Thesis (M.S. in M.S.E.)--School of Materials Science and Engineering, Georgia Institute of Technology, 2004. Directed by C.P. Wong. / Includes bibliographical references (leaves 94-102).

Thesis (M.S. in Ch. E.)--School of Chemical Engineering, Georgia Institute of Technology, 2004. Directed by Paul A. Kohl. / Includes bibliographical references (leaves 88-91).

Thesis (Ph. D.)--University of Texas at Austin, 2000. / Vita. Includes bibliographical references (leaves 140-141). Available also in a digital version from Dissertation Abstracts.

Thesis--M. Phil., University of Hong Kong, 1977.

Discrete charge-trapping flash memories are more promising than their floating-gate counterparts due to their physically discrete-trapping and coupling-free nature. Si3N4 is conventional material as charge-trapping layer (CTL) for charge storage. The shortcomings of Si3N4 are its low dielectric constant and small barrier height at its interface with SiO2 tunneling layer. Therefore, this research aims to investigate new materials as CTL for improving the performance of the memory devices. The charge-trapping characteristics of La2O3 with and without nitrogen incorporation were investigated. Compared with the memory device with La2O3 as CTL, the one with nitrided La2O3 (LaON) showed larger memory window, higher program/erase (P/E) speeds and smaller charge loss, due to the nitrided La2O3 film exhibiting less crystallized structure, higher trap density induced by nitrogen incorporation, and suppressed leakage by nitrogen passivation. In order to further improve the performance of the memory device with LaON CTL, a device with band-engineered LaTiON/LaON structure as CTL was also explored, and demonstrated to have better performance than the one with LaON CTL. This was ascribed to the variable tunneling path of charge carriers under P/E and retention modes (realized by the band-engineered charge-trapping layer), high trap density of LaTiON, and large barrier height at the LaTiON/SiO interface. SrTiO 3and BaTiO3 ,both ofwhich are typical perovskite-type dielectrics, also possess distinguished characteristics as CTL, including remarkably high dielectric constant and large conduction-band offset relative to SiO2. The charge-trapping properties of SrTiO3 with and without fluorine incorporation were studied. The device with fluorinated SrTiO3 film showed promising performance in terms of higher P/E speeds at a low gate voltage, better endurance and data retention compared with that without fluorine treatment. These advantages were associated with generated deep-level traps, reduced leakage path, and enhanced strength of the film due to the highest electro-negativity of the fluorine atoms incorporated in the film. The charge-trapping properties of BaTiO3 with and without Zr incorporation were also investigated, where Zr incorporated in BaTiO3 could strengthen the dielectric film and improve its thermodynamic stability. The device with Zr incorporation exhibited similar memory window as the one without Zr incorporation, but higher program speed at low gate voltage, better endurance and data retention, due to the Zr-doped BaTiO3 exhibiting higher charge-trapping efficiency and higher density of traps with deeper energy levels. Besides nitride-based memories, nanocrystal-based memories are another type of charge-trapping memories, where nanocrystals (NCs) embedded into a dielectric are used for charge storage. Memory devices with Ga2O3 NCs as CTL were investigated, which are compatible with the CMOS process. The Ga2O3 NCs displayed higher trap density than the Ga2O3 dielectric film. Moreover, compared with the device with Ga2O 3NCs as CTL, the one with nitrided Ga2O3 NCs showed larger memory window, higher operating speed and better data retention, mainly due to higher charge-trapping efficiency of the nitrided Ga2O3 NCs and nitrogen-induced suppressed formation of interlayer at the Ga2O/SiO interface. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Discrete charge-trapping flash memory is being developed for the next-generation commercial flash-memory applications due to its advantages over the traditional floating-gate counterpart. Currently, Si3N4 is widely used as charge-trapping layer (CTL). However, Si3N4 has low dielectric constant and small conduction-band offset with respect to the SiO2 tunneling layer, imposing limitation on further applications. Therefore, this research emphasized on investigating new dielectrics with appropriate fabrication methods to replace Si3N4 as CTL for achieving improved memory performance. Firstly, GeON CTL annealed at different temperatures was investigated. The memory device with post-deposition annealing at 600 0C exhibited the largest memory window, the best charge retention performance, and the highest reliability. These good results are due to the fact that optimal annealing temperature could suppress shallow traps and also produce new traps with desirable energy levels in the CTL. Since ZnON has a negative conduction-band offset (NCBO) with respect to Si, the traps located in the bandgap of ZnON should have deep energy levels. The memory performances of ZrON film with and without Zn doping were studied. Experimental results showed that ZrZnON film had higher program speed and better charge retention performance due to many deeper trap levels induced by the Zn doping, as well as higher erase speed due to the direct recombination of electrons at these deeper trap levels with incoming holes and the intermediary role of these deeper trap levels under erase mode. MoO3 is another NCBO dielectric with a high K value and many oxygen vacancies. La2O3, a rare-earth metal oxide, is a promising dielectric as CTL. To combine the advantages of both La2O3 and MoO3, Mo-doped La2O3 was proposed as a new CTL. Compared to the device with pure La2O3, the one with LaMoO film as CTL had significantly larger C-V hysteresis window, much higher P/E speeds, and better charge retention due to the deeper-level traps and deeper quantum wells created by the LaMoO film. Nitrogen incorporation is a popular approach to increase the trap density in the bulk of CTL. In this research, the memory performances of GdTiO films with and without nitrogen incorporation were compared. Since the nitrogen incorporation induced smaller equivalent oxide thickness, produced nitride-related traps with desirable energy level and larger cross-section for charge capture, the GdTiON film possessed better memory performance than the GdTiO film. Finally, fluorine plasma was employed to improve the quality of blocking layer. The memory device with AlOF blocking layer obtained higher program speed, better reliability and better charge retention than that based on AlO blocking layer. The improved performance was due to the fact that the fluorine incorporation passivated the defects and removed the excess oxygen in the bulk of the blocking layer. In summary, dielectric plays important roles in the performance of charge-trapping flash memory. Memory devices with GeON, ZrZnON, LaMoO, or GdTiON as charge trapping layer and AlOF as blocking layer can produce large memory window, high program/erase speed and good charge retention. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

