Evaluate Processing of Thin Films

Thin film materials processing covers a range of techniques, including deposition and etching. Lasers are often applied for etching, scribing, or marking defects. The Zeta 3D optical profiler, able to image a surface in 30 seconds, quickly acquires metrology data to analyze laser processing of thin films.

 

Accurate Edge Detection

Trenches are often created using laser ablation to separate materials in thin films. The integrity, dimensions, and pileup of the trench need to be determined for product development and improvement.

Indium tin oxide (ITO) thin films on glass are used in flat panel displays, transparent electrodes, and organic light emitting devices (OLED). Laser ablating trenches in ITO coatings on glass are used for high efficiency structuring of transparent conductors.

Laser direct write (LDW) is a maskless, dry process that allows easy change of the contact pattern. Well-defined edges and good electrical isolation at a short separation between conductor lines are required. Sharp edges are especially important when the distance between the conductor lines shrinks down to 10 μm.   

Zeta 3D optical profiler image of laser-ablated trench scribed in ITO thin film on glass

Zeta 3D optical profiler image of laser-ablated trench scribed in ITO thin film on glass

A laser confocal tool will show interference artifacts on such transparent samples with irregular topography, whereas the Zeta 3D™ optical profiler using the ZDot™ focusing technology is able to acquire meaningful data on such samples. This scribe is 8.6 µm in width and 0.2 µm in depth, showing clearly defined trench edges.

Trench Dimensions

In thin film solar cells, electrical isolation is important and for this, trenches are created to isolate the P and N-doped regions of the solar cell.  In some thin film cells, the laser scribe should not breach the underlying glass substrate and must be contained within the thin films.  The trench may also be heavily textured to increase the light absorption.  Controlling the trench dimensions and the surface texture is key to improving the efficiency of the solar cell.  For this, ultrafast pulsing lasers are used to produce cleaner, sharper micro-channels. The challenge is to automatically locate these trenches on large panels and provide critical information about their roughness, depth and width. 

Zeta 3D optical profiler image of laser-scribed trench in thin film solar cell on glass

Zeta 3D optical profiler image of laser-scribed trench in thin film solar cell on glass

The scribe shown above is 74 µm in width and 0.50 µm in depth. The Zeta 3D™ optical profiler uses a high precision motorized XY stage and pattern recognition software to automatically detect the scribe lines and scan multiple locations on the solar cell.

Measure Laser Scribe Dimensions

Zeta optical profiler image in 3D for GaN on sapphire

Zeta optical profiler image in 3D for laser-scribed GaN thin film on sapphire wafer

Laser scribing is a widely used technique to separate an LED wafer into individual dies. The scribe process creates a deep and narrowing trench and leaves behind a lot of debris. Such a geometry precludes the use of normal imaging tools such as interferometers and laser confocal microscopes. Zeta’s high efficiency optical design and the ZDot™ focusing technology allows the maximum possible light to be collected from such a sample.  The scribe shown above is 9.1 µm in diameter and 15.84 µm in depth, with very rough, tapering side walls.

Evaluate Laser Power Effects

The Zeta 3D optical profiler provides fast metrology data. The effect of laser power on an aluminum coating is determined using 3D images of resulting craters.

Zeta 3D optical profiler image and analysis of an aluminum coating on tungsten substrate, evaluating effect of laser power.

Zeta 3D optical profiler image and analysis of an aluminum coating on tungsten substrate

Research using different pulsed wattage laser power shows how it correlates to the depth and shape of the crater on a variety of materials.  Shown here are craters created on a tungsten surface coated with aluminum, scanned with the ZDot™ focusing technology.  

Zeta 3D optical profiler images of Al on W at 3 different pulsing wattage laser power

Zeta 3D optical profiler images of craters in Al on W at 3 different pulsing wattage laser power


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