Nicole Ahner

Surface Energy and Wetting Behaviour of Plasma Etched Porous SiCOH Surfaces and Plasma Etch Residue Cleaning Solutions

The removal of plasma etch residues by wet cleaning is an alternative or additional process to plasma processes, which are known to degrade low-k and ultralow-k dielectric materials. Besides Cu/low-k compatibility wetting is an important issue for wet cleaning. Surface energy of solid and liquid is the key to understand the wetting behaviour. In this study we examined the energetic character of plasma etched/stripped solid surfaces, etch polymers and several cleaning solutions by contact angle measurements. The results show, that variations of the etching process can heavily change the energetic character of the solid. Calculating the surface energies of solid and liquid provides the possibility to make a prediction if a cleaning liquid will wet the surface which has to be cleaned.

Surfactants as an Additive to Wet Cleaning Solutions for Plasma Etch Residue Removal: Compatibility to a Porous CVD-SiCOH Ultra Low-k Dielectric Material

With decreasing feature sizes and integration of porous low-k dielectrics within the interconnect system of integrated circuits, plasma etch residue removal becomes challenging. Plasma cleaning processes are known to degrade low-k materials properties and wet cleaning becomes a promising alternative. Using water based cleaning solutions turns out to be critical as they may not be able to wet low-energy residue surfaces or to penetrate into small features. Lowering the surface tension of the solutions will be essential and the application of surfactants is a promising approach. We investigated the static and dynamic surface tension of different surfactant solutions in DIW and their compatibility to a porous CVD-SiCOH low-k dielectric. The choice of the rinsing solution applied after surfactant treatment turned out to be essential for removing residual surfactant species. Optical, electrical and structural analysis showed that in contrast to DIW an IPA-rinse is able to remove remaining surfactant species.

Optimized Wetting Behavior of Water-Based Cleaning Solutions for Plasma Etch Residue Removal by Application of Surfactants

Wet chemical plasma etch residue removal is a promising alternative to low-k dielectric degrading plasma cleaning processes. With decreasing feature dimensions the wetting behavior of the liquid on low energetic surfaces present after dielectric patterning will be an important issue in developing wet cleaning solutions. High surface energy liquids may not only be unable to wet low energetic surfaces, but can also cause nonwetting of small structures or pattern collapse. The improvement of the wetting behavior of a cleaning liquid by lowering its surface energy by the addition of surfactants is the strategy followed in this study. We show that with choosing the appropriate rinsing solution a wet chemical process using surfactant aided cleaning solutions compatible to the materials used in BEOL (porous low-k, copper, barriers) can be found. The results show a distinct improvement of the wetting behavior of the modified solutions on several low energetic solid surfaces like copper or polymers deposited during dry etching.

Wetting Behavior of Plasma Etch Residue Removal Solutions on Plasma Damaged and Repaired Porous ULK Dielectrics

Porous ultra low constant materials (ULK) for isolation within the interconnect system of integrated circuits are a promising approach to reduce crosstalk and RC-delays due to shrinking feature sizes [1]. Due to their porosity and the integration of carbon rich species like methyl groups into the Si-O-Si backbone of currently fabricated PECVD SiCOH dielectrics those materials are highly sensible towards plasma processing, e.g. dry etching or resist stripping [2]. Metal hard mask approaches, e.g. using TiN hard masks are widely used to prevent the resist stripping plasma directly attacking the low-k material [3]. To reduce further plasma damage like carbon depletion and formation of polar silanol groups the development of less aggressive etching processes is in the focus of research and development activities. Nevertheless dry etching will attack the sidewalls and cause a material degradation. That is why repair processes, mainly based on silylation, are considered to follow the patterning step to reintegrate carbon rich species and to recover the dielectric’s properties [3]. Subsequently to dry etching and repairing the dielectric the wet chemical plasma etch residue removal process is performed. Besides material compatibility and effectiveness in residue removal the wetting behavior of the applied cleaning solutions towards the surface which has to be cleaned is crucial, especially looking on wetting issues like the incomplete wetting of very small via holes or pattern collapse. In this study we investigate in which way different silylation based repair processing regimes are affecting the wettability of the dielectric by water based cleaning solutions using contact angle based surface energy calculations.

Determination of Surface Energy Characteristics of Plasma Processed Ultra Low-K Dielectrics for Optimized Wetting in Wet Chemical Plasma Etch Residue Removal

The integration of porous ultra low dielectric constant materials (ULK) for isolation within the interconnect system of integrated circuits is a promising approach to reduce RC-delays and crosstalk due to shrinking feature sizes [1]. Actually the focus is on porous CVD-SiCOH materials, which consist of a Si-O-Si backbone and organic species (e.g. CH3) to lower polarizability and prevent moisture uptake to remarkably decrease the k-value [2]. The integration of porous low-k materials is very challenging, especially looking at patterning, resist stripping and etch residue removal, where commonly plasma processing has been applied. But plasma processing of ULK materials, especially using oxygen plasmas, is known to degrade electrical, optical and structural material properties by removing carbon from the film and densification of the surface near areas of the ULK [5]. Carbon depletion may also lead to the incorporation of-OH groups, which easily form silanols and therefore increase moisture absorption and k-values [2]. Besides the development of nondamaging plasma processes, wet cleaning is a promising alternative to avoid ULK damage while removing organic plasma etch residues. Additionally wet cleaning steps are always necessary to remove inorganic residues, which do not form volatile reaction products and can therefore not be removed by plasma processing.

Surface modification of porous low-k material by plasma treatment and its application on reducing the damage from sputtering and CMP process

The influence of CH<inf>4</inf>, H<inf>2</inf>, NH<inf>3</inf> and He plasma on the properties of porous low-k material is studied. It is found that the H<inf>2</inf>, He, NH<inf>3</inf> plasma can cause huge carbon depletion in the porous low-k material, and change the low-k surface from hydrophobic to hydrophilic, which will induce moisture uptake into the low-k material during the CMP process, and results in the increase of the k value and leakage current. The CH<inf>4</inf> plasma can make low-k material more resist against moisture uptake and keep the k value and leakage current of low-k films stable.