J.C. Banks

Impact of passivation layers on enhanced low-dose-rate sensitivity and pre-irradiation elevated-temperature stress effects in bipolar linear ICs

Final chip passivation layers are shown to have a major impact on the total dose hardness of bipolar linear technologies. It is found that devices fabricated without passivation layers do not exhibit enhanced low-dose-rate sensitivity (ELDRS) or pre-irradiation elevated-temperature stress (PETS) sensitivity, whereas devices from the same production lot fabricated with either oxide/nitride or doped-glass passivation layers are ELDRS and PETS sensitive. In addition, removing the passivation layers after fabrication can mitigate ELDRS and PETS effects. ELDRS and PETS effects do not appear to be inherently related to circuit design or layout, but are related to mechanical stress effects, hydrogen in the device, or a combination of the two. These results suggest that proper engineering of the final chip passivation layer might eliminate ELDRS and PETS effects in bipolar integrated circuits.

The Si surface yield as a calibration standard for RBS

Abstract The Rutherford backscattering spectroscopy (RBS) surface height of a pure bulk material can be used as an absolute standard value to calibrate the detector solid angle. This work presents the results of an international collaboration started at the beginning of 1998 to define the surface height of the RBS spectrum ( H 0 ) of Si, amorphized by ion implantation to avoid channeling. The analyses were performed with 1–3 MeV He beams and 170° scattering angle. The detector solid angle was estimated in the different laboratories either by geometrical measurement or by a calibrated standard. The agreement of the experimental H 0 values is of the order ±2%, the claimed accuracy for RBS. The results are also consistent at 2% level with both the stopping power measurements of Konac et al. (1998), and the measurements of Lennard et al. (1999).

Heavy ion backscattering spectrometry for high sensitivity

Abstract Heavy ion backscattering spectrometry (HIBS) using moderate energy (a few hundred keV) heavy ions has demonstrated sensitivity for medium-to-heavy surface impurities on Si more than 1000 × greater than conventional Rutherford backscattering spectrometry (RBS). Problems with pileup are eliminated by a thin, self-supporting foil in front of the surface barrier detector (SBD), ranging out ions scattered from the substrate and allowing only ions scattered from impurities heavier than the substrate to reach the detector. Limitations to a SBD approach arise from relatively poor energy resolution at low energies, leading to the inability to resolve closely spaced impurity masses (such as Fe and Cu), as well as requiring an analysis beam of 250 keV or higher. In order to bypass these limitations and explore means of increasing sensitivity and mass resolution, we have built a time-of-flight (TOF) HIBS prototype, optimized for large solid angle.

Electronic sputtering of solids by slow, highly charged ions: Fundamentals and applications

Electronic sputtering in the interaction of slow (v < vBohr), highly charged ions (SHCI) with solid surfaces has been subject of controversial discussions for almost 20 years. We review results from recent studies of total sputtering yields and discuss distinct microscopic mechanisms (such as defect mediated desorption, Coulomb explosions and eAects of intense electronic excitation) in the response of insulators and semiconductors to the impact of SHCI. We then describe an application of ions like Xe 44a and Au 69a as projectiles in time-of-flight secondary ion mass spectrometry for surface characterization of semiconductors. ” 2000 Elsevier Science B.V. All rights reserved.

Using heavy ion backscattering spectrometry (HIBS) to solve integrated circuit manufacturing problems

Abstract Heavy Ion Backscattering Spectrometry (HIBS) is a new IBA tool for measuring extremely low levels of surface contamination on very pure substrates, such as Si wafers used in the manufacture of integrated circuits. HIBS derives its high sensitivity through the use of moderately low energy (∼100 keV) heavy ions (e.g. C12) to boost the RBS cross-section to levels approaching 1000 b, and by using specially designed time-of-flight (TOF) detectors which have been optimized to provide a large scattering solid angle with minimal kinematic broadening. A HIBS User Facility has been created which provides US industry, national laboratories, and universities with a place for conducting ultra-trace level surface contamination studies. A review of the HIBS technique is given and examples of using the facility to calibrate Total-Reflection X-ray Fluorescence Spectroscopy (TXRF) instruments and develop wafer cleaning processes are discussed.

