›

What is the meaning of the appearance of horizontal lines in the layout layer?

Chen_0925Chen_0925
in KLayout Support

In the layout generated by KLayout, one can clearly observe the appearance of many horizontal lines. These horizontal lines have no spacing between them and are usually rather short, so the waveguide is essentially connected. However, in this particular case in the figure, there is one very long horizontal line that runs across the waveguide. This line originates from KLayout itself and cannot be merged (after applying merge, the line disappears, but once saved and reopened, the line reappears).

After fabrication, we found that this section of the waveguide exhibits unexpected reflection. Our current analysis suggests that this horizontal line may have a physical meaning in the stepper lithography process—namely, that when reaching a boundary, the stepper turns off the light source.

Therefore, I would like to know how such zero-distance horizontal lines are generated in KLayout, what their actual significance is, and how they can be eliminated? Thank you.

Comments

  • tomas2004tomas2004

    Hello,

    This is not KLayout related but GDS/OAS format related...

    https://www.klayout.de/doc-qt5/programming/geometry_api.html#h2-171

    ==> Polygon objects are not compatible with the GDS2 or OASIS format and will be converted to SimplePolygon objects by introducing cutlines when writing them...

    Moreover, the GDS format has a vertices limit, with older versions of the format limiting polygons to 200 vertices, while modern GDSII specifications support up to 8191 vertices per polygon, so polygons with more points will be fragmented resulting in these horizontal lines when writing the GDS file.

    Cheers,

    Tomas

  • sekigawasekigawa
    edited October 3

    Hello,

    First, I assume you saved the design in GDS2.
    These (horizontal) cut lines are inevitable if...
    1. A shape is represented by a polygon with holes OR
    2. A polygon contains too many vertices (number is somewhat controllable; see below).

    Does your case meet both conditions?

    1. Initial design with PCells


    2. Flattened PCells

    3. Merged polygons



    • The total number of vertices is below the limitation, but holes cause the horizontal cut lines.

    4. An idea to eliminate the horizontal cut lines


    5. Other ideas

    I'm totally unfamiliar with the type of lithography equipment you're using, but...
    1. Divide the design into two regions in the X direction and three in the Y direction. The dividing lines in the Y direction should run through the wide spaces.
    2. Allow a slight overlap at the dividing boundaries.
    3. Increase the resolution of your lithography equipment.
    etc.

    Kazzz-S

  • Chen_0925Chen_0925

    Many thanks to the experts above for their professional and timely answers. I also tried the suggested methods and found that by merging only the two sections where the long horizontal lines appeared, the horizontal curve disappeared smoothly! I would like to summarize the issue here, hoping it may help others with similar problems:

    1. The reason for the horizontal lines is that the number of vertices in the polygon exceeds the limitation of the GDSII file format. For DUV steppers, such boundaries mean the light source switches off. If such a horizontal line appears in the middle of a waveguide, it can cause uneven exposure.

    2. The solution is to split the original polygon so that the cut lines are as short as possible.

    Once again, many thanks — this has deepened my understanding of the GDS file format.

Sign In or Register to comment.
Powered by Vanilla