BALL Builds World's First Working Transistor on Spherical Surface

Staff -- Semiconductor International, 12/1/1998

BALL Semiconductor Inc. (Allen, Texas) has fabricated a working transistor on the surface of a 1 mm silicon sphere. This is the first time that a transistor has been built on a spherical surface. Using a combination of traditional and unique processes, BALL was able to produce a 5 µm NMOS transistor whose electrical characteristics equaled those of a traditional wafer transistor. "Our entire company is celebrating this success, as it is a significant breakthrough for BALL Semiconductor," said Akira Ishikawa, BALL CEO and president. "This milestone is important for two reasons. First, it proves our theories for placing a transistor on a spherical surface, and second, we now have the fundamental processes in hand for shifting gear to the full scale pilot line and for producing diodes, transistors and select sensors."

Required processes for fabricating the spherically-placed NMOS transistor include mask data generation and fabrication using the 5 µm design rule, atmospheric Chemical Vapor Deposition (CVD), high-temperature oxidation at 1250°C, spherical resist-coating process, spherical lithography, etching and probe-testing of the transistor. Processes created by BALL include the spherical lithography process, which allows the company to align and expose six individual masks on the sphere; the resist-coating process, which requires the sphere to not only drop down an 8 m tube through a "soap bubble" of coating material but to also dry within 1 sec and the atmospheric CVD process. BALL is working to produce an electrically functioning IC on the 1 mm sphere, inductance on the sphere and a pilot manufacturing line. BALL hopes to reduce the cost of semiconductor manufacturing by up to 90% through use of hermetically sealed tubes in place of cleanrooms and by reducing processing time to days vs. months.