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6CCVD Research

Burger Model as the Best Option for Modeling of Viscoelastic Behavior of Resists for Nanoimprint Lithography

At a Glance

Section titled “At a Glance”
MetadataDetails
Publication Date2021-11-04
JournalMaterials
AuthorsHubert Grzywacz, Piotr Jenczyk, MichaƂ Milczarek, Marcin MichaƂowski, Dariusz M. Jarząbek
InstitutionsWarsaw University of Technology, Institute of Fundamental Technological Research
Citations9
AnalysisFull AI Review Included

Technical Documentation & Analysis: Viscoelastic Modeling for Nanoimprint Lithography

Section titled “Technical Documentation & Analysis: Viscoelastic Modeling for Nanoimprint Lithography”

Executive Summary

Section titled “Executive Summary”

This documentation analyzes the research on modeling the viscoelastic behavior of PMMA resists for Nanoimprint Lithography (NIL) using Atomic Force Microscopy-based Nanoindentation (AFM-NI). The findings highlight the critical role of ultra-hard materials, such as those provided by 6CCVD, in achieving reliable nanoscale mechanical characterization.

  • Core Achievement: The Burger model was identified as the most suitable constitutive model for representing the viscoelastic and viscoplastic behavior of PMMA thin films, crucial for accurate NIL process simulation.
  • Methodology: AFM-NI utilized a Diamond-Like Carbon (DLC) coated tip (Young’s Modulus E = 1147 GPa) to measure Hardness (H), Young’s Modulus (E), and Viscosity (η) across temperatures ranging from 20 °C to 80 °C.
  • NIL Optimization Parameter: A simple ratio, Hardness at demolding temperature (H) divided by Viscosity at molding temperature (η), was introduced as a predictive parameter for resist suitability in NIL.
  • Material Performance: The thinner PMMA film (235 nm) demonstrated superior NIL suitability (H/η ratio of 0.51) compared to the thicker film (513 nm, H/η ratio of 0.32).
  • Diamond Relevance: The reliance on a DLC-coated tip underscores the necessity of extremely hard, dimensionally stable diamond materials for high-precision, high-stress nanoscale mechanical testing and NIL mold fabrication.
  • 6CCVD Value Proposition: 6CCVD provides the high-quality Single Crystal Diamond (SCD) and Polycrystalline Diamond (PCD) required to manufacture durable, ultra-low roughness NIL molds and advanced AFM tips, enabling the replication and extension of this critical research.

Technical Specifications

Section titled “Technical Specifications”

Data extracted from the analysis of PMMA thin films using AFM nanoindentation with a DLC-coated tip.

ParameterValueUnitContext
AFM Tip MaterialDLC (Diamond-Like Carbon)N/ACoating on NSC14/Hard/ALBS cantilever
DLC Tip Young’s Modulus1147GPaUsed for indentation
DLC Tip Poisson’s Ratio0.07N/AUsed for indentation
PMMA Film Thickness (Thin)235 ± 5nmPMMA-235 sample
PMMA Film Thickness (Thick)513 ± 4nmPMMA-513 sample
Test Temperature Range20, 40, 60, 80°CControlled by sample-heating stage (± 2 °C accuracy)
Normal Load Range200 to 500nNApplied during nanoindentation
Loading/Unloading Rate40nN/sConstant rate
Creep Dwell Time40sUsed for viscoelastic modeling
Maximum Hardness (H)~2.8GPaPMMA-235 at 20 °C, 200 nN (Oliver & Pharr)
Maximum Viscosity (η)~170GPa·sPMMA-235 at 20 °C (Burger Model)
Burger Model Fit (Max R2)0.99536N/APMMA-513, 60 °C, 400 nN creep compliance
NIL Suitability Ratio (H/η)0.51N/AThinner film (235 nm) at 20 °C (H) / 80 °C (η)

Key Methodologies

Section titled “Key Methodologies”

The experiment focused on characterizing the viscoelastic response of PMMA thin films using AFM-NI, emphasizing precise control over material properties and testing environment.

  1. Sample Preparation: Poly(methyl methacrylate) (PMMA) thin films (235 nm and 513 nm) were prepared on silicon substrates via spin-coating using e-beam resist AR-P 672.045.
  2. AFM Setup: A Flex-Axiom AFM was employed, utilizing an NSC14/Hard/ALBS cantilever equipped with a Diamond-Like Carbon (DLC) coated tip for high-modulus indentation.
  3. Environmental Control: Experiments were conducted under controlled Relative Air Humidity (RH) (25 ± 5%) and precise temperature control (20 °C, 40 °C, 60 °C, and 80 °C).
  4. Indentation Protocol: Nanoindentation loads ranged from 200 nN to 500 nN. Creep behavior was measured using a fixed dwell time of 40 s at a constant loading/unloading rate of 40 nN/s.
  5. Initial Mechanical Analysis: Hardness and Young’s Modulus were calculated using the established Oliver and Pharr (OP) method.
  6. Viscoelastic Modeling: Creep compliance curves were fitted using three Standard Linear Solid (SLS) models (Maxwell, Kelvin, and Burger) to determine Young’s modulus, creep compliance J(t), and viscosity (η).
  7. Substrate Correction: Young’s Modulus values were corrected for the influence of the silicon substrate using King’s method, essential for accurate thin-film characterization.

