Markus Renno

Recent results on EUV mask blank multilayers and absorbers

Mask Blanks for EUV Lithography require a lot of new properties and features compared to standard Chrome-on-Glass mask blanks. SCHOTT Lithotec has introduced all relevant technology steps to manufacture EUV mask blanks. Starting from completely new low thermal expansion substrate materials with significantly improved surface quality over multilayer coatings for EUV reflection up to new absorber layers with improved dry etching and inspection properties. New polishing and cleaning technologies, improved sputter technology and updated metrology enable us to routinely produce EUVL mask blanks meeting already many of the ITRS roadmap requirements. Further R&D is ongoing to path the way to the production of EUV mask blanks which meet all requirements An important focus of this report is to present recent results on EUVL multilayer properties such as defect density, optical properties like reflectivity and uniformity in the EUV range. In addition a new design of EUVL absorber material will be reported, including optical performance at inspection wavelength, dry etch performance and resistance to cleaning steps. Finally improvements on our metrology methods for EUVL components, such as high throughput EUV-reflectometry will be elucidated.

Absorber stack optimization toward EUV lithography mask blank pilot production

EUV Lithography requires high end quality defect free layers from the backside coating to the absorber stack. Low thermal expansion materials (LTEM) substrates with super flat surfaces are already available with low defect backside coating for E-Chuck technology. The multilayer stack is well developed from a physical point of view and major effort relies nowadays on the layer defectivity. On the other hand, absorber stack becomes one of the main challenges in terms of stress, optical behavior for ultraviolet wavelengths and dry etching behavior. Schott Lithotec is currently developing absorber stack solutions that will fulfill the requirements of next generation lithographies. There are several options for achieving the mechanical, optical and chemical specs for buffer layers and absorber coatings. Some of them are already integrated in our production processes. Buffer layers were evaluated and reach almost the physical and chemical level necessary to fit with the mask processing. TaN based absorber coatings were designed and deposited by an ion beam sputter tool optimized for low defect deposition (LDD-IBS). The chemical composition of our layer and its manufacturing process is already optimized to achieve high quality etching behavior. The current results of defect density for the absorber stack will be presented.

Development of a new PSM film system for 157-nm extensible to high-transmission 193 nm lithography

A new attenuated phase shifting film system for 157 nm lithography is presented. The system is designed for 6% transmission but is tunable to higher values. Tests for laser stability and chemical durability show excellent performance. First results of defect density and phase and transmission homogeneity are presented. The phase shifting film achieves a high etch selectivity to the substrate. The film system is extensible to be used as a high transmission phase shifter for 193 nm lithography. Further it is feasible to repair the film system using electron beam repair technology.

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.

NIL template manufacturing using a variable shaped e-beam writer and a new pCAR

A resolution of 45nm dense lines has been be realized in a 100nm thick commercial available positive tone chemically amplified resist (pCAR) using the Leica SB350 variable shaped beam writer. On the basis of this resist process and by optimization of photomask blank material as well as by adaptation of chrome and quartz etching processes, a nanoimprint template technology has been developed which enables patterning of 50nm dense lines. The sensitivity of the selected pCAR as well as the performance of the implemented dynamical stage control of the Leica pattern generator, facilitates an acceptable throughput even for complex pattern. We characterized the templates in terms of feature profile, CD linearity and pattern fidelity. The final imprinting of different pattern proved the applicability of the manufactured stamps for the nanoimprint technology.

New solutions for inspection contrast tuning, enhanced chemical durability, and a new ultrahigh-transmission PSM

Schotts already commercially available two layer Ta/SiO2 phase shift system can be tuned from 6% up to 30% transmission for 157, 193 and 248 nm lithography wavelengths. Thus one film patterning process provides a wide product range. 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. Our newest development enhances our phase shift layer system. An inspection layer provides an improved contrast for inspection at 257 nm and 365 nm by adjusting reflection to the optimum range from 7% to 20%. Chemical durability against standard mask cleanings was already shown to be good but can be further enhanced by an protection layer. Furthermore a new two layer phase shift system was designed achieving ultra-high transmission above 90% at 193 nm lithography wavelength as an alternative to hard shifter 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.

