Abstract: The Bosch process is seeing increasingly broad application in high-aspect-ratio etching, yet the reactive ion etching lag (RIE-lag) effect continues to constrain etching uniformity and achievable aspect ratios. This study utilizes a multi-scale simulation approach, coupling global, sheath, and feature-scale etching models, to simulate the Bosch process using SF₆ and C₄F₈ gases under high-aspect-ratio conditions. It investigates the impact of key discharge parameters on the RIE-lag phenomenon. Findings reveal that both bias power and frequency influence RIE-lag primarily through modifications to the ion energy angular distribution (IEAD). An increase in ion energy from a low baseline enhances ion density at the etch front, initially improving RIE-lag; however, beyond a critical energy threshold, the RIE-lag effect worsens. Coil power directly modulates the plasma density, thereby altering the RIE-lag, which exhibits a non-monotonic trend—first decreasing and then increasing—with rising power. Increasing the pressure during the passivation step extends the time required to clear the passivation layer, which in turn improves RIE-lag performance. Analysis of the etch depth progression within the Bosch cycle timing shows that parameters such as bias power, bias frequency, and coil power concurrently affect the etch rates of both the passivation layer and the silicon substrate, leading to complex variations in RIE-lag. In contrast, adjusting only the passivation phase pressure leaves the silicon etch rate largely unchanged, resulting in a horizontal shift of the etch line and offering a more controllable means of influencing RIE-lag. These insights hold significant value for the optimization of the Bosch process in practical engineering applications.