Grey-scale electron beam lithography has been used to create high-efficiency (63%, output normalized) blazed gratings suitable for use at extreme ultraviolet (EUV) wavelengths (i.e. 13.4 nm). The total blaze height at these wavelengths is ≈ 7 nm. The surface topography was generated in a single processing step in hydrogen silsesquioxane (HSQ). This material converts to SiO 2 upon exposure, forming a robust substrate for subsequent operations, unlike conventional organic resists. The HSQ is overcoated with a Mo/Si multilayer to provide reflectivity at EUV wavelengths. The grating efficiency is determined by the fidelity of the profile to the ideal and by the surface roughness of the HSQ. A region of the resist response curve was identified that enabled sufficient topography to be generated while maintaining the surface roughness of the resist below 2.5 nm RMS. Large area ( 0.5 x 2.0 mm 2 ) gratings were fabricated, and the delivered dose profile was adjusted during the course of the exposure to compensate for observed delay-time/reciprocity effects in HSQ. INTRODUCTIONHigh efficiency gratings in the soft X-ray and extreme ultraviolet (EUV) regimes are desirable in many applications as monochromators.1 In this paper we report on the fabrication of a highly efficient blazed grating for use as a spectral purity filter in the lithographically interesting wavelength range centered around 13.4 nm. The grating is coated with a Mo/Si reflective multilayer and used at near-normal incidence in first order.Currently available sources for EUV lithography systems, whether synchrotron 2 or laser 3 /pinch 4 /discharge 5 generated plasma based are broadband. Because there are no materials that are transparent at EUV wavelengths, only reflective optical systems can be employed. This means that essentially all wavelengths, down to the deep-UV, from the source can propagate through the system to the wafer. However, in order to minimize the heat load on the optics infrared (IR) radiation must be prevented from passing through, while ultraviolet (UV) wavelengths cannot be permitted to travel to the wafer plane and expose the resist. For these reasons a spectral purity filter is required to eliminate all but the desired EUV wavelengths, and it must transmit these with very high efficiency.A blazed grating (Figure 1) can perform this function effectively. When the angle of a diffracted order coincides with the specular reflection angle from a single blaze, then essentially all of the power is contained in that order. 6 The conditions are:

Diffractive optics play an important role in a variety of fields such as astronomy, microscopy, and lithography. In the extreme ultraviolet region of the spectrum they have been difficult to make due to the extremely precise control required of their surface structure. We have developed a robust fabrication technique that achieves the required topographic control through the deposition of a thin film of Si on a Cr etch stop. We have fabricated binary phase gratings using this approach that have an efficiency of 80% of the theoretical maximum. This technique could be applicable to similar binary phase structures requiring precise topography control.

As the development of extreme ultraviolet (EUV) lithography progresses, interest grows in the extension of traditional optical components to the EUV regime. The strong absorption of EUV by most materials and its extremely short wavelength, however, makes it very difficult to implement many components that are commonplace in the longer wavelength regimes. One such example is the diffuser often implemented with ordinary ground glass in the visible light regime. Here we demonstrate the fabrication of reflective EUV diffusers with high efficiency within a controllable bandwidth. Using these techniques we have fabricated diffusers with efficiencies exceeding 10% within a moderate angular singlesided bandwidth of approximately 0.06 radians.

Articles you may be interested inFabrication of trench nanostructures for extreme ultraviolet lithography masks by atomic force microscope lithography J.Thermal modeling of extreme ultraviolet and step and flash imprint lithography substrates during dry etchThe authors have developed processes for producing nanoscale programed substrate defects that have applications in areas such as thin film growth, extreme ultraviolet lithography, and defect inspection. Particle, line, pit, and scratch defects on the substrates between 40 and 140 nm wide, 50-90 nm high have been successfully produced using e-beam lithography and plasma etching in both silicon and hydrogensilsesquioxane films. These programed defect substrates have several advantages over those produced previously using gold nanoparticles or polystyrene latex spheresmost notably, the ability to precisely locate features and produce recessed as well as bump-type features in ultrasmooth films. These programed defects were used to develop techniques for planarization of film defects and results are discussed.

For many thin-film applications substrate imperfections such as particles, pits, scratches, and general roughness, can nucleate film defects which can severely detract from the coating's performance. Previously we developed a coat-and-etch process, termed the ion beam thin film planarization process, to planarize substrate particles up to ∼70 nm in diameter. The process relied on normal incidence etching; however, such a process induces defects nucleated by substrate pits to grow much larger. We have since developed a coat-and-etch process to planarize ∼70 nm deep by 70 nm wide substrate pits; it relies on etching at an off-normal incidence angle, i.e., an angle of ∼70° from the substrate normal. However, a disadvantage of this pit smoothing process is that it induces defects nucleated by substrate particles to grow larger. Combining elements from both processes we have been able to develop a silicon-based, coat-and-etch process to successfully planarize ∼70 nm substrate particles and pits simultaneously to at or below 1 nm in height; this value is important for applications such as extreme ultraviolet lithography (EUVL) masks. The coat-and-etch process has an added ability to significantly reduce high-spatial frequency roughness, rendering a nearly perfect substrate surface.