Ahmet S. Ozcan

Sharp Reduction of Contact Resistivities by Effective Schottky Barrier Lowering With Silicides as Diffusion Sources

An extremely low contact resistivity of 6-7 × 10^-9 Ω·cm² between Ni_0.9Pt_0.1Si and heavily doped Si is achieved through Schottky barrier engineering by dopant segregation. In this scheme, the implantation of B or As is performed into silicide followed by a low-temperature drive-in anneal. Reduction of effective Schottky barrier height is manifested in the elimination of nonlinearities in IV characteristics.

Real-time x-ray studies of Mo-seeded Si nanodot formation during ion bombardment

The formation of self-organized Si nanostructures induced by Mo seeding during normal incidence Ar+ ion bombardment at room temperature is reported. Silicon surfaces without Mo seeding develop only power-law roughness during 1000eV ion bombardment at normal incidence, in agreement with scaling theory expectations of surface roughening. However, supplying Mo atoms to the surface during ion bombardment seeds the development of highly correlated, nanoscale structures (“dots”) that are typically 3nm high with a spatial wavelength of approximately 30nm. With time, these saturate and further surface roughening is dominated by the growth of long-wavelength corrugations.

Strained Si Channel MOSFETs with Embedded Silicon Carbon Formed by Solid Phase Epitaxy

Current drive enhancement is demonstrated in sub-40 nm NFETs with strained silicon carbon (Si:C) source and drain using a novel solid-phase epitaxy (SPE) technique for the first time. The very simple process uses no recess etch or epi deposition steps, adds minimal process cost, and can be easily integrated into a standard CMOS process. With a record high 1.65 at% substitutional C concentration in source and drain, 615 MPa uniaxial tensile stress was introduced in the channel, leading to a 35% improvement in electron mobility and 6% and 15% current drive increase in sub-40 and 200 nm channel length devices respectively.

Complex and incommensurate ordering in Al0.72Ga0.28N thin films grown by plasma-assisted molecular beam epitaxy

Structures with incommensurate ordering along the [0001] direction are observed in wurtzite Al0.72Ga0.28N alloys grown by plasma-assisted molecular beam epitaxy on c-plane sapphire. Films grown in environments with group-III/N ratios greater than 1 exhibit ordered superlattice structures that are incommensurate with the wurtzite crystal lattice. In contrast, films grown under nitrogen-rich conditions exhibit ordered structures with a periodicity of four cation-N monolayers. The increasing complexity of the ordering with increasing Ga-rich growth environment suggests that the ordering is related to the presence of a Ga overlayer believed to exist on the surface of the growing film.

Texture of TiSi2 thin films on Si (001)

The texture of blanket C49 and C54 phase TiSi2 films on Si (001) substrates was examined with x-ray pole figure analysis. Textures were studied both in films with initial Ti deposited by sputtering and by low-temperature, plasma assisted chemical vapor deposition. Detailed differences were observed between silicide films grown by subsequently annealing films deposited with the two different methods. However, in both cases, the dominant C49 phase orientational relationships develop with respect to the substrate (001) planes. In contrast, we find that the dominant crystallographic relationships of the C54 phases in both cases are not with the surface (001) plane of the substrate, but instead with the Si (111) planes. Texturing in the case of the sputtered films is particularly complex with one prominent orientation having C54 (11¯0)‖(1¯11) Si with C54 (331)‖(011) Si and a second having C54 (1¯03¯)‖(111) Si with C54 (040)‖(11¯0) Si. These orientations, which suggest local epitaxy of the disilicide with...

Ultra Low Contact Resistivities for CMOS Beyond 10-nm Node

Contact resistances are directly measured for contacts with sizes from 25 to 330 nm using e-beam based nano-TLM devices. Record low contact resistivities ~1.5 × 10^-9 Ω· cm² are extracted from Ni(Pt) silicide contacts on in situ boron-doped Si_0.7Ge_0.3 with a chemical boron-doping density of 2 × 10²¹/cm³. This is very promising for pMOS applications beyond the 10-nm node. A clear dependence of contact resistance on the silicide thickness has also been found.

