SiNx BOE Etch

Written by NTS, Dec 2013. Modified NTS 20140306, 20170414.

• The basic idea is to have patterned SiN on substrate samples, prepare the HF-based BOE acid solution, and perform the etch. This procedure is written to be useful for SiNx HF etch development and standard use. HF acid is dangerous, take all proper precautions.

Prepare Samples

SiNx Dep

• See PECVD procedure

  • Deposit SiN on substrate piece (wafer/sample) for desired time (10 min standard)

Litho

• See lithography procedure.

  • You can use any ‘spare’ mask with features. I recommend Laser 2011 Mask 1. Do not use Laser 2013 masks unless making Lasers.

• Dektak sample features to check PR thickness (optional, do if planning to re-etch samples)

Prepare BOE Acid Solution

(Cleanroom or LASE acid hood, on left side, with careful acid, water, wipe waste collection)

• You should know what mixture you are using or testing beforehand. Sol 17 (1:10) is standard.

• Don PPE

• Clean workspace and set out beakers (proper beakers for samples and process)

• Mix acid solution; e.g. (Sol 17): BOE(6:1):H2O 1:10 (0.1) = 9 mL BOE, 90 mL H2O

  • Measure DI water in PP grad cylinder and pour into Etch beaker

  • Pour BOE into PP grad cylinder using PP funnel (one hand on acid, one hand on funnel)

    • Pour excess acid from PP grad cylinder into the excess BOE beaker

  • Pour BOE acid into Etch beaker (acid to water)

• Triple rinse graduated cylinder and funnel

• Aspirate excess BOE beaker and triple rinse

Feature Etch

• Etch samples for Y seconds. 120 seconds for Sol 17 (1:10) is standard.

  • Etch rate of Sol 17 (1:10) is ~2.6-3 nm/s, so 80 seconds ought to etch through 200+ to 250 nm of SiNx. An extra 10-20 seconds to ensure etch through is good, GaSb is not very affected by the etchant.

• DI rinse 2 min

• Blow dry with N2

• Repeat etch as needed for each sample

• Clean beakers and workspace

• Remove PPE

• Dektak to determine etch rate, or wait til PR removal if not re-etching

  • Dektak several times at multiple points of a feature to find averages and differences

• (Optional) Etch sample again and Dektak to gather more data

• When done with etching, clean off PR

• Dektak sample to find or confirm etch data (may not want to do on Laser except for at an edge)