Marie Laure Locatelli

A Comparative Study of High-Temperature Aluminum Post-Implantation Annealing in 6H- and 4H-SiC, Non-Uniform Temperature Effects

4H-and 6H-SiC small samples were implanted by keV Al + ions at room temperature and annealed in an induction heating furnace, at the center of the susceptor, for different temperatures and times in the range 1600-1800°C and 5-60 min, respectively. The implanted layers were amorphous but the SiC crystalline structures were recovered after annealing, as measured by Rutherford Back-Scattering analyses in Channeling geometry. Al + electrical activation determined by sheet resistance and Hall effect measurements increases with the annealing temperature or time, on both polytypes. When whole SiC wafers were annealed in the same induction heating furnace, sheet resistance mapping systematically presented a radial gradient from the center to the periphery of the wafer. The measured linear dependence between sheet resistance and temperature allowed us to rebuild the radial temperature gradient at the crucible-susceptor furnace during the annealing process. Introduction Silicon carbide (SiC) is envisaged as a promising semiconductor material for a wide variety of high-temperature, high-power and high-frequency electronic applications. Ion implantation, an indispensable technique to locally dope silicon carbide still presents many problems in particular for p-type zone creation. High ionization energy of dopants imposes to raise the implanted dose above the amorphization threshold for room temperature implantations. Structure recrystallization and electrical activation of dopants, i.e. their incorporation in active SiC atomic sites, require high temperature annealing, about 1700°C in special configuration, with an overpressure of silicon and carbide. In this work p-type 6H and 4H-SiC layers created by Aluminum (Al) ion implantations followed by high temperature annealings are studied in order to realize efficient p +-n junctions for bipolar power diodes. Dopant electrical activation dependence on the post-implantation annealing conditions is discussed considering the non-uniform temperature at the SiC sample surface during this process.

Polyimide Passivation Effect on High Voltage 4H-SiC PiN Diode Breakdown Voltage

A polyimide (PI) has been used for the passivation of maximum 7.8 kV 4H-SiC P+N–N+ (PiN) diodes with a 60 µm-thick base epilayer and a junction termination extension (JTE) periphery protection. The dielectric strength of PI films is studied versus area and temperature. The reverse electrical characterization of the PI–passivated PiN diodes is presented for different natures of the environmental atmosphere. The results are compared to those obtained from same devices passivated with a deposited SiO2 thick film. The highest experimental breakdown voltages are obtained for PI–passivated PiN diodes immersed in PFPE oil, with a 5-6 kV typical value, and a 7.3 kV maximum value. Experimental observations are discussed in correlation with the insulating film properties.

Endurance of