NOVELTY - Method for selenizing copper-indium-gallium precursor film at high temperatures involves: forming copper-indium-gallium precursor film on substrate; heating substrate to first temperature at 350-450 degrees C in inert gas at 1-2 atmospheres; exposing copper-indium-gallium precursor to source of selenium at 600-700 Torr; heating substrate to second temperature of 450-550 degrees C in inert gas at 1-2 atmospheres; exposing copper-indium-gallium precursor to source of selenium at 600-700 Torr; and heating substrate to third temperature of 550-650 degrees C in inert gas at 1-2 atmospheres.    USE - For selenizing copper-indium-gallium precursor film at high temperatures, including processing substrate having the precursor in combinatorial manner (all claimed), where copper-indium-gallium selenide is useful in thin film solar cell.    ADVANTAGE - The method for selenizing copper-indium-gallium precursor film at high temperatures, provides efficient method for forming different types of CIGS thin film photovoltaic (TFPV) devices that can be evaluated. A common problem encountered in prior art selenization is Ga segregation towards Mo back contact due to different reaction kinetics of In and Ga with H2Se. This produces non-uniform band gap in depth of absorber. The Ga poor surface layer has low band gap that limits open circuit voltage (Voc) of solar cell. In addition, lattice mismatch caused by large inhomogeneity in depth can introduce structural defects and recombination centers in space charge region, which adversely impacts device performance. The method produces high performance CIGS films with control over Ga distribution. In the high temperature selenization of Cu-In-Ga film high pressure of 1-2 atm maintained at first temperature decreases agglomeration of In within precursor film. Once temperature is stable, pressure is lowered to 600 Torr and Cu-In-Ga precursor film is exposed to Se source to selenize film and form Cu-In-Ga-S film. After selenization, film is annealed at 550-650 degrees C in inert atmosphere to control In and Ga compositional profiles throughout film. The process allows for processing substrate in combinatorial manner on single substrate without need of consuming equivalent number of monolithic substrates per material(s), processing condition(s), sequence(s) of processing conditions, and/or sequence(s) of processes; to process sequence integration in order to arrive at globally optimal sequence of TFPV manufacturing operations by considering interaction effects between unit manufacturing operations, process conditions used to effect such unit manufacturing operations, hardware details used during processing, as well as materials characteristics of components utilized within unit manufacturing operations. Rather than only considering series of local optimums i.e. where best conditions and materials for each manufacturing unit operation is considered in isolation, combinatorial process considers interactions effects introduced due to multitude of processing operations that are performed and order in which such multitude of processing operations are performed when fabricating TFPV device. A global optimum sequence order is therefore derived and as part of this derivation, unit processes, unit process parameters and materials used in unit process operations of optimum sequence order are also considered. This greatly improves both speed and reduces costs associated with discovery, implementation, optimization, and qualification of material(s), process(es), and process integration sequence(s) required for manufacturing TFPV device.    DETAILED DESCRIPTION - Method for selenizing copper-indium-gallium precursor film at high temperatures involves: forming copper-indium-gallium precursor film on substrate; heating substrate to first temperature at 350-450 degrees C in inert gas at 1-2 atmospheres; exposing copper-indium-gallium precursor to source of selenium at 600-700 Torr; heating substrate to second temperature of 450-550 degrees C in inert gas at 1-2 atmospheres; exposing copper-indium-gallium precursor to source of selenium at 600-700 Torr; and heating substrate to third temperature of 550-650 degrees C in inert gas at 1-2 atmospheres. The first temperature is 400-450 degrees C. The Cu concentration in copper-indium-gallium precursor film is 0.8-1 and is calculated as (Cu/(In+Ga)). The Ga concentration in copper-indium-gallium precursor film is 0.2-0.4 and is calculated as (Ga/(Ga+In)). The method is performed in batch system or rapid thermal processing (RTP) system. The method further involves processing substrate in combinatorial manner by: forming several copper-indium-gallium precursor films on isolated regions of substrate where composition of copper-indium-gallium precursor films is varied in combinatorial manner; followed by heating substrate to first temperature; exposing copper-indium-gallium precursor to source of selenium; heating substrate to second temperature; exposing copper-indium-gallium precursor to source of selenium; and heating substrate to third temperature.    DESCRIPTION OF DRAWING(S) - The figure shows flow chart that summarizes steps of method for selenizing copper-indium-gallium precursor film at high temperatures.