PC-Tue-P19 - Correlation Study of AlGaN/GaN HEMT Structures Performed with Novel Wafer Level Capacitance Mapping Technique and Spectroscopic Ellipsometry

2. Physics and characterization
Marshall Wilson¹ , Dmitriy Marinskiy¹, Adam Wincukiewicz¹, Carlos Almeida¹, Ivan Shekerov¹, Jacek Lagowski¹, Anna Bölcskei-Molnár², Peter Basa², Fanni Flach², Zsolt Szekrényes², Leon Schiller³, Sven Besendoerfer^3
1 Semilab SDI, Tampa,FL USA
² Semilab, Budapest, Hungary
³ Fraunhofer IISB, Erlangen, Germany

Abstract text
In general, a correlation study is the statistical comparison of a range of different properties and the investigation of relations amongst them. For the purpose of epitaxial process tuning, it is essential to perform such correlations in a fast and reliable way on a full wafer-scale. In this work this is demonstrated by mapping of 200mm AlGaN/GaN HEMT wafers and analyzing different material and electrical properties corresponding to the same sites. Measurements were performed with a Corona noncontact Capacitance-Voltage metrology tool (CnCV). This technique includes biasing with corona charge deposition, ΔQ, and noncontact measurement of the surface voltage response, V, with a Kelvin probe. For fast wafer mapping, a novel CnCV “kinetic mode” approach was used wherein short millisecond duration UV pulses follow a single large negative corona charge, removing the charge in steps for the C-V measurement [1]. The HEMT structure active layer parameters determined from C-V characteristics include the pinch-off voltage, V_P, the two-dimensional electron gas sheet density, N_S, and the electrical thickness of the Al_xGa_1-xN barrier layer, d_AlGaN. The aluminum composition x, and the optical AlGaN thickness were additionally measured by spectroscopic ellipsometry and photoluminescence on the same wafer sites. 

The results show radial symmetry distribution patterns visible in V_P, N_S, d_AlGaN, optical AlGaN thickness, and x with the following findings:

1. Uniformity of d_AlGaN, optical AlGaN thickness, and x does not guarantee uniformity of N_S and V_P. This is demonstrated by results on a wafer with 1σ=1.1% and 2.0% for d_AlGaN and x, respectively, while exhibiting 1σ = 20% and 34% for N_S and V_P, respectively.
2. An anticorrelation between N_S and d_AlGaN was observed on some wafers, opposite to general literature expectations [2], and could be explained by an opposite spatial variation in x which dominates N_S compared to that of d_AlGaN.

The results show the importance of a complete multiparameter characterization of 2DEG wafer uniformity and a need for inclusion of other elements in modeling in addition to the AlGaN thickness and Al composition. 

[1] M. Wilson et al., 2024 IEEE 11th Workshop on Wide Bandgap Power Devices & Applications (WiPDA), Dayton, OH, USA, 2024, pp. 1-5. DOI: 10.1109/WiPDA62103.2024.10773289

[2] O. Ambacher et al., J. Appl. Phys. 87, 334, 2000.