Patent EP-2468931-A1 (EP)
Inventor: BRUEL MICHEL
IPC: C30B29/06
Filed: 2011-12-22
Abstract: The process comprises forming a stress generating structure locally integrated with a surface of a substrate (1), forming a fragile area in the substrate to provide split along the fragile area, producing an incipient crack in the substrate to a depth of plane, and applying a heat treatment to the structure at a temperature of 20-500[deg] C to cause expansion or contraction of the structure for generating stresses in the substrate. The stress generating structure is a cellular structure of which walls (2") of cells (2') are perpendicular to the surface of the substrate. The process comprises forming a stress generating structure locally integrated with a surface of a substrate (1), forming a fragile area in the substrate to provide split along the fragile area, producing an incipient crack in the substrate to a depth of plane, and applying a heat treatment to the structure at a temperature of 20-500[deg] C to cause expansion or contraction of the structure for generating stresses in the substrate. The stress generating structure is a cellular structure of which walls (2") of cells (2') are perpendicular to the surface of the substrate and are composed of materials (2a, 2b) having different coefficients of heat expansion arranged to allow different deformations of the walls under the effect of heat treatment so that the structure is adapted to expand or contract in a plane parallel to the surface of the substrate under the effect of the heat treatment. The stress is greater than a mechanical resistance of the substrate in a plane of splitting parallel to the surface of the substrate defining the layer to be detached, and produces split of the substrate along the plane. The walls of cells are bimetallic strips formed of a first and a second material having positive and negative coefficients of heat expansion. The first and second materials of the bimetallic strips are separated by vacuum or by a strip of a third material. The stress generating structure is further adapted to expand or contract under the action of a magnetic field, and is fixed to the surface of the substrate by a bonding layer. The materials of walls are magnetostrictive materials. The heat treatment is applied at a temperature of less than Curie temperature of the magnetostrictive material. The process further includes applying a magnetic field to the structure to cause an elongation or retraction of the magnetostrictive material. The stress generating structure is fabricated by etching trenches in a layer of first material, filling the trenches with second material, masking portions of the layer of the first material for the formation of the bimetallic strip, and selectively etching the layer to remove the unmasked portions of the first material. A thickness of the layer to be detached from the substrate is 50 mu m. A ratio between the thickness of the layer to be detached and a thickness of the stress generating structure is 0.1-10. The stress generating structure is removed from the layer after detachment of the substrate, and is recycled after removal of the detached layer for splitting the substrate. Independent claims are included for: (1) an assembly including a substrate and a stress generating structure; and (2) a semiconductor device for photovoltaic, optoelectronic or electronic applications.