Larissa Juschkin

Comparison of different source concepts for EUVL

There are some candidates discussed as potential high power EUV sources for EUV lithography. Laser produced and discharge produced plasmas are most promising. In principle, the most efficient steady state plasma can be well defined with respect to plasma temperature and density. However, the conversion efficiency of a practical EUV source is mainly determined by the efficiency of plasma generation and heating and by the dynamics during the emitting phase. The different approaches to achieve the most efficient EUV source imply different heating mechanisms, different plasma geometries, different plasma densities and different time scales. Moreover, each approach has individual technical aspects that influence the efficiency and the technical chances of realization. A general approach for comparing different EUV source concepts is presented based on a discussion of fundamental aspects of the plasma generation and based on technical issues.

Metrology tools for EUVL-source characterization and optimization

The development of suitable radiation sources is a major challenge for extreme ultraviolet lithography (EUVL). For the optimization of these sources and for the determination of the parameters needed for the system design and the system integration these sources have to be characterized in terms of the absolute in-band power, the spectral distribution in the EUV spectral region and the out-band spectral regions, the spatial distribution of the emitting volume and the angular distribution of the emission. Also the source debris has to be investigated. Therefore, JENOPTIK Mikrotechnik GmbH is co-operating with the Laser Laboratorium Goettingen, the Physikalisch-Technische Bundesanstalt (PTB) and the AIXUV GmbH in developing ready-for-use metrology tools for EUVL source characterization and optimization. The set of the tools employed for EUV-source characterization is presented in detail as well as concepts of for calibration and measurement procedures.

Status of EUV-lamp development and demonstration of applications

Compact, flexible laboratory sources offer advanced flexibility in developing components for EUV-lithography by supplementing beamlines at storage rings. Hence, they are the basis for transferring EUV-metrology and technology to individual, industrial and university R&D labs. Laboratory sources have features similar to the sources planned for EUVL production on one hand and offer high flexibility like storage ring beamlines on the other hand. Discharge based EUV sources offer some flexibility, which allow for tuning of the spectral and spatial characteristics of their emission. Depending on the system complexity sources can be supplied in various forms ranging from low budget semi-manual systems over OEM components to fully automatic stand-alone sources. As power scaling has been demonstrated by just adding higher power generators and cooling, these sources can be matched to various levels of flux requirements. AIXUV’s discharge based EUV-sources have been used as beamline supplement for tasks closely connected with the development of EUV-Lithography. Examples are: development of tools for EUV source characterization (prototype testing, qualification and calibration), “in-band-EUV” open frame resist exposure, reflectometry of EUV mask blanks and EUV mirrors and for basic research using XUV radiation as thin film analytics and EUV microscopy.

High-throughput EUV reflectometer for EUV mask blanks

A prototype of a reflectometer for masks and mask blanks has been set-up in autumn 2003 for in-house quality check of EUV mask blanks at Schott Lithotec. The target specifications are those under discussion as SEMI standard for EUV mask blank reflectometry. Additionally, the identified demands for semiconductor capital investment for future actinic EUV metrology, high throughputs and small measuring spots, were taken into account for the tool development. Effective use of the emission from a laboratory discharge source is achieved by using polychromatic reflectometry, which has been shown to deliver results about a factor of 100 faster with the same source power and needs less mechanical overhead than a monochromatic reflectometer. The hardware concept, first results and discussion of a test of the performance with respect to resolution, uncertainty and reproducibility will be represented. Jointly with the Physikalisch-Technische Bundesanstalt’s laboratory for radiometry at BESSY II the traceability to storage ring metrology, the calibration and the validation of the concepts will be assessed.

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.

High speed reflectometer for EUV mask-blanks

AIXUV GmbH and partners have developed a high speed Reflectometer for EUV mask-blanks which is fully compliant with the SEMI-standard P38 for EUV-mask-blank metrology. The system has been installed in June 2004 at SCHOTT Lithotec AG. It features high throughput, high lateral and spectral resolution, high reproduci-bility and low absolute uncertainty. Using AIXUVs EUV-LAMP and debris mitigation, low cost-of-ownership and high availability is expected. The spectral reflectance of up to 3 mask-blanks per hour can be measured with at least 20 spots each. The system is push button-controlled. Results are stored in CSV file format. For a spot size of 0.1×1 mm2, 2000 spectral chan-nels of 1.6 pm bandwidth are recorded from 11.6 nm to 14.8 nm. The reflectance measurement is based on the comparison of the sample under test to two reference mirrors calibrated at the PTB radiometry laboratory at BESSY II. The three reflection spectra are recorded simultaneously. For each spot more than 107 photons are ac-cumulated in about 20 s, providing statistical reproducibility below 0.2 % RMS. The total uncertainty is below 0.5 % absolute. Wavelength calibration better than 1 pm RMS over the whole spectral range is achieved by refe-rence to NIST published wavelengths of about 100 xenon emission lines. It is consistent with the wavelength of the krypton 3d-5p absorption resonance at 13.5947 nm to better than 2 pm.