The back end of the line (BEOL) copper (Cu) interconnect line width and spacing is decreasing with each advancement in technology node. It is important to understand how the decreasing dimensions will impact BEOL chemical mechanical planarization (CMP) process. This study is focused on evaluation of Cu CMP using three categories of slurry formulations (i.e. alumina abrasive, silica abrasive and abrasive-less) by utilizing test structures with dimensions relevant to sub-20 nm technology. The results presented in this study show the key factors driving the performance of slurry formulation (e. g. liner selectivity, defects) are strongly dependent on the copper (Cu) interconnect line width and spacing. The results show the blanket rate selectivity does not translate to equivalent selectivity on patterned structures. In addition, the slurry formulations lost selectivity to liner as interconnect width/spacing is reduced from 40 nm to 32 nm highlighting the need to account for pattern density when predicting selectivity. Furthermore, evaluation of Cu CMP slurry formulations with cobalt (Co) liner indicates that existing formulations exhibit no Cu to Co selectivity. Overall, the results on multiple interconnect dimensions from this study are very important for researchers focused on slurry formulation development and CMP modeling. (C) 2013 The Electrochemical Society. All rights reserved.

In the attempts to push the resolution limits of 193nm immersion lithography, this work demonstrates the building of 3 metal level 56nm pitch copper dual-damascene interconnects, using Negative-Tone Development Lithography-Etch-Lithography-Etch (LELE) Patterning at line level. Line Resistance and intra-level capacitance can be affected by the double patterning integration, but a good process window has been demonstrated, showing no impact on RC performance. The introduction of a self-aligned via (SAV) process with a TiN hard-mask is able to provide a robust process window in terms of via-metal short yield at line and via level. SAV implementation at these dimensions also affects the aspect-ratio of the structures and leads to new challenges in metallization: optimized profile, without bowing or undercut, is mandatory to enable the filling of 28nm lines. The metal hard-mask has to be removed or at least faceted by erosion. This can be achieved by conventional RIE process optimization, but pushes the RIE selectivity to challenging limits. Physical dimensions on target and via chain yield have been demonstrated by fine tuning RIE process. Profile improvement can also be achieved by the introduction of new WET process, helping the removal of the metal hard-mask while being neutral to the ULK. We have demonstrated good yield and reliability with an integration using hard-mask wet removal.

This work demonstrates the building of a 56 nm pitch copper dual damascene interconnects which connects to the local interconnect level. This M1/V0 dual-damascene used a triple pitch split bi-directional M1 and a double pitch split contact (V0) scheme where the local interconnects are with double pitch split in each direction, respectively. This scheme will provide great design flexibility for the advanced logic circuits. The patterning scheme is multiple negative tone development lithography-etch. A memorization layer is utilized in the triple patterned M1 and the double patterned V0 levels, respectively. After transferring the two via levels into the metal memorization layer, a self-aligned-via (SAV) RIE scheme was used to create vias confined by line trenches such that via to line spacing is maximized for better reliability. Seven litho/etch steps (LIP1/LIP2/V0C1/V0C2/M1P1/M1P2/M1P3) were employed to present this revolutionary interconnects.

Spacer-defined double patterning was investigated as a patterning option for 20/14-nm logic technology's back-end-of-line (BEOL), and compared with the double patterning options of front-end-of-line (FEOL). Negative spacer-defined double patterning was used to provide less overlay impact and variable CD control on the metal lines compared with other double patterning techniques. Block lithography as a 2nd exposure was able to maintain better tip-to-tip and tip-to-line fidelity by forming lines that behave as a additive etch block. SiO2 spacer was directly deposited on resist core-mandrel via a low-temperature deposition process. Resist integrity was optimized through aerial image and mask optimization as well as resist selection processes. Design decomposition of the BEOL layout was identified as a major challenge in enabling the spacer-defined double patterning. Finally, successful integration of the patterning into the BEOL device was demonstrated.

We are evaluating the readiness of extreme ultraviolet (EUV) lithography for insertion into production at the 15 nm technology node by integrating it into standard semiconductor process flows because we believe that device integration exercises provide the truest test of technology readiness and, at the same time, highlight the remaining critical issues. In this paper, we describe the use of EUV lithography with the 0.25 NA Alpha Demo Tool (ADT) to pattern the contact and first interconnect levels of a large (similar to 24 mm x 32 mm) 22 nm node test chip using EUV masks with state-of-the-art defectivity (similar to 0.3 defects/cm(2)). We have found that: 1) the quality of EUVL printing at the 22 nm node is considerably higher than the printing produced with 193 nm immersion lithography; 2) printing at the 22 nm node with EUV lithography results in higher yield than double exposure double-etch 193i lithography; and 3) EUV lithography with the 0.25 NA ADT is capable of supporting some early device development work at the 15 nm technology node.