Atomic Layer Deposition of Amorphous Hafnium-based Thin Films with Enhance Thermal Stabilities

Atomic Layer Deposition of Amorphous Hafnium-based Thin Films with Enhance Thermal Stabilities
Author: Tuo Wang
Publisher:
Total Pages: 280
Release: 2010
Genre:
ISBN:
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The continuous scaling of microelectronic devices requires high permittivity (high-k) dielectrics to replace SiO2 as the gate material. HfO2 is one of the most promising candidates but the crystallization temperature of amorphous HfO2 is too low to withstand the fabrication process. To enhance the film thermal stability, HfO2 is deposited using atomic layer deposition (ALD), and incorporated with various amorphizers, such as La2O3, Al2O3, and Ta2O5. The incorporation is achieved by growing multiple ALD layers of HfO2 and one ALD layer of MO[subscript x] (M = La, Al, and Ta) alternately (denoted as [xHf + 1M]), and the incorporation concentration can be effectively controlled by the HfO2-to-MO[subscript x] ALD cycle ratio (the x value). The crystallization temperature of 10 nm HfO2 increases from 500 °C to 900 °C for 10 nm [xHf + 1M] film, where x = 3, 3, and 1 for M = La, Al, and Ta, respectively. The incorporation of La2O3, and Ta2O5 will not compromise the dielectric constant of the film because of the high-k nature of La2O3, and Ta2O5. Angle resolved X-ray photoelectron spectroscopy (AR-XPS) reveals that when the HfO2-to-MO[scubscript x] ALD cycle ratio is large enough (x> 3 and 4 for La and Al, respectively), periodic structures exist in films grown by this method, which are comprised of repeated M-free HfO2 ultrathin layers sandwiched between HfM[subscript x]O[scubscript y] layers. Generally, the film thermal stability increases with thinner overall thickness, higher incorporation concentration, and stronger amorphizing capability of the incorporated elements. When the x value is low, the films are more like homogeneous films, with thermal stabilities determined by the film thickness and the amorphizer. When the x value is large enough, the periodically-repeated structure may add an extra factor to stabilize the amorphous phase. For the same incorporation concentration, films with an appropriately high periodicity may have an increased thermal stability. The manner by which the periodic structure and incorporated element affect thermal stability is explored and resolved using nanolaminates comprised of alternating layers of [scubscript y]HfO2 and [xHf + 1M] x n, where y varied from 2 to 20, x varied from 1 to 2, and n varied from 4 to 22.

Microstructure and Properties of Hard and Optically Transparent HfO2 Films Prepared by High-rate Reactive High-power Impulse Magnetron Sputtering

