Line-profile and critical-dimension monitoring using a normal incidence optical CD metrology

Abstract

As lithographic technology drives the minimum integrated circuit feature size toward 0.1 m and below, process tolerances for critical-dimension profile excursion are becoming increasingly demanding. In response, optical critical dimension metrology (OCD), an optical-wavelength light-diffraction technique, is emerging as a fast, accurate, and nondestructive sub-100-nm linewidth and profile monitor. As such, a detailed understanding of the correlation between OCD and existing metrology tools is required. Correlation between CD measurements using OCD and CD-scanning electron microscopy (SEM) techniques is investigated by measuring two types of important structures, e.g., photoresist gratings on a polysilicon gate film stack and shallow trench isolation. Intragrating CD variation is shown to account for scatter in the correlation plot. A qualitative line-profile correlation between cross-section SEM (X-SEM) and OCD is presented for photoresist gratings in a focus exposure matrix. Finally, a summary of the capability of OCD as a monitor for various processing stages is presented.Index Terms-Critical dimension (CD), diffraction, optical critical dimension (OCD), optical metrology, process control.

Optical wafer metrology sensors for process-robust CD and overlay control in semiconductor device manufacturing

“…Fortunately, over the years optical scatterometry [27] has gradually evolved into a suitable in-line CD metrology technique (often referred to as optical CD: OCD) that offers sub-nm precision at measurement times as low as ≈0.1 s per sample. There is a vast amount of literature available on OCD for example [27-30] so here we limit ourselves to a summary of the operating principle.…”