Computational System for the Fab
Because the essential task of a semiconductor wafer fab is to print patterns onto the wafer, Anchor’s computational system is designed to be pattern centric. The CAD layout is a database of patterns. OPC is performed on patterns. Mask writers etch patterns (contained in MEBES files). Lithography process windows are determined using FEM/PWQ techniques that analyze patterns in each focus/exposure modulation. Test chips are composed of a diversity of patterns. DFM (Design for Manufacturing) databases record weak patterns. DRC (Design Rule Check) rule decks are designed to avoid problematic pattern layouts.
Patterns are indeed essential components. But the notion of patterns takes a back seat in the operation of the wafer fab. This is not necessarily desirable, but it is understandable because (a) the design house is CAD based, (b) the OPC team is CAD based, and (c) the mask house is CAD based. But not the fab. Once the reticle or mask enters the fab, the digital side of manufacturing is essentially complete (where every digital “run” produces identical results), and the analog side begins (where every analog “run” produces slightly different results). Like snowflakes, no two wafers nor any two die are exactly alike. There are differences every time the wafer is exposed or developed or etched or planarized or implanted or cleaned. The process steps leading from the front end of line to the back end of line are analog steps.
For a fab operating in the analog domain to communicate and coordinate more effectively with the Design, OPC and Mask teams that operate in the digital domain, it needs to adopt the language of patterns as well.
For years, fabs have struggled to cope with patterns, often spending days or weeks of manual effort to analyze large quantities of FEM/PWQ results, for example, and provide actionable information to the OPC team or to appropriate process modules.
Anchor’s computational system arises from the intersection of the two primary domains of intended and printed patterns, and is founded on three fundamental pillars:
- Printed Pattern Database
- Design Decomposition Database
- Machine Learning
We encourage you to read the JoMM paper linked above.