This research focused on general microfabrication processes that have been used in the semiconductor industry and on specific processes that would allow vias to be micromachined in silicon wafers. In this research, a via is defined as a hole that has been micromachined through a silicon wafer. Micromachined vias in silicon wafers can serve as openings through which fluid or gas can flow. They can also be used as an integral part of electrical feedthrough connections. The processes necessary t o bulk micromachine these vias were researched and tested at the Univeristy of Louisville.
The first phase of this research focused on several general microfabrication techniques, which are required to micromachine silicon. This included thermal oxidation, photolithography, etching, and evaporation. Each of these techniques was first researched and then an experimentalprocedure was developed in-house fo r each process.
The second phase of this research focused on the specific processes that are used to micromachine vias in silicon wafers. it was found that the above procedures, in a specific sequence, enabled creation of vias on the silicon wafer. Successful etching of the vias was accomplished by 45% potassium hydroxide (KOH) at 50° C. rounding of the via edges was accomplished by the use of an isotropic etch composed of 48% hydrofluoric acid (HF), 69.5% nitric acid (HNO3), and deionized water.
The Si(100) etch rate in 45% potassium hydroxide was approximately 7.0 um per hour. the Si(100) etch rate for the isotropic etch composed of 40 ml of 48% hydrofluric acid (HF), 320 ml of 69.5% nitric acid (HNO3), and 40 ml deionized water (H2O). The isotropic etch rate for an elapsed time of 60 seconds was approximately 0.500 um/second, and the etch rate for an elasped time of 111 seconds was aproximately 0.300 um/second.
An etch rate was also determined for a buffered oxide solution that was complosed of 60 ml of 48% HF and 300 ml of 40% NH4F. The etch rate was experimentally determined to be 0.19647 um/min for this 5:1 mixture.