Shih-Chin Chang

Mechanism of enhanced formation of C54–TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si

Enhanced formation of C54-TiSi2 in high-temperature deposited Ti thin films on preamorphized (001)Si has been investigated by high-resolution transmission electron microscopy in conjunction with autocorrelation function analysis. The increase in the thickness of the amorphous TiSix layer is due to the preamorphization implantation for the most part. The dominant effect of high-temperature sputtering is to increase the density of crystallites in the amorphous TiSix layer. The enhanced formation of C54–TiSi2 in high-temperature deposited samples is attributed to the more extensive presence of silicide crystallites, which serve as nucleation sites, in the amorphous TiSix layer than that in samples deposited at room temperature.

Silicide Contacts for Sub-0.25 μm Devices

Low resistivity TiSi 2 , CoSi 2 and NiSi are the three primary candidates for metal contacts in sub-0.25 μ m devices. In the present paper, we review recent progress in the investigations of lowresistivity contacts, which include enhanced formation of C54-TiSi 2 on (001)Si by tensile stress, high temperature sputtering, and interposing Mo or TiN layer, improved thermal stability of C54-TiSi 2 by the addition of N 2 during Ti sputtering or N implantation in (001)Si, self-aligned formation of CoSi 2 on the selective epitaxial growth silicon layer on (001)Si, effects of stress on the epitaxial growth of CoSi 2 on (001 )Si, improvement of thermal stability of CoSi 2 by nitrogen ion implantation or high temperature sputtering, and improvement of thermal stability of NiSi by nitrogen ion implantation or compressive stress.

Electrical Switching of Al-Doped Amorphous SiO x Thin Films

This papers investigations aimed to tackle crystal defects, which lead to reliability issues of resistive memory and we explored films of Al-doped amorphous SiOx as homogeneous matrix. The electrical resistance switching of Pt/Si(Al)Ox/TiN stacks was studied. After a forming process, the SET and RESET voltages are 2.2 and 1.1 V, respectively. The high- and low-resistance states are distinguishable with a resistance ratio ~102 and stable for at least 500 Hz and retaining for over 104 s under an electrical stress of 0.1 V. Because of the formation of bubbles, we tried to use larger current compliance to unveil the possible mechanisms based on filament model and the switching process occurs near the Pt/Si(Al)Ox interface. Finally, we proposed a possible conduction mechanism to describe the resistive switching behavior for Pt/Si(Al)Ox/TiN stacks.

Crystallization kinetics and x-ray photoelectron spectroscopy of Ga2TeSb7 thin film

Ga2TeSb7 films were deposited on SiOx/Si(100) wafers by radio-frequency magnetron sputtering to assess its potential as a phase-change memory material. Electrical resistance of the film versus temperature (R-T) was measured at various heating rates. Crystallization kinetics was analyzed using the R-T curves. Crystallization temperature 253–260 °C and activation energy of crystallization 5.76 eV were deduced using Kissinger’s plot. The kinetic exponent (n) obtained from Ozawa’s plot decreases from 2.5 to 1.0 upon crystallization at 253 to 265 °C. The n value is less than 1.5 when crystallizing at ≥257 °C, denoting a growth-dominated mechanism. X-ray diffraction shows that the amorphous phase crystallizes into the R3m Sb-structure and surface roughness of the crystallized Ga2TeSb7 is 0.3 nm at all annealing temperatures. X-ray photoelectron spectra reveal little change in bonding status of the three elements before and after crystallization.

Transmission electron microscopy investigation of the formation of C54-TiSi2 phase on stressed (001)Si

The effects of stress on the formation of C54-TiSi2 phase in Ti/(001)Si samples have been investigated by high-resolution transmission electron microscopy in conjunction with auto-correlation function (ACF) analysis. The C54-TiSi2 phase transformation temperature in tensily stressed samples was found to be lowered by about 100 degrees C than that in compressively stressed samples. The thickness of amorphous interlayers (a-interlayers) between Ti metal thin films and Si substrates was found to be thicker and thinner in the tensily and compressively stressed Si samples, respectively. Furthermore, the thicker a-interlayer was found to consist of a higher density of crystallites from the ACF analysis. With a higher density of crystallites in the a-interlayer, the grain size of C49-TiSi2 was reduced since more nucleation sites are available for the formation of C49-TiSi2. The small grain size of C49-TiSi2 in turn enhances the formation of C54-TiSi2. As a result, the phase transformation of C49- to C54-TiSi2 is enhanced by the tensile stress present in silicon substrates.

Mechanisms for the improved stability of C54–TiSi2 on (001)Si by the addition of N2 to Ar during Ti sputtering

Addition of N2 to Ar during Ti sputtering has been found to improve the thermal stability of TiSi2. For samples sputtered with a mixture of Ar and N2, TiSi2 was found to be stable after 1050 °C, 30 s annealing. Furthermore, the phase transformation temperature from the C49 to C54 phase was not affected with the addition of a small amount of nitrogen. The stuffing of grain boundaries of TiSi2 and TiN/TiSi2 interfaces by nitrogen atoms is thought to retard the transport of Si and Ti atoms. In addition, titanium nitride particles embedded in TiSi2 near the TiN/TiSi2 interface may also protect the TiSi2 films from plastic deformation and retard the grain growth during high temperature annealing. Smaller average grain size of C54–TiSi2 in samples prepared with the addition of N2 to Ar during Ti sputtering than that in pure Ti samples is also beneficial in enhancing the thermal stability.

Enhanced formation of low-resistivity TiSi2 contacts for deep submicron devices

Low resistivity C54-TiSi2 is currently the most commonly used silicide for metal contacts in ultralarge scale integrated circuits devices. In the present paper, we review recent results of investigations on the effects of stress and high temperature sputtering on the formation of C54-TiSi2. Enhanced formation of C54-TiSi2 on (001)Si by tensile stress and high temperature sputtering is correlated to the growth of thicker amorphous interlayer at the Ti/(001)Si interface. The enhanced transformation is attributed to the presence of higher density of silicide crystallites, which serve as the nucleation sites for the C49-TiSi2, in the amorphous layer. As a result, the average grain size of C49-TiSi2 is smaller which leads to lower C49- to C54-TiSi2 transformation temperature.