Multilayer-wiring substrate and method for fabricating same

A multilayer-wiring substrate comprising:

• a first wiring conductor having top and bottom surfaces;
• a first insulating layer formed on the top surface of the first wiring conductor;
• a first via-hole penetrating through the first insulating layer;
• and a first columnar via-conductor formed in the via-hole,
• wherein the first wiring conductor has a first recessed surface formed at the top surface of the first wiring conductor so that a bottom end of the first columnar via-conductor contacts the first recessed surface of the first wiring conductor, a depth of the recessed surface is 5-30% of the thickness of the wiring conductor, and said conductor comprises copper.

A method for fabricating a multilayer-wiring substrate having a via-conductor in a via-hole, said multilayer-wiring substrate comprising:

• a wiring conductor with a recessed surface formed by etching a surface of the wiring conductor,
• a first insulating layer formed on a surface of the wiring conductor except over the recessed surface so that a via-hole penetrates through the insulating layer to the recessed surface;
• a via-conductor plated on an inner peripheral wall of the via-hole and extendingly plated on the recessed surface of the wiring conductor that forms a bottom of the via-hole;
• and
• a second insulating layer formed on the other surface of the wiring conductor, wherein a depth of the recessed surface is 5-30% of the thickness of the wiring conductor, and said conductor comprises copper,
• said method comprising:
• forming an insulating layer on a wiring conductor comprising copper;
• forming a via-hole in the insulating layer by removing the insulating layer to an extent that the insulating layer in the via-hole becomes fragmented and adheres to the wiring-conductor located at the bottom of the via-hole;
• then etching the wiring conductor located at the bottom of the via-hole so that the fragments are removed and a recessed surface is formed in an amount of 5-30% of the thickness of the wiring conductor;
• then forming a via-conductor in the via-hole by plating a metal on an inner peripheral wall of the via-hole and extendingly plating the metal on the recessed surface of the wiring conductor;
• and
• forming a second insulating layer on the other surface of the wiring conductor.

A method for fabricating a multilayer-wiring substrate, said multilayer-wiring substrate comprising:

• a wiring conductor having top and bottom surfaces;
• an insulating layer formed on the top surface of the wiring conductor;
• a via-hole penetrating through the insulating layer;
• and
• a columnar via-conductor formed in the via-hole,
• wherein the wiring conductor has a recessed surface formed at the top surface of the wiring conductor so that a bottom end of the first columnar via-conductor contacts the recessed surface of the wiring conductor, a depth of the recessed surface is 5-30% of the thickness of the wiring conductor, and said conductor comprises copper,
• said method comprising the steps of:
• forming a photosensitive resin layer on a wiring conductor comprising copper;
• exposing the photosensitive resin layer and then developing to form a via-hole therein;
• chemically etching resin at a surface of the photosensitive resin layer and resin at an inner wall of the via-hole;
• chemically etching a surface of the wiring conductor exposed at a bottom of the via-hole so as to form a recessed surface in an amount of 5-30% of the thickness of the wiring conductor;
• and
• forming a via-conductor in the via-hole by plating a metal on an inner peripheral wall of the via-hole and extendingly plating the metal on the recessed surface of the wiring conductor.