Electron beam lithography presents a great opportunity for bit-patterned media (BPM) applications due to its resolution capability and placement accuracy. However, there are still many challenges associated with this application including tool availability, resist capability, process development, and associated metrology needs. This paper will briefly discuss these challenges and show the results of sub-25 nm pitch (1 Tdots/in.(2)) patterning from both a simulation and experimental perspective. The simulation results indicate that the energy contrast between the exposed and unexposed areas goes down quickly as the pitch size gets smaller and smaller, making it more difficult for image formation of high-resolution dot patterning. The strategy to overcome this issue is to optimize the development process, which aims at increasing the resist contrast and enlarging the process window. By using this approach, the authors have successfully demonstrated a pitch resolution down to 18 nm for a positive-tone resist ZEP520 and 12 nm for a negative-tone resist silsesquioxane, corresponding to the areal density of similar to 2.0 and similar to 4.5 Tdots/in.(2), respectively. Using the ZEP520 resist process, a Cr dot array with a pitch of 21 nm (similar to 1.5 Tdots/in.(2)) for template fabrication is demonstrated. High-quality scanning electron microscopy and atomic force microscopy images were used as primary metrology for both the dot size uniformity and the placement accuracy analysis. (c) 2007 American Vacuum Society.

Electron beam lithography has been implemented with a chemically amplified negative tone NEB-31 resist to fabricate the write top pole and read sensors for magnetic recording. To better understand the proximity effect and optimize these two critical components in electron beam patterning, Monte Carlo simulation with SELID software has been employed to characterize the energy distribution of the write top pole structure and simulate the resist profile in the break point (BP) region. To obtain a sharp BP angle and a pole area that has a uniform and narrow pole width, the authors have optimized the computer-aided design and the yoke/pole dose ratios based on their simulation results. The authors have also experimentally verified these results with NEB-31 resist. In addition, the electron backscattering effect from the relevant metallic underlayers, such as NiFe and Ta of varying thickness on the top pole critical dimension as a function of BP angle was simulated and analyzed. Experiments were conducted to verify the simulation results, and both are in good agreement.

Due to the limits of conventional perpendicular magnetic recording, it appears that alternative technologies are needed at areal densities > 500 Gb/in(2). Heat-assisted magnetic recording (HAMR) is a promising approach to extend areal densities to 1 Tb/in(2) and beyond. All of the unique components necessary for a working HAMR system have been demonstrated. Although HAMR permits writing on high Hc media with lower magnetic fields and can produce higher write gradients than conventional magnetic recording, head/media spacing and the development of high Hc media with small grains remains challenging.

In this paper we present experimental heat assisted magnetic recording results using a planar solid immersion mirror (PSIM) fabricated on an Al2O3–TiC slider. The heads were flown at a velocity of 14 m/s, 20–25 nm above a Co/Pt multilayer medium which was deposited on a 60 mm glass disk. It was found that the track width and carrier-to-noise-ratio (CNR) increased with the applied magnetic field. Recording experiments were also performed with PSIMs terminated with 125 µm apertures. This led to narrower tracks and smaller CNR values for the same applied fields compared to recording with a PSIM only.

Understanding the proximity effect is crucial to fabricating repeatable sub-100 nm features for magnetic recording devices. Top down CD-SEM measurements have been used to measure the proximity effect parameters in negative and positive resists at dimensions below 100 nm. The goal of this work is to experimentally determine the values of the parameters alpha, beta and eta and what they depend on.

We have characterized the e-beam proximity effect as it applies to the write pole break-point angle of magnetic recording heads. These narrow isolated negative resist lines have been measured using an automated CD-SEM. The CD data allows us to quantify the e-beam proximity effect on silicon wafers with thin metallic films of varying thickness. Nickel and tantalum have atomic numbers of 28 and 73, respectively, and this difference is quantified by the increase in the CD of the Ta films compared to Ni. The CD was found to change at a rate of 0.17nm per degree of break-point angle for the Ni films, and 0.25nm per degree for Ta. We have analyzed the experimental data by comparing it to two relevant models. First, we compare the data to the traditional expression used to describe e-beam exposure, a double Gaussian. From both the CD data and the double Gaussian, we calculate a proximity effect term we refer to as the dose fraction. This dose fraction has a linear relationship with the “eta” parameter, which also relates the contribution of forward to back scattered electrons in the final exposure profile. We determine both a dose fraction, and the “eta” parameter, for each substrate material and thickness. Second, we compare this dose fraction term to a simple Rutherford elastic scattering model. The final outcome of this work is a quantifiable measure of how the break-point angle contributes to the final CD of the write pole when employing e-beam lithography. This work also demonstrates a practical way to quantify the e-beam proximity effect by the calculation of dose fraction and “eta” as a metric of metal layer material and thickness.

