(Invited) Al+ Ion Implanted 4H-SiC: Electrical Activation versus Annealing Time
Authors: Nipoti Roberta , Parisini Antonella 
Published: February 2020

The selected area doping by ion implantation is often used in the fabrication of 4H-SiC electronic devices; DMOSFETs and JTE are here cited as examples. In the ion implantation technology, the key parameters are: implantation temperature, dose rate per ion energy, ion implanted dopant depth profile, post implantation annealing temperature, and post implantation annealing time. In the case of 4H-SiC, the most of the litterature focus on finding the post implantation annealing parameters that maximize the doping efficiency per ion implanted dopant concentration, or, that give the sufficient electrical activation for obtaining the desired device performance. This results in a multitude of reported electrical data, taken in heterogeneous samples. Recently, an empirical model for previewing the electrical activation per ion implanted dopant species versus dopant concentration has been proposed [1] on the base of published data. This model [1] could be a useful tool for sufficiently reliable device designs. Nevertheless, recent results on the electrical activation of ion implanted P and Al in 4H-SiC [2-3] show that the data trends used in [1] may require adjustments. Moreover, a full description of the thermodynamics controlling the phenomenon of the electrical activation of ion implanted dopants in 4H-SiC, should require dedicated experiments; examples of which can be found in [4-5]. It is relevant to cite the fact that the results of [4] allowed the authors to perform realistic previsions about the electrical trasport in Al ion implanted 4H-SiC after post implantation annealing at a temperature and for times never explored before, as shown in [6].

The present work will resumes the latest results on the electrical activation of aluminum [2] and phosphorous [3] ion implanted in 4H-SiC with typical concentration values for n-channel DMOSFETs. These values are in the range 3×1018 - 1×1019 cm-3. Post implantation annealing temperature is relative low: 1600 °C. This is a conservative value for minimizing step bunching formation at the oxide/semicondutor interface in the channel region. The annealing time ranges from 5 min to 15 h. The temperature dependence of resistivity and Hall coefficent is measured in the range 70-640 K. Experimental data are analysed to extract donor and acceptor concentration, dopant compensation, and carrier mobility.

For comparison purposes, both published and original results obtained for identical ion implanted dopant species and similar ion implanted dopant concentration in high purity semi insulating (HPSI) 4H-SiC, but higher post implantation annelaing temperature, will be shown too.

The aim of this work is to produce results that help in featuring the balance between electrical activation and compensation as far as the annealing time increases at a fixed annealing temperature. The DMOSFETs doping configuration has been chosen because timely.

[1] V. Simonka et al., "Transient model for the electrical activation of aluminium and phosphorous-implanted silicon carbide", J. Appl. Phys. 123, 235701 (2018).

[2] R. Nipoti et al., "Low concentration Aluminum ion implantation in 4H-SiC", submitted to ICSCRM2019, Tokyo, Sept. 29 - Oct. 4, 2019.

[3] A. Parisini et al., "Phosphorous doping by ion implantation in 4H-SiC DMOSFETs", submitted to ICSCRM2019, Tokyo, Sept. 29 - Oct. 4, 2019.

[4] R. Nipoti et al. "About the Electrical Activation of 1×1020 cm-3 Ion Implanted Al in 4H-SiC at Annealing Temperatures in the Range 1500 - 1950°C", Mater. Sc. Forum, 924, 333-338 (2018).

[5] R. Nipoti et al., "Activation energy for the post implantation annealing of 1019 cm-3 and 1020 cm-3 ion implanted Al in 4H SiC.", proceedings of ECSCRM2018, Birmingham, accepted for publication in Mater. Sc. Forum on Jan. 29, 2019.

[6] R. Nipoti et al., "1300°C Annealing of 1×1020 Al+ Ion Implanted 3C-SiC", proceedings of ECSCRM2018, Birmingham, accepted for publication in Mater. Sc. Forum on Jan. 29, 2019.