Ultraviolet pyrometry
Wafer surface temperature for IR-transparent substrates
Real GaN surface temperature is the most critical parameter of nitride epitaxial processes. A precise temperature variation across the wafer is necessary to meet the upcoming specs of LED manufacturing for solid state lighting (SSL) applications as well as for power electronic devices.
One major reason for non-uniformity is the process-induced bowing of wafers. When a wafer bows, the deviation between wafer surface temperature and pocket temperature increases in the case of a 4” sapphire substrate, for example, by up to 20 K or more. For e.g. InGaN/GaN multiple quantum wells (MQW), this results in a significant indium content variation and, as a result, in strong variations in emission wavelength. Thus, surface temperature is fundamental for the homogeneous growth of the active layers and the color uniformity of the final devices.
Features
Growth monitoring on transparent substrates
When it comes to bowed transparent substrates like sapphire or SiC, a conventional infrared (IR) pyrometer can measure only the pocket temperature. The GaN surface temperature can only be measured using ultraviolet (UV) pyrometry around 400 nm due to increased absorption in the UV range. The screenshot below shows surface temperature variations during a laser growth.
The conventional pyrometer (blue) does not "notice" the drop in wafer temperature by 20 K after changing the reactor pressure. But Pyro 400 does! The red curve in the screenshot shows the exact wafer surface temperature as measured by LayTec's Pyro 400.
LayTec’s solution
Our Pyro 400 measures the surface temperature of GaN on sapphire and SiC and enables direct temperature control during growth of InGaN MQW layers. Furthermore, the increased absorption also facilitates high precision temperature measurements for GaN on Si epitaxy. Find out more on the Pyro 400 product page and in the application section.
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