In this work, we demonstrate a self-aligned litho-etch litho-etch (SALELE) process flow for 18nm pitch patterning of subtractive Ru structures. This process combines many individual steps from a standard damascene double patterning flow with a spacer pull process to adapt it for subtractive patterning. Requiring two EUV exposures, this process flow enables a broad design space comparable to existing SALELE solutions for damascene integrations. Utilizing this process flow, we have demonstrated successful patterning of complex designs including intertwined comb-serpentines and various mixed pitch patterns. We report matched resistance for both mandrel and non-mandrel resistors. Additionally, we demonstrate equivalent yields for 1mm long intertwined comb-serpentine structures with serpentines formed from both mandrel and non-mandrel patterns.
Multi-channel gate all around (GAA) semiconductor devices require measurements of more target parameters than FinFET devices, due in part to the increased complexity of the different structures needed to fabricate nanosheet devices. In some cases, multiple measurement techniques are required to be used in a hybrid-metrology technique in order to properly extract the necessary information. Optical scatterometry (optical critical dimension, or OCD) is an inline metrology technique which is used to measure the geometrical profile of the structure, but it may not ordinarily be sensitive to very small residues. X-ray based metrologies, such as x-ray fluorescence (XRF) can be used to identify which materials are present in the structure, but are not able to measure profile information for complex 3D structures.
This paper reviews a critical etch process step, where neither OCD nor XRF can extract all of the necessary information about the structure on their own, but, when hybridized, are able to provide enough information to solve the application. In GAA structures, the nanosheets are formed from alternating layers of thin SiGe and Si layers which are deposited on a bulk Si substrate. To form the nFET channel, the SiGe must be removed. However, in some cases, there is still remaining SiGe residue on the surface of the Si nanosheets, present in small amounts that are difficult to measure with conventional OCD. Additionally, it is desirable to know at which level of the stacked nanosheets the residue is present. In order to properly characterize the amount of SiGe remaining, data from both OCD and XRF are used. By measuring before and after the etch, the XRF can calculate the percentage of SiGe that is remaining after the etch. This percentage can be used as a constraint in the OCD model to allow the OCD to accurately measure the amount of SiGe, and to enable the OCD model to identify the location of the residue.
Multi-channel gate all around (GAA) semiconductor devices march closer to becoming a reality in production as their maturity in development continues. From this development, an understanding of what physical parameters affecting the device has emerged. The importance of material property characterization relative to that of other physical parameters has continued to increase for GAA architecture when compared to its relative importance in earlier architectures. Among these materials properties are the concentration of Ge in SiGe channels and the strain in these channels and related films. But because these properties can be altered by many different process steps, each one adding its own variation to these parameters, their characterization and control at multiple steps in the process flow is crucial. This paper investigates the characterization of strain and Ge concentration, and the relationships between these properties, in the PFET SiGe channel material at the earliest stages of processing for GAA devices. Grown on a bulk Si substrate, multiple pairs of thin SiGe/Si layers that eventually form the basis of the PFET channel are measured and characterized in this study. Multiple measurement techniques are used to measure the material properties. In-line X-Ray Photoelectron Spectroscopy (XPS) and Low Energy X-Ray Fluorescence (LE-XRF) are used to characterize Ge content, while in-line High Resolution X-Ray Diffraction (HRXRD) is used to characterize strain. Because both patterned and un-patterned structures were investigated, scatterometry (also called optical critical dimension, or OCD) is used to provide valuable geometrical metrology.
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