Microstructure and Properties of Hard and Optically Transparent HfO2 Films Prepared by High-rate Reactive High-power Impulse Magnetron Sputtering
Author: Nai-Wen Pi
Publisher:
Total Pages: 50
Release: 2016
Genre:
ISBN:
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Hafnium Dioxide (HfO2) has an extraordinary high bulk modulus, high hardness, high chemical stability, high melting point and high thermal stability. This material can be used as protective coatings for application involving high temperature environments. HfO2 films were fabricated on Si using high-rate reactive high-power impulse magnetron sputtering (HiPIMS) using different deposition-averaged target power density Sd and voltage pulse durations t1. Five HfO2 films were prepared with (1) t1 = 25 microsecond, Sd = 7.6 Wcm−2 (T25S7), (2) t1 = 100 microsecond Sd =7.2 Wcm−2 (T100S7), (3) t1 = 200 microsecond, Sd =7.3 Wcm−2 (TS200S7), (4) t1 = 200 microsecond, Sd =18 Wcm−2 (T200S18) and (5) t1 = 200 microsecond, Sd =54 Wcm−2 (T200S54). Atomic force microscopy (AFM) images of the T200S54, T200S18 and T200S7 films exhibit a coarser granular structure with a similar grain size varying from 25 nm to 120 nm in diameter and an average grain size of ~70 nm. AFM images of the T25S7 and T100S7 films show smaller granular structures compared to the other three films. Transmission electron microscopy (TEM) studies show that all films are composed of an interlayer next to the Si interface followed by a nano-columnar structure layer. The interlayer structure of the films consists of a population of lower density nanoscale regions. A reduction in t1 and Sd in films T200S54, T200S18, T200S7 and T100S7 caused an increase in the interlayer thickness and a decrease in the width of the nano-columnar structures from ~46 nm to ~21 nm. This microstructural change was accompanied by a concomitant change of the grain boundary structure from tight and interlocking in films T200S54 and T200S18, to rough and thicker (~1 nm) boundaries in films T200S7 and T100S7. Film T25S7 exhibited an entirely different microstructure composed of a multilayered interlayer (~3 nm) and nano-columnar (~15 nm) structure. Films prepared with large t1 (200 microsecond) have a monoclinic HfO2 structure and that with small t1 (25 microsecond) an orthorhombic HfO2 structure. Film prepared with an intermediate t1 value (100 microsecond) exhibited a mixture of both monoclinic and orthorhombic phases. A high hardness of 17.6-17.0 GPa was shown for films with a monoclinic HfO2 structure. The films exhibited a refractive index of 2.02-2.11 and an extinction coefficient between [less than or equal to] 2x10-3 and 0.1x10-3 (both at a wavelength of 550 nm). High optical quality was achieved for films T200S54 and T200S18 owing to the presence of a dense microstructure with sharp and interlocking grain boundaries.

Atomic Layer Deposition for Semiconductors

Atomic Layer Deposition for Semiconductors
Author: Cheol Seong Hwang
Publisher: Springer Science & Business Media
Total Pages: 266
Release: 2013-10-18
Genre: Science
ISBN: 146148054X
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Offering thorough coverage of atomic layer deposition (ALD), this book moves from basic chemistry of ALD and modeling of processes to examine ALD in memory, logic devices and machines. Reviews history, operating principles and ALD processes for each device.

Understanding the Structure of Amorphous Thin Film Hafnia - Final Paper

Understanding the Structure of Amorphous Thin Film Hafnia - Final Paper
Author:
Publisher:
Total Pages: 8
Release: 2015
Genre:
ISBN:
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Hafnium Oxide (HfO2) amorphous thin films are being used as gate oxides in transistors because of their high dielectric constant ([kappa]) over Silicon Dioxide. The present study looks to find the atomic structure of HfO2 thin films which hasn't been done with the technique of this study. In this study, two HfO2 samples were studied. One sample was made with thermal atomic layer deposition (ALD) on top of a Chromium and Gold layer on a silicon wafer. The second sample was made with plasma ALD on top of a Chromium and Gold layer on a Silicon wafer. Both films were deposited at a thickness of 50nm. To obtain atomic structure information, Grazing Incidence X-ray diffraction (GIXRD) was carried out on the HfO2 samples. Because of this, absorption, footprint, polarization, and dead time corrections were applied to the scattering intensity data collected. The scattering curves displayed a difference in structure between the ALD processes. The plasma ALD sample showed the broad peak characteristic of an amorphous structure whereas the thermal ALD sample showed an amorphous structure with characteristics of crystalline materials. This appears to suggest that the thermal process results in a mostly amorphous material with crystallites within. Further, the scattering intensity data was used to calculate a pair distribution function (PDF) to show more atomic structure. The PDF showed atom distances in the plasma ALD sample had structure up to 10 Å, while the thermal ALD sample showed the same structure below 10 Å. This structure that shows up below 10 Å matches the bond distances of HfO2 published in literature. The PDF for the thermal ALD sample also showed peaks up to 20 Å, suggesting repeating atomic spacing outside the HfO2 molecule in the sample. This appears to suggest that there is some crystalline structure within the thermal ALD sample.