Custom Photomask Ordering Guide (For Lithography, Microfabrication & Thin-Film Labs)

Photomasks are essential in:

• Photolithography
• MEMS fabrication
• Microfluidic devices
• Semiconductor prototyping
• Shadow mask / deposition mask alignment
• Optical patterning
• R&D device development

A well-prepared photomask design ensures accurate pattern transfer, high yield, and minimal fabrication delays.

This guide explains materials, resolutions, file requirements, tolerances, and the ordering process.

Step 1 — Choose the Photomask Material

Most common materials:

1. Chrome on Soda-Lime Glass (5–7 mil thickness)

• Affordable
• Suitable for most lithography systems
• Resolution ~5 µm

2. Chrome on Quartz (Fused Silica)

• Low thermal expansion
• High stability
• High UV transmission
• Used for i-line / DUV lithography
• Resolution ~1–2 µm, depending on process

3. PET / Polymer Film Masks

• Flexible
• Fast turnaround
• Low cost
• For >50 µm features
• Not suitable for high-precision lithography

Step 2 — Minimum Feature Size & Tolerance

Important:
Photomask is different from a shadow/deposition mask:

• Photomask = transparency for UV lithography
• Shadow/Deposition mask = thick metal plate with cut openings

Step 3 — Mask Polarity (Very Important)

Two main types:

1. Clear Field Mask

• Background is transparent
• Patterns are chrome

2. Dark Field Mask

• Background is chrome
• Patterns are transparent

If unsure, choose “Clear Field (positive resist)” — most common.

Step 4 — Layer-to-Layer Alignment (For 2–5 Layer Masks)

For multilayer microfabrication:

• Add alignment crosses (≥ 100 µm)
• Add global + local markers
• Keep each layer in its own file
• Provide the exact orientation (top/bottom view)

Step 5 — File Format Requirements

The mask design must be vector-based, not a bitmap.

Accepted formats:

• GDSII
• DXF
• DWG
• AI (vector)
• SVG
• Hand draft (clear discription)

Resolution ≠ Feature precision → must be vector-based.

Step 6 — Mask Size Options

Common sizes:

• 3" × 3" (76 mm)
• 4" × 4" (101.6 mm)
• 5" × 5"
• 7" × 7" (large area)

Film masks also come in A4 or US Letter size.

Step 7 — What Customers Should Provide Before Ordering

To avoid delays, you should prepare:

• Mask size (3", 4", 5", or custom)
• Material (chrome glass, quartz, film)
• Minimum feature size
• Polarity (clear field / dark field)
• File format (GDS preferred)
• Number of layers
• Alignment marks
• Critical dimensions (CD values)
• Thickness of mask (if needed)

This information ensures fast and accurate manufacturing.

Photomask vs Shadow Mask (Clear Comparison)

Your business covers both, which is a rare and strong advantage.

Common Problems & How to Avoid Them

Problem: Small gaps less than 5 µm

Fix: Increase feature size or use quartz mask.

Problem: Poor alignment

Fix: Add global + local alignment marks.

Problem: Masks peeling during lithography

Fix: Ensure chrome thickness ≥ 100 nm.

Problem: Wrong polarity

Fix: Confirm mask type before ordering.

Frequently Asked Questions

Q1. What is the minimum feature size of a photomask?

1–2 µm for quartz masks; 5 µm for standard chrome masks.

Q2. What file format do I need?

GDSII is preferred; vector formats only.

Q3. What polarity should I pick?

Clear field for positive resist; dark field for negative resist.

Q4. Can I print multiple layers on one mask?

Not recommended — use separate masks for high precision.

Q5. What is the difference between film masks and chrome masks?

Film masks are low cost (>50 µm), chrome masks are high precision (1–5 µm).