As Moore's law drives the semiconductor industry to tighter specifications, challenges are becoming real for overlay metrology. A lot of work has been done on the metrology tool capability to improve single-tool precision, tool-to-tool matching and Tool-Induced Shift (TIS) variability. But nowadays these contribute just a small portion of the Overlay Metrology Error (approximately 10% for 90nm technology). Unmodeled systematic, scanner noise and process variation are becoming the major contributors. In order to reduce these effects, new target design was developed in the industry, showing improvements in performance. Precision, Residual analysis, DI/FI (Develop Inspection / Final Inspection) bias and Overlay Mark Fidelity (OMF) are common metrics for measurement quality. When we come to measurement accuracy, we do not have any direct metric to qualify targets. In the current work we evaluated the accuracy of different AIM (developed by Kla-Tencor) and Frame-In-Frame (FIF) targets by comparing them to reference "SEM" targets. The experiment was conducted using a special designed 65nm D/R reticle, which included various overlay targets. Measurements were done on test wafers with resist on etched poly printed on 248nm scanner. The results showed that, for this "straight-forward" application, the best accuracy performance was achieved by the Non Segmented (NS) AIM target and was estimated in the order of 1.5 nm site-to-site. This is slightly more accurate than hole-based target and far more than NS FIF target in this particular case. When using the non-accurate NS FIF target, correctable parameters and maximum overlay prediction error analysis, showed up to 24nm overlay error at the edge of the wafer. We also showed that part of this accuracy error can be attributed to the non-uniformity of BARC deposition.

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Layer to layer alignment in optical lithography is controlled by feedback of scanner correctibles provided by analysis of in-line overlay metrology data from product wafers. There is mounting evidence that the "high order" field dependence, i.e. the components which contribute to residuals in a linear model of the overlay across the scanner field will likely need to be measured in production scenarios at the 45 and 32 nm half pitch nodes. This is in particular true in immersion lithography where thermal issues are likely to impact intrafield overlay and double pitch patterning scenarios where the high order reticle feature placement error contribution to the in-die overlay is doubled. Production monitoring of in-field overlay must be achieved without compromise of metrology performance in order to enable sample plans with viable cost of ownership models. In this publication we will show new results of in-die metrology, which indicate that metrology performance comparable with standard scribeline metrology required for the 45 nm node is achievable with significantly reduced target size. Results from dry versus immersion on poly to active 45 nm design rule immersion lithography process layers indicate that a significant reduction in model residuals can be achieved when HO intrafield overlay models are enabled.

Ion implantation in semiconductor devices frequently leads to a substantial wafer surface charge build up. Control of this charge during high current implantation is a major process issue, as it may affect the yield and reliability of thin dielectric layers. In addition, the charge build up may affect the ion beam resulting in a non-uniform implant and a reduction in device yield. Control of a specific machine parameter, that will give the charge condition of the ion implanter will enable to neutralize the charge build up.In this study, Disk Current Monitoring (DCM) is shown to be a reliable method for monitoring the Electron Shower (ES) performance in real time. A correlation was found between DCM level and yields, and between DCM level and breakdown voltage, as well as different maintenance activities regarding me ES. A simple 5 steps method is described to achieve a reliable, real time charge monitor, to insure operation within the “High Yield Range”.

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