• Out gassing from clean room construction products (floor, walls, adhesives, paints etc.)
  
• Emissions from PC components, wafer carriers etc.
  
• Plastics
  
• Clean room consumables e.g. gloves, garments, tape, cleaners
  
• HEPA and ULPA filters
  
• People

Known problematic organic contaminants (molecular condensables) include:

• Polymer/plastics additives e.g. plasticizers (phthalates), antioxidants
  
• Siloxanes
  
• Amines/amides
  
• Flame retardants e.g. Organophosphates
  
• Decomposition compounds
  
  

• Surface properties e.g. Hydrophobicity
  
• Lower breakdown voltage
  
• Unintentional doping
  
• Haze degredation
  
• Oxide growth rate and quality
  
• Delamination
  
• Optic and mask hazing
  
• Reduced long-term device reliability

It is, therefore, crucial for disk drive manufacturers to monitor clean room air quality for semi-volatile organic vapours and to monitor and minimize emissions from PC component parts and clean room materials. As a first-line-of-defence most HDD manufacturers now screen all materials for the out gassing levels of condensables and amines, prior to them being taken into the clean room environments. 

The most widely used and accepted approaches for screening out gassing levels within the semi-conductor industry include direct and indirect outgassing methods. Direct outgassing methods include the weight loss method, for total outgassing assessment, and direct thermal desorption GCMS for quantitative and qualitative identification of released compounds. 

Monitoring clean room air

The routine monitoring of clean room air can be achieved by sampling (pumped) onto sorbent tubes typically packed with quartz wool (10 mm) backed up by conditioned Tenax TA 35-60 mesh (50 mm) followed by TD-GC/MS.

Direct thermal desorption

Direct thermal desorption can be achieved by placing a small section of test material (typically 20-50 mg) weighed into an empty sample tube followed by thermal desorption (extraction) and GCMS analysis. 

Larger samples (5-10 grammes) or complete components, wafers, hard disc drives, etc. can be placed into small temperature controllable chambers, such as the Markes Micro-Chamber / Thermal Extractor (µ-CTE) where released vapours are swept onto sorbent tubes followed by TD-GCMS analysis. 

The Micro-Chamber / Thermal Extractor (µ-CTE) is capable of sampling up to 6 samples simultaneously. 

Industry standard methods

Industry standard methods include ASTM F1982-99 (standard test methods for analysing organic contaminants on silicon wafer surfaces by thermal desorption gas chromatography) and ASTM F1227-89 (standard test method for total mass loss of materials and condensation of outgassed volatiles on microrelectronics & related substrates). 


Useful literature references

J. A. Lebens et al., Unintentional doping of wafers due to organophosphates in the cleanroom ambient, J. Electrochem. Soc., 143 (9), 2906-2909 (1996) 

M. Tamaoki, et al., The effect of airborne contaminants in the cleanroom for ULSI manufacturing process, IEEE/SEMI Advance Semiconductor Manufacturing Conference, 322-326 (1995) 

K. Saito, H. Simizu, T. Ogawa, Computation program system for structural analysis and quantification of organic contaminants on silicon wafer surfaces from mass spectra, Analytical sciences 16, 593-596 (2000) 

Camenzind, M.J; Liang, H; Fucsko, J; Balaz, M.K, How clean is your cleanroom air?, MICRO, 49-54, (1995)

Thermal Desorption Technical Support Literature 

TDTS 14: Monitoring Labile, High-Boiling Organic Vapours such as those found in “Clean room Air” in Semiconductor Fabrication Plants 

TDTS 53: Quantitative Recovery of High Boiling (> 450°C) Semi-Volatiles (sVOCs) using Thermal Desorption - GCMS

TDTS 62: Materials emissions testing in the semiconductor and associated industries 


Useful Links 

Fraunhofer- Institute for Manufacturing and Automation (IPA)