The Diffraction effect in proximity printing for different mask wafer spacing is shown in Fig. 3.58. Three cases are illustrated (a) s is small (b) s is larger and (c) s is the largest.
After the alignment is accomplished the wafer is exposed to few hundred mJ/cm2 of high energy light in any one of the printing schemes described above.
Developing :
Due to the exposure selected regions of the resist is changed and the developing is used to dissolve the weak regions of photo resist. Development of optical resists takes place in an alkaline solution. Acetone or trichloroethylene is used to develop positive photo resists. Methyl ethyl ketone (MEK i.e. CH3COC2H5) or Methyl isobutyl ketone (MIBK i.e. CH3COC4H9) can be used for negative photo resists.
