Optoprofiler 200 mm Semiautomatic Scanning Tool for Wafer Thickness and Topography Analysis: Advanced Method for Spectra Analysis

The reflection measurement of multilayer samples is a standard technique in thin-film fabrication. The typical system used for such measurements is shown in Figure 1.?

Figure 1: Measurement of multilayer sample, in this simplified model comprising two layers 81 and 82. The reflectance probes 2, 3 are mounted on stages 21 and 31 are probing sample 8 comprising two layers 81 and 82 and three reflecting interfaces 810, 812, and 820.

The reflectance signal as shown in Figure 2 is quite complicated. The analysis of reflectance spectra is complicated by the fact that sample structure is not uniquely determined its reflectance.?

Figure 2: Reflectance signal from the system shown in Figure 1.

For example, the reflectivity of the multilayer sample and sample flipped upside down (or left to right as shown in Figure 3) must be the same. One can see this because of the 2nd Law of Thermodynamics. If such a filter existed, then one could place it inside a cavity containing photons and (after some time) concentrate all photons on one side of the cavity which lowers the entropy of the system and violates the 2nd Law of Thermodynamics.

Figure 3: Cavity divided by two-layer sample. If reflectance for the photons traveling from left to right side is larger than reflectance from right to the left side, then after some time we obtain a state (b) having lower entropy than the state (a) which contradicts the 2nd Law of Thermodynamics.?

We developed a special probe that resolves this ambiguity problem and allows the efficient sorting of the complicated reflection spectrum represented in Figure 2, as shown in Figure 4. The processed signal allows clear identification of all optically accessible interfaces.?

Figure 4: Identified interfaces of sample 8 shown in Figure 1.

The reflection sorting algorithm (RSA) was found successful for most of the practically encountered multilayer systems, where all layers of interest are optically accessible. This patent-pending system and RSA method are commercially available from Optoprofiler LLC.

The system is commercially available. Optoprofiler LLC is accepting customers' samples for the system demonstration and method validation.?Please contact us at [email protected], or call us at 267 626 3075.