A new method that explores turn-by-turn beam position monitor (BPM) data to calibrate lattice models of accelerators is proposed. The turn-by-turn phase space coordinates at one location of the ring are first established using data from two BPMs separated by a simple section with a known transfer matrix, such as a drift space. The phase space coordinates are then tracked with the model to predict positions at other BPMs, which can be compared to measurements. The model is adjusted to minimize the difference between the measured and predicted orbit data. BPM gains and rolls are included as fitting variables. This technique can be applied to either the entire or a section of the ring. We have tested the method experimentally on a part of the SPEAR3 ring.
A weak vertical coupled-bunch instability with oscillation amplitude of the order of a few m has been observed in SPEAR3 at nominal vacuum pressure. The instability becomes stronger with increasing neutral gas pressure as observed by turning off vacuum pumps, and becomes weaker when the vertical beam emittance is increased. These observations indicate that the vertical beam motion is driven by ions trapped in the periodic potential of the electron beam. In this paper we present a series of comprehensive beam measurements, impedance-based stability analysis, and numerical simulations of beam-ion interactions in SPEAR3. The effects of vacuum pressure, gas species, beam current, bunch fill pattern, chromaticity, and vertical beam emittance are investigated.
Trench dislocations in a 0.25um BiCMOS SRAM technology were traced to defects arising during S / D processing. It is argued that these defects coalesce to form dislocations, typically near the trench edge, under the combined influence of mechanical stress and high temperature processing. Process variables impacting the generation of these dislocations, including layout geometry; trench depth, profile, and densification; the presence of a liner under the gate spacer nitride; and S / D implant condition and anneal are studied. Based on this analysis, a defect-free BiCMOS process is proposed. It is shown that although the incidence of trench dislocations could be decreased by reducing the overall stress in the flow, eliminating Sill implant defects is the key to completely removing the trench dislocations.Controlling process-induced stress is an increasing concem with each succeeding generation of IC process. Increasing packing density and reducing feature size lead to higher wafer stress levels [I]. With the drive toward low thermal budget processing, the ability of materials to relieve stress by flow processes decreases as well. A number of recent publications have discussed silicon dislocations observed with the introduction of shallow trench isolation [2-41. These papers have invoked mechanical stress as the primary cause of these dislocations and have identified methods to reduce stress in the silicon to eliminate these dislocations. However, they do not clearly identify the process step which is the source of these dislocations and reducing the stress alone does not always eliminate the defects completely. In this work, we demonstrate that point defects generated during heavy sourcddrain implantation form the nuclei for trench dislocations, which under the combined influence of mechanical stress and high temperature processing typically glide to the region of maximum stress.We also propose a defect free solution based on annealing the implant damage to ensure that any subsequent changes in the process or the layout do not regenerate these dislocations.Description of Defects This work was based on a 0.25pm BiCMOS SRAM technology with shallow trench isolation which was reported previously [51. This triple poly/triple metal BiCMOS SRAM process consisted of buried layer and epitaxy followed by shallow trench isolation. The active pattern was defined using DUV lithography and etched to create 3500A deep trenches. The trenches were filled with 0,-TEOS and annealed at high temperature prior to trench CMP. The gate stack consisted of poly-Si /Wsi,/ Si,N, cap with Si,N, spacers. Heavy dose arsenic n+ sourcddrain implants were followed by a poly-2 self-aligned contact formation. Poly-3 load resistor and backend processing for the contacts and metal layers completed the process. Figure 1 is a E M cross-section of this technology.Trench dislocations were observed in the memory array of this 0.25um 1Mb SRAM at the end of line. These dislocations were typically initiated near the bottom comer of the trench, terminating eith...
Although the linearized theory of small amplitude synchrotron oscillations and the instability thresholds derived from it have long been understood, there is no satisfactory description of the large amplitude highly non-linear synchrotron motion of a bunched beam. With an appropriate tuning of the RF cavity impedance, large amplitude, low frequency, self-sustained relaxation oscillations of this synchrotron motion are generated. This paper presents detailed experimental data of such behavior, tracking code results that reproduce the important characteristics, and a simple analytical model that explains the key features of the relaxation oscillation: growth of the instability, saturation of the oscillation, breakup of the bunch, and subsequent damping of the system back to the beginning of the next cycle of the relaxation oscillation.
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