Insulating properties of some liquids after an electrical arc

The insulating properties of a liquid are commonly studied before a breakdown occurs. In HV industrial apparatus such as high energy plastic metallized and liquid impregnated films capacitors, some local breakdowns, named self-healing, occur and the ability of the liquid to remain insulating after electrical degradation is of interest. To understand the influence of the liquid on the behavior of such capacitors, the post-arc behavior of the liquid alone has to be studied in a range of energy (~mJ) close to the self-healing process. The present work deals with the study of the ability of different liquids to restore in the millisecond range their insulating property after an electrical arc. Using an experimental apparatus based on the repetitive charging with a dc HV generator and discharging through an arc of a resistor-capacity system, different kind of liquids were tested. The liquids we used were alcane, esters, alkyl benzene and polyaromatic. We showed as expected that liquids with the smallest ratio of carbon versus hydrogen in their molecular formula present the best restoration property after an electrical arc, property that is crucial for liquids impregnating metallized capacitors     

Multiwavelength interferometry and competing optical methods for the thermal probing of thin polymeric films

Multiple‐wavelength interferometry (MWI), a new optical method for the thermal probing of thin polymer films, is introduced and explored. MWI is compared with two standard optical methods, single‐wavelength interferometry and spectroscopic ellipsometry, with regard to the detection of the glass transition temperature (T_g) of thin supported polymer films. Poly(methyl methacrylate) films are deposited by spin coating on Si and SiO₂ substrates. MWI is also applied to the study of the effect of film thickness (25–600 nm) and polymer molecular weight (1.5 × 10⁴ to 10⁶) on T_g, the effect of film thickness on the coefficients of thermal expansion both below and above T_g, and the effect of deep UV exposure time on the thermal properties (glass transition and degradation temperatures) of the films. This further exploration of the MWI method provides substantial insights about intricate issues pertinent to the thermal behavior of thin polymer films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4764–4774, 2006     

UV impact on the optical properties of thin films of positive tone chemically amplified resist

Chemically amplified photo resist are blend materials whose main compounds are a polymer matrix and an added photo acid generator. Lithography processes that allow imaging patterns in a CAR resist films consist in exposing at first the film to UV light and then to post-bake the film in order to initiate a chemical reaction that induces a local solubility switch of the resist. Sensitivity of the resist is measured by monitoring the UV dose needed to induce the proper solubility switch. For positive tone resist, the efficiency of the photolysis of the PAG to an acid and the deprotection kinetic during the post-exposure bake directly govern the resist sensitivity. This article deals with measurements of the PAG photolysis efficiency by real time spectroscopic ellipsometry. C Dill parameter of 193 nm photoresists is then measured for various film thicknesses and PAG loading.     

Inverse problem solving and optical index determination of resist films by ellipsometry

Spectroscopic ellipsometry (SE) is known to be a technique of great sensitivity in thickness determination of thin layers. The sensitivity is said to be close to some angstrom when optical indexes of materials are perfectly known. However, for resist films, those optical indexes are unknown and can vary from one process to another. Optical indexes and film thicknesses are determined by using Fresnel laws in order to calculate theoretical ellipsometry signatures and by solving the inverse problem. This article presents two strategies developed by LTM in order to accurately determine optical indexes and the thickness of resist films.