Primary Ion Energy Research Articles

Thin Co films on Cu(111) studied by electron capture spectroscopy

AbstractWe have studied thin films of Co on Cu(111) single crystals with electron capture spectroscopy (ECS). The magnetism from the cobalt layer can be detected clearly in remanence and as a function of the outer magnetic field. The measured circular polarization of the emitted light is related directly to the structural and magnetic changes of the system, depending on the cobalt layer thickness. We find the set‐in of in‐plane magnetization at ∼2 monolayers of cobalt and the saturation of our signal at a film thickness of 7–8 monolayers. At coverages above 3–4 monolayers the increasing growth of hcp cobalt domains at the expense of fcc cobalt domains gives rise to a linearly increasing ECS signal up to 7.5 monolayers. We attribute this to the fact that the fcc cobalt domains are covered with copper, whereas the hcp cobalt domains expose cobalt in the upper layer. Monte‐Carlo simulations of our ion scattering experiments show that great experimental care has to be taken in order to avoid excessive sputtering damage to the sample. By using moderate primary ion energies and small angles of incidence, thin films can be investigated with ECS in the grazing incidence geometry without changing the film structure. Copyright © 2005 John Wiley & Sons, Ltd.

Evaluation of BN-delta-doped multilayer reference materials for shallow depth profiling in SIMS: round-robin test

SIMS with low energy (down to 250 eV) primary ions has been widely used for ultra-shallow dopant profiling for ULSI device development. In spite of its high performance in depth resolution, there still remain ambiguities to be overcome in SIMS technique for accurate depth and concentration calibrations in the shallow depth regions. In order to get accurate ultra-shallow boron depth profiles, BN-delta-doped multilayer reference materials were developed and evaluated in a round-robin study using low energy SIMS. Those delta-doped layers were used to measure the sputter rate change in the initial stage of oxygen–ion bombardment.

Cluster primary ion bombardment of organic materials

In order to evaluate their potential for molecular surface analysis, we applied monoatomic (Ga, Cs, Au, Bi) as well as polyatomic (SF 5, Au n , Bi n , C 60) primary ions to a series of organic samples. For the model system Irganox 1010 on LDPE we determined the secondary ion yield, the disappearance cross section and the resulting ion formation efficiency as a function of the primary ion energy. As a general result the efficiency is improved with the mass of the monoatomic primary ion. A further increase is obtained by the use of polyatomic primary ions. According to this, highest efficiencies are obtained for C 60, the lowest for Ga. Additionally, molecular imaging was performed on real world samples (electronic components, pharmaceuticals): for this a cluster LMIS operated with Ga, AuGe or Bi was applied. The results reveal the potential of cluster SIMS to overcome existing limitations and to establish TOF-SIMS for new applications in the fields of polymers, biology and medicine.

Accurate depth profiling for ultra-shallow implants using backside-SIMS

We studied methods for accurate depth profiling for ultra-shallow implants using backside-SIMS. For the measurement of ultra-shallow profiles, the effects of surface transient and atomic mixing are not negligible. Therefore, we applied backside-SIMS to analyze ultra-shallow doping in order to exclude these effects. Backside-SIMS profiles show a sharper ion implantation tail than surface-side-SIMS profiles. In addition, the primary ion energy dependence becomes weaker when backside-SIMS is used [Surf. Interf. Anal. 29 (2000) 362; Appl. Surf. Sci. 203–204 (2003) 264; J. Vac. Sci. Technol. B 21 (2003) 1422]. However, the peak concentration of the backside sample was lower than that of the surface-side sample. Therefore, the sample flatness was estimated using the SIMS response function. Furthermore, SIMS profiles were simulated using SIMS response functions. This simulation shows how the sample flatness affects the SIMS profile.

Evaluation of BN-delta-doped multilayer reference materials for shallow depth profiling in SIMS: round-robin test

SIMS with low energy (down to 250 eV) primary ions has been widely used for ultra-shallow dopant profiling for ULSI device development. In spite of its high performance in depth resolution, there still remain ambiguities to be overcome in SIMS technique for accurate depth and concentration calibrations in the shallow depth regions. In order to get accurate ultra-shallow boron depth profiles, BN-delta-doped multilayer reference materials were developed and evaluated in a round-robin study using low energy SIMS. Those delta-doped layers were used to measure the sputter rate change in the initial stage of oxygen–ion bombardment.

