Fred A. Stevie

Secondary ion mass spectrometry characterization of the diffusion properties of 17 elements implanted into silicon

A systematic investigation of the diffusion of Be, B, Na, Mg, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Zn, Ge, Rb, and Mo in silicon has been carried out. The elements were implanted into silicon wafers as low dose impurities, and then postheat treatments of the ion-implanted samples were conducted at different temperatures for a specific time. Following the anneals, the depth profiles were obtained by secondary ion mass spectrometry analyses. A wide range of diffusion behavior has been observed for these elements. Based on differences in the depth profiles the diffusion mechanism was identified where possible.

Diffusion of 18 elements implanted into thermally grown SiO2

Diffusion data are presented for 18 elements implanted in SiO2 layers thermally grown on silicon and annealed at temperatures ranging from 300 to 1000 °C. Most species studied, (e.g., Be, B, Al, Sc, Ti, V, Zn, Ga, and Mo), showed negligible diffusion over the examined temperature range. In general, this study has shown that the diffusivity of dopants or impurities in SiO2 is significantly smaller than that in silicon. However we also observed that several elements (e.g., Rb and In) have a higher diffusivity in SiO2 than in Si. Because Ga and In are both used as sources for focused ion beam analyses, the lack of Ga diffusion and the movement of In in SiO2 is of interest.

Diffusion profiles of high dosage Cr and V ions implanted into silicon

The depth profiles of high dosage 52Cr+ and 51V+ ions implanted in (100) crystalline silicon after thermal anneal at temperatures between 300 °C and 1000 °C are studied by secondary ion mass spectrometry and cross-sectional transmission electron microscopy. At dosages of 1×1015 ions/cm2 and above, the surface layer of silicon substrate is amorphorized. During the subsequent thermal annealing, the depth profiles of the implanted ions are strongly coupled with the solid phase epitaxial growth of amorphous silicon. Silicide precipitate formation is important to understand the differences between Cr and V diffusion. After anneal of the 1×1015 ions/cm2 implanted samples at 900 °C and 1000 °C, most of the Cr has left the silicon, but only 10% of the V has escaped. The 1×1014 ions/cm2 Cr-implanted sample shows Cr ions exist only near the surface after 1000 °C anneal. The V-implanted sample, on the other hand, only shows a narrowing of the V profile after 1000 °C anneal.

Nitrogen incorporation and trace element analysis of nanocrystalline diamond thin films by secondary ion mass spectrometry

Nitrogen has been successfully incorporated into nanocrystalline diamond films produced by a CH4/N2 microwave plasma-enhanced chemical vapor deposition method. High mass resolution secondary ion mass spectrometry (SIMS) characterization shows that the density of the incorporated nitrogen, monitored via CN−, can be as high as 1021 atoms/cm3, depending on the ratio of CH4 to N2 in the reactant gas and on the substrate temperature used for the film preparation. SIMS depth profiles demonstrate that the incorporated nitrogen is uniform within the diamond films (about 1.5 μm thick) except at the surfaces and at the interface between film and substrate. Furthermore, the SIMS analyses reveal that alkali elements such as Na, K, and Li appear to be contaminants at the surface of nanocrystalline diamond films produced using a CH4/Ar or CH4/H2 discharge, but are bulk impurities only for the films prepared using a CH4/N2 plasma. These alkali impurities can play an important role in electronic properties such as electr...

TEM and SIMS Analysis of (100), (110), and (111) Single Crystal Niobium

Single crystal niobium specimens of (100), (110) and (111) crystal orientations have been analyzed using TEM and SIMS. The TEM specimens were prepared using Focused Ion Beam (FIB) and show niobium oxide thicknesses ranging from 4.9 to 8.3 nm for the three specimens after buffer chemical polishing. The oxide layers appear uniform and no significant sub‐oxide region was noted. SIMS analysis was made for all three orientations on hydrogen, carbon, and oxygen before and after heat treatments at 90, 600, and 1250 °C. Hydrogen is at a high level between the oxide layer and niobium, but at a relatively low level in the oxide. No high oxygen concentration region was noted in the niobium below the oxide. C contamination on the surface is detected mainly at the surface. Analysis after heat treatments showed some decrease in hydrogen after the 600 °C heat treatment, and significant oxidation of the niobium after the 1250 °C heat treatment.

