Gi Bum Kim

Interfacial reaction and formation mechanism of epitaxial CoSi2 by rapid thermal annealing in Co/Ti/Si(100) system

A ternary compound of Co3Ti2Si is suggested as a reaction barrier for the formation of epitaxial CoSi2 in the Co/Ti/Si system when adopting the rapid thermal annealing process. It controls Co diffusion to the Si substrate, followed by formation of epitaxial CoSi2. After the epitaxial CoSi2 was formed, the interfacial morphology of the upper layer/ CoSi2 interface was very different according to silicidation temperature, that is, the interface was planar at 800 °C, but rough at 900 °C. This was attributed to the reaction between the upper layer consisting of Co–Ti–Si and the CoSi2 layer at 900 °C, which resulted in Ti-rich precipitates at the surface. The Ti-rich precipitates acted as a diffusion sink of dopant, thus, the leakage current density for the silicidation temperature of 900 °C was much higher than that for the temperature of 800 °C. These results suggest that the silicidation temperature is one of the most critical factors in determining the leakage current of the p+n junction diode.

Control of Co flux through ternary compound for the formation of epitaxial CoSi2 using Co/Ti/Si system

A ternary compound of Co3Ti2Si is suggested as reaction barrier for the formation of epitaxial CoSi2 in the Co/Ti/Si system. It has a role to control Co diffusion to the Si substrate, followed by formation of CoSi2. After Co3Ti2Si was formed, CoO and Ti oxide were formed at surface, depending on Ti thickness. In the case of Ti oxide being at surface, the outdiffusion of Ti in ternary compound was accelerated. Then, the decomposition of Co3Ti2Si occurred by reaction with Ti oxide, resulting in uniform epitaxial CoSi2. However, in the case of CoO being at surface, the Ti outdiffusion was suppressed, followed by thermally decomposition of Co3Ti2Si. This caused nonuniform Co supply to form nonuniform CoSi2.

Improved thermal stability of Ni silicide on Si (100) through reactive deposition of Ni

The effect of reactive deposition of Ni on the thermal stability of Ni silicide has been investigated in this study. In the case of room-temperature-deposited Ni, the agglomeration of Ni silicide, which induced the thermal instability during subsequent annealing, started to appear at 600 °C and the sheet resistance was increased abruptly after high-temperature anneals. However, when the Ni was deposited on the heated Si substrate (reactive deposition of Ni), the sheet resistance of Ni silicide film exhibited a constant value of about 7.91 Ω/□ at the whole reaction temperature, especially at 900 °C.

Effect of Ti-capping thickness on the formation of an oxide-interlayer-mediated-epitaxial CoSi2 film by ex situ annealing

A modified oxide mediated epitaxy process using a single deposition and ex situ annealing by Ti capping has been suggested in this study. It has been shown that in the case of pure Co on SiOx-covered Si, the reaction between Co and Si did not occur up to 800 °C during ex situ annealing. However, Co silicidation occurred in the case of Ti-capped Co on SiOx-covered Si. The crystalline nature of CoSi2 formed in this case strongly depends on the Ti capping thickness. When a thin Ti capping layer of thickness less than 5 nm was used, Ti oxidation occurred nonuniformly, and the morphology of the surface Ti oxide layer was very rough. This caused an exposure of Co to the oxygen in the ambient, resulting in the formation of polycrystalline CoSi2 due to the suppressed Co diffusion towards the Si substrate. In the case of Ti capping thickness being more than 10 nm, however, a uniform Ti oxide surface layer, which blocks the incoming oxygen retarding Co diffusion, was formed, and it led to uniform Co diffusion into ...

Polarized light emission from GaInN light-emitting diodes embedded with subwavelength aluminum wire-grid polarizers

We demonstrate a back-emitting (sapphire-substrate emitting) linearly polarized GaInN light-emitting diode (LED) embedded with a subwavelength-sized aluminum wire-grid polarizer (WGP). Rigorous coupled wave analysis is implemented to study the polarization characteristics of such a WGP LED. The aluminum nanowire grating with a period of 150 nm is located on the sapphire backside of a GaInN LED structure and is fabricated by electron-beam lithography and inductively coupled plasma reactive-ion etching. A polarization ratio of 0.96 is demonstrated for a WGP GaInN LED in good agreement with simulation results.

