Method of production of light emitting diodes

• US 4,966,862 A
• Filed: 08/28/1989
• Issued: 10/30/1990
• Est. Priority Date: 08/28/1989
• Status: Expired due to Term

• Current Assignee: CREE Incorporated (Wolfspeed, Inc.)
• Original Assignee: Cree Research, Inc.
• Inventors: Edmond, John A.
• Primary Examiner(s): Hearn, Brian E.
• Assistant Examiner(s): Fleck, Linda J.
• Application Number:
  US07/400,279
• Time in Patent Office: 428 Days
• Field of Search: 437/100, 437/226, 437/227, 437/905, 437/906
• US Class Current: 438/27
• CPC Class Codes: H01L 2924/00 Indexing scheme for arrangements or methods for connecting or disconnecting semiconductor or solid-state bodies as covered by H01L24/00
• CPC Class Codes: H01L 2924/0002 Not covered by any one of groups H01L24/00, H01L24/00 and H01L2224/00
• CPC Class Codes: H01L 33/145 with a current-blocking structure
• CPC Class Codes: H01L 33/20 with a particular shape, e.g. curved or truncated substrate
• CPC Class Codes: H01L 33/387 with a plurality of electrode regions in direct contact with the semiconductor body and being electrically interconnected by another electrode layer
• CPC Class Codes: H01L 33/44 characterised by the coatings, e.g. passivation layer or anti-reflective coating
• CPC Class Codes: H01L 33/60 Reflective elements
• CPC Class Codes: H01L 33/62 Arrangements for conducting electric current to or from the semiconductor body, e.g. lead-frames, wire-bonds or solder balls

Abstract

The invention is a method for preparing a plurality of light emitting diodes on a single substrate of a semiconductor material. The method is used for structures where the substrate includes an epitaxial layer of the same semiconductor material that in turn comprises layers of p-type and n-type material that define a p-n junction therebetween. The epitaxial layer and the substrate are etched in a predetermined pattern to define individual diode precursors, and deeply enough to form mesas in the epitaxial layer that delineate the p-n junctions in each diode precursor from one another. The substrate is then grooved from the side of the epitaxial layer and between the mesas to a predetermined depth to define side portions of diode precursors in the substrate while retaining enough of the substrate beneath the grooves to maintain its mechanical stability. Ohmic contacts are added to the epitaxial layer and to the substrate and a layer of insulating material is formed on the diode precursor. The insulating layer covers the portions of the epitaxial layer that are not covered by the ohmic contact, any portions of the one surface of the substrate adjacent the mesas, and the side portions of the substrate. As a result, the junction and the side portions of the substrate of each diode are insulated from electrical contact other than through the ohmic contacts. When the diodes are separated they can be conventionally mounted with the junction side down in a conductive epoxy without concern that the epoxy will short circuit the resulting diode.

Claims

1. A method for preparing a plurality of light emitting diodes on a single substrate of a semiconductor material having a p or n conductivity type, and in which the resulting diodes can be separated and mechanically fixed to transmit from their substrate side rather than the junction side using otherwise conventional mounting techniques, and wherein the substrate includes an epitaxial layer of the same semiconductor material on one surface thereof in which the epitaxial layer comprises a layer of p-type material and a layer of n-type material adjacent one another and that form a p-n junction therebetween, the method comprising;

etching the epitaxial layer and the substantially transparent substrate in a predetermined pattern to define individual diode precursors and wherein the etch is deep enough to form mesas in the epitaxial layer that delineate the p-n junctions in each diode precursor from one another;

grooving the substrate from the side of the epitaxial layer and between the mesas of the diode precursors to a predetermined depth into the substrate to define side portions of the device precursors in the substrate while retaining enough of the substrate beneath the grooves to maintain the mechanical stability of the substrate;

adding an ohmic contact to the epitaxial layer;

forming a layer of an insulating material that covers the portions of the epitaxial layer that are not covered by the ohmic contact and that covers any portions of the one surface of the substrate adjacent the mesas that are not covered by the epitaxial layer and that covers portions of the side portions of the substrate for insulating the one surface, the junction and the side portions of the substrate of each diode precursor from electrical contact other than through the ohmic contact; and

adding an ohmic contact to the substrate.

2. A method according to claim 1 further comprising separating the diode precursors into individual diodes by cutting the substrate from the side opposite the epitaxial layer and along positions corresponding to the grooves so that the amount of substrate cut is minimized and the epitaxial layer and the junctions are substantially protected from the mechanical stress of the cutting step.

