Paper EM-WeA10
Copper Deposition and In Situ Chamber Cleaning using Pulsed-CVD Technique

Wednesday, October 21, 2015, 5:20 pm, Room 210E

Due to the conformity required for deposition of metals in high aspect ratio vias, Physical Vapor Deposition is replaced by techniques from the Chemical Vapor Deposition (CVD) family. Conformity wise, the Atomic Layer Deposition (ALD) appears to be the best of the CVD techniques, but the low throughput is dissuasive for layers thicker than 10nm. At the edge between CVD and ALD, the Fast Atomic Sequential Technique (FAST) developed and patented by Altatech, enables deposition of layers with conformity close to the ALD at a higher throughput.

Through Silicon Vias are extensively used for interconnections and necessitate highly conductive materials in holes of aspect ratio higher than 10. Of all low-resistivity metals, namely Ag, Al, Au, Cu and W, studies showed that Cu is the best for filling trenches. Therefore, both the metal and the technique used are imposed, i.e. Cu deposition by CVD is the most suitable solution.

The main obstacle for a complete adoption of Cu as an interconnection metal is the difficulty to clean the chamber after process, since Cu cannot be etched by the usual fluorinated in-situ dry etching processes.

Successful deposition of conformal Cu layer was performed in vias with an aspect ratio of 10, using Altatech AltaCVD deposition chamber and a commercially available Cu precursor. Optimised deposition parameters resulted in low resistivity Cu, down to few µΩ.cm, with deposition rates higher than 100 nm.min^-1. Plotting the deposition rate depending on the substrate temperature highlighted an Arrhenius law behaviour, which in turn provided the optimal deposition temperature. Complementary SEM observation showed Cu layer with low roughness.

Futhermore, taking advantage of the Altatech pulsed solution, FAST, an in-situ dry cleaning process was developed using hexafluoroacetylacetone (hfacH) solvent. The main scheme for Cu etching comprise one step of Cu surface oxidisation and a second step where CuO_x compounds react with hfacH solvent to form volatile species. Several approaches were assessed; the following one will be presented and discussed:

1. O₂ and hfacH introduced simultaneously in the chamber
2. Alternation of O₂ plasma and hfacH fill
3. Pulsed alternation of O₂ and hfacH fill
4. O₂ plasma and pulses of hfacH

Optimising and understanding the influence of each process parameter was made possible by the use of a Residual Gaz Analyzer (RGA) and an Optical Emissions Spectrometer (OES). Cleaning efficiency at the particle generation level of all the approaches are compared, after few microns of Cu deposition and a chamber clean.

Finally, the efficiency of the most promising approach will be investigated on different chamber coatings.