Ex situ formation of oxide-interlayer-mediated-epitaxial CoSi2 film using Ti capping

A modified oxide mediated epitaxy process using a single deposition and ex situ annealing by Ti capping has been developed in this study. With pure Co on Shiraki oxide, the reaction between Co and Si did not occur even at 800 °C during ex situ annealing, because of the adsorption of oxygen on the Co film. However, when the pure Co on the Shiraki oxide was capped by Ti, a uniform Ti oxide surface layer was formed during the initial stage of annealing, which had a role to eliminate the adsorption of oxygen on the Co film. It led to uniform Co diffusion into the Si substrate through the Shiraki oxide, resulting in epitaxial CoSi2. A good channeling χmin value of 18% comparable to that of the Ti/Co bilayer system was measured in the epitaxial CoSi2 formed from this modified oxide mediated epitaxy process.

Effects of phase and thickness of cobalt silicide on field emission properties of silicon emitters

Cobalt silicide emitters showed the enhanced emission properties in I-V characteristics and long-term current stability, compared to bare silicon emitters. They are mainly caused by the increase of emission area and the formation of chemically stable surface of silicide emitters. Detailed results about the effects of phase and thickness of cobalt silicide on electron emission are discussed.

Strong light-extraction enhancement in GaInN light-emitting diodes patterned with TiO2 micro-pillars with tapered sidewalls

An effective method to enhance the light extraction for GaInN light-emitting diodes (LEDs) is reported. The method employs TiO2 micro-pillars with tapered sidewalls, which are refractive-index-matched to the underlying GaN. The tapered micro-pillars are fabricated by using reflowed photoresist as mask during CHF3-based dry etch, with O2 added in order to precisely control the taper angle. LEDs patterned with TiO2 micro-pillars with tapered sidewalls show a 100% enhancement in light-output power over planar reference LEDs. The measured results are in good agreement with ray-tracing simulations, showing strong potential of optical surfaces that are controlled in terms of refractive index and lateral structure.

Investigation of the mechanism of titanium silicide reaction using ion-beam-assisted deposition

In order to promote the formation of C54 TiSi2, the suppression of C49 TiSi2 formation by ion-beam-assisted deposition of Ti film was investigated. When the Ti film was deposited without ion bombardment, C49 TiSi2 was formed at 600 °C. In contrast, in the case where the Ti film was deposited with concurrent ion bombardment, TiSi formation occurred at the same temperature. The formation of TiSi was attributed to the enhancement of both Si and Ti diffusion below 600 °C, due to grain refinement induced by Ar-ion-beam bombardment. By the adoption of ion-beam-assisted deposition to the conventional Ti silicide process, the gate line width dependence of C54 TiSi2 formation can be eliminated, since this formation is achieved via a direct interfacial reaction between TiSi and Si, and not a conversion of C49 TiSi2.

Mosaic structure of various oriented grains in CoSi2/Si(001)

We investigated the mosaic structure of CoSi2/Si(001) film in a synchrotron x-ray scattering experiment. The CoSi2 film, formed by thermal reaction of a 120 A Co film on Si(001), was composed largely of epitaxial grains of various orientations. In particular, the twin oriented (B-type) CoSi2(111) grains were grown epitaxially on the Si{111} facets that were generated during annealing. Two distinct mosaic structures were observed in the CoSi2 grains; the epitaxial grains of the same orientation with the Si substrate, such as the CoSi2(001) [the CoSi2(111)] grains lying on the Si(001) [the Si{111} facets], showed a small mosaicity of ∼0.5° full width at half maximum (FWHM), while those of different orientations demonstrated a rather broad mosaicity of ∼2.5° FWHM. We attributed the smaller mosaicity of the epitaxial grains of the same orientation to the reduced interfacial energy due to higher coincidence site density.