Process for forming the ridge structure of a self-aligned semiconductor laser

Claim 1

A process for forming a self-aligned ridge structure for a III-V compound semiconductor double heterostructure laser device, comprising the steps of: providing an epitaxially grown, layered heterostructure comprised of, from top to bottom: a) a contact layer; b) a first cladding layer; c) an active region for recombination and light generation; d) a second cladding layer, wherein said first and second cladding layers form a waveguide for light confinement and gain; depositing a first silicon oxynitride layer on top of said contact layer in a PECVD process, at a high (RF) excitation frequency; depositing and patterning a photoresist layer on top of said first silicon oxynitride layer for use as a mask for the definition of the ridge structure; reactive ion etching (RIE) said first silicon oxynitride layer, thereby leaving the section covered by said photoresist layer intact; selective etching said contact layer down to said first cladding layer, thereby obtaining underneath said first silicon oxynitride layer a crystallographic etch angle and a small undercut; selective etching said first cladding layer to a predetermined depth, leaving said contact layer substantially unaffected; depositing a conformal, second silicon oxynitride layer in a low (LF) exitation frequency, PECVD process, said second silicon oxynitride layer thereby having an etch rate lower than that of said first silicon oxynitride layer; lift-off of the part of said second silicon oxynitride layer deposited on top of said photoresist layer by dissolving said photoresist layer, thereby exposing said first silicon oxynitride layer; and selective removal of said first silicon oxynitride layer, thereby leaving said second silicon oxynitride layer and said contact layer substantially unaffected.