EXPERIMENT 01

Photolithography: Fabricating Micro-QR Codes

(Instructor Guide)

PART 1: INSTRUCTOR’S GUIDE & PREPARATION

(Confidential: For Teaching Assistants and Faculty Use Only)

1. Experiment Overview

In this experiment, students will perform UV Photolithography. They will use a spin coater to create thin films of photosensitive resin and use a photomask to pattern a functional QR code. This mimics the industrial process used to manufacture semiconductor microchips.

2. Materials & Consumables

• Spin Coater: Instras Scientific SCK-300 (or similar).
• UV Source: UV Curing Box (405nm). Must have safety interlock.
• Resin A (Base): Standard White 3D Printer Resin.
• Resin B (Active): Standard Black 3D Printer Resin.
• Substrates: 50mm x 50mm Glass or PMMA squares.
• Barrier Film (CRITICAL): FEP Film (Fluorinated Ethylene Propylene).
  • Source: Spare FEP sheets for 3D printer vats. Cut into 50mm squares.
  • Purpose: Non-stick surface. Prevents resin from bonding to the mask.
• Developer: Isopropyl Alcohol (IPA) 90%+.

3. The Secret Message (The Quiz)

4. Process Parameters (Master Recipe)

Use these values to program the spin coater and UV box.

Layer	Step 1: Spread	Step 2: Spin	UV Cure Time (Box)
1. White Base	500 RPM (10s)	2500 RPM (30s)	60 - 90 seconds
2. Black Active	500 RPM (10s)	2500 RPM (30s)	20 - 30 seconds*

*Exposure time is critical. >45s will cure the background (overexposure). < 15s will wash away the image (underexposure).

5. Grading Rubric (Total: 100 pts)

Category	Points	Criteria
Functionality	30	QR Code scans instantly. Matches Secret Message.
Film Quality	25	Smooth, glossy films. No bubbles, comets, or dewetting.
Lithography	25	Sharp pixel edges. No "bridging" or fuzziness.
Safety/Process	10	Proper PPE usage. Clean workstation.
Analysis	10	Student understands "Negative Resist" concept.

EXPERIMENT 01

Student Lab Manual: UV Lithography

Name: ______________________________    Date: _______________

1. Objective

To fabricate a functional data-storage device (a QR Code) using industrial microfabrication techniques. You will verify your success by decoding the hidden message inside the fabricated chip.

2. Theory

Photolithography is the process of transferring a geometric pattern from a photomask to a light-sensitive chemical "photoresist" on a substrate.

In this lab, we use 3D printer resin as a Negative Resist:

• Exposed Areas: Polymerize (harden) and remain on the substrate.
• Unexposed Areas: Remain liquid and dissolve in the developer solvent.

To create a black QR code on a white background, we coat a white base layer, then a black active layer, and expose it through a mask that only lets light hit the "black" pixels.

3. Safety

1. UV HAZARD: Never look directly at the UV light source. Ensure the Curing Box door is closed before activation.
2. CHEMICAL HAZARD: Resin is a skin irritant. Nitrile gloves and Safety Glasses are MANDATORY. If resin touches skin, wash immediately with soap and water (not alcohol).

4. Procedure

Phase A: The Base Layer (White)

1. Clean: Wipe your 50mm substrate with Isopropyl Alcohol (IPA).
2. Dispense: Place substrate on the spin chuck. Pour a coin-sized amount (~1ml) of White Resin in the center.
3. Spin: Run the program:
   • Spread: 500 RPM for 10s.
   • Thinning: 2500 RPM for 30s.
4. Cure: Place in UV Box for 60-90 seconds.
5. Clean: Wipe the hard surface firmly with an IPA-soaked paper towel to remove the sticky layer.

Phase B: The Active Layer (Black)

1. Dispense: Pour ~1ml of Black Resin onto the cured white base.
2. Spin: Run the same program (500 RPM -> 2500 RPM).
3. REST: Wait 30 seconds for bubbles to pop. Do not cure yet!

Phase C: Contact Lithography (The Critical Step)

We use FEP Film (Fluorinated Ethylene Propylene) as a barrier. This is a special non-stick plastic used in 3D printing. Resin will not stick to it, allowing you to peel it off without damaging your QR code.

1. The Stack: Assemble the following stack on the floor of the UV box (remove turntable if present):
   1. Substrate (Bottom, with wet black resin).
   2. FEP Barrier Film: Gently roll the FEP sheet onto the wet resin. Avoid trapping bubbles.
   3. Photomask: Place your QR transparency on top of the FEP.
   4. Weight: Place a clean glass slide on top to press the mask flat.
2. Expose: Close the door. Cure for 20 - 30 seconds.

Phase D: Development

1. Peel: Remove the weight and mask. Gently peel off the FEP film. The resin should separate easily from the FEP but stick to the white base.
2. Develop: Spray or submerge the substrate in IPA. Agitate gently for 60 seconds. The unexposed black resin will wash away, revealing the white background.
3. Dry: Use compressed air to dry the chip.
4. Final Cure: Place the dry chip in the UV box for 60 seconds to fully harden the surface.
5. Test: Attempt to scan the code with your phone.

5. Troubleshooting Matrix

Observation	Likely Cause	Correction
Entire black layer washes away.	Underexposure	Increase UV time by 10s.
QR Code is solid black block.	Overexposure	Decrease UV time. Light "bled" into the background.
Image is blurry / fuzzy.	Poor Contact	Press the glass weight down firmly. Gap between mask and resin was too large.
Resin stuck to FEP film (rare).	Dirty FEP	Ensure FEP sheet is clean. Do not use scratched FEP.

6. Post-Lab Questions