Airborne Molecular Contamination Research Articles

Evaluation of Chemical Filters Using Wafer Exposure Method and Experimental FFU

Airborne molecular contaminants (AMCs) have become a serious problem with recent advances in semiconductor manufacturing technology. The use of chemical filters to remove AMCs in cleanrooms is critical for improving the yield of semiconductor devices. The experimental FFU is designed for the evaluation of chemical filters. Silicon wafers exposed in the downstream air of chemical filters in the experimental FFU were investigated by Wafer Thermal Desorption—Gas Chromatography-Mass Spectrometry (WTD-GC-MS). Organic contaminants caused by outgassing from the chemical filter were detected on the surface of the silicon wafer and compared among various chemical filters. Results showed that the volatile organic compounds (VOCs) emitted from chemical filters adsorbed on the surface of silicon wafers located downstream of the filters. It was also found that the organic contamination on the surface was related to the amount of outgassing from the chemical filters. In addition, the rates of decrease of organic contamination emitted from various ULPA filters were compared using the experimental FFU. The rate of decrease of organic contamination emitted from the low-outgassing ULPA filter was also superior to that of the normal ULPA filter.

Evaluating the Effectiveness of AMC Control Strategies with Reactivity Monitoring

The control of airborne molecular contaminants (AMC) is becoming a design requirement for all semiconductor manufacturing facilities. Chemical filtration in many forms is being employed in makeup air handling units, recirculation air handlers, minienvironments, fan filter units, and process tools. Suppliers of chemical filtration systems are being asked how best to determine if their systems are working and, if so, whether they are meeting design requirements. Just as there are many ways to apply chemical filtration for the control of AMC, there are many different methods being used to measure AMC and to evaluate filter system performance. Employed in either real-time or passive form, reactivity monitoring has been used in a number of fabs for several years as a way to gauge AMC levels and to evaluate the effectiveness of AMC control strategies. Whether controlling AMC directly or indirectly, reactivity monitoring can provide an overall indication of ambient air quality as well as AMC levels within the controlled spaces. This paper will focus on the use of reactivity monitoring as an air monitoring technique. Results of reactivity monitoring from semiconductor manufacturing facilities will be presented, illustrating both the validity of this air monitoring technique in general as well as its ability to gauge the effectiveness of chemical filtration when applied to the control of AMC.

揮発性有機化合物の材料内部濃度分布測定による発生機構の検討

Airborne molecular contaminants in indoor or cleanroom air have been recognized as the important problems of human health or semiconductor processes. It was reported that the emission flux of volatile organic compounds (VOC) was controlled by the evaporation from building material surfaces and the internal diffusion within the building materials, therefore the internal behavior is the important factor for understanding the emission mechanisms. In this study, the VOC emission from the surface and the concentration of VOC within the building material were evaluated by using the small environmental chamber methods under different temperatures and using the screening test method, respectively. Then the model with the factor of VOC diffusion in the materials and the mass transfer from the material surfaces was used for estimating the emission flux from the experimental internal concentration data within the material. As a result, the emission flux that could be extrapolated by the model agreed with the chamber test data therefore it was clarified that the internal concentration within the material had a great effect on the emission flux.

Reducing airborne molecular contamination by efficient purging of FOUPs for 300-mm wafers-the influence of materials properties

The control of airborne molecular contamination (AMC) plays an increasing role in semiconductor manufacturing processes. A method to reduce AMC is purging of wafer boxes with inert gas. In this study, data on the practicability and optimization of purging a front opening unified pod (FOUP), a wafer box for 300-mm wafers, are presented. Different parameters for the purge process are evaluated experimentally. Key values for the assessment of efficiency are the time-dependent content of oxygen and humidity in the FOUP. The increase in the key values after the purge was measured and the construction of the FOUP was modified in order to obtain sufficient tightness. Spatially resolved measurements reveal the homogeneity of the purge. Experimental data are compared to data obtained by a simulation using a computational fluid dynamics program. Values for oxygen are in agreement with the calculated curves. In contrast to this, an additional, long-lasting contribution that was not taken into account in the simulations makes depletion of humidity slower than expected. This contribution is explained with the desorption and permeation of humidity through the plastic walls of the FOUP. The presence of both effects, desorption and permeation, is proved and quantified. Materials properties turn out to heavily affect purge effectiveness and the postpurge ingress of certain contaminants in a wafer box.

Countermeasures against Airborne Molecular Contaminants in Clean Room

Countermeasures against Airborne Molecular Contaminants in Clean Room

Reactivity Monitoring: An Alternative to Gas Monitoring in Semiconductor Cleanrooms?

One environmental parameter that is increasingly targeted for tighter control in semiconductor cleanrooms is airborne molecular contaminants (AMC). The biggest problem today is not whether specified levels of AMC can be achieved, but whether they can be accurately measured to ensure compliance with any standards or control criteria. A number of manufacturers are turning to environmental classification via reactivity (or corrosion) monitoring. This paper describes reactivity monitoring and examines its use for: • Performing environmental assessments in cleanrooms as part of contamination control programs based on the presence (or absence) of corrosive AMC. • Providing the short-term data required to manage and mitigate contaminant-specific episodes. • Evaluating long-term air quality trends in a facility. • Conducting research studies designed to determine relationships, if any, between contaminant levels and possible damaging effects.

Effects of Airborne Molecular Contamination on DUV Photoresists.

This paper will report post-exposure delay results using Shipley UVIBISTM deep UV resist. The variables of the experiments include: processing delays (expose to post-exposure-bake and coat to exposure), different levels of ammonia, different substrates, and processing conditions. Better delay stability is observed when standing waves are reduced by processing. When standing waves are present, scumming tends to occur at the nodes; acid depletion near the nodal region prevents adequate deprotection for development to occur.The methods for detecting airborne contamination are ion mobility spectrometry for ammonia and thermal desorption gas chromatography for 1-methyl-2-pyrrolidone (NMP). Fourier transfer infrared (FFIR) spectroscopy is used to monitor the deprotection reaction of UVIIHS photoresist films with and without delays.