Papers by Keyword: Nitrogen Implantation

Abstract: Effect of a shallow nitrogen implantation in the channel region of n-channel 4H-SiC Hall bar MOSFETs on their electrical properties has been characterized by Hall effect. A significant improvement of Hall mobility in normally-off devices is observed with increasing nitrogen implantation dose up to 10¹³ cm^-2 with a peak Hall mobility of 42.4 cm².V^-1.s^-1. Coulomb scattering as dominant scattering mechanism up to room temperature is demonstrated using temperature dependent MOS-Hall effect characterization.

Abstract: In this paper, we studied the influence of nitrogen implantation dose on both physical and electrical properties in 3C-SiC grown on Si (100) substrate. Scanning Transmission Electron Microscopy characterizations prove that high dose is responsible for amorphization of the implanted layer and the high defect density after annealing. A high V-shape defect density is still found in the implanted layer after an annealing at 1350°C. By lowering the dose, the layer is less damaged and no amorphization is observed. For the different doses, low Specific Contact Resistances are measured using Ti/Ni contacts. The Specific Contact Resistance value decreases from 8x10^-6 Ω.cm² for the high dose to 3.2x10^­6 Ω.cm² with decreasing the dose. Furthermore, the dopant activation ratio, evaluated by quantitative SSRM measurements, is improved at the same time from 17% (for the high dose) to 60% (for the low dose). This work demonstrates that high activation ratio can be achieved consecutively to a nitrogen implantation at reasonable implantation fluence.

Abstract: Two electrical characterization methods were used to study 3C-SiC epilayers doped by nitrogen implantation: circular Transfer Length Method (c­TLM) which allows extracting the specific contact resistance and Scanning Spreading Resistance Microscopy (SSRM) used to measure activated doping concentration. 3C-SiC samples were implanted at room temperature with different energies (ranging from 30 to 150keV) and doses (from 1 to 5.4x1015cm-2) in order to obtain a 300nm thick box-like profile at 5x1020cm-3. To activate the dopant, the samples were then annealed from 1150°C to 1350°C for 1h to 4h. Titanium-nickel c-TLM contacts annealed at 1000°C under argon showed the best results in terms of specific contact resistance (8x10-6.cm2) after a 1350°C–1h annealing. For this annealing condition, the activation rate was assessed by SSRM around 13%. This value confirms the difficulty to activate the dopants introduced into the 3C-SiC as the temperature is limited by the silicon substrate. However, this work demonstrates that low resistance values can be achieved on 3C-SiC, using nitrogen implantation at room temperature.

Abstract: The evolution of the normal strain induced by nitrogen implantation in 4H-SiC was investigated through X-ray diffraction measurements and compared to previous studies on helium implanted SiC. The shape of the normal strain profile in the near surface region shows that the accumulation of point defects is not the only mechanism operative at room temperature. In the highly damaged region, the normal strain profile fits the N concentration.

Abstract: We report investigations on the fabrication and electrical characterization in the range 27°C -290 °C of normally off 4H-SiC circular MOSFET devices manufactured on p-type semiconductor. An high quality SiO2/SiC interface is obtained by nitrogen ion implantation conducted before the thermal oxidation of SiC. Two samples with different nitrogen concentration at the SiO2/SiC interface and one un-implanted have been manufactured. The sample with the highest N concentration at the interface presents the highest channel mobility and the lowest threshold voltage. With increasing temperature, in all the samples the threshold voltage decreases and the electron channel mobility increases, reaching the maximum value of about 40 cm2/Vs at 290 °C for the sample with the highest N concentration. The observed improvement of the mobility is related to the beneficial effect of the N presence at the SiO2/SiC interface, which leads to the reduction of the interface trap density with energy close to the conduction band. Our results demonstrate that N implantation can effectively be used to improve the electrical performance of surface n-channel 4H-SiC MOSFETs.

Abstract: Aiming to minimize the interface state density, we fabricated MOS capacitors on n-type 4H-SiC by using wet oxidation of nitrogen implanted layers. We investigated a wide range of implantation dose, including a high dose able to amorphise a surface SiC layer with the intent to reduce the oxidation time. The oxide quality and the SiO2-SiC interface properties were characterized by capacitance-voltage measurements of the MOS capacitors. The proposed process, in which nitrogen is ion-implanted on SiC layer before a wet oxidation, is effective to reduce the density of interface states near the conduction band edge if a high concentration of nitrogen is introduced at the SiO2-SiC interface. We found that only the nitrogen implanted at the oxide-SiC interface reduces the interface states and we did not observe the generation of fixed positive charges in the oxide as a consequence of nitrogen implantation. Furthermore, the concentration of the slow traps evaluated from the Slow Trap Profiling technique was low and did not depend on the nitrogen implantation fluence.

Abstract: A near-surface Gaussian nitrogen (N) profile is implanted into the Si- or C-face of n-/ptype 4H-SiC epilayers prior to a standard oxidation process. The corresponding MOS capacitors are investigated by conductance and internal photoemission spectroscopy. The effect of N-implantation on the density of interface traps Dit is studied and a model is proposed, which consistently explains the observed results.

Abstract: A surface-near Gaussian nitrogen (N) profile is implanted into n-type 4H-SiC epilayers prior to a standard oxidation process. Depending on the depth of the oxidized layer and on the implanted N concentration, the density of interface states DIT determined in corresponding 4H-SiC MOS capacitors decreases to a minimum value of approx. 1010 cm-2eV-1 in the investigated energy range (EC-(0.1 eV to 0.6 eV)), while the flat-band voltage increases to negative values due to generated fixed positive charges. A thin surface-near layer, which is highly N-doped during the chemical vapour deposition growth, leads to a reduction of DIT only close to the conduction band edge.