High-aspect ratio silicon structures by displacement Talbot lithography and Bosch etching

Abstract

Despite the fact that the resolution of conventional contact/proximity\nlithography can reach feature sizes down to ~0.5-0.6 micrometers, the accurate\ncontrol of the linewidth and uniformity becomes already very challenging for\ngratings with periods in the range of 1-2 {\\mu}m. This is particularly relevant\nfor the exposure of large areas and wafers thinner than 300{\\mu}m. If the wafer\nor mask surface is not fully flat due to any kind of defects, such as\nbowing/warpage or remaining topography of the surface in case of overlay\nexposures, noticeable linewidth variations or complete failure of lithography\nstep will occur. We utilized the newly developed Displacement Talbot\nlithography to pattern gratings with equal lines and spaces and periods in the\nrange of 1.0 to 2.4 {\\mu}m. The exposures in this lithography process do not\nrequire contact between the mask and the wafer, which makes it essentially\ninsensitive to surface planarity and enables exposures with very high linewidth\nuniformity on thin and even slightly deformed wafers. We demonstrated pattern\ntransfer of such exposures into Si substrates by reactive ion etching using the\nBosch process. An etching depth of 30 {\\mu}m or more for the whole range of\nperiods was achieved, which corresponds to very high aspect ratios up to 60:1.\nThe application of the fabricated gratings in phase contrast x-ray imaging is\npresented.\n