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In this study, wafer weak points sensitive to mask mean-to-nominal values are characterized for a process with very high MEEF (normally more than 4). Aerial image CD uses fixed threshold to detect the wafer weak points. By using WLCD through threshold and focus window, the efficiency of wafer weak point detection is also demonstrated. A novel method using contrast range evaluation is shown in the paper. Use of the slope of aerial images for more accurate detection of the wafer weak points using WLCD is also discussed. The contrast range can also be used to detect the wafer weak points in advance. Further, since the mean to nominal of the reticle contributes to the effective contrast range in a high MEEF area this work shows that control of the mask error is critical for high MEEF layers such as poly, active and metal layers. Wafer process based weak points that cannot be detected by wafer lithography CD or WLCD will be discussed.
In this manuscript, this conventional issue will be demonstrated which is either over exposure in logic area or under exposure in bitcell area. The selective rule-based re-targeting concerning active layer will also be discussed, together with the improved wafer CDSEM data. The alternative method is to achieve different mean-to-nominal in different reticle areas which can be realized by lithography tolerance MPC during reticle process. The investigation of alternative methods will be presented, as well as the trade-off between them to improve the wafer uniformity and process margin of implant layers.
Simulation predicts that NTD resist profiles should often have retrograde sidewall angles due to the attenuation of light as it propagates down through the resist. Resist shrinkage induced from both the de-protection during PEB and from exposure to electrons during SEM can cause CD and sidewall changes. The interplay between the shrinkage and the retrograde sidewalls is discussed.
Deprotection-induced shrinkage is measured by AFM while SEM induced shrinkage is estimated from repeated SEM measurements. SEM images for various features are analyzed and compared to simulation.
We have investigated three manufacturing sites for a 28nm first-metal layer reticle. Two of them were manufactured with a comparable process using the same advanced reticle binary blank material. For the third site a different reticle blank material with a relatively thin absorber layer thickness was used which was made with a comparable reticle process. The optical proximity correction (OPC) test patterns were designed with two different dummy patterns. The CD differences of the three reticles will be demonstrated for different dummy pattern and will be discussed individually. All three reticles have been exposed and the respective wafer critical dimension through pitch (CDTP) and linearity performance is demonstrated. Also the line-end performance for two dimensional (2D) structures is shown for the three sites of the reticle. The wafer CD difference for CDTP, linearity, and 2D structures are also discussed.
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