Update on the EUVL mask blank activity at Schott Lithotec

Schott Lithotec has introduced all relevant technology steps to manufacture EUV mask blanks in its advanced quality mask blank manufacturing line -- ranging from Low Thermal Expansion Material (LTEM) high quality substrate polishing to low defect blank manufacturing. New polishing and cleaning technologies, improved sputter technology and updated metrology enable us to produce EUVL mask blanks meeting already some of the roadmap requirements. Further R&D is ongoing to path the way to the pilot production of EUV blanks which meet the beta-specifications end of 2005. We present the status of our EUVL substrate program and report on the recent results of our activities for low defect multilayer, buffer and absorber coating including new absorber materials. Recent results from the production of full LTEM EUV blanks with multilayer, buffer and absorber coatings will be presented. Process steps in the EUVL mask blank fabrication in a production environment were characterized in terms of defects; the process improvement potential is discussed. We will also throw a light on the aspects of changed layer properties after a longer period of storage. In addition, special metrology methods for EUVL components are currently being developed within the program. The status of the high throughput EUV-Reflectometer for mask blanks will be presented. We developed new processes to achieve EUVL requirements.

Dry etch behavior of different TaN absorber layers for EUVL mask making

Extreme Ultraviolet Lithography (EUVL) is the favourite next generation lithography candidate for IC device manufacturing with feature sizes beyond 32nm. Different absorber layers and manufacturing concepts have been published for the fabrication of reflective EUVL masks. A mandatory step in the EUVL mask making is the patterning of sub 100nm features. The layer composition of such a TaN absorber consists of an anti reflective coating (ARC) on top of a base layer. We investigated the dry etch behaviour of TaN based absorbers with four different top ARC layers. Our focus was to determine a dependency of patterning criteria e.g. etch selectivity, minimum resolution, CD uniformity and linearity on the different ARC layers. Before, the deposition parameters of the top ARC layers have been optimized by SCHOTT Lithotec towards minimum stress and the appropriate reflectance property at the 257nm inspection wavelength. The mask blank exposure was done on a 50kV Vistec SB350 MW variable shaped e-beam writer using a 300nm thick Fuji FEP171 resist film. Our test pattern covered a quality area of 132mm x 132mm and comprised dense/iso line structures and contacts from 60nm-1200nm. Testmasks with the four different TaN based absorbers have been dry etched on an Oerlikon mask etcher III. The dry etch recipe and parameters have been kept constant for the different absorber testmasks. Line and contact hole patterns with a minimum feature size of ~70nm and perpendicular profiles have been realized. CD uniformity on 180nm L&S and linearity measurements on dense and iso features from 100nm-1200nm havbe been carried out. Overall, a TaN based absorber including dry etch process has been developed, able to fulfill the requirements for IC device manufacturing with feature sizes down to 22nm - suitable for EUV-Lithography.

Process window enhancement for 45-nm node using alterable transmission phase-shifting materials

A case study was carried out investigating the influence of different transmission and phase shift materials on lithographic performance at 45 nm node. The bilayer approach for embedded attenuated Phase Shift Masks (EAPSM) offers the advantages to adjust phase shift and transmission independently. The transmission of Ta/SiO2 can be tuned up to 40% depending on the required application. Three different PSM blank types with the stacks Ta/SiO2-6%, Ta/SiO2-30% and Ta/SiON-30% have been manufactured and characterized. Afterwards, an identical line pattern, consisting of different feature sizes and duty cycles, has been patterned in each of the three PSM types as well as in the MoSi-6% for reference. Using the AIMSTM 45-193i tool we have evaluated the lithographic performance of the four PSM in terms of contrast and process latitude using unpolarized and TE polarized illumination. The case study showed that the process window for Ta/SiO2-6% is comparable to standard MoSi-6%. For dense line application a 6% EAPSM is preferable. The Ta/SiO2-30% EAPSM provides a significantly larger process window for higher duty cycles compared to MoSi-6%. This means a 50% increase in depth of focus (DOF) at 10% exposure latitude (EL). Therefore for logic application with higher duty cycles a EAPSM material with 30% transmission is preferable.