A new imprint directed self-assembly (DSA) route is developed for creating high resolution line patterns consisting of in-plane polystyrene-block-polydimethylsiloxane (PS-b- PDMS) cylinders. Resist line prepatterns are prepared by nanoimprint and trimmed by oxygen plasma to proper feature geometry and dimension. Registered block copolymer line patterns with exceptional long-range order are generated after DSA then, with the smallest half-pitch of 6 nm or so. Excellent stretching capability of PS-b-PDMS polymer chains indicates a broad process window for DSA. Initial pattern transfer results at 16.5 nm pitch imply the potential of this approach for future nanodevice fabrication at ultra-high pattern resolution.
Directed self-assembly (DSA) of block copolymers (BCPs) proves to be a viable solution for the ultrahigh density bit-patterned media (BPM) application. However, servo design integration is still extremely challenging since the servo layouts require more complex patterns than the simple arrays naturally achieved by the DSA process. We present an integration scheme to create BPM servo patterns by utilizing the BCP dot-array patterns. This proposed method is based on an imprint guided two-step DSA process, combined with conventional optical lithography to define two separate zones. Both the data zone and servo zone consist of self-assembled hexagonal dot arrays: a regular pattern in the data zone and an arbitrary pattern in the servo zone. This method was successfully used to fabricate a servo-integrated BPM template with an areal density of 1.5 Teradot/inch2 (Td/in.2) (Lo=22.3 nm). Using the fabricated quartz template, CoCrPt BPM media has been successfully patterned by nanoimprint lithography and subsequent ion-beam etching process on a 2.5 in. disk. Further, using patterned-in servo wedges on 1.5 Td/in.2 patterned CoCrPt media, we are able to close the servo control loop for track-following on a spin-stand test. The standard deviation of repeatable run-out over the full revolution is calculated to be about 4% of the 38.6 nm track pitch. This method is currently being used to fabricate a template at a much higher density of 3.2 Td/in.2 (Lo=15.2 nm).
We studied the erosion and feature stability of fused silica patterns under different template cleaning conditions. The conventional sulfuric acid and hydrogen peroxide mixture (SPM) cleaning is compared with an advanced nonacid process. Spectroscopic ellipsometry optical critical dimension measurements were used to characterize the changes in pattern profile with good sensitivity. This study confirmed the erosion of the silica patterns in the traditional acid-based SPM cleaning mixture (H 2 SO 4 +H 2 O 2 ) at a rate of ∼0.1 nm per cleaning cycle. However, the advanced nonacid cleaning process only showed critical dimension shift of ∼0.01 nm per cleaning. Contamination removal and pattern integrity of sensitive 20-nm features under MegaSonic assisted cleaning was also demonstrated.
We studied the erosion and feature stability of fused silica patterns under different template cleaning conditions. The
conventional SPM cleaning is compared with an advanced non-acid process. Spectroscopic ellipsometry optical
critical dimension (SE-OCD) measurements were used to characterize the changes in pattern profile with good
sensitivity. This study confirmed the erosion of the silica patterns in the traditional acid-based SPM cleaning mixture
(H2SO4+H2O2) at a rate of ~0.1nm per cleaning cycle. The advanced non-acid clean process however only showed
CD shift of ~0.01nm per clean. Contamination removal & pattern integrity of sensitive 20nm features under
MegaSonic assisted cleaning is also demonstrated.
A hydrogen silisesquioxane (HSQ) bilayer process and a top surface imaging (TSI) process are investigated for application as low-voltage electron beam resist systems. Namatsu, van Delft, and others have reported printing exceptionally small features using high-voltage electron beam exposure of HSQ at high-exposure doses (~2000 µC/cm2 at 100 kV). The shallow penetration depth of low-voltage electrons results in greatly reduced dose requirements, and smooth, high-resolution images are generated at 1 kV with an exposure dose of less than 60 µC/cm2. HSQ's high silicon content enable it to be used in a bilayer form utilizing reactive ion etching with an oxygen plasma, thus generating high aspect ratio images. TSI has been studied in the past by numerous researchers at low voltages using various TSI schemes. We investigate the use of a chemically amplified TSI resist process based on poly (t-BOC-hydroxystyrene). The effect of base quencher loading in the resist formulation on line edge roughness and resolution is investigated, and is found to have a dramatic influence. High-resolution, high aspect ratio images are printed down to 40 nm, and exhibit only moderate levels of line edge roughness. Furthermore, proximity effects at 1, 2, and 3 kV are examined and compared to simulation.
KEYWORDS: Etching, Electron beams, Monte Carlo methods, Photoresist processing, Hydrogen, Imaging systems, Electron beam lithography, Photomasks, Oxygen, Reactive ion etching
Namatsu, van Delft, and others have reported printing exceptionally small features using high voltage (>50kV) electron beam exposure of hydrogen silsesquioxane (HSQ). They also reported that HSQ has very high exposure dose requirements (~2000(mu) C/cm2 at 100kV). We have explored the utility of HSQ as a resist for low-voltage electron beam lithography. Because low energy electrons have a very limited penetration depth, a thin film imaging technique must be employed in conjunction with anisotropic oxygen reactive ion etching to generate the high aspect-ratio features required to provide adequate etch resistance for subsequent image transfer steps. HSQ's exceptionally low oxygen plasma etch rate makes it an excellent top layer for a bilayer process of this sort. High resolution, high aspect ratio images were printed with this system using 1kV electrons with an imaging dose of less than 60 (mu) C/cm2. The resulting features have very smooth sidewalls. Monte Carlo simulations have been performed for the exposure process and compared to experimental results.
Evangelia Tegou, Evangelos Gogolides, Panagiotis Argitis, Ioannis Raptis, George Patsis, Nikos Glezos, Zoilo Tan, Kim Lee, Phuong Le, Yautzong Hsu, Michael Hatzakis
An epoxidized novolac resist (EPR) has been evaluated for high resolution negative and positive tone electron beam lithography. EPR is a chemically amplified experimental resist developed in 'Demokritos' for e-beam lithography. It is characterized by high resolution, high sensitivity and very good post-exposure bake (PEB) latitude. Wet development after the post exposure bake (PEB) step gives a negative tone process while silylation and dry development gives a positive tone process. In this work, EPR's high resolution capabilities (below 0.25 micrometer) are demonstrated for both processes. Critical process parameters such as the photo acid generator (PAG) content of the resist, the PEB temperature and the effect of the delay time between exposure and PEB are examined. Delay effects are studied both for directly e-beam written resist profiles as well as for silylated profiles. The experimental work is accompanied by detailed modeling of lithographic processes, including acid diffusion, gel formation, silylation and delay effects.
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