Lateral movement of screw dislocations during homoepitaxial growth and devices yielded therefrom free of the detrimental effects of screw dislocations
AssigneeThe United States of America as represented by the Administrator of the National Aeronautics and Space Administration
InventorsPhilip G. Neudeck, J. Anthony Powell
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Abstract
The present invention is related to a method that enables and improves wide bandgap homoepitaxial layers to be grown on axis single crystal substrates, particularly SiC. The lateral positions of the screw dislocations in epitaxial layers are predetermined instead of random, which allows devices to be reproducibly patterned to avoid performance degrading crystal defects normally created by screw dislocations.
Claims72
A method for growing at least one single crystal layer on a selected single crystal substrate having an average density of replicating nonremovable stepsource dislocations, wherein said at least one single crystal layer contains at least one replicating nonremovable stepsource dislocation, confined to selected lateral point locations, said method comprising the steps of:
- a) choosing a single crystal substrate material which exhibits a property that the material therein contains at least one growth plane orientation whereby under selected growth conditions the growth rate due to step-flow growth along the basal plane is greater than at least one hundred (100) times a growth rate perpendicular to the basal plane due to growth involving two-dimensional nucleation;
- b) preparing a planar first growth surface on said single crystal substrate that is parallel to within a predetermined angle relative to a selected crystal plane of said single crystal substrate;
- c) removing material in said first growth surface so as to define at least one selected separated second growth surface with top surface area that is selected to be less than twice the inverse of said average density of replicating nonremovable stepsource dislocations in the said single crystal substrate and with border shape selected to have at least one enclosed hollow region, said selected separated second growth surface defining a cumulative hollow region area enclosed by at least one interior border shape selected to obtain lateral coalescence at said selected lateral point location, wherein said cumulative hollow region area is selected greater than half the inverse of the said average density of replicating nonremovable stepsource dislocations in said single crystal substrate;
- d) treating said at least one selected separated second growth surface so as to remove any removable sources of unwanted crystal nucleation and any removable sources of steps therein;
- e) depositing a homoepitaxial film on said separated second growth surface under selected conditions so as to provide a step-flow growth while suppressing two-dimensional nucleation;
- f) continuing said deposition of said homoepitaxial film so that said step-flow growth results and produces at least one lateral cantilevered web structure growing laterally toward the interior of said at least one enclosed hollow region;
- g) continuing said deposition of said homoepitaxial film until said at least one lateral cantilevered web structure completes its lateral coalescence at said selected lateral location thereby completely covering said at least one enclosed hollow region with at least one complete crystal roof forming at least one selected separated third growth surface of desired size and shape;
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- h) continuing said deposition of said homoepitaxial film until homoepitaxial film of desired vertical thickness on top of said selected separated third growth surface is achieved.
A method for combining screw dislocations on a selected single crystal substrate having a basal plane, thickness in the direction normal to the basal plane, and an initial first average density of replicating nonremovable stepsource dislocations, said method comprising the steps of:
- (a) choosing a single crystal substrate material which exhibits a property that the material therein contains a basal plane whereby under selected growth conditions the growth rate due to step-flow growth along the basal plane is greater than at least one hundred (100) times a growth rate perpendicular to the basal plane due to growth involving two-dimensional nucleation;
- (b) preparing a planar first growth surface on the single crystal substrate that is parallel to within 10 degrees to the basal plane;
- (c) removing material in the first growth surface to form holes completely through the single crystal substrate thickness so as to define at least one selected separated second growth surface with border shape selected to have at least one enclosed hollow region with interior border shape selected to obtain lateral coalescence at a lateral point and a cumulative hollow region area selected greater than half the inverse of the said average density of nonremovable stepsource dislocations in said single crystal substrate;
- (d) treating said at least one selected separated growth surface so as to remove any removable sources of unwanted crystal nucleation and any removable sources of growth steps therein;
- (e) depositing a homoepitaxial film on said separated second growth surface under selected conditions so as to provide a step-flow growth along the basal plane while suppressing two-dimensional nucleation;
- (f) continuing said deposition of said homoepitaxial film so that the step-flow growth produces lateral growth toward the interior of said at least one enclosed hollow region;
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- (g) continuing said deposition of said homoepitaxial film until the lateral growth completes lateral coalescence at point within said at least one enclosed hollow region forming a third growth surface with second average screw dislocation density characteristic that is less than said first average screw dislocation density characteristic.
Dependencies are inferred from the claim text.