Jae Yeob Shim

Silicide formation in cobalt/amorphous silicon, amorphous CoSi and bias-induced CoSi films

Abstract The silicide formation in cobalt/amorphous silicon multilayer films, amorphous cobalt-silicon films, and bias-induced cobalt-silicon films has been examined by differential scanning calorimetry, X-ray diffraction, and transmission electron microscopy. For amorphous cobalt-silicon and bias-induced cobalt-silicon films, Co 2 Si forms as a firstsilicide phase, followed by the formation of CoSi and CoSi 2 . For a Co/a-Si multilayer film with the atomic concentration ratio of the cobalt to silicon layer being 1:2, CoSi is found to be formed as the first silicide phase. It is confirmed that CoSi, Co 2 Si, CoSi, and CoSi 2 form sequentially as the scanning temperature increases. The observed phase sequence is analyzed by the effective heat of formation. A structure factor in addition to the effective heat of formation is used to explain the difference in the formation of the firstphase between cobalt/amorphous silicon multilayer films, amorphous cobalt-silicon alloy films, and bias-induced cobalt-silicon films. For the case of bias-induced cobalt-silicon films prepared at various substrate temperatures and bias conditions, the phase sequence and crystallinity of cobalt silicide have a stronger dependence on the substrate bias voltage than on the substrate temperature due to the effects of collisional cascade mixing, in-situ cleaning, and an increase in the number of nucleation sites by ion bombardment on the growing surface. Also, bias-induced epitaxial CoSi 2 layer is grown at 200 °C,a much lower temperature than molecular beam epitaxy. In order to quantitatively explain low-temperature epitaxial growth of the CoSi 2 layer, the Ar ion energy transferred to Co and Si atomsand the resputtering yield as a function of substrate bias voltage are calculated.

Fabrication of amorphous-carbon-nitride field emitters

To improve silicon field emitters, an amorphous-carbon-nitride (a-CN) coating was applied by helical resonator plasma-enhanced chemical vapor deposition. By this process, a-CN was very uniformly coated on silicon tips without any damage. Microstructural and electrical investigation of the silicon and a-CN coated field emitters were performed. a-CN coating lowered turn-on voltage and increased emission current. Negative electron affinity of carbon nitride is suggested for enhancing emission current.

Structural, Optical, and Field Emission Properties of Hydrogenated Amorphous Carbon Films Grown by Helical Resonator Plasma Enhanced Chemical Vapor Deposition.

Hydrogenated amorphous carbon films have been prepared by helical resonator plasma enhanced chemical vapor deposition using CH4 and H2 mixtures. Films with various physical properties were obtained from different deposition conditions. The structural and optical properties of hydrogenated amorphous carbon (a-C:H) films were more sensitive to the substrate bias than the substrate temperature. This reflects that the energetic ion bombardment modified the films more effectively than the thermal energy. The a-C:H films deposited with no bias applied show characteristics of polymeric films with a large content of C–H bond while the a-C:H films deposited as a function of the substrate temperature at a bias of 40 W show characteristics ranging from diamond-like carbon (DLC) to graphitic nature with a significantly reduced C–H bond. From elastic recoil detection analysis, the hydrogen content in the films also significantly reduced with an increase of substrate temperature at a bias of 40 W. The field emission from bare Si emitters and a-C:H coated Si emitters has been examined in an ultrahigh vacuum chamber. The field emission characteristic of the a-C:H coated Si emitters is better than that of the bare Si emitters. For the a-C:H coated Si emitters, the emission current of the a-C:H coated (at 150°C/40 W) Si emitters is higher than the that of the a-C:H coated (at 260°C/40 W) Si emitters. This difference in field emission characteristic is attributed to the structural and optical properties as well as hydrogen content.

Effects of heat treatment on the field emission property of amorphous carbon nitride

As a coating material for silicon field emitters, amorphous carbon nitride (a-C:N) by helical resonator plasma enhanced chemical vapor deposition has been proposed. Thermal annealing in nitrogen ambient up to 600 °C was carried out to investigate the effects of heat treatment on the field emission. The structural and compositional modifications induced by the annealing were followed by several analytical techniques: Fourier transformation infrared (FTIR) spectroscopy, elastic recoil detection analysis (ERDA), and x-ray photoelectron spectroscopy. FTIR and ERDA analyses indicate that hydrogen loss occurs for annealing temperatures higher than 300 °C. Amorphous-C:N films significantly lowered the turn-on voltage and increased the emission current of the silicon emitters. After annealing at 600 °C, the field emission property was further enhanced presumably due to the efficient conduction through the a-C:N films induced by an increase of the number and/or the size of the graphitic domains.

Mechanism of field emission from chemical vapor deposited undoped polycrystalline diamond films

Field emission characteristics of undoped polycrystalline diamond films with different structural properties have been investigated. By introducing positive bias voltage and/or increasing CH4/H2 ratio, the film quality is significantly deteriorated together with the increase of nondiamond carbon component and the surface morphologies of the films lost their unique facet shape. The reason for the increase of nondiamond carbon content is described in terms of both the increase of substrate temperature and the excessive generation of CHn radicals. It is confirmed that an increase in the nondiamond carbon content markedly enhances field emission properties of diamond films. From the spatial distribution of emission sites, it is suggested that the transport path of field-emitted electrons depends on the nondiamond carbon content: for the film with a large amount of nondiamond carbon, electrons transport preferentially through the conducting mediums such as grain boundaries while for the film with a relatively ...

