EpiNet 2017 targets in-situ wafer curvature monitoring
Fig. 1: Configuration panel of EpiNet 2017 showing the test run configuration: Pocket 5- 3x2 inch, Pocket 6 - 3x2 inch, Pocket 8 - 1x2 inch reference wafer, all other - dummy wafers.
While in-situ reflectance and temperature on a multi-pocket satellite susceptor can be measured very accurately, in-situ curvature monitoring is more tricky because it is challenging to find the wafer centre. Laytec says that its latest release of EpiNet 2017 control and analysis software provides a solution for this problem.
Figure 1, shows the susceptor layout for a GaN/Sapphire run performed at Ferdinand-Braun-Institute (Berlin, Germany): Pocket #8 was loaded with a single 2inch reference wafer, Pockets #5 and #6 contain three 2inch wafers each, Pockets #1"“4, 7 have dummy wafers.
Fig 2: In-situ measurements of GaN/Sapphire run (standard buffer growth on Sapphire as used for LEDs). Green transients - curvature signals, red - temperature, blue - reflectance.
In figure 2 above, the wafer bow signals of the pockets loaded with epi wafers are compared. The values of the multi-pockets comply nicely with the those of the single-pocket. Analysis functions for wafer bow like curve slope (marked by a red line) work well both on single and multi-pocket. Besides, the signal-to-noise ratio (SNR) of the measurements on multi-pockets (shown here without filtering) stays within spec like that of the single wafer pocket.