LOR 5B Lift-off Process

Introduction

LOR5B is used as an underlying layer in lift-off processes to create an undercut. This undercut in conjunction with evaporation techniques will produce a discontinuity in the deposited layer allowing optimal lift-off in the adequate solvent.

Read this to get familiar with LOR processing

Equipment needed

Preleminaries

Process Steps

Step# Step Name Tool Recipe Comments
1 Clean Solvent WB Solvent Clean A solvent clean is necessary to ensure optimal surface quality of the substrate prior to processing. For harsher cleaning refer to the Piranha Cleaning SOP
2

Priming

(optional)

Yes Oven

HMDS priming @ 150°C - program 1.

Improves the adhesion by removing moisture from the surface.
3 Coat and softbake Site Service Spin coater or Laurell

Coat LOR5B using either spin coaters: refer to spin curve to set up the optimal speed. Optimal thickness depends on the final metalization thickness. The rule of thumb is that LOR layer has to be 1.5 x thicker than final metal thickness.

Bake LOR5B according to the process table below

4 Coat imaging resist  Site Service Spin coater or Laurell S1813 recipe  
5 Exposition EVG620 D=90 mJ/cm² The exposure dosage will vary depending on the resist thickness. Report to process table for more details.
6 Develop Lithowb 2 beakers

Develop into MF319 developer @ room temperature. Develop time is to be tuned to obtain the desired undercut. Refer to process table for values.

DO NOT HARD BAKE THE SAMPLE

7 Metal Dep. ebeam evaporator

 

8 Lift-off Solvent WB 2-10min

In the solvent bench, use Remover PG or Remover 1165 at 70°C into the ultrasonic bath to perform the lift-off. Lift-off time depends on the size of the sample or wafer, the size of features and the amount of resist to be dissolved.

Rinse in a clean bath of DI water.

Process Table and Data

Spin LOR5B SB Spin S1813 SB Expose Dev Undercut
500rpm 5s, 1000rpm 45s 5min @ 180°C 500rpm, 5s, 3950rpm 30s 1min @ 115°C 90mJ/cm2 MF-319 45s 2-3 um.

LOR 5B thickness vs. spin speed for Laurell coater

Coating conditions are:

- spread at 500 rpm for 5 s with acceleration of 10005 rpm/s

- spin between 1500 and 5000 rpm for 45 s with acceleration of 10005 rpm/s

- bake at 180 °C for 5 min

The following table gives thicknesses vs. speed measured at the center of silicon samples of 1x1 cm².

Spin speed (rpm) Thickness measured with ellipsometer (nm) Thickness measured with reflectometer (nm)
1500 689 713
2000 599 606
3000 480 487
4000 424 430
5000 374 377