Overview

Birck supplies a selection of photoresists for both optical and electron beam lithography. The chemical mechanism for each resist may be slightly different, so be sure to verify the appropriate process for each resist.

Optical Lithography:

• AZ1518: Positive photoresist, thicknesses from 1-4 μm
• AZ9260: Positive photoresist, thicknesses from 5-20 μm
• SU-8: Positive resist

Electron Beam Lithography:

• 950 PMMA A4: Positive resist
• XR1541 (HSQ): Negative resist

Optical Photoresists

General Properties of AZ/Ti Photoresists

AZ1518

Composition

The AZ positive resists consist of a resin (Novolak), a photoactive compound or PAC (a DNQ compound), and a solvent (PGMEA).

References:

• AZ 1500 Series Technical Datasheet
• Microchemicals: AZ1518

• AZ 1500 Series Positive Photoresist

AZ9260

References:

•  MicroChem: AZ9200
• Clariant: AZ9200
• AZ Electronic Materials: AZ9260 Photoresist
• UMN: Thick AZ9260 - Double Coat
• CMI: AZ9260 Parameters

Electron Beam Photoresists

950 PMMA A4

Properties

• Composition: 4% polymethylmethacrylate of average molecular weight 950,000 dissolved in anisole.
• Positive tone.
• Refractive Index: 1.49-1.52 at 632.8nm.
  Pros:
• Good adhesion to most substrates
• Very high resolution (down to 10 nm).
• Long shelf life and spun film life
• Insensitive to white light
• Resistant to water, IPA/Methanol, TMAH based developers, and dilute acids for short periods
  Cons:
• Poor etch resistance for dry etching
• Low contrast
• Attacked by acetone, HF, Piranha.

Manufacturer recommended process: (summarized from Microchem PMMA Data Sheet)

1. Solvent clean of substrate.
2. Dispense 5 - 8 mL for a 150 mm wafer.
3. Ramp to 500 RPM for 5 s OR let sit without rotation for 10 s.
4. Quick ramp to spin speed, holding for 45 s.
5. Prebake on hot plate at 180 C for 60-90 s.
6. Expose with dose between 50-500 μC/cm² depending on equipment and polymer.
7. Development: For high resolution, 1:3 MIBK to IPA for 60-120 s. Rinse in IPA or DI water immediately following develop to prevent scumming. Blow dry.
8. (Optional) Postbake: 100 C hot plate for 60-90 s. Note that PMMA will reflow above 125 C.
9. Removal: Will generally be removed by common positive PR strippers, including acetone. Thorough removal can be accomplished with Remover PG at 50-60 C.

Notes:

Sensitivity of PMMA depends on the concentration, developer used, and accelerating voltage of the exposure (e.g. Rooks 2002) . At 100 kV for our PMMA, developed in 1:3 MIBK/IPA, 700 μC/cm² may be a good dose for 2D features (Hoole 1997), with small isolated lines requiring a dose >3000 μC/cm² .

PMMA References:

• Microchem product page
• Microchem PMMA FAQ
• Microchem PMMA Data Sheet
• Microchem technical reference list
• Optical constants of PMMA 950

XR1541 (HSQ)

Properties

References

MicroChemicals Photoresist references:

General Properties of AZ/Ti Photoresists