6CCVD Solutions & Capabilities

Section titled “6CCVD Solutions & Capabilities”

The research demonstrates the critical need for ultra-hard, highly stable materials for both nanoscale mechanical testing (DLC tips) and the resulting application (NIL molds). 6CCVD specializes in providing the MPCVD diamond solutions necessary to advance this research, offering superior material properties compared to standard DLC coatings.

Applicable Materials & Components6CCVD CapabilityTechnical Advantage for NIL/AFM
High-Modulus Indenter TipsOptical Grade Single Crystal Diamond (SCD)SCD offers intrinsic hardness and stability far exceeding DLC, ensuring minimal tip wear and highly repeatable measurements for precise viscoelastic modeling (Burger Model).
Durable NIL Molds/StampsHigh-Purity Polycrystalline Diamond (PCD) Wafers.We supply PCD wafers up to 125mm in diameter, providing the extreme durability and thermal stability required for high-throughput thermal NIL processes (up to 80 °C molding temperature).
Ultra-Low Roughness SurfacesAdvanced Polishing Services (SCD Ra < 1 nm; PCD Ra < 5 nm).Minimizing friction and adhesion is paramount in NIL. Our ultra-smooth diamond surfaces reduce defects (fracture, delamination) and improve the accuracy of nanoscale tribology studies.
Custom Mold/Tip FabricationCustom Dimensions, Thicknesses, and Laser Cutting.We provide SCD thicknesses from 0.1 ”m to 500 ”m and PCD substrates up to 10 mm, allowing researchers to fabricate custom-geometry NIL stamps or specialized AFM tips for specific pattern heights.
Functionalized Diamond SurfacesIn-House Metalization (Ti, Pt, Au, W, Cu, Pd).To investigate anti-adhesion layers or electrical effects, 6CCVD can apply custom metal stacks directly onto the diamond surface, mimicking or extending the mold surface modifications discussed in the paper.
Material Selection SupportIn-House PhD Engineering Team Consultation.Our experts assist clients in selecting the optimal diamond grade (SCD, PCD, or Boron-Doped Diamond (BDD)) based on specific application requirements, such as high thermal conductivity or electrical properties needed for advanced NIL projects.

For custom specifications or material consultation, visit 6ccvd.com or contact our engineering team directly.

View Original Abstract

In this study, Atomic Force Microscopy-based nanoindentation (AFM-NI) with diamond-like carbon (DLC) coated tip was used to analyze the mechanical response of poly(methyl methacrylate) (PMMA) thin films (thicknesses: 235 and 513 nm) on a silicon substrate. Then, Oliver and Pharr (OP) model was used to calculate hardness and Young’s modulus, while three different Static Linear Solid models were used to fit the creep curve and measure creep compliance, Young’s modulus, and viscosity. Values were compared with each other, and the best-suited method was suggested. The impact of four temperatures below the glass transition temperature and varied indentation depth on the mechanical properties has been analyzed. The results show high sensitivity on experiment parameters and there is a clear difference between thin and thick film. According to the requirements in the nanoimprint lithography (NIL), the ratio of hardness at demolding temperature to viscosity at molding temperature was introduced as a simple parameter for prediction of resist suitability for NIL. Finally, thinner PMMA film was tentatively attributed as more suitable for NIL.

Tech Support

Section titled “Tech Support”

Original Source

Section titled “Original Source”

References

Section titled “References”
  1. 2016 - Next generation lithography—The rise of unconventional methods? [Crossref]
  2. 2021 - Friction-Induced Nanofabrication: A Review [Crossref]
  3. 2008 - The effect of temperature on the nanoscale adhesion and friction behaviors of thermoplastic polymer films [Crossref]
  4. 2010 - Tribology issues in nanoimprint lithography [Crossref]
  5. 2021 - Demolding force dependence on mold surface modifications in UV nanoimprint lithography [Crossref]
  6. 2006 - AFM characterization of anti-sticking layers used in nanoimprint [Crossref]
  7. 2011 - Thermomechanical properties of polymer nanolithography using atomic force microscopy [Crossref]
  8. 2017 - Investigation of the anti-adhesion layers for nanoimprint molding [Crossref]
  9. 2016 - Alternative nano-structured thin-film materials used as durable thermal nanoimprint lithography templates [Crossref]

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