Mask development for nanoscale atom beam lithography.

摘要

Lithography, the process of transferring an image of a master pattern into a polymeric resist, has provided the foundation for advances in integrated circuit technology for the past half-century. This has been accomplished by shrinking the wavelength of the exposing radiation from visible light in the early years to the deep ultra-violet photons of today. This paradigm of reducing wavelength may continue with electrons, light ions and extreme ultraviolet, or it may shift to imprinting techniques which have molecular level resolution. These techniques face challenges for which manufacturable solutions are not known. Three of these challenges are addressed in this thesis. Specifically, we developed a technique for measuring the distortion of stencil masks for ion beam lithography, developed a novel radiation resistant coating to protect ion beam lithography masks from ion implantation damage, and explored the advantages of using energetic neutral atoms instead of ions for nanolithography.;We present, for the first time, an experimental method for evaluating thermal-and radiation-induced distortion of stencil masks during ion projection lithography (IPL). The approach uses a new technique, atom beam proximity lithography, to copy the mask onto glass photomask plates under normal IPL exposure conditions and to infer the resulting mask distortion from that of the copy, as measured by a Zeiss LMS IPRO pattern-placement metrology tool. The use of energetic neutral atoms instead of ions is necessary to avoid distortion in the copying process itself due to charging of the photomask blank.;We also report on a process for coating stencil masks for ion and atom beam nanolithography with a radiation resistant coating of amorphous hydrogenated carbon. The coating is formed by an optimized two-step process in which a high stress, hard (hardness=3GPa), stiff (elastic modulus-30 GPa) film is first deposited by plasma enhanced chemical vapor deposition (PECVD) in a helium atmosphere from methylmethacrylate precursor onto silicon or silicon nitride stencil mask. The stress of the film is subsequently relieved by annealing at 250°C, a process that lowers the hardness to 0.6 GPa and the elastic modulus to 12 GPa. An optimized O2/SF6 reactive ion etching process transfers the stencil mask pattern into the protective coating without undercutting, redeposition, or other etching artifacts on the scale of 5 nm. Qualitative evaluation shows that compressive stress remains below 20 MPa for ion doses up to 5 mC/cm2 and that the stress of the implanted films is stable in atmosphere for extended periods of time (more than a few months).;The masks described above were used to make a detailed comparison of line-edge roughness (LER) in ion and atom beam nanolithography, showing for the first time that 15 nm LER in ion beam proximity lithography with nominally conducting masks is completely absent in atom beam lithography. We show, in addition, that the use of a high pressure charge transfer cell in atom beam lithography has significantly higher resolution than either ion beam lithography or atom beam lithography without the charge transfer cell.