Y. Setiawan

Thermal stability of rare-earth based ultrathin Lu2O3 for high-k dielectrics

Lu2O3 thin film was deposited on n-type (100) Si substrates using pulsed laser deposition. A k value of 15.95 with an equivalent oxide thickness (EOT) of 1.10nm and a current density of 2.6×10−5A∕cm2 at +1V accumulation bias is achievable for the 4.5nm thick Lu2O3 thin film deposited at room temperature after postdeposition annealing at 600°C in oxygen ambient. Annealing a similar sample at 900°C caused the EOT and leakage current density to increase to 1.68nm and 1×10−4A∕cm2, respectively. High resolution transmission electron microscopy analysis has shown that Lu2O3 film remains amorphous at high temperature annealing at 900°C. An x-ray reflectivity analysis on a separately prepared sample with lower annealing temperature (800°C) suggested a formation of Lu-based silicate layer. It is believed that the formation of low-k silicate layer may have contributed to the observed increase in EOT and the reduction in the k value.

Effect of low fluence laser annealing on ultrathin Lu2O3 high-k dielectric

The effect of low fluence single pulse laser annealing on a pulsed laser deposited high-k dielectric, Lu2O3 is reported. With low fluence laser irradiation, high “k” of 45 is achieved with an equivalent oxide thickness of 0.39nm, without taking into account the quantum mechanical tunneling effect. High-resolution transmission electron microscopy micrograph revealed well-ordered epitaxial-like interfacial layer. High-resolution Rutherford backscattering confirmed the presence of Lu-based silicate layer at the interface. It was proposed that the high dielectric constant was caused by the increased ionic polarizability in the film, thereby increasing the ionic contribution of the dielectric constant.

Laser-induced Ni(Ti) silicide formation

Effects of Ti alloying during laser-induced Ni silicide formation is studied. Unique triple layer microstructures were found with the presence of supercell in the NiSi2 grains formed at the interface. This supercell formation was caused by a local ordering of Ni and Si atoms that favor lower free energy during rapid solidification. Ti rapidly segregates from the alloy melt and forms a protective TiOx overlayer on the surface during solidification. Melt front progressing towards the Ni-rich region leads to quenching of an amorphous layer sandwiched between NiSi2 grains and the TiOx overlayer.

Lu2O3∕Al2O3 gate dielectrics for germanium metal-oxide-semiconductor devices

Effect of Ge out diffusion into Lu2O3∕Al2O3 high-k dielectric stack was investigated. Increasing Ge signal intensity with increasing annealing temperature was observed, which suggests that there may be excessive Ge incorporation into the high-k film. The electrical measurement shows an improvement of the k value with annealing temperature, as well as an increasing trend in the leakage current density suggesting degradation in electrical performance due to Ge incorporation. Our work suggests that 8.8at.% of Ge in the film is excessive and result in degradation of the electrical performance of the device due to the increased leakage current.

Nickel silicide formation using multiple-pulsed laser annealing

The effect of multiple-pulsed laser irradiation on Ni silicide formation in Ni(Ti)∕Si system was studied. A layered structure consisting of both crystalline NiSi2 and Ni-rich Ni–Si amorphous phases with a protective TiOx overlayer was formed after five-pulsed laser annealing at 0.4Jcm−2. Different solidification velocities caused by a variation in the atomic concentration across the melt have led to the formation of this layered structure. On the other hand, by increasing the number of laser pulses, a continuous layer of polycrystalline NiSi was obtained after a 20-pulsed laser annealing at 0.3Jcm−2 laser fluence. Its formation is attributed to a better elemental mixing which occurred during subsequent pulses. Enhancement of surface absorption and remelting of the phases formed is proposed as the mechanism governing the continuous NiSi layer formation.

Formation of SrTiO3 nanocrystals in amorphous Lu2O3 high-k gate dielectric for floating gate memory application

We have developed a method based upon pulsed laser deposition to produce SrTiO3 nanocrystals embedded in amorphous Lu2O3 high-k dielectric. The high resolution transmission electron microscopy study revealed the complete isolation of SrTiO3 nanocrystals embedded in Lu2O3 matrix with 4nm diameter and well distributed with an area density estimated to be about 8×1011cm−2. A pronounced capacitance-voltage hysteresis is observed with a memory window of ∼1.5V under the 6V programming. In addition, the retention characteristics are tested to be robust.

Laser-induced Ni(Pt) germanosilicide formation through a self-limiting melting phenomenon on Si1−xGex∕Si heterostructure

Laser-induced Ni(Pt) germanosilicide formation on Si1−xGex∕Si substrate has resulted in the formation of smooth Ni(Pt) germanosilicide/Si interface with minimum interface roughness which is preferred as a contact material. A confined (self-limiting) melting phenomenon occurred during the laser-induced silicidation process at laser fluence of 0.4Jcm−2 (just at the melting threshold of the sample). This phenomenon is caused by significant differences in material properties of Si1−xGex alloy and Si substrates. Formation of highly textured [Ni1−v(Pt)v](Si1−yGey) phase was detected in the sample after 20-pulsed laser thermal annealing at 0.4Jcm−2. The formation mechanism of the Ni(Pt) monogermanosilicide is discussed.

LaAlO3 nanocrystals embedded in amorphous Lu2O3 high-k gate dielectric for floating gate memory application

A novel method to fabricate the memory structure of LaAlO 3 nanocrystals embedded in amorphous Lu 2 O 3 high-k dielectric by the pulsed laser deposition method using a rotating target was successfully developed. The average mean size and aerial density of the LaAlO 3 nanocrystals are estimated to be about 6 nm and 1.1 X 10 12 cm -2 , respectively. Superior performances in terms of a large memory window, long data retention, and robust endurance were observed.

Textured Ni(Pt) germanosilicide formation on a condensed Si1-xGex/Si substrate

cInstitute of Microelectronics, Singapore 117685 A study of Ni and NiPt germanosilicidation on a condensed Si1�xGex/Si substrate was performed. The partial relaxation of the condensed SiGe layer resulted in an improvement in the morphological stability of the germanosilicide through the alleviation of compressive stress. Pt alloying to the Ni film resulted in highly textured NiPt germanosilicide grains, particularly in the 002 orientation, due to the reduction in the interfacial energy caused by the presence of Pt alloy. Pt atoms diffuse slowly and result in a variation in lattice parameters in the NiPtSiGe grain as a function of depth. Nevertheless, Pt alloying has increased the morphological stability of the NiPtSiGe film.

Formation of SiO2 nanocrystals in Lu2O3 high-k dielectric by pulsed laser ablation and application in memory device

We have successfully developed a method based on pulsed laser deposition (PLD) to produce SiO2 nanocrystals embedded in Lu2O3 high-k dielectric. The mean size and aerial density of the SiO2 nanocrystals embedded in Lu2O3 are estimated to be about 7 nm and 6 × 1011cm−2, respectively. This metal–oxide–semiconductor capacitor can be operated under smaller operation voltages, and exhibits a large memory window with a good retention time.