Process control of aluminum interconnect deposition involves the analysis of AlCu films on a Si substrate, where the film thickness and Cu concentration have to be determined. Due to its excellent selectivity and precision, wavelength dispersive X-ray fluorescence spectrometry is the ideal technique for AlCu monitoring on wafers in IC manufacturing.
The PANalytical 2830 ZT determines layer composition, thickness, dopant levels and surface uniformity for a wide range of process films and stacks.
Process control of aluminium interconnect deposition involves the analysis of AlCu films on a Si substrate, where the film thickness and Cu concentration have to be determined. Due to its excellent selectivity and precision, wavelength dispersive X-ray fluorescence spectrometry is the ideal technique for AlCu monitoring on wafers in IC manufacturing.
A Malvern Panalytical 2830 ZT XRF Wafer Analyzer equipped with fixed channels for Al and Cu. Details of the measurement conditions are presented in Table 1.
The amount of copper is determined from the Cu-Kα signal. The Cu-Kα signal is influenced by both the copper concentration and the film thickness. Because the thickness range is lower than the Cu-Kα information depth, a special unit is applied: mu%, obtained by multiplying the Cu in wt% with the film thickness in µm. The Al-Kα signal can be used to quantify the film thickness of the film.
Calibration lines for copper content and film thickness were set up. Fundamental parameter correction was implemented in the calibration to ensure validity over the whole calibration range in terms of composition and film thickness. To demonstrate the analytical precision, a 15-cycle repeated measurement was carried out. The wafer was loaded and unloaded from the instrument between each measurement.
| Tube | Tube setting | Channels | Measuring time | Spot size | Software package |
|---|---|---|---|---|---|
| 4 kW Rh anode,
SST-mAX50 | 32 kV
125 mA | Fixed channels:
Al-Kα, Cu-Kα | 100s | 40 mm diameter | SuperQ,
FP Multi |
Calibration lines for the copper content and AlCu film thickness are presented in Figure 1 and Figure 2 respectively. In these calibrations copper content is expressed in the unit mu% and layer thickness in µm (thickness x concentration in wt%). Results for the repeated measurements on the copper concentration and AlCu film thickness are shown in Table 2. SuperQ automatically calculates the copper concentration by dividing the copper content by the film thickness.
| Seq. | Cu (wt %) | AlCu layer thickness (Å] |
|---|---|---|
| 1 | 0.47 | 14608 |
| 2 | 0.47 | 14623 |
| 3 | 0.47 | 14623 |
| 4 | 0.46 | 14613 |
| 5 | 0.47 | 14620 |
| 6 | 0.47 | 14624 |
| 7 | 0.47 | 14605 |
| 8 | 0.46 | 14615 |
| 9 | 0.47 | 14620 |
| 10 | 0.47 | 14626 |
| 11 | 0.47 | 14623 |
| 12 | 0.47 | 14614 |
| 13 | 0.47 | 14615 |
| 14 | 0.47 | 14699 |
| 15 | 0.47 | 14603 |
| Mean | 0.47 | 14603 |
| RMS | 0.001 | 9 |
| RMS rel. (%) | 0.21 | 0.06 |
The Malvern Panalytical 2830 ZT XRF Wafer Analyzer can accurately and simultaneously analyze copper concentration and film thickness of AlCu films. The calibration ranges of copper content and film thickness can be adapted to customer requirements. With the Al-Kα signal, film thickness up to 50,000 Å can be determined.
