20 October 2010


LayTec presents latest Pyro 400 results at IWN

At the International Workshop on Nitrides (IWN 2010) in Tampa, FL, USA (20–24 September), Dr Kolja Haberland of LayTec GmbH of Berlin, Germany (which provides in-situ optical metrology systems for thin-film processes) presented the latest results obtained by its new in-situ tool Pyro 400 on an Aixtron AIX metal-organic chemical vapor deposition (MOCVD) Planetary Reactor in combination with its EpiCurve TT sensor. Figure 1 shows the effects of reactor pressure changes on temperature during the LED growth process.

During standard gallium nitride (GaN) growth conditions and standard pressure (2), the pocket temperature and wafer temperature in the wafer center are in good agreement. When changing process conditions — lower reactor pressure and increased process temperature (3) — the wafer temperature (red) drops 20K below the pocket temperature (orange), undetected by conventional pyrometry. The cause is less effective heat transfer by the carrier gas from the pocket to the wafer. Understanding and controlling this effect is crucial for temperature management during device growth and can only be measured with the Pyro 400, says LayTec.

Figure 2 demonstrates that the temperature distribution across the wafer differs at different growth steps and depends on the specific growth conditions:

1. Before growth: Pyro 400 shows the flat temperature profile of the pocket under the bare sapphire.

2. GaN buffer growth: the center of the wafer is hotter than the edges due to concave wafer bow.

3. Superlattice growth: cool center due to lower reactor pressure and changed heat transport from pocket to wafer.

4. Multi quantum well growth (MQW): flat temperature profile due to the flat wafer.

LayTec says that the UV-sensing Pyro 400 measures the temperature directly on the GaN surface, revealing temperature changes at the growth surface that are not visible with a conventional pyrometer.

*LayTec invites all its customers in Korea to a technical training session in the Ramada Hotel Suwon, Korea on 23 November, where LayTec engineers, customers and Korean partners will report on the monitoring of LED processes using the firm’s in-situ systems.

See: LayTec Company Profile

Search: LayTec Pyro 400 EpiCurve TT LEDs GaN MQW


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