Growth optimization during III-nitride multiwafer MOVPE using real-time curvature, reflectance and true temperature measurements

Novel technique for monitoring of MOVPE processes

“…The reason of such a behavior is not yet understood and, as it has been mentioned earlier [6], requires additional studies. The bow we registered is greater than ever observed [7], likely due to higher temperature gradients along the substrate. The differences in optical thickness of the entire object (substrate+ film) measured ''along the phase'' and ''along the envelope'' becomes more pronounced with increasing thickness of the growing GaN film.…”

Quantitative analysis of in situ wafer bowing measurements for III-nitride growth on sapphire

“…In previous work four main contributions of total curvature were identified: an initial bowing of the substrate 1=R initial c , a curvature 1=R DT vert c caused by a vertical temperature gradient, a lattice mismatch induced change in bow during growth at constant temperatures 1=R growth c and bowing contributions due to different linear thermal expansion coefficients of substrate and film 1=R a c [9]. The initial substrate bow depends on the respective manufacturing process of the substrate and represents a constant positive or negative offset for the total curvature.…”

“…Strain control has been reported to be used for developing crack-free GaN on Si [7] or for strain engineering using AlN interlayers [3,8] and various kinds of buffer layers [4]. In a previous study we used the in situ measured wafer curvature to optimize growth recipes for zero wafer bow in critical growth steps where a uniform temperature distribution is essential [9].…”

InGaN/GaN multi-quantum well and LED growth on wafer-bonded sapphire-on-polycrystalline AlN substrates by metalorganic chemical vapor deposition

“…Continuing issues remain, in particular the CTE mismatch is known to cause film stress and wafer bowing during growth of InGaN/GaN LED structures on sapphire [4], leading for example to within-wafer and run-to-run wavelength non-uniformity. Strategies incorporating in situ curvature monitoring have been implemented on 2-in sapphire to improve the wavelength uniformity [4,5], however, even with such growth controls in place it is not possible to eliminate the CTE mismatch effects entirely. For example the issue of high residual stress upon cooldown [6] remains, which can impact the yield of post growth processing steps.…”

“…The thermal conductivity of P-AlN is also approximately five times higher than that of sapphire. It is therefore expected that substrate bowing attributed to thermal gradients across the thickness of the sapphire substrate [5] as well as the CTE mismatch induced bowing experienced during growth on sapphire, can be substantially eliminated with these composite substrates. The reduced substrate bow and the higher thermal conductivity should result in improved temperature uniformity.…”