This paper presents an in-depth overview of the present status and novel developments in the field of plasma processing of low dielectric constant (low-k) materials developed for advanced interconnects in ULSI technology. The paper summarizes the major achievements accomplished during the last 10 years. It includes analysis of advanced experimental techniques that have been used, which are most appropriate for low-k patterning and resist strip, selection of chemistries, patterning strategies, masking materials, analytical techniques, and challenges appearing during the integration. Detailed discussions are devoted to the etch mechanisms of low-k materials and their degradation during the plasma processing. The problem of k-value degradation (plasma damage) is a key issue for the integration, and it is becoming more difficult and challenging as the dielectric constant of low-k materials scales down. Results obtained with new experimental methods, like the small gap technique and multi-beams systems with separated sources of ions, vacuum ultraviolet light, and radicals, are discussed in detail. The methods allowing reduction of plasma damage and restoration of dielectric properties of damaged low-k materials are also discussed.

We report a new curing procedure of a plasma enhanced chemical vapor deposited SiCOH glasses for interlayer dielectric applications in microelectronic. It is demonstrated that SiOCH glasses with improved mechanical properties and ultralow dielectric constant can be obtained by controlled decomposition of the porogen molecules used to create nanoscale pores, prior to the UV-hardening step. The Young's modulus ͑YM͒ of conventional SiOCH-based glasses with 32% open porosity hardened with porogen is 4.6 GPa, this value is shown to increase up to 5.2 GPa with even 46% open porosity, when the glasses are hardened after porogen removal. This increase in porosity is accompanied by significant reduction in the dielectric constant from 2.3 to 1.8. The increased YM is related to an enhanced molecular-bridging mechanism when film is hardened without porogen that was explained on the base of percolation of rigidity theory and random network concepts.

The effect of He/H 2 downstream plasma on chemical vapor deposition ͑CVD͒ low-k films with different porosities was studied. The results show that this plasma does not reduce the concentration of Si-CH 3 bonds in the low-k matrix and that the films remain hydrophobic. However, mass loss and reduction in bulk C concentration were observed. The latter phenomena are related to the removal of porogen residue formed during the UV curing of the low-k films. It is demonstrated that the porogen residue removal changes the films' porosity and mechanical properties. The depth of the modification is limited by the penetration of H radicals into the porous low-k films. The plasma-induced damage of porous SiCOH-type low-k materials is one of the key problems in Cu/low-k integration.1 The most severe plasma damage occurs during photomask ͑resist͒ removal. 2The reason for this phenomenon is the hybrid nature of the SiCOH materials. These materials contain a SiO 2 -like matrix where part of the terminating oxygen atoms is replaced by organic groups ͑most often CH 3 ͒. The organic groups provide the films' hydrophobicity, which is important for the dielectric constant reduction. The hybrid nature is the reason for the different reactivities of the low-k components. For instance, the reactive species from plasma such as O radicals penetrate into the porous network of the low-k films and may result in substantial carbon depletion, thus leading to an increase in the k value. The depth of penetration is defined by the diffusion coefficient of active radicals into the pores and their recombination probability on the pore wall. 3Two commonly known approaches are used for the resist removal: ͑i͒ a low temperature, low pressure anisotropic plasma, where the photoresist is removed by an ion-assisted process, oxidizing or reducing plasma chemistries at low temperatures and ͑ii͒ hydrogen-based downstream plasma ͑DSP͒ where the resist is removed at high temperatures by a thermally activated chemical process. According to recent publications, the option with He/H 2 and Ar/H 2 DSPs prevents carbon depletion from the low-k materials matrix.4-6 Therefore, the degradation of the dielectric constant is minimal, and these processes are considered the most attractive options for the microelectronic industry.The porosity in advanced chemical vapor deposition ͑CVD͒ low-k films is created after deposition by the removal of a sacrificial phase ͑porogen͒ by UV-assisted thermal curing. UV curing also results in formation of the Si-O-Si network with improved mechanical properties. 7,8 The porogen molecules are normally cyclic hydrocarbons 9 that are photodissociated by UV light with the formation of volatile hydrocarbons and nonvolatile carbon-rich residues.10,11 The effect of the porogen residues on the low-k properties and the plasma processing compatibility are largely unknown. Fourier transform infrared ͑FTIR͒ spectrometry has a limited sensitivity to amorphous carbon ͑CvC and C-C bonds͒, and this is the reason why it is difficult to monitor porogen r...