Overview

Birck supplies a selection of photoresists for both optical and electron beam lithography.

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

AZ1518

Composition

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

AZ 1500 Series Technical Datasheet

Microchemicals: AZ1518

AZ9260

MicroChemicals: AZ9200

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 .