This paper reviews issues leading to technology changes in magnetic recording heads. Magnetic recording systems balance three competing needs: (1) signal-to-noise, (2) thermal stability, and (3) the ability to write magnetic transitions on high coercivity media. In this paper particular attention is paid to write issues with a design and processes for a single turn perpendicular write head. The use of chemical mechanical polish (CMP) and electron beam lithography were key ingredients leading to successful magnetic recording head fabrication. A CMP process was developed to planarize copper, nickel iron, and alumina to a planar even interface, forming a single coil with a self-aligned process. The fabricated head was demonstrated to have an extremely fast response and a recording density of up to 93 Gb/in(2), limited by perpendicular media noise.

We have implemented traditional CD-SEM metrology complimented with the 3D imaging capability of the VERASEM 3D CD-SEM from Applied Materials. 3D imaging is performed by tilting the SEM beam to capture images at two unique angles. Reconstruction of these images allows for the determination of resist thickness and sidewall angle at the same point the critical dimension, CD, is measured. These three output parameters provide the user with automated multi-metric lithographic process control. We have used these techniques to characterize e-beam lithography of isolated lines in ~0.6μm of negative resist at CDs between ~50 and ~100 nm. The flexibility of our e-beam lithography system allows us to expose an array of identical features with 30 distinct dose values over a small area of a wafer. We have characterized the resist CD and thickness as a function of small incremental decreases in dose. As the dose decreases so does the CD of the isolated resist line at a rate of ~1 nm per 1μC/cm2 of area exposure. At a nominally high dose where the isolated line CD is ~100 nm the resist is measured by 3D imaging to be close to full thickness. The main observation is that the resist thickness erodes at a rate of ~5 nm in height per every 1nm decrease in CD down to the resolution limit of 50-60 nm. As the dose is further lowered the resist is then completely washed away. This subtle but significant loss in resist etch mask integrity could not have been observed by traditional top-down CD-SEM metrology alone. This also demonstrates the tilt capability of the VERASEM 3D to measure very thin resist films of ~100 nm. Additionally, we have successfully used this methodology to characterize this effect as a function of isolated line length from ~0.5-2.0μm, and resist thickness from ~0.25-0.6 μm. The CD is strongly correlated with the total isolated line length due to the e-beam proximity effect, while the resist erosion rate remains fairly constant. The resist erosion rate is also similar for the resist films regardless of initial thickness. However, we also confirm the trend that identical area doses produce larger CDs for thicker resist films with some subtle effects for the thinner films.

We report an electron-beam lithography method for printing and plating sub-50 nm isolated trenches with a high aspect ratio (AR) for the nanofabrication of magnetic thin-film heads. To eliminate the issues of resist footing and resist residue in the narrow trench process, we coated a thin dissolution layer of polymethylglutarimide (PMGI) as an undercoat layer between a seed layer and a resist layer. The undercoat PMGI layer was easily and more quickly dissolved than the top resist layer, so it completely cleared the trench during the develop process. In addition, a vertical sidewall at the bottom of the narrow trench was achieved by controlling the processing conditions, e.g., bake temperature and thickness of the dissolution layer. All of these allowed us to facilitate plating the narrow trench with a high magnetic moment material. In this work, narrow trenches were electroplated with both 1.0 T NiFe and 1.8 T CoNiFe alloys. We demonstrated the capability of fabricating narrow electrodeposited magnetic write top pole structures with a critical dimension (CD) of 30 nm in a 0.24 μm resist (AR=8:1) and a CD of 22 nm in a 0.11 μm resist (AR=5:1).

Heat-assisted magnetic recording (HAMR), also known as hybrid recording, has been, proposed to enable storage densities greater than 1 Tb/in(2) in hard disc drives while circumventing the superparamagnetic limit. Light is delivered in the near field to the recording medium to heat just the spot which is to be recorded. Techniques based on apertures, antennas, waveguides,, and solid immersion lenses have been suggested for delivering substantial amounts of optical power into subwavelength spots in the near field. A practical transducer for HAMR may require a combination of techniques.

