Marangoni Dryers

Wafer Drying:

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 industrys 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.

IPA Vapor Dryers

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?

HF Last Marangoni Drying (option):

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

Standard Marangoni Drying:

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 

Benefits of HF Last Marangoni Drying:

 

The HF Last process step leaves the surface of the wafer in a Hydrogen Terminated state. The benefit of HF Last is that the wafers can go for an extended period of time without growing a native oxide.  A native oxide is the undesired contaminating oxide that slows or kills IC device switching speed.

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. 
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