Flames - Measurement system for functional layers

LayTec Flames is a multi-head optical metrology system for monitoring multi-layer thin-film structures in large area processes. It measures multi-traces of layer thickness, reflectance, and transmittance uniformity directly after the deposition in in-line processes with thickness resolutions down to less than  1 nm. Typical applications are functional layers in display industries, foil coating (roll-to-roll), and glass coatings. Flames is suitable for nearly any thin-film production line. With its contact-free optical approach it measures close to the process and allows closed-loop control of layer deposition and etching. With LayTec Flames you get homogeneity information of layers at the tact rate of your line, directly after processing, complete with statistical analysis. You can apply quality thresholds and alarms for fast reaction of operators.

Antireflective coatings on solar glass

In order to minimize efficiency losses due to reflection of sun light on the front glass of PV modules, high-end solar glass is often equipped with an antireflective coating. The coating is deposited as a liquid by spray-coating or by printing techniques. Thereafter it is dried and annealed in consecutive production steps. The properties of the coating must be optimized in a way that the minimum of the reflectance matches the spectral absorption and conversion efficiency of the solar cells. Hence, spectral reflectance measurements directly deliver the most relevant information to characterize the coating in the production line. Fig. 1 shows the reflectance of uncoated glass and of glass coated by two different ARCs.
Reflectance spectra of uncoated glass and of AR coated glass with reflection minima at 665 nm and 760 nm.
Fig. 1. Reflectance spectra of uncoated glass and of AR coated glass with reflection minima at 665 nm and 760 nm.

As the reflectance of an ARC on glass is very low (this is the very purpose of the ARC) and it is mostly deposited on rolled glass which is used in this field of application, in-line measurements are quite challenging. However, optimisation of the optical metrology system’s design allows measurements with a repetition rate of up to 100 Hz even under these conditions.

Download the poster "Optical in-line monitoring of deposited layers in large area coating lines" (presented at ICCG-11)

Example: Measuring a-Si layer in display production








Application: in-line reflectance measurement for on-the-fly layer thickness analysis of an a-Si/SiO/SiN stack with metal contact pattern on Gen8 glass panel, directly after deposition in a cluster system. The system has no impact on the tact time and is easily integrated into the line on a conveyor. The measurement was performed on five traces with five measurement heads. Each trace yields 100 measurement points per panel. This allows detailed homogeneity control and statistics (min, max, ave, percentiles) over the whole panel size.

TF-Display: a-Si functional layers

LayTec Flames delivers high-accuracy information on the fly for production control. Cross-panel thickness fluctuations can be tracked as well as long-term drifts. Improve mean time to clean (MTTC) and yield by 100% control of your panels.

Fig. 1+2: a-Si thickness on two substrates A and B: in-line Flames is compared to ex-situ reference (Horiba)        

a-Si layer determined by ex-situ reference ellipsometer is thicker due to smaller refraction index. Same thickness fluctuations are resolved by both measurements. The Flames in-line measurement is done on the fly and covers 100% of substrates while the ex-situ reference method takes several minutes and can be applied to only a few % of substrates.

Stack 50nm a-Si / 100nm SiO / 50nm SiN

LayTec Flames offers nanometer accurate in-line monitoring of complete layer stacks (here: a-Si, SiNx, SiOx). Save lab analysis time and tighten product quality assurance by direct multi-layer analysis! The example shows the in-line measurement of SiNx and SiOx, additionally to a-Si in a 45nm a-Si / 100nm SiO / 50nm SiN stack with sub nanometer resolution. 


CdTe and CIGS based thin-film PV

Combining two Flames metrology systems of different spectral range gives access to measuring the properties and thickness of all layers throughout thin-film solar cell manufacturing processes, including transparent conducting oxide (TCO) and absorber and buffer layers. Especially, with the IR spectral range included, the position and number of interference fringes of the thick absorber layers can be automatically analyzed and fitted to determine the absorber’s film thickness on-line. By measuring the reflectance after each deposition step, the thickness of each layer can be determined with high precision.

While TCO and CdS film thicknesses are detected with a spectrometer operating in the visible to near-infrared spectral range (500–1000 nm), a determination of the film thickness of the absorber layer requires an infrared reflectance measurement, as these materials are designed to completely absorb visible light. The thickness measurement accuracy is typically 1–2 %. LayTec has built upon its extensive expertise in fitting optical data and accurately measuring optical properties (n and k values) in multi-layer processes to create the most precise automated thickness analysis available for thin-film PV.

To find out how Flames can optimize your process please contact mail@laytec.de or simply call +49(0)30 89 00 55-0.