With the scaling of devices, integration of porous ultra low-κ dielectric materials into Cu interconnect becomes necessary. Low-k dielectric materials usually consist of a certain number of methyl groups and pores incorporated into a SiO₂ backbone structure to reduce the dielectric constant. They are frequently exposed to various plasmas, since plasma is widely used in VLSI semiconductor fabrication such as etching, ashing and deposition. This dissertation is aimed at exploring the interaction between plasma and low-κ dielectric surfaces. First, plasma assisted the atomic layer deposition (ALD) of Ta-based Cu barriers. Atomic layer deposition of Ta barriers is a self-limited surface reaction, determined by the function groups on the low-κ dielectric surface. But it was found TaCl₅ precursor could not nucleate on the organosilicate low-κ surface that was terminated with methyl groups. Radical NH[subscript x] beam, generated by a microwave plasma source, could activate the surface through exchanging with the methyl groups on the low-κ surface and providing active Si-NH[subscript x] nucleation sites for TaCl₅ precursors. Results from Monte Carlo simulation of the atomic layer deposition demonstrated that substrate chemistry was critical in controlling the film morphology. Second, the properties of low-κ dielectric materials tended to degrade under plasma exposure. In this dissertation, plasma damage of low-κ dielectric surface was investigated from a mechanistic point of view. Both carbon depletion and surface densification were observed on the top surface of damaged low-κ materials while the bulk remained largely uninfluenced. Plasma damage was found to be a complicated phenomenon involving both chemical and physical effects, depending on chemical reactivity and the energy and mass of the plasma species. With a downstream plasma source capable of separating ions from the plasma beam and an in-situ x-ray photoelectron spectroscopy (XPS) monitoring of the damage process, it was clear that ions played a more important role in the plasma damage process. Increase of dielectric constant after plasma damage was mainly attributed to moisture uptake and was confirmed with quantum chemistry calculation. Annealing was found to be effective in mitigating moisture uptake and thus restoring κ value. Finally, oxygen plasma damage to blanket and patterned low-κ dielectrics was studied in detail. Energetic ions in oxygen plasma contributed much to the loss of film hydrophobicity and dielectric constant through the formation of C=O and Si-OH. Based on results from residual gas analyses (RGA), three possible reaction paths leading to carbon depletion were proposed. This was followed by analytical solution of the evolution of carbon concentration during O₂ plasma damage. O₂ plasma damage to patterned CDO film was studied by TEM/EELS. And the damage behavior was simulated with Monte Carlo method. It was found that the charging potential distribution induced by plasma was important in determining the carbon loss in patterned low-k films. The charging potential distribution was mainly related to the geometry of low-k trench structures. To recover the dielectric constant, several recovery techniques were tried and briefly discussed. / text

published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

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