A system and method to form beam tunnels in interaction circuits. Forms, such as fibers or sheets can be located and secured above a substrate at a desired size and desired shape to form the final shape of the beam tunnels. Fiber holders can be utilized to position the forms above the substrate. A photoresist can then be applied over the substrate embedding the forms. A single exposure LIGA process can be performed on the photoresist, including the steps of ultraviolet photolithography, molding, and electroforming. After the process, the forms can be removed to leave the beam tunnels in the interaction circuits.