Volume 32, Issue 3, May 2014
Index of content:
- Special Issue: High-k Dielectrics
32(2014); http://dx.doi.org/10.1116/1.4818254View Description Hide Description
Thin [(x)Al2O3 + (y)TiO2] nanolaminates (NLs) films of various TiO2 and Al 2O3 volume fractions were deposited on n-Si substrates at 250 °C using remote plasma-assisted atomic layer deposition. While the overall thickness of the dielectric was held relatively constant at ∼16 nm, the relative ratio of Al 2O3 to TiO2 in the NL was varied by changing the number of deposition cycles of each component. This permitted the evaluation of changes in the dielectric constant κ, index of refraction Nf, optical band gap, Eg, and the electrical performance of the resulting oxides. Capacitance–voltage and current–voltage results on 100 μm diameter circular capacitors were obtained. The data reveals that the high-content TiO2 films show limited evidence of oxide charge trapping and relatively large dielectric constants (k ∼ 15) with reduced reverse-biased leakage current, whereas the high-content Al 2O3 films offer a larger optical band-gap and excellent insulating character with reduced leakage currents. In addition, the authors present composition assessments of the oxides by x-ray photoelectron spectroscopy, transmission electron microscopy, and electron energy loss spectroscopy.
Effect of process temperature on the structural and electrical properties of atomic layer deposited ZrO2 films using tris(dimethylamino) cyclopentadienyl zirconium precursor32(2014); http://dx.doi.org/10.1116/1.4825109View Description Hide Description
The authors investigate the deposition of ZrO2 by atomic layer deposition (ALD) process using tris(dimethylamino) cyclopentadienyl zirconium (Cp-Zr) as a precursor, and the effect of deposition temperature on the structural and electrical properties of ZrO2 thin films are studied. The ALD process window of Cp-Zr is found at 300–350 °C, and no noticeable change in the film composition occurs within the ALD process window and the films are all stoichiometric. However, the crystallinity of the film is significantly affected by the deposition temperature. At 300 °C, only the cubic and tetragonal phases are detected, while the monoclinic peak starts to appear at 325 °C. Consequently, the highest dielectric constant (35.8) is observed for the ZrO2 films deposited at 300 °C. In contrast, ZrO2 films deposited at 350 °C show the lowest leakage current. This trend is due to the lower carbon impurity contents along with the increase in deposition temperature. To study the electrical properties of ZrO2 films in more detail, capacitance–voltage hysteresis measurements are carried out; the hysteresis is reduced abruptly with an increase in deposition temperature.
Effect of substrate bias and oxygen partial pressure on properties of RF magnetron sputtered HfO2 thin films32(2014); http://dx.doi.org/10.1116/1.4825234View Description Hide Description
Among all dielectric materials, hafnium oxide qualifies to be one of the most significant candidates as high index optical coating material due to its excellent chemical and thermal stability with SiO2, the low refractive index material, apart from its excellent laser radiation resistance. In this article, microstructural, physical, and optical properties of two sets of hafnium oxide thin films deposited by radio frequency (RF) magnetron reactive sputtering under a mixed ambient of argon and oxygen have been investigated: one set at various oxygen partial pressure and with substrate biasing by 50 W pulse direct current (DC) and another set at similar gaseous ambient as above but without any substrate bias. Structure of all the HfO2 thin films have been found to be monoclinic through grazing incidence x-ray diffraction measurements. Mass density of the samples has been estimated by grazing incidence x-ray reflectivity measurements and compared with the atom density of the samples estimated through Rutherford back scattering study. The evolutions of optical properties of the films with respect to the variation of oxygen partial pressure and substrate biasing have been investigated by transmission spectrophotometry and spectroscopic ellipsometry. It has been observed that RF sputtering with pulse DC substrate bias and with 15–30% oxygen partial pressure in the ambient helps in achieving better quality HfO2 films with low void fraction and high refractive index.
Physical and electrical characterization of Ce-HfO2 thin films deposited by thermal atomic layer deposition32(2014); http://dx.doi.org/10.1116/1.4826174View Description Hide Description
This paper describes the deposition and characterization of Ce-modified HfO2 thin films. Layers were deposited on Si(100) substrates by thermal atomic layer deposition using (MeCp)2Hf(OMe)(Me), Ce(mmp)4, and H2O as the precursors. Spectroscopic ellipsometry and medium energy ion scattering were used to measure the thicknesses and compositions of the deposited films. After postdeposition annealing, a metastable cubic phase is found to be stabilized in the films. Capacitance–voltage measurements have been used to characterize the dielectric properties of deposited films before and after two annealing regimes. The equivalent oxide thickness of an as-deposited sample with nominal high-κ dielectric thickness of 6 nm is circa 2.8 nm from which the dielectric constant 31 was calculated. The leakage current density is in order of 10−6 A/cm2 at ±1 V. The fabrication of Ce-HfO2 films without plasma or O3-based atomic layer deposition represents a potentially useful manufacturing route for future scaled devices.
32(2014); http://dx.doi.org/10.1116/1.4837295View Description Hide Description
The physical and electrical properties of the gate stack high-k/Al2O3/GeO2/p-Ge were studied in detail, where the high-k is either HfO2 or alloyed HfO2 (HfZrOy, HfGdOx, or HfAlOx). Electrical measurements combined with x-ray photoelectron spectroscopy chemical bonding analysis and band alignment determination were conducted in order to assess the suitability of hafnium-based high-k for this kind of gate stacks, with emphasis on low density of interface states and border traps. HfAlOx was found to be the most promising high-k from those studied. The authors have also found that the current- voltage trends for the various systems studied can be explained by the band alignment of the samples obtained by our x-ray photoelectron spectroscopy analysis.