| 摘要 |
PROBLEM TO BE SOLVED: To decrease the stress distribution in a core layer by forming a groove having a narrower width than the core pitch in the core layer or lower clad layer on which the region between cores is to be projected before a rectangular core is formed. SOLUTION: The lower clad layer 2 is formed on a substrate 1 by spin coating a varnish type polyimide resin and heating to cure, and further, a core layer 3 having a higher refractive index than the lower clad layer 2 is formed thereon. A first mask 4 is covered with a second mask 5 consisting of a resist in such a manner that the cross section of the first mask 4 is included in the cross section of the second mask 5. In this state, neutral reactive etching is performed in an oxygen atmosphere to form a groove 6 in the core layer 3. Then the residual second mask is removed with a peeling liquid to expose the first mask 4 as the outermost surface, which is subjected to reactive ion etching in an oxygen atmosphere to form a core 7. Then the first mask 4 is removed with hydrofluoric/nitric acid, and an upper clad layer 8 is laminated on the core 7 by the same method as that for the lower clad layer 2. |
