A brief overview for recent progress of cluster ion beams is presented in conjunction with atomistic collision dynamics, cluster size effects and nano-process developments. Unique characteristics of cluster ion beam are utilized not only for nano-processing but also metrology for organic materials. Molecular dynamics study on cluster-solid interactions and size dependence of sputtering with Ar or Cl2 cluster ions reveal that both incident energy and chemical potential energy are effectively transfer to the surface to enhance the sputtering yield. In addition to these, less damage was remained on organic surface bombarded with cluster ions. Organic depth profiling of XPS or SIMS are realized with cluster ion beams.
In Electrospray Droplet Impact (EDI), the charged liquid droplets formed by ambient electrospray are introduced through an orifice into vacuum, accelerated by 10 kV and impact the samples prepared on the metal substrate. The secondary ions are detected by an orthogonal-type time-of-flight mass spectrometer. EDI can afford soft ionization/desorption for various kinds of real-world samples such as biological tissues, dyes, pigments, synthetic polymers, and inorganic materials with no special sample preparation. EDI is capable of atomic- and molecular-level etching with leaving little damage on the etched surface. Moreover, the useful yield (total ions generated divided by the total atoms or molecules desorbed) was found to be larger than 10-2. Due to these unique natures, EDI may be promising for the next-generation nano-scale 3D imaging.
The characteristics of a cluster beam interaction with a solid target are reviewed from the viewpoint of computer simulation. The similarity and dissimilarity of irradiation effects between single and cluster ion beams are mentioned for small clusters. The scaling of the excitation process based on the concept of the stopping force fails for the case of cluster impacts because of the size effect. In the case of a huge cluster with a very low velocity as low as the sound velocity, such a scaling rule is not significant. The Clusterelectric effect is important, thus a new type of algorithm of the “coarse-grained quantum molecular dynamics” that should prove the observed Clusterelectric effect.
We applied B18HX+ as an alternation of B+ or BF2+ to the implantation for source-drain extension in pMOSFETs corresponding to 65 nm and 28 nm technology nodes. We could obtain identical or better characteristics compared to the cases of conventional ions. In addition, we found from blank wafer that larger impact damage to Si atoms in B18HX+ implantation leads to more advantageous Rs−Xj in activation processing with only millisecond annealing.
Metal cluster complexes are chemically-synthesized organometallic compounds, which have a wide range of chemical compositions with high molecular weight. Using a metal-cluster-complex ion source, sputtering characteristics of a silicon substrate bombarded with normally incident Ir4(CO)7+ ions were investigated. Experimental results showed that the sputtering yield at 10 keV was 36, which is higher than that with Ar+ ions by a factor of 24. Further, secondary ion mass spectrometry (SIMS) of boron-delta-doped silicon samples and organic films of poly (methyl methacrylate) (PMMA) was performed. Using the Ir4(CO)7+ ion beam, the depth resolution of 0.9 nm was obtained at 5keV, 45o with oxygen flooding of 1.3×10−4 Pa. Additionally, it was confirmed that Ir4(CO)7+ ion beams significantly enhanced secondary ion intensity in high-mass range.
In secondary ion mass spectrometry (SIMS) of organic molecules, the mass of molecular ions currently detectable is at best only as high as the 1000 Da, which for all practical purposes prevents the technique from being extended to apply to bio molecules with larger mass. We developed SIMS equipment capable of bombardment in which the primary ions were argon cluster ions having a kinetic energy per atom controlled down to 1eV. By applying this equipment to several peptides and proteins, the intensity of fragment ions was decreased by a factor of 102 when the kinetic energy per atom was decreased below 5 eV, and molecular ions of insulin (molecular weight: 5808), cytochrome C (molecular weight: 12327) and chymotrypsin (molecular weight: 25000) were detected without using any matrix. Furthermore, we found that adjusting the kinetic energy per atom can realize site-specific bond breaking within a molecule. Based upon the above results, a future prospect of argon-cluster projectile for SIMS is discussed.
Organometallic sandwich clusters of M (benzene)2 (M = V and Cr) synthesized in gas phase reaction are soft-landed onto a self-assembled monolayer of n-alkanethiol (C4-C22 SAM) at a collision energy of 10-20eV. The resulting adsorption states and thermal desorption kinetics of the soft-landed clusters are studied with infrared reflection absorption spectroscopy and temperature-programmed desorption. The clusters keep their native sandwich structure intact on the SAM substrate. The soft-landed cluster are oriented with their molecular axes largely tilted off the surface normal of the SAM substrate, and exhibit unusually large desorption activation energies (Ed = ∼130 kJ/mol). The desorption of the embedded clusters in the SAM is suppressed to around room temperature, and may be associated with the crystal-rotator phase transitions of the SAM matrix.
The capability of an analysis system consisting of a low voltage scanning electron microscope, which is superior in spatial resolution and surface sensitivity, and a superconducting transition edge sensor (TES), which is under development, has been evaluated. The analysis system equipped with the TES, which has a superior energy resolution by about an order of magnitude to a conventional energy dispersive x-ray spectrometer (EDS), is useful for chemical state analysis that makes use of the strength ratio of characteristic x-rays of the same series. Elemental segregation in microstructures, whose size is several tens of nanometers as for simple energy-window maps or around 10 nm as for point analysis, is also detectable. It is expected that precise distribution of minor elements, which overlap with major elements in conventional EDS spectra, and chemical state maps of specific elements can be evaluated if the data processing of spectral imaging is incorporated into the system.