Neutron Damage Mechanisms in Silicon at 10°k
Neutron-irradiation effects on the photoconductivity and electrical properties of arsenic-doped silicon were measured at 10K so that the degradation mechanisms in infrared detectors fabricated from doped silicon could be examined. The measurements were performed at reduced optical background so that both thermal and optical generation were minimized as they are in the conditions under which the detectors are operated. The primary effects of the neutrons on the measured properties were (l) the introduction of acceptors (at a rate to 16 cm-1) which decreased the electron (majority-carrier) lifetime and thus the optical response, and (2) the production of bandtailing, which may be associated with cluster damage. The bandtailing diminished significantly, or even disappeared, with annealing up to 100K, but all the other effects remained essentially unchanged with annealing as high as 673K. The possibility of the bandtailing remaining after 100K annealing appeared to be related to the amount of damage present. It was hypothesized that a certain defect concentration and/or cluster size was required for the bandtailing to be observed.
Nuclear and space radiation effects in infrared detectors
Nuclear and space radiation can produce a number of undesirable effects in infrared detectors. Steady-state ionizing particle fluxes, such as electron, proton, or gamma fluxes, produce a series of pulses in both intrinsic and extrinsic detectors. Many of these pulses have amplitudes large enough to result in their detection as false signals by the sensor. Alternatively, the combined effect of such pulses is to increase the rms noise level and the leakage current in the detector. Steady-state ionizing fluxes also cause an increase or a decrease in the optical response in extrinsic silicon detectors as a result of the trapping of the ionization-generated carriers on the optically active sites. Displacement damage, caused by electron, proton, or neutron fluences, gives rise to centers that decrease the optical responsivity. In extrinsic detectors, this decrease is the result of the radiation-induced defects compensating the optically active sites. Total-dose deposition has its largest effect in insulators and at semiconductor-insulator interfaces. This is particularly trouble-some in detector arrays where interaction between previously isolated elements can result. Total-dose deposi-tion can also affect the characteristics (decreased zero-bias resistance and increased reverse leakage current) of photovoltaic detectors. The purpose of this paper is to present an overview of the effects that radiation can produce in infrared detectors.
Ultrathin Wafer Pre-Assembly and Assembly Process Technologies: A Review
Ultrathin silicon wafer technology is reviewed in terms of the semiconductor applications, critical challenges, and wafer pre-assembly and assembly process technologies and their underlying mechanisms. Mechanical backgrinding has been the standard process for wafer thinning in the semiconductor industry owing to its low cost and productivity. As the thickness requirement of wafers is reduced to below 100 μm, many challenges are being faced due to wafer/die bow, mechanical strength, wafer handling, total thickness variation (TTV), dicing, and packaging assembly. Various ultrathin wafer processing and assembly technologies have been developed to address these challenges. These include wafer carrier systems to handle ultrathin wafers; backgrinding subsurface damage and surface roughness reduction, and post-grinding treatment to increase wafer/die strength; improved wafer carrier flatness and backgrinding auto-TTV control to improve TTV; wafer dicing technologies to reduce die sidewall damage to increase die strength; and assembly methods for die pick-up, die transfer, die attachment, and wire bonding. Where applicable, current process issues and limitations, and future work needed are highlighted.