Gabriel Baralia

Closing the gap for EUV mask repair

The EUV-photomask is used as mirror and no longer as transmissive device. In order to yield defect-free reticles, repair capability is required for defects in the absorber and for defects in the mirror. Defects can propagate between the EUV mask layers, which makes the detection and the repair complex or impossible if conventional methods are used. In this paper we give an overview of the different defect types. We discuss the EUV repair requirements including SEMinvisible multilayer defects, and demonstrate e-beam repair performance. The repairs are qualified by SEM, AFM and through-focus wafer prints. Furthermore a new repair strategy involving in-situ AFM is introduced. Successful repair is demonstrated on real defects.

The door opener for EUV mask repair

The EUV-photomask is used as mirror and no longer as transmissive device. In order to yield defect-free reticles, repair capability is required for defects in the absorber and for defects in the mirror. Defects can propagate between the EUV mask layers, which makes the detection and the repair complex or impossible if conventional methods are used. In this paper we give an overview of the different defect types. We discuss the EUV repair requirements including SEMinvisible multilayer defects and blank defects, and demonstrate e-beam repair performance. The repairs are qualified by SEM, AFM and through-focus wafer prints. Furthermore a new repair strategy involving in-situ AFM is introduced. We will apply this new strategy on real defects and verify the repair quality using state of the art EUV wafer printing technology.

Improving extreme UV lithography mask repair

Driven by the consumer market and keeping pace with Moore’s law, integrated circuit components are continuously shrinking in dimension. To make smaller circuit features, the microelectronics industry is developing next-generation extreme-UV (EUV) lithography for high-volume chip manufacturing.1 The technology’s 13.5nm wavelength imposes very strict requirements on the quality of the involved optical elements, such as the light source, mirrors, and masks. In switching from the transmissive 193nm optics used in conventional photolithography to reflective EUV optics, the mask architecture has had to evolve. EUV masks include a multilayer Bragg mirror onto which an absorber pattern is defined. Defects can arise in these masks from multiple sources: optically imperfect mirrors due to local deviations from flatness; wrongly written absorber patterns; and even dust particles lying on the mask. A mask suitable for a production environment must be free of defects, both at blank level and absorber pattern level, so that they do not get printed onto the integrated circuit. However, even when meeting very strict quality standards, it is hard to avoid some defects. A solution to this quality gap can be mask repair. Electron-beam-based repair for transmissive photomasks has been around for 10 years.2 Since then, the microelectronics industry has extensively used the Carl Zeiss MeRiT R tool line based on this technology for the production of defect-free masks. Two different generations of the instrument addressed chip technology based on active component dimensions of 65 and 45nm.3 We are now upgrading the tool for 32nm component sizes for EUV masks.4 To start, an automated inspection machine visually maps defects on the EUV mask with respect to reference coordinates.5 The MeRiT tool navigates to the listed coordinates, and then reviews and fixes them. It usually performs the review by Figure 1. Example repair results for real opaque absorber defects on a 32nm extreme-UV (EUV) mask reticle. Scanning electron microscopy (SEM) top views of the defects, and views of the NXE:3100 EUV scanner wafer prints from the defect areas before (left) and after electronbeam etch repair (right).