In the photovoltaic industry, accurate measurement of film thickness is crucial to ensure the photoelectric conversion efficiency of solar cells. The In-Line Thin Film Thickness Tester launched by Millennial Solar uses industry-leading micro-nano film optical measurement technology to provide an efficient and accurate thickness detection solution for solar cell production, greatly optimizing the production process and improving product quality.

Application of optical interference principle

The principle of optical interference is a measurement technology based on the interference phenomenon of light waves. It uses the coherent properties of light waves to measure small physical quantities, such as film thickness. In-Line Thin Film Thickness Tester uses this principle to accurately measure the thickness of solar cell films.

Optical path schematic diagram

 Spectral Analysis Technology-When two beams of light are reflected from the film and the reference surface back to the beam splitter and coincide on the detector, their phase difference will cause interference, forming alternating light and dark interference fringes. By analyzing these stripes, particularly their spacing and shape, it is possible to deduce very precisely the difference in the path light travels through the film and thus calculate its thickness. In-Line Thin Film Thickness Tester uses spectral analysis technology to further improve measurement accuracy. By analyzing the spectrum of reflected light—how different wavelengths of light interact with the film—this difference can be used to accurately determine the film's physical properties, such as its refractive index and thickness.

Reflected light interference pattern

 Interference of Reflected Light-Interference of reflected light is a key physical phenomenon used to accurately measure film thickness. This process involves the reflection of light waves at the interface between the film surface and the substrate. These reflected light waves interfere when they meet in space due to their coherence. When these coherent light waves meet at a detector, their phase differences (due to differences in path lengths) cause them to reinforce each other (coherence enhancement) or cancel each other out (coherence cancellation), creating interference phenomena.

Constitutive interference: When the phase difference between two light beams is 0 or an integer multiple of 2π, the two light waves add together to form bright stripes.

Destructive interference: When the phase difference between two light beams is π or an odd multiple of π, the two light waves cancel each other out, forming dark stripes.

Reflected light interference technology provides a non-contact, non-destructive measurement method with very high sensitivity and accuracy. It allows precise measurements of objects without physical contact, thus avoiding the risk of possible damage to the sample or instrument.

Broad spectral coverage and ultra-wide measurement range

In-Line Thin Film Thickness Tester uses LED lights with an effective spectrum range of 320nm to 1100nm, emitting a continuous spectrum covering all light bands from ultraviolet to infrared. This broad spectral coverage enables the equipment to process thin films of many different materials and is suitable for a variety of different process conditions. At the same time, the measurement range is from 20nm to 2000nm, which can accurately measure the thickness of extremely thin single-layer films and thicker multi-layer composite films.

The role and challenges of thin film deposition

During the thin film deposition stage of the solar cell manufacturing process. Among them, the thickness control of the transparent conductive oxide (ITO) layer is an important factor in ensuring the efficiency and stability of solar cells. As a key transparent conductive layer, the ITO layer's main function is to allow light to penetrate and collect electrons, and it must also have good conductive properties. The thickness of the ITO layer has a direct impact on overall performance, including photoelectric conversion efficiency and long-term durability. If the thickness is too thin, it may lead to insufficient conductivity and affect power output; if the thickness is too thick, it may reduce light transmittance and also reduce efficiency.

Precisely controlling the thickness of the ITO layer is not only technically demanding, but also relatively costly. Thickness non-uniformity can cause inconsistencies in performance, resulting in performance fluctuations throughout the batch.

In-Line Thin Film Thickness Tester measures film thickness based on spectroscopy, which is essentially the interference principle of light. When the film thickness meter emits measurement light in the visible spectrum range to the film to be measured, the reflected light from the upper interface of the film layer will interfere with the reflected light from the lower interface of the film layer to form a reflection spectrum. Given the dispersion model of the dielectric constant of the film material When using the thin film layer structure model, the reflection spectrum is only related to the wavelength and film thickness. Therefore, under a given visible band wavelength range, the film thickness can be obtained by inversion algorithm of the measured reflection spectrum.

Schematic diagram of film thickness measurement with spectroscopy

In-Line Thin Film Thickness Tester

In-Line Thin Film Thickness Tester not only completes the accurate detection of film thickness, but also connects to the industrial testing process, allowing manufacturers to use this equipment to conduct large-scale systematic testing in the deposition process production line, thereby greatly saving testing time and improving production efficiency and quality assurance!

E-mail: market@millennialsolar.com

·Fast and automatic 5-point simultaneous scanning of samples

·Obtain film thickness distribution information at different locations of the sample

·Customized measurement dimensions according to customer sample size

·In-line monitoring and detection achieves zero fragmentation rate

·Realize automated testing of the entire production line

In-Line Thin Film Thickness Tester provides a reasonable scientific evaluation of the deposition process based on its unique advantages and optical technology, helping manufacturers with subsequent production and effective optimization of solar cells!