TSMC PDK Stream Layer "ref" (0;0) purpose?

[mult]

Hi,

does anybody know what is the purpose of "ref" layer, number 0, datatype 0 in TSMC PDK?

streamLayers(
;( layer streamNumber dataType translate )
;( ----- ------------ -------- --------- )
( ("ref" "drawing") 0 0 t )

This layer appears in GDS file, which is result of TSMC "DUMMY OD POLY INSERTION UTILITY" usage.

Thanks.

 

[erikl]

I guess it's the background layer (because of layer name ref & layer number 0).