Active solid-state devices (e.g. – transistors – solid-state diode – Physical configuration of semiconductor – With specified crystal plane or axis
Reexamination Certificate
1995-06-07
2001-05-08
Prenty, Mark V. (Department: 2822)
Active solid-state devices (e.g., transistors, solid-state diode
Physical configuration of semiconductor
With specified crystal plane or axis
C257S198000
Reexamination Certificate
active
06229197
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to electronic semiconductor devices and circuits, and, more particularly, to methods of fabrication with epitaxial overgrowth and devices so fabricated.
Various semiconductor processing flows include formation of epitaxial layers on substrates. Such epilayers may provide a change in doping level, a crystal superior to the substrate's, or even a change in material such as a gallium arsenide (GaAs) substrate with an aluminum gallium arsenide (Al
x
Ga
1−x
As) epilayer for heterojunction devices. Epilayer growth by metalorganic chemical vapor deposition (MOCVD) on {100} oriented GaAs substrates produces smoother surfaces when the substrate orientation is tilted 2° in the {110} direction, and industry standard GaAs wafers have such an orientation tilt. This tilt provides a slightly terraced surface (terrace widths on the order of 100-200 Å) which apparently insures smooth epilayer growth.
Certain processing flows include epitaxial overgrowth of nonplanar structures. In particular, silicon bipolar transistor processes frequently have a buried layer formed by epitaxial overgrowth of a doped region which has been depressed below the substrate surface by an oxidizing drive-in cycle. But more significantly, heterojunction bipolar transistors (HBTs) and self-aligned structure (SAS) lasers can be fabricated with epitaxial growth over steps in a GaAs layer. See Plumnton et al, Planar AlGaAs/GaAs HBT Fabricated by MOCVD Overgrowth with a Grown Base, 37 IEEE Trans. Elec. Dev. 118 (1990)(growth of n−Al
x
Ga
1−x
As emitter over p−GaAs base mesa for an HBT) and Noda et al, Effects of GaAs/AlAs superlattice buffer layers on selective area regrowth for GaAs/AlGaAs self-aligned structure lasers, 47 Appl. Phys. Lett 1205 (1985)(molecular beam epitaxy growth of p−Al
x
Ga
1−x
As over n−GaAs antiguiding mesa for a SAS laser).
However, such epitaxial overgrowth on step structures has problems including finding growth conditions for enhancing device performance.
SUMMARY OF THE INVENTION
The present invention provides epitaxial overgrowth with II-V compound semiconductor (compounds of elements from groups III and V of the periodic table) over steps in substrates with the substrate having a surface orientation without tilt to avoid formation of a ledge at the step in the direction of the tilt
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Kim Tae Seung
Plumton Donald Lynn
Brady W. James
Hoel Carlton H.
Prenty Mark V.
Telecky , Jr. Frederick J.
Texas Instruments Incorporated
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