Indirect Broadband Monitoring

OptiLayer allows you to simulate depositions in vacuum chambers equipped with broadband monitoring devices. Simulation with witness chips is also available in OptiLayer.

Distribution of layers on witness chips are specified in the monitoring spreadsheet (Results --> Monitor) as in the case of monochromatic monitoring.

Example. a 25-layer edge filter operating at the angle of incidence of 45 degrees and exhibiting high reflectance in the range 583-683 nm and high transmittance in the range 670-710 nm. Spectral reflectance and transmittance of the filter are shown in Fig. 2 and its refractive index profile is shown in Fig. 3.

The design comprises layers of high-index material Nb2O5 with n=2.2 and low-index material SiO2 with n=1.47. Materials abbreviations are H and L, respectively.

broadband monitoring

Fig. 1. Broadband monitoring (BBM) simulations using witness chips (see Fig. 4).

edge filter spectral properties

Fig. 2. Spectral reflectance and transmittance of the 25-layer edge filter.

dichroic filter thicknesses

Fig. 3. Refractive index profile (layer thicknesses) of the 25-layer edge filter.

In order to monitor the deposition of the edge filter, four witness chips were chosen. The distribution of design layers is shown in Fig. 4. Chips 1 and 3 contain H-layer only. The first layers on Chips 1 and 3 are H-layers and the next layers are L-layers. 

IndirectMon Mono Chips

Fig. 4. Distribution of layers of the 25-layer edge filter on witness chips. Chips 1 and 3 accumulate H-layers only. It is seen also in the course of the simulations (Fig. 1).

In the Monitoring spreadsheet (Results --> Monitor), the layer distribution on chips should be specified in column C (Chip). The number of chips and the substrates should be specified on the right-side panel.

monitoring with witness chips

Fig. 5. Monitoring spreadsheet generated for 4 chips (Suprasil), distribution of layers is schematically shown in Fig. 4. On the bottom panel, you can switch between all separate layers (with Chips 1-4 tab) or separate layers corresponding to separate chips (1, 2, 3, and 4 tabs). Using Options button, you can specify some important settings (see Fig. 6).

Important: to be able to specify chips and related issues, you need to check Permit reusing Chips check box: Options button (left vertical panel) --> Options button --> Misc. tab --> Permit reusing chips checked.

In order to perform broadband monitoring simulation, you should specify important parameters such as deposition rates and their fluctuations, systematic/random deviations in layer refractive indices, shutter delays and their fluctuations, noise in measurements data, spectral range, wavelength step, drifts etc. You can specify the parameters in the six-step dialog:

Analysis --> Broadband Monitoring Simulation.

broadband monitoring optical coatings

Fig. 6. You can specify deposition rates of layer materials and their fluctuations. Correlation time and its RMS defines the pattern of the rates.

broadband optical monitoring

Fig. 7. At the Step 2, you specify random or/and systematic deviations of the layer refractive indices from the nominal ones. Also, you specify the mean shutter delay and its RMS. In order to activate broadband monitoring with chips, Use Chips distribution check box should be checked.

broadband monitoring with witness chips

Fig. 8. At Step 3, you can choose the spectral characteristic to be monitored. Also, monitoring spectral range, number of spectral points and scan interval are specified.  

broadband optical monitoring with chips

Fig. 9. Setting at the Step 4 are related to the quality of the experimental data: random errors (noise) in the recorded spectra, fluctuations, calibration, drifts.

broadband monitoring

Fig. 10. BBM simulations are performed. Instead of spectral curves corresponding to the layers on the substrate, you observe spectral curves on chips.

indirect broadband monitoring

Fig. 11. Resulting performance of one of the simulated deposition runs.

In the case of indirect broadband monitoring with witness chips, you can estimate production yield using BBM simulation tools of OptiLayer.  For this purpose, an appropriate range target should be loaded (Fig. 12).

Of course, the design may not violate the range target, i.e. merit function must be zero (see MF on the bottom of the analysis window).

monitoring witness chips

Fig. 12. Range target and spectral characteristics of the 25-layer edge filter.

broad band monitoring

Fig. 13. Using Yield button you can open Broadband Monitoring Yield window (Fig. 4) where you specify the number of simulations (Number of tests field). Through Start button you can run BBM simulations.

optical monitoring yield

Fig. 14. Broadband Monitoring Yield window shows the number of successful (green bar) and unsuccessful (red bar) simulated deposition runs. At Step 6, you observe spectral performances of all simulated deposition runs plotted by green (successful) and by red (unsuccessful). 

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