The Field Emission Characteristics of a-C:H Thin Films Prepared by Helical Resonator Plasma Enhanced Chemical Vapor Deposition

The field emission characteristics of hydrogenated amorphous carbon (a-C:H) films prepared by helical resonator-plasma enhanced chemical vapor deposition (HR-PECVD) are examined. a-C:H films are deposited with CH4/H2 and CH4/Ar gases under different substrate RF bias conditions. The properties of a-C:H films are investigated by Raman spectroscopy, Fourier transform IR (FT-IR), UV spectroscopy and elastic recoil detection (ERD). Field emission characteristics of a-C:H coated on Si whiskers which are grown by the vapor-liquid-solid (VLS) method are tested under ultrahigh vacuum. Highly efficient field emission characteristics are achieved in the specimen deposited at a substrate RF bias higher rather than in the ground deposition condition regardless of the nature of the reactant gas. As the substrate RF bias is changed from ground to a higher RF substrate bias, the deposited a-C:H films have lower hydrogen contents and higher sp2-bonds. Therefore, the field emission characteristics of a-C:H thin films are affected by the hydrogen contents of the films rather than by the sp3/sp2 ratio.

0.15 /spl mu/m gate length InAlAs/InGaAs power metamorphic HEMT on GaAs substrate with extremely low noise characteristics

The 0.15 /spl mu/m gate-length power metamorphic HEMTs (MHEMT) with wide head T-shaped gate has been fabricated and the DC, microwave, and noise performance of the device were characterized. The MHEMT device shows the DC output characteristics having an extrinsic transconductance of 740 mS/mm and a threshold voltage of -0.75 V. The f/sub T/ and f/sub max/ obtained for the 0.15 /spl mu/m /spl times/ 100 pm MHEMT device are 150 GHz and 240 GHz, respectively. The MHEMTs exhibit the minimum noise figure, NF/sub min/, of 0.79 dB and associated gain of 10.5 dB at 26 GHz. The NF/sub min/ measured at 40 GHz is 1.21 dB with associated gain of 6.41 dB. This noise data is the lowest value ever reported for power MHEMT devices with InGaAs channel of 53% In. The excellent noise characteristics might result from the low gate resistance due to the wide head T-shaped gate and the improved device performance.

Effect of non-diamond carbon etching on the field emission property of highly sp2 bonded nanocrystalline diamond films

Abstract The effect of the non-diamond carbon etching on the electron field emission behavior of highly sp 2 bonded nanocrystalline diamond films has been systematically investigated by performing hydrogen treatments. Field emission properties and emission patterns of the films are initially enhanced and then degraded with an increase in the hydrogen treatment time. The most uniform distribution of the emission site is obtained for a 1-min hydrogen-treated film, and the reason for this is explained in terms of the increase of triple junction site due to etching of the sp 2 bonded carbon by atomic hydrogen. On the other hand, the degraded emission property of the films treated for more than 10 min is due to the decrease of triple junction, which is indirectly confirmed by Raman and Auger electron spectroscopy.

Field emission characteristic of diamond films grown by electron assisted chemical vapor deposition

Abstract By introducing positive substrate bias, ranging from 0 to 200 V, to the substrate during the growing procedure of diamond at 1, 2, and 3% CH4 concentration, we have investigated the effect of electron bombardment on modification of the structural property and the surface morphology of diamond films, and consequently the field emission properties. When increasing the bias voltage for each CH4 concentration, the structural properties of diamond films are significantly deteriorated together while the non-diamond carbon component increased and the surface morphologies of the films lost their unique facet shape. The reason for the deterioration of the structural property was attributed to both the increase of substrate temperature and the excessive generation of CHn radicals. Especially for the films deposited at 2% CH4 concentration under 100 V, it was observed that their morphological and structural characteristics approached those of graphitic carbon nature. The field emission properties of diamond films were substantially improved with increasing the CH4 concentration and with the application of bias voltage for each CH4 concentration. In order to investigate the correlation between the enhancement of field emission properties and the emission sites, we have examined the spatial distribution of the emission sites. From this result, a possible emission mechanism is discussed.

Solid state reactions in cobalt/amorphous-silicon multilayer thin films

Abstract Solid state reactions in Co/amorphous-Si multilayer thin films were investigated using differential scanning calorimetry and X-ray diffraction. The results are compared with the predictions of effective driving force (EDF) and effective heat of formation (EHF) models. Amorphous silicide growth does not occur in Co/amorphous-Si multilayer thin films; this is consistent with the predictions of the EDF model. The first crystalline phase formed by solid state reaction is found to be CoSi, rather than Co2Si which is predicted by the EHF model to form first. The difference in the experimental and predicted first crystalline silicide is dicussed. For Co:Si atomic concentration ratios of 2:1 and 1:2, the phase sequences are CoSi → Co2Si and CoSi → Co2Si → CoSi → CoSi2 respectively. These reactions are analyzed using the EHF diagram. The formation of CoSi and CoSi2 is controlled by nucleation and the activation energies for the formation of CoSi, Co2Si, and CoSi2 are 1.71, 2.34, and 2.79 eV respectively.