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.

Two modes of surface roughening during plasma etching of silicon: Role of ionized etch products

“…The ion mass spectrum with the ionizer off indicates that the predominant ions are ionized etch products/byproducts, SiCl þ and SiCl 3 þ followed by SiCl 4 þ , which are more abundant than the dominant feed gas ions Cl 2 þ , as has been observed and/or concluded in a few QMS measurements during Cl 2 and Cl 2 -containing plasma etching of Si. [89][90][91] This essential feature for the predominant ionic species during etching (SiCl x þ , and not Cl x þ ) has been different from most modeling predictions, [92][93][94] while has lastly been predicted by the recent modeling simulations. 88 The neutral mass spectrum with the ionizer on exhibits several peaks of impurity species O, OH, H 2 O, and HCl (m/e ¼ 16, 17, 18, and 36/38), in addition to peaks of etch product/ byproduct SiCl x (x ¼ 0-4) and feed gas Cl x (x ¼ 1, 2) species.…”

Investigation of the radially resolved oxygen dissociation degree and local mean electron energy in oxygen plasmas in contact with different surface materials

“…Furthermore, the wafer material itself and the condition of the other wall materials in the reactor affect the absolute number densities of reactive species due to wall loss processes, the probability for which is dependent on many factors. [12][13][14][15][16][17][18][19][20][21][22][23][24][25] This makes it particularly difficult to accurately control the densities of highly reactive species, such as atomic oxygen, in industrial processing applications. Previous investigations have sought insight into these processes by measuring the density of atomic oxygen and its surface recombination probability for various materials using twophoton absorption laser-induced fluorescence (TALIF), 12,[26][27][28][29][30] optical emission spectroscopy (OES), 21,22,[31][32][33][34] and VUV absorption spectroscopy.…”

Non-invasive in situ plasma monitoring of reactive gases using the floating harmonic method for inductively coupled plasma etching application

“…It is well known that depositions on chamber walls chemically affect plasma and change etch properties over time. 15,29,30 In order to remove depositions from chamber walls and to keep etch properties the same, chamber should be cleaned periodically. This process inevitably changes plasma chemistry including plasma parameters.…”