Novel electroplating technique for selective thick-metal structure formation utilizing a thin photoresist

Great effort has been exerted by many researchers on a selective forming technique for a thick metal using an electroplating process for realizing various three-dimenstional (3D) structures. To fabricate such thick 3D metal structures, photolithography using a thick photoresist (PR) is essential for forming an electroplating mold. This PR mold is filled with a thick metal by the electroplating process. However, the process using a thick PR has many problems such as high cost, complex fabrication and difficulty in PR removal. To avoid these problems, we propose a new method of producing a 3D thick metal structure. A deeply etched Si mold is first prepared and the mold is then patterned with a thin PR for selective metal filling in deeply etched Si trenches by electroplating. During the thin PR patterning, exposure and development processes are repeatedly conducted several times to remove the PR residue possibly remaining in the deeply etched trenches. As a result, a thin PR is perfectly patterned without residues in the trenches and thick metal structures are selectively formed in deeply etched trenches by the electroplating process.