Simon Waid

Focused-ion-beam-inflicted surface amorphization and gallium implantation—new insights and removal by focused-electron-beam-induced etching

Recently focused-electron-beam-induced etching of silicon using molecular chlorine (Cl(2)-FEBIE) has been developed as a reliable and reproducible process capable of damage-free, maskless and resistless removal of silicon. As any electron-beam-induced processing is considered non-destructive and implantation-free due to the absence of ion bombardment this approach is also a potential method for removing focused-ion-beam (FIB)-inflicted crystal damage and ion implantation. We show that Cl(2)-FEBIE is capable of removing FIB-induced amorphization and gallium ion implantation after processing of surfaces with a focused ion beam. TEM analysis proves that the method Cl(2)-FEBIE is non-destructive and therefore retains crystallinity. It is shown that Cl(2)-FEBIE of amorphous silicon when compared to crystalline silicon can be up to 25 times faster, depending on the degree of amorphization. Also, using this method it has become possible for the first time to directly investigate damage caused by FIB exposure in a top-down view utilizing a localized chemical reaction, i.e. without the need for TEM sample preparation. We show that gallium fluences above 4 × 10(15) cm(-2) result in altered material resulting from FIB-induced processes down to a depth of ∼ 250 nm. With increasing gallium fluences, due to a significant gallium concentration close beneath the surface, removal of the topmost layer by Cl(2)-FEBIE becomes difficult, indicating that gallium serves as an etch stop for Cl(2)-FEBIE.

Nanoimprint lithography stamp modification utilizing focused ion beams

Nanoimprint lithography (NIL) has been established as a high-throughput technique to fabricate sub-25-nm patterns at a low cost. The fabrication of NIL templates with features in the submicrometer range is currently a bottleneck of the NIL technology. The replication of errors on NIL templates places a major challenge on the reusability of templates. Focused ion beam (FIB) technology is employed to modify prestructured NIL templates. In this work, repair strategies for NIL stamps are discussed. Excess material from stamps has been removed by ion milling. Nanoscale trenches and ultrathin lamellas fabricated with a focused ion beam and their corresponding imprints are presented. It has been confirmed that commercial UV-NIL stamps can be modified by FIB milling and imprinted line patterns were successfully replicated by UV-NIL using the repaired templates. Furthermore, the potential of three-dimensional NIL templates structured by FIB was evaluated. Three-dimensional imprints with features down to 80nm with ...

Quantitative simulation of ion-beam induced deposition of nanostructures

Gas-assisted etching and deposition with focused ion beams are unique and flexible methods for the fabrication of nanostructures. To understand and improve these processes the ability to accurately simulate and predict the resulting structures is very important. In this paper we present a nonlocal recoil-based algorithm for topography simulation of ion-beam induced gas-assisted deposition. We have fabricated flying roof like overhanging structures and found very good agreement between simulation and experiment. These structures cannot be explained with a local model. Furthermore, we demonstrate a considerable influence of the beam diameter on the resulting structure by comparing otherwise identical simulations with different beam diameter.

Focused Ion Beam Lithography

Optical lithography is the unrivalled mainstream patterning method that allows for costefficient, high-volume fabrication of microand nanoelectronic devices. Current optical photolithography allows for structures with a reproducible resolution below 32 nm. Nevertheless, alternative lithography methods coexist and excel in all cases where the requirement for a photomask is a disadvantage. Especially for low-volume fabrication of microdevices, the need for a photomask is inefficient and restricts a fast structuring, such as required for prototype device development and for the modification and repair of devices. The necessity of high-resolution masks with a price well above €10k is too cost intensive for the fabrication of single test devices. For this reason ‘direct-write’ approaches have emerged that are popular for several niche applications, such as mask repair and chip repair. Optical direct-write lithography and electron beam lithography are among the most prominent techniques of direct-write lithography. Less known, but highly versatile and powerful, is the ion beam lithography (IBL) method. Optical direct-write lithography uses laser beam writers with a programmable spatial light modulator (SLM). With 500 mm2/minute write speed and advanced 3D lithography capabilities, optical direct-write lithography is also suitable for commercial microchip fabrication. However, with a resolution of 0.6-μm minimum feature size of the photoresist pattern, optical direct-write lithography cannot be considered a nanopatterning method. Electron beam lithography uses a focused electron beam to expose an electron beam resist. Gaussian beam tools operate with electron beams with a diameter below 1 nm so that true nanofabrication of structures is feasible. A resolution of 10 nm minimum feature size of the e-beam resist pattern has been successfully demonstrated with this method. However, special resists are required for e-beam lithography, that are compatible with the high energy of forward scattered, back-scattered and secondary electrons. A common resist for sub-50nm resolution is polymethylmetacrylate (PMMA) requiring an exposure dose above 0.2 μC/μm2. For highest resolution (below 20 nm) inorganic resists such as hydrogen silsesquioxane (HSQ) or aluminium fluoride (AlF3) are used, which unfortunately require a high electron exposure dose. Hence, high-resolution electron beam lithography (EBL) is linked to long exposure times which, in combination with a single scanning beam, results in slow processing times. Therefore, this high-resolution method is only used for writing photomasks for optical projection lithography and for a limited number of high-end applications. A resolution to this dilemma may be the use of multi-beam electron tools, as are currently under development. Also electron projection lithography has been under

