Overview

Birck supplies a selection of photoresists for both optical and electron beam lithography. Resists that are not supplied may be purchased for use by individual research groups. The chemical mechanism for each resist may be slightly different, so be sure to verify the appropriate process for each resist.

Optical Lithography:

BNC Supplied:

AZ1518: Positive photoresist, thicknesses from 1-4 μm
AZ9260: Positive photoresist, thicknesses from 5-20 μm

Used at facility (not supplied):

SU-8: Negative epoxy resist

Electron Beam Lithography:

BNC Supplied:

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

Used at facility (not supplied):

ZEP520A: Positive 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:

AZ9260

References:

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

LOR3B

IMPORTANT CONTAMINATION NOTE

Per Microchem: Ensure that acetone and resist waste are kept separate from LOR/PMGI waste streams. LOR/PMGI will precipitate in the presence of acetone, PGMEA, and ethyl lactate and may clog lines or form unwanted solids in the collection area.

LOR3B is a mixture of the solvents Cyclopentanone and 1-Methoxy-2-propanol, with a 'Polyaliphatic imide copolymer' as the polymer. Edge beads can be removed with EBR PG, and it can be lifted off with Remover PG.

References:

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)

Solvent clean of substrate.
Dispense 5 - 8 mL for a 150 mm wafer.
Ramp to 500 RPM for 5 s OR let sit without rotation for 10 s.
Quick ramp to spin speed, holding for 45 s.
Prebake on hot plate at 180 C for 60-90 s.
Expose with dose between 50-500 μC/cm² depending on equipment and polymer.
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.
(Optional) Postbake: 100 C hot plate for 60-90 s. Note that PMMA will reflow above 125 C.
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:

XR1541 (HSQ)

Properties

ZEP520A

ZEP520 References:

ZEP520A Technical Report - Zeon Chemicals

References

MicroChemicals Photoresist references:

General Properties of AZ/Ti Photoresists