Takayuki Hasegawa

EUV wavefront measurement of six-mirror optics using EWMS

The wavefront measurements have been performed with the EUV Wavefront Metrology System (EWMS) for the first time using a prototype projection optic as a test optic. The wavefronts of the test optic was measured at the five positions in the exposure field with the Digital Talbot Interferometer (DTI). The RMS magnitude of the wavefront errors ranged from 0.71 λ (9.58 nm) to 1.67 λ (22.75 nm). The results obtained with the DTI were compared to those with the Cross Grating Lateral Shearing Interferometer (CGLSI). As a result of a repeatability assessment, it was found that the EWMS can stably measure the wavefronts of the test optic. Additionally, unwrapping of the phase map was found to be related to the precision of the measurement.

Comparison of EUV interferometry methods in EUVA project

We are developing an at-wavelength interferometer for EUV lithography systems. The goal is the measurement of the wavefront aberration for a six-aspherical mirror projection optic. Among the six methods that EEI can measure, we selected CGLSI and PDI for comparison. PDI is a method well-known for its high accuracy, while CGLSI is a simple measurement method. Our comparison of PDI and CGLSI methods, verified the precision of the CGLSI method. The results show a difference between the methods of 0.33nm RMS for terms Z5-36. CGLSI measurement wavefronts agree well with PDI for terms Z5-36, and it is thought of as a promising method. Using FFT analysis, we estimated and then removed the impact of flare on the wavefront. As a result of having removed the influence of flare, the difference between CGLSI and PDI improved to only 0.26nm RMS in Zernike 5-36 terms. We executed PDI wavefront retrieval with FFT, which has not been used till now. By confirming that the difference between methods using FFT and Phase shift is 0.035nm RMS for terms Z5-36, we have proven that PDI wavefront analysis with FFT is possible.

Recent Progress of EUV Wavefront Metrology in EUVA

The recent experimental results of EUV wavefront metrology in EUVA are reported. EUV Experimental Interferometer (EEI) was built at the NewSUBARU synchrotron facility of University of Hyogo to develop the most suitable wavefront measuring method for EUV projection optics. The result is to be reflected on EWMS (EUV Wavefront Metrology System) that measures wavefront aberrations of a six-aspherical mirror projection optics of NA0.25, of a mass-production EUV lithography tool. The experimental results of Point Diffraction Interferometer (PDI) and Lateral Shearing Interferometer (LSI) are shown and the error factors and the sensitivity of astigmatism measurements of these methods are discussed. Furthermore, for reducing these kinds of errors, another type of shearing interferometer called DTI (Digital Talbot interferometer) is newly introduced.

Development of an experimental EUV interferometer for benchmarking several EUV wavefront metrology schemes

An experimental extreme UV (EUV) interferometer (EEI) using an undulator light source was designed and constructed for the purpose of developing wavefront measurement technology with the exposure wavelength of the projection optics of EUV lithography systems. EEI has the capability of performing five different EUV wavefront metrology methods.

EUV wavefront metrology system in EUVA

An Experimental extreme ultraviolet (EUV) interferometer (EEI) using an undulator as a light source was installed in New SUBARU synchrotron facility at Himeji Institute of Technology (HIT). The EEI can evaluate the five metrology methods reported before. (1) A purpose of the EEI is to determine the most suitable method for measuring the projection optics of EUV lithography systems for mass production tools.

Canon's development status of EUVL technologies

Canon has been developing the EUVL technologies for more than ten years. The current development status of EUVL technologies is presented. The small field exposure tool (SFET) is positioned as a cornerstone of the manufacturing technologies for the EUVL beta tool. LPP source and the DPP source are the most expecting methods for the EUVL beta tools.

EUV-wavefront metrology at EUVA

Precise measurements of the wavefront aberrations of projection optics with 0.1 nm RMS accuracy are indispensable to develop the extreme ultraviolet (EUV) lithography. In order to study measurement methods, we built the Experimental EUV Interferometer (EEI) that has built-in Schwarzschild-type optics as test optics and was supplied with EUV radiation of 13.5 nm in wavelength from a synchrotron radiation facility as a source light. The EEI can evaluate several methods of EUV interferometory replacing optical parts easily. Those methods are dividable into two categories, namely point diffraction interferometer (PDI) and lateral shearing interferometer (LSI) and those were experimentally compared. Finally, 0.045nm RMS of reproducibility was achieved with PDI method and the residual systematic error after removing specified errors was reduced to 0.064nm RMS excluding axial symmetrical aberrations. In addition, one of LSI-type methods also proved to have almost enough accuracy for the assembly of the projection optics.

LPP-based reflectometer for characterization of EUV lithography systems

An EUV reflectometer, based on a laser-produced plasma (LPP) light source, has been developed for characterization of EUV lithography systems. The reflectometer consists of the LPP light source, a prefocusing toroidal mirror, a grating monochromator, a polarizer, a beam intensity monitor, a refocusing toroidal mirror and a sample stage. The LPP light source is driven by a Nd:YAG laser; the laser beam is focused onto a copper tape target. A debris mitigation system that uses a rotating shutter was developed. Higher-orders formthe grating monochromator were suppressed to less than 0.2% of incident beam intensity by total reflection of three grazing incidence mirros. In order to compensate for beam intensity instability, a beam intensity monitor using a grating beamsplitter was installed between the refocusing mirror and the sample. Beam intensity instability can be corrected to less than 0.1% by using the beam intensity monitor.

Development status of Canon's full-field EUVL tool

EUVL is the most promising candidate of 32 nm generations and beyond. In this paper, we present Canons development status of EUVL technologies. The system design of the EUV full field high volume manufacturing tool (VS2) is under way. The specification of VS2 is presented in this paper. The fabrication of six-aspheric-mirror prototype projection optics (PO1) of NA 0.3 has been started. The PO1 is fabricated to evaluate and improve our technologies of polishing and measuring the figure of mirrors. We present some results of the figuring accuracy of the mirror. EUVL will be required to resolve sub-twenty nm L&S patterns. We are studying off-axis illumination technologies and high- NA technologies. The simulation results of the resolution capability and the DOF are presented.

Wavefront Metrology for EUV Projection Optics by Soft X-ray interferometry in the NewSUBARU

Precise measurement of the wavefront errors of projection optics with 0.1 nm RMS accuracy is necessary to develop extreme ultraviolet (EUV) lithography. To accomplish this, an experimental EUV interferometer was developed and installed at the NewSUBARU SR facility, with which various types of interferometry experiments can be carried out by replacing optical parts easily. The wavefront error of a Schwarzschild‐type test optics was measured by several methods. Finally, reproducibility below 0.045 nm RMS was achieved with the point diffraction interferometer (PDI) method, and the residual systematic error was reduced to 0.066 nm RMS excluding axial symmetric aberration.