Lids for wafer-scale optoelectronic packages
A method for forming a lid for a wafer-scale package includes (1) forming a cavity in a substrate, (2) forming an oxide layer over the cavity and over a bond area around the cavity on the substrate, (3) forming a reflective layer over the oxide layer, (4) forming a barrier layer over the reflective layer, (5) etching a portion of the barrier layer down to a portion of the reflective layer over the bond area, and (6) forming a solder layer on the portion of the reflective layer. The reflective layer can be a titanium-platinum-gold metal stack and the barrier layer can be a titanium dioxide layer.
1 . A method for forming a lid for a wafer-scale package, comprising:
forming a cavity in a substrate;
forming an oxide layer over the cavity and over a bond area around the cavity on the wafer;
forming a reflective layer over the oxide layer;
forming a barrier layer over the reflective layer;
etching a portion of the barrier layer down to a portion of the reflective layer over the bond area; and
forming a solder layer on the portion of the reflective layer.
2 . The method of claim 1 , wherein said. forming a cavity in the substrate comprises anisotropically etching the substrate to form the cavity, the substrate comprising a first crystallographic plane at an offset from a wafer top surface and the cavity comprising a surface along a second crystallographic plane.
3 . The method of claim 2 , wherein the first crystallographic plane is oriented so that the second crystallographic plane is oriented 45° from a normal to the wafer top surface and said anisotropic etching comprises a wet etch using a KOH solution.
4 . The method of claim 1 , wherein said forming an oxide layer comprises thermally growing the oxide layer.
5 . The method of claim 1 , wherein said fonning a reflective layer comprises forming a metal stack layer.
6 . The method of claim 5 , wherein said forming a barrier layer comprises thermally depositing a metal oxide layer upon the metal stack layer.
7 . The method of claim 6 , wherein the metal stack layer comprises a titanium layer, a platinum layer atop the titanium layer, and a gold layer atop the platinum layer, and the metal oxide layer comprises a titanium dioxide layer.
8 . The method of claim 7 , wherein said etching a portion of the barrier layer comprises a wet etch using a diluted HF and nitric acid solution.
9 . The method of claim 5 , wherein said forming a barrier layer comprises a method selected from the group consisting of thermally depositing, sputtering, reactive sputtering, chemical vapor deposition, and plasma enhanced chemical vapor deposition.
10 . The method of claim 9 , wherein the barrier layer is selected from the group consisting of nitride, boride, fluoride, fluorocarbon, and polyimide.
11 . The method of claim 1 , wherein said forming a solder layer comprises plating the solder layer on the portion of the reflective layer.
12 . The method of claim 1 , wherein said etching a portion of the barrier layer comprises:
patterning a photoresist layer over the barrier layer to form a window over the portion of the reflective layer; and
etching the portion of the barrier layer exposed by the window.
13 . The method of claim 12 , further comprising stripping the photoresist after said forming the solder layer on the portion of the reflective layer.
14 . The method of claim 12 , further comprising stripping the photoresist prior to said forming the solder layer on the portion of the reflective layer.
15 . The method of claim 1 , wherein said solder layer comprises a gold-tin solder.