In today’s semiconductor and display industries, the margin for error is measured in nanometers. Ensuring that your photomask blanks—the very foundation of every lithographic step—meet the strictest dimensional tolerances is paramount. Chemical milling (a.k.a. chemical etching) of chrome on quartz substrates delivers the edge definition, uniformity, and repeatability that high-volume manufacturing demands.
High-Precision Substrate Core Introduction
What is a photomask blank?
A photomask blank is a high-quality quartz (fused silica) plate coated with a uniform chrome layer. This blank serves as the canvas for patterning the opaque and transparent regions that define your IC or display circuitry. Through chemical milling, the chrome layer is selectively removed to achieve the critical dimensions (CD) required for sub-10 nm linewidths.
Core Process & Goal:
Utilize precision chemical milling to sculpt chrome films with nanometer-level accuracy, ensuring CD uniformity and edge definition that translates into higher wafer yields and better device performance.
Core Features & Advantages
| Feature | Benefit |
|---|---|
| Nanometer-level CD Control | Achieve edge definition down to sub-20 nm with <1 nm CD variation across the blank. |
| No Mechanical Stress | Chemical etching avoids mechanical or thermal damage, preserving quartz integrity. |
| High Selectivity & Sidewall Steepness | Optimize chrome removal rate for steep, smooth sidewalls, reducing light scatter. |
| Batch-to-Batch Consistency | Stable chemistry and automation yield repeatable results across hundreds of blanks. |
| Ultra-Low Defectivity | Cleanroom processing and filtration minimize particle contamination and surface defects. |
| Superior Material Combination | Fused silica offers low thermal expansion and high DUV transmission; chrome provides crisp opacity. |
Chemical Milling Process Advantages
- Stress-Free Patterning
Unlike laser or plasma ablation, chemical milling exerts no mechanical or thermal stress, ensuring the quartz substrate remains pristine. - Tailored Chemistry
Advanced etchants and masks allow fine tuning of etch rates, delivering both high selectivity and sidewall control—critical for resolution enhancement techniques (RET). - Scalability
From R&D to full production, chemical milling setups can handle single-wafer and batch-mode operations, making them ideal for both specialized and high-volume applications.
Materials System: Quartz & Chrome
- Fused Silica Substrate
- Low coefficient of thermal expansion for dimensional stability.
- High DUV transparency (193 nm and below) ensures minimal absorption.
- Exceptional surface flatness (<0.5 nm RMS roughness).
- Chrome Absorber Layer
- Uniform thickness (30–100 nm) for optimal optical density.
- Excellent adhesion and low defect density.
Quality Control & Inspection
To guarantee every blank meets stringent specifications, deploy:
- CD-SEM & AFM for nanometer-scale measurements of linewidth and sidewall angle.
- Optical Scatterometry to assess CD uniformity across the entire blank.
- Particle Inspection Systems to detect sub-50 nm surface contaminants.
Applications & Industry Case Study
Semiconductor Lithography (10 nm Nodes and Beyond)
Photomask blanks patterned via chemical milling are the backbone of advanced optical lithography. For instance, Applied Materials’ Centura® Tetra™ Z Photomask Etch system delivers the precision etch performance required for logic and memory devices at 10 nm and beyond.
EUV Mask Blank Development
With the industry racing toward EUV lithography, mask-blank suppliers like AGC and Hoya are expanding capacity—and exploring chemical-milling strategies—to meet sub-5 nm requirements semiengineering.com.
Customization & Next Steps
- Standard Specs:
- Blank Sizes: 152 mm–248 mm square
- Quartz Thickness: 0.5 mm–6 mm
- Chrome Thickness: 30 nm–100 nm
- CD Uniformity: <1 nm RMS
- Tailored Solutions:
- Special sizes (circular, rectangular)
- Alternative absorber materials (MoSi, TaN)
- Custom surface treatments (anti-reflective coatings, backside coatings)
Ready to define your next generation of critical dimensions?
Contact our technical sales team for detailed datasheets, sample blanks, and process integration support.