Marangoni Dryers

There are 3 common ways that wafers are dried after wet processing:

Spin Rinse Dryers (SRD)

IPA Vapor Dryer

Marangoni Dryer

Wafers in a cassette are spun at high speeds. Water is removed by centrifugal force.

A chamber with some liquid IPA is heated. Heat combined with a cooling coil causes the liquid IPA to form a cloud. Wafers exposed to this vapor cloud are dried.

Wafers submerged in water are slowly passed through a thin layer of IPA liquid. The wafers are dried by the surface tension gradient between IPA & H2O.

Benefits:

• Low capital cost

• No IPA consumed

Drawbacks:

• Water Marks

• Vias may retain moisture (okay for low tech drying)

• Rough mechanical wafer handling occasionally breaks wafers

• No cassetteless option

Benefits:

• Gentle wafer handling

• Good drying results

• Dries wafer carriers well

• Integrates nicely with bench

Drawbacks:

• More expensive than spin drying

• Process time is longer than Marangoni

• Consumes more IPA than Marangoni

• Limited availability

Benefits:

• Gentle wafer handling

• Accepted as the industry’s best drying method. No watermarks.

• No exposure to air during dry

• Insitu -HF last is possible

• Integrates nicely to a wet bench

• Best cassetteless

Drawbacks:

• Most expensive

• Consumes IPA, but very little

Marangoni Dryers are more often called Surface Tension Gradient dryers, STG Dryers, or Gradient Dryers. Whatever the name, this type of drying is indisputably the dryer of choice for critical cleaning. IPA Vapor Dryers do a reasonably good job too, but all high tech factories must use Marangoni to get the best results on the wafer.

Prior to the Semiconductor Industry embracing Marangoni Dryers, IPA Vapor Dryers were extremely popular. today, most IPA Vapor Dryer suppliers had been acquired, gotten out of that business, or just plain went out of business all together. Some brand name IPA Vapor Dryer manufacturers were S&K, Yield Up, and Kimmon.

Early 2000, there was a plethora of lawsuits surrounding the coveted Marangoni Drying technology. Although the Marangoni concept is very old, certain aspects had been successfully patented for semiconductor. Not being a lawyer, and not knowing the legal aspects, I can only offer up my observations of what went on around the 1998 timeframe:

CFM, a company that is no longer in business, licensed the Marangoni technology for use in their very unique wet cleaning platform. Sometime thereafter, Steag and CFM teamed up and became partners. Mattson Technology then purchased or merged with both CFM and Steag. DNS and other Wet Bench market share leaders needed this drying technology. They somehow settled up with Mattson so that they could use the critical drying technology. Mattson divested out of the wet bench business and sold the Marangoni Dryer rights to Santa Clara Plastics. Santa Clara Plastics then sold the rights to Applied Materials.

How does a Marangoni Dryer Work?

Wafers are submerged in dilute HF
DI water introduced to the bath until all HF overflows (rinses out)
Then, Marangoni Drying as described below

1.Wafers submerged in DI Water

2.An air tight cover is over the bath creating a sealed process chamber.

3.All air is purged with N2 and an IPA Bubbler introduces IPA into the chamber

4.An invisible liquid layer of IPA eventually forms on the DI water surface

5.Wafers are slowly passed through this meniscus and into the load locked N2 environment

Marangoni Dryer Process Chamber

Wafers submerged in water are slowly passed through a thin layer of IPA on the water's surface. The surface tension gradient between IPA & H2O dries the wafer and helps remove impurities and particles.