AVS 46th International Symposium
    Plasma Science and Technology Division Wednesday Sessions
       Session PS-WeM

Paper PS-WeM4
Does Mask Charging Influence Sidewall Trench Formation ?

Wednesday, October 27, 1999, 9:20 am, Room 609

Session: Feature Profile Evolution
Presenter: H.C. Lee, California Institute of Technology
Authors: H.C. Lee, California Institute of Technology
G.S. Hwang, California Institute of Technology
H.S. Lee, Hyundai Electronics Co. Ltd., Korea
K.P. Giapis, California Institute of Technology
L. Desvoivres, France Telecom-CNET, France
L. Vallier, France Telecom-CNET, France
O. Joubert, France Telecom-CNET, France
Correspondent: Click to Email
There has been some controversy in the etching community about how and to what extent charging effects influence profile evolution during the main etch in high-density plasmas. Microtrenching, for example, is believed to occur as a result of forward scatt ering of ions at the sidewalls. While charging is not essential for microtrenching, simulations have shown that mask charging could perturb the ion trajectories so that more ions scatter at the sidewalls; the resulting increase in scattered ion flux causes deeper microtrenches. This effect is difficult to prove when the mask is made of polymeric material because mask erosion influences the profile. Mask faceting, in particular, could increase the scattered ion flux to the trench bottom thereby dominating microtrench formation. It is then imperative that a hard mask be used to prevent any chemical or physical interference with trench profile evolution. We have performed a combined experimental and theoretical study of the contribution of mask charging to m icrotrenching. A Si wafer was patterned with gratings of hard oxide masks of linewidths down to 0.2 µm and then etched in a high-density, pure Cl@sub 2@ plasma to various depths. Three different mask thicknesses were tried: 0.2, 0.5, and 0.7 µm. Profile evolution simulations in the ion-limited regime predict that microtrenching should worsen with mask thickness because of increased scattering due to: 1) the larger sidewall area, and 2) ion deflection caused by upper mask sidewall charging. For mask aspect ratios larger than 3:1, charging of the lower part of the sidewall leads to an ion focusing effect that decreases significantly the microtrench depth resulting in rounded trench bottom profiles. While the experimental results generally support these trends, we find also important differences in the profile shapes. A side-by-side comparison will be shown and the charging contributions to microtrenching will be discussed.