Computer Aided Patterning Design for Self-Assembled Microsphere Lithography (SA-MSL)

In this paper, we use a finite difference time domain solver to simulate the near field optical properties of self-assembled microsphere arrays when exposed to an incoherent light source. Such arrays are typically used for microsphere lithography where each sphere acts as a ball lens, focusing ultraviolet light into an underlying photoresist layer. It is well known that arrays of circular features can be patterned using this technique. However, here, our simulations show that additional nanometer scale features can be introduced to the pattern by optimising the sphere dimensions and exposure conditions. These features are shown to arise from the contact points between the microspheres which produce paths for light leakage. For hexagonally close packed arrays, the six points of contact lead to star shapes in the photoresist. These star shapes have subfeature sizes comparable to the current achievable resolution of low-cost fabrication techniques.