| AVS 61st International Symposium & Exhibition | |
| Plasma Science and Technology | Tuesday Sessions |
| Session PS-TuA |
| Session: | Advanced BEOL/Interconnect Etching |
| Presenter: | Mokrane Mebarki, STMicroelectronics, France |
| Authors: | M. Mebarki, STMicroelectronics, France M. Darnon, LTM - MINATEC - CEA/LETI, France C.J. Jenny, STMicroelectronics, France D. Ristoiu, STMicroelectronics, France N. Posseme, Cea-Leti, Minatec O. Joubert, LTM - MINATEC - CEA/LETI, France |
| Correspondent: | Click to Email |
The reduction of device dimension at the sub-15nm technological node requires the use of double patterning for contact etching. Line and space patterns are defined first in a thin TiN layer. Then, a trilayer stack with Si-containing anti reflection coating (SiARC) and organic planarizing layer (OPL) is used to define open areas. The mask is defined by the intersections of both hard mask of TiN and OPL patterns and is used to etch contacts into silicon oxide (TEOS).
The OPL mask must conserve straight profiles during the different etching steps and TiN is exposed to the plasma during silicon oxide etching. The OPL can be etched by different plasmas (N2/H2, O2/SO2, O2/CO2) that may induce a passivation layer on the sidewalls via different passivation elements such has CN, CS, CO. Such passivation layers, as well as the presence of TiN during contact etching, can interfere with the SiO2 etching process and change the final pattern profile. In this study, we investigated the OPL mask etching in COS/O2 plasma in comparison with N2/H2 plasma.
The XPS analyses are performed into Theta300 angle resolved XPS system from Thermo Scientific, ellipsometry measurements are done with spectra FX 200th multiwavelength ellipsometer from KLA-Tencor and OES spectra are recorded with a SD1024 spectrograph detector from SpectraView.
Electronic microscopy observations of OPL patterns etched in N2/H2 or in COS/O2 with various COS/O2 ratios show that straight profiles without undercut can be obtained. After SiO2 etching using a fluorocarbon-based plasma, we observe strong profiles variations in the SiO2 depending on the OPL etch process. After the COS/O2 OPL open, during the first seconds of the SiO2 etching, strong emission lines originating from CS species are observed by OES. In addition, EDX analyses after COS/O2 OPL etching reveal a large amount of sulfur on OPL sidewalls and TiN surface. TiN mask profile is also degraded during the over etch of the OPL and Ti residues are redeposited on all the surfaces. To precise the interaction mechanisms, XPS analyses are performed on TiN, OPL and TEOS after exposure to the various OPL etching processes. We evidenced that the contact profile is influenced by both the process used during OPL opening and the presence of TiN on the wafer. Degradation of masks profiles leads to Ti or S containing residues formation which tends to block the SiO2 etching. These effects can be reduced by an increase of COS/O2 ratio during OPL etching.