How Marangoni Drying Produces Superior Surface Conditioning for Wafer Processing

How Marangoni Drying Produces Superior Surface Conditioning for Wafer ProcessingAt the end of a particular step in silicon wafer processing, wafers often have to be cleaned, rinsed and dried. The resulting wafer surfaces must be free of water, watermarks, particles and organic residues. Older technologies such as spinning the wafers rapidly or heat drying can no longer fulfill the requirements of high density electronic devices on today’s silicon wafers. Water is hard to remove completely from complicated geometries and drying can leave contaminating watermarks and particles.

Such contamination can lead to product defects in subsequent processing steps or to high failure rates as the contamination impacts quality. IPA (isopropyl alcohol) drying using the Marangoni drying effect leads to dry silicon wafer surfaces without watermarks or particles. Modutek’s IPA vapor dryer is cost effective and can be integrated in a wet bench process without adding drying transfer steps.

How it Works

In Modutek’ IPA drying process, IPA vapor is introduced at the top of the drying tank to ensure even vapor distribution. Because the IPA has a lower surface tension than water, it introduces a surface tension gradient where it interfaces with the water on the wafer surface. As a result of the Marangoni drying effect, water flows off the surface of the silicon wafer and leaves it dry and clean.

The departing water also takes along any impurities or particles suspended within it. No watermarks are present because the water does not dry on the wafer surface and ozone can be introduced into the drying tank to eliminate trace organic contamination. There are no moving parts inside the chamber so physical wafer damage is eliminated and drying cycles typically last ten to fifteen minutes.

Modutek’s Design

The stand-alone Modutek IPA dryer is a 30″ wide cabinet of polypropylene construction. It features wiring to NFPA 70 & 79 and has all Teflon fitting, valves and tubes. A touch screen controls operation with a graphic user interface and the dryer has a multiple recipe function.

The unit has an N2 head case purge with an interlock, a hot N2 dry feature, a continuous flow DI water manifold and an auto lid with foot switch open. PVC side shields are removable and there is DI water degassing function using a membrane contactor. Third party certification for NEC and NFPA is available.

Dryer options include PVC construction, a manual lid and a quick dump feature. Data logging and online support are available. Other options include a static eliminator, resistivity monitoring, HEPA fan filter units and a fire suppression system. Modutek can customize any dryer to customer specifications.

IPA Dryer Operation

The Modutek MVD series IPA dryer is a competitive solution with a single drying chamber for DI water rinsing and IPA vapor drying. The IPA vapor is generated in a one gallon bottle installed at deck level for easy changing. Introducing the vapor at the top of the tank is an efficient way of achieving even distribution of the vapor and reduces IPA consumption. The dryer can handle all wafer sizes and glass substrates and Modutek can integrate the IPA drying function into wet bench stations to eliminate a transfer step.

Benefits of Modutek’s IPA Vapor Dryer

Modutek’s specialists work with customer engineering teams to design a dryer that best matches the process application. Modutek’s design and software implementations are all carried out in house and acceptance testing with de-ionized water is available. The company’s extensive experience in the semiconductor manufacturing industry lets it provide first class customer support at all stages of a contract and after delivery. If you need to improve your wafer processing quality and want a free consultation or quote on using an IPA Vapor Dryer, call Modutek or email Modut[email protected].

Using RCA Clean in a Wet Bench Process

Using RCA Clean in a Wet Bench ProcessBefore processing a silicon wafer under high temperatures, semiconductor process engineers will use RCA clean as part of a wet bench process. This procedure removes organic residue from a silicon wafer and replaces the surface layer of oxide with a thin, new layer. The application of two chemical solutions, SC-1 and SC-2, make up this process.

SC-1 removes impurities attached to silicon, quartz and oxide surfaces in a 15 minute soak. In addition, it initiates the regeneration of surface oxide layers. The mixture consists of:

  • 1 part NH4OH (ammonium hydroxide)
  • 1 part H2O2 (hydrogen peroxide)
  • 5 parts deionized (DI) water.

After an SC-1 application, cleanliness is ensured by soaking a wafer in SC-2 for 10 minutes. This mixture does not etch silicon, but targets and eliminates microscopic metal hydroxides, alkali residue and any other remaining metal. SC-2 consists of:

  • 1 part HCl (hydrochloric acid)
  • 1 part H2O2 (hydrogen peroxide)
  • 5 parts DI water

Fortunately, Modutek offers an array of wet bench equipment that support both steps of RCA clean. With a custom station, you can rinse and dry wafers in one place within 15 minutes.

Modutek Wet Bench Equipment

Modutek produces high-tech, high-yield wet bench processing equipment suited for RCA clean. Stations conserve DI water and operate with precise process controls via SolidWorks Flow Simulation software. Expedite your applications with a station designed in-house according to your specific requirements. Standard features include:

  • DI water hand spray
  • Continuous flow DI water chamber
  • Teflon N2 gun

Modutek IPA Vapor Dryer

Eliminate the need for separate rinsing and drying chambers with Modutek’s Marangoni drying system, also called an IPA Vapor Dryer. Incorporated into your wet bench, the IPA Vapor Dryer’s single chamber makes finalizing the cleaning process quick and convenient. In addition, this advanced system allows for ozone introduction in a post-solution clean. Safe and simple bottle change happens at deck level where IPA vapor precipitates inside your gallon container under level sensor protection. Additional safety features include an Emergency Power Off button and the absence of moving parts inside the drying chamber. IPA vapor distributes evenly through the top of the chamber, reducing IPA use while providing sufficient surface tension drying for all substrates and silicon wafers.

Modutek has been designing and manufacturing wet bench equipment for customers for 30+ years. Certified specialists will work with you from design to installation, ensuring you have the perfect wet bench and IPA Vapor Dryer for your cleaning and processing applications. Email [email protected] or call 866-803-1533 for inquiries.