An electron beam lithography method for printing and plating sub-50 nm isolated trenches with a high aspect ratio has been developed for the nanofabrication of magnetic thin film heads. To eliminate the issues of resist footing and resist residue in the narrow trench process, we put a thin dissolution layer of polymethylglutarimide (PMGI) as an undercoat layer between a seed layer and a resist layer. The undercoat dissolution layer competely cleared off the seed layer by the developer solution such that the sides of the narrow trench are vertical, particularly at the bottom of the narrow trench, thus facilitating plating the narrow trench with a high magnetic moment material. In this work, the narrow trenches were electroplated with both 1.0T NiFe and 1.8T CoNiFe. Three key issues in our trench process will be discussed here, including: 1) critieria for the selection of the undercoat dissolution layer materials; 2) processing conditions control , e.g. the thickness and the bake temperature of the dissolution layer to achieve vertical and smooth sidewalls; and 3) PEB delay on the narrow trench CD control, pattern degeneration, and the results from the resist top coat (RTC) experiments. With our new narrow trench process, we demonstrated the capability of fabricating narrow electrodeposited magnetic write structures with a CD of 35 nm in 0.35 μm resist (AR=10:1) and a CD of 30 nm in 0.25 μm resist (AR=8:1).

Electron beam lithography has been implemented with a commercially available DUV chemically amplified positive resist. Post exposure delay stability in vacuum was found to be non-critical. Post exposure delay after removal from vacuum in our clean room is a critical variable, with a change in critical dimension of approximately 0.6 nm per minute of PEB delay. This result was achieved without amine filtration. Wafers were transported in cassettes from the e- beam exposure tool to an FSI Polaris 2000 photocluster tool. The PEB delay effect on critical dimensions can be significantly reduced by using a water soluble protective top coat with a slight change in nominal does. E-beam lithography was performed with a Leica VB6 operating at 50eV, using a n 800 micrometers field, and a 12.5 nm minimum grid size. The original CAD had a negative bias added to compensate for any proximity effect, to take advantage of dose control to achieve targeted line width, and to optimize exposure latitude. Characterization with a dual beam FIB/SEM to obtain cross-sectional SEM images, typically demonstrate a foot on plated structures from the initial resist profile. A 30 percent decease in nominal dose was observed on device wafers compared to scout wafers. Device wafers have metal structures buried below the approximate 100 nm thick plating seed layer that also cause profile changes. This is presumably due to the back scattering of the electrons from the initial area of exposure. Plating rates in isolated trenches also show a strong dependence o n the critical dimension of the narrow resist trench. Plated structures with critical dimensions of 80 nm in 0.65 microns of resist were fabricated.

Using 3D-boundary element modeling, guidelines for designing an ultra-high density perpendicular system were defined. Both geometrical and material influences were investigated. The theoretical principles developed to choose dimensions and materials were experimentally verified using a wafer test structure and spin-stand experiments with a 60nm wide focused ion beam trimmed head.

Summary form only given. The complete presentation was not made available for publication as part of the conference proceedings.

A new reflected mode magneto-optic spatial light modulator (R-MOSLM) has been developed for miniature optical correlators and computers. A factor of 4 improvement in pixel switching sensitivity, compared to the conventional transmission mode magneto-optic spatial light modulator, has been achieved by the use of narrower drive lines, and burying the conductor into the film. A factor of 3 higher resolution and a factor of 2 higher optical efficiency have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively. The progress that has been made in the design of the R-MOSLM, issues concerning its fabrication, a comparison by finite element analysis of field modeling to experimentally determined current requirements to drive individual lines, and some optical characteristics are discussed.

This paper is a report on the characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of Miniature Ruggedized Optical Correlators for Optical Pattern Recognition. Pixel size is under one mil center to center, one-third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems.

This paper is a report on the advanced development and characteristics of a new high resolution, high frame rate, reflected R-MOSLM. This effort is aimed at the production of miniature ruggedized optical correlators (MROC) for optical pattern recognition. Pixel size is under one mil center to center, one third the dimension of present transmission mode devices, thereby reducing the optical path length by an order of magnitude. This development includes optimization of the optical and functional characteristics of the MOSLM for Mil Spec Systems. The device research and process development has been performed at Carnegie Mellon University NSF Data Storage System Center under contract from Litton Data Systems. The Litton Electron Device Division is transitioning the device to production. The MROC system description is described in companion paper (1959-09).

A new reflected mode magneto-optic spatial light modulator (R-MOSLM) has been developed for miniature optical correlators and computers. An improvement by a factor of four in pixel switching sensitivity, compared to the conventional transmission mode magneto-optic spatial light modulator (T-MOSLM), has been achieved by the use of narrower drive lines, and burying the conductor into the film. A higher resolution by a factor of three and a higher optical efficiency by a factor of two have also been achieved by the use of smaller pixels and narrower pixel gaps. The smaller pixels and improved switching sensitivity permit an order of magnitude reduction in optical path length and increase in frame rate, respectively.<>