In semiconductor industry, depth measurement is usually performed using the optical critical dimension (OCD) metrology, the atomic force microscopy (AFM) and transmission electron microscope (TEM). However, there are some limits in the depth measurements using OCD metrology or AFM. Therefore, this paper presents a new monitoring method for local depth using scanning electron microscopy (SEM) and a feasible verification method using AFM. This paper considers monitoring of local hole depth for the direct contact (DC). First, this paper proposes a depth monitoring index based on gray level (GL) of SEM image. The index includes not only the GL of the hole but also the GL of the background to reduce the effect of the GL inconsistency. Second, this paper verifies the effectiveness of the proposed depth monitoring index using in-FAB AFM. The reliability of the in-FAB AFM measurements as the reference for local depth is verified by TEM.
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