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Determination of stress in composite engineered substrates for GaN-based RF power devices

Marek Guziewicz ¹, Eliana Kaminska ¹, Anna Piotrowska ¹, Krystyna Golaszewska ¹, Jaroslaw Domagala ², Hacene Lahreche ³, Robert Langer ³, Marie-Antoinette Poisson ⁴, Philippe Bove ³

1. Instytut Technologii Elektronowej (ITE), al. Lotników 32/46, Warszawa 02-668, Poland
2. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
3. Picogiga Int., Place Marcel Rebuffat, Parc de Villejust, Courtaboeuf 91960, France
4. Alcatel Thales Lab, Route de Nozay, Marcoussis 91461, France

Abstract

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.

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