| AVS 64th International Symposium & Exhibition | |
| Plasma Science and Technology Division | Wednesday Sessions |
| Session PS-WeM |
| Session: | Advanced BEOL/Interconnect Etching |
| Presenter: | QuocToan Le, IMEC, Belgium |
| Authors: | Q.T. Le, IMEC, Belgium E. Kesters, IMEC, Belgium F. Holsteyns, IMEC, Belgium |
| Correspondent: | Click to Email |
Porous low-k dielectrics have been commonly used in micro- and nanotechnologies since the past decade. In back-end of line interconnect, the dielectric layer is typically patterned by dry etching through a photoresist or metal hard mask using fluorocarbon-containing plasmas, followed by electroplating of Cu inside the etched patterns. Residues are always formed during the pattern etching, regardless of the hard mask type.
This study focused on the types of residues generated during, and after, the plasma patterning of TiN hard mask/ porous low-k damascene stack. The porous dielectric s used in this study were CVD organosilicate glass (OSG) with target k-values of 2.2 and 2.55. Stacks of Si substrate/ OSG/SiO2/TiN (from bottom to top) of 45 nm ½ pitch were prepared as test vehicles. Several methods commonly used for blanket surface characterization were applied for the patterned structure under study, including contact angle, Fourier transform Infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Using fluorocarbon-based dry etch plasma to pattern the OSG, for both 45 nm ½ pitch stacks, etch residues were detected on the TiN surface, dielectric sidewall and bottom (Figure 1, after aging, Supplemental document). The XPS F1s core-level spectra collected from the patterned OSG consisted of two main components: a sharp peak centered at ~684.6 eV corresponds to F-Ti bonds and the peak at higher binding energy (chemical shift ~3.9 eV) can be assigned to C-F bonds. In order to have further insight into the residue location, XPS spectra were collected at various take-off angles (TOA, measured with respect to the surface normal) with the beam perpendicular to the low-k lines. While the polymer-based residues (CFx) are mainly detected on trench sidewall and bottom (measured at low TOA, Figure 2, Supplemental document), the metal-based residues (TiFx) are mainly formed on the top surface (at high TOA). For the high binding energy component, the apparent chemical shift recorded at low and high TOA’s is estimated to be ~0.85 eV, suggesting the presence of organometallic-type residues close to the top surface.
The effect of moisture and aging time on the density of the residues were investigated. Ti-containing residues tended to grow upon aging. The saturation level of the growth appeared to depend on the amount of the residues initially present on the surface. In terms of residue removal, the effect of a subsequent plasma treatment (post-etch treatment) and/or a wet clean on the removal of these residues was also studied.