Application of Huygens-Fresnel diffraction principle for high aspect ratio SU-8 micro-/nanotip array.

A high-aspect-ratio (approximately 30) SU-8 micro-/nanotip array whose shape is defined by diffraction was fabricated by a single UV photolithography procedure and its exposed dose control. The fabrication result of the tip agrees well with the Rayleigh-Sommerfeld solution of the Huygens-Fresnel principle at wide observation distances. In a near field below distance 2 microm (only several times of wavelength), necking points also agree with the solution, although it is assumed that the distance is much larger than wavelength. It can be also applied to control the shape of the tip and to determine the critical dose D(c) of SU-8 and other photocurable polymers.