What is the difference between cworst/rcworst and C / RC corners? Why do we need to consider different RC corners?

o   Traditional Corners (Simplified View - often just called C corners initially): Used for short nets where resistance can be ignored or very less.

o    Cworst (Maximum Capacitance, Cmax): Models process variations that maximize interconnect capacitance (e.g., wider wires, thicker metal, smaller spacing, higher dielectric constant). Often assumes minimum resistance for these conditions (though not always explicitly linked). Used primarily for setup timing analysis (longest path delay).

o    Cbest (Minimum Capacitance, Cmin): Models process variations that minimize interconnect capacitance (e.g., narrower wires, thinner metal, larger spacing, lower dielectric constant). Often assumes maximum resistance. Used primarily for hold timing analysis (shortest path delay).

o   RC Corners (More Detailed View): These corners consider the interplay between R and C more explicitly, especially the impact on crosstalk and longer nets where resistance also dominates.

o    RCworst (Maximum Delay Corner): Models conditions maximizing the overall RC product, leading to the slowest signal propagation. This often involves thinner wires (higher R) and potentially adjusted capacitance values (sometimes minimum Cg - ground capacitance, minimum Cc - coupling capacitance, although specifics vary by foundry). Used for setup timing analysis.

o    RCbest (Minimum Delay Corner): Models conditions minimizing the overall RC product, leading to the fastest signal propagation. This often involves wider wires (lower R) and adjusted capacitance. Used for hold timing analysis. Xtalk corner.

o    (XTALK Corners - sometimes separate): Foundries may provide additional corners specifically optimized for worst-case crosstalk analysis, often focusing on maximizing coupling capacitance (Cc) relative to ground capacitance (Cg) or total C. E.g., a corner maximizing Cc might be used for noise analysis or delta-delay calculations in STA. RCbest itself is sometimes referred to as an XTALK corner because minimum R and potentially higher Cc can lead to faster aggressor signals causing more noise.

o    https://www.vlsi-expert.com/2013/04/parasitic-interconnect-corner-rc-corner.html?m=1