We investigated the deposition of the molecular contaminants on Cr, MoSi and quartz photomask surfaces by means of representative Cr, MoSi and SiO₂ layers deposited on wafers using TD-GCMS for the organics and LPE-IC for the SO₂ analysis. Mask-like layers were exposed to organic contaminants outgassed by three different types of mask pods during storage steps and Cr films were put in SO₂ controlled contaminated atmosphere. Organic species contaminating the different mask surfaces were identified depending on time. A rapid contamination kinetic was highlighted. Results have shown that low volatile organic compounds have higher deposition rates and that few specific molecules (such as caprolactam ; acrylic acid, dodecyl ester, butyldiglycol...) contribute in very significant levels (few E+13 atC/cm²). It also appeared that organics present a higher affinity for quartz and MoSi layers than for Cr surfaces but also that some compounds can have a specific affinity depending on the surface. These affinity differences have been quantified through the calculation of the contaminants sticking coefficients. Regarding the SO₂ deposition, Cr surfaces have showed a strong ability to be polluted in clean room conditions, up to a saturation level just higher than 1E+14 SO₂/cm². The kinetic is rapid and in good agreement with a Langmuir-type adsorption model allowing the determination of the deposition kinetic constant. Furthermore, it was showed a significant enhancement of SO₂ deposition with air humidity. Finally, this work contributes to a better knowledge of the molecular contaminants deposition behavior on mask surfaces providing relevant data to control the photomask contamination in order to prevent crystal growth issues.

Date Published: 15 May 2010
PDF: 12 pages
Proc. SPIE 7545, 26th European Mask and Lithography Conference, 75450I (15 May 2010); doi: 10.1117/12.863877

Published in SPIE Proceedings Vol. 7545:
26th European Mask and Lithography Conference
Uwe F.W. Behringer; Wilhelm Maurer, Editor(s)