Layout regularity for design and manufacturability

Abstract

In nowadays nanometer technology nodes, the semiconductor industry has to deal with the new challenges associated to technology scaling. On one hand, process developers face increasing manufacturing cost and variability, but also decreasing manufacturing yield. On the other hand, circuit designers and electronic design automation (EDA) developers have to reduce design turnaround time and provide the tools to cope with increasing design complexity and reduce the time-to-market. In this scenario, closer collaboration between all the actors involved is required. New approaches considering both design and manufacturing need to be explored. These are the so called design for manufacturability (DFM) techniques.
 A DFM trend that is becoming dominant is to make circuit layouts more regular and repetitive. The regular layout fabrics are based on the configuration of a simplied mask set, therefore reducing the manufacturing cost. Moreover, a reduced number of layout patterns is used, allowing better process variability control and optimization. Hence, regularity reduces layout complexity and therefore design complexity, allowing faster time-to-market.
 In this thesis, we explore forcing maximum layout regularity focusing on future technology nodes, with increasing design and manufacturability issues, where we expect layout regularity to be mandatory. With this objective, we have developed a new regular layout fabric called Via-Configurable Transistor Array (VCTA). The physical design is fully explained involving layout and geometrical considerations for transistors and interconnects.
 Initially, VCTA layouts developed manually have been evaluated in terms of manufacturability, but also in terms of area, energy and delay. For digital design, 32-bit binary adders designed with VCTA have been compared to standard cell layouts. For analog design, a delay-locked loop design using VCTA has been compared to its full custom version.
 We have also developed a physical synthesis tool that allows us to obtain VCTA circuit layouts in an automated way. Developing our own automation tool lets us controlling all the decisions made during the physical design flow to ensure that maximum layout regularity is respected. In this case the work is based on several algorithms, for instance for routing, that we have oriented to the area optimization of the layouts.
 Finally, in order to demonstrate the benefits of layout regularity, we have proposed a new layout regularity metric called Fixed Origin Corner Square Inspection (FOCSI). It is based on the geometrical inspection of the patterns in the layouts and it allows designers to compare regularity of designs but also how their regularity will impact their manufacturability. The FOCSI layout analysis tool can be used to optimize manufacturability.