A novel boundary-confined method for microlens arrays fabrication

Abstract

We present a technique to improve microlens arrays (MLAs) uniformity after the thermal reflow process. Traditional photo resist thermal reflow processes cause micro lenses merge together easily due to an inexact reflow time and temperature distribution. This results in poor uniformity and low lens height. A new MLAs fabrication method, called the boundary-confined method, was proposed and demonstrated. By two tones of photoresist (PR), positive and negative, only one photo mask and two photolithography steps are needed in the process. After lithography processes, the positive PR is a slightly little smaller than the circular pattern on a photo mask and negative PR is slightly larger than it. Two tones of PR increase tolerance to mask alignment. Fill-factor is high because of high resolution on a thin boundary. All of flowing PR is stopped by the boundary; uniformity is improved without tight thermal dose constrains. Meanwhile, microlenses with a large height are achievable due to no cling effect. The method has advantages, not only for large area MLAs but also for a microlens that require precision diameter or positioning. Besides, we replicate MLAs with the optical polymer to verify some optical specifications. Both the fabrication and replication are straightforward and reliable. Our results show that the microlens is approximately a hemispherical profile. The gap between microlenses with 48 μm diameter in hexagonal arrangement is 2 μm and the height of microlens is 22 μm.