Kouji Kondou

Depth resolution improvement in secondary ion mass spectrometry analysis using metal cluster complex ion bombardment

Secondary ion mass spectrometry analyses were carried out using a metal cluster complex ion of Ir4(CO)7+ as a primary ion beam. Depth resolution was evaluated as a function of primary ion species, energy, and incident angle. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same experimental condition due to reduction of atomic mixing in the depth. The authors obtained a depth resolution of ∼1nm under 5keV, 45° condition. Depth resolution was degraded by ion-bombardment-induced surface roughness at 5keV with higher incident angles.

Ion-beam characteristics of the metal cluster complex of Ir4(CO)12

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a metal cluster complex which has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, it has been demonstrated that stable ion beams of Ir4(CO)7+ were produced. Energy dependence of sputtering yield of silicon bombarded with Ir4(CO)7+ ions was investigated at a beam energy from 2to10keV at normal incidence. Experimental results showed that the sputtering yield varied substantially with beam energy. The sputtering yield at 10keV was higher than that with SF5+ or Ar+ ions by a factor of 3–24, whereas the sputtering yield at 3keV was lower than that with Ar+ ions. In the case of 2keV, deposition was found to occur. The substantial variation in the sputtering yields was examined using empirical equations for calculating sputtering yields. It was shown that the high sputtering yield at 10keV would be due to what is called “nonlinear effect” unique to complex-projectile bombardment. It was also indicated that the substantial variation in the sputter...

Production of Stable Ion Beam of Os3(CO)12 with Compact Metal-Cluster-Complex Ion Source

Metal-cluster-complex ion beams were produced stably using a cluster ion source, which is compact enough to be installed in commonly used secondary ion mass spectrometry (SIMS) systems. As a metal cluster complex, triosmium dodecacarbonyl, Os3(CO)12, was utilized, which has a molecular weight of 906.7. Since precise temperature control is necessary to sublimate the metal cluster complex stably without thermal decomposition, the ion source was equipped with compact heat-removal devices in addition to an external heater. Experimental results showed that the crucible temperature of the metal cluster complex can be maintained at about 130 °C in continuous operation, which is an appropriate temperature for sublimation without the problem of decomposition. The ion source produced steady-state beams of Os3(CO)n+ (n=7 or 8) ions with a beam current exceeding 10 nA at 10 keV. Beam current increased with gas pressure, depending on the temperature of the crucible holding the metal cluster complex. The rate of the change in beam current was within a few percent per hour; hence, in view of stability, the ion source was confirmed as usable in SIMS. Furthermore, beam profile was investigated using a Faraday cup with a knife-edge as well as a GaAs/AlAs multilayer substrate as a beam target.

Secondary Ion Mass Spectrometry of Organic Thin Films Using Metal-Cluster-Complex Ion Source

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a metal cluster complex that has a molecular weight of 1104.9. Using a metal-cluster-complex ion source, secondary ion mass spectrometry (SIMS) of poly(methyl methacrylate) (PMMA) thin films on silicon substrates was performed with a quadrupole mass spectrometer. The secondary ion intensity of PMMA bombarded with Ir4(CO)7+ ions was investigated in the beam energy ranging from 3 to 10 keV at an incident angle of 45°. For comparison, bombardment with oxygen ions, O2+, was also tested. It was confirmed that the use of Ir4(CO)7+ ions enhanced secondary ion intensity by at least one order of magnitude compared with that of O2+ ions. Experimental results also showed that secondary ion intensity increased with beam energy; particularly, high-mass secondary ion intensity markedly increased.

Observation of Sputtered Si Surface Irradiated with Metal Cluster Complex Ions

In this paper, we report the result of surface sputtering of Si using a proto-type compact cluster ion source which has been developed using Os3(CO)12 as a low damage-sputtering source. The surface roughening of Si under the acceleration energy 10 key at incidence angles about 0/spl deg/ and 60/spl deg/ has been studied. The sputtered Si surface was observed by using AFM (atomic force microscope) and SEM (scanning electron microscope).

Secondary-Ion-Mass-Spectrometry Depth Profiling of Ultra-shallow Boron Delta Layers in Silicon with Massive Molecular Ion Beam of Ir4(CO)7+

Tetrairidium dodecacarbonyl, Ir4(CO)12, is a massive compound called metal cluster complex, which has a molecular weight of 1104.9. Using an Ir4(CO)7+ primary ion beam, secondary ion mass spectrometry (SIMS) of boron-delta-doped silicon samples was performed. Depth resolution, defined by 1/e decay length for the trailing edge of the boron delta layer, was investigated in the beam energy ranging from 2.5 to 10 keV at an incident angle of 45°. Experimental results showed that the depth resolution improved with oxygen partial pressure at a beam energy of 5 keV. It was confirmed that the depth resolution without oxygen flooding monotonically improved as beam energy decreased. Furthermore, it was found that the favorable effect of oxygen flooding on depth resolution weakened as beam energy was reduced.

Beam-induced Nanoscale Ripple Formation on Silicon with the Metal-Cluster-Complex Ion of Ir4(CO)7+

The surface topography of Si(100) bombarded with 2.5–10 keV Ir4(CO)7+ at an incident angle of 45° was investigated by atomic force microscopy. Experimental results showed that self-organized ripple structures with a wavelength below 30 nm were produced at a beam energy of 5 keV. It was found that the wavelength of the ripples increased with decreasing beam energy, which is different from results obtained using conventional ion beams. In addition, surface roughness proved to increase with decreasing beam energy. The phenomena were explained by considering a substantial decrease in sputtering yield and the subsequent compositional change in the target at lower-beam-energy Ir4(CO)7+ bombardment. Furthermore, the surface roughness was also confirmed to increase with increasing oxygen partial pressure.

Characteristics of altered layers formed by sputtering with a massive molecular ion containing diverse elements with large mass differences

Tetrairidium dodecacarbonyl (Ir4(CO)12) is an organometallic compound called metal cluster complex which has a molecular weight of 1104.9. To investigate its irradiation effect, silicon substrates sputtered with 10keV Ir4(CO)7+ were analyzed by high resolution Rutherford backscattering spectrometry. Experimental results were examined on the basis of a conventional theory of simultaneous implantation and sputtering. The introduction of oxygen gas during sputtering proved to form a thick oxide layer in the substrate, resulting in iridium segregation at the silicon-oxide interface and carbon accumulation near the surface. It was confirmed that oxygen partial pressure significantly affected the characteristics of an altered layer beneath a sputtered surface.

High depth resolution SIMS analysis using metal cluster complex ion bombardment

SIMS depth profiles were measured using metal cluster complex ions of Ir4(CO)7+ as a primary ion beam in order to obtain high depth resolution. Depth resolution was evaluated as a function of primary ion species, energy and incident angle using a multiple boron delta-doped silicon sample. The depth resolution obtained using cluster ion bombardment was considerably better than that obtained by oxygen ion bombardment under the same bombardment condition due to reduction of atomic mixing in the depth. The best depth resolution was 0.9 nm under the bombardment condition of 5 keV, 45° with oxygen flooding, which approaches the value measured with state of the art SIMS analyses. However, depth resolution was not improved by decreasing the cluster ion energy (less than 5 keV), even though the roughness of the sputtered surface was suppressed. The limit of depth resolution improvement may be caused by a carbon cover-layer that prevents the formation of surface oxide that buffers atomic mixing. To overcome this issue, it will be necessary to eliminate carbon from the cluster ion.