Redistribution of implanted species in polycrystalline silicon films on silicon substrate

Redistributions of implanted species after thermal annealing in polycrystalline silicon (poly-silicon) were studied by secondary ion mass spectrometry. Ten different elements were implanted into poly-silicon films grown on Si substrates. The implanted energies were chosen such that the expected ion range is within the poly-silicon film. Thermal anneals were carried out at temperatures between 300°C and 1000°C in flowing high purity Ar gas. Three different diffusion behaviors have been observed for these elements. For Be, Na, Ga, and Cr, most of the implanted ions diffused out to the surface of the poly-silicon film after anneal at 1000°C. For K, Ca, Ti, and Ge, the impurity ions diffused deeper into the bulk after anneal at 1000°C. For Cl and Mn ions, the concentration distributions became narrower when annealed at high temperatures.

Focused Ion Beam Gases for Deposition and Enhanced Etch

The utility of a focused ion beam (FIB) to provide material removal for micromachining via sputtering with resolution of better than 10 nm has led to many important applications. In addition, FIB combined with a gas source containing the chemical precursors for deposition of materials or for enhanced, selective material removal provides the capabilities for a much wider range of micromachining applications. This chapter introduces FIB material deposition and chemically enhanced material removal processes, lists some of the FIB chemical precursors in common use and discusses the parameters for their use, and presents several examples.

Analysis of Interstitial Elements in Niobium with Secondary Ion Mass Spectrometry (SIMS)

Superconducting Radio Frequency (SRF) cavities provide enhanced efficiency and reduced energy utilization in present day particle accelerators. Niobium (Nb) is the material of choice for these cavities due to its high critical temperature and critical magnetic field. In order to understand why certain treatments, especially a low temperature bake, improve performance, it is important to study Nb surface characteristics and identify elemental contamination that can affect the performance of the cavity. H, C, O, and N are of interest because they are interstitial impurities in Nb. In earlier work, SIMS analysis using a CAMECA IMS‐6F with Cs+ primary beam showed that C and N were probably not significant factors impacting performance but there was a very high level of H in the Nb. Ion implants of C, N, O, and D into Nb provided quantification of C, N, O and indicated that D is very mobile in the Nb. Further analyses showed that heat treated Nb has lower levels of surface H than non heat treated Nb and subseq...

Segregation and enhanced diffusion of nitrogen in silicon induced by low energy ion bombardment

A sample of nitrogen-doped, single crystal Czochralski silicon was subjected to several different surface preparations. Secondary ion mass spectrometry depth profiling has shown that prolonged glancing-angle bombardment by 3–5kV Ar+ ions significantly increases the nitrogen concentration in the near surface by up to an order of magnitude over the bulk value. Concentrations are observed to be elevated over the bulk value to a depth up to 25μm. Nitrogen-implanted samples and samples with a 1nm surface nitride did not exhibit nitrogen segregation under the same conditions, but a sample with 100nm of surface nitride did exhibit ion bombardment induced drive-in. In nitride-free samples, the source of the nitrogen is indicated to be a nitrogen-rich layer in the first micron of material. The diffusion behavior of nitrogen in silicon is discussed and the Crowdion mechanism for diffusion is suggested as the enabling mechanism for the enhanced low temperature diffusion.

SIMS measurement of hydrogen and deuterium detection limits in silicon: Comparison of different SIMS instrumentation

Hydrogen is the most abundant element in the universe, but it cannot be detected by many analytical techniques. This element is used to improve interface quality and reduce the impact of defects in silicon technology. Knowledge of the amount and distribution of hydrogen is of significant interest for many technologies, such as ZnO and glass manufacturing. Secondary ion mass spectrometry (SIMS) can provide analysis for hydrogen and the isotopes deuterium and tritium. Lower instrument vacuum will improve the hydrogen detection limit. Vacuum conditions can be optimized by methods such as overnight pumping of samples and sample holder heating. Adsorption of hydrogen from the vacuum environment during analysis can be minimized with use of high sputtering rate. The species monitored may be atomic or molecular, such as H− or Cs2H+. The latter species provides a practical means for hydrogen profiling in dielectric films in magnetic sector instruments with conventional charge compensation. It is of interest to com...