Dy-incorporated HfO₂ gate oxide with TaN gate electrode nMOS device has been developed for high performance CMOS applications in 22nm node technology. DyO /HfO bi-layer structure shows thin EOT with reduced leakage current and less charge trapping compared to HfO₂. Excellent electrical performance of the DyO-capped HfO₂ oxide n-MOSFET such as lower V[subscript TH], higher drive current, and improved channel electron mobility are reported. DyO/HfO samples also show better immunity for V[subscript TH] instability and less severe charge trapping characteristics. Its charge trapping characteristics, conduction mechanisms and dielectric reliability have been investigated in this work. As an application to memory device, HfON charge trapping layered NAND flash memory is developed and characterized. First, temperature-dependent Dy diffusion and the diffusion-driven Dy dipole formation process are discussed to clarify the origin of V[subscript TH] shift, and eventually modulate the effective work function in Dy-Hf-O/SiO₂ system. The Dy-induced dipoles are closely related to the Dy-silicate formation at the high-k/SiO₂ interfaces since the V[subscript FB] shift in Dy₂O₃ is caused by the dipole and coincides with the Dy-silicate formation. Dipole formation is a thermally activated process, and more dipoles are formed at a higher temperature with a given Dy content. The Dy-silicate related bonding structure at the interface is associated with the strength of the Dy dipole moment, and becomes dominant in controlling the V[subscript FB]/V[scubscript TH] shift during high temperature annealing in the Dy- Hf-O/SiO₂ gate oxide system. Dy-induced dipole reduces the degradation of the electron mobility. Second, to understand the reduced leakage current of the DyO/HfO sample, the effective barrier height of Dy₂O₃ was calculated from FN tunneling models, and the band diagram was estimated. The higher effective barrier height of Dy₂O₃, which is around 2.32 eV calculated from the F-N plot, accounts for the reduced leakage current in Dy incorporated HfO₂ nMOS devices. The lower barrier height of HfO₂ result in increased electron tunneling currents enhanced by the buildup of hole charges trapped in the oxide, which causes a severe increase of stress-induced leakage current (SILC), leading to oxide breakdown. However, the increased barrier height in Dy incorporated HfO₂ inhibits a further increase of the electron tunneling from the TaN gate, and trapped holes lessen the hole tunneling currents, resulting in a negligible SILC. The lower trap generation rate by the reduced hole trap density and the reduced hole tunneling of the Dy-doped HfO₂ dielectric demonstrates the high dielectric breakdown strength by weakening the charge trapping and defect generation during the stress. Based on these fundamental studies of the dielectric breakdown, modeling of time-dependent dielectric breakdown (TDDB) was done. The intrinsic TDDB of the Dy-doped HfO₂ gate oxide having 1 nm EOT is characterized by the progressive breakdown (PBD) model. At high temperature, the PBD becomes severe, since thermal energy causes carrier hopping between the localized weak spots. The voltage acceleration factor derived from the power law shows a realistic prediction in comparison with those from the 1/E model. The increase of the voltage acceleration factor at lower stress voltage is due to the lower trap generation rate in Dy- incorporated HfO₂. This voltage acceleration factor can be easily extended to include temperature dependency, and the effective activation energy derived from the power law is voltage dependent. Lastly, I studied the device characteristics of thin HfON charge-trap layer nonvolatile memory in a TaN/Al₂O₃/HfON/SiO₂/p-Si (TANOS) structure. A large memory window and fast erase speed, as well as good retention time, were achieved by using the NH₃ nitridation technique to incorporate nitrogen into the thin HfO₂ layer, which causes a high electron-trap density in the HfON layer. The higher dielectric constant of the HfON charge-trap layer induces a higher electric field in the tunneling oxide at the same voltage compared to non-nitrided films and, thus, creates a high Fowler-Nordheim (FN) tunneling current to increase the erase and programming speed. The trap-level energy in the HfON layer was calculated by using an amphoteric model. / text

The performance and power scaling of metal-oxide-semiconductor field-effect-transistors (MOSFETs) has been historically achieved through shrinking the gate length of transistors for over three decades. As Si complementary metal-oxide-semiconductor (CMOS) scaling is approaching the physical and optical limits, the emerging technology involves new materials for the gate dielectrics and the channels as well as innovative structures. III-V materials have much higher electron mobility compared to Si, which can potentially provide better device performance. Hence, there have been tremendous research activities to explore the prospects of III-V materials for CMOS applications. Nevertheless, the key challenges for III-V MOSFETs with high-[kappa] oxides such as the lack of high quality, thermodynamically stable insulators that passivate the gate oxide/III-V interface still hinder the development of III-V MOS devices. The main focus