Abstract
The purpose of this dissertation is to design and implement an optical pickup head to be the light source for direct laser writing lithography. It is difficult to use the commercial optical pickup head as the light source for direct laser writing lithography due to two reasons. Firstly, the lateral stability of the actuator of the optical pickup head is not good since it adopts the six-wired suspension structure. Secondly, the optical power from continuous focusing servo of the optical pickup head may expose the photoresist between two successive exposed spots. To solve the first problem, a special design of a single-axial actuator was proposed. By using two planar springs with three-armed structure, the lateral stability of the actuator was improved. For solving the difficulty of the measurement of the lateral stability of the actuator while the focusing servo is activated, the original “modified push-pull method” was proposed. The measurement results showed that the lateral jitters of the actuator in two orthogonal directions were less than 2 nm. To solve the second problem, a new design of the dual-wavelength optical pickup head with both 405 nm and 650 nm wavelengths was proposed and implemented. The 405 nm beam was used to expose the photoresist, including inorganic and organic photoresists, while the 650 nm beam was used to execute the focusing servo. Numerical aperture of the objective lens was 0.85 at 405 nm. Both focused spots of the two beams by the objective lens were confocal and the detailed procedure of the confocal adjustment was also given. However, since the inorganic photoresist is heat sensitive, we suggest the two focused spots should be separated by at least 1.58 m to prevent from the optical power of the 650 nm spot affecting the exposure of the inorganic photoresist. Finally, the dual-wavelength optical pickup head with the single-axial actuator was used to expose both GeSbSnO inorganic photoresist and EPG 512 organic photoresist. The photoresist was coated on a 4” Si wafer and was spin with the linear velocity of 1 m/s. For the exposure of GeSbSnO photoresist, the minimum diameter of the pierced exposed spots was 0.19 um with 65 nm in depth. For the exposure of EPG512 photoresist, the minimum diameter of the pierced exposed spots was 0.52 um with 1um in depth. Besides, exposed spots with diameter of 0.29 um and with 0.24 um in depth were obtained. The exposure results showed that the procedure of the confocal adjustment was effective, and the dual wavelength optical pickup head was suitable to be used as the light source to expose those devices with feature size near 1 um or below.