Justin Hwu

Integration of nanoimprint lithography with block copolymer directed self-assembly for fabrication of a sub-20 nm template for bit-patterned media

We propose a novel strategy to integrate the nanoimprint lithography (NIL) technique with directed self-assembly (DSA) of block copolymer (BCP) for providing a robust, high-yield, and low-defect-density path to sub-20 nm dense patterning. Through this new NIL-DSA method, UV nanoimprint resist is used as the DSA copolymer pre-pattern to expedite the DSA process. This method was successfully used to fabricate a 1.0 Td in(-2) servo-integrated nanoimprint template for bit-patterned media (BPM) application. The fabricated template was used for UV-cure NIL on a 2.5-inch disk. The imprint resist patterns were further transferred into the underlying CoCrPt magnetic layer through a carbon hard mask using ion beam etching. The successful integration of the NIL technique with the DSA process provides us with a new route to BPM nanofabrication, which includes the following three major advantages: (1) a simpler and faster way to implement DSA for high-density BPM patterning; (2) a novel method for fabricating a high-quality dot pattern template through an iterative imprint-DSA-template procedure; and (3) an uncomplicated integration scheme for implementing non-periodic servo features with BCP patterns, thus accelerating the transition of moving the DSA technique from laboratory research to the BPM manufacturing environment.

Mueller matrix measurement of asymmetric gratings

Scatterometry has been used extensively for the characterization of critical dimensions (CDs) and detailed sidewall profiles of periodic structures in microelectronics fabrication processes. In most cases devices are designed to be symmetric, although errors could occur during the fabrication process and result in undesired asymmetry. Conventional optical scatterometry techniques have difficulties distinguishing between left and right asymmetries. We investigate the possibility of measuring grating asymmetry with Mueller matrix spectroscopic ellipsometry (MM-SE) for a patterned hard disk sample prepared by a nanoimprint technique. The relief image on the disk sometimes has an asymmetrical sidewall profile, presumably due to the uneven separation of the template from the disk. Cross section SEM reveals that asymmetrical resist lines are typically tilted toward the outer diameter direction. Simulation and experimental data show that certain Mueller matrix elements are proportional to the direction and amplitude of profile asymmetry, providing a direct indication to the sidewall tilting. The tilting parameter can be extracted using rigorous optical critical dimension (OCD) modeling or calibration methods. We demonstrate that this technique has good sensitivity for measuring and distinguishing left and right asymmetry caused by sidewall tilting, and can therefore be used for monitoring processes for which symmetric structures are desired.

Low-temperature plasma etching of high aspect-ratio densely packed 15 to sub-10 nm silicon features derived from PS-PDMS block copolymer patterns

The combination of block copolymer (BCP) lithography and plasma etching offers a gateway to densely packed sub-10 nm features for advanced nanotechnology. Despite the advances in BCP lithography, plasma pattern transfer remains a major challenge. We use controlled and low substrate temperatures during plasma etching of a chromium hard mask and then the underlying substrate as a route to high aspect ratio sub-10 nm silicon features derived from BCP lithography. Siloxane masks were fabricated using poly(styrene-b-siloxane) (PS-PDMS) BCP to create either line-type masks or, with the addition of low molecular weight PS-OH homopolymer, dot-type masks. Temperature control was essential for preventing mask migration and controlling the etched features shape. Vertical silicon wire features (15 nm with feature-to-feature spacing of 26 nm) were etched with aspect ratios up to 17 : 1; higher aspect ratios were limited by the collapse of nanoscale silicon structures. Sub-10 nm fin structures were etched with aspect ratios greater than 10 : 1. Transmission electron microscopy images of the wires reveal a crystalline silicon core with an amorphous surface layer, just slightly thicker than a native oxide.

Application of analytic scanning electron microscopy to critical dimensions metrology at nanometer scale

Scanning electron microscopy (SEM) metrology involves significant uncertainty of the linewidth measurement because the SEM image brightness is a complex function of SEM setup, pattern materials, and shape. In this work, the authors used an analytical SEM for critical dimensions metrology applications on a quartz nanoimprint template. The SEM was tuned to find the best condition for consistent operation. Beam characterization was done using BEAMETR beam measurement technique. SEM images of templates were taken at optimum conditions. The measurements were done using two methods: regular imaging processing software based on brightness threshold and using physical model based processing tool myCD. The quartz template was then measured using transmission electron microscopy cross sections at selected sites to reveal profile information as metrology comparison reference. The metrology capability and limitations of analytical SEM with regular image processing were identified. The considerable improvement of accu...

Study of spin-coated resist coverage on nanoscale topography using spectroscopic ellipsometry

Using spectroscopic ellipsometry and rigorous coupled wave analysis, we studied the spin-coated resist coverage on 72.6 nm pitch line-and-space patterns of various depths (from ∼20 to ∼130 nm). Within the margin of measurement error, we find the tested nano-patterns have no apparent effect on the spin-coated resist thickness. The result suggests that, during the spinning, the resist ceased to flow at a critical thickness much larger than the pattern depth, and the resist thinning afterwards was dominated by solvent evaporation. The methods and results demonstrated in this work can improve the characterization and process control in a number of applications where spin coating on high-density nano-scale topographies is required.

