Optical metrology for real time control of elemental composition, distribution, and thickness of Cu(In1−xGax)Se2 thin films

An in situ optical metrology has been developed to provide real time control of three crucial film properties during the 3-stage deposition of Cu(In_1-xGa_x)Se₂ thin films. These properties include: (1) the overall Cu/(In+Ga) ratio; (2) the distribution of indium and gallium between the 1^st and 3^rd stages; and (3) the film thickness. The accuracy and reliability of this metrology were experimentally verified. It has been established as a routine process control tool for CIGS depositions at NREL. This metrology greatly expands the parameter space that can be systematically explored. It also holds the promise for applications in PV module manufacturing.