Development of virtual metrology using plasma information to predict mask shape in HAR etch process

The mask pattern erosion transferring ions and neutrals to high aspect ratio etching profile is studied. For a facet on mask edge and sidewall, it has been previously demonstrated that several facet angles were defined by equilibrium between angle dependent etching by reactive directional ions and isotropic passivation by deposited neutrals. On facet planes of the mask, energetic ions incoming through sheath are reflected in deeper profile with spread angle distribution. Modified energetic ions directing sidewall of inner profile can make worse profile distortion such as bowing. In this study, mask shape variables determining entering ions characteristics were predicted with a linear combination of plasma information(PI) variables representing ion-inhibited etching reaction in fluorocarbon gas-based plasma. For mask etching species, O ion density correlated with O atom density was measured with OES actinometry. Ion energies were defined by 2 variables with low and high region from voltage-current sensor assuming bi-modal energy distribution. Results show that linear combination of high energy oxygen ion flux and its ratio to CF₂ neutral flux variables expected well mask etched area. Facets were determined by surface positions, edge corner and sidewall of mask. The angle of the 1st facet on edge was predicted with low energy O ion flux and its ratio to CF₂ neutrals, although the angle of the 2nd facet on sidewall was dominantly estimated with etch byproduct resulted from etching on the 1st facet. Furthermore, by using phenomenologically devised PI variable of reflected high energy ion flux with spread angle on 2nd facet, bowing on mask sidewall was well explained.