Highly Manufacturable Deep (Sub-Millimeter) Etching Enabled High Aspect Ratio Complex Geometry Lego-Like Silicon Electronics

A novel hybrid soft (sacrificial)/hard mask layer for deep reactive ion etching (DRIE) of sub-millimeter structures was demonstrated. First, negative tone PR AZ 5214E with image reversal capability is spun. Pyrolysis bake is then carried out followed by broadband exposure, an image reversal bake, and a final flood exposure dose. This makes the complete PR layer insoluble in AZ 726 MIF developer. Next, a thin aluminum layer is sputtered at room temperature followed by positive tone PR AZ ECI 3027 layer spinning and patterning. The aluminum layer is patterned using the PR mask and metal RIE using inductively coupled plasma (ICP), Cl2, BCl3, and Ar mixtures at 80 °C. Then, the negative tone PR is etched in O2 plasma RIE followed by DRIE of silicon. Finally, the hybrid dual PR/Al mask is removed by immersing in acetone bath. To assess the effect of the new process on the etched features and the underlying silicon substrate surface, Zygo profiler measurements, for surface roughness, and scanning electron microscopy (SEM) imaging, for feature size measurements, were carried out. This process allows easy and clean removal of metallic hard masks, preserves the high-quality interface of underlying substrate, and endures during long duration etches. This technique enables 'Lego'-like IC chip placement on soft substrates for free-form electronics.