We first reported on a process for on-axis InSb crystal growth in 2014. As we have further developed on-axis (111) crystal growth, we have observed and measured a new distinct regime of interface-controlled dopant segregation. This effect is usually overshadowed by the facet effect and the resulting order of magnitude step change in the carrier concentration profile. When this large step change is eliminated, another interface-controlled effect becomes measurable. We present experimental data showing the magnitude of this effect and the crystal growth techniques used to engineer the interface where this effect is uncovered. We also discuss the atomic scale growth mechanisms that explain it.
This work proves useful in predicting the range of mechanical and electronic properties of wafers cut from ingots that are grown on-axis. More specifically, by understanding the effect of the melt/solid growth interface on the physical properties on the crystal, growth conditions can be optimized to produce more electrically uniform wafers that minimize pixel-to-pixel variation in FPAs.
We present a new method to produce low-cost, high quality gallium antimonide (GaSb) substrates for IR imaging
applications. These methods apply high-volume wafer manufacturing standards from the silicon industry to increase
performance and value of our wafers. Encapsulant-free GaSb single crystals were grown using the modified Czochralski
method, yielding more than seventy 150mm wafers per crystal or several hundred 75mm or 100mm wafers per crystal.
These were processed into epi-ready substrates on which superlattice structures were grown. Wafer and epitaxy structure
characterization is also presented, including transmission X-ray topography, dopant level and uniformity.
InSb focal plane array (FPA) detectors are key components in IR imaging systems that significantly impact both cost and
performance. Detector performance is affected by the electronic and crystallographic quality and uniformity of the
semiconductor substrate. High-volume, high-yield production of InSb wafers to the standards required for FPA device
manufacture requires growth of on-axis {111} crystals. An inherent source of variation hindering on-axis Czochralski
crystal growth is anisotropic dopant incorporation. We report on newly developed growth methods that eliminate the
negative effects of anisotropic dopant incorporation enabling high volume manufacturing of {111}-oriented substrates
and discuss the consequential manufacturing benefits. We also report on a characterization technique to characterize
microscale dopant variation across the wafer.
Focal plane arrays (FPAs) made on InSb wafers are the key cost-driving component in IR imaging systems. The electronic and crystallographic properties of the wafer directly determine the imaging device performance. The “facet effect” describes the non-uniform electronic properties of crystals resulting from anisotropic dopant segregation during bulk growth. When the segregation coefficient of dopant impurities changes notably across the melt/solid interface of a growing crystal the result is non-uniform electronic properties across wafers made from these crystals. The effect is more pronounced in InSb crystals grown on the (111) axis compared with other orientations and crystal systems. FPA devices made on these wafers suffer costly yield hits due to inconsistent device response and performance. Historically, InSb crystal growers have grown approximately 9-19 degree off-axis from the (111) to avoid the facet effect and produced wafers with improved uniformity of electronic properties. It has been shown by researchers in the 1960s that control of the facet effect can produce uniform small diameter crystals. In this paper, we share results employing a process that controls the facet effect when growing large diameter crystals from which 4, 5, and 6” wafers can be manufactured. The process change resulted in an increase in wafers yielded per crystal by several times, all with high crystal quality and uniform electronic properties. Since the crystals are grown on the (111) axis, manufacturing (111) oriented wafers is straightforward with standard semiconductor equipment and processes common to the high-volume silicon wafer industry. These benefits result in significant manufacturing cost savings and increased value to our customers.
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