Keith Mountfield

Heat-Assisted Magnetic Recording

Due to the limits of conventional perpendicular magnetic recording, it appears that alternative technologies are needed at areal densities >500 Gb/in2. Heat-assisted magnetic recording (HAMR) is a promising approach to extend areal densities to 1 Tb/in2 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

Challenges in 1 Teradot∕in.2 dot patterning using electron beam lithography for bit-patterned media

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 Z...

Light Delivery Techniques for Heat-Assisted Magnetic Recording.

Heat-assisted magnetic recording (HAMR), also known as hybrid recording, has been proposed to enable storage densities greater than 1 Tb/in2 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.

Near Field Heat Assisted Magnetic Recording with a Planar Solid Immersion Lens

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.

Fabrication of sub-50 nm critical feature for magnetic recording device using electron-beam lithography

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 w...

Spin stand characterization of dielectric optical waveguides fabricated on AlTiC sliders for heat-assisted magnetic recording

Heat-assisted magnetic recording (HAMR), also known as hybrid recording, is one of the technologies proposed for extending hard disk drive areal densities beyond a Tb/in2. Due to their planar nature and compatibility with existing hard disk drive head fabrication techniques, dielectric optical waveguides have been suggested as a means for delivering light directly to the recording medium or near field optical transducer. In this paper we present spin stand experimental results from a dielectric optical slab waveguide fabricated on an AlTiC slider.

Fabrication of dielectric optical waveguides on AlTiC sliders for heat-assisted magnetic recording

In this paper we show the feasibility to integrate waveguide optics into magnetic recording sliders using current recording head manufacturing techniques. Thin film planar waveguides were deposited on ceramic substrates and structured to yield rectangular waveguides positioned on the front face of recording sliders that fly at 20 nm spacing over a glass disk. The thin film waveguide is equipped with a diffraction grating that allows light to be coupled into the waveguide and directed towards the air bearing surface. Optical properties of selected waveguide stacks are presented together with photographs of etched waveguide structures on AlTiC sliders.

Electron beam lithography for data storage: Quantifying the proximity effect as a function of CAD design and thin metal layers

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 als...

Electron-beam lithography method for sub-50-nm isolated trench with high aspect ratio

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 of isolated trenches with chemically amplified positive resist

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.