The following study summarizes a thorough work in characterization the effects of different leveling modes in step-and-repeat exposure tool NSR-2205i11D on photolithography process parameters. The experimental work consisted on flatness measurements using the focus system of the stepper, critical dimensions measurements on Hitachi SEM 8600 and leveling sensor images on CCD camera. The study was performed on production wafers at via and metal layers and deal with phenomena that are related to the layout of products and do not appear on bare wafers. The conclusion that came out form this study is that standard leveling mode may have reduced performance due to misleading defraction pattern on its sensor, and optimal setting for the leveling mode should be made for each product and layer solely.
The following paper describes a modular monitoring approach for the photolithography environment, which takes individual measurements and generates three-level monitor. This method is aiming to simplify the process monitoring activity and make it more constructive. The basic monitoring level consists of Normalized indexes for each cell (cluster) -- each raw measurement is transformed into a value between 0 and 1. Second level is Cell index that unites all the Normalized indexes of each cell into one index. The upper level is the Photo index, which combine all the Cell indexes into one parameter. The concept that underlies this approach has few levels. The process engineers that monitor the equipment and process can use the Cell index as a qualitative tool for viewing the current general state of each cell and follow trends. When degradation is observed the Normalized indexes will be used for targeting the source of the degradation. The Photo index and the Cell index will also allow the management personnel to easily track the overall performance of the photolithography equipment and process, and achieve long term improvement by defining goals for the Cell and Photo indexes. The paper describes different options for generating each index in order to manipulate its sensitivity to the characteristic behavior of each individual measured parameter. Additionally, experimental data is presented to demonstrate the performance of the suggested methodology. The raw data is based on more than 120 individual parameters obtained from eight clusters.
The sensitivity of lithographic process window to global planarity of the inter metal dielectric layers is established in this work. The inter metal dielectric layers, between the metal layers, were prepared by utilizing the H2O2/SiH4 chemistry known as the 'Advanced Planarity Layer (APL)'. Four degrees of global planarity were tested within the APL process window, utilizing different H2O2 stabilization pressures. SEM cross sections were used to determine the degree of planarity in the CMOS product and at lithographic test structures. The lithographic process window and the effect of the stepper leveling system were defined for typical high and low topographies. The results how a strong link between the lithographic process window to degree of global planarity of the APL. Good global planarity enlarged depth of focus and energy latitude, allowing a wider lithographic process window. Also, in cases of improved APL planarity, the stepper leveling system had only a limited contribution to a lithographic process window. This control over the global planarity of the inter metal dielectric layers and the wide lithographic process window that results eliminate the need for CMP at 0.5 (mu) technology.
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