Different types of thin films have a direct impact on the measurement performance of the film thickness gauge. The main influencing factors include the material properties, refractive index, absorbance, surface flatness, etc. of the film. Starting from several common types of thin films, we will explore the applicability and limitations of online film thickness gauges.

1. Metal thin film

Metal thin films usually have high reflectivity, which enables online film thickness gauges to effectively measure their film thickness through methods such as optical interferometry. Metal thin films such as copper, aluminum, gold, and other materials are commonly used in electronic devices, solar cells, catalysts, and other fields. Due to the high and uniform refractive index of metal thin films, optical interferometry is usually not greatly limited in measurement.

However, when the thickness of the film is too thick, optical interferometry may be affected by signal attenuation, leading to measurement errors. Therefore, in the measurement process of thick film metal films, it is necessary to use a film thickness gauge with a high dynamic range or adopt other measurement methods such as X-ray fluorescence.

2. High refractive index thin film

High refractive index materials, such as certain metal oxides (such as indium tin oxide ITO, aluminum nitride, etc.) and certain ceramic thin films, have difficulty in measuring their film thickness. Due to the high refractive index of these materials, optical interference signals may be severely affected, thereby reducing the accuracy of film thickness measurement.

For such thin films, the measurement effect can be enhanced by optimizing the light source selection of the film thickness gauge (such as selecting light of different wavelengths) and improving the detector sensitivity. In addition, combining other technologies such as laser reflection or X-ray technology can improve measurement accuracy and reliability.

3. Low refractive index thin film

Low refractive index thin films, such as certain organic materials, low-k dielectric materials, etc., usually exhibit low light reflection signals, making it difficult to measure their film thickness. When measuring these thin films using optical interferometry, the reflected signal is weak and susceptible to noise interference.

To overcome this limitation, in addition to enhancing the light source power of the instrument and improving the sensitivity of reflected signal detection, more complex signal processing algorithms can also be used to eliminate noise and improve the accuracy of film thickness measurement.

4. Multi-layer thin film

For multi-layer thin film systems (such as optical coatings), due to the possible differences in thickness, refractive index, absorbance, and other characteristics of each layer, a single film thickness gauge may be difficult to accurately measure the film thickness of all layers. Especially in cases where the thin film layer is very thin or very thick, it may not be possible to accurately distinguish the interference signals between the layers.

In this case, it is necessary to use more complex measurement systems or combine optical interferometry with other methods such as X-ray reflection, laser reflection, etc. to obtain accurate multi-layer film thickness information.

5. Non-uniform thin film

In some production processes, due to fluctuations in equipment, environment, or process, the film may exhibit non-uniform distribution. In this case, the measurement accuracy will be affected, especially in areas with significant changes in film thickness.

To address this issue, online film thickness gauges are typically equipped with scanning systems that provide more accurate thin film thickness distribution maps by measuring multiple points at different locations.

Different types of thin film materials have different optical and physical properties, so it is necessary to choose appropriate measurement methods and instruments based on the specific type of film. For complex membrane structures or special thin film materials, it may be necessary to combine multiple technical means to improve the accuracy and stability of film thickness measurement.