of this dissertation is to develop the proper processes and structures for III-V MOS devices that result in good interface quality and high device performance. Firstly, fabrication processes and device structures of surface channel MOSFETs were investigated. The interface quality of In[subscript 0.53]Ga[subscript 0.47]As MOS devices was improved by developing the gate-last process with more than five times lower interface trap density (D[subscript it]) compared to the ones with the gate-first process. Furthermore, the optimum substrate structure was identified for inversion-type In[subscript 0.53]Ga[subscript 0.47]As MOSFETs by investigating the effects of channel doping concentration and thickness on device performance. With the proper process and channel structures, the first inversion-type enhancement-mode In[subscript 0.53]Ga[subscript 0.47]As MOSFETs with equivalent oxide thickness (EOT) of ~10 Å using atomic layer deposited (ALD) HfO₂ gate dielectric were demonstrated. The second part of the study focuses on buried channel InGaAs MOSFETs. Buried channel InGaAs MOSFETs were fabricated to improve the channel mobility using various barriers schemes such as single InP barrier with different thicknesses and InP/InAlAs double-barrier. The impacts of different high-[kappa] dielectrics were also evaluated. It has been found that the key factors enabling mobility improvement at both peak and high-field mobility in In[subscript 0.7]Ga[subscript 0.3]As quantum-well MOSFETs with InP/InAlAs barrier-layers are 1) the epitaxial InP/InAlAs double-barrier confining carriers in the quantum-well channel and 2) good InP/Al₂O₃/HfO₂ interface with small EOT. Record high channel mobility was achieved and subthreshold swing (SS) was greatly improved. Finally, InGaAs tunneling field-effect-transistors (TFETs), which are considered as the next-generation green transistors with ultra-low power consumption, were demonstrated with more than two times higher on-current while maintaining much smaller SS compared to the reported results. The improvements are believed to be due to using the In[subscript 0.7]Ga[subscript 0.3]As tunneling junction with a smaller bandgap and ALD HfO₂ gate dielectric with a smaller EOT. / text

Aggressive scaling required to augment device performance has caused conventional electrode materials to approach their physical scaling limits. Alternative metal gate/high dielectric constant (MG/High-[kappa]) stacks have been implemented successfully in commercial devices and hold promise for further scaling based performance advances. Existing MG/High-[kappa] technology does not achieve a single metal n-MOS to p-MOS effective work function (EWF) tuning range suitable for bulk silicon (Si) device applications. Dual metal gates (DMGs) utilizing a separate metal for n-MOS and p-MOS electrodes increases the cost and complexity of fabrication. The research presented herein introduces a method by which the cost and complexity of MG/High-[kappa] device fabrication may be reduced. Innovative fin field effect transistors (FinFETs) incorporating 3 dimensional ultra thin body silicon on oxide (3-D UTB-SOI) technology display superior electrical characteristics compared to bulk Si devices at the nanometer (nm) dimension and require only a +/-200meV n-MOS to p-MOS EWF tuning range around the Si mid-gap. Single metals capable of achieving this +/-200meV EWF tuning range have been evaluated herein and the tuning mechanisms investigated and engineered to develop a single MG/High-[kappa] FinFET the fabrication complexity of which is reduced by 40%. More specifically, the research shows that the metal thickness of titanium nitride/hafnium silicon oxide (TiN/HfSiOx) gate stack may be engineered to achieve an n-MOS (thinner TiN) to p-MOS (thicker TiN) appropriate FinFET EWF tuning range. FinFETs may be fabricated by depositing a single p-MOS appropriate TiN thickness which may be selectively etched back to achieve thinner, n-MOS appropriate films. Similar electrical behavior is exhibited by etched back and as deposited TiN electrode FinFETs. The single metal etch back fabrication method removes many of the additional steps required for DMG fabrication and preserves the integrity of the MG/High-[kappa] interface between n-MOS and p-MOS devices. These advantages result in reduced fabrication complexity and improved reliability and reproducibility. / text

<p>Converting wood into paper is a complex process involving many different stages, one of which is pulping. Pulping involves liberating the wood fibres from each other, which can be done either chemically or mechanically. This thesis focuses on the most common chemical pulping method, the kraft cooking process, and especially on a recently developed improvement of the impregnation phase, which is the first part of a kraft cook.