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US 11,377,758 B2Granted
Cleaving thin wafers from crystals
OwnerStephen C. Baerinventor
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OwnerStephen C. Baerinventor
Estimating the term…
A method of creating thin wafers of single crystal silicon, sapphire and similar materials, wherein an ingot of single crystalline material, or a ribbon of single crystalline material is cleaved, in a plane parallel to a surface, with laser light focused to a line in the desired plane of cleavage, near the growing cleavage furrow. The light is of a wavelength that the material is transparent to, but for which the material has strong two- or three-photon absorption. Consequently the light is not appreciably absorbed until it reached the desired focal line. The light is presented in an extremely short pulse, which heats and expands the material at the line focus, before the heat can be dissipated. This expansion creates tangential stresses around the focal line. These stresses are designed to be precisely normal to the growing cleavage furrow. Therefore the stresses are able to induce cleavage in the desired plane, without inducing cleavage in other possible cleavage planes that may happen to intersect with the growing cleavage edge. In this way, extremely thin wafers and ribbon shaped wafers can be produced, with extremely high quality cleaved faces. Methods of initiating the cleavage furrow and separating the cleaved wafer from the rest of the crystal are also discussed.
A method for producing planar fracture at a chosen plane in a mass of material having at least one flat surface, wherein said chosen plane is parallel to said flat surface, wherein said material is in a class comprising single crystals, in which case said chosen plane is a crystallographic plane, and comprising amorphous materials lacking crystallographic planes, providing a beam of radiation that passes through said surface in a direction normal to said chosen plane to converge on a focal region at said chosen plane, timing said beam so it heats said focal region rapidly enough to induce tensile stresses in the interior of said material sufficient to induce fracture at a chosen location in said chosen plane, wherein said tensile stresses are generally perpendicular to said chosen plane at said chosen location, thereby increasing the likelihood that the resulting fracture will take place in said chosen plane compared to taking place in another potential fracture plane intersecting said chosen location, and moving the focus of said radiation and/or moving said mass of material to create relative movement between said focus and said material, thereby creating relative movement between said material and the region in said material heated by said focus, to spread said fracture over said chosen plane, thereby fracturing said material at said chosen plane.
Dependencies are inferred from the claim text.