Cluster primary ion bombardment of organic materials

In order to evaluate their potential for molecular surface analysis, we applied monoatomic (Ga, Cs, Au, Bi) as well as polyatomic (SF5, Aun, Bin, C60) primary ions to a series of organic samples. For the model system Irganox 1010 on LDPE we determined the secondary ion yield, the disappearance cross section and the resulting ion formation efficiency as a function of the primary ion energy. As a general result the efficiency is improved with the mass of the monoatomic primary ion. A further increase is obtained by the use of polyatomic primary ions. According to this, highest efficiencies are obtained for C60, the lowest for Ga. Additionally, molecular imaging was performed on real world samples (electronic components, pharmaceuticals): for this a cluster LMIS operated with Ga, AuGe or Bi was applied. The results reveal the potential of cluster SIMS to overcome existing limitations and to establish TOF-SIMS for new applications in the fields of polymers, biology and medicine.

Atomic mechanism of radiation‐induced erosion of field electron emitters

AbstractThe features of erosion of the surface of field electron emitters bombarded by helium and neon ions were studied. Experiments showed that ion bombardment produced tungsten atom transport, the number of atoms transported being proportional to the ion fluence. Analysis of ion bombardment‐induced atomic‐scale surface roughness showed evidence of a non‐dynamic surface atom displacement for primary ion energies below a threshold for stable Frenkel pair formation and cathode sputtering. A quasi‐static mechanism of surface erosion is considered, according to which the process is related to the displacement of metal atoms into low‐coordinated positions upon evolution of the energy of formation of interstitial inert gas atoms. Copyright © 2004 John Wiley & Sons, Ltd.

Factors affecting the retention of Cs + primary ions in Si

X-ray photo-electron spectroscopy (XPS), Rutherford backscattering spectroscopy (RBS) along with MARLOWE and TRIM computer simulations were used to study the retention of Cs + primary ions in Si substrates during sputtering. Cs concentrations were found to depend on (a) primary ion energy, (b) primary ion incidence angle, and (c) sputtering time (within the transient region). With the exception of the XPS and RBS data collected as a function of Cs + impact energy, Cs concentration variations, Δ[Cs], appear to correlate with sputter yield variations, ΔSY, via Δ[Cs] ∝ 1/(ΔSY+1). Computer simulations reveal variations in Cs + scattering with impact energy, etc. This and/or self sputtering may explain the inconsistencies noted with impact energy.

Influence of primary ion bombardment conditions on the emission of molecular secondary ions

In order to further our understanding of the secondary ion emission behavior from organic surfaces, we have performed a systematic study on the influence of the primary ion parameters. As model sample Irganox 1010 on low density polyethylene (LDPE) was used. Both monoatomic (Ga, Cs, Au) and polyatomic (Au 2, Au 3, SF 5, C 60) primary ions were used. Additionally, the primary ion energy was varied. The data were evaluated by calculating secondary ion yields, disappearance cross sections and ion formation efficiencies (yield/damage cross section). The results show that heavier monoatomic ions are more efficient than lighter ones and that polyatomic primary ions are more efficient than monoatomic ones. Highest efficiency values are found for C 60 bombardment at 20 keV. Compared to Ga bombardment the efficiency gain in this case is more than 2000-fold. Additionally it can be shown that the higher efficiency is correlated with a softer ionization, i.e. less fragmentation. The results suggest a much more homogeneous energy distribution in the sample surface by polyatomic primary ions compared to monoatomic ones.

