In the present paper, a complex chemical process involving laser-materials interaction within a strong absorbing gas phase is investigated and characterized. The process utilizes excimer laser pulses to dissociate methylene iodide (CH2I2) in the gas phase and to locally heat the surface of a silicon substrate. These effects induce chemical reactions leading to efficient etching of silicon within the laser-irradiated surface area, in combination with simultaneous deposition of carbon material outside. Because of the sensitive behavior of the photoinduced substrate surface temperature on the absorption conditions in the gas phase, model calculations were performed to improve the design of the system and to analyze the observed experimental results.