The complexity of Resolution Enhancements Techniques (RET) will increase dramatically in the next four generations of optical lithography, requiring careful qualification of new reticle designs when they arrive at the wafer fab and before commiting them to printing product. Low k1 and high MEF lithography increase the printability and frequency of yield impacting repeating defects from reticle defects and RET layout errors. Therefore, reticle qualification must include qualifying the reticles for mask processing errors as well as for RET design rule violations. The former is performed on a reticle inspection tool and the latter on a wafer inspection tool after printing wafers with a specific layout using the reticles of interest. The output from the wafer inspection tool followed by detailed analysis provides information on the regions of marginality within the reticle field or features within the die which have smaller process window than expected. We call this the Process Window Qualification Output, PWQ Output and it can be applied to single and multi-die reticle designs. Once these locations are identified by PWQ and the features are determined to be critical to the functionality of the device, further process window analysis on the CD SEM is performed to identify if sufficient process window overlap exists between these features and all other critical features in the device. If the process window overlap of the marginal features with other critical features is acceptable, the reticle can be used to print product. These marginal regions are then carefully monitored on product by CD Metrology. If insufficient overlap in the process windows is found, the PWQ Output features are overlayed with the CAD design and a design fix might be required, followed by the manufacturing of a new reticle. In this paper we describe how we used the PWQ methodology to identify RET design errors for three different reticle designs; in the first example, the marginal feature is an OPC sizing error causing the below design rule spacing in a 0.13μm Gate reticle design to bridge within the process window and the second example is that of a marginal feature associated with improper biasing and a phase error for an Attenuated PSM reticle. The final example shows how PWQ was used to verify the printing of an assist feature within the process window for a Gate 0.13μm reticle.
For sub-0.13um lithography, attenuated phase shifting mask (AttPSM) with optical proximity correction (OPC) is reported as one of the potential methods to achieve manufacturable process by using 248nm exposure wavelength. Unfortunately, the low-k1 imaging process in 130nm lithography imposes much more stringent requirements on defect repair, especially on AttPSM reticle. Therefore, the imperfect repairs will have a significant impact on wafer process window due to quartz damage and phase distortion caused by Ga+ ion stain removal and added carbon material, respectively.
In this paper, we have prepared AttPSM test masks having programmed defects with various opaque defects. Each defect area was inspected with KLA-Tencor's SLF27 inspection system to acquire defect coordinates and image, simulated with AIMS to assess the intensity and transmission loss induced by repair process. All of masks were made by DuPont Photomasks Taiwan (DPT) by using the Jbx9000MV2 E-beam writer and dry Chrome etch process. All lithographic experiments were performed on 300mm wafer using high NA ASML AT750S scanner and high contrast CAR resist. In this study, we have focused on the impact of quartz damage and phase error on wafer process window by comparing the wafer CD and pattern profile through focus. In order to establish a efficient way to perform effective judgement on repair defect between mask shop and wafer fab, both AIMS and wafer results will be compared and correlated.
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