Apparatus for stressing semiconductor substrates
Apparatus for use in preparing heterostructures having a reduced concentration of defects including apparatus for stressing semiconductor substrates to allow them to conform to a crystal having a different crystal lattice constant.
1. An apparatus for stressing a generally circular semiconductor substrate comprising silicon, the substrate having a central axis, a front surface and a back surface which are generally perpendicular to the central axis, a peripheral edge extending from the front surface to the back surface, and a ring bonded to the back surface adjacent the peripheral edge, the apparatus comprising:
a chamber,
a heater for heating the chamber,
a substrate holder mounted in the chamber, the holder including:
a generally planar back support having a flange adapted to engage the ring on the back surface of the substrate,
the support being movable radially to exert stress on the substrate by stretching or compressing the substrate,
the support (1) being made of a material that expands at a greater rate than silicon and wherein the flange is interior to the ring such that heat applied to the substrate and support will cause stretching of the substrate or (2) being made of a material that expands at a lesser rate than that of silicon and wherein the ring is interior to the flange such that heat applied to the substrate and support will cause compression of the substrate.
2. The apparatus as set forth in claim 1 further comprising a front support disposed adjacent the front surface of the substrate.
3. The apparatus as set forth in claim 1 further comprising a pressure modulator for causing a pressure differential across the substrate sufficient to exert stress on the substrate,
the substrate holder further including:
a front ring and a back ring,
each ring including an annular support for contacting the substrate at a discrete radial position adjacent a peripheral edge of the substrate, the front ring adapted to contact the front surface and the back ring adapted to contact the back surface of the substrate.
4. The apparatus as set forth in claim 3 wherein the front and back rings are adapted to form a seal with the substrate to facilitate causing a pressure differential across the substrate.
5. The apparatus as set forth in claim 3 wherein the annular support includes a substantially sealed cavity and a single vent, the support adapted to contact one of the surfaces of the substrate and form a seal therewith, the vent enabling a vacuum to be pulled through the cavity for exerting stress on the substrate.
6. The apparatus as set forth in claim 1 in combination with the substrate, the substrate including a coating disposed adjacent the peripheral edge.
7. The apparatus as set forth in claim 1 wherein the chamber is an epitaxial chamber for applying an epitaxial layer.
8. The apparatus as set forth in claim 1 in combination with the substrate, wherein the ring of the substrate extends axially outward from a surface of the substrate.
9. The apparatus as set forth in claim 1 wherein the heater comprises radiant heating lamps, resistance heaters or inductive heaters.
10. The apparatus as set forth in claim 1 wherein the heater comprises radiant heating lamps disposed above and below the chamber.