Gas Cluster Ion Beam Treatment Research Articles

Double-step gas cluster ion beam smoothing

In this study we use the double step gas cluster ion beam treatment to improve smoothing process of mechanically polished 4H-SiC (1000) wafers and compare it with conventional single-step smoothing. The first step is a higher energy treatment with 15 keV Ar cluster ions, and the second step is a lower 5 keV treatment. Single-step treatments are performed at 15 and 5 keV. It is shown that single-step 15 keV smoothing as compared with lower 5 keV one is very effective for removing the initial surface morphological feature (scratches), however, cluster ions impacting on the surface can create larger craters, resulting in roughness <i>R</i><i><sub>q</sub></i> of 1.05 nm. Whereas, 5 keV treatment at a selected fluence cannot remove initial scratches, which requires using higher fluences, i.e. such smoothing becomes time consuming. On the other hand, crater morphology with such a treatment is less developed, hence, the roughness slightly decreases to 0.9 nm. Using the double-step treatment, one can obtain the surface with lower <i>R</i><sub><i>q</i></sub> roughness of 0.78 nm as compared with single-step treatment, at the same total cluster ion fluence. Therefore, the double-step treatment combines the advantages of the effective smoothing of scratches at high energy and smaller crater morphology at low energy. To evaluate the contribution of the cluster morphology introduced by the accelerated clusters into the total roughness, the cluster ion beam treatment of an atomically smooth 4H-SiC (1000) surface is also carried out. It is shown that the crater diameter increases in a range of 15–30 nm with the cluster energy increasing. More detailed analysis of the smoothing process is carried out by using two-dimensional isotropic PSD function. It is shown that the cluster treatment of mechanically polished 4H-SiC wafers effectively reduces the roughness in a wavelength range of 0.05–0.20 μm and the efficiency of smoothing is higher at higher cluster energy. In a range of 0.02–0.05 μm, a roughening effect is observed, which is due to the formation of craters. This roughening effect can be effectively reduced by the subsequent lower energy step treatment, which can be shown by the PSD function analysis of the smooth SiC surface treated initially by cluster ion beam.

Method of formation of super-smooth optical surfaces using GCIB and ANAB processing

Optical glass–ceramic is a promising material for the elements of precision optical systems operating in a wide temperature range. However, conventional methods such as the chemical–mechanical or ion polishing do not allow to form a substrate surface with less than 0.2 nm root mean square roughness. The method of gas cluster ion beam (GCIB) and accelerated neutral atom beam (ANAB) processing of glass–ceramic substrates is proposed to obtain super-smooth optical surfaces.The experimental samples were characterized by atomic force microscopy and X-ray diffractometry. It is shown that the surface is modified with the disappearance of linear defects (scratches) and the roughness parameters are improved. Only residual chaotic relief with the average roughness value (Ra) of 0.2 – 0.3 nm is observed after GCIB treatment. Subsequent ANAB processing allows to decrease the Ra parameter down to 0.15 nm. The improvement of surface characteristics is confirmed by the analysis of PSD-function in the investigated range of spatial frequencies. As a result of this work the method for super-smooth optical substrates fabrication was developed and the characteristics of obtained surfaces were investigated.

Gas cluster ion beam assisted NiPt germano-silicide formation on SiGe

We report the formation of very uniform and smooth Ni(Pt)Si on epitaxially grown SiGe using Si gas cluster ion beam treatment after metal-rich silicide formation. The gas cluster ion implantation process was optimized to infuse Si into the metal-rich silicide layer and lowered the NiSi nucleation temperature significantly according to in situ X-ray diffraction measurements. This novel method which leads to more uniform films can also be used to control silicide depth in ultra-shallow junctions, especially for high Ge containing devices, where silicidation is problematic as it leads to much rougher interfaces.

