Characterization of Defect States Responsible for Leakage Current in Tantalum Pentoxide Films for Very-High-Density Dynamic Random Access Memory (DRAM) Applications

Abstract

Defect states in tantalum pentoxide films grown by low-pressure metal-organic chemical vapor deposition on silicon wafers have been studied with Al/Ta2O5/p+-Si and Al/Ta2O5/n+-Si capacitor structures by the zero-bias thermally stimulated current technique. It was demonstrated that a shallow band of defect states is responsible for leakage current. The shallow band of defect states can be suppressed by low-temperature post metallization annealing, resulting in a reduction of leakage current for both positive gate bias and negative gate bias. However, the reduction in leakage current for positive gate bias is much stronger than that for negative gate bias.

Mechanism of Difficulty to Study the Physics of Leakage Current Reduction by Nitridation of Silicon before High-k Dielectric Deposition Due to Change in Nucleation Characteristics and Some Other Factors

“…Ta 2 O 5 was deposited onto (100) n + -Si substrates by low-pressure metal-organic chemical vapor deposition (LP-MOCVD) as discussed before (2). The physical thickness of the film was from 8-100 nm.…”

“…Post-deposition anneal of Ta 2 O 5 samples was done by RTP (rapid thermal processing) in O 2 or N 2 O at 700-900 o C. Al top contacts were deposited by electron beam evaporation. Zero-bias thermally stimulated current (ZBTSC) spectroscopy measurements were performed for the characterization of defect states at a ramp rate of 0.5 K/s as before (2). Rapid thermal nitridation (RTN) was sometimes performed on silicon substrates at 950 o C in an ammonia ambient at atmospheric pressure.…”

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 low-pressure metalorganic chemical vapor deposition (LP-MOCVD), as discussed before [17]- [22]. The precursor used was tantalum ethoxide with the chemical formula of Ta(OC 2 H 5 ) 5 .…”

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

Efficient Detection of Oxygen Vacancy Double Donors in Capacitors with Ultra-thin Ta2O5 Films for DRAM Applications by Zero-bias Thermally Stimulated Current Spectroscopy

“…For DRAM applications, the two most important requirements are high capacitance, limiting film thickness to < 10 nm, and low leakage current, which may be related to defect states in Ta [3], which will make Ta 2 O 5 a very weakly n-type large bandgap semiconductor, resulting in leakage current. In 1995, we explained the principle of zerobias thermally stimulated current (ZBTSC) spectroscopy and demonstrated the detection of defect states in capacitors with relatively thick Ta 2 O 5 [4]. In 1995, we explained the principle of zerobias thermally stimulated current (ZBTSC) spectroscopy and demonstrated the detection of defect states in capacitors with relatively thick Ta 2 O 5 [4].…”