Frequently asked questions: Requirements to your growth system

For using our standard systems (EpiTT, EpiCurve^®TT, EpiR, EpiRAS^®TT) a normal incidence viewport is required, together with enough space next to the window. Optical access to the sample must not be blocked within the reactor by additional apertures. Ceilings or inner liner tubes between viewport and sample need to have small holes. In case of a multi-wafer system a "reset" pulse once per revolution is needed for wafer selective measurements.

See the page Processes >

The LayTec in-situ tools are adapted to typical sample wobble of standard MOCVD and MBE systems by  LayTec's patented wobble compensation module. 

For customized MOCVD and MBE systems the maximal tolerable wobble is dependent on the geometry. Please contact LayTec  for a detailed analysis of possible adoptions. A tool to evaluate the current wobble can be provided on request.

Window depositions should be avoided. We therefore strongly recommend purged or heated view-ports. The influence of minor  window deposition to reflectance and temperature measurements can be compensated by automated normalization procedure to the substrate reflectance. However, increasing deposition on windows will increase absorption and lead to a lower signal. Hence signal-to-noise-ratio and temperature measurement  will be affected.

Most LayTec  in-situ sensors  can be used on non-rotating samples and for slowly rotating up to the fast speed rotating systems (5rpm-300rpm).

Vibrations need to be considered in the design and mounting of the in-situ sensor, Please specify vibration by a simple laser reflectance measurement.  Fiber-optical access as realized in LayTec's EpiTT and EpiR DA TT sensors is advantageous in case of strong vibrations!

It is necessary to install an additional external optical rotation sensor that has to be customized.

Yes, EpiRAS and EpiR M are capable to measure in Aix 200/4 3x2” configuration  (not wafer selective). Find more in our application note >

Yes, EpiTT and EpiTwin TT are capable to measure at multi wafer pockets (recess)  configuration  (not wafer selective). In case of 42 or 49x2” with a center wafer on each recess, a wafer selective measurement can be measured for the center wafer.

One full rotation of the wafer under the view-port is necessary for a RAS measurement with the standard EpiRAS or EpiRAS TT sensors. If wafers are not rotating, customized RAS solutions are required. Please contact LayTec directly.

The RAS signal depends on the azimuth of the wafer relative to the fixed polarization of the measurement light. After measuring a full revolution a Fourier analysis can be used to obtain the RAS amplitude from the sinusoidal signal.