Andrew R. Eckert

Electron-beam SAFIER process and its application for magnetic thin-film heads

We have coupled the SAFIER™ (shrink assist film for enhanced resolution) process with electron-beam lithography for the fabrication of the write top pole structures for thin-film heads. The SAFIER™ process is designed to physically shrink trench patterns and contact holes with very little deterioration of the resist profile. In this article, we will present the experimental results of the SAFIER™ process for the fabrication of the write top pole. We investigate the SAFIER™ process concerning several key processing issues, including shrink resolution capability, repetition of the SAFIER™ process, shrink-sensitive baking conditions, resist sidewall profile, and line edge roughness (LER) after shrinking of the trench. The experimental results show that this process not only shrinks the size of resist trenches and contact holes, but also improves LER and critical dimension variation. We demonstrate the capability of printing top pole structures with pole widths of sub-20nm in a 0.30-μm-thick resist (aspect ra...

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...

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.

Resist formulation effects on contrast and top-loss as measured by 3D-SEM metrology

We have implemented 3D-SEM metrology to measure resist height as a function of dose for negative e-beam resists. Converting the resist height to a dissolution rate produces a new way to determine resist contrast. We have used this method to demonstrate improved aspect ratios for a low contrsat resist compared to a high contrast resist. We have also found that increasing the cross-linker concentration causes an increase in the resist dissolution rate and contrast. We have measured this change in contrast using the 3D-SEM technique for three resists systems with varying cross-linker concentration. We have plotted the dissolution rate as a function of e-beam exposure intensity, and used this information to model how contrast effects the final resist profile. Both the model and the experimental data suggest that the higher contrast resist gives a straighter side-wall angle with a negligible effect on the final CD.

E-beam proximity effect parameters for sub-100-nm features

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 α, β and η and what they depend on.

Method for read width determination at high track densities by imaging the magnetic field emitted by narrow Cu waveguides

In this paper, we have characterized the magnetic field from waveguides with widths ranging from 1 /spl mu/m to < 100 nm, in both single and dual wire geometrics. Our Cu waveguides are fabricated by a combination of conventional optical lithography and electron beam lithography. The magnetic field of the wire is detected using giant magnetoresistance (GMR) read sensors, and the measurements are performed.

Three-dimensional imaging of isolated lines of negative e-beam resist

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.