A Radar for Ultra-thin High-k Dielectric Film: Zero-Bias Thermally Stimulated Current Spectroscopy

Abstract

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).

Mechanisms of Difficulty to Correlate the Leakage Current of High-k Capacitor Structures with Defect States Detected Spectroscopically by the Thermally Stimulated Current Technique

“…Ta 2 O 5 was deposited onto (100) n + -Si or p + -Si wafers by lowpressure metal-organic chemical vapor deposition (LP-MOCVD), as discussed before. [17][18][19][20][21][22] The precursor used was tantalum ethoxide with the chemical formula of Ta(OC 2 H 5 ) 5 . As deposited Ta 2 O 5 film is amorphous and very leaky.…”

“…ZBTSC (zero-bias thermally stimulated current) measurements were performed at a ramp rate of 0.5 K/s as before. [17][18][19][20][21][22] Conventional TSC technique suffers from a serious parasitic current problem because of the need to apply a bias voltage to the sample. The purpose of "zero bias" is to solve this parasitic current problem.…”

“…This problem can be partially solved by using a novel zero-bias thermally stimulated current (ZBTSC) spectroscopy technique. [17][18][19] The purpose of zero bias is to get rid of a parasitic leakage current that can interfere with the measurement. Experience shows that even ZBTSC may not be sufficient such that a more sophisticated technique like zero-temperature gradient ZBTSC has to be used, 20,21 as shown in Fig.…”

Mechanisms of Difficulty to Correlate the Leakage Current of High-k Capacitor Structures with Defect States Detected Spectroscopically by the Thermally Stimulated Current Technique

“…This situation is particularly serious if the high-k dielectric is in the form of an ultrathin film. This problem can be partially solved by using a novel zero-bias thermally stimulated current (ZBTSC) spectroscopy technique [17]- [19]. The purpose of zero bias is to get rid of a parasitic leakage current that can interfere with the measurement.…”