Modeling of precursor coverage in ion-beam induced etching and verification with experiments using XeF2 on SiO2

Focused ion beams are an established but inherently slow technique for many nanopatterning applications. One way to increase its processing speed is by gas-assisted ion-beam induced etching. However, to understand and improve this process, the ability to accurately simulate the precursor coverage is very important, because it strongly affects the efficiency of the process. In this paper, the authors present a recoils-based simulation model that considers precursor adsorption, decomposition, and diffusion. The authors provide a non-steady-state solution for translational symmetry, which they use to investigate the influence of the precursor diffusion coefficient on the etching process. They find that the diffusion coefficient influences the shape of the bottom of the irradiated structure. Furthermore, they compare the simulation results to experiments of SiO2 etched by XeF2 using a focused Ga ion beam, and extract model parameters such that the etching rate of numerous experiments with different current de...

Substituted triphenylamines as building blocks for star shaped organic electronic materials

A versatile synthetic protocol toward a series of various substituted triphenylamine derivatives serving as building blocks for organic electronic materials was developed. Key steps during synthesis were either Ullmann condensations or nucleophilic aromatic substitutions giving rise to structural modification of triphenylamines and their electronic nature. In turn, these scaffolds were exemplarily attached to a dendritic tris(2-thienyl)benzene core affording star shaped organic semiconducting materials which were characterized regarding their photo-physical, electro-chemical and thermal properties. A strong influence of the substituents nature on both photo-physical and morphological thin film characteristic of star shaped target compounds was observed. The applicability of these materials in organic electronic devices was demonstrated in an organic field effect transistor configuration yielding a hole mobility of nearly 10−3 cm2 V−1 s−1. The performance of the materials can be correlated to the substituents applied.

Generation of 3D nanopatterns with smooth surfaces

Ga implantation into Si and reactive ion etching has been previously identified as candidate techniques for the generation of 3D nanopatterns. However, the structures manufactured using these techniques exhibited impedingly high surface roughness. In this work, we investigate the source of roughness and introduce a new patterning process to solve this issue. The novel patterning process introduces an additional layer absorbing the implanted Ga, thus preventing the clustering of the implanted Ga observed with uncoated Si substrates. This process enables 3D nanopatterning with sub-100 nm lateral resolution in conjunction with smooth height transitions and surface roughness down to 4 nm root mean square. Such patterns are ideally suited for optical applications and enable the manufacturing of nanoimprint lithography templates for low-profile Fresnel lenses.

Focused ion beam direct patterning of hardmask layers

Inorganic hardmasks are routinely employed in reactive ion etching (RIE) processes due to their excellent etch resistance. However, since pattern definition is commonly performed using organic resist materials, the enhanced etch resistance provided by the inorganic hardmasks comes at the expense of added process complexity. In this work, the authors introduce the method of direct patterning of hard masks (DPHM) utilizing milling and gas assisted deposition (GAD) with a focused ion beam (FIB). DPHM by FIB allows to structure hardmask materials, which are otherwise not accessible with standard processes. Further, it reduces the high number of (typically seven) processing steps required for resist based patterning down to only three using FIB milling of hardmasks or even two using FIB GAD for patterning. The authors found that by FIB milled hard masks made of oxide such as aluminum zinc oxide exhibited excellent pattern clarity. For other materials, effects such as ion beam induced dewetting were found to af...

Focused ion beam induced Ga-contamination—An obstacle for UV-nanoimprint stamp repair?

Ultravoilet (UV)-nanoimprint lithography (NIL) master stamps are subject to wear due to the mechanical nature of the imprint process. To extend the useful lifespan of expensive NIL master stamps, a focused ion beam repair process is highly desirable. Due to the inevitable Ga-staining induced by the focused ion beam processing the transmissivity of repaired NIL stamps is locally degraded. In this work, the authors investigate the impact of Ga-induced transmission losses on the imprint process. Experimental results indicate that the reduced transparency mainly impacts the amplitude of bow deformations in the imprint. These deformations are strongly enhanced by Ga-staining of the master stamp. The authors present a method for quantification of such bow-deformations. The introduced bowing-factor allows to make a qualified decision on whether the occurring deformation is acceptable for the target application. The authors have achieved control over the extent of the Ga-induced bow-deformation by tuning the UV-d...