Petri Raisanen

Nucleation and growth of atomic layer deposited HfO2 gate dielectric layers on chemical oxide (Si-O-H) and thermal oxide (SiO2 or Si-O-N) underlayers

A study was undertaken to determine the efficacy of various underlayers for the nucleation and growth of atomic layer deposited HfO2 films. These were compared to films grown on hydrogen terminated Si. The use of a chemical oxide underlayer results in almost no barrier to film nucleation, enables linear and predictable growth at constant film density, and the most two-dimensionally continuous HfO2 films. The ease of nucleation is due to the large concentration of OH groups in the hydrous, chemical oxide. HfO2 grows on chemical oxide at a coverage rate of about 14% of a monolayer per cycle, and films are about 90% of the theoretical density of crystalline HfO2. Growth on hydrogen terminated Si is characterized by a large barrier to nucleation and growth, resulting in three-dimensional, rough, and nonlinear growth. Thermal oxide/oxynitride underlayers result in a small nucleation barrier, and nonlinear growth at low HfO2 coverages. The use of chemical oxide underlayers clearly results in the best HfO2 layer...

Morphology and crystallization kinetics in HfO2 thin films grown by atomic layer deposition

We report the effects of annealing on the morphology and crystallization kinetics for the high-κ gate dielectric replacement candidate hafnium oxide (HfO2). HfO2 films were grown by atomic layer deposition (ALD) on thermal and chemical SiO2 underlayers. High-sensitivity x-ray diffractometry shows that the as-deposited ALD HfO2 films on thermal oxide are polycrystalline, containing both monoclinic and either tetragonal or orthorhombic phases with an average grain size of ∼8.0 nm. Transmission electron microscopy shows a columnar grain structure. The monoclinic phase predominates as the annealing temperature and time increase, with the grain size reaching ∼11.0 nm after annealing at 900u200a°C for 24 h. The crystallized fraction of the film has a strong dependence on annealing temperature but not annealing time, indicating thermally activated grain growth. As-deposited ALD HfO2 films on chemical oxide underlayers are amorphous, but show strong signatures of ordering at a subnanometer level in Z-contrast scannin...

Suppressed crystallization of Hf-based gate dielectrics by controlled addition of Al2O3 using atomic layer deposition

We demonstrate significantly improved thermal stability of the amorphous phase for hafnium-based gate dielectrics through the controlled addition of Al2O3. The (HfO2)x(Al2O3)1−x films, deposited using atomic layer deposition, exhibit excellent control over a wide range of composition by a suitable choice of the ratio between the Al and Hf precursor pulses. By this method, extremely predictable hafnium aluminate compositions are obtained, with Hf cation fractions ranging from 20% up to 100%, as measured by medium energy ion scattering. Using x-ray diffraction, we show that (HfO2)x(Al2O3)1−x films with Hf:Al∼3:1 (25% Al) remain amorphous up to 900u200a°C, while films with Hf:Al∼1:3 (75% Al) remain amorphous after a 1050u200a°C spike anneal.

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.

Impact of the precursor chemistry and process conditions on the cell-to-cell variability in 1T-1R based HfO 2 RRAM devices

The Resistive RAM (RRAM) technology is currently in a level of maturity that calls for its integration into CMOS compatible memory arrays. This CMOS integration requires a perfect understanding of the cells performance and reliability in relation to the deposition processes used for their manufacturing. In this paper, the impact of the precursor chemistries and process conditions on the performance of HfO2 based memristive cells is studied. An extensive characterization of HfO2 based 1T1R cells, a comparison of the cell-to-cell variability, and reliability study is performed. The cells’ behaviors during forming, set, and reset operations are monitored in order to relate their features to conductive filament properties and process-induced variability of the switching parameters. The modeling of the high resistance state (HRS) is performed by applying the Quantum-Point Contact model to assess the link between the deposition condition and the precursor chemistry with the resulting physical cells characteristics.