Due to the excellent selectivity and precision, wavelength dispersive X-ray fluorescence spectrometry is the ideal technique for monitoring TaNx films.
The 2830 ZT Wafer Analyzer is the latest in a successful series of process control tools designed specifically for semiconductor and data storage metrology.
Production control of integrated circuits(ICs) frequently involves the analysis of TaNx films on Si substrates. Sometimes the TaNx film is buried under a Cu film. The Cu metal film is used as an interconnect and TaNx film is used as an adhesion layer for Cu. Also, TaNx film is used as a barrier layer and the amount of N incorporation in the film is critical in determining the layer’s barrier performance.
Due to the excellent selectivity and precision, wavelength dispersive X-ray fluorescence spectrometry is the ideal technique for monitoring these films.
A Malvern Panalytical 2830 ZT XRF Wafer Analyzer equipped with a fixed channel for Ta and for N is used for this report. Details of the measurement conditions are presented in Table 1.
The TaNx layer thickness is determined from the Ta-Lα signal, whereas the N-Kα signal is used to determine the stoichiometry of the layer. The Cu-Kα signal can be used to quantify the layer thickness of the Cu film. Due to a line overlap between Cu-Kα and Ta-Lα the Cu-Kβ line is used.
For thin Cu films (up to 1200 Å) it is possible to determine the stoichiometry, using the N signal and the film thickness using the Ta signal. If the Cu film is too thick (above 1200 Å) the film absorbs almost all of the N radiation. In this case our fundamental parameter program FP Multi is used to analyze the TaN film thickness by calculating the absorption in the different layers.
| Tube | Tube setting | Channels | Measuring time | Spot size | Software package |
|---|---|---|---|---|---|
| 4 kW anode, SST-mAX50 | 32 kV
125 mA | Fixed channels: N-Kα, Cu-Kß, Ta-Lα | 100s | 40 mm diameter | SuperQ, FP Multi |
Calibration lines for TaNx and Cu layer thicknesses and N stoichiometry are presented in Figures 1-3. In these calibrations the layer thicknesses for TaNx and Cu are expressed in Angström whereas the concentration of N is expressed in µm*wt%, indicating the dependence of the N signal on the concentration and the thickness of the TaNx film. Figures 4 to 6 and Table 2 show the obtained reproducibility results. The results illustrate the excellent measurement reproducibility exhibited by the system.
| Seq. | Cu layer (Å) | TaNx layer (Å) | X |
|---|---|---|---|
| 1 | 787.6 | 498.0 | 0.4025 |
| 2 | 787.8 | 498.9 | 0.4022 |
| 3 | 787.7 | 498.0 | 0.4018 |
| 4 | 787.8 | 498.8 | 0.4020 |
| 5 | 787.5 | 498.8 | 0.4024 |
| 6 | 787.9 | 498.1 | 0.4026 |
| 7 | 787.5 | 498.0 | 0.4025 |
| 8 | 787.6 | 498.2 | 0.4016 |
| 9 | 787.6 | 498.1 | 0.4027 |
| 10 | 787.5 | 498.2 | 0.4023 |
| 11 | 787.7 | 498.7 | 0.4022 |
| 12 | 787.8 | 498.8 | 0.4022 |
| 13 | 787.5 | 498.0 | 0.4018 |
| 14 | 787.7 | 498.8 | 0.4020 |
| 15 | 787.7 | 498.0 | 0.4025 |
| 16 | 787.7 | 498.0 | 0.4024 |
| 17 | 787.7 | 498.8 | 0.4021 |
| 18 | 787.6 | 498.9 | 0.4019 |
| 19 | 787.5 | 498.0 | 0.4027 |
| 20 | 787.9 | 498.0 | 0.4020 |
| 21 | 787.7 | 498.1 | 0.4025 |
| 22 | 787.8 | 498.9 | 0.4026 |
| 23 | 787.4 | 498.0 | 0.4019 |
| 24 | 787.5 | 498.0 | 0.4025 |
| 25 | 787.9 | 498.9 | 0.4024 |
| 26 | 787.4 | 498.0 | 0.4018 |
| 27 | 787.7 | 498.0 | 0.4022 |
| 28 | 787.8 | 498.9 | 0.4021 |
| 29 | 787.5 | 498.8 | 0.4025 |
| 30 | 787.7 | 498.9 | 0.4019 |
| Mean | 787. | 498.0 | 0.4022 |
| RMS | 0.140 | 0.123 | 0.0003 |
| RMS rel. (%) | 0.018 | 0.025 | 0.075 |
The Malvern Panalytical 2830 ZT XRF Wafer Analyzer can accurately and simultaneously analyze Cu and TaNx film thickness as well as the stoichiometry of the TaNx film.
787.The TaNx film thickness calibration including the stoichiometry calibration can be adapted to customer requirements up to a Cu thickness of 1200 Å. The TaNx film thickness calibration, excluding the stoichiometry, can be adapted up to a Cu film thickness of 40,000 Å. When focusing only on the Cu film a calibration up to 150,000 Å can be achieved.
