A method for detecting faults in the navigation and control system of deep space satellites is presented. A new method for computing the probability of a fault given multiple different types of residuals processors is presented. The method uses the Shiryayev sequential probability ratio test to estimate the probability of the presence of a fault signal given the residuals generated from either parity relationships or fault detection filters, a fault map of the impact of each fault signal on the residuals, and an adaptive fault estimation scheme that enables processing with fewer residuals. This new methodology is applied to the detection of the fault signals in the attitude control system and navigation system of deep space satellites. First a sensor fusion process is presented for blending star tracker data, gyro data, accelerometer data, and information from the vehicle control system to form the best estimate of the navigation state. Then a set of fault detection filters are developed that detect and uniquely identify faults in each of the sensors or actuators. Decision-making is handled through the sequential processing. Simulation results for a single-satellite system are presented.

The International Roadmap for Semiconductors requires ultrashallow, highly activated, abrupt dopant profiles in the source/drain extension regions, for technology nodes beyond 45nm. The authors contrast B and BF2 implants in Si and silicon on insulator (SOI) substrates with and without a preamorphizing implant (PAI). The objective of the study is to compare between Si and SOI substrates, PAI and non-PAI condition, and B and BF2 implants. The results show the absence of the “reverse annealing effect” in BF2 implants, which is observed in B implants. The presence of F appears to impede the formation of boron interstitial clusters, which is shown in the case of B implant. The BF2 implants follow a similar trend for SOI and Si with and without PAI.

The effects of surface proximity and B concentration on end-of-range defect formation during nonmelt laser annealing in preamorphized silicon have been studied. These effects were analyzed by observing the activation and diffusion of an ultrashallow B implant, using Hall effect and secondary ion mass spectrometry measurements. By adjusting the preamorphizing implant and laser annealing conditions, B deactivation and diffusion were minimized, resulting in a sheet resistance of similar to 600 Omega/sq with a 16 nm junction depth. This is attributed to a combination of enhanced dissolution of end-of-range defects and preferential formation of B-interstitial clusters due to the surface proximity and high B concentration, respectively. (C) 2008 American Institute of Physics.

Activation/deactivation of 500eV B implants in pre-amorphised Si after non-melt laser annealing with multiple scans at 1150 degrees C and isochronal rapid thermal post-annealing has been investigated. Under the thermal conditions used for non-melt laser at 1150 degrees C, a substantial residue of end-of-range defects remained after I laser scan, evidenced by end-of-range defect decoration by B atoms after 700 degrees C post-annealing and by transient enhanced diffusion after 800 degrees C post-annealing. Dramatic boron deactivation is also observed after post-annealing the I-scan samples. Most of these features were not present in samples receiving 5 or 10 laser scans, indicating that the end-of-range defects had been stabilised or dissolved within 5 and 10 scans. The results show that the detrimental effects of end-of-range defects can be removed during non-melt laser annealing and is therefore an achievable method for stabilisation of highly activated B profiles in pre-amorphised Si.

Electrical activation and redistribution of 500eV boron implants in preamorphized silicon after nonmelt laser annealing at 1150°C and isochronal rapid thermal postannealing are reported. Under the thermal conditions used for a nonmelt laser at 1150°C, a substantial residue of end-of-range defects remained after one laser scan but these were mainly dissolved within ten scans. The authors find dramatic boron deactivation and transient enhanced diffusion after postannealing the one-scan samples, but very little in the five- and ten-scan samples. The results show that end-of-range defect removal during nonmelt laser annealing is an achievable method for the stabilization of highly activated boron profiles in preamorphized silicon.

P -type ultrashallow junctions are widely fabricated using Ge preamorphization prior to ultralow-energy boron implantation. However, for future technology nodes, issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). An understanding of the effect of the buried Si∕SiO2 interface on defect evolution, electrical activation, and diffusion is needed in order to optimize the preamorphization technique. In the present study, boron has been implanted in germanium preamorphized silicon and SOI wafers with different preamorphizing implant conditions. Subsequent to implantation an isothermal annealing study of the samples was carried out. Electrical and structural properties were measured by Hall-effect and secondary-ion-mass spectroscopy techniques. The results show a variety of interesting effects. For the case where the Ge preamorphization end-of-range defects are close to the buried oxide interface, there is less dopant deactivation and less transient-enhanced diffusion, due to a lower interstitial gradient towards the surface.

The fabrication of preamorphized p-type ultrashallow junctions in silicon-on-insulator (SOI) has been investigated. Electrical and structural measurements after annealing show that boron deactivation and transient enhanced diffusion are reduced in SOI compared to bulk wafers. The reduction is strongest when the end-of-range defects of the preamorphizing implant are located deep within the silicon overlayer of the SOI silicon substrate. Results reveal a very substantial increase in the dissolution rate of the end-of-range defect band. A key player in this effect is the buried Si∕SiO2 interface, which acts as an efficient sink for interstitials competing with the silicon surface.

Ultra-shallow B and BF 2 implants in silicon pre-amorphised with Ge have been activated using a scanning non-melt laser. The implants were activated either by using 1 or 10 laser scans. Isochronal 60s post-laser annealing between 700-1000°C were then undertaken to study the deactivation and reactivation of the B. Both B and BF2 samples were implanted with a dose of 1×10 15 B cm -2 at an effective energy of 500eV. The presence of F from the BF 2 implants, which is superimposed over the boron profile increases the sheet resistance of the initial fabricated junction (from 600-700 ohms/sq from B implants only to 750-1100 ohms/sq for BF2 implants). Fluorine also changes the deactivation and reactivation behaviour of the boron during the post-anneals by increasing the amount of deactivation of the boron. © 2006 Materials Research Society.

