Characterization of Ion Implanted Silicon Annealed with a Graphite Radiation Source
A Varian IA-200 isothermal annealer has been used to anneal ion implantation damage and electrically activate dopants in As and B implanted silicon with minimal redistribution of the impurity. The anneal occurs in vacuum using infrared radiation from a resistively heated sheet of graphite. Good quality anneals of /sup 11/B implanted samples have been obtained with minimal boron diffusion. Arsenic implanted wafers have also be annealed with excellent results except for a substantial loss of As which occurs unless the wafer has an SiO/sub 2/ cap. The anneal quality of (100) wafers was independent of dose, however, the anneal quality of the (111) wafers improved with increasing As dose.
Activation of shallow, high‐dose BF+2 implants into silicon by rapid thermal processing
Rapid thermal processing has been used to activate shallow p+ layers (∼0.1–0.15 μm) following BF+2 implantation (49 keV, 2–6×1015 cm−2) into amorphized silicon. For doses of 2×1015 cm−2, the shallow as‐implanted boron profile was preserved, unlike the case of furnace annealing (900 °C, 30 min). Sheet resistance of 85 Ω/sq following rapid annealing was close to that calculated assuming 100% activation of dopants in their as‐implanted distribution. At 6×1015 cm−2 dose, however, these same rapid annealing conditions (10–15 sec exposure to a 1250 °C heater) produce considerable dopant redistribution (≳2000 A) with peak carrier concentration of ∼1020 cc−1, which is far below the as‐implanted value of ∼1021 cc−1. A two‐step anneal is described which permits shallow junctions of ∼1500 A to be obtained for the 6×1015 cm−2 dose implants; however, maximum carrier concentration was still ≲1020 cc−1. The present data suggests that the concentration limit for activation of implanted boron encountered when furnace anne...
Differences in the length of initial hospital stay in very preterm infants
Aim: To investigate the effect of maternal, infant and birth hospital district related factors on the length of initial hospital stay in very preterm infants. In addition, rehospitalization rate within the first year from the initial discharge was studied.