Hydrodynamic Shear Driven Inner Layer Copper Trace Washout in Ultra Thin Micro Channels
Controlling wet-process nozzle velocity below two meters per second prevents hydrodynamic trace stripping on ultra-thin inner layer copper channels.
Sub-Micron Copper Seed
Metallization Base
Discontinuous or ultra thin layers of conductive metal applied to a non conductive substrate provide the necessary surface for subsequent electrolytic plating. In high density interconnect manufacturing, a sub-micron copper seed is deposited using physical vapor deposition or electroless processes to initiate circuit formation. This layer must be thick enough to conduct current but thin enough to be removed easily during the final etching step.
This layer provides the foundation for semi additive processing.
Deposition Quality
The uniformity of the coating depends on the plasma energy or the chemical balance of the deposition bath. A sub-micron copper seed that is too thin will result in plating voids or poor adhesion to the dielectric. If the layer is too thick, the over etching required to remove the background copper will damage the fine traces.
Control of the grain structure at this scale is necessary for achieving smooth trace walls. The process requires a highly clean environment to prevent particles from creating defects in the seed layer.
Adhesion Boundary
Chemical bonds at the interface between the dielectric and the metal determine the reliability of the finished trace. A sub-micron copper seed often requires a prior tie layer or a plasma roughened surface to ensure it does not peel during thermal cycling. This adhesion is tested using standard tape tests or cross sectional analysis.