G. Vereecke

Wafer thermal desorption spectrometry in a rapid thermal processor using atmospheric pressure ionization mass spectrometry

This paper demonstrates the possibility of performing thermal desorption spectrometry (TDS) on wafers in an atmospheric pressure rapid thermal processor (RTP). A special gas sampling system is described, which allows the analysis of gas composition inside the RTP chamber with atmospheric pressure ionization mass spectrometry (APIMS). Sampling is controlled with no valve operation and high dilution of the sample gas flow can be achieved while maintaining a short sample transfer time. It is shown how gas flows can be optimized to improve the sensitivity and resolution of TDS spectra. The RTP-APIMS setup was used in a study of H/sub 2/O absorption by low dielectric constant fluorinated silica glass (FSG) films, helping to develop a cap that reduced H/sub 2/O absorption upon storage by a factor of 60. NH/sub 3/ is shown to desorb from FSG and SiO/sub 2/ films deposited by plasma-enhanced chemical vapor deposition (PECVD), which may be of concern for the reliability of integrated circuits.

Degradation of 248 nm Deep UV Photoresist by Ion Implantation

Wet processes are gaining a renewed interest for removal of high dose ion implanted photoresist (II-PR) in front-end-of-line semiconductor manufacturing because of their excellent selectivity towards the wafer substrate and gate materials. The selection of wet chemistries is supported by an insight into the resist degradation by ion implantation. In this work, different analytical techniques have been applied for in-depth characterization of the chemical changes in 248 nm DUV PR after arsenic implantation. A radical mechanism of resist degradation is proposed involving cross-linking and chain scission reactions. The cross-linking of the resist is dominant especially for high doses and energies. It leads to significant depletion of hydrogen and formation of carbon macroradicals that recombine to form C-C cross-linked crust. Moreover, formation of ab-unsaturated ketonic and/or quinonoid structures by cross-linking reactions is suggested. In addition, the dopant species may provide rigid points in the PR matrix by chemical bonding with the resist. For higher doses and energies further dehydrogenation occurs, which leads to formation of triple bonds in the crust. Different p-conjugated structures are formed in the crust by cross-linking and dehydrogenation reactions. No presence of amorphous carbon in the crust is revealed.

Gaseous Impurities in Co Silicidation: Impact and Solutions

With the application of a Co salicide process in deep submicrometer integrated circuits manufacturing, the potential benefit of its linewidth independent sheet resistance could he hindered due to the interaction of traces of gaseous impurities from different sources with silicide formation. In this work, we first analyze in situ the thermal desorption behavior of various dielectric and metal layers encountered in Co salicide process, by using the rapid thermal processing tool-atmospheric pressure ionization mass spectrometry, Based on these results as well as information from the literature, the detrimental impact of gascous impurities (mainly O 2 and H 2 O) has been analyzed. The key facts are that Si has a stronger chemical affinity to O than Co, and the interaction of Co and Si oxide occurs only with great difficulty. We also argue that impurities from thermal desorption can have a stronger impact to the silicidation (edge thinning effect) compared to the impurities already in the processing ambient, duc to its strong and direct interaction to the adjacent Co/Si interface. The fundamental principle of a technical solution is that the process should prevent O from coming into the Co/Si interface, and/or should be capable of removing the Si oxide already there. A few solutions reported m fiterature, including depositing Co at elevated temperatures, Co with reactive or nonreactive capping, and the use of Co(Ti) alloys, are analyzed.

Removal of High-Dose Ion-Implanted 248 nm Deep UV Photoresist Using UV Irradiation and Organic Solvent

Wet processes using organic solvents are gaining a renewed interest for stripping high dose ( ≧ 1 × 10 15 atoms. cm -2 ) ion-implanted photoresist (II-PR) in front-end-of-line semiconductor manufacturing because of their excellent selectivity to ultrashal-low implanted substrates and novel materials. However, the highly cross-linked resist layer (so-called crust), formed on the top and sidewalls of the resist has very limited solubility in organic solvents unlike the underlying nonimplanted resist (bulk). This study investigates the effect of UV pre- and post-treatment on II-PR for enabling its removal by organic solvent. Moreover, the impact of the UV wavelength, dose, and power density on the crust and bulk is presented. Optimal conditions of the UV pre- and post-treatment can be determined. Short ( < 200 nm) and long wavelengths (300-400 nm) at low doses induce more scission of the crust with less cross-linking of the bulk, resulting in higher solubility of the II-PR in organic solvents. Moreover, the short wavelength pretreatment is advised because of its bigger effect on the crust, resulting in significant enhancement of the residue removal. In addition, a post-treatment using short wavelengths has high removal efficiency in contrast to the long wavelengths treatment. Finally, no significant impact of the power density is revealed.

Characterization of Modification of 193-nm Photoresist by HBr Plasma

[Vereecke, G.; Claes, M.; Le, Q. T.; Kesters, E.; Struyf, H.] IMEC, B-3001 Heverlee, Belgium. [Carleer, R.; Adriaensens, P.] Univ Hasselt, IMO Div Chem, B-3590 Diepenbeek, Belgium. nguy.vereecke@imec.be

Challenges and novel approaches for photo resist removal and post-etch residue removal for 22 nm interconnects

The critical challenges of removal of post metal hard mask etch photo resist removal and post low-k etch residue removal are described. An overview of some new non-plasma based approaches is presented.

