FormFactor's technology should be capable of probing any device at the die or wafer level. Once they are patterned and released, the contacts simply curl up. The metal film is sputtered onto a substrate at low temperature, and the stress gradient is built into the film by varying the argon pressure during the sputtering process. The metal is sputtered onto the substrate, starting with a very low argon pressure, which makes the film compressive. The argon pressure is increased gradually so the film gradually changes from compressive at the start to tensile at the end of the deposition.
Gold is added to improve contact characteristics.
After patterning and etching the metal film, the release layer holding the metal fingers in place is developed away. Typically, one third of the length of the probe fingers is kept in contact with the substrate. The curled-up probe fingers have demonstrated good resilience. The temperature is never high enough to remove any of the built-in stress. Since the probe fingers are defined lithographically, the linear pitch limit probably will be determined by material properties, not the fabrication process.