Time-of-flight heavy ion backscattering spectrometry

A new time-of-flight (TOF) ion detection system for Heavy Ion Backscattering Spectrometry (HIBS) is described. Examples are also given of the use of the system for measuring low-level contamination on Si wafers. Currently, the TOF-HBIS system has a sensitivity of 1 {times} 10{sup 9}/cm{sup 2} for the heaviest of surface impurity atoms and a mass resolution capable of separating Fe from Cu. The sensitivity is expected to improve by an additional order of magnitude on a industrial TOF-HIBS system being constructed for SEMATECH.

Trace element sensitivity for Heavy Ion Backscattering Spectrometry

Abstract Heavy Ion Backscattering Spectrometry (HIBS) is an ion beam analysis tool for measuring very low levels of surface contamination. HIBS uses low-energy (100–200 keV), heavy ions (C + . N + ) for analysis combined with a thin carbon foil to range out the increased backscattering yield from the substrate. A new HIBS system has been built at Sandia National Laboratories under a cooperative research agreement with Sematech, which was made available as a user facility for Si wafer contamination analysis beginning in July 1995. A number of factors have influenced the detection limits which are being achieved, including detector efficiency; choice of beam species and energy, sputtering by the incident beam, and spectral background due to multiple scattering and random coincidences. Because of the increased sensitivity of this new system, we have identified sources of background which had not been a problem in a research prototype. These include problems with beam scattering in the chamber, molecular contamination in O and N beams, and forward scattering of H by the incident beam. In its first tests the system has demonstrated detection limits of ∼ 6 × 10 9 atoms/cm 2 for Fe to ∼ 3×10 8 atoms/cm 2 for Au on Si.

Sputtering and migration of trace quantities of transition metal atoms on silicon

Abstract We have investigated the behavior of low levels of transition metal atoms on silicon surfaces subject to nitrogen bombardment. Submonolayer coverages of gold, iron, copper, molybdenum and tungsten were deposited on 〈100〉 silicon surfaces. Samples were analyzed using 270 keV He + time-of-flight backscattering before and after irradiation with 6 mC of 270 keV N + at current levels in the hundreds of nanoamps. The yield of sputtered metallic atoms ranged from 1.0 × 10 −3 per incident nitrogen ion to 3.3 × 10 −3 per incident ion. Lower yields were correlated with migration of the metallic species into the silicon. The implications for ultra-high sensitivity measurement of contamination on silicon wafers by time-of-flight heavy-ion backscattering spectrometry are discussed.

Hall-Petch Hardening in Pulsed Laser Deposited Nickel and Copper Thin Films

Very fine-grained Ni and Cu films were formed using pulsed laser deposition on fused silica substrates. The grain sizes in the films were characterized by electron microscopy, and the mechanical properties were determined by ultra-low load indentation, with finite-element modeling used to separate the properties of the layers from those of the substrate. Some Ni films were also examined after annealing to 350 and 450 C to enlarge the grain sizes. These preliminary results show that the observed hardnesses are consistent with a simple extension of the Hall-Petch relationship to grain sizes as small as 11 nm for Ni and 32 nm for Cu.

Composition and structure of sputter deposited erbium hydride thin films

Erbium hydride thin films are grown onto polished, a-axis {alpha} Al{sub 2}O{sub 3} (sapphire) substrates by reactive ion beam sputtering and analyzed to determine composition, phase and microstructure. Erbium is sputtered while maintaining a H{sub 2} partial pressure of 1.4 x 10{sup {minus}4} Torr. Growth is conducted at several substrate temperatures between 30 and 500 C. Rutherford backscattering spectrometry (RBS) and elastic recoil detection analyses after deposition show that the H/Er areal density ratio is approximately 3:1 for growth temperatures of 30, 150 and 275 C, while for growth above {approximately}430 C, the ratio of hydrogen to metal is closer to 2:1. However, x-ray diffraction shows that all films have a cubic metal sublattice structure corresponding to that of ErH{sub 2}. RBS and Auger electron that sputtered erbium hydride thin films are relatively free of impurities.