To improve lithographic process throughput, it has become a general trend to link coater, stepper, and developer to an integrated PHOTO cell. In fine photolithography, TARC (top anti-reflective coating) is utilized intensively to obtain better CD (critical dimension) control. However, the coating of photoresist and TARC is not performed successively. A baking step about 90 seconds is employed in between these two coating steps. Throughput is thus affected and coating step becomes the bottleneck of whole lithography process. A series of experiments were investigated to coat TARC right after photoresist coatings. Results show that throughput was greatly improved. But for certain TARC and photoresist pairs, resist scumming due to inter-mixing of these two chemicals was found after exposure and developing. In some cases, the coater drain piping was stuck by the occurrence of precipitation resulted from the interaction between TARC and photoresist. To prevent this event from happening, precipitation tests of TARC and photoresist are investigated. Experiment was performed by adding TARC to photo resist with/without dilution by thinner. The occurrence of precipitation was observed. Seven kinds of photo resist and three kinds of TARC, provided by different vendors, are studied at different volume ratios on these tests. Results show that the lower photoresist to TARC ratio is, the more precipitation formed. Adding thinner, affecting the precipitation in different ways, induces more precipitation in most cases and cause the precipitation to disappear in some systems. One TARC is found to be inert to most photo resists. Photo resists with higher viscosity turn to gel when interacting with TARC.