Method to trim and smooth high index contrast waveguide structures
AssigneeAgency for Science, Technology and Research
InventorsChang Chang, Chi Tsang, My Doan, Ramana Badam, Vladimir Bliznetsov
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Abstract
Formation, through etching, of structures whose minimum width is less than can be achieved by optical means alone has been achieved by inserting a layer of sandwiching material between the photoresist (or hard mask if used) and the structure. By adjustment of the relative etch rates of this layer and the structure, a uniform lateral width reduction and surface smoothing of the structure is achieved.
Claims35
A method of forming a high index contrast waveguide, comprising:
- on a substrate, providing a film stack that includes a high refractive index core and a low refractive index cladding layer;
- depositing a sandwich layer on said stack;
- on said sandwich layer, depositing and patterning a photoresist layer to form a mask having a first minimum width;
- anisotropically etching all exposed areas in a vertical direction and then removing the photoresist;
- and
- then isotropically etching, using an etchant that preferentially etches said film stack relative to said sandwich layer, whereby said film stack acquires a second minimum width that is less than said first minimum width.
A method of smoothing a vertical surface of a high index contrast waveguide to reduce scattering loss, comprising:
- using a chemistry that selectivity etches said vertical surface more rapidly than it etches a sandwich layer located on said waveguide above said vertical surface.
A method to prevent any reduction in thickness during trimming and smoothing of vertical walls in a structure, comprising:
- placing a sandwich layer on a top horizontal surface of said structure;
- and
- performing said smoothing and trimming process by means of an isotropic etchant that etches said vertical walls at a faster rate than said sandwich layer.
A method of forming a thick waveguide having a tapered region that includes a fine tip, comprising:
- on a substrate, providing a film stack that includes a high refractive index core and a low refractive index cladding layer;
- depositing a dielectric sandwich layer on said stack;
- depositing a metal hard mask layer on said dielectric sandwich layer;
- depositing and patterning a photoresist layer on the metal hard mask layer and then forming a metal hard mask having a first minimum width;
- anisotropically etching all exposed areas in a vertical direction and then removing any residual photoresist;
- and
- then removing said metal hard mask and isotropically etching, using a wet chemistry etchant that preferentially etches said film stack relative to said sandwich layer, whereby said film stack acquires a second minimum width that is less than said first minimum width.
Dependencies are inferred from the claim text.