Barry Lieberman

Advanced photolithographic mask repair using electron beams

Mask repair plays an important role in yielding advanced masks that support the lithography roadmap. It is also one of the more challenging parts of mask fabrication. Electron beam induced deposition and etching have shown great potential for mask repair applications. Our work has demonstrated that e-beam mask repair provides the superior resolution and damage-free process that is needed to support mask generations for the 32nm technology node and beyond. This article describes an installed e-beam mask repair tool at Intel Mask Operation and discusses the capabilities of this enabling technology based on results obtained from repairing masks with “defects” intentionally inserted into the design (programmed defect masks). Specifically, results are presented for quartz etch repair of alternating phase shift masks and TaBN absorber etch of extreme ultraviolet masks, two of the most difficult types of mask to repair using conventional methods.

Evaluation of the Capability of a Multibeam Confocal Inspection System for Inspection of EUVL Mask Blanks

Extreme ultraviolet (EUV) multilayer defects (phase defects) are a defect type unique to extreme ultraviolet lithography (EUVL) masks. A manufacturable inspection capability for these defects is key to the success of EUV lithography. Simulations of EUV scattering from multilayer defects suggest that defect printability is related to the phase error induced by the defect, which is in turn strongly coupled to the size of a multilayer surface protrusion or intrusion. We can adopt a strategy of measuring the multilayer surface to detect phase defects. During the past year a working group composed of members of Intel Corporation, Lawrence Berkeley and Lawrence Livermore National Laboratories, and International Sematech searched for a commercial tool for EUVL mask substrate and blank inspection. This working group established the tool requirements, methodologies for tool evaluation, collected data and recommended a supplier for further development with International Sematech. We collected data from several vendors and found that a multibeam confocal inspection (MCI) system had a capability significantly better than the tools used today. We will present our strategy, requirements, methodologies and results. We will discuss in detail our unique programmed substrate and multilayer defect masks used to support the tool selection, including their actinic characterization. We will present data that quantifies the inspection capability of the MCI system.

EUV mask pilot line at Intel Corporation

The introduction of extreme ultraviolet (EUV) lithography into high volume manufacturing requires the development of a new mask technology. In support of this, Intel Corporation has established a pilot line devoted to encountering and eliminating barriers to manufacturability of EUV masks. It concentrates on EUV-specific process modules and makes use of the captive standard photomask fabrication capability of Intel Corporation. The goal of the pilot line is to accelerate EUV mask development to intersect the 32nm technology node. This requires EUV mask technology to be comparable to standard photomask technology by the beginning of the silicon wafer process development phase for that technology node. The pilot line embodies Intels strategy to lead EUV mask development in the areas of the mask patterning process, mask fabrication tools, the starting material (blanks) and the understanding of process interdependencies. The patterning process includes all steps from blank defect inspection through final pattern inspection and repair. We have specified and ordered the EUV-specific tools and most will be installed in 2004. We have worked with International Sematech and others to provide for the next generation of EUV-specific mask tools. Our process of record is run repeatedly to ensure its robustness. This primes the supply chain and collects information needed for blank improvement.

Rigorous model for registration error due to EUV reticle non-flatness and a proposed disposition and compensation technique

The non-telecentricity of EUV lithography exposure systems translates into a very severe specification for EUV mask flatness that is typically 10 times tighter than the typical current specification for masks used in 193 nm wavelength exposure systems. The mask contribution to the error budget for pattern placement dictates these specifications. EUV mask blank suppliers must meet this specification while simultaneously meeting the even more challenging specification for defects density. This paper suggests a process flow and correction methodology that could conceivably relax the flatness specification. The proposal does require that the proposed method of clamping the mask using an electrostatic chuck be accurate and reproducible. However, this is also a requirement of the current approach. In addition, this proposal requires the incorporation of an electrostatic chuck into a mask-shop metrology tool that precisely replicates the behavior of the chuck found in the EUV exposure tool.

