Wafer carrier having retention pockets with compound radii for chemical vapor desposition systems
A wafer carrier for use in a chemical vapor deposition (CVD) system includes a plurality of wafer retention pockets, each having a peripheral wall surface surrounding a floor surface and defining a periphery of that wafer retention pocket. Each wafer retention pocket has a periphery with a shape defined by at least a first arc having a first radius of curvature situated around a first arc center and a second arc having a second radius of curvature situated around a second arc center. The second arc is different from the first arc, either by its radius of curvature, arc center, or both.
1. A wafer carrier for use in a system for growing epitaxial layers on one or more wafers by chemical vapor deposition (CVD), the wafer carrier comprising:
a body formed symmetrically about a central axis, and including a generally planar top surface that is perpendicular to the central axis;
a plurality of wafer retention pockets recessed in the body from the top surface, each of the wafer retention pockets including:
a floor surface generally parallel to the top surface; and
a peripheral wall surface surrounding the floor surface and defining a periphery of that wafer retention pocket,
wherein each wafer retention pocket has a pocket center situated along a corresponding wafer carrier radial axis that is perpendicular to the central axis; and
for each wafer retention pocket, a first arc having a first radius of curvature is defined around a first arc center and a second arc having a second radius of curvature is defined around a second arc center,
wherein each wafer retention pocket has a proximal end and a distal end relative to the central axis, and in the periphery of each wafer retention pocket, the first arc defines the proximal end and the second arc defines the distal end, and
wherein the periphery corresponding to the wafer retention pocket is entirely defined by the first arc and the second arc wherein the second arc is different from the first arc by the following:
the first radius of curvature being smaller than the second radius of curvature; and
the first arc center being different from the second arc center.
2. The wafer carrier of claim 1 , wherein in the periphery of each wafer retention pocket, the first arc and the second arc intersect.
3. The wafer carrier of claim 1 , wherein the first arc is situated symmetrically about the wafer carrier radial axis corresponding to the wafer retention pocket having the periphery defined by the first and the second arcs.
4. The wafer carrier of claim 1 , wherein the second arc is situated symmetrically about the wafer carrier radial axis corresponding to the wafer retention pocket having the periphery defined by the first and the second arcs.
5. The wafer carrier of claim 1 , wherein the first arc and the second arc are each situated symmetrically about the wafer carrier radial axis corresponding to the wafer retention pocket having the periphery defined by the first and the second arcs.
6. The wafer carrier of claim 1 , wherein the first arc is situated asymmetrically about the wafer carrier radial axis corresponding to the wafer retention pocket having the periphery defined by the first and the second arcs.
7. The wafer carrier of claim 1 , wherein the second arc is situated asymmetrically about the wafer carrier radial axis corresponding to the wafer retention pocket having the periphery defined by the first and the second arcs.
8. The wafer carrier of claim 1 , wherein the first arc and the second arc are each situated asymmetrically about the wafer carrier radial axis corresponding to the wafer retention pocket having the periphery defined by the first and the second arcs.
9. The wafer carrier of claim 1 , further comprising:
a first wafer retention pocket and a second wafer retention pocket; and
wherein a ratio between a length of the first arc to a length of the second arc of a common wafer retention pocket is different among the first wafer retention pocket and the second wafer retention pocket.
10. The wafer carrier of claim 1 , further comprising:
a first wafer retention pocket and a second wafer retention pocket; and
wherein a ratio between a radius of curvature of the first arc to a radius of curvature of the second arc of a common wafer retention pocket is different among the first wafer retention pocket and the second wafer retention pocket.
11. The wafer carrier of claim 1 , wherein the periphery of each wafer retention pocket is constructed such that, when a wafer is situated in the wafer retention pocket during CVD processing, a gap between an outer edge of the wafer and the periphery of the wafer retention pocket is generally uniform in size around at least 50% of a circumference of the wafer.
12. The wafer carrier of claim 1 , wherein the periphery of each wafer retention pocket is constructed such that, when a wafer is situated in the wafer retention pocket during CVD processing, a gap between an outer edge of the wafer and the periphery of the wafer retention pocket is generally uniform in size around at least 75% of a circumference of the wafer.
13. A method for constructing a wafer carrier for use in a system for growing epitaxial layers on one or more wafers by chemical vapor deposition (CVD), the method comprising:
forming a body symmetrically about a central axis to include a generally planar top surface that is perpendicular to the central axis; forming a plurality of wafer retention pockets recessed in the body from the top surface, each of the wafer retention pockets including: a floor surface generally parallel to the top surface; and
a peripheral wall surface surrounding the floor surface and defining a periphery of that wafer retention pocket,
wherein each wafer retention pocket has a pocket center situated along a corresponding wafer carrier radial axis that is perpendicular to the central axis; and
for each wafer retention pocket, a first arc having a first radius of curvature is defined around a first arc center and a second arc having a second radius of curvature is defined around a second arc center,
wherein each wafer retention pocket has a proximal end and a distal end relative to the central axis, and in the periphery of each wafer retention pocket, the first arc defines the proximal end and the second arc defines the distal end, and
wherein the periphery corresponding to the wafer retention pocket is entirely defined by the first arc and the second arc wherein the second arc is different from the first arc by the following:
the first radius of curvature being smaller than the second radius of curvature; and
the first arc center being different from the second arc center.