C. Mihalcea

Multipurpose sensor tips for scanning near‐field microscopy

The reproducible micromachining of hollow metal tips on Si cantilevers and their applicability to scanning probe microscopy techniques are described. Provided with apertures below 130 nm and hollow pyramidal tips proved to be highly suited probes for scanning near‐field optical microscopy (SNOM). First results of combined SFM/SNOM measurements together with scanning electron microscopy (SEM) photographs of the new sensors are presented. The SNOM images show a resolution of about 100 nm demonstrating the usefulness of these probes.

Fabrication of integrated diamond cantilevers with tips for SPM applications

Abstract The fabrication of diamond cantilevers with diamond tips integrated on silicon wafers for scanning probe microscopy (SPM) applications is reported. Hot filament CVD diamond deposition and standard techniques of silicon micro-machining are employed. The deposition of well-developed tips depends critically on the pretreatment applied to enhance nucleation density. With an optimized process, well-shaped tips with a radius of curvature in the order of 30 nm are obtained. According to micro-Raman investigations they consist of high quality diamond. Another critical step is the definition of the cantilever area. It can be solved by proper process design. Preliminary performance tests show the cantilevers to possess high resonance frequencies.

Novel micromachined cantilever sensors for scanning near-field optical microscopy*

The reproducible micromachining of hollow metal tips on Si cantilevers and their applicability to scanning near‐field optical microscopy (SNOM) is described. This sensor is fabricated using semiconductor compatible technologies. A hollow metal pyramid is employed as an optical aperture sensor for SNOM and simultaneously as a force sensor for scanning force microscopy applications. Apertures down to 120 nm were realized. To confirm the feasibility of the sensor we present measurements on microstructured chromium films as well as on hot filament chemical vapour deposition grown (111) diamond membranes. The SNOM images show a resolution of about 100 nm, demonstrating the usefulness of these probes.

Modified fabrication process for aperture probe cantilevers

We report the development of cantilever‐ and fibre‐based probes for scanning near‐field optical microscopy. Both probe concepts rely on the integration of a microfabricated aperture tip with reproducible optical and mechanical properties. Numerical calculations were carried out using a finite integration code to investigate the polarization‐sensitive transmission behaviour of aperture tips. In order to establish technological guidelines for the optimization of the properties of the optical tip the distinct influence of the tip geometry on the intensity distribution in the vicinity of the aperture is studied in detail.

Fabrication of monolithic diamond probes for scanning probe microscopy applications

A process relying on the molding technique for the fabrication of diamond cantilevers with diamond tips integrated on silicon wafers for scanning probe microscopy applications is described. Either hot filament or microwave CVD diamond deposition and standard techniques of silicon micro-machining are employed. The deposition of well- developed tips depends critically on the pretreatment applied to enhance nucleation density; abrasive treatment with diamond powder as well as the bias-enhanced nucleation turned out to be successful. With optimized processes, well- shaped tips with a radius of curvature in the order of 30 nm can be obtained. They consist of high quality diamond according to micro-Raman spectroscopy. The definition of the cantilever area is another critical step which can be solved by proper process design. The fabrication of conductive tips/cantilevers is possible by boron doping. Finally, first performance tests of the diamond tips and cantilevers are presented.

Improved anisotropic deep etching in KOH-solutions to fabricate highly specular surfaces

Abstract We report on an improved standard etching method to fabricate deep etched 〈100〉-oriented Silicon surfaces with a mirrorlike finish. It is shown that the addition of minimal quantities of an antimony or arsenic compound (in the mmol range) to a 40% wt. KOH-solution has a deep impact on the etching characteristics of single crystalline silicon. The compounds undergo reduction to the elements at the silicon surface and form covalent bonds to the substrate. As etching proceeds, a film of the elements Sb or As floats on the surface, changes the oxidation/dissolution behavior of the silicon and finally leads to surfaces with an rms roughness of below 2 nm.

Less than 0.1 μm linewidth fabrication by visible light using super-resolution near-field structure

Abstract We have achieved less than 0.1 μm linewidth fabrication in a photoresist film by using visible light together with a super-resolution near-field structure (Super-RENS). This technique enables to produce an optical aperture with sub-wavelength dimensions at a fixed distance to the photoresist film. Illumination of this aperture leads to a strong laterally confined optical near-field which exposes the photoresist. For this achievement, we have used polished SiO 2 disk substrates, which have an atomically flat surface, in order to reduce edge roughness and also to improve our process. Additionally, optical properties of antimony films as one key material of super-RENS have been estimated and laser heat effects influencing the formation mechanism of the grooves in the photoresist film will be discussed in this paper.

Micromachined probes for high-frequency scanning force microscopy and scanning thermal microscopy

The spatial and time resolved characterization of electronic devices by scanning probe microscopy demands the fabrication of proximal probes with well defined properties. To fulfill these requirements micromachining is the most appropriate technique, as it allows probe fabrication in a batch process with highest reproducibility. In this paper we describe the development of electrical and thermal near-field probes which can be employed for high frequency scanning force microscopy (HFSFM) and scanning thermal microscopy (SThM) respectively. Both probes have been completely fabricated in a micromachining batch process based on an almost identical technological design. For electrical imaging by HFSFM a coplanar wave guide probe was developed. The probes wave guide properties have been characterized by network analysis. A novel thermal probe consisting of a Schottky diode at the tip of a silicon cantilever was developed for SThM. Preliminary results on electrical and thermal characterization will be presented.

Experimental and theoretical characterization of aperture probe cantilevers for polarization-sensitive SNOM

Microfabricated aperture probes for SNOM applications revealed polarization properties which seem to depend on the aperture geometry which is well defined due to the fabrication process. A finite integration approach was used to theoretically calculate the optical transmission characteristics of these probes. In particular the influence of the aperture aspect ratio and the metal film thickness on the transmission and the polarization properties is studied in detail. A modified tip geometry is proposed to improve both, the light confinement at the tip apex and the polarization properties of the aperture probe.

Application and characterization of combined SNOM/SFM cantilever probes

A combined SNOM/SFM aperture probe is presented which is based on a conventional scanning force microscopy cantilever. Probe fabrication was performed in a batch process which allows to get reproducible mechanical and optical properties. For SNOM applications a tip is integrated at the very end of the cantilever which consists of a hollow metal pyramid with a miniaturized aperture of about 60 nm. To select the appropriate tip material the transmissivity of different metals were investigated in the visible range. The SNOM/SFM probes were characterized both mechanically and optically, e.g. the transmission of apertures is measured as a function of their size. To determined the lateral resolution in the optical transmission mode measurements on test samples are shown. Additionally, a novel probe design is introduced where the geometry of the single aperture tip is altered to obtain a double aperture tip.