Magnetron reactive sputtering of TaN and TaON films for EUV mask applications

We have developed and characterized a stack of TaN (absorber) and TaON (ARC) using reactive magnetron sputtering method. Two DOE (design of experiments) were performed with varying gas and power parameters and their effects on the various film parameters are discussed. We characterized the stress, uniformity, reflectivity (for defect inspection and EUV wavelengths), defect adders, and etch performance. Film property characterization was performed with AFM, Optical reflectance measurement tool, Particle inspection tool and profilometer. Optimized film stack met or exceeded ITRS guideline for EUV lithography mask with film stress less than 200MPa, inspection wavelength reflectivity at 9%, and thickness uniformity less than 5%. Defect adder number (< 0.5 / cm2) was a strong function of underlying film surface roughness and cleanliness of surface as well as deposition parameters.

Study of rigorous effects and polarization on phase shifting masks through simulations and in-die phase measurements

As lithography mask process moves toward 45nm and 32nm node, phase control is becoming more important than ever. Both attenuated and alternating PSMs (Phase Shift Masks) need precise control of phase as a function of both pitch and target sizes. However conventional interferometer-based phase shift measurements are limited to large CD targets and requires custom designed target in order to function properly, which limits phase measurement. Imaging simulations, both, in a rigorous and a Kirchhoff regime, show the dependency of the phase in the image plane of a microlithography exposure tool on numerical aperture, polarization, and on the so-called balancing of the mask for features close to the size of the used wavelength. For these feature sizes, the image phase does not coincide with the etch depth equivalent phase calculated from the nominal depth and optical constants of the shifter material. Additionally, for PSMs generating phase jumps deviating from 180°, the resulting phase in the image plane of a microlithography exposure tool depends on the transmitted diffraction orders through the aperture of the imaging system. Consequently Zeiss, in collaboration with Intel, has started the development of a laterally resolving Phase Metrology Tool (Phame) for in-die phase measurements. In this paper we present this optical metrology tool capable of phase measurement on individual line/spaces down to 120nm half pitch. Alternating PSM, Attenuated PSM, Cr-less masks were measured on various target sizes and simulations were performed to further demonstrate the capability and implication of this new method to measure the scanner relevant phase in-die, taking into account NA, polarization, and rigorous effects.

PRIMADONNA: a system for automated defect disposition of production masks using wafer lithography simulation

Todays reticle inspection tools can provide a wealth of information about defects. We introduce here a system called DIVAS: Defect Inspection Viewing, Archiving, and Simulation that fully uses and efficiently manages this wealth of defect information. In this paper, we summarize the features of DIVAS and describe in more detail PRIMADONNA, one of its components. Current reticle defect specifications are based, primarily, on defect size. Shrinking design rules, increasing MEEF and use of Optical Enhancement Techniques cause size to be an inadequate criterion for disposition. Furthermore, visual disposition of defects is not automated, strictly reproducible, or directly tied to wafer lithography. To compensate for these inadequacies, reticle specifications are set conservatively adding direct and hidden costs to the manufacturing process. PRIMADONNA, utilizing Prolith as the simulation engine, retrieves all defect and reference images saved from a KLA SLF77 inspection tool and processes them through a series of increasingly rigorous simulation stages. These include pre-filtering, aerial image formation, and post filtration. Difference metrics are used to quantify a defects wafer impact. We will report results comparing PRIMADONNA decisions to manual classifications for a significant volume of inspections. Correlation between PRIMADONNA results and AIMS metrology will be presented.

DIVAS: fully automated simulation based mask defect dispositioning and defect management system

This article presents the evolution of the first fully automated simulation based mask defect dispositioning and defect management system used since late 2002 in a production environment at Intel Mask Operation (IMO). Given that inspection tools flag defects which may or may not have any lithographic significance, it makes sense to repair only those defects that resolve on the wafer. The system described here is a fully automated defect dispositioning system, where the lithographic impact of a defect is determined through computer simulation of the mask level image. From the simulated aerial images, combined with image processing techniques, the system can automatically determine the actual critical dimension (CD) impact (in nanometers). Then, using the product specification as a criteria, can pass or fail the defect. Furthermore, this system allows engineers and technicians in the factory to track defects as they are repaired, compare defects at various inspection steps and annotate repair history. Trends such as yield and defect commonality can also be determined. The article concludes with performance results, indicating the speed and accuracy of the system, as well as the savings in the number of defects needing repair.