Abstract As large-scale integration (LSI) devices have shrunk, plasma etching has encountered challenges such as microloading and critical dimension (CD) shift. To clarify the underlying mechanisms, we developed an etching-rate model based on precursor-mediated adsorption with surface diffusion. Applied to silicon (Si) etching, the model reproduced reactant-limited behavior at low pressure through efficient utilization of incident chlorine (Cl). When extended to aluminum (Al) etching, the model incorporated adsorption of etching by-products, showing that microloading was governed by etchant flux limitation and Al etching by-product adsorption at low pressure, whereas ion shadowing dominated at high pressure, indicating an optimal pressure near 2 Pa. CD shift was formulated based on the balance among deposition of photoresist by-products, ion sputtering, and reactions with Cl and O radicals at the sidewall. The model reproduced differences between isolated and dense patterns and center-to-edge variations, providing mechanistic insights and practical guidance for plasma etching.