Eric Shero

Thermal stability of polycrystalline silicon electrodes on ZrO2 gate dielectrics

Thermal stability of gate stack structures composed of ZrO2 gate dielectrics and silicon electrodes was investigated. The ZrO2 films were deposited by atomic layer deposition, while the polycrystalline silicon electrodes were deposited using different variants of chemical (CVD) and physical vapor deposition (PVD). Zirconium silicide formation was noted in all CVD-electroded samples after subsequent annealing treatments at temperatures above 750 °C, but not in the room temperature PVD-electroded samples, even after gate annealing at 1050 °C. The dependence of zirconium silicide formation on the Si deposition process was explained using thermodynamic arguments which explicitly include the effects of oxygen deficiency of the metal oxide films.

Adsorption of Moisture and Organic Contaminants on Hafnium Oxide, Zirconium Oxide, and Silicon Oxide Gate Dielectrics

Hafnium oxide (HfO 2 ) and zirconium oxide (ZrO 2 ) are two high-K materials having the potential to replace silicon oxide (SiO 2 ) as the gate dielectric. Atmospheric molecular contamination can affect the quality of the new gate dielectric film in a manner similar to SiO 2 . Characterization of contaminant adsorption behavior of these high-K films should assist in deciding their potential for successful integration in silicon metal oxide semiconductor technology. The interaction of moisture and organics (in particular, isopropanol, IPA) as common interfacial contaminants with a 5 nm HfO 2 film deposited by atomic layer chemical vapor deposition (ALCVD), which is a trademark of ASM International) is investigated using atmospheric pressure ionization mass spectrometry (APIMS); the kinetics and mechanism are compared to that of ZrO 2 and SiO 2 . HfO 2 and ZrO 2 have similar moisture adsorption loading, but are significantly higher than that of SiO 2 . However, almost all the adsorbed moisture can he removed from SiO 2 and HfO 2 after a 300°C bake under nitrogen purge, whereas ZrO 2 surfaces retain 20-30% of the adsorbed moisture. Experiments with IPA show that the adsorption loading on the three surfaces has the following order: ZrO 2 > HfO 2 > SiO 2 . A multilayer model for adsorption of water and IPA is developed to understand the mechanism of interactions of contaminants with the three surfaces. Results from the application of this multilayer model to the experimental data indicate that ZrO 2 forms the strongest surface-hydroxyl (X-OH) bond.

Ozone Based Atomic Layer Deposition of Hafnium Oxide and Impact of Nitrogen Oxide Species

It has recently been reported that nitrogen oxide species (e.g., N 2 O 5 , NO 2 , NO 3 , and/or N 2 O) can have an impact on ozone based atomic layer deposition (ALD) of metal oxides when ozone is generated by dielectric barrier discharge (DBD) in O 2 /N 2 mixtures. In this work, we further investigate the effect of the O 2 /N 2 ratio in the DBD for Hfo 2 ALD using HfCl 4 as metal precursor. Using O 3 in the absence of nitrogen oxides, uniform HfO 2 layers are obtained between 200 and 250°C in a hot wall cross flow reactor. The self-limiting nature of the O 3 and HfCl 4 reaction is demonstrated at 225°C and the growth-per-cycle is 0.12 nm. At higher temperature, O 3 decomposes at the HfO 2 coated reactor walls, resulting in a decreasing HfO 2 thickness over Si substrates in the direction of the gas flow. Using O 3 in combination with nitrogen oxides by DBD in N 2 /O 2 mixtures, we obtained uniform HfO 2 layers in the 200-300°C temperature range. At 300°C, the GPC is 0.14 nm and the HfO 2 films show a low impurity content. Both processes produce high quality dielectric layers in Pt gated capacitors.

New Mechanisms for Ozone-Based ALD Growth of High-k Dielectrics via Nitrogen-Oxygen Species

Ozone (O3) is a commonly used oxidant in ALD of various high-k metal oxides. Commercially available ozone delivery systems commonly rely on the dielectric barrier discharge and often utilize nitrogen in the feed gas to provide consistent ozone generation. Through a complex series of plasma reactions, various NxOy species can also form within the corona from O2 in the presence of N2. These species, while present in various concentrations in the generator effluent, are unregulated by the delivery system which measures and actively controls the O3 concentration only.

Atomic Layer Deposition: An Enabling Technology for Microelectronic Device Manufacturing

Atomic layer deposition (ALD) recently emerged as an enabling technology for microelectronic device fabrication. This technique provides the unique capability to deposit ultra thin films with the thickness control, uniformity, step coverage, and electrical/mechanical properties required to support device manufacturing at the 45 nm node and beyond. This paper will review the fundamentals of ALD processing and describe the equipment used. Applications of ALD in the fabrication of advanced gate stacks, on-chip capacitors, and thin film magnetic heads are presented.

Highly scalable ALD-deposited hafnium silicate gate stacks for low standby power applications

The electrical performance of hafnium silicate (HfSiOx) gate stacks grown by atomic layer deposition (ALD) has been evaluated in capacitors and transistors. First, scaling potential of HfSiOxlayers was studied as function of composition and thickness. It is shown that the equivalent oxide thickness scales down with decreasing layer thickness and increasing Hf-content. The gate leakage (at Vfb-1V), however, is mainly determined by the physical layer thickness. For the same equivalent oxide thickness (EOT) target, the lowest leakage is observed for the layers with the highest Hf-content. Leakage values as low as 1×10-3 A/cm 2 for an equivalent oxide thickness of 1.3 nm have been obtained, Second, the thermal stability against crystallization of the ALD HfSiO x has been studied and related to their electrical properties. The thermal stability of HfSiOx decreases with increasing Hf-content that necessitates the use of nitridation. The influence of various annealing conditions on the nitrogen incorporation is also studied, Finally, the effect of HfSiOx composition and postdeposition nitridation is discussed on transistor level. TaN metal gate transistor data indicate that nitridation reduces the gate leakage and that Hf-rich HfSiOx layers show the best scaling potential, i.e., highest performance for the lowest gate leakage.

Sources and transport mechanisms of gaseous impurities in vertical thermal reactors

This work focuses on the different mechanisms of impurity transport and distribution in process equipment, with particular emphasis on moisture distribution in vertical thermal reactors. The results are important in both control and metrology of gaseous impurities during startup and process cycles. In addition to direct measurements, a comprehensive theoretical model is developed which is useful for process parametric study to optimize the process parameters or improve the reactor design. The results show that the impurity purge during startup is controlled by the diffusion in the wafer spacing; this diffusion becomes a bottleneck for large wafers and high furnace loading. The major sources of impurities during the wafer introduction (wafer push) stage are backdiffusion, impurity diffusion from the wafer spacing and outgassing of wafers as they enter the reactor. The primary sources during operation are permeation through the quartz reactor walls and leakage, together with backdiffusion, from the furnace outlet gaskets. A constant source of impurity is permeation through the polymeric tubing and fittings commonly used on the inlet side of the furnace. The kinetics and the mechanisms of each of these sources are determined through a combination of experimental measurements and process simulation.