Atomic Layer Deposition Passivation Basics for Quartz Resonator Stability
Sub-nanometer ALD alumina passivation prevents quartz electrode oxidation and surface adsorption, capping decade frequency drift below two parts per million.
Spectroscopic Ellipsometry
Meaning
Non-destructive optical metrology technique measures the change in polarization of light reflected from a sample to determine its physical properties. Using spectroscopic ellipsometry allows engineers to calculate the thickness and refractive index of thin films with sub-nanometer precision. The method relies on comparing a mathematical model of the stack to the measured data.
Thin Film Analysis
Polarization changes are highly sensitive to the presence of extremely thin layers on a substrate. Applying spectroscopic ellipsometry to semiconductor wafers provides data on the quality of oxides, nitrides, metals and photoresists. Multiple wavelengths are measured simultaneously to provide enough data points for complex multi-layer structures.
Process Control
Monitoring the deposition rate in real time or between batches ensures that coatings meet the design specifications. Because spectroscopic ellipsometry does not require contact with the surface, it can be added to automated production lines without risking contamination. Variations in the film properties are identified immediately, allowing for rapid correction of the manufacturing parameters.
Material Characterization
Determination of the complex dielectric function provides insight into the electronic structure of new materials. Beyond simple thickness, spectroscopic ellipsometry reveals the roughness and porosity of a surface. Reliability of the measurement depends on the accuracy of the underlying model and the quality of the light source.
Final reports from the instrument show the goodness of fit between the theoretical curve and the actual measurement. These software-generated models are calibrated using known standards to eliminate instrumental bias. Operators verify the results by checking the mean squared error value.