Papers by Keyword: Surface Preparation

Abstract: Optimizing the performance and reliability of welding techniques for dissimilar aluminum (Al) to titanium (Ti) is a promising way to establish new applications in aerospace industry. Due to structural weight reduction, lightweight materials can help to minimize fuel consumption and save emissions. Solid-state welding technologies allow short joining cycles and metallurgical changes, residual stresses and severe intermetallic compound formation can be reduced by limited thermal exposure. Besides temperature and plastic deformation, intimate contact plays an important role for diffusion. In this work, AlMgSi alloys with systematic variations of Mg and Si alloying elements, were welded to Ti6Al4V (Ti64) by refill Friction Stir Spot Welding. The focus lays on the effect of Ti64 sheet surface roughness, varied by different surface preparations. Additionally, the influence of the plunge depth, the distance between the tool and the Ti64 sheet surface is analyzed. It was found that a reduced tool to interface spacing has a beneficial influence on joint integrity. Grinding trenches allowed better bonding compared to the pit-like surface structure generated by sandblasting, which led to an increase in mechanical lap-shear properties. Knurling the grinded surfaces resulted in high standard deviation, as most likely not the whole interface area was bonded. However, the partially outstanding properties showed that a beneficial effect can be expected due to mechanical interlocking mechanisms, when sufficient diffusion is ensured.

Abstract: Laser Thermal Annealing (LTA) is a necessary fabrication step to improve the 4H-SiC devices by reducing their ON-state resistance. Because the LTA annealing is achieved at the end of the front-end fabrication, the classical Radio Corporation of America cleaning (RCA) cannot be used without affecting the material deposited on the frontside. Therefore, in this study, we investigate the argon (Ar) plasma surface treatment, achieved in our sputtering tool, before the ohmic contact fabrication, as an alternative surface preparation to the RCA sequence. As the Ar plasma modifies the SiC surface morphology, it affects its wetting properties. That can play a key role in the ohmic contact formation by LTA since the nickel turns into liquid phase during the laser irradiation. For an Ar plasma treatment of 30 min, a specific contact resistance of 5.0×10^-5 Ω.cm² has been obtained for an annealing at 5.0 J.cm², which is in the same range than the contact fabricated by LTA involving a classical RCA cleaning.

Abstract: We studied the impact of plasma polish dry etch (PPDE) on SiC substrates and its effect on epilayers grown on PPDE treated substrates. PPDE treatment on chemo mechanical polished (CMP) surface shows no significant degradation in surface roughness even with 3µm removal. On the other hand, when a mechanical polished (MP) surface was treated by PPDE, surface roughness was improved, demonstrating that PPDE can smooth a rough surface post MP process. Selective etching of threading screw dislocations (TSD) was evident from pit formation on the substrate surface. These pits may generate extended structural defects (e.g. triangular defects) during the epilayer growth depending on the sizes of the pits. No evidence was found that PPDE selectively etched BPD in the substrate and, hence, no improvement in BPD conversion was seen after epilayer growth. Ideally, PPDE treated surface pits needed to be minimized at TSD sites and mild etching at BPD sites is preferable and subject to future optimization.

Abstract: The steam oxidation of SiGe shows a transition from Si-like to Ge-like oxidation behavior depending on Ge concentration and oxidation temperature. Ge-like oxidation is described by the generation of oxygen vacancies (VO) at the interface between the oxide and SiGe virtual substrate. [1] Due to the different oxidation behavior, the presence of a Ge-oxide-free interfacial layer (IL) can suppress SiGe oxidation. [2] Here we show how a passivating interfacial layer can be grown using low-pressure oxidation and highlight the importance of SiGe surface preparation prior to low-pressure oxidation.

Abstract: Epilayers grown on substrates etched by various etching conditions were studied for stacking fault defects. Substrates were etched by H₂, H₂+ HCl and H₂ + C_xH_y gases prior to epilayer growth for comparison. High density of SF was observed in the epilayers when H₂+HCl or H₂+C_xH_y gas mixtures were used. On the other hand, much lower density of stacking faults (SF) (<1 cm^-2) was observed in the epilayer grown on the surface etched by only H₂ gas. However, a high number of pits were generated in the epilayer grown on substrate etched by H₂ only, which can be considered to be tradeoff of achieving low SF in epilayer by substrate etching. We also conclude from our experimental results that C rich surface is more favorable to generate SF in epilayer compared to Si rich surface.

Abstract: The semiconductor industry is undergoing a transition driven by end use markets. In recent years, mobile devices have been the leading generator of growth. Now the connection of various products and machines to the internet is generating new and extensive demands for memory (storage of the data), logic (intelligent processing of the data including machine learning), and sensing (e.g., image sensors generating visual data). Thus the versatile planar MOS transistor based semiconductor technology has diverged into various specialized and complex branches, with each technology type using unique approaches to address scaling challenges. These lead to specific requirements for semiconductor wafer surface preparation. This paper will review the high level industry trends and how they affect surface preparation specifically.

Abstract: The integration of III-V and Ge materials on Si surface causes many issues with complexity such as lattice mismatch with silicon. In particular, the surface preparation and passivation of InGaAs is very challenging, because the formation of InGaAs/high-K interface is important, but not well understood. For the systematical study of InGaAs surface during wet processes, the effect of various wet etching processes on the surfaces of binary III-V compound semiconductors (GaAs, InAs, GaSb and InSb) was studied from the viewpoints of surface oxidation, material loss (dissolution), and passivation. Based on that, further effort to understand the surface reactions on ternary InGaAs compound semiconductor was made. In addition, process sequential effect on the InGaAs surface was investigated.

Abstract: Metal/polymer joints as well as metal/metal joints bonded by epoxy adhesive have been widely used for automotive, electrical device and others. In the present study, the adhesion strength of a stainless-steel/epoxy joint was evaluated by using of the shear test and the 4-point bending test. Three kind of the surface finishing condition of the stainless steel were selected, and the effect of the surface morphologies of the interface on the adhesion strength in the metal/epoxy joint was investigated. The relationship between the interface morphology and the loading mode in the metal/epoxy joint was discussed.

Abstract: In this work the etching kinetics of Ge (100) is studied in acidic solutions containing and oxidizing agent. It is shown that the etch rate in the low etch-rate range is controlled by the concentration of the acid, oxidizing agent and the hydrodynamics of the system. The surface termination during etching has strong impact on the etching kinetics. Finally, we discuss the stability of the Ge (100) surface in water and relate this to the low solubility of the Ge suboxides

Abstract: In Situ gas phase passivation methods can enable new channel materials. Toward this end pure anhydrous HOOH and H2NNH2 membrane gas delivery methods were developed. Implementation led to Si-OH passivation of InGaAs(001) at 350C and Si-N-H passivation of SiGe(110) at 285C. XPS and initial electrical characterization has been carried out. Feasibility for In Situ dry surface preparation and passivation was demonstrated.