ИСТИНА

Scaling of ULSI devices brings new challenges to semiconductor industry. One of the important problems is related to interconnect delay, dynamic power consumption and crosstalk [1,2]. This compels introduction and integration of new materials with low dielectric permittivity (low-k materials) as insulator in interconnects. One of such materials under consideration for sub 10 nm technology node is a spin-coated organosilicate glass layer with ordered porosity (37-40%) and a k-value of 2.2 (OSG 2.2). High porosity of this material leads to significant challenges during the integration and one of them is a dielectric material degradation during the plasma etching step [1,3,4]. Exposing to etching plasma induces loosing material hydrophobicity, subsequent moisture adsorption, dramatic increase of the k-value and degradation of reliability. To be able to step down to 10 nm and 7 nm technology nodes the thickness of the damaged layer of low-k film must be in order of few nanometers. One way to solve this problem is to find the less-damaging etching chemistry. The low-k samples have been etched in a CCP double frequency plasma chamber from TEL. Several etching chemistries with fluorocarbon gases have been evaluated under different plasma conditions. Standard recipes developed for microporous materials with k>2.5 and based on mixture of C4F8 and CF4 with N2, O2 and Ar were found significantly damaging ULK materials and the degree of damage increases with pore size. In this work, the standard etch recipe was compared with oxygen free etch chemistries based on mixture CF4 with CH2F2 and Ar assuming that the presence of oxygen in the first recipe will have significant negative impact in high porous ULK materials. The film damage (loss of methyl groups and moisture uptake) has been analyzed using FTIR spectroscopy [5] and the k-value has been extracted by capacitance CV-measurements. Three plasma components can cause low-k damage: radicals, ions and photons. In this study, it is shown that chemistry of use and hence radicals doesn’t play a significant role for low-k damage, even when oxygen presents in a recipe, but plasma conditions such as applied power and chamber pressure mainly control it. Etching at varying low-frequency power, which controls the ion energy within certain recipe, shows that ion bombardment impact on low-k degradation to be quite small. There is also an indirect evidence that vacuum ultraviolet photons cause the main damage of low-k, whereas radicals and ions are not so harmful. Except of the low damage, a good structure profile and low roughness are demanded. Structure profile quality becomes very important at small scales and sufficiently small surface roughness is needed for a desirable quality of a barrier deposition. To evaluate the patterning capability of this recipes trench structures have been etched in low-k film with two samples for every recipe. After the etching one sample underwent HF dipping and then both were examined by cross-SEM. HF dipping had an aim to remove the damaged part of low-k and visualize the sidewall damage. It was shown that recipes with addition of polymer formed fluorocarbon gases passivate sidewalls and top of the structure with polymer that provides a good profile by reducing of hardmask faceting and isotropic etching. As was expected and verified with AFM, decreasing of energy at low frequency helps one to improve the surface smoothness after the etching step, which can be very important for further integration. The results of the research allowed to optimize the patterning process for dual damascene integration. 1. Mikhail R. Baklanov, Paul S. Ho, Ehrenfried Zschech. Advanced interconnects for ULSI technology. Ch.1, John Willey and Sons, Chichester, 2012. 2. K. Maex, M. R. Baklanov et al. J. Appl. Phys., 93, 8793 (2003). 3. R. J. O. M. Hoofman, G. J. A. M. Verheijden et al. Microelectronic Engineering, 80, 337 (2005). 4. M. R. Baklanov, J-F. de Marneffe et al. 113, 041101 (2013). 5. Alfred Grill and Deborah A. Neumayer. J. Appl. Phys. 94, 6697 (2003).