High-Brightness LED
Automated PSS Height, Diameter and Pitch. Post-Epi Mesa Step Heights, Roughness.
Patterned sapphire substrates (PSS) have a dense pattern of micron-scale bumps that reduce crystal dislocations and also improve optical emission efficiency by reducing internal reflection. To maintain uniform LED performance, PSS wafers need to be inspected for uniformity of diameter, pitch, and height.
However, the small dimensions and steep sidewalls of the PSS make characterization difficult for conventional metrology systems such as stylus profilers, interferometer and laser confocal systems. PSS bumps are too small to develop fringes for interferometers and the regular pattern causes interference effects for laser confocal systems that must heavily filter data. Stylus and AFM measurements take too long (>10 minutes) and do not provide sufficient statistical information on the wafer.
Zeta optical profilers can perform a scan in less than 10 seconds while providing automatic size, pitch and height critical dimension data. As shown in the images, the PSS bumps are resolved with high clarity, enabling quantitative results over a much larger area as compared to an AFM, stylus profiler and most confocal microscopes.
In addition to automated measurements, our Zeta3D software allows the user to draw multiple profile cross sections across features on your sample to gauge step height and roughness (Ra, Sa). Measurement cursors can be automatically positioned to calculate feature height and width after a scan. All 3D surface information is stored in our data file so sample data can be reopened and re-examined later. Data are exportable to a variety of formats that can be imported into spreadsheets and databases.
Post-Epitaxy Mesa Structure Analysis
The roughness and step height of post-epitaxy LED structures can be easily measured in a non-destructive manner using Zeta profiler tools.
Knowing the height, size and roughness of the structures on your wafers gives you a clear indication of how close your manufacturing parameters are to your target levels. Zeta optical profilers can get you that data quickly with minimal operator training so you can monitor your processes without sacrificing any of your revenue-generating product, or requiring specialized metrology staff to operate your tools.
LED cover plates and diffusers
Plastic diffusers used as cover plates cannot be inspected with other optical profilers due to the steep wall angles on the features of interest.
- Stylus and AFM profilers are slow and will not yield statistically significant data in a short time.
- Curved surfaces and large surface features will rule out the use of AFM.
The Zeta-20 is an ideal solution in this application. A 94µmX70µm scan is accomplished in about a minute. As shown in the images, the PSS bumps are resolved with high clarity, enabling quantitative results over a much larger area as compared to an AFM or a stylus profiler.
Zeta technology can image surfaces with very low reflectivity and high roughness
- Ideal for measuring features on patterned sapphire substrates as well as the plastic diffuser cover plates for LED packages
Zeta-20 can image a large area in a short time compared to other tools used to measure PSS
- The large area 3D images allow the user to get more meaningful data from their substrates as opposed to a few line traces with other tools