Width and space

A strap has a thickness of its own, and the gap beside the next strap is a different number. A factory can reject either one.

Opening the gap does not fatten a thin strap, and fattening the strap without moving its neighbor can shrink the gap. Width is the strap's thickness, measured across it, from one long edge to the other. Space is the gap between two shapes, from an edge of one to an edge of the other. A strap 0.05 micrometers wide is illegal in an empty field when the minimum width is 0.15. A gap of 0.05 where the rule wants 0.15 can bridge, and two nets become one. Thin metal opens. A tight gap fills in and shorts. You have to change the number that is actually wrong.

The picture at the top of this page shows both measurements on the same neighbors. Two teal straps sit with a clearly wide gap. Two navy straps sit with a clearly tight gap, and one of that tight pair is also thinner than its partner. The wide gap does not excuse the tight pair. The thin member does not earn a smaller gap by being thin. It adds a second violation. Measure the teal gap edge to edge, not center to center, and measure the navy gap the same way. If each teal strap is 0.20 micrometers wide and the centers are 0.50 apart, the gap is 0.30. That number is space. The navy gap is the one that can fill in.

Measure the strap, then the gap

The second picture isolates width. It is a clearly thin strap beside a clearly thick one, with no second strap stealing the reading.

The teal strap is thick enough to print as a wire. The orange strap above it is very thin. Width, on this picture, is the thickness of each strap by itself, with the field empty of a neighbor. If the minimum width on that metal is 0.15 micrometers, a strap 0.05 micrometers wide fails in that empty field. The real minimum for each metal comes from the foundry's design rules, which ship in its process design kit. Etch, or the exposure that sets the edge, will narrow it further or break it. The drawn 0.05 becomes an open, and the net that needed the strap is gone. The orange strap will not survive. It is not a second legal wire in a decorative color.

Space uses the other ruler, and it is the picture at the top. The clearly wide teal gap and the clearly tight navy gap are different numbers. One navy strap is also thinner, so the pair can fail twice: the thin strap opens, or the gap shorts, or the two failures show up on different wafers. Opening the navy gap until it matches the teal gap does not fatten the thin strap. Fattening the thin strap without moving its neighbor can eat the gap you opened.

A layer carries its own minimums. Lower metal and upper metal can demand different widths. Both can look like straps on the screen. The limit follows the layer, not the resemblance.

The thin strap and the tight gap

The width failure is the orange strap. It looks continuous in the editor. At the factory it may not print, or it may print as beads that break when the part is stressed. Length along the route is not the measurement. Width is across the strap, at the narrowest place, including a neck where it joins another shape. A strap that is healthy in the middle and 0.05 micrometers wide at one neck fails at the neck. The second picture draws that thinness as the whole strap, so you can see the thickness without a crowded neighbor.

The space failure is the navy pair at the top, a clearly tight gap beside the teal pair's clearly wide gap. Jammed straps short. The short may be uncommon, which is harder to catch than a short on the first wafer, because a rare bridge slips past a small sample and returns as lost yield. Same kind of object. The gap is what changed. Beside the wide pair, the tight gap is a measurement. Alone, "it looks close" is only a feeling.

Do not trade one against the other on instinct. A wide strap and a narrow gap are not a bargain you invent in the editor. Some processes publish a table where a wider wire may sit closer, and that table is still a list of numbers. Unless you are using that table, meet width and meet space as separate limits.

When you repair the drawing, change one thing and measure both again. On the top picture, move the navy straps apart until the gap meets the same limit the teal pair already clears, and fatten the thin strap until it matches the healthy width. Then remember the second picture. A strap with no neighbor can still be illegal. Space needs two edges. Width needs one strap. If a wire looks like the orange strap, widen it before you spend time on the gap beside it.

Change one number, then measure both

On the top picture the teal pair already clears the gap and the thin strap does not clear the width. Move the navy straps apart until the gap meets the same limit the teal pair clears. Then fatten the thin strap until it matches the healthy width. Measure both again after each edit. A repair that fixes the gap and thins the strap has traded one failure for the other.

A strap with no neighbor, the orange one in the second picture, can still be illegal. Space needs two edges. Width needs one strap. A gap of 0.05 micrometers fails a 0.15 micrometer space even when both wires are wide. A wire of 0.05 micrometers fails a 0.15 micrometer width even when the next wire is far away. The 0.20 micrometer strap is the healthy width in the top picture, not the limit. Unless the process table explicitly lets a wider wire sit closer, meet the two limits as separate numbers. Wider than the space rule is allowed. Narrower than the width rule is not.