Papers by Keyword: Dopant Activation

Abstract: This paper demonstrates for the first time a new annealing scheme to form p-type junctions in SiC by high temperature ion implantation followed by laser annealing without the use of a protective carbon capping layer. This novel approach leverages higher substrate temperatures during implant to minimize implant-induced defects during ion implantation, which enables the use of reduced thermal budget laser annealing for dopant activation. Laser annealing enables higher surface temperatures in the implanted layer than conventional annealing using a high temperature furnace. The shorter thermal budget results in higher dopant activation while minimizing, the formation of extended defects observed during high thermal budget furnace annealing, which can lead to undesirable degradation in device performance. By using laser annealing with no carbon capping layer, the sheet resistance of the implanted layers is reduced up to 6 times with respect to the conventional process (using a furnace anneal and carbon capping layers).

Abstract: The Smart CutTM process offers an advantageous opportunity to provide a large number of performance-improved SiC substrates for power electronics. The crystalline quality and the electrical activation of the 4H-SiC transferred layer are then at stake when it comes to the power device reliability. In this study, we find that the H⁺ ion implantation used for the Smart CutTM process leads to electrical deactivation of dopants and partially disorders the material. The transferred layer fully recovers its initial crystalline quality after a 1300°C anneal, with no further evolution beyond this temperature. At this point however, the n-type dopants are still inactive. The dopant reactivation occurs in the same temperature range than that of implanted nitrogen: between 1400°C and 1700°C. After 1700°C, the initial doping level of bulk SiC is recovered.

Abstract: In this paper, we explore the effects of excimer laser irradiation on heavily Aluminum (Al)-implanted silicon carbide (4H-SiC) layer. 4H-SiC layers were exposed to UV-laser radiation (308 nm, 160 ns), at different laser fluences and the effects of the laser exposure surface were evaluated from morphological, micro-structural and nano-electrical standpoints. Depending on the irradiation condition, significant near-surface changes were observed. Moreover, the electrical characteristics of the implanted layer, evaluated by means of transmission line method, gave a sheet-resistance of 1.62×10⁴ kW/sq for the irradiated layer, linked to a poor activation of the p-type dopant and/or a low mobility of the carriers in the laser-modified 4H-SiC layer. This study can be useful for a fundamental understanding of laser annealing treatments of 4H-SiC implanted layers.

Abstract: This paper discusses a novel annealing technique for 4H-SiC implants which involves the use of pulsed XeCl laser (l=308 nm). In particular, an absorbing graphitic coating is used to protect the sample from surface atoms desorption or phase separation. Both conventional furnace annealing and laser annealing on P and Al implants, commonly employed for source and body in metal-oxide-semiconductor field-effect transistors (MOSFETs), were examined through Transmission Electron Microscopy (TEM), u-Raman spectroscopy and Scanning Electron Microscopy (SEM). It is shown that the implant activated through traditional thermal annealing at 1650 °C for 30 min has a large network of dislocation loops, while they do not appear to be present in the laser annealed implant. Through Raman spectroscopy and SEM investigations both the crystalline quality of the laser annealed sample and the integrity of the surface were attested.

Abstract: In this work, we have studied the crystal defectiveness and doping activation subsequent to ion implantation and post-annealing by using various techniques including photoluminescence (PL), Raman spectroscopy and transmission electron microscopy (TEM). The aim of this work was to test the effectiveness of double step annealing to reduce the density of point defects generated during the annealing of a P implanted 4H-SiC epitaxial layer. The outcome of this work evidences that neither the first 1 hour isochronal annealing at 1650 - 1700 - 1750 °C, nor the second one at 1500 °C for times between 4 hour and 14 hour were able to recover a satisfactory crystallinity of the sample and achieve dopant activations exceeding 1%.

Abstract: A novel diode-pumped solid-state continuous-wave (CW) laser technology has been demonstrated for high-performance low-temperature polycrystalline silicon thin-film transistors (TFTs) fabrication. The CW laser-crystallized (CWC) poly-Si thin films indicated the excellent crystallinity with the flat surface morphology at grain boundary. Besides, the CW laser activation is a low-thermal budget process and can achieve the lower sheet resistance of 50 Ω/□ and uniformly redistributed dopant profiles. The n-channel CWC TFTs revealed the superior field-effect mobility reaching 505 cm²/V-s and the lower subthreshold swing as compared with the conventional excimer laser-crystallized ones.

Abstract: The formation of shallow junctions in germanium substrates, compatible with deep submicron CMOS processing is discussed with respect to dopant diffusion and activation and damage removal. Examples will be discussed for B and Ga and for P and As, as typical p- and n-type dopants, respectively. While 1 to 60 s Rapid Thermal Annealing at temperatures in the range 400-650oC have been utilized, in most cases, no residual extended defects have been observed by RBS and TEM. It is shown that 100% activation of B can be achieved in combination with a Ge pre-amorphisation implant. Full activation of a P-implant can also be obtained for low-dose implantations, corresponding with immobile profiles. On the other hand, for a dose above the threshold for amorphisation, a concentration-enhanced diffusion of P occurs, while a lower percentage of activation is observed. At the same time, dose loss by P out-diffusion occurs, which can be limited by employing a SiO2 cap layer.

Abstract: Interaction of boron and aluminum with interstitial carbon is studied using first principles calculations. It is shown that carbon can form very stable complexes with Al and B, forming a family of negative-U bistable defects with deep levels. The influence of this effect on the activation rate of p-type implants is discussed.