Ultra-shallow depth profiling with secondary ion mass spectrometry

Estimation methods for ultra-shallow profiling with secondary ion mass spectrometry (SIMS) were investigated. The depth and concentration of ultra-shallow profiles were calibrated using multi-delta-doped samples and bulk-doped samples. Boron profiles, whose implantation energy is 200 eV or less, were measured by backside SIMS analysis in order to minimize the atomic mixing effect. This analysis enabled accurate junction depth measurements for even 200 eV boron implanted samples when the primary oxygen ion energy was 500 eV or less, but the sample preparation time was relatively long. SIMS depth resolution functions were then extracted from surface-side and backside (true) profiles in order to deconvolute degraded surface-side profiles. This deconvolution analysis of SIMS (surface-side) profiles, using the depth resolution functions, provided profiles of similar quality to those obtained by backside SIMS analysis and was a relatively quick process.

Depth profiling for ultrashallow implants using backside secondary ion mass spectrometry

We studied accurate depth profiling for ultrashallow implants using backside secondary ion mass spectrometry (SIMS). For measuring ultrashallow dopant profiles such as 200 eV B implantation profiles, the effects of surface transient and atomic mixing are not negligible. We applied backside SIMS to analyze ultrashallow doping in order to exclude these effects. Comparing the SIMS profiles of surface side and those of backside, backside SIMS profiles showed a shallower ion implantation tail than surface-side SIMS profiles. Furthermore, backside SIMS profiles showed almost no dependence on primary ion energy. This indicates that backside SIMS provides sharp B profiles suitable for analyzing ultrashallow implants, even in the case where higher primary ion energy is used in comparison with implantation energy. The backside SIMS technique has a good potential to be used for the development of next-generation devices.

Energy and mass dependence of isotopic enrichment in sputtering

Silver, copper, and boron (from a boron nitride target) were sputtered with xenon ions. The isotopic composition of secondary ions of silver was measured at ion energies ranging from 300 eV to 3 keV and, for copper and boron, at 2.0, 2.5, and 3.0 keV. An ion gun was used to generate the ion beam. The secondary ions were detected at a small emission angle by a quadrupole mass spectrometer. The secondary-ion flux of silver was found to be enriched in heavy isotopes at lower incident-ion energies. The heavy-isotope enrichment was observed to decrease with increasing primary-ion energy. Beyond 500 eV, light isotopes of silver were sputtered preferentially with the enrichment increasing to a constant value of 1.018. The sputtered flux of copper and boron also indicated constant enrichments (1.008 and 1.281 for copper and boron respectively) in light isotopes at high ion energies.

Thermal spikes observed during the tantalum sputtering by gold cluster ions

The emission of atomic and cluster ions during the sputtering of a tantalum target by gold cluster ions was experimentally studied for primary ion energies ranging from 6 to 21 keV. An increase in the number of atoms in the bombarding cluster ions of gold leads to a considerable increase in the yield of atomic ions of tantalum possessing quasithermal energies. The results provide experimental evidence for the appearance of thermal spikes in the target bombarded with cluster ions, with the corresponding contribution to the emission of atomic ions.

Experimental and computer investigation of the diagnostic mirror behavior under sputtering and duct material deposition

Experiments on stainless steel duct material, W and Mo mirror surfaces as well as modeling of the experiment using a new computer code which takes into account scanning tunnelling microscope measured surface topography are described. Simulations of the sputtering yield as a function of the primary ion energy and the angle of incidence for ion irradiated targets demonstrated the difference in behavior for ideally smooth, non-irradiated and irradiated targets.

Characterization of high- k gate dielectric films using SIMS

Recently, the high- k materials (Al 2O 3, Ta 2O 5, HfO 2, ZrO 2,…,etc.), which are alternative dielectrics to silicon dioxide for memory and logic devices, come into notice. We have applied SIMS to the characterization of the ultra-thin HfO 2 films. SIMS with low energy primary ion has proven to be a beneficial technique to see depth profiles of impurities and their behaviors due to annealing. As for Si substrate without native oxide, Si diffusion as well as the formation of amorphous Hf x Si 1− x O y layer at HfO 2/Si interface seem to occur during growth of HfO 2 film, which has been confirmed by SIMS and other analytical techniques. Furthermore, it is found that ion yield of carbon in HfO 2 is larger than that in SiO 2 by more than two orders of magnitude.

