Proceedings Article | 23 February 2005
KEYWORDS: Nickel, Photomasks, Chromium, Electroplating, Ultraviolet radiation, Quartz, Resistance, Electron beam lithography, Deposition processes, Electron beams
We present a fabrication method of high aspect ratio 100nm-scale nickel stamper using e-beam writing on the chrome/quartz mask for the injection molding of optical grating patterns. Conventional nickel stamper is fabricated by nickel electroplating process which is followed by photoresist patterning. In the nickel electroplating process, seed layer deposition step is indispensable process. Seed layer of several tens or hundreds nanometer thickness may cause dimension error after fabrication of 100nm-scale nickel stamper. In this paper, we suggest new fabrication process of a 100nm-scale nickel stamper simplified the fabrication process using blank mask. By using chrome layer on blank mask as seed layer of electroplating process, we would like to simplify nickel stamper fabrication process and improve accuracy of the fabricated nickel stamper. Generally, blank mask used in lithography process consists of chrome layer and photoresist layer on quartz substrate. The chrome layer is composed of UV anti-reflection layer of CrON and UV shade layer of Cr(94%Cr-6%C). The UV anti-reflection layer of CrON plays a role of absorption of UV light in UV lithography process in order to prevent interference of incident light and reflection light. Conventional blank mask consists in order of PR, CrON, Cr and Quartz (PR/CrON/Cr/Qz). However, anti-reflection layer of CrON is electrically nonconducting material. Therefore, we have prepared blank mask without anti-reflection layer of CrON in order to use chrome layer as a seed layer of electroplating process. In the PR mold fabrication, we have changed the dosage of electron beam of 9μmC/cm2, 8.5μC/cm2, and 8μC/cm2 to find optimum e-beam dosage for the PR/Cr/Qz blank mask. At the optimum electron beam dosage condition of 8.5μC/cm2, PR molds on PR/Cr/Qz blank mask were fabricated within the maximum error of 24nm. The fabricated PR mold shows height of 300±10nm. The electric resistance of Cr layer in the fabricated PR mold of PR/Cr/Qz mask is measured as 100Ω. In the electroplating process, unfortunately, the 75nm-thick Cr layer underneath PR of PR/Cr/Qz mask was damaged due to the high resistance. In this work, we have deposited additional seed layer materials of Ni as thick as 100nm. Finally we got the resistance of 10Ω. Instead of 75nm-thick Cr layer, if we prepare 200nm-thick Cr layer PR/Cr/Qz blank mask, we can carry out electroplating process without additional deposition process of seed layer. After nickel electroplating process, the thickness of the fabricated nickel stamper was approximately 330±20μm. The minimum width of the fabricated nickel line was measured as 116±6nm. Using SPM (scanning probe microscope), we have measured the height of nickel line as 240±20nm. Finally we have fabricated 2.5-AR (Aspect Ratio) nickel stamper with the minimum width of 116±6nm. The fabricated 100nm-scale nickel stamper showed the maximum error of 20nm comparing the PR mold. Consequently, we have optimized electron-beam dosage for the PR/Cr/Qz blank mask and fabricated 100nm-scale nickel stamper of the optical grating patterns with 2.5-aspect ratio.
