Comprehensive investigation of HgCdTe metalorganic chemical vapor deposition

The principal objective of this experimental and theoretical research program was to explore the possibility of depositing high quality epitaxial CdTe and HgCdTe at very low pressures through metalorganic chemical vapor deposition (MOCVD). We explored two important aspects of this potential process: (1) the interaction of molecular flow transport and deposition in an MOCVD reactor with a commercial configuration, and (2) the kinetics of metal alkyl source gas adsorption, decomposition and desorption from the growing film surface using ultra high vacuum surface science reaction techniques. To explore the transport-reaction issue, we have developed a reaction engineering analysis of a multiple wafer-in-tube ultrahigh vacuum chemical vapor deposition (UHV/CVD) reactor which allows an estimate of wafer or substrate throughput for a reactor of fixed geometry and a given deposition chemistry with specified film thickness uniformity constraints. The model employs a description of ballistic transport and reaction based on the pseudo-steady approximation to the Boltzmann equation in the limit of pure molecular flow. The model representation takes the form of an integral equation for the flux of each reactant or intermediate species to the wafer surfaces. Expressions for the reactive sticking coefficients (RSC) for each species must be incorporated in the term which represents reemission from a wafer surface. The interactions of MOCVD precursors with Si and CdTe were investigated using temperature programmed desorption (TPD) in ultra high vacuum combined with Auger electron spectroscopy (AES). These studies revealed that diethyltellurium (DETe) and dimethylcadmium (DMCd) adsorb weakly on clean Si(100) and desorb upon heating without decomposing. These precursors adsorb both weakly and strongly on CdTe(111)A, with DMCd exhibiting the stronger interaction with the surface than DETe

Substrate and Passivation Techniques for Flexible Amorphous Silicon-Based X-ray Detectors

Flexible active matrix display technology has been adapted to create new flexible photo-sensing electronic devices, including flexible X-ray detectors. Monolithic integration of amorphous silicon (a-Si) PIN photodiodes on a flexible substrate poses significant challenges associated with the intrinsic film stress of amorphous silicon. This paper examines how altering device structuring and diode passivation layers can greatly improve the electrical performance and the mechanical reliability of the device, thereby eliminating one of the major weaknesses of a-Si PIN diodes in comparison to alternative photodetector technology, such as organic bulk heterojunction photodiodes and amorphous selenium. A dark current of 0.5 pA/mm2 and photodiode quantum efficiency of 74% are possible with a pixelated diode structure with a silicon nitride/SU-8 bilayer passivation structure on a 20 µm-thick polyimide substrate

Downstream oxygen etching characteristics of polymers from the parylene family

As dictated by the International Technology Roadmap for Semiconductors, there is an immediate need to develop low dielectric materials for use in metalization and packaging schemes in integrated circuits. The etching characteristics of a family of low dielectric polymers, the parylenes, are discussed. These are good models for polymer dielectrics, and are attractive for packaging applications. Three types of parylene are studied: parylene-N, parylene-C, and parylene AF-4. Parylene films on silicon substrates were etched in a downstream microwave oxygen plasma system. The goal was to characterize the chemical reactions that occurred on the parylene in the afterglow of the microwave oxygen plasma. The effect of temperature on the etch rate of each polymer was studied and an apparent activation energy was determined. The apparent activation energy for the etch process is approximately 7.0 kcal/mol for each polymer. Infrared analysis showed carbonyl formation during etching in the parylene-N and -C. Based on these analyses and the calculated activation energies, it was determined that a likely rate-limiting step in the etching was the ring opening

Downstream oxygen etching characteristics of polymers from the parylene family

As dictated by the International Technology Roadmap for Semiconductors, there is an immediate need to develop low dielectric materials for use in metalization and packaging schemes in integrated circuits. The etching characteristics of a family of low dielectric polymers, the parylenes, are discussed. These are good models for polymer dielectrics, and are attractive for packaging applications. Three types of parylene are studied: parylene-N, parylene-C, and parylene AF-4. Parylene films on silicon substrates were etched in a downstream microwave oxygen plasma system. The goal was to characterize the chemical reactions that occurred on the parylene in the afterglow of the microwave oxygen plasma. The effect of temperature on the etch rate of each polymer was studied and an apparent activation energy was determined. The apparent activation energy for the etch process is approximately 7.0 kcal/mol for each polymer. Infrared analysis showed carbonyl formation during etching in the parylene-N and -C. Based on these analyses and the calculated activation energies, it was determined that a likely rate-limiting step in the etching was the ring opening