Slava Libman

Chief Executive Officer

Based in Colorado Springs, CO, USA

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Particle Precursors in Ultrapure Water

What are particle precursors in ultrapure water and why are they important in semiconductor manufacturing?

What are particle precursors in ultrapure water? 
The history of particle precursors, a new contamination risk for semiconductors, is tied with the development of the cutting-edge particle metrology. Semiconductor manufacturing is becoming increasingly sensitive to particles at the single digit nanometer size, as defined by the International Roadmap for Devices and Systems Yield Enhancement (IRDS YE). At these dimensions, it is becoming difficult to distinguish between particles and large molecules. This was the challenge facing nebulization-based particle metrology, as particle formation in aerosol was contributed to by both liquid-born particles and those originating from dissolved large organic molecules. While this particle detection technology can’t distinguish between particles and large organic molecules, both contaminants pose a serious threat to semiconductor manufacturing. 

Kanomax FMT, the developer of the Liquid Nanoparticle Sizer (LNS) demonstrated particle (aerosol) formation by addition of a known high molecular weight (HMW) polymer to UPW. Reference: Libman et al., 2019.

Why are particle precursors important in semiconductor manufacturing? 
This made industry experts wonder if the same effect of particle formation from HMW organics naturally occurring in UPW or high purity chemicals may occur on the wafer in semiconductor manufacturing, thus killing the device. The extent of the risk is driven by three facts: 

  1. The number of molecules is incomparably higher than number of particles in UPW resulting from Avogadro’s number considerations. 
  2. UPW system materials are practically all made of polymers, whereas ion exchange resin are known to leach large amounts of organic material. 
  3. UPW filtration was not designed to remove dissolved organics. 

The UPW IRDS team (a subset of the IRDS YE forum) embarked on investigating the issue. A series of experiments were conducted to address the concern and all of them indicated particle formation on the silicon wafer surface when UPW was spiked with HMW organics with low parts per billion as total organic carbon (TOC). The most recent experiment conducted by UPW IRDS was a collaboration CT Associates, an advanced analytical laboratory based in Minnesota, a major semiconductor fab, and UNISERS, a startup company developing single digit particle monitoring technology.

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Particle precursors, a new risk for semiconductors 
UPW IRDS, in communication with the National Institute of Standards and Technology (NIST), defined particle precursor as a dissolved molecular compound, which may form particles when dried on the wafer surface. NIST is setting targets for particle precursors in UPW to support research and development efforts for metrology and filtration technology companies. The discovery of particle precursors and the IRDS targeted research is driving development of the new SEMI standard for qualifying methods for particle precursor metrology. This effort is planned for 2021. 

It is highly recommended to consider risks associated with particle precursors in the design of new and existing operation of UPW systems. Use of SEMI Standards, such as SEMI C79 and SEMI C93 could help to mitigate some of the risks. 

If you are looking for additional information about particle precursors in ultrapure water and their effects on semiconductor manufacturing, please explore UPM resources or contact FTD Solutions.

Slava is the CEO of FTD Solutions, Co-chair of IRDS Yield Enhancement Forum and UPW IRDS, and Chair of SEMI High Purity Water Task Force. 

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