MOCVD of Hafnium Silicate Films Obtained from a Single‐Source Precusor on Silicon and Germanium for Gate‐Dielectric Applications

Abstract

In this work, hafnium silicate layers on Si and Ge wafers for gate dielectric application in metal-oxide-semiconductor devices are investigated. Films are deposited by metal-organic (MO)CVD using the single-source precursor Hf(acac) 2 (OSi t BuMe 2 ) 2 .This precursor exhibits good properties in terms of hydrolysis stability, volatility, and deposition. However, precursor decomposition is affected by surface conditions. Films deposited on Si wafers reveal high C contamination (up to 20 at %) and low Si content (up to 20 at %). In contrast, for film deposition on Ge wafers, no C contamination can be detected and Si incorporation is delayed until after about 15 nm HfO 2 dielectric growth. Post-deposition rapid thermal annealing in an O 2 atmosphere causes crystallization of deposited films, Si and Ge redistribution in the dielectric, respectively, and interfacial layer growth. However, oxygen annealing was also found to reduce effective oxide thickness (EOT) significantly compared to as-deposited films, which is attributed to crystallization effects. However, scaling of EOT is limited by that interfacial layer growth. Leakage currents are mainly caused by trap-related conduction mechanisms. Energy levels of involved traps decrease with increasing crystallization and/or Hf content, and values of 0.5 eV and 1 eV related to Hf and Si bonds, respectively, are obtained.

High-K: Latest Developments and Perspectives

“…The deposition behaviour of Hf(acac) 2 (OSi t BuMe 2 ) 2 precursor changes compared to Si wafers. As discussed previously [51], TEM images (not shown here) reveal a three-layer structure of the dielectric stack similar to the results obtained for Si wafers. But, in contrary to the depositions on Si wafers, RTA causes no den-…”

“…As presented recently [51], C is a main issue for leakage current, especially for high-k oxides deposited by MOCVD. Therefore, post-deposition RTA in O 2 atmosphere is required.…”

“…2 nm to 5 nm depth from the surface after Ar sputter cleaning. As discussed previously [51,52], C-free films can only be obtained after an O 2 -RTA (A, B compared to C to F), which leads to structural changes (i.e., decreasing physical thickness d annealed (C to F)) and Si redistribution in the layers (i.e., change in stoichiometry compared to uniform as-deposited films [52] (A, D to F)). With decreasing layer thickness, Si enrichment in the dielectric film was observed after anneal (D to F).…”

“…Electrical Characterization. High-frequency (100 kHz to 1 MHz) capacitance-voltage (C-V) and temperature dependent current density-voltage (J-V) measurements of the samples labeled A to F in Table 1 and O 2 -annealed layers deposited on nitrided [51] Ge wafers (sample label Ge) were performed. Extracted parameters for selected films are summarized in Table 2.…”

A combined ab initio and Franck–Condon factor simulation study on the photodetachment spectrum of HfO2−

“…In the present article, we propose to study low-lying electronic states of molecular HfO 2 and the recently published photodetachment spectrum of HfO 2 À recorded in the gas phase 6 by high-level ab initio electronic structure calculations and Franck-Condon (FC) factor spectral simulation. Since the thin film growth techniques of chemical vapour deposition (CVD), such as atomic layer deposition (ALD) 7 and metal-organic CVD (MOCVD), 8 are generally preferred for the production of CMOS devices because of good step coverage and scalability, the characterization of HfO 2 in the gas phase by a spectroscopic technique, such as laser induced fluorescence (LIF) spectroscopy [9][10][11] or ultraviolet absorption spectroscopy (UVAS), [12][13][14] would be useful for the in situ monitoring of gaseous species near and above thin films. Reliable ab initio calculations on low-lying electronic states of HfO 2 reported in the present paper will contribute to the assignments of electronic spectra of HfO 2 , when they are recorded, and may contribute to efficient process-control of an industrial high yield CVD reactor for the production of a HfO 2 CMOS device.…”