SEM metrology on bit patterned media nanoimprint template: issues and improvements

Critical dimension measurement is the most essential metrology needed in nanofabrication processes and the practice is most commonly executed using SEMs for its flexibility in sampling, imaging, and data processing. In bit patterned media process development, nanoimprint lithography (NIL) is used for template replication and media fabrication. SEM imaging on templates provide not only individual dot size, but also information for dot size distribution, the location of dots, pitch and array alignment quality, etc. It is very important to know the SEM measurement limit since the feature nominal size is less than 20 nm and the dot feature size and other metrics will relate to the final media performance. In our work an analytical SEM was used. We performed and compared two imaging analysis approaches for metrology information. The SEM beam was characterized using BEAMETR test sample and software for proper beam condition setup. A series of images obtained on a 27 nm nominal pitch dot array patterns were analyzed by conventional brightness intensity threshold method and physical model based analysis using myCD software. Through comparison we identified the issues with threshold method and the strength of using model based analysis for its improvement in feature size and pitch measurement uncertainty and accuracy. TEM cross sections were performed as accuracy reference for better understanding the source of measurement accuracy deviation.

Spectroscopic ellipsometry optical critical dimension measurements of templates and imprinted resist for patterned magnetic media applications

The authors have applied spectroscopic ellipsometry optical critical dimension (SE-OCD) measurement to grating templates and imprinted resist patterns with a pitch of 72.6 nm, corresponding to a track density of 350 ktpi (kilotracks per inch) for discreet track recording media. Their experiments indicate that SE-OCD is sensitive in detecting topography features in template profiles. The measurement of imprinted resist pattern is complicated by parameter correlation. Comparison of SE-OCD reported template and imprinted resist profiles can be used to study imprint pattern fidelity.

Scatterometry measurement of asymmetric gratings

Scatterometry has been used extensively for the characterization of critical dimensions (CD) and detailed sidewall profiles of periodic structures in microelectronics fabrication processes. So far the majority of applications are for symmetric gratings. In most cases devices are designed to be symmetric although errors could occur during fabrication process and result in undesired asymmetry. The problem with conventional optical scatterometry techniques lies in the lack of capability to distinguish between left and right asymmetries. In this work we investigate the possibility of measuring grating asymmetry using Mueller matrix spectroscopic ellipsometry (MM-SE). A patterned hard disk prepared by nano-imprint technique is used for the study. The relief image on the disk sometimes has asymmetrical sidewall profile, presumably due to the uneven separation of the template from the disk. The undesired tilting resist profile causes difficulties to the downstream processes or even makes them fail. Cross-section SEM reveals that the asymmetrical resist lines are typically tilted towards the outer diameter direction. The simulation and experimental data show that certain Mueller matrix elements are proportional to the direction and amplitude of profile asymmetry, providing a direct indication to the sidewall tilting. The tilting parameter can be extracted using rigorous optical critical dimension (OCD) modeling or calibration method. We demonstrate that this technique has good sensitivity for measuring and distinguishing left and right asymmetry caused by sidewall tilting, and can therefore be used for monitoring processes, such as lithography and etch processing, for which symmetric structures are desired.

P1–15: Patterning of high density magnetic nanodot arrays by imprint lithography with hole tone template

Nanoimprint Lithography presents unique opportunities for high density patterning due to its advantages of sub-10nm resolution capability and high throughput. Imprint and pattern transfer with Pillar tone template were widely studies recently. However, there are several critical issues that still remain very challenging, including fabrication of pillar templates and pattern reverse from imprint holes to nano dots array at high density. In this Paper, we will demostrated the feasibility of imprint with hole tone template and its application in high-density nanodot array patterning. The authors have successfully demonstrated hole-tone template fabrication process and pattern transfer results with imprint pillar. The profile of imprint resist pillar was analyzed with cross-section scanning electron microscope(SEM). Pattern was transferred to underneath Co alloy thin films by ion beam milling into aligned dots with pitch of 50nm. Magnetic dots array were investigated with SEM and M-H loop measurement. Strong perpendicular anisotropy was induced by the patterning process. Magnetic measurement reveals through ion milling process, magnetization reversal was changed from domain wall pinning dominated to Stoner-Wohlfarth coherent rotation dominated. Coercivity and Remanence change during Ion beam etching were discussed. Extendibility to ultra-high density patterning is also investigated.

Application of analytic SEM to CD metrology at nanometer scale

SEM metrology involves uncertainty of the linewidth measurement because the SEM signal formation is an extremely complex process. In this work, we used an analytical SEM for CD metrology applications on quartz nanoimprint template. The SEM was tuned first to find the best reasonable condition for consistent operation. Beam characterization was done using BEAMETR beam measurement technique. SEM images of templates were taken at optimum conditions. The measurements were done using a) regular imaging processing software and b) using physical model based processing tool myCD. The quartz template was then measured using TEM crossections at selected sites to reveal profile information as metrology comparison reference. The metrology capability and fundamental limitation of analytical SEM operation with regular imaging processing was identified. Information about SEM setup and materials was used. The considerable improvement using the physical modeling imaging process was found.