A photo-mask is typically made of quartz with chrome plating, controls where the radiant energy will strike the photoresist. Photo-masks are often made with electron beam patterning tools.

In optical mask making process, a computer tape is used to drive an optical pen which directly writes the pattern on the reticle mask.

This approach has advantage that, mask errors can be readily corrected by altering the computer tape and it avoids the need for making unmanageably large drawings as chip size increases.

Optical method has a diffraction limit which is set by wavelength of light. Electron beams do not practically suffer diffraction and hence are ideal for mask making.

In e-beam pattern generation, layout information is provided in the form of computer tapes which are used to control e-beam. An e-beam can be driven to directly produce a hard surface reticle mask at a x1 to x10 magnification.

The larger magnification has advantage that feature sizes in reticle can be made larger than those. But it also has disadvantage of increased probability of defects on mask.

A writing time of about 4 hours for a 20 cm x 20 cm mask is acceptable.

Starting with a x10 or x5 reticle mask, the convenient approach is to use step and repeat (S/R) camera to form master mask.

This camera is an inverted microscope which projects a x1 on emulsion coated glass plate.

This glass plate is mounted on a mechanical stage which is programmed to move after each pattern is exposed in S/R manner. The S/R process can be speed up by use of multi-barrel camera which projects four images of reticle at a time.

Contact printing of the master, or of an immediate submaster, is used to make multiple working masks which are used to define pattern on each microcircuit wafer.