Color filters are widely used in projector system or virtual reality system to provide RGB primary colors from a white light source. The conventional projector system generally uses separately assembled color filters. More particularly, the color filters are separately manufactured and then assembled to the projector system. The manufacture tolerance is not important issue for the color filters.
To provide more compact color filters, method involving microelectronic and microlithography process are proposed to manufacture color filter films on transparent substrate.
FIG. 1 shows a prior art process for color filter film (U.S. Pat. No. 5,711,889):                S100: preparing a substrate 112, as shown in FIG. 1A;        S102: forming a releasing layer 114 by evaporation atop the substrate 112, as shown in FIG. 1B;        S104: applying a photoresistor layer 116 atop the releasing layer 114 by conventional spin technology and then backing the photoresistor layer 116, as shown in FIG. 1C;        S106: exposing a predetermined portion of the photoresistor layer 116 by photolithography to define a dent 116′ on the photoresistor layer 116, where the optical filter will be positioned, as shown in FIG. 1D;        S108: etching a portion of the releasing layer 114 below the dent 116′, as shown in FIG. 1E;        S110: depositing an optical filter material 124 into the dent 116′ by electron gun evaporation, as shown in FIG. 1F;        S112: removing the remaining photoresistor layer 116 by suitable photoresistor remover such as acetone to expose underlying releasing layer 114, as shown in FIG. 1G;        S114: etching underlying releasing layer 114 to form optical filter material 124 with predetermined pattern, as shown in FIG. 1G.        
The optical filter material 124 with predetermined pattern can form Archimedes pattern on the substrate 112 and used with a light pipe to provide light filtering effect for a projector system.
However, in above-mentioned process, the step of depositing an optical filter material 124 in step S110 is a “cold process” because the photoresistor layer 116 cannot resist high-temperature process. In conventional deposition by electronic gun, the substrate is heated to a relatively high temperature to enhance the quality of deposited film. Due to poor thermo stability of the photoresistor layer 116, optical filter material 124 with high quality is hard to form and extinct ratio of the optical filter using the optical filter material 124 is also poor.