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*"storage box" AND particles AND cleanroom | *"storage box" AND particles AND cleanroom | ||
==Organic airborne contamination on Si wafers (Toni)== | ==Organic airborne contamination on Si wafers and its quantitative characterization (Toni)== | ||
Revision as of 15:22, 11 November 2017
Search Terms
- "storage box" AND particles AND cleanroom
Organic airborne contamination on Si wafers and its quantitative characterization (Toni)
===Walter Den, Hsunling Bai, and Yuhao Kang, “[http://jes.ecsdl.org/content/153/2/G149.full Organic Airborne Molecular Contamination in Semiconductor Fabrication Clean Rooms A Review]” Journal of The Electrochemical Society, 153(2), G149-G159, 2006.===
- Volatile or semivolatile organic contaminant have been detected e.g. by subjecting sampling tubes to gas chromatography (GC) coupled with mass spectrometer (MS) => GC-MS.
- These provide very low detection limits but are very elaborating and time-consuming
- Monolayer contamination has been studied by XPS or TOF-SIMS
- Both require high vacuum => loos of volatile components may become significant. Neither is capable of full wafer analysis
- The adsorbed organic molecules can be thermally desorbed and swept into a sampling tube with a metered stream of carrier gas => sorption tube is analyzed by TD-GC/MS.
- Even commercially manufactured infrared-heated full-wafer vacuum chamber are available for this purpose => this type of analytical technique has become accepted and issued as the industrial standard method for organic analysis of Si wafer surfaces
- Contamination on surfaces and those found in cleanroom air are two different things. Species with low concentration in air may tend to adsorb on a surface
- [From another reference] Wafers stored in a box. Organic contaminant with –C=O or –S=O functional groups tended to be adsorbed on a wafer surface within 2 days of storage, while those with –O- groups were detected only after nearly 10 days. => Degree of polarity of the contaminants has a critical role in the adsorption of organic molecules. Adsorption behavior depends heavily on the electronegative difference of the surface and the contaminant.
Yong-Jun Liu and Hua-Zhong Yu, “Effect of Organic Contamination on the Electrical Degradation of Hydrogen-Terminated Silicon upon Exposure to Air under Ambient Conditions” Journal of The Electrochemical Society, 150(12), G861-G865, 2003.
- Organic contamination from air has an important role on degradation of electrical properties of H-terminated Si surfaces. The electrical performance was studied by measuring IV characteristics of mercury-Si junctions.
Hitoshi Habuka, Syuichi Ishiwari, Haruo Kato, Manabu Shimada, and Kikuo Okuyamad, “Airborne Organic Contamination Behavior on Silicon Wafer Surface” Journal of The Electrochemical Society, 150(2), G148-G154, 2003.
- The fundamental behavior of airborne organic contaminants is modelled using the MOSAIC model developed by the authors in earlier publications. In addition, the silicon plate sampling (SPS) method is used experimentally.
- The maximum concentration of contaminants and ratio of desorption and adsorption are independently described from each other by the model.
- Conclusion: The nature of airborne organic contamination can be comprehensively evaluated by integrating MOSAIC model and SPS method.
Syuichi Ishiwari, Haruo Kato, and Hitoshi Habuka, “Development of Evaluation Method for Organic Contamination on Silicon Wafer Surfaces” Journal of The Electrochemical Society, 148(11), G644-G648, 2001.
- A “silicon plate method” is developed to evaluate the amount of organic contamination on a Si wafer surface coming from cleanroom air.
- As the amount of some organic species start to decrease after a peak concentration, it seems that organic species compete for the adsorption sites on Si wafer surfaces.
- Traditional way to measure organic contamination really complex (WTD-GC-MS or TOF SIMS)
- In this developed method, TD-GC-MS (thermal desorption gas chromatography mass spectrometry) is still used, but one heating step is removed. Contamination is evaluated directly from the Si plate, and additional exposure to cleanroom air is prevented.
- Time-dependent behavior of contamination adsorption is evaluated by multicomponent organic species adsorption-induced contamination (MOSAIC) model.
Hitoshi Habuka, Manabu Shimada and Kikuo Okuyama, “Adsorption and Desorption Rate of Multicomponent Organic Species on Silicon Wafer Surface” Journal of The Electrochemical Society, 148(7), G365-G369, 2001.
Fumitoshi Sugimoto and Sigeru Okamura, “Adsorption Behavior of Organic Contaminants on a Silicon Wafer Surface” Journal of The Electrochemical Society, 146(7), 2725-2729, 1999.
- The authors study behavior of organic contaminants absorbed onto Si wafer surface by solvent-dissolution GC-MS technique.
