Combination of Mass Metrology with Scatterometry to obtain bottom Width of deep Trenches : AM: Advanced Metrology

Abstract

Three different in-line metrology techniques are combined to calculate the bottom width of trenches, 3μm and 42μm deep. CD-SEM gives the top critical dimension (CD) of trenches and scatterometry provides the trench depth. An average value for the trench bottom width or bottom CD is obtained from a mass loss determination with a pre- and post-etch measurement, in combination with the available top CD and depth values. This hybrid metrology approach has been demonstrated in case of the 3μm deep trench, where the conventional physical scatterometry modelling with rigorous coupled wave analysis (RCWA) is used to determine the trench depth and shape. The physical RCWA modelling is not applicable to the 42μm deep trenches with a pitch of >5μm. Hence, the proposed combined metrology method is verified with SEM cross-sections from wafers with different trench side-wall angles.