A systematic study of the surface roughening and sputter rate variations occurring during SIMS ultrashallow depth profile analysis of Si with Cs +

Sputter rate variations and surface roughening occurring during the initial stages of secondary ion mass spectrometry ultrashallow depth profiling of Si with Cs + are examined for a range of primary ion incident energies (0.25–5.0 keV) and incident angles (40–80°). Sputter rate variations were derived over the 4.15–36.4 nm range through the analysis of a Boron delta layered structure. A reduction in the sputter rate with sputtering time was noted, with the variation increasing with decreasing primary ion energy and increasing incident angle. From this data set, a relation expressing these sputter rate variations as a function of the primary ion energy and incident angle was derived which, in turn, allows for depth and intensity scale corrections to be carried out. Surface roughening culminating in ripple formation was also observed using atomic force microscopy. These were observed under conditions resulting in excessive sputter rate variations.

Copper drift in low dielectric constant insulator films caused by O 2+ primary ion beam

Copper depth profiling in low- k material methylsilsesquioxane (MSQ) was investigated. Cu was implanted into MSQ or thermally grown SiO 2 and depth profiling was carried out with O 2 + primary ions, and charge neutralization with electron flooding using a quadrupole SIMS. The obtained profile was deeper and broader than the theoretically predicted ones and Cu drifting during the depth profiling was implied. Though the primary ion energy was lowered to 1 keV, it was not enough to suppress the redistribution. Though MSQ showed shrinking by electron irradiation, this did not seem to be the major origin of the Cu redistribution.

Comparison between Xe + and O 2+ primary ions, at low impact energy, on B delta-doping, SiGe–Si superlattice and Al/Ti multilayer structures

To improve depth resolution in secondary ion mass spectrometry (SIMS) low energy and heavy primary ions can be used. We present results obtained with xenon, at low energies (down to 500 eV), on specially chosen samples (B delta-doping, SiGe–Si superlattices and Al/Ti multilayers) to evaluate the depth resolution enhancement in ultra-shallow implants and abrupt transitions. The depth resolution parameters extracted are compared with those found with O 2 + primary beam. Analyses of B delta showed an improvement for xenon at energies between 2 and 3 keV. Below 1 keV, sputter-induced roughness adversely affected the advantages of xenon. For SiGe–Si, O 2 + beam, without O 2 flooding remains the best choice to obtain a smaller decay length. On Al/Ti multilayers, depth profiles acquired with xenon are more suitable. This can be explained by a poor reactivity of Xe + with metallic target atoms.

Oxygen-ion-induced ripple formation on silicon: evidence for phase separation and tentative model

We have investigated the ripple topography on silicon surfaces developed by 2–10 keV O 2 + bombardment at an impact angle of 45°. The ripple amplitude increased with the depth of erosion and finally became comparable with the ripple wavelength. This caused the local impact angle of ripples facing the oxygen-ion beam to reach the critical angle of SiO 2 formation, promoting the phase separation between silicon dioxide and silicon. As observed before, the critical depth for SiO 2 formation decreased with decreasing the primary ion energy. This appears to be related to the amount of erosion necessary to reach the critical angle of SiO 2 formation. The decrease of wavelength at lower primary ion energies is interpreted as the result of reduced surface diffusivity which is enhanced by ion bombardment.

Accurate SIMS depth profiling for ultra-shallow implants using backside SIMS

We studied accurate depth profiling for ultra-shallow implants using backside SIMS. In the case of measuring ultra-shallow profiles, the effects of surface transient and knock-on are not negligible. Therefore, we applied backside SIMS to analyze ultra-shallow doping to exclude these effects. Comparing the SIMS profiles of surface-side and those of backside, backside profiles show a sharper ion implantation tail than surface-side profiles. Furthermore, backside SIMS profiles show almost no dependence on primary ion energy. This indicates that backside SIMS provides sharp B profiles suitable for analyzing ultra-shallow implants, using higher primary ion energy in comparison with implantation energy. The backside SIMS technique has a good potential to be used for next generation devices.