Next-generation extreme ultraviolet (EUV) systems with numerical apertures of 0.55 have the potential to provide sub-8-nm half-pitch resolution. The increased importance of stochastic effects at smaller feature sizes places further demands on scanner and mask to provide high contrast images. We use rigorous mask diffraction and imaging simulation to understand the impact of the EUV mask absorber and to identify the most appropriate optical parameters for high NA EUV imaging. Simulations of various use cases and material options indicate two main types of solutions: high extinction materials, especially for lines spaces, and low refractive index materials that can provide phase shift mask solutions. EUV phase masks behave very different from phase shift masks for DUV. Carefully designed low refractive index materials and masks can open up a new path toward high contrast edge printing.
Pushing the novel anamorphic NA=0.55 EUV projection optics to k1 values below 0.4 and to its ultimate resolution limit will require an alternative mask absorber stack. This paper describes the application of rigorous imaging simulations in combination with multi-objective optimization to access the performance of novel absorber materials for the NA=0.55 system. Simulations of various use cases and material options indicate two main types of solutions: high k materials (k>0.05, especially for vertical lines/spaces) and low n materials (n ~ 0.9) to provide phase shift mask solutions for contact arrays.
With the EUV high volume manufacturing becoming reality and the closing gap of EUV mask infrastructure, EUV lithography is seeing or will shortly see the first production chips being fabricated with EUV. Pilot production in EUV HVM is most likely realized in a mix-and-match process with 193nm techniques. The degree of complexity introduced by the EUV lithographic process is transferred in parallel also to EUV mask: the combination of process sensitive 3D effects and material dependent EUV reflectivity make even the simplest EUV mask what the community is recognizing to be a very complex phase object. The qualification of such a complex piece of Infrastructure as the EUV mask is being addressed from many directions: defect review application is always more backed up by ancillary applications which aim at qualifying the printing behavior of the mask with the fundamental precondition of a full scanner emulation. ZEISS and the SUNY POLY SEMATECH EUVL Mask Infrastructure consortium have developed and commercialized the EUV aerial image metrology platform, the AIMS™ EUV platform, which fully addresses the industry requirements for EUV defectivity review. Additionally, this tool platform allows for mask qualification applications based on the employment of aerial image proven technology.
In this paper, the status and recent achievements of the AIMSTM EUV platform will be presented. Promoting the detailed exploration of the aerial image content potential for EUV process understanding and mask qualification, we will present recent results on a printability study of embedded EUV multilayer defects, along with providing further insights into the relevance of mask 3D effects.
The understanding, characterization, and mitigation of three-dimensional (3-D) mask effects including telecentricity errors, contrast fading, and best focus shifts become increasingly important for the performance optimization of future extreme ultraviolet (EUV) projection systems and mask designs. We explore the potential of attenuated phase shift mask (attPSM) to mitigate 3-D mask effects and exploit them for future EUV imaging. The scattering of light at the absorber edges results in significant phase deformations, which impact the effective phase and the lithographic performance of attPSM for EUV. Rigorous mask and imaging simulations in combination with multiobjective optimization techniques are employed to identify the most appropriate material properties, mask, and source geometries. The resulting imaging performance is compared to the achievable performance of binary EUV masks.
The understanding, characterization and mitigation of 3D mask effects including telecentricity errors, contrast fading and best focus shifts becomes increasingly important for the performance optimization of future extreme ultraviolet (EUV) projection systems and mask designs. The scattering of light at the absorber edges results in significant phase deformations, which impact the effective phase and the lithographic performance of attenuated phase shift mask (attPSM) for EUV. We employ rigorous mask and imaging simulations in combination with multi-objective optimization techniques to identify the most appropriate material properties, mask and source geometries and to explore the potential of attPSMs for future EUV imaging.