Papers by Author: Eddy Simoen

Abstract: To solve the problem of the limitation to improve device performance in standard Si integration technologies and to develop radiation-harsh devices, the irradiation effects of Si_1-xC_x source/drain (S/D) n-type metal oxide semiconductor field effect transistors (n-MOSFETs) have been investigated. It is shown that the drain current and the maximum electron mobility of Si_1-xC_x n-MOSFETs decrease by electron irradiation. The reduction of the device performance can be explained by the radiation-induced lattice defects in the devices. However, the electron mobility enhancement effect by adding C remained after an electron irradiation up to 5×10¹⁷ e/cm².

Abstract: For the purpose of increasing the conductivity of β-Ga₂O₃ films, Sn doping in the β-Ga₂O₃ films has been explored using co-sputtering. Growth of β-Ga₂O₃ was confirmed by the XRD pattern for the undoped sample. However, it is shown that the Ga₂O₃ phase is transformed from the β to the γ phase by Sn doping, because of the increase of the phase transition temperature from the γ to the β phase. To improve the crystalline quality, additional annealing at 900°C for 60 min is performed to the Sn doped film. The XRD peaks corresponding with β-Ga₂O₃ could be confirmed after the additional annealing.

Abstract: The effect of 2-MeV electron irradiation of Si_1-xGe_x S/D p-MOSFETs with different gate length and Ge concentration is studied. After electron irradiation, the maximum hole mobility decreases with increasing electron fluence for all gate lengths. In particular, after 5 x 10¹⁷e/cm² irradiation, the maximum hole mobility drastically decreases at short channel region for x = 0.3. Furthermore, a negative shift of the threshold voltage is clearly observed. These degradations can be explained both by the lattice defects and the stress relaxation in the Si channel created by atomic displacements.

Abstract: For the purpose of improving the crystalline quality of undoped and Si doped β-Ga₂O₃ films, high temperature annealing at 900°C was performed. The crystalline quality of the films investigated using scanning electron microscopy and X-ray diffraction. Also the conductivity of the films is compared before and after the annealing. After the 900°C annealing, the XRD peaks intensity corresponding to β-Ga₂O₃ is increased. This result indicates that the crystalline quality improves by the high temperature annealing.

Abstract: Results are presented of a comparative study of diodes processed on n-type Cz grown Si substrates without and with Ge doping concentration of about 10¹⁹ cm^-3 and 10²⁰ cm^-3. In order to investigate thermal donor formation, isothermal annealing at 450°C for 0.5 – 5 h was carried out. As processed diodes were also irradiated with 2 MeV electrons with fluences in the range between 10¹⁴ and 10¹⁷ e/cm² to investigate the Ge doping influence on irradiation induced defect formation. Diodes after thermal and radiation treatments have been investigated by combining different techniques.

Abstract: Several device concepts have been further evaluated after the successful implementation of epitaxial Si, SiGe and/or Si:C layers. Most of the next device generations will put limitations on the thermal budget of the deposition processes without making concessions on the epitaxial layer quality. In this work we address the impact of ex-situ wet chemical cleans and in-situ pre-epi bake steps, which are required to obtain oxide free Si surfaces for epitaxial growth. The combination of defect measurements, Secondary Ion Mass Spectroscopy, photoluminescence, lifetime measurements, and electrical diode characterization gives a very complete overview of the performance of low-temperature pre-epi cleaning methods. Contamination at the epi/substrate interface cannot be avoided if the pre-epi bake temperature is too low. This interface contamination is traceable by the photoluminescence and lifetime measurements. It may affect device characteristics by enhanced leakage currents and eventually by yield issues due to SiGe layer relaxation or other defect generation. A comparison of state of the art 200 mm and 300 mm process equipment indicates that for the same thermal budgets the lowest contamination levels are obtained for the 300 mm equipments.

Abstract: In order to identify an appropriate low-temperature surface passivation that could be used for bulk lifetime estimation of high resistivity (HR) (> 1 k
·cm) silicon for radiation detectors, different passivating layers were evaluated on n-type and p-type standard Czochralski (CZ), HR magnetic CZ and HR float zone (FZ) substrates. Minority carrier lifetime measurements were performed by means of a μW-PCD set-up. The results show that SiNx PECVD layers deposited at low temperatures (≤ 250°C) may be used to evaluate the impact of different processing steps and treatments on the substrate characteristics for radiation detectors. First results are obtained about a preliminary thermal treatment experiment to evaluate the thermal stability of the passivating layers, as well as the potential impact of the generation of thermal donors on minority carrier lifetime.

Abstract: Fast neutron irradiation of germanium has been used to study vacancy reactions and vacancy clustering in germanium as a model system to understand ion implantation and the vacancy reactions which are responsible for the apparently low n-type doping ceiling in implanted germanium. It is found that at low neutron doses (~1011cm-2) the damage produced is very similar to that resulting from electron or gamma irradiation whereas at higher doses (> 1013cm-2) the damage is similar to that resulting from ion implantation as observed in the region near the peak of a doping implant. Electrical measurements including CV profiling, spreading resistance, Deep- Level Transient-Spectroscopy and high resolution Laplace Deep-Level Transient-Spectroscopy have been used in conjunction with positron annihilation and annealing studies. In germanium most radiation and implantation defects are acceptor like and in n-type material the vacancy is negatively charged. In consequence the coulombic repulsion between two vacancies and between vacancies and other radiation-induced defects mitigates against the formation of complexes so that simple defects such as the vacancy donor pair predominate. However in the case of ion implantation and neutron irradiation it is postulated that localized high concentrations of acceptor like defects produce regions of type inversion in which the vacancy is neutral and can combine with itself or with other radiation induced acceptor like defects. In this paper the progression from simple damage to complex damage with increasing neutron dose is examined.

Abstract: The degradation and recovery behavior of device performance on GaAlAs LEDs (Light emitting diodes) irradiated by 2-MeV electrons and 70-MeV protons are investigated. The reverse current increases after irradiation, while the capacitance decreases. The device performance degradation is proportional with fluence. For electron irradiation, fluence rate is also effective for degradation. Low fluence rate shows more large degradation compared to high fluence rate resulting from heat impact in bulk. DLTS measurement reveals the DX center in epitaxial substrate, and this spectrum increases with fluence. The radiation damage of proton is larger than that of electron irradiation, which is caused by the difference of mass and possibility of nuclear collision for the formation of lattice defects. After irradiation, the device performance recovers by thermal annealing.

Abstract: In this study, Co germanide Schottky barrier diodes on n-Ge (100) substrate were fabricated by sputtering metal Co on Ge, followed by annealing in vacuum at 700°C. The influence of annealing time was investigated on both the electrical properties of Co germanide Schottky barrier diodes and on the phase formation on n-Ge (100) substrate. With increasing annealing times growing or transformation of germanide entities occurs leading to reduction of the trap concentration and therefore the leakage current.