24/10/2016 15:00



Extreme ultraviolet (EUV) wavelength range (5 nm to 30 nm) offers unique opportunities such as the potential to achieve the highest spatial resolution, reaching below ten nanometers, in photolithography. This opportunity comes together with various scientific challenges such as spectral analysis and filtering of the EUV light source, and optical component design and development. Here we describe the development of a new class of optical components for enhancing the imaging performance of EUV photolithography tools that enables fabrication of more energy efficient and faster electronic devices. The first part of the talk explains a broadband spectrometer based on a high resolution transmission grating for spectral monitoring of the EUV light sources from EUV to visible wavelengths. The transmission geometry enables a compact design and a straightforward alignment. Measurements that were carried out at three different EUV sources provide detailed and comprehensive spectral information that is immediately available for analysis and optimization of the source conditions towards achieving a higher chip production in EUV lithography process. In the second part of the talk described is a mirror design that can be used to enhance the spectral quality of EUV light sources. 

Our design consists of a diffractive Fresnel zone plate patterned in the surface of a curved mirror to achieve spectral purification, i.e., removing undesired wavelengths of the EUV light sources. The removed light is recycled to produce more EUV light. This design achieves four orders of magnitude purification and provides a 35% improvement in efficiency. The last part describes a new class of adaptive multilayer mirrors that can be used to correct wavefront distortions or reflectance degradations. These adaptive optics contain integrated crystalline piezoelectric thin films of which the film thickness can be adjusted by an externally applied voltage. Because the optics substrates typically have an amorphous structure, so far it was not possible to grow high quality crystalline piezoelectric films on them. We utilized crystalline nanosheets on these substrates to grow the highest quality piezoelectric films (PbZr0.52Ti0.48O3, PZT). 

The PZT films show a record high piezoelectric coefficient of 98 pm/V, although the piezoelectric response in this case is still reduced due to clamping by the substrate. We minimized the clamping effect by depositing films with a columnar structure, which enhances the voltage-controlled change in film thickness. In these films we measured a piezoelectric response of 250 pm/V, the highest value reported on glass substrates. Importantly, the developed films can produce a stroke of 25 nm. This order of magnitude is useful when considering to correct EUV wavefront distortions.


   Elektrik-Elektronik Müh. Böl.