The goal of the project is to determine whether ma-N 1420 photoresist can be used with Heidelberg laser direct write tool, and to optimize the ma-N photoresist sidewall profile. The process starts by applying a negative photoresist onto a surface of a silicon wafer followed by an exposure to an ultraviolet light using a Heidelberg laser tool. The 410nm laser is applied directly to the photoresist without the use of a photomask, which is normally used for the purposes of exposing the wafers. The Heidelberg process is optimized in a manner that has not been possible previously at UW. This requires studying the thickness of the photoresist using reflectometry and optimizing the spin speed during spin coating. Various exposures on the Heidelberg system are then tested to make sure that the ideal exposure conditions have been achieved. The next step is to deposit a thin metal film on top of the photoresist. The deposition is achieved via an evaporation of metal inside the chamber of the device in which the metal is melted and evaporated by high speed electrons and is then deposited on a cooler silicon surface. The undesired metal is then stripped away from the surface of the wafer by removing the photoresist from under the metal film in a process the engineers refer to as “liftoff.” The optimization part of the project refers to testing different development times to make sure the development gives ideal photoresist overhang for the liftoff process. Finally, the sidewalls of the photoresist mask are analyzed using Scanning Electron Microscope (SEM). An SEM is used as the thickness of photoresist can be thinner than 1µm. The research was performed to verify that ma-N photoresist is suitable to use with Heidelberg system to complete a nanofabrication process.

In the fabrication of integrated circuits and microscale devices a technique known as electroplating is often used to deposit thick layers of metals such as gold and copper. The electroplating process requires a conductive layer to facilitate electroplating, commonly referred to as a “seed” layer. In many cases, the seed material will not bond well with the base materials, necessitating the use of an intermediate “adhesion layer” to improve adhesion between the substrate material and the plated metal. In this project, Electron Beam Physical Vapor Deposition (EBPVD) was investigated as a means to deposit a 25nm titanium adhesion layer followed by a 300nm copper seed layer to promote the adhesion of electroplated copper to a silicon dioxide substrate. EBPVD is a process in which a collimated beam of high energy electrons is used to boil metal atoms off of a target and deposit them on a substrate. These systems operate in high vacuum to increase the mean free path of metal atoms ejected from the target surface, allowing for highly anisotropic deposition on the substrate. The stress states of EBPVD deposited seed layers and electroplated wafers were also observed as residual stress can adversely affect the performance of active circuitry that IPDs are bonded to. The deposition of this seed layer, followed by electroplating of copper, is but one step in the fabrication of prototype signal filtering devices for mobile applications. These micrometer scale inductors and capacitors, referred to as “Integrated Passive Devices,” are built directly atop silicon wafers, with the intent of eliminating the need for larger surface mounted signal filtering devices in applications where working volume is at a premium, such as in mobile phones and tablets. We hope our research will allow for production of higher quality prototypes and accelerate development of this emerging technology.