Seasoning of plasma etching reactors: Ion energy distributions to walls and real-time and run-to-run control strategies

Abstract

Wafer-to-wafer process reproducibility during plasma etching often depends on the conditioning of the inside surfaces of the reactor. Passivation of reactor surfaces by plasma generated species, often called seasoning, can change the reactive sticking coefficients of radicals, thereby changing the composition of the radical and ion fluxes to the wafer. Ion bombardment of the walls may influence these processes through activation of surface sites or sputtering, and so the spatial variation of ion energies on the walls is important. These seasoning processes may occur during a single etching process or on a wafer-to-wafer basis. The seasoning of plasma etching reactors will be discussed using results from a computational investigation of p-Si etching in chlorine plasmas. The transport of etch products, passivation of walls, and sputtered products from walls are accounted for, as well as differentiating the ion energy distributions to different surfaces. A real-time, closed-loop control of etch rate to counter the effects of seasoning was achieved using the bias voltage as an actuator.