A Silicon-Based, Sequential Coat-and-Etch Process to Fabricate Nearly Perfect Substrate Surfaces

Abstract

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.

Analysis of Printability of Scratch Defect on Reflective Mask in Extreme Ultraviolet Lithography

“…Since a phase defect is printable even though the surface of the multilayer may be completely flat, various techniques have been devised to detect defects at the exposure wavelength (13.5 nm). [1][2][3][4] Some researchers have pursued ways of producing practical masks [5][6][7][8][9][10][11] with a very low defect density of 0.003 defects/cm 2 , as measured with 25-nm-diameter polystyrene latex spheres (PSLs). 12,13) Smoothing deposition and the introduction of an underlying layer to cover defects 10) have been found to be effective ways of reducing the printability of particles and bump defects.…”

“…[1][2][3][4] Some researchers have pursued ways of producing practical masks [5][6][7][8][9][10][11] with a very low defect density of 0.003 defects/cm 2 , as measured with 25-nm-diameter polystyrene latex spheres (PSLs). 12,13) Smoothing deposition and the introduction of an underlying layer to cover defects 10) have been found to be effective ways of reducing the printability of particles and bump defects. On the other hand, simulations are useful for investigating the influence of defects on the creation of the printed image of a device pattern with a half pitch of 32 nm or less.…”