Wavelength tunability of ion-bombardment-induced ripples on sapphire

A study of ripple formation on sapphire surfaces by 300-2000 eV Ar{sup +} ion bombardment is presented. Surface characterization by in-situ synchrotron grazing incidence small angle x-ray scattering and ex-situ atomic force microscopy is performed in order to study the wavelength of ripples formed on sapphire (0001) surfaces. We find that the wavelength can be varied over a remarkably wide range -- nearly two orders of magnitude -- by changing the ion incidence angle. Within the linear theory regime, the ion induced viscous flow smoothing mechanism explains the general trends of the ripple wavelength at low temperature and incidence angles larger than 30{sup o}. In this model, relaxation is confined to a few nm thick damaged surface layer. The behavior at high temperature suggests relaxation by surface diffusion. However, strong smoothing is inferred from the observed ripple wavelength near normal incidence, which is not consistent with either surface diffusion or viscous flow relaxation.

Exploitation of a self-limiting process for reproducible formation of ultrathin Ni1−xPtx silicide films

This letter reports on a process scheme to obtain highly reproducible Ni1−xPtx silicide films of 3–6 nm thickness formed on a Si(100) substrate. Such ultrathin silicide films are readily attained by sputter deposition of metal films, metal stripping in wet chemicals, and final silicidation by rapid thermal processing. This process sequence warrants an invariant amount of metal intermixed with Si in the substrate surface region independent of the initial metal thickness, thereby leading to a self-limiting formation of ultrathin silicide films. The crystallographic structure, thickness, uniformity, and morphological stability of the final silicide films depend sensitively on the initial Pt fraction.

AXIOTAXY OF COSI2 THIN FILMS ON SI(100) SUBSTRATES AND THE EFFECTS OF TI ALLOYING

The texture of CoSi2 films on Si(001) substrates has been examined using synchrotron based high-resolution pole figure analysis. We find that axiotaxy, a recently recognized type of texture which was observed in NiSi thin films on Si(001), is also occurring in CoSi2 layers. Typical of axiotaxy texturing, the CoSi2 pole figures show symmetrical patterns of lines. Calculations show that these features on the pole figures are created by three off-normal fiberlike texture components. These off-normal fiber orientations are a consequence of the alignment of CoSi2〈110〉 planes with Si〈110〉 planes because of very similar d spacings, which causes a periodic arrangement along Si〈100〉 directions in the plane of the interface. This one-dimensional periodicity may provide a lower interfacial energy; however, the periodic arrangement along the Si〈100〉 directions may also be indicative of growth anisotropy. The influence of Ti alloying has been investigated by using in situ x-ray diffraction measurements, as well as pol...

Real-time x-ray studies of gallium nitride nanodot formation by droplet heteroepitaxy

Self-organized gallium nitride nanodots have been fabricated using droplet heteroepitaxy on c-plane sapphire by plasma-assisted molecular beam epitaxy at different substrate temperatures and Ga fluxes. Nanoscale Ga droplets were initially formed on the sapphire substrate at high temperatures by Ga deposition from an effusion cell in an ultrahigh vacuum growth chamber. Subsequently, the droplets were converted into GaN nanodots using a nitrogen plasma source. The process was monitored and controlled using real-time grazing-incidence small-angle x-ray scattering. The samples were examined postgrowth by in situ grazing incidence x-ray diffraction and reflection high-energy electron diffraction, which confirmed the epitaxial relationship between the GaN nanodots and the sapphire surface. X-ray diffraction indicated that the wurtzite phase was dominant at higher substrate temperature (710°C), but a mixture of wurtzite and zinc blende phases was present at a substrate temperature of 620°C. Ex situ atomic force ...