The critical role of the metal / porous low-k interface in post direct CMP defectivity generation and resulting ULK surface and bulk hydrophilisation

Surface hydrophilisation of pristine low-k (ULK) is known as a CMP-induced damage mechanism. This phenomenon already enhanced by several factors (e.g. mechanical polishing action, solid content in the slurry, pH of the slurry solution, presence of organic residues, etc ...) extends to bulk hydrophilisation when polishing metal/ULK systems. The degree of bulk hydrophilisation depends on the nature of the selected metal/low-k combination, the metal being either a hard mask (for low damage patterning purposes) or a Cu diffusion barrier. The phenomenon is more or less pronounced depending on the nature of the overlaying metal film (Ta>TaN>Ti>TiN). It also correlates with the post CMP defects generation and more specifically with the presence of scratches with depths ranging from ~178 nm down to ~6 nm as measured with a 0.19 mum tip depending on the metallic layer. These scratches can be reduced in number and depth by overpolishing leading thereby to reduced hydrophilicity. Besides selecting properly the overlaying metal film, UV curing the ULK for mechanical properties improvement and/or engineering the metal/ULK interface by inserting an ultra-thin dielectric layer with higher mechanical properties to prevent the metal from contacting the low-k surface significantly limits the direct CMP-induced bulk hydrophylisation.

In-situ ATR-FTIR for dynamic analysis of superhydrophobic breakdown on nanostructured silicon surfaces

Superhydrophobic surfaces are highly promising for self-cleaning, anti-fouling and anti-corrosion applications. However, accurate assessment of the lifetime and sustainability of super-hydrophobic materials is hindered by the lack of large area characterization of superhydrophobic breakdown. In this work, attenuated total reflectance−Fourier transform infrared spectroscopy (ATR-FTIR) is explored for a dynamic study of wetting transitions on immersed superhydrophobic arrays of silicon nanopillars. Spontaneous breakdown of the superhydrophobic state is triggered by in-situ modulation of the liquid surface tension. The high surface sensitivity of ATR-FTIR allows for accurate detection of local liquid infiltration. Experimentally determined wetting transition criteria show significant deviations from predictions by classical wetting models. Breakdown kinetics is found to slow down dramatically when the liquid surface tension approaches the transition criterion, which clearly underlines the importance of more accurate wetting analysis on large-area surfaces. Precise actuation of the superhydrophobic breakdown process is demonstrated for the first time through careful modulation of the liquid surface tension around the transition criterion. The developed ATR-FTIR method can be a promising technique to study wetting transitions and associated dynamics on various types of superhydrophobic surfaces.

Application of UV Irradiation in Removal of Post-etch 193 nm Photoresist

This study focused on the effect of UV irradiation on modification of polymethyl methacrylate-based photoresist, and then on wet photoresist (PR) removal of patterned structure (single damascene structure). Three single-wavelength UV sources were considered for PR treatment, with λ = 172, 222, and 283 nm. Modification of blanket PR was characterized using Fourier-transform infrared spectroscopy (FTIR; chemical change), spectroscopic ellipsometry (SE; thickness change), and dissolution in organic solvent (solubility change). While for patterned samples, scanning electron microscopy (SEM) was used for evaluation of cleaning efficiency. In comparison to 172 nm, the PR film irradiated by 222 nm and 283 nm photons resulted in formation of higher concentration in C=C bond. Immersion tests using pure N-methyl pyrrolidone (NMP) at 60 °C for 2 min showed that some improvement in PR removal was only observed for PR films treated by 283 nm UV for short irradiation times. Irradiation by photons at the other two wavelengths did not result in an enhancement of removal efficiency. The PR film treated by 222 nm photons was chosen for further study with O 3 /H 2 O vapor at 90°C. Experimental results showed a complete PR and BARC removal for UV-treated PR, which can be explained by C=C bond cleavage by the oxidizer.

Conversion of a Patterned Organic Resist Into a High Performance Inorganic Hard Mask for High Resolution Pattern Transfer.

Polyphthalaldehyde is a self-developing resist material for electron beam and thermal scanning probe lithography (t-SPL). Removing the resist in situ (during the lithography process itself) simplifies processing and enables direct pattern inspection, however, at the price of a low etch resistance of the resist. To convert the material into a etch resistant hard mask, we study the selective cyclic infiltration of trimethyl-aluminum (TMA)/water into polyphthalaldehyde. It is found that TMA diffuses homogeneously through the resist, leading to material expansion and formation of aluminum oxide concurrent to the exposure to water and the degradation of the polyphthalaldehyde polymer. The plasma etch resistance of the infiltrated resist is significantly improved, as well as its stability. Using a silicon substrate coated with 13 nm silicon nitride and 7 nm cross-linked polystyrene, high resolution polyphthalaldehyde patterning is performed using t-SPL. After TMA/H2O infiltration, it is demonstrated that pattern transfer into silicon can be achieved with good fidelity for structures as small as 10 nm, enabling >10× amplification and low surface roughness. The presented results demonstrate a simplified use of polyphthalaldehyde resist, targeting feature scales at nanometer range, and suggest that trimethyl-aluminum infiltration can be applied to other resist-based lithography techniques.