In order to improve the process repeatability of silicon dioxide etching, surface control of reactor wall based on ion bombardment is proposed. In this new technique, a reactor wall is almost fully covered with two floating bias walls; and rf bias is applied between the two walls with transformer coupling at 400 kHz. The biased walls are alternately bombarded by energetic ions in the negative phase of the rf bias. This alternating ion bombardment (ALB) technique enables us not only to suppress the polymer deposition during dielectric etching but also to clean the walls deposited with polymer during run-to-run etching. The AIB has little influence on electron density and plasma potential during etching. The radical diagnostics revealed that, during the AIB, mainly CF and CF, densities increase due to ion-enhanced desorption from the wall at the rate estimated from the removal rate of the fluorocarbon polymer layer.