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Structural changes in a positive resist resulting from plasma exposure during the reactive ion etching process are studied using Fourier transform infrared (FTIR) spectroscopy and atomic force microscopy. The internal process parameters such as electron density and reactive species concentration are investigated for correlation with the structural change of the photoresist. It is found that the low-energy bonds of the resist material are removed when the plasma is ignited even at low RF power. At a higher power level, the photoresist surface of the patterned silicon has changed its topography due to the removal of more low-energy bonds that affect the surface roughness and etching profile. The removal of materials from the photoresist material surface also affects the internal process parameters such as electron and fluorine density, and we have found that higher electron density at higher power influenced to break more hydroxyl (OH) and carbohydrate (CH) bond and increased the H concentration by increasing the H emission intensity measured by optical emission spectroscopy. There is a correlation between the fluorine concentration, and electron density at different RF power shows that higher electron density means more F concentration by dissociation of SF6 reactive gas.