DRC

Design rule checking is software that validates whether a circuit layout meets the physical and electrical constraints set by the fabrication process. Before a design goes to the photomask shop, DRC catches violations that would either destroy the chip during manufacturing or cause it to fail electrically in the field. It examines everything from metal line widths and spacings to via stacking, antenna ratios, and density windows.

Every foundry publishes a design rule manual specific to their process node, defining minimum feature sizes, spacing rules, and layer-to-layer interactions. A 5 nanometer process might require metal lines no thinner than 20 nanometers with 24 nanometer minimum spacing to adjacent traces. DRC rules also enforce process-specific constraints like maximum metal density in a region (to avoid planarity problems during chemical-mechanical polishing) or minimum via size depending on the metal layer pair being connected. The checker reads these rules as a database file, usually in a format like Calibre or a proprietary rule language, then scans the layout geometry layer by layer.

Common failure modes and variants

Layout designers encounter acute angle violations, where two metal edges meet at less than the allowed angle (typically 45 degrees minimum to reduce process variation effects). Density violations occur when a region has too little metal, starving the chemical-mechanical polishing process of material to polish uniformly. Antenna violations arise when a long metal line connected to a gate can accumulate charge during processing and rupture the gate oxide. Many design teams run DRC in multiple modes: fast geometrical checking first, then slower electrical checks that verify connectivity and measure resistance and capacitance from the actual drawn geometry.

DRC is not optional and not a suggestion. A chip that passes DRC but contains a subtle real-world violation may still fail in volume production, but one that fails DRC will almost certainly never work. For this reason, foundries are conservative; their design rules include margin. The term also appears as a verb: designers say a layout 'does not DRC clean' or 'DRCs with violations' when the checker flags problems.