min_notch

Minimum notch — the dual of min_width: a concave gap between two facing, inward-pointing walls of the same merged region (as opposed to min_space, which measures the gap between two different regions).

Semantics

Runs on the same per-tile merged cache and facing-wall scan as min_width, but inverted: instead of measuring the metal between two facing walls, it measures the empty gap between them. A notch narrower than value is a violation; each distinct notch is reported once. Three passes run, covering every combination of wall orientation:

• Rectilinear scan. Two vertical walls (a horizontal-direction notch) or two horizontal walls (a vertical-direction notch), found by sweeping bands across the region and pairing facing edges whose empty span is under value.

• Oblique pass (oblique_notches). Two mutually anti-parallel diagonal walls — the same style of scan, generalized to non-axis-aligned edges, with the gap measured along each edge’s own normal and the reported span limited to where the two edges’ projected overlap actually runs.

• Mixed pass (mixed_notches). One rectilinear wall facing one diagonal wall — the case neither of the above two passes can see, since they only ever pair edges of the same orientation class. This is the shape a diagonal stroke makes closing in on a straight stem (the tip of a “V”, the leg of a “K” or “M” — this is exactly what a diagonal font-glyph stroke does, which is how the gap was originally found). It uses the general segment-to-segment closest-point primitive (the same one min_space uses for inter-region gaps) rather than a parallel-corridor projection, since the pair isn’t parallel at all; the result is only accepted as a real notch when each edge’s closest point on the other lies on its own empty (right of direction-of-travel) side — every edge in a merged region carries metal on its left, a convention shared by all three passes — so a pair that’s actually metal-filled between the two walls is correctly rejected.

Layers

One layer — the notch is measured within its own merged geometry (holes included).

Parameters

None beyond layers and value (µm, the minimum required notch width).

Violation markers

One edge marker per notch, spanning the gap between the two facing walls at their narrowest point.

KLayout equivalent

Region#space(value) on a single region — KLayout’s native spacing check reports both inter-polygon gaps and same-polygon (concave) notches from one operator; gdscheck splits these into min_space and min_notch as two separate rules sharing one rule ID (e.g. IHP’s TM2.b is min_space + min_notch together).

Example

- id: TM2.b
  check: min_notch
  layers: [TopMetal2]
  value: 2.00