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Photomask Inspection Criteria

Critical Dimension

The Critical Dimension is often the size of the smallest feature on your photomask, although not always.  It could be the width of a line, the distance between parallel edges of a polygon, or a space between a pair of lines or polygons.  

For Laser PG Photomasks, the standard minimum CD is 6 Ám, although we can supply these large area masks with CD's as small as 3.0 or even 2.0 Ám in size.

CD Tolerance

The CD Tolerance defines the upper an lower limits of the allowable size of the Critical Dimension.  It is usually specified in terms of +/-x.xx in units of microns, or in fractions of microns. 

For Laser PG photomasks, the standard minimum CD Tolerances are as follows:
For CD's smaller than 10.0 Ám: +/-0.5 microns
For larger CD's up to 50.0 Ám: +/-1.0 Ám
For larger CD's up to 127.0 Ám: +/-1.3 Ám
For larger CD's up to 250.0 Ám: +/-1.9 Ám
For larger CD's greater than 250.0 Ám: +/-2.54 Ám.

For Super Large Area photomasks, the standard tolerance range is +/-2.5 to +/-7.5 microns.

If your design has a CD that is very large, but you wish to apply a smaller CD tolerance, then you might consider placing a smaller feature in a non-critical area of your mask that we can use for our CD measurements.

Inspection Type

Visual inspection is used as the primary inspection method whenever the two above methods are not practical.  This inspection is done at very high magnification, and uses image comparison as one of the defect detection processes.  There are no extra charges associated with this type of inspection.  The standard defect size that can be detected with this process is about 5.0 microns, with 3.0 Ám as the minimum size.

Die-to-Die Registration

Die-to-die registration refers to the tolerance allowed on the placement of, or the center to center distance between, a set of two adjacent repeated images, instances, blocks, or cells.

The typical die-to-die registration limit for Laser PG masks is +/-0.4 Ám per linear inch, but not less than +/-0.5 Ám.

The typical die-to-die registration limit for S-LAM masks is +/-2.5 Ám.

Layer-to-Layer Registration

Layer-to-layer registration refers to the tolerance allowed on the overall size of the image on the photomask, and therefore defines how closely the images of one photomask will align with the images of another photomask within a mask set.  This criterion can only be applied to a mask set that has more than one mask or layer.

The typical mask registration limit for Laser PG masks is +/-0.4 Ám per linear inch, but not less than +/-0.5 Ám.

The typical mask registration limit for S-LAM masks is about +/-12.5 Ám per meter.

Smaller Feature/Space Sizes

This specification should be used to notify us if there are any features on the photomask that are smaller than the CD.  This will help us to determine which manufacturing process is best suited for your particular job.

Usually, these are manufactured on a "best efforts" basis.