Sybren Sijbrandij

Membrane folding by helium ion implantation for three-dimensional device fabrication

The authors demonstrate that silicon nitride membranes can be folded out of plane into three-dimensional structures by helium ion implantation. The folds have a radius of 1μm and can be directed both up or down by varying implant energy.

Elemental analysis with the helium ion microscope

The newly developed helium ion microscope is an instrument well suited to high resolution surface specific imaging with several unique contrast mechanisms. In addition to its imaging capabilities, the focused helium ion beam (subnanometer in size) has recently been used for elemental analysis. The scattering probability, angular distribution, and recoil energy combine to provide valuable information about the specimen being analyzed.

Material analysis with a helium ion microscope

The helium ion microscope, a new imaging technology, is being applied also to sample modification. The application opportunity exists due to the extreme high resolution and the ability to gather analytical data as well as images. Possible applications include inspection, elemental analysis, and dopant concentration measurements.

Towards Secondary Ion Mass Spectrometry On The Helium Ion Microscope

The ORION Helium Ion Microscope (HIM) has become a well-established tool for high-resolution microscopy [1]. It is based on the atomic-sized ALIS gas field ion source, which has a brightness of 4×10 A cm sr. This leads to probe sizes of less than 0.5 nm. The source can operate with helium and, after special prototype modifications, with neon [2]. While secondary electrons are used for high-resolution high-contrast imaging, detection of backscattered atoms can provide only limited specimen composition information. By contrast, Secondary Ion Mass Spectrometry (SIMS) is an extremely powerful technique for analyzing surfaces due to its excellent sensitivity, high dynamic range, very high mass resolution and ability to differentiate between isotopes (see Figure 1). In order to get chemical information with a higher sensitivity and a high lateral resolution, we have investigated the feasibility of performing SIMS on the Helium Ion Microscope. To reach these objectives, the secondary ion formation process under He and Ne bombardment has to be investigated and optimized along with the experimental beam parameters such as spot size and dwell time. High secondary ion yields are crucial when using a small low current analytical probe. To investigate secondary ion formation an experimental study was performed, to investigate sputtering effects on resolution a simulation approach was taken. First, secondary ion yields for different elements sputtered from different materials exposed to helium and neon ion beams were experimentally determined on a test set-up. The basic yields were, as expected due to the use of noble gas primary ions, lower than those of conventional SIMS. However, yields may be increased by using reactive gas flooding during analysis, eg. oxygen flooding for positive secondary ions [3] and cesium flooding for negative secondary ions [4]. Figure 2 shows the measured useful yield enhancement (up to three orders of magnitude) with O2 flooding for different analyzed materials. Detection limits have been calculated taking into account the experimentally obtained useful yields. Figure 3 shows the detection limit for Ne bombardment on silicon with oxygen flooding in secondary positive mode. Depending on the dwell time, ppm sensitivity can be obtained. Second, a detailed study of the sputtering phenomena was carried out in order to determine the effect of the collision cascade on the lateral resolution. He and Ne bombardment of different materials was studied using TRIM simulations [5]. In particular, the effects of the different beam and target parameters were investigated in order to estimate the best achievable lateral resolution, taking into account the competition between sputtering and imaging. The diameter (FW50) of the area from which sputtered atoms originate has been calculated for 10 keV He and Ne bombardment of different materials. The simulations show that a lateral resolution smaller than 10 nm can be obtained and that the mass and density of the target material are important parameters in determining the achievable resolution. The results obtained are very encouraging and the prospects of performing SIMS on the ORION are very interesting. The combination of high-resolution microscopy and high-sensitivity chemical mapping on a single instrument will lead to a new level of correlative microscopy. This paper will present an overview of our experimental and simulation results and will discuss the prospects of SIMS on the Helium Ion Microscope in terms of detection limits and lateral resolutions.

Imaging Contrast with Multiple Ion Beams

A commercial Ga-FIB/SEM system can directly image samples using an ion beam or e-beam before, after or during milling/depositing process. This capability provides important feedback for process control. Because of the limited spatial resolution and Ga contamination of the Ga ion beam, the e-beam is often considered as the primary imaging tool. But ion beam imaging also provides important information about the samples. Orion Nanofab integrates He, Ne and Ga focused ion beams on one single platform. He and Ne ion beams are based on the gas field ion source (GFIS) technology. The images generated by He/Ne ion beams are sub-nm in resolution capturing intricate details of the samples[1]. Nanofab also provides an optional state of art Ga-FIB. With this unique configuration, Orion Nanofab provides a great platform to study ion beam imaging with a variety of ion species.