0.8 eV) was experimentally detected in Ta2O5 capacitors with ultrathin (physical thickness <10 nm) Ta2O5 films using zero-bias thermally stimulated current spectroscopy and correlated with leakage current. Defect state D can be more efficiently suppressed by using N2O rapid thermal annealing (RTA) instead of using O2 RTA for postdeposition annealing and by using TiN instead of Al for top electrode. We believe that defect D is probably the first ionization level of the oxygen vacancy deep double donor. Other important defects are Si/O-vacancy complex single donors and C/O-vacancy complex single donors.

Ultra-thin high-k dielectric films have attracted world-wide interest for DRAM capacitor or gate dielectric applications. Defect states in high-k dielectric are responsible for leakage current or mobility degradation due to remote Coulomb scattering. Hence there is a need to develop a technology to detect those defect states. We have successfully developed a novel zero-bias thermally stimulated current (ZBTSC) spectroscopy technique which is applicable to capacitors with sub-10 nm high-k dielectric. Tantalum oxide was used as an example to demonstrate the value of this technique. The ZBTSC technique can be further improved by migration to zero-temperature-gradient ZBTSC (ZTGZBTSC).

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.