Experimental
- Wafers precleaned via RCA, wafers covered with native oxide
- Wafers expose to a conventional cleanroom for several hours and placed vertically on a quartz carrier
- Other wafers were sealed and stored for several days in two polypropylene boxes (commercially finished products): (i) not used prior the experiment (“new box”), (ii) box was left open in clean room for several months before the experiment (“used box”)
- Exposure time and storage time varied
- Characterization by GC-MS analysis:
- Organic contaminants collected by dissolving them in a solvent (pure acetone used: suitable for this kind of study, see details from the paper)
- Contaminants then studied from the solvent
Results
- Cleanroom air
- Organic contaminants found from a wafer exposed to clean room air for only 1 h
- Different contaminants are found after 24 h cleanroom air exposure than after 1 h exposure
- Contaminants with low boiling point were adsorbed immediately and decreased with exposure time; those with high bp increased with exposure time (does not apply for everything) => Organic contaminants having a low boiling point were replaced by those with higher boiling points
- New box
- No cleanroom airborne contaminants found but other contaminants resulting from the plastic additives: crosslinking agent (DAB), antioxidant (DBQ) and plasticizer (DBP)
- Used box
- Airborne contamination peaks found due to contamination already present in the box which was stored open beforehand. Nevertheless, the amount considerable smaller than on wafers stored in cleanroom air directly.
- In this case, the adsorption time did not depend on the boiling points of the contaminants but instead on their structure: Contaminants containing C=O or S=O groups were adsorbed immediately; those having -O- groups only after several days. This is due to different polarities of the molecules.
Koichiro Saga and Takeshi Hattori, “Identification and Removal of Trace Organic Contamination on Silicon Wafers Stored in Plastic Boxes” Journal of The Electrochemical Society, 143(10), 3279-3284, 1996.
- SUMMARY: TD-GC/MS is used to study organic contaminants originated form plastic boxes supplied by major Si wafer vendors. Also outgassing from the box materials is studied to identify the source of contaminants. Various wet cleaning solutions are evaluated based on their ability to remove such contaminants.
- Volatile organic contaminants adsorb onto wafer surface from polymeric wafer boxes.
- Dilute HF or ozonized ultrapure water can be used to entirely remove the organic contaminants.
- After cleaning, organic contaminants adsorb more easily on the ozonized water-treated surface than on the dilute HF-treated surface.
- Adsorption of organic contaminants can be reduced by preventing native oxide growth in N2 atmosphere after HF dip.
- In the past, organic contaminants have been detected by XPS, TOF-SIMS, FTIR or thermal desorption spectroscopy (TDS). More suitable options are TD-GC/MS or TD-IMS/MS.
Experimental
- Wafers stored in four different boxes from different suppliers for more than one month. No wafer cleaning beforehand.
- All boxes were polypropylene: some parts were made of several kind of plastics (including polycarbonate) or thermoplastic polyester elastomers.
- TD-GC/MS used to analyze the contaminants on wafer surfaces. Desorption by heating up to 400 C in an inert gas.
- HS-GC/MS used to analyze outgassing of the box materials.
- Different wet cleanings applied to wafers prior to storage: NH4OH/H2O2, H2SO4/H2O2, HNO3, dilute HF, O3/H2O
- Storage for 1 month in a box, interior continuously purged with N2 or O2 (5 l/min)
Results
- The lower the vapor pressure and/or smaller the molecular weight of the contaminant compounds, the more easily they will adsorb onto the surface.
- H2SO4/H2O2 and HNO3 could not completely remove a monolayer of organic contaminants. Dilute HF and O3/H2O succeeded in this. Reasons for these discussed in the paper, relates to the polarity of the molecules.
- Oxygen purging resulted in the same amount of organic contaminants than with no purging, whereas purging with N2 reduced the amount of organic additives adsorbing on the wafer surfaces significantly. Reason for this: native oxide did not grown in N2 ambient, and the surface hence remained nonpolar. O2 oxidized the surface, which thus became polar and attracted contaminants.
- Conclusion: boxes should be filled with N2 if organic contamination should be prevented.
K. J. Budde, W. J. Holzapfel, and M. M. Beyer , “Application of Ion Mobility Spectrometry to Semiconductor Technology: Outgassings of Advanced Polymers under Thermal Stress” Journal of The Electrochemical Society, 142(3), 888-897, 1995.
- Outgassing characteristics of PP (natural, antistatic, and blue), PC, PFA, PVDF, ABS, and PTFE
- Polymers heated up from 60 C to 20 C below their softening temperatures. Amount of outgassing continuously monitored, and outgassing compounds separately identified.
- PTFE and PFA showed lowest amount of outgassing over the entire temperature range; PVDF and PC almost as good.
- Separate tables for outgassing of each material (all list various outgassing compounds)
- For analytical determination of the volatile contaminants at typical temperatures (25-100 C), only ion mobility spectrometry (IMS) has the required sensitivity and selectivity. However, it may still take even with this technique 320 days at RT to accumulate enough substance to distinguish different products, when advanced polymers are studied.