Günter Hess

EUV mask image placement management in writing, registration, and exposure tools

Due to the non-telecentricity of the EUV illumination, the EUV mask flatness budget dictates the use of an electrostatic chuck in the exposure tool. Since the mask backside flattening provided by the electrostatic chuck in the exposure tool is very different from the 3-point mounts currently employed to hold reticles in pattern generation and registration measurement tools, this raises the question of which mounting techniques to apply in future patterning and registration tools. In case drastic changes need to be made to the tool configurations, it is important to know, and as early as possible, whether backside chucking of reticles, via an electrostatic or vacuum chuck, is absolutely required or if a 3-point mounting scheme can suffice in these tools. Using finite element simulations, the effects on EUV mask image placement of stressed layers and their patterning, as well as substrate and chuck non-flatness were predicted for these different conditions. The results can be used to calculate image placement error budgets and determine what substrate and blank specifications are needed for the implementation of EUV at the 32-nm node.

Determination of mask layer stress by placement metrology

The present paper will show an approach for a local and global stress determination by the application of a Leica LMS IPRO II mask registration tool. Changes in placement due to a full or partial layer removal on single materials as well as material stacks with respect to a reference grid were determined. Simulation using finite element modeling was conducted to calculate stress values from the placement information. Finally, an estimate was made of the acceptable stress level for a sample design to meet placement requirements for future lithography nodes.

EUVL mask blanks: Recent results on substrates, multilayers and the dry-etch process of TaN-absorbers

Continuous reduction of feature size in semiconductor industry and manufacturing integrated circuits at low costs requires new and innovative technology to overcome existing limitations of optics. Tremendous progress in key areas like EUVL light source technology and manufacturing technology of EUVL masks with low defect rates have been made recently and EUVL is the leading technology capable to be extended so Moores law, the shrinkage of IC critical features, can continue to be valid. SCHOTT Lithotec has introduced all relevant technology steps to manufacture EUV mask blanks, ranging from Low Thermal Expansion Material (LTEM) with high quality substrate polishing to low defect blank manufacturing. New polishing and cleaning technologies, improved sputter technology and updated metrology enable us to routinely produce EUVL mask blanks meeting already many of the roadmap requirements. Further R&D is ongoing to path the way to the production of EUV blanks which meet all requirements. An important focus of this paper is to present the recent results on LTEM substrates, which include defect density, roughness and flatness simultaneously, as well as EUVL multilayer properties such as defect density, optical properties like reflectivity and uniformity in the EUV range and optical resistance to cleaning steps. In addition the design of EUVL absorber material will be discussed, including optical performance at EUV wavelength and its contrast behavior. Finally, IMS Chips has developed the dry etch process of these EUV Mask Blanks by optimizing etch selectivities, profiles and etch bias. Results on CD uniformity, linearity and iso/dense bias will be presented.

The first full-field EUV masks ready for printing

ASMLs first EUV alpha demo tool (ADT) is ready for lithographic set up, driving the need for qualified and fully compliant EUV masks. EUV reflection masks are different in blank and mask processes compared to current technologies e.g. masks for 193nm. Although in recent years individual EUV mask parameters have been demonstrated, it is only with the fabrication on the ADT mask set that fully compliant masks have been made. In this paper we discuss the typical requirements of a EUV full-field mask, and show first results from achieving the important milestone of fabricating EUV masks.

Production challenges of making an EUV mask blank

Mask Blanks for EUV Lithography require a lot of new properties and features compared to standard COG blanks. Starting from completely new low thermal expansion substrate materials with significantly improved surface quality over multilayer coatings for EUV reflection, buffer layers, up to new absorber layers with improved dry etching and inspection properties. This papers introduces in the special features of Low Thermal Expansion Materials (LTEM), their manufacturing and the special metrology for the Coefficient ofThermal Expansion (CTE). We will look into some details ofpolishing methods for much better flatness of the substrates. The process and the metrology of low defect EUV multilayer coatings will be elucidated and some aspects of this will be explained in detail. In addition we will present new results from no-chrome alternative absorber materials.

Performance data of a variable transmission phase shifting mask blank for 193nm lithography enhanced by inspection contrast tuning

Schotts already commercially available two layer Ta/SiO2 phase shift system can be tuned from 6% up to 40% transmission for 157, 193 and 248 nm lithography wavelengths. Thus one film patterning process provides a wide product range. Attenuated phase shift masks for 6%, 20% and 30% transmission at 193nm were produced. Tests for laser stability and chemical durability show excellent performance. The phase shifting film achieves a high etch selectivity to the substrate. Dry etch process development is done at IMS chips in Stuttgart, Germany, to provide our customers the service of a good start process for patterning. Results of phase and transmission uniformity are included. Our newest development enhances the layer system and provides a better contrast for inspection in reflection mode. Transmission of our standard two layer Ta/SiO2 PSM system is below the required 20% at inspection wavelengths. The reflectivity of 30% to 40% can be lowered by insertion of an additional contrast layer. The thickness of this contrast layer is adjusted to achieve the required reflection at inspection wavelengths, while the other film thicknesses are tuned to preserve the desired transmission and 180° phase shift at the design wavelength. As first examples 6% and 20% transmission PSM for 193 nm were tested. Reflection at 257 nm and 365 nm inspection wavelengths can be lowered from initial 30% to 40% down to about 10%.

Antireflection solutions for next generation 193-nm binary and phase-shifting masks

Reflections occur at every interface of a mask and are known as flare. Flare effects have a negative impact on the resist exposure at the wafer level. In this paper total antireflection (AR) solutions are presented to eliminate flare effects at mask level. These are next generation binary and phase shifting mask blanks, where AR coatings are effective not only on top of the absorber, but also eliminate internal as well as back side reflections. Substrate reflection can be reduced both internally and externally by an order of magnitude to below 0.5%. Internal (backside) reflection of a binary chrome or a phase shifting layer are reduced from about 40% to below 0.1%. Reflection in the etched area is also addressed and reduced by an order of magnitude. A sophisticated absorber AR coating is presented, where reflection at 193 nm lithography can be reduced to zero while at the same time reflection at 257 nm inspection wavelength is tuned to the maximum sensitivity range of 7% to 20%.

Performance data on new tunable attenuating PSM for 193-nm and 157-nm lithography

A new phase shifting film system based on tantalum and silicon dioxide is presented. The tantalum film works as a transmission control layer and furthermore as an etch stop layer due to its good etch selectivity. The silicon dioxide phase control layer is tuned to 180° phase shift. Excellent laser stability and chemical durability were already shown. The two layer system can be easily tuned to various transmission values for three different lithography wavelengths. Transmission and phase shift uniformity fulfill already the final production specifications according to ITRS. An optimized deposition process yields excellent film surface roughness values equal to an uncoated substrate. Defect density could be significantly reduced recently. First SEM pictures of structured films show promising results.