Methods to fabricate a photoactive substrate suitable for shaped glass structures
This invention provides an inexpensive and rapid method for fabricating a high-anisotropic-etch ratio, shaped glass structures using a novel photosensitive glass composition. Structures of the photosensitive glass may include micro-channels, micro-optics, microposts, or arrays of hollow micro-needles. Furthermore, such shaped glass structures can be used to form a negative mold for casting the shape in other materials.
1. A method to fabricate a shaped glass structure, comprising:
preparing a photosensitive glass substrate having a composition comprising: less than 76 weight % silica, at least 0.15 weight % Ag 2 O, at least 0.75 weight % B 2 O 3 , at least 11 weight % Li 2 O, and at least 0.0014 weight % CeO 2 ;
exposing at least one portion of the photosensitive glass substrate with an activating energy source, such as ultraviolet light (300 to 320 nm) or a directed source of protons using an activation exposure of 0.1-15 J/cm 2 , while leaving at least a second portion of said glass substrate unexposed;
heating the glass substrate for at least ten minutes at a temperature that is in a temperature range of 420-520° C., heating the glass substrate for at least ten minutes at a temperature that is in a temperature range of 520-620° C., and cooling the glass substrate thereby transforming at least part of the exposed glass substrate to a crystalline material; and
etching the glass substrate in an HF-containing etchant solution, wherein an etch ratio of exposed portion to said unexposed portion is at least 40:1, to provide a shaped glass structure.
2. The method of claim 1 , wherein the glass substrate is heated at a temperature that is in a temperature range of 420-520° C. for between 10 minutes and 2 hours and then heated at a temperature that is in a temperature range of 520-620° C. for between 10 minutes and 2 hours.
3. The method of claim 1 , further comprising the steps of:
applying a surface-smoothing acid containing nitric acid to dissolve surface metallic silver; and
applying hydrochloric acid to dissolve surface cerium metal during or after the HF etch,
thereby reducing surface roughness of at least one micro-optic device in the shaped glass structure and whereby increasing light transmission through surfaces of a micro-optic device.
4. The method of claim 3 , wherein the shaped glass structure contains at least one micro-optic micro-post.
5. The method of claim 3 , wherein the exposed glass substrate is etched away to leave a glass micro-optic micro-post.
6. The method of claim 5 , further comprising the step of:
forming in the glass substrate a layer of photosensitive glass overlying a layer of non-photosensitive glass of lower index of refraction than said photosensitive glass, to substantially prevent light being guided by the micro-optic micro-post leaving the bottom of the micro-optic micro-post in at least one portion of the micro-optic micro-post.