The Focus Margin Gain and Limitation Realized by Focus Drilling in 28 nm Hole-Like Design Rules

Since the device integration and relating lithography process progressively increasing in complexity, more integrated approach to process control has been very necessary. There is more function in scanners that can be used to improve process window, CDU and OVL etc. When semiconductor technology node achieves to 28 nm, some function of scanner comes out contribution on process window increase. Focus drilling is the scanner implementation to increase the depth of focus (DoF) for contact-hole or via fabrication processes [1-7]. The basic principle is to smear out the maximum image contrast at best focus (BF) over a specific defocus range. This function applies a wafer stage R x -tilt (X-axis tilt) when scanning along the Y-direction (scanning direction). This allows the wafer stage to scan along a plane parallel to its tilt. This paper relies on Focus drilling to improve DoF of 28nm Via process, meanwhile also to analyze its negative impact on EL and CDU etc. And then try to find a balance focus range (Rx tilt) for 28 nm product. But the experiment result showed focus marginal gain is about 15nm, meanwhile it is hard to increase DoF through Rx tilt expanded.