3. A method according to claim 2 further comprising positioning a separated diode into a reflective cup formed of a conductive material and fastening the diode in the cup with a conductive material and fastening the diode in the cup with a conductive epoxy and with the epitaxial layer adjacent the cup and the substrate facing outwardly from the cup, and with the insulating layer forming an insulating barrier between the conductive epoxy and the epitaxial layer, the substrate, and the junction, so that conductive contact with the epitaxial layers is limited to the ohmic contact and the substrate.

4. A method for preparing a plurality of blue light emitting diodes on a single substrate, and in which the resulting diodes can be separated and mechanically fixed to transmit from their substrate side rather than the junction side using otherwise conventional mounting techniques, the method comprising:

forming an epitaxial layer of alpha silicon carbide on one surface of a substantially transparent silicon carbide substrate having a p or n type conductivity in which the epitaxial layer comprises a layer of p-type silicon carbide and a layer of n-type silicon carbide adjacent one another and that form a p-n junction therebetween;

etching the epitaxial layer and the substrate in a predetermined pattern to define individual diode precursors and wherein the etch is deep enough to form mesas in the epitaxial layer that delineate the p-n junctions in each diode precursor from one another;

grooving the substrate from the side of the epitaxial layer and between the mesas of the diode precursors to a predetermined depth into the substrate to define side portions of the device precursors in the substrate while retaining enough of the substrate beneath the grooves to maintain the mechanical stability of the substrate;

adding an ohmic contact to the epitaxial layer;

forming a layer of an insulating material that covers the portions of the epitaxial layer that are not covered by the ohmic contact and that covers any portions of the one surface of the substrate adjacent the mesas that are not covered by the epitaxial layer and that covers portions of the side portions of the substrate for insulating the one surface, the junction and the side portions of the substrate of each diode precursor from electrical contact other than through the ohmic contact; and

adding an ohmic contact to the substrate.

5. A method according to claim 4 further comprising the step of separating the diode precursors into individual diodes.

6. A method according to claim 5 wherein the step of separating the diode precursors into individual diodes comprises cutting the substrate from the side opposite the epitaxial layer and at positions corresponding to said grooves to avoid mechanical stress upon the epitaxial layer or the junction.

7. A method according to claim 6 and further comprising:

adding an overlay contact to the ohmic contact to the substrate to facilitate wire bonding thereto;

applying a noble metal to the ohmic contact on the epitaxial layer to prevent oxidation of the ohmic contact; and

mounting the separated diodes junction side down in a reflective cup using a conductive epoxy.

8. A method according to claim 7 wherein the step of adding an overlay contact to the ohmic contact to the substrate comprises adding a metal contact selected from the group consisting of aluminum, gold, or silver.

9. A method according to claim 7 wherein the step of applying a noble metal comprises applying a noble metal selected from the group consisting of platinum, palladium, gold, and silver.

10. A method according to claim 4 wherein the step of adding ohmic contacts to the exposed epitaxial layer further comprises selectively etching the oxide to expose the epitaxial to the ohmic contacts.

11. A method according to claim 4 wherein the step of forming an epitaxial layer of alpha silicon carbide on one surface of a silicon carbide substrate comprises forming an epitaxial layer on a wafer of silicon carbide.

12. A method according to claim 4 wherein the step of forming a layer of insulating material comprises thermal oxidation of the grooved epitaxial layer and substrate.

13. A method according to claim 4 wherein the step of adding an ohmic contact to the exposed epitaxial layer comprises adding an aluminum or aluminum alloy contact to the epitaxial layer.

14. A method according to claim 4 wherein the step of forming an epitaxial layer of alpha silicon carbide on one surface of a silicon carbide substrate comprises homoepitaxially depositing a film of an alpha silicon carbide polytype on a prepared surface of an alpha silicon carbide substrate wherein the planar surface is inclined more than one degree off axis with respect to a basal plane thereof substantially towards one of the <

1120>

directions.

15. A method according to claim 4 wherein the step of forming an epitaxial layer comprises forming an epitaxial layer having an n-type conductivity on a substrate having an n-type conductivity on the n-type epitaxial layer.

16. A method according to claim 15 wherein the step of forming an n-type epitaxial layer comprises forming a compensated n-type epitaxial layer, and the step of forming a p-type epitaxial layer comprises forming a p-type epitaxial layer in which the carrier concentration is greater than the carrier concentration in the n-type epitaxial layer.