Residual stresses and their impact on the performance of semiconductor devices are of permanent interest for crystal growers and device manufacturers. This is especially true for GaN-based RF power devices fabricated on mismatched substrates such as Si and SiC. Moreover, aiming at bridging the gap between the low-performance, low-cost single crystal Si and the high-performance, high cost single crystal silicon SiC as the starting substrates for the growth of device structures, composite engineered substrates based on silicon and silicon carbide materials have been recently proposed [1]. These substrates, namely mono-Si on poly-crystalline SiC (SopSiC) and mono-SiC on polycrystalline SiC (SiCopSiC), are engineered using Smart Cut™ technology.

In this paper we show the results of stress measurements in the composite SopSiC and SiCopSiC substrates as well as AlGaN/GaN HEMT structures grown on them. These have been compared with standard AlGaN/GaN HEMTs grown on sapphire and bulk Si substrates.

Two methods have been applied to determine the stress: (a) high resolution X-ray diffraction technique, using PHILIPS X’Pert MRD diffractometer to evaluate the lattice strain and (b) wafer curvature-based techniques, using ADE Mapper Shape Metrology System and Tencor®FLX-2320 Stress Measurement System, enabling stress measurement in temperature range of room temperature – 500 ^oC.

We have found that the results of HRXRD measurements are similar to those obtained by curvature-based methods on SopSiC and SiCopSiC substrates. The average film stress of -390 MPa is here in the Si(445nm)/SiO₂(210nm) bilayer of the SopSiC substrate, and the stress of -290 MPa is in the Si(955nm)/ SiO₂(270nm) bilayer.

Residual stresses in HEMT structure grown on the composite substrate is 200 MPa and 100 MPa for SopSiC and SiCopSiC substrates, respectively. The AlGaN/GaN structure grown on sapphire is compressively stressed up to -600 MPa, and the HEMT structure grown on the (111)Si substrate is under low compression. The measurements of temperature dependence of stress σ show that σ = -225 MPa @ 500 ^oC for the HEMT structure grown on SopSiC substrate.

[1] http://www.hyphen-eu.com/

Part of the research was supported by the grant from the EC HYPHEN Contract Number: FP6-027455.