Fabrication method of quartz aspheric microlens array for turning mask
Wang Hao1,2, Dong Lianhe1, Zhu Guodong2, Zhang Dong2, Zhang Weiguo2     
1. School of Opto-Engineering, Changchun University of Science and Technology, Changchun, Jilin 130022, China;
2. Micro-Nano Manufacturing and System Integration Center, Chongqing Institute of Green and Intelligent Technology, Chinese Academy of Sciences, Chongqing 400714, China

Overview: In the existing mature processing methods, the processing of micro optical structure can be divided into two major categories: microstructural lithography and single point diamond turning. Microstructural lithography can be used to process inorganic materials, such as quartz, silicon and so on. However, microstructural lithography has not been able to solve the problem of micro and nano structure shape control. The single point diamond turning technology can achieve precise control of the surface shape, but it is difficult to process the inorganic and brittle materials.

In order to solve the two difficult problems of quartz aspheric microlens array processing, such as poor controllability and low surface accuracy, a method of making quartz glass based on turning mask and etching is proposed. The single point diamond turning technology and micro photomask technology is innovatively combined. The mask layer pattern is made by single point diamond turning, and then the mask pattern is transferred by reactive ion etching. Finally the fabrication of quartz glass aspheric microlens array element is completed.

We mainly make the selection of the mask material and study the etching performance and turning performance of PMMA and AZ50XT photoresist. We find that the addition of AZ50XT photoresist in PMMA can effectively improve the anti etching performance, not only meet the requirements of single point diamond turning, and after reactive ion etching after the mask pattern can be maintained by the original still. By analyzing the surface roughness of mask after single point diamond turning and the surface roughness of mask after reactive ion etching, we get the most suitable mask material for this processing method. Finally, the new material is used to make the mask. The pattern is made on the mask surface by single point diamond turning, and the mask pattern is transferred to the quartz substrate by reactive ion etching technology. The aspheric microlens array with area of 5 mm×5 mm is obtained.

The experimental results are compared with the expected parameters. The analysis shows that the root mean square error of the quartz glass element manufactured by this method is 1.155 nm and the accuracy of face shape error is 0.47%. The experimental results show that this method possesses not only the advantages of single point diamond turning technology, such as high surface accuracy, high processing stability and mature technology, but good anisotropy of reactive ion etching technology. This method has great potential for development, and it also provides a strong support for the wider application of quartz glass materials.