Al diffusion at AlN/Si interface and its suppression through substrate nitridation

Abstract

One of the challenges for GaN-on-Si radio frequency (RF) device applications is the RF loss, which is mainly associated with a parasitic channel formed at the interface of AlN and high-resistivity Si substrates. However, the type of conductivity and formation mechanism of the parasitic channel remains controversial. Here, we report unambiguous evidence of Al diffusion at the AlN/Si interface and its effect on RF loss. Hall measurements reveal p-type conductivity at the interface. By combining with secondary ion mass spectroscopy measurements, the p-type conductivity is attributed to the Al diffusion from the AlN layers into the Si substrates, with Al being an acceptor in Si. Experimental data and simulations are in good agreement. We also demonstrate that substrate nitridation can indeed promote the formation of an amorphous silicon nitride layer, which plays a role in suppressing the Al diffusion and, thus, reducing the RF loss.

Electrical activity at the AlN/Si Interface: identifying the main origin of propagation losses in GaN-on-Si devices at microwave frequencies

“…After Si oxide removal under H 2 around 1000 °C, a thin 20 nm nucleation layer is grown at low temperature (1100 °C thermocouple setpoint, real temperature around 900 °C). The nucleation is performed using a NH 3 preflow to limit the risk of Al diffusion towards the substrate 13 . Then, the substrate temperature is rapidly increased to grow the AlN film with a total thickness up to 200 nm.…”

Reduction in RF Loss Based on AlGaN Back-Barrier Structure Changes

“…Structure Loss Time Meneghesso G. [29] Si/(AlGa)N/GaN/AlN 0.9 dB/mm @ 10 GHz 2013 Cao L. [30] Si/(AlGa)N/GaN/AlGaN 0.58 dB/mm @ 5 GHz 2017 Cordier Y. [15] Si/(AlGa)N/GaN 0.3 dB/mm @ 10 GHz 2018 Cao L. [20] Si(HR)/(AlGa)N/GaN/AlGaN 0.27 dB/mm @ 20 GHz 2018 Chandrasekar H. [28] GaN-on-Si 0.6 dB/mm @ 6 GHz 2019 Wei L. [11] Si/AlN 1.47 dB/mm @ 6 GHz 2020 Ghosh S. [31] Si/AlN 12.7 dB/mm @ 5 GHz 2021 Si/(AlGa)N/GaN/AlN 0.9 dB/mm @ 10 GHz 2013 Cao L. [30] Si/(AlGa)N/GaN/AlGaN 0.58 dB/mm @ 5 GHz 2017 Cordier Y. [15] Si/(AlGa)N/GaN 0.3 dB/mm @ 10 GHz 2018 Cao L. [20] Si(HR)/(AlGa)N/GaN/AlGaN 0.27 dB/mm @ 20 GHz 2018 Chandrasekar H. [28] GaN-on-Si 0.6 dB/mm @ 6 GHz 2019 Wei L. [11] Si/AlN 1.47 dB/mm @ 6 GHz 2020 Ghosh S. [31] Si/AlN…”

“…For the GaN HEMT RF device, there is still a very serious challenge, which is that the conductive layer is more likely formed at the interface between the Si substrate and the nucleation layer. The GaN HEMT device usually introduces an AlN nucleation layer between the Si substrate and the GaN layer, but its Al atoms will diffuse on the surface and on the inside of the Si substrates to form a conductive layer, which will cause RF loss in the devices working at high frequency and results in limiting output power and efficiency [11]. According to reports, wafer warpage caused by mismatch is greatly improved by adding a suitable Al(Ga)N stress control layer [12], and gold-free ohmic contacts technology has achieved a breakthrough in the compatibility issue mentioned above [13].…”

“…Optimizing the parameters of the substrate and epitaxial structure to suppress the RF loss is key to improving the performance of the Sibased GaN device. In the past ten years, researchers have made a lot of progress in reducing RF loss, such as by etching trenches between the coplanar waveguide (CPW) conductors (Marti et al 2010) [14], using a low-temperature aluminum nitride (AlN) nucleation layer (Cordier et al 2017) [15], and Si substrate nitridation (Wei et al 2020) [11]. They all reduce the RF loss by changing the process conditions, while there are not many reports on the reduction in the RF loss based on the optimization of the buffer layer structure parameters, and this is the focus of our work.…”

AlInGaN/GaN HEMTs With High Johnson’s Figure-of-Merit on Low Resistivity Silicon Substrate

“…The physical origin of this parasitic conduction is still under debate [23]. For instance, several authors have reported Ga/Al diffusion into the silicon substrate in the order of 10 16 cm -3 to 10 18 cm -3 with up to 3 m roll-off into the silicon substrate [24]. The Ga/Al atoms into the Si substrate act as acceptors and form a p-type conductive layer at the top surface of the substrate.…”