To demonstrate the repeatability of the 2830 ZT wafer analyzer a 30-cycle measurement was carried out, with the wafer being unloaded and loaded between each cycle.
The operating speed of semiconductor devices in very large scale integration is affected by the resistivity of the material of the interconnect materials used in transmitting signal from one circuit component to another.
The operating speed of semiconductor devices in very large scale integration is affected by the resistivity of the material of the interconnect materials used in transmitting signal from one circuit component to another. Metal silicides such as tungsten silicides have been used increasingly as interconnect materials because of their low resistivity.
Monitoring WSix deposition processes is not only limited to measurement of the layer thickness. It is also crucial to determine the Si content, usually expressed as an atomic ratio or stoichiometry, because it affects the resistivity of the layer.
Both parameters need to be determined with high accuracy. Wavelength dispersive X-ray fluorescence spectroscopy is ideal for this purpose.
A Malvern Panalytical 2830 ZT XRF Wafer Analyzer equipped with a fixed W-Lα channel and a special WSi high performance channel for the composition is used for this report. Details of the measurement conditions are presented in Table 1.
A fundamental parameter software package is used to calculate the results of WSix film analysis. This produces theoretically derived intensities for reference samples of known composition and thickness, which are then related to the actually measured intensities in order to calibrate the system.
WSix reference films vary in thickness between 500 Å and 2000 Å, with a stoichiometry (x) range of 2.4 to 2.9. The W-Lα signal is very sensitive to variation in the film thickness. The WSi channel is specially designed to determine the composition of the film.
To demonstrate the repeatability of the wafer analyzer a 30-cycle measurement was carried out, with the wafer being unloaded and loaded between each cycle.
| Tube | Tube setting | Channels | Measuring time | Spot size | Software package |
|---|---|---|---|---|---|
4 kW Rh anode, SST-mAX 50 | 32 kV
125 mA | Fixed channels: W-Lα,
high performance fixed channel: WSi | 100s | 40 mm diameter | SoperQ, FP Multi |
Results of the repeated measurement are shown in Table 2 and displayed in Figures 1 and 2. Uniformity measurements, based on 49 spots are shown in Figures 3 and 4.
| Seq. | WSix | |
|---|---|---|
| X | thickness (Å) | |
| 1 | 2.520 | 1505.5 |
| 2 | 2.515 | 1505.7 |
| 3 | 2.511 | 1505.1 |
| 4 | 2.521 | 1506.1 |
| 5 | 2.512 | 1504.8 |
| 6 | 2.511 | 1505.8 |
| 7 | 2.510 | 1505.1 |
| 8 | 2.516 | 1505.8 |
| 9 | 2.512 | 1505.6 |
| 10 | 2.521 | 1506.1 |
| 11 | 2.515 | 1505.8 |
| 12 | 2.516 | 1505.4 |
| 13 | 2.510 | 1504.6 |
| 14 | 2.514 | 1505.2 |
| 15 | 2.513 | 1504.9 |
| 16 | 2.515 | 1505.2 |
| 17 | 2.517 | 1504.7 |
| 18 | 2.514 | 1505.2 |
| 19 | 2.512 | 1504.5 |
| 20 | 2.513 | 1505.7 |
| 21 | 2.519 | 1506.1 |
| 22 | 2.517 | 1505.1 |
| 23 | 2.514 | 1504.9 |
| 24 | 2.508 | 1505.1 |
| 25 | 2.521 | 1505.7 |
| 26 | 2.512 | 1505.4 |
| 27 | 2.520 | 1505.2 |
| 28 | 2.512 | 1505.8 |
| 29 | 2.518 | 1505.6 |
| 30 | 2.514 | 1505.9 |
| Mean | 2.515 | 1505.4 |
| RMS rel. (%) | 0.14 | 0.03 |
Figure 1. Repeatability of the stoichiometry measurement over a 48 h period
Figure 2. Repeatability of the 48 h period
Figure 3. Thickness map, based on a 49-spot measurement. Figure 4. Stoichiometry map, based on a 49-spot measurement
The Malvern Panalytical 2830 ZT XRF Wafer Analyzer, together with the fundamental parameter software package FP Multi, allows accurate analysis of WSix films. Measured film thicknesses can easily extend down to 100 Å, or up to more than 2000 Å. The flexibility and accuracy of the system and software combine to provide an excellent metrology tool for monitoring the WSix deposition process
