Source Of Dislocation Generation Research Articles

Getters in silicon

Gettering of rapidly diffusing metallic impurities and structural defects in silicon which is the main material for IC fabrication, high-power high-voltage devices and neutron doped silicon has been studied. Structural defect based getters and gas phase getters based on chlorine containing compounds have been analyzed. Formation of structural defect based getters requires producing intrinsic sources of dislocation generation and precipitate/dislocation agglomerate formation. We show that dislocations are generated at microcrack mouths and form a low-mobility dislocation network at inactive wafer sides. In the latter case the defects are generated in the wafer region adjacent to the active layer of the electronic component. The generation of intrinsic getters is based on the decomposition of the supersaturated oxygen solid solution in silicon which favors the formation of a complex defect system in silicon that consists of various precipitate/dislocation agglomerates. Stacking faults also form, i.e., oxide precipitates with Frank’s dislocation loop clouds. Two intrinsic getter formation methods have been considered: one is related to oxygen impurity drain from the wafer surface region and the other implies accurate control of vacancy distribution over wafer thickness. We have analyzed the effect of getters as defect structures on the reduction of the mechanical stress required for dislocation generation onset which may eventually determine the mechanical strength of silicon wafers. The mechanism of impurity and defect gettering by gas phase medium with chlorine-containing compound additions has been considered. We show that silicon atom interaction with chlorine in the surface wafer region at high temperatures may cause the formation of vacancies which may penetrate to the specimen bulk with some probability. This leads to the case ∆Сv > 0 and ∆Ci ≤ 0, which changes the composition and density of the microdefects. Examples have been given for practical use of heat treatment of silicon wafers in a chlorine-containing atmosphere during oxide film application with the aim to dissolve microdefects, drain rapidly diffusing impurities from crystal bulk and prevent the formation of generation/recombination centers during device fabrication and silicon neutron doping.

Crystalline Defects Induced during MPCVD Lateral Homoepitaxial Diamond Growth.

The development of new power devices taking full advantage of the potential of diamond has prompted the design of innovative 3D structures. This implies the overgrowth towards various crystallographic orientations. To understand the consequences of such growth geometries on the defects generation, a Transmission Electron Microscopy (TEM) study of overgrown, mesa-patterned, homoepitaxial, microwave-plasma-enhanced, chemical vapor deposition (MPCVD) diamond is presented. Samples have been grown under quite different conditions of doping and methane concentration in order to identify and distinguish the factors involved in the defects generation. TEM is used to reveal threading dislocations and planar defects. Sources of dislocation generation have been evidenced: (i) doping level versus growth plane, and (ii) methane concentration. The first source of dislocations was shown to generate <110> Burgers vector dislocations above a critical boron concentration, while the second induces <112> type Burgers vector above a critical methane/hydrogen molar ratio. The latter is attributed to partial dislocations whose origin is related to the dissociation of perfect ones by a Shockley process. This dissociation generated stacking faults that likely resulted in penetration twins, which were also observed on these samples. Lateral growth performed at low methane and boron content did not exhibit any dislocation.

Characterization of structural defects in the silicon crystal grown with various seeds

To see the effect of the seeds on the crystallization of the silicon ingot, two types of seed were prepared and applied to the mono-like multi-crystalline silicon crystallization. One of them was conical shaped seed divided vertically into 4 pieces and the other one was chipped silicon seeds. Both of the seeds were placed at the bottom of the crucible before the growth of the multi-crystalline silicon material with a conventional directional solidification process. Compared to the conventional thin and flat seeds, conical shaped seed result in the larger single crystalline portion in the ingot although the gap of the seed division might act as source of dislocation generation during the crystal growth. This was expected to be due to the lateral growth of the silicon single crystalline grown from the conical seed which is taller than normal flat seeds. And also, comparison of the Minority Carrier Life Time (MCLT) between the silicon crystal grown from the chipped silicon seeds and the silicon crystal grown without any seed was conducted. It was found that the silicon crystal grown with chipped silicon seeds shows higher MCLT than the silicon crystal grown without seeds, although both crystals look similar as multi-crystalline silicon.