DrcRules

Create an empty DRC rule set.

Add a minimum width rule for a layer.

Add a minimum spacing rule between two layers.

Use the same layer for both arguments to check intra-layer spacing.

Add a minimum area rule for a layer.

Add an enclosure rule (inner layer must be enclosed by outer layer).

Add a rule requiring overlap between two layers.

Add a rule forbidding overlap between two layers. Can also be used with the same layer for both arguments to detect overlapping polygons within a single layer. In TOML config, use no_overlap = true in a per-layer section as a shorthand for forbid_overlap(layer, layer).

Add a rule restricting polygon edge angles to specified values (in degrees).

Add a minimum edge length rule for a layer. Catches tiny jogs and notches.

Add a self-intersection check for a layer. Detects invalid (self-crossing) geometry.

Add a maximum width rule for a layer. Useful for enforcing single-mode waveguide constraints.

Add a snap-to-grid check for a layer. Verifies all polygon vertex coordinates are multiples of the manufacturing grid pitch. Off-grid geometry causes mask fracturing errors and is rejected by most foundries.

Unlike other per-polygon rules, snap-to-grid checks run on fully-transformed (world) coordinates so that off-grid translations of cell instances are caught.

Common grid pitches: 0.001 (1 nm) or 0.005 (5 nm).

In TOML config, use snap_to_grid = 0.001 in a per-layer section.

Add an acute interior angle check for a layer. Flags convex polygon vertices whose interior angle is strictly less than threshold_deg.

Reflex (concave, > 180°) vertices are ignored because they represent the polygon turning outward and are not a lithography risk. Only inward-pointing sharp corners, which round off during lithography and can cause fracturing issues, are reported.

A common threshold in photonic PDKs is 60.0 degrees.

In TOML config, use acute_angle = 60.0 in a per-layer section.

Add a not-inside / exclusion-zone rule. Flags polygons on inner that are fully contained inside the union of polygons on outer.

Partial crossings, where an inner polygon crosses an outer boundary, are not violations. The inner polygon must sit wholly inside an outer region for the rule to trigger. Use this for keep-out zones, such as no-fly regions for a routing layer.

Distinct from forbid_overlap, which flags any overlap at all.

In TOML config, add to the [[drc.rules]] array:

[[drc.rules]]
type = "not_inside"
inner = "silicon"
outer = "keepout"
name = "KEEPOUT.SI"

Add a layer density (CMP uniformity) check.

Tiles a region with a sliding window × window square, stepping by step, and flags every window position where the area fraction covered by layer falls outside [min, max].

Foundries require density within a band for CMP (chemical-mechanical planarization) uniformity, a likely tape-out blocker if omitted. Typical photonic-PDK values: silicon device layer min=0.20, max=0.80 over a 100 µm window with 50 µm step.

At least one of min or max must be provided. If region_layer is set, the union of polygons on that layer defines the region over which density is measured; otherwise the bounding box of all placed geometry in the design is used (equivalent to Library.cell_bbox on the top cell). Designs with no geometry at all skip the check silently.

In TOML config, use the grouped [drc.layers.<layer>.density] subtable:

[drc.layers.silicon.density]
min = 0.20
max = 0.80
window = 100.0
step = 50.0         # optional; defaults to window / 2
# region_layer = "prbnd"   # optional; defaults to placed-geometry bbox

Set a global warning margin (in design units, typically µm). Near-threshold violations on length-based numeric rules whose measured value is within margin of the required threshold are reported as severity == "warning" instead of "error". Warnings do not cause DrcResult.passed to be False and do not fail rosette check / rosette drc.

For example, with min_width = 0.12 and warning_margin = 0.01:

• width < 0.11 → error
• width in [0.11, 0.12) → warning
• width ≥ 0.12 → no violation

Applies to min_width, min_spacing, min_enclosure, min_edge_length, and max_width, all of which compare in length units.

Excluded: min_area thresholds are in squared units and density values are dimensionless fractions, so neither is commensurate with a length-unit margin; both remain strict errors. Categorical / binary checks (allowed_angles, require_overlap, forbid_overlap, no_self_intersection, snap_to_grid, acute_angle, not_inside) are also unaffected.

Pass 0.0 (or any non-positive value) to disable. The default behavior, where every violation is an error, is preserved until you opt in.

In TOML config:

[drc]
warning_margin = 0.01