Photoresist stripping processes based on hydrogen reductive chemistry have emerged as attractive replacements of the conventional treatments performed using O 2 plasma. H 2 discharges and plasma processes based on gas mixtures containing H 2 provide, in fact, adequate stripping rates while reducing the chemical modifications of the porous ultralow-k ͑ULK͒ dielectric materials employed in interconnect technology. In this work the authors investigate the chemical modification of a number of organosilicate low-k dielectrics interacting with remote H 2 plasma. The materials include both spin-on and plasma-enhanced chemical vapor deposited dielectrics with k, porosity, and chemical composition spanning on a broad range of values. The mechanisms of plasma/dielectric reaction and the depth of interaction are evaluated by means of time of flight secondary ion mass spectrometry. In order to study the nature of the plasma/dielectric interactions and the chemical modifications introduced in the ULK materials, deuterium ͑D 2 ͒ is used to substitute for H 2 in the discharge. Although the plasma-generated radicals interact strongly with the materials, negligible stoichiometry modifications are observed during exposure of silica-rich ULK materials. On the other hand, the dielectrics with higher carbon content undergo major compositional changes. The chemical damage introduced by H 2 -based discharges depends strongly on the formulation of the organosilicate material. The substrate temperature is also seen to affect the influx of plasma species. This acts on the extent of material modifications. Nevertheless, the nature of plasma/dielectric interactions does not vary for processes performed in the temperature range of 200-300°C.

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Effect of plasma interactions with low-κ films as a function of porosity, plasma chemistry, and temperature J.Blanket films of ultralow dielectric constant ͑ULK͒ materials and 193 nm photoresist films have been processed downstream from hydrogen and deuterium-based discharges produced using an inductively coupled plasma reactor. Photoresist ashing rates and ULK modifications have been determined as a function of process parameters. The explored ULK materials differed widely in porosity and carbon content. The effect of processing time, substrate temperature ͑200-300°C͒, and gas composition on the surface and bulk chemical composition of ULK materials was monitored and quantified by ex situ ellipsometry and time-of-flight secondary ion mass spectrometry ͑SIMS͒. The stripping rates of 193 nm photoresist films were found to strongly depend on processing temperature and only weakly on the nature of the H 2 /additive gas mixture. The authors found that hydrogen ͑or deuterium͒ fully penetrates the high porosity ULK layer, whereas for low porosity materials, such penetration is limited to a 50 nm near-surface region. SIMS measurements also reveal that H 2 ͑D 2 ͒ diffusion into carbon-rich ULK layers can cause substantial carbon depletion throughout the penetration region. ULK damage values increase with temperature and injection of gas additives such as argon, helium, and nitrogen to H 2 or D 2 process gases. For each ULK material, the amount of damage depends on the gas mixing ratio; in general, high percentages of nitrogen in H 2 /N 2 ͑or D 2 /N 2 ͒ mixtures cause the most damage. Overall, the results demonstrate that ULK ashing damage depends strongly on both ULK material properties and H 2 -based plasma process parameters. In addition, the authors observed in this work a kinetic isotope effect for stripping of 193 nm photoresist films in H 2 /D 2 /N 2 -based discharges. For given ashing process conditions, the photoresist ashing rate decreases by a factor of 1.414 ͑or square root of 2͒ in D 2 plasma compared to H 2 plasma. This can be explained by the influence of the H or D mass on the chemical reaction rate through a change in the frequency of nuclear vibrations of the reacting atoms. The presence of the kinetic isotope effect for gas mixtures provides unambiguous evidence of the rate-limiting role of atomic hydrogen in the fundamental etching reaction. Simultaneously processed ULK materials showed minor film thickness changes ͑Ͻ10 nm͒ in H 2 or D 2 discharges, and the ULK damage level does not reflect a kinetic isotope effect. Therefore the H / D isotope effect can be used to separate H 2 /D 2 associated ashing and etching processes from other chemistries or mechanisms.

The formation and melting of Pluronic F127 gels in the presence of polyethylene glycols (PEGs) has been studied. All the PEGs studied raised T1 and lowered T2 of 20% F127 gels; this effect was proportional to PEG concentration. At a certain critical "no-gel" concentration of PEG (Cng), F127 lost its ability to form gels. Cng was found to be inversely proportional to PEG molecular weight. An empirical relationship between Cng and PEG molecular weight was obtained which can be used to predict effects of PEGs of any molecular weight on F127 gelation.

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