Design of continuous-relief harmonic diffractive microlens array for maskless lithography

In order to achieve the focusing in real time and to obtain the high writing resolution and diffraction efficiency in the exposure process, a new maskless lithography based on a continuous-relief harmonic diffractive microlens (DMs) array is proposed. The lithography takes the continuous-relief harmonic diffractive microlens array as an objective array of the maskless lithography to integrate the defocus-detecting array and the writing array by taking both the writing resolution and diffraction efficiency into consideration, and to design the array with a deep relief to make the array fabrication easy. To verify its validity, the continuous-relief harmonic diffractive microlens array with F/7.5 and a design wavelength of 441.6 nm is designed, and fabricated after analysis on the characteristics of maskless lithography. Experimental results indicate that the developed array can be used to synchronously focus the writing laser and the autofocusing laser into the same spots, and can achieve a diffraction efficiency over 70% for both writing wavelength and defocus-detecting wavelength.