For CMOS technology, generations beyond the 65nm node a major goal is achieving highly activated, ultra-shallow and abrupt profiles. In the case of p-type (boron) implants, one method to achieve this is using Ge preamorphization (PAI) prior to ultra-low energy B implantation. However, for future technology nodes, new issues arise when bulk silicon is supplanted by silicon-on-insulator (SOI). Understanding the strong impact of the buried Si/SiO2 interface, will enable tests of fundamental models on defect evolution, electrical activation and diffusion. In the present study, boron has been implanted in germanium-preamorphized silicon and SOI wafers. Subsequent to implantation, an isochronal and isothermal annealing study of the samples was carried out. Electrical and structural properties were measured by Hall effect and SIMS techniques. The results show a range of effects in both substrate types, including TED and deactivation driven by interstitials from the end-of-range (EOR) defects. However, in the SOI material there is a lower boron deactivation and the EOR defects are eliminated at a lower thermal budget in SOI than in the bulk silicon due to competition between the upper SOI interface and the Si surface which both act as sinks for interstitials.

The work carried out here examines the suitability of BBr2+ and B++Br+ implants into crystalline (100) silicon for ultra-shallow junctions (USJ) applications. Rutherford backscattering spectroscopy (RBS) shows that an amorphous region is created during implantation of BBr2+, eliminating the need for a separate pre-amorphising implant. This amorphous region re-grows during subsequent rapid thermal annealing and there is evidence that bromine retards the re-growth velocity. Hall Effect measurements after rapid thermal annealing show a difference in electrical activation between the BBr2+ and B++Br+ implants with the latter having the lower activation. Anomalous Hall mobility is also observed for the molecular implant at lower annealing temperatures.

This paper investigates the electrical activation of boron halide molecular implants into silicon and compares them to boron implants at the same effective energy. The implanted species: B+, BF2+, BCl2+ and BBr2+ were implanted to doses of 2 x 10(14) and 1 x 10(15) B cm(-2) the energy of the molecular implants was calculated to give an effective boron implant energy of 5 keV. Samples cut from the wafers were annealed for 30 s at temperatures ranging from 800 degrees C to 1100 degrees C. Hall effect measurements were used to compare and contrast the electrical activation of the boron between the different halide species and doses. It was found that molecular implants of BBr2+ and BCl2+ do not enhance the elec trical activation of boron to the same extent that BF2+ implants do. The BBr2+ implants are only comparable with boron after annealing at high temperatures (above 1000 degrees C). The BF2+ implants show enhanced electrical activation with 2 respect to boron for all the annealing temperatures and doses studied. Rutherford backscattering spectroscopy (RBS) of silicon implanted with BBr2+ to a dose of 1 X 10(15) boron 2 atoms cm(-2), shows that an amorphous region is created during the implantation. This region fully re-grows after annealing at 1100 degrees C lower temperature anneals remove only part of the amorphous layer. RBS channelling shows that a fraction of the bromine takes up substitutional lattice sites upon implantation, and that this fraction increases as the samples are annealed at temperatures above 600 degrees C with 40% of the B being in substitutional sites after annealing at 1050 degrees C. (c) 2005 Elsevier B.V. All rights reserved.

The formation of highly activated ultra-shallow junctions (USJ) is one of the key requirements for the next generation of CMOS devices. One promising method for achieving this is the use of Ge preamorphising implants (PAI) prior to ultra-low energy B implantation. In future technology nodes, bulk silicon wafers may be supplanted by Silicon-on-Insulator (SOI), and an understanding of the Solid Phase Epitaxial (SPE) regrowth process and its correlation to dopant electrical activation in both bulk silicon and SOI is essential in order to understand the impact of this potential technology change. This kind of understanding will also enable tests of fundamental models for defect evolution and point-defect reactions at silicon/oxide interfaces. In the present work, B is implanted into Ge PAI silicon and SOI wafers with different PAI conditions and B doses, and resulting samples are annealed at various temperatures and times. Glancing-exit Rutherford Backscattering Spectrometry (RBS) is used to monitor the regrowth of the amorphous silicon, and the resulting redistribution and electrical activity of B are monitored by SIMS and Hall measurements. The results confirm the expected enhancement of regrowth velocity by B doping, and show that this velocity is otherwise independent of the substrate type and the Ge implant distribution within the amorphised layer. Hall measurements on isochronally annealed samples show that B deactivates less in SOI material than in bulk silicon, in cases where the Ge PAI end-of-range defects are close to the SOI back interface.

Purpose: The authors describe an immunocompetent patient who developed multiple recurrent branch retinal artery occlusions (BRAOs) associated with the varicella zoster virus (VZV). Methods: A 69-year-old woman with mild bilateral vitritis developed superior and inferior BRAOs in her right eye with decreased visual acuity to 20/40, and a peripheral BRAO inferotemporally in her left eye. One month later, the inferotemporal BRAO progressed proximally in her left eye with a decrease in visual acuity to 20/40. After an extensive negative systemic evaluation, she underwent a diagnostic pars plana vitrectomy of her right eye. Results: Vitreous fluid was positive for VZV DNA by polymerase chain reaction (PCR). The patient was treated with intravenous acyclovir and systemic oral steroids. After remaining disease free for 3 months, the patient had two recurrences: 1) a mild vitritis and 2) development of a new superior temporal artery occlusion in the left eye. Both recurrences were treated with oral acyclovir and systemic steroids. The patient remained recurrence free for 12 months on a maintenance dose of oral acyclovir, and for 4 additional months without acyclovir. Conclusions: Varicella zoster virus can be associated with the syndrome of multiple recurrent BRAOs. The diagnosis of VZV-associated BRAO can be established by PCR of intraocular fluid.