CPD - Internal Resources

iLab Name: Critical Point Dryer
iLab Kiosk: BRK Packaging and Assembly Core
FIC: Dimitrios Peroulis
Owner:Ethan Zhang
Location: Cleanroom - L Bay
Maximum Wafer Size: 6"/150 mm

Overview

General Description

A supercritical dryer to dry a sample immersed in a liquid, without the negative effects of the liquid-gas phase transition (evaporation).

Specifications

• Samples may be from .25" to 6" wafers

• Samples should be immersed in IPA before starting.

Technology Overview

 Supercritical drying allows a phase transition from liquid to gas without crossing the liquid-gas phase boundary. On the phase diagram below, it follows the red arrow:

This transition relies on turning the chamber fluid into a supercritical fluid:

For carbon dioxide, this is accomplished at 31.1 C and 1072 PSI. IPA is introduced into the chamber, then replaced with liquid CO₂, which is then turned into a supercritical fluid, and then into a gas. This allows the sample to dry without the negative effects of a phase transition.

A close look at supercritical carbon dioxide CO2

Sample Requirements and Preparation

Samples should be free of any contaminants or metals that will flake off upon introduction to the chamber. Samples should be free of organics (i.e. Photoresist) and immersed in clean IPA before loading into the chamber.

Standard Operating Procedure

Questions & Troubleshooting

May I use methanol instead of IPA?
Methanol is an allowed substitute for IPA, but IPA is preferred. The lack of a strong difference between the two intermediaries and the fact that methanol is considered toxic means that IPA is the preferred choice.

References

Manufacturer Webpage

"Super Critical Carbon Dioxide in Semiconductor Cleaning", Handbook of Semiconductor Manufacturing Technology, Robert Doering and Yoshio Nishi, 2007.