Dry-etch two-dimensional (2D) model functions have been investigated via 2D SEM image analyses. To evaluate dry-etch bias with respect to its 2D geometry, critical 2D pattern shapes of pre- and post-dry-etch process were compared. From the geometrical evaluation results we have confirmed that dry-etch biases can be expressed by a linear function of 2D pattern/space densities, for which integration should be taken only inside of nearest-neighbor pattern edges. It is guessed that those specific densities are required for estimating the thickness of passivation polymer films upon etching trench sidewall, which is assumed to be a critical factor for etch bias variations. We have obtained good correlations between etch bias and inside-edge pattern/space density; correlation coefficients of 0.95 for SiO2 trench etching process and 0.94 for Si trench etching process have been obtained, respectively. Optimum kernel radii of these processes were about 600 nm - 800 nm in our experiment. These distances would indicate the scope of micro-loading effect. If device pattern complexities come to these sizes, 2D pattern correction by 2D model function should be required for dry-etch biases instead of current rule-based correction.
Line end shortening (LES) effects and their corrections for ArF attenuated phase shift mask (PSM) technology toward 65 nm node, both in photomask and wafer processes, have been investigated. From critical dimension (CD) measurements on photomasks, it was found that line end distance and line width are the relevant factors for line end deviations on clear field and dark field types, respectively. We confirmed that these mask errors can significantly be reduced by rule base process proximity effect correction (PPC). Subsequently we analyzed resist LES on wafers and found that resist LES shows a down slope in case line end distance is less than 200 nm. We also assessed mask error enhancement factor (MEEF) around line end. Line end MEEF for a clear field mask indicates 3.4 when line end distance is 80 nm. By examining the relation between line end rounding on photomask and corresponding resist LES, we confirmed line end area loss on photomask surely induced larger resist LES. Lastly, we have evaluated a new optical proximity effect correction (OPC) approach in which correction for mask errors is separated from wafer OPC calculation. It is confirmed that new integrated OPC is promising for improving LES.
Because of the mask error enhancement factor (MEEF), iso-dense biases of mask patterns are amplified when the image is transferred to a wafer. A slight critical-dimension (CD) difference between an OPC test mask and an OPCed mask may cause a significant OPC error on the wafer. The impact of the mask CD error on OPC accuracy has never been evaluated, however, to evaluate the impact of the inter-mask CD error (IMCDE), we measured the CD errors of various line-and-space patterns on attenuated phase-shifting masks for ArF exposure. We investigated the effect of IMCDE and the iso-dense biases of test-mask patterns on OPC accuracy. We found that a degree of IMCDE is tolerable in attenuated phase-shifting ArF masks. This tolerable degree of IMCDE is useful to gauge the effectiveness of the OPC, with an eye to developing a lithographic process for semiconductor production. Furthermore, based on experimental results showing that a wafer CD is controllable when scanner conditions such as numerical aperture (NA) and partial coherence factor (sigma) are optimized, a new mask-matching method to compensate for the IMCDE is proposed.
We have investigated a new pattern correction method for reducing pattern critical dimension (CD) errors due to a variety of pattern layouts and densities. Together with conventional proximity effect correction and fogging functions in an electron beam (EB) writing process, the new pattern correction was introduced for correcting CD errors that occur during a dry etching process. A rule-based OPC software was used to modify EB pattern shapes. In addition to the spaces between neighboring patterns, the surrounding pattern density was chosen as a correction parameter. First, we optimized the pattern correction table by measuring the CDs of various symmetric 3 lines with 5 levels of surrounding pattern densities. Next, we applied the pattern correction to semi real device patterns. From the measurement for 100 patterns of them, CD uniformity of 15.0 nm (3-sigma) was obtained. We confirmed the effectiveness of the pattern correction method.
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