</p><p>Extended impregnation kraft cooking (EIC) technique is demonstrated to be an improvement of the kraft pulping process and provides a way to utilize softwood to a higher degree, at higher pulp yield. We demonstrate that it is possible to produce softwood (<em>Picea abies</em>) kraft pulp using a new cooking technique, resulting in a pulp that can be defibrated without inline refining at as high lignin content as 8% on wood, measured as kappa numbers above 90. Lignin is the wood constituent that holds the wood fibres together in the wood matrix. The new cooking technique uses the differences in reaction rate between the diffusion and consumption of hydroxide ions; it is used to ensure a homogenous impregnation of wood chips at lower impregnation temperatures and longer impregnation times than are generally used in the industry. The applied cooking temperatures are also substantially lower than those used in conventional kraft pulping systems, promoting uniform delignification. This results in a narrower kappa number distribution than in lab-cooked conventional kraft pulp.</p><p>High-kappa-number pulps were investigated for pulp sheet properties such as tensile strength, tensile stiffness, and compression strength. It was demonstrated that an EIC pulp of kappa number 95 has strength properties comparable to those of a conventional pulp of kappa number 82. Comparing the effects of starch multilayers on conventional and EIC pulps reveals similar effects. The use of the starch multilayer treatment increased the tensile index and decreased the tensile stiffness and short-span compression test (SCT) indices.</p><p>The EIC technique has also been used to produce a series of bleachable-grade pulps. The results indicate the possibility of increasing the lignin content of the pulp entering the oxygen delignification stage, since the reject content of gently defibered pulp is lower than 0.1% at kappa number 49.</p><p>In this thesis, we recommend that wood chips be impregnated for 2 h at 110 °C to neutralize acidic compounds in the wood and impregnate the chips with cooking chemicals, and that the ensuing cook be performed at 135–140 °C, depending on the target kappa number. We also recommend increasing the available amounts of cooking chemicals in the impregnation stage by using a higher liquor-to-wood ratio and keeping the alkali profile fairly high in the ensuing cook. This concept will reduce the amount of reject material, increase the pulping uniformity, and increase the selectivity towards lignin degradation in the kraft cook.</p> / <p>Omvandling av ved till papper är en komplicerad process som består av många olika steg där ett är massaframställningen (eng. <em>pulping</em>). Massaframställning medför att vedfibrerna frigörs från varandra på kemisk eller mekanisk väg. Denna avhandling fokuserar på den vanligaste kemiska metoden, sulfatkokning och speciellt den nyligen utvecklade förbättringen av impregnerings fasen, som är den första delen av ett sulfatkok. <em></em></p><p>Här visas att<em> Extended Impregnation kraft Cooking </em>(EIC) innebär en förbättring av sulfatkokningen och ett sätt att uppnå högre vedutnyttjande vid högre utbyte för barrved. Vi visar att det är möjligt att producera barrvedsmassa med en ny kokningsprincip som resulterar i en massa som är defibrerbar utan inline-raffinering vid så högt lignin innehåll som 8% (på ved), mätt som kappatal över 90. Lignin är den vedkomponent som håller ihop vedfibrerna i vedmatrisen. Kokningsprincipen utnyttjar skillnaderna i reaktionshastighet mellan diffusion och konsumtion av hydroxidjoner och nyttjas till att skapa en homogen impregnering av vedflisen vid lägre impregneringstemperatur och under längre tid än vad som vanligen används i industrin. De använda koktemperaturerna är också betydligt lägre än vid konventionell sulfatkokning vilket gynnar jämn delignifiering. Detta resulterar i en smalare kappatalsfördelning jämfört med laboratoriekokade konventionella massor.</p><p>Massor med höga kappatal undersöktes med avseende på egenskaper hos handark, såsom dragstyrka, dragstyvhet och kompressionsstyrka Det visades att handark från EIC massa vid kappatal 95 hade jämförbara styrkeegenskaper med konventionell massa vid kappatal 82. Vid jämförelse av effekten av stärkelse multilager på konventionella och EIC massor avslöjar liknande effekter. Användningen av stärkelsemultilager ökade dragindex och minskade dragstyvhets- och kompressions index (SCT, short-compression test).</p><p>Kokprincipen har även använts för att ta fram en serie blekbara massor. Resultaten visar på möjligheten att öka lignininnehållet i massan in till i syrgasdelignifierings-steget eftersom spetinnehållet för milt defibrerad massa var lägre än 0,1% vid kappatal 49.</p><p>I den här avhandlingen rekommenderar vi att vedflis impregneras i 2 timmar vid 110 °C för att neutralisera sura komponenter i veden och impregnera flisen med kokkemikalier, samt att utföra det efterföljande koket vid 135–140 °C beroende på önskat kappatal. Vi rekommenderar även att öka den tillgängliga mängden kokkemikalier i impregneringssteget genom att använda högre vätske-ved förhållande och att hålla alkali profilen relativt hög i det efterföljande koket. Detta koncept reducerar spetmängden, ger jämnare kokning och ökar selektiviteten för nedbrytning av lignin i sulfatkoket.</p>

