Morphology Evolution of Pyramid-Like Nanostructures on Cobalt Thin Films During Deposition by Sputtering

ABSTRACTThe cobalt thin films are grown by D.C. magnetron sputtering as a function of the target-to-substrate distance, bias and power on both Si (100) and (111) substrates. The crystal structure and morphology of the thin films are characterized by 4-point probe, x-ray diffraction, scanning electron microscopy, transmission electron microscopy and atomic force microscopy. It is found that the cobalt crystal structure can be varied from HCP to FCC by varying the target to-substrate distance from 6 to 10 cm. The resistivity, roughness and the preferred orientation of the thin films are greatly affected by the substrate bias and power. The lowest resistivity of Co films is 9.8 -cm when deposited at the target to-substrate distance of 6cm, the applied power of 50W and the substrate bias of -75 volts. In addition, pyramid-like nanostructures with sharp tips are formed on the surface of the thin films when negative bias is applied. The faceted planes on the nanostructures depend on the resulting Co crystal structure while the size and density are determined by the growth parameters. The evolution of the surface nanostructures are systematically examined as a function of substrate bias and thin film thickness. The formation mechanism of the surface nanostructures is discussed in the paper.

Ohmic and Rectifying Contacts to n and p-type GaN Films

ABSTRACTElectrical contacts to both n and p-type GaN films have been investigated using electron-beam evaporated and sputtered films of metals such as Al, Au, Cr, Cu, Ni, Pt, and Ti. Films deposited by electron-beam evaporation for the n-type films with doping levels of 1 × 1018/cm3 and lower showed rectifying characteristics with all the metals studied with the exception of Al. Aluminum contact diodes were ohmic in the as-deposited state. The Pt rectifying contact was near-ideal with an ideality factor close to 1.0. Ideality factors for the other metals were much greater than 1. This deviation from thermionic behavior was interpreted as space charge limited current conduction in the presence of deep-level states. Sputtered films showed very similar characteristics to electron-beam deposited films, with the exception of Ti. The Ti contact was ohmic in the as-deposited state. Non-linear Cu contacts to n-type films became ohmic on annealing. However, for p-type films, Ar ion sputter-cleaning prior to metal deposition by sputtering created ohmic contacts with Cu and Pt. Low resistance ohmic contacts were achieved by ion implantation and anneal of Si in n-type and Mg in p-type films, prior to metallization. The implant parameters and anneal temperatures are currently being optimized.

Thin Film Microstructure Control Using Glancing Angle Deposition by Sputtering

Thin films with microstructures controlled on a nanometer scale have been fabricated using a recently developed process called glancing angle deposition (GLAD) which combines oblique angle evaporation with controlled substrate motion. Critical to the production of GLAD thin films is the requirement for a narrow angular flux distribution centered at an oblique incidence angle. We report here recent work with low-pressure, long-throw sputter deposition with which we have succeeded in fabricating porous titanium thin films possessing “zig-zag,” helical, and “pillar” microstructures, demonstrating microstructural control on a level consistent with evaporated GLAD. The use of sputtering for GLAD simplifies process control and should enable deposition of a broader range of thin film materials.

Interference Effects In X-Ray Specular Reflectivity from Thin Films

ABSTRACTA strong resonance effect in the specular reflectivity of a C layer deposited on a Ni surface has been measured. The e.m. field intensity distribution has been monitored by measuring the fluorescence intensity of an ultra-thin Ti layer placed in the C film. The reflected intensity and the fluorescence yield of Ti and Ar (this last trapped in the film because of the deposition by sputtering) have been measured in different samples with a different location of the Ti layer. The results show that with this method a nondestructive, accurate determination of the Ti position can be achieved with a relative accuracy of 10−2

Epitaxial growth of Cu2O films on MgO by sputtering

The epitaxial growth of Cu2O films is of significant interest for the unique potential they offer in the development of multilayer devices and superlattices. While fundamental studies may be carried out on epitaxial films prepared by any technique, the growth of artificially layered superlattices requires that films grow epitaxially during deposition. The present study examined the growth of Cu2O on MgO substrates directly during deposition by sputtering. Although epitaxial thin films of Cu2O could be produced, a mosaic structure was observed. The structure of the film may be related to the growth mechanism in which islands coalesce to form a continuous film.

Chromium deposition by sputtering

Previous works have shown the benefits of depositing ultrathin films (0.5-3.0 nm) of chromium onto SEM specimens to permit improved resolution at higher magnification. The finer grain structure of the chromium permits closer replication of the specimen surface topography than is possible with the conventional 10 nm of gold. This paper presents the results of an ongoing program at Denton Vacuum to develop guidelines for successful, repeatable deposition of ultrathin chromium films by sputtering.Chromium can be deposited using a high vacuum evaporator by either evaporation of chips from baskets or sputtering. Sputtering is the more desirable method since it has the potential for better rate control, coverage, repeatability and least specimen exposure to radiant heat.

Rapid Solidification of Metastable Materials

ABSTRACTThere are numerous processing methods available for the fabrication of rapidly-solidified metastable alloys. Examples include splat quenching, melt-spinning, surface melting and quenching, melt atomization and solidification, and deposition by sputtering and evaporation. Experimental aspects of each of these fabrication methods will be discussed. These include solidification and quench rate, process control, and final product morphology and microstructure. Some properties of an amorphous alloy prepared by several of these processing methods will be discussed.