ガスクラスタイオンビーム加工によるガラス面の表面特性の変化

ガスクラスタイオンビーム加工によるガラス面の表面特性の変化

Influence of surface roughness and coating on the friction properties of nanometer-thick liquid lubricant films

The friction properties of nanometer-thick lubricant films are crucial in the reliability and durability of miniaturized moving mechanical components in micro- and nanoelectromechanical systems and hard disk drives. In this work, gas cluster ion beam treatments were applied to prepare smoothed glass sliding pins and diamond-like carbon (DLC) coated sliding pins for pin-on-disk friction tests to study the effect of the surface roughness and the DLC coating on the friction properties of perfluoropolyether (PFPE) films. The effect of the texture of the solid surface on the friction properties was also investigated. The friction properties were not exclusively determined by the surface energies of the solids. The friction coefficients of the nanometer-thick PFPE films, confined between solid surfaces were sensitive to the surface roughness of the solids. The friction coefficient generally increased with an increasing surface roughness (the composite standard deviation of the surface roughnesses of the pair of solid surfaces). This tendency was reversed when there was a strong longitudinal roughness effect at the contact interface. Moreover, the DLC-coated sliding pins had lower friction coefficients than the glass sliding pins, indicating that the friction properties were noticeably affected by the hardness and Young׳s modulus of the contact materials. The mechanisms for the effects of the surface roughness, surface texture and contact materials on the friction properties are discussed.

J111022 ガスクラスターイオンビーム加工によるガラス面の表面粗さおよび表面エネルギーの変化([J11102]マイクロナノ理工学:nmからmmまでの表面制御とその応用(2))

J111022 ガスクラスターイオンビーム加工によるガラス面の表面粗さおよび表面エネルギーの変化([J11102]マイクロナノ理工学:nmからmmまでの表面制御とその応用(2))

Modification on surface oxide layer structure and surface morphology of niobium by gas cluster ion beam treatments

Recently, it was demonstrated that significant reductions in field emission on Nb surfaces could be achieved by means of a new surface treatment technique called gas cluster ion beam (GCIB). Further study as shown in this paper revealed that GCIB treatments could modify surface irregularities and remove surface asperities leading to a smoother surface finish as demonstrated through measurements using a 3D profilometer, an atomic force microscope, and a scanning electron microscope. These experimental observations were supported by computer simulation via atomistic molecular dynamics and a phenomenological surface dynamics. Measurements employing a secondary ion mass spectrometry found that GCIB could also alter Nb surface oxide layer structure. Possible implications of the experimental results on the performance of Nb superconducting radio frequency cavities treated by GCIB will be discussed. First experimental results on Nb single cell superconducting radio frequency cavities treated by GCIB will be reported.

Magnetic tunnel junctions on magnetic shield smoothed by gas cluster ion beam

In this work, a technique, gas cluster ion beam (GCIB), was introduced to smooth the bottom NiFe magnetic shield for magnetic tunnel junction (MTJ) read heads. The GCIB treatment can bring the surface roughness of the shield from 15 to 20 Å to around 5 Å, and the most of scratch marks can be removed. The efficiency of the GCIB process is dependent on the initial surface morphology. The MTJs grown on the magnetic shield smoothed by the GCIB show that the resistance area product RA is increased from 60 to ∼100 Ω μm2 with the GCIB dose up to 1×1016 ions/cm2, arising from a smooth insulating layer, meanwhile, the tunneling magnetoresistance (TMR) is almost constant or slightly decreases. This GCIB process can also improve breakdown voltage (approximately 0.019 V per 1015 ions/cm2) of the MTJs, and slightly increase the ferromagnetic coupling mainly due to the change of the surface morphology. Using this technology, an RA as low as 3.5–6.5 Ω μm2 together with a TMR of 14%–18% can be obtained for MTJs grown on the GCIB treated NiFe magnetic shield.

The smoothness, hardness and stress in titanium nitride following argon gas cluster ion beam treatment

The surface smoothing of TiN coatings, deposited by CVD or PVD methods, by argon ion clusters comprising a few hundred to a few hundred thousand atoms and carrying a single positive charge has been confirmed. In addition, the present work has shown that there was no change in the mechanical condition, nanohardness or residual stress, of the PVD coatings after treatment. In contrast, the nanohardness in the near-surface region of the CVD TiN coating was increased but, remarkably, there was no concomitant increase in residual stress. A comparison is made with the established effects of classical single ion implantation on the near-surface properties of TiN where a high compressive residual stress is developed if the ion energy lies beyond a threshold value. It was concluded that only a fraction of the atoms in the cluster impact the surface and the vast majority of argon atoms move sideways. It appears to be generic that the smaller clusters are responsible for the increase in hardness as well as the well-known lateral sputtering effects associated with the technology. Larger clusters do not carry enough energy per atom to cause such effects and their energy is dissipated in the substrate as heat.