Laser induced fluorescence monitoring of the etching processes with the inward plasma

Laser induced fluorescence (LIF) spectroscopy has been used to monitor the etching processes in a localized plasma etching system. An inward plasma was employed for etching in which etching gas was discharged in the narrow gap between the etched sample and the entrance of an evacuating capillary tube. By observing the LIF spectrum, it was confirmed that the etch product SiF2 exists near the both Si and SiO2 sample surfaces being etched with CF4 inward plasma. The plasma gas temperature was estimated to be ∼400 K from the comparison of the LIF spectrum with the rotational simulation. LIF method was applied to the etching endpoint detection of two kinds of material, thermally-grown SiO2 on Si and spin-coated Polyimide Isoindoro Quinazorindione (PIQ) film on Si. The endpoint was detected from the onset of SiF2 production by the etching of Si substrate in the case of PIQ/Si. The signal intensity of SiF2 from the Si substrate during etching was several times larger than that from the SiO2 layer, and thus, the endpoint of SiO2 etching was detected by the abrupt increase of SiF2 signal. The etch rates of PIQ and SiO2 at the center of the capillary were determined to be 1.09 μm/min and 1.66 μm/min, respectively.