Method of making isolation grids in bodies of semiconductor material

A method for making a grid arrangement in a body of semiconductor material of a semiconductor device to produce a plurality of regions of semiconductor material of the body electrically isolated from one another, the method comprising

• a. selecting a body of single crystal semiconductor material having a preferred crystallographic structure, two major opposed surfaces being respectively the top and botton surfaces thereof, a preferred planar orientation of at least the top surface, a first selected type conductivity, a selected level of resistivity and having a vertical axis substantially aligned with a first axis of the crystal structure which is substantially perpendicular to the selected surface of the body;
• b. forming a first region of second type conductivity in the body substantially parallel to the two major opposed surfaces and having a major surface coextensive with the bottom surface thereof;
• c. disposing a first array of metal wires on the selected major surface having the preferred planar orientation, the metal comprising at least one dopant material, the direction of the metal wires being oriented substantially aligned with at least one of the other axes of the crystal structure;
• d. heating the body and the first array of metal wires to a preselected elevated temperature sufficient to form an array of liquid wires of metal-rich semiconductor material on the body;
• e. establishing a temperature gradient substantially parallel to the vertical axis of the body and the first axis of the crystal structure, the surface on which the liquid wires are formed being at the lower temperature;
• f. migrating the first array of liquid wires through the body from one major opposed surface to the other major opposed surface substantially aligned with the axis of the body and the first axis of the crystal structure to at least intersect with the first region and to form a plurality of first planar regions of recrystallized semiconductor material of the body having solid solubility of the dopant material of the wire therein to provide a substantially uniform level of resistivity throughout the entire region which imparts a second type conductivity thereto, each first planar region being integral with the first region;
• g. disposing a second array of metal wires on the selected top surface of the body, the metal of the wire comprising at least one dopant, material, each of the metal wires having a second preferred wire direction which is oriented substantially aligned with a second different axis of the crystal structure and at a first preselected angle to the first stable wire direction;
• h. heating the body and the second array of metal wires to an elevated temperature sufficient to form an array of liquid wires of metal-rich semiconductor material on the top surface;
• i. establishing a temperature gradient substantially parallel to the vertical axis of the body and the first axis of the crystal structure, the top surface being at the lower temperature;
• and
• j. migrating the second array of liquid wires through the body from the top to the bottom surface substantially aligned with the vertical axis of the body and the first axis of the crystal structure to at least intersect with the first region and to form a plurality of second planar regions each of which intersects and is integral with the first region and at least one of the plurality of first planar regions, the material of the second planar regions comprising recrystallized semiconductor material of the body having solid solubility of at least the dopant metal of the wire therein to provide a substantially uniform level of resistivity throughout the entire region which imparts a second type conductivity thereto, thereby forming a plurality of unit cells of semiconductor material of the initial body electrically isolated from each mutually adjacent cell and from the bottom major surface of a composite which includes the body of semiconductor material and the first region.