For an exposure wavelength , the minimum line period, achieved with a coating of photo resist with thickness is given by

The resolution is largely limited by the light scattering in the photo resist.

Disadvantages : Contact with the mask degrades the mask (pinholes and scratches are created on the metal-oxide layers of the mask, Particles or dirt are directly imaged in the wafer, local loss of planarization results in non-uniform resolution due to mask-wafer gap variations, the mask is expensive since it has the same size of the wafer and no magnification.

Proximity printing

Resist is almost but not in contact with the mask and 1:1 magnification is achieved.

Advantages : No mask wear and contamination, inexpensive equipment, faster process, the entire wafer is exposed at once.