Converting wood into paper is a complex process involving many different stages, one of which is pulping. Pulping involves liberating the wood fibres from each other, which can be done either chemically or mechanically. This thesis focuses on the most common chemical pulping method, the kraft cooking process, and especially on a recently developed improvement of the impregnation phase, which is the first part of a kraft cook. Extended impregnation kraft cooking (EIC) technique is demonstrated to be an improvement of the kraft pulping process and provides a way to utilize softwood to a higher degree, at higher pulp yield. We demonstrate that it is possible to produce softwood (Picea abies) kraft pulp using a new cooking technique, resulting in a pulp that can be defibrated without inline refining at as high lignin content as 8% on wood, measured as kappa numbers above 90. Lignin is the wood constituent that holds the wood fibres together in the wood matrix. The new cooking technique uses the differences in reaction rate between the diffusion and consumption of hydroxide ions; it is used to ensure a homogenous impregnation of wood chips at lower impregnation temperatures and longer impregnation times than are generally used in the industry. The applied cooking temperatures are also substantially lower than those used in conventional kraft pulping systems, promoting uniform delignification. This results in a narrower kappa number distribution than in lab-cooked conventional kraft pulp. High-kappa-number pulps were investigated for pulp sheet properties such as tensile strength, tensile stiffness, and compression strength. It was demonstrated that an EIC pulp of kappa number 95 has strength properties comparable to those of a conventional pulp of kappa number 82. Comparing the effects of starch multilayers on conventional and EIC pulps reveals similar effects. The use of the starch multilayer treatment increased the tensile index and decreased the tensile stiffness and short-span compression test (SCT) indices. The EIC technique has also been used to produce a series of bleachable-grade pulps. The results indicate the possibility of increasing the lignin content of the pulp entering the oxygen delignification stage, since the reject content of gently defibered pulp is lower than 0.1% at kappa number 49. In this thesis, we recommend that wood chips be impregnated for 2 h at 110 °C to neutralize acidic compounds in the wood and impregnate the chips with cooking chemicals, and that the ensuing cook be performed at 135–140 °C, depending on the target kappa number. We also recommend increasing the available amounts of cooking chemicals in the impregnation stage by using a higher liquor-to-wood ratio and keeping the alkali profile fairly high in the ensuing cook. This concept will reduce the amount of reject material, increase the pulping uniformity, and increase the selectivity towards lignin degradation in the kraft cook. / Omvandling av ved till papper är en komplicerad process som består av många olika steg där ett är massaframställningen (eng. pulping). Massaframställning medför att vedfibrerna frigörs från varandra på kemisk eller mekanisk väg. Denna avhandling fokuserar på den vanligaste kemiska metoden, sulfatkokning och speciellt den nyligen utvecklade förbättringen av impregnerings fasen, som är den första delen av ett sulfatkok. Här visas att Extended Impregnation kraft Cooking (EIC) innebär en förbättring av sulfatkokningen och ett sätt att uppnå högre vedutnyttjande vid högre utbyte för barrved. Vi visar att det är möjligt att producera barrvedsmassa med en ny kokningsprincip som resulterar i en massa som är defibrerbar utan inline-raffinering vid så högt lignin innehåll som 8% (på ved), mätt som kappatal över 90. Lignin är den vedkomponent som håller ihop vedfibrerna i vedmatrisen. Kokningsprincipen utnyttjar skillnaderna i reaktionshastighet mellan diffusion och konsumtion av hydroxidjoner och nyttjas till att skapa en homogen impregnering av vedflisen vid lägre impregneringstemperatur och under längre tid än vad som vanligen används i industrin. De använda koktemperaturerna är också betydligt lägre än vid konventionell sulfatkokning vilket gynnar jämn delignifiering. Detta resulterar i en smalare kappatalsfördelning jämfört med laboratoriekokade konventionella massor. Massor med höga kappatal undersöktes med avseende på egenskaper hos handark, såsom dragstyrka, dragstyvhet och kompressionsstyrka Det visades att handark från EIC massa vid kappatal 95 hade jämförbara styrkeegenskaper med konventionell massa vid kappatal 82. Vid jämförelse av effekten av stärkelse multilager på konventionella och EIC massor avslöjar liknande effekter. Användningen av stärkelsemultilager ökade dragindex och minskade dragstyvhets- och kompressions index (SCT, short-compression test). Kokprincipen har även använts för att ta fram en serie blekbara massor. Resultaten visar på möjligheten att öka lignininnehållet i massan in till i syrgasdelignifierings-steget eftersom spetinnehållet för milt defibrerad massa var lägre än 0,1% vid kappatal 49. I den här avhandlingen rekommenderar vi att vedflis impregneras i 2 timmar vid 110 °C för att neutralisera sura komponenter i veden och impregnera flisen med kokkemikalier, samt att utföra det efterföljande koket vid 135–140 °C beroende på önskat kappatal. Vi rekommenderar även att öka den tillgängliga mängden kokkemikalier i impregneringssteget genom att använda högre vätske-ved förhållande och att hålla alkali profilen relativt hög i det efterföljande koket. Detta koncept reducerar spetmängden, ger jämnare kokning och ökar selektiviteten för nedbrytning av lignin i sulfatkoket. / QC 20120216