How is the Reading Sense of a photomask specified?
The Reading Sense of a mask defines the transformation that has been applied between the original design data and the pattern that appears on the photomask. If you imagine a letter F defined as polygons in the design data, the most common requirement is to want a photomask with the letter F mirrored about it’s vertical axis, when the photomask is viewed with the Chrome surface upwards. This is called an Incorrect or Wrong Reading photomask with the Chrome Upwards, and is equivalent to a Correct Reading photomask with the Chrome downwards. If the photomask were to be used to make a contact print, then the master would need to be made Correct Reading Chrome Upwards in order for the Contact Printed copy photomask to be Incorrect Reading Chrome Upwards. Mask makers always prefer to define the reading sense with the Chrome surface upwards, as this is the way that all operations are performed on the photomask during manufacture.