Edge etch method for producing narrow openings to the surface of materials

A planar process for producing a charge-coupled device of the type having a single level of electrodes separated from one another by narrow gaps comprising the steps of:

• a. forming an electrically insulating layer on a substantially planar surface of a semiconductor substrate;
• p1 b. forming an electrically conductive layer on the upper surface of said electrically insulating layer;
• c. forming a plurality of narrow interelectrode gaps in said electrically conductive layer, each interelectrode gap being formed by a process comprising the steps of;
• i. forming on a portion of said electrically conductive layer an etchable mask having a first narrow-opening-forming lateral edge disposed along a selected edge of the to-be-formed interelectrode gap;
• ii. forming a protective layer of a material possessing a set of etch characteristics different from etch characteristics of said electrically conductive layer on the adjacent exposed surface of said electrically conductive layer, said protective layer being formed at a thickness substantially less than the thickness of said etchable mask and with a second narrow-opening-forming lateral edge contiguous to and juxtaposed said first narrow-opening-forming lateral edge;
• iii. etching said first narrow-opening-forming lateral edge on said mask to expose an unprotected portion of said electrically conductive layer to produce a narrow opening to the surface of said electrically conductive layer;
• and,
• iv. etching said electrically conductive layer through said narrow opening and down to said electrically insulating layer to thereby form one of said narrow interelectrode gaps.