Raster Direction

GDS_RIP can be configured to produce bitmaps that are synchronized with the need of the imaging or inspection machine. For most IC applications, we don't want to produce one giant raster file as it becomes very difficult to transfer, manipulate and to access pixels inside a multi-GByte file.

Instead we divide the area to be rasterized into stripes. The size, width and orientation of the stripes are under our control and we create the stripes in a way to organize the pixels in the same fashion as the imaging machinery needs it.

A few examples follow. To illusrate this we are going to use layer 8 from a small and simple GDSII file, demo8.gds, but the principles apply to the much larger real life cases one must deal with.

Case 1 - a Linear CCD

Let's assume our optics uses a CCD camera that contains an linear array of detectors of 1 x 1024. The CCD is moved down the mask in a vertical direction. Then it is shifted and moved again. This is repeated until the entire area is covered. Let's further assume that our pixel size = 1.0 um.

We wish to produce a series of stripes that are 1024 pixels wide and whose height covers the entire mask. A quick calculation shows that the memory required to compose each stripe is [1024 x 10,000 x 1]/8 = 1.28 MB. So this is not a problem for us to allocate as RAM.

The GDS2TIFF Command Line

There are no "breaks" in the command line. They are only shown this way so that the command line can be annotated.

Gds2Tiff                                 gds2tiff application
 demo8.gds                               input GDSII file
  TOPMSPCHIP1                            structure to process
   +8                                    layer to process
    -ram:8                               RAM for raster buffer
      -pixelsize:1                       pixel size in um
        -extents:-5000,-5000,5000,5000   area to rasterize
          -out:raster_v                  output file basename
            -left_edge_golden            reference left edge
              -vertical                  vertical striping
                -bitmap_clip_dim:1024    clip bitmap to 1024 wide

Note: On windows the executable is gds2tiff_win.exe

The Output

We can expect 10 columns of pixels - 10 x 1024. Since this is more than the 10,000 pixels we expect to see in a 10 x 10 mm one has to know which side (in this case the left side) is aligned with the image.

You can see that 10 files are generated. They are different sizes because the tiff output is compressed and depending on the complexity of the bitmap in each stripe, the reduction due to compression may be higher or lower. if we use Photoshop to examine these bitmaps we will see that in fact we have vertical stripes.

You are looking at the first file, raster_v_0.tif which starts in the upper left hand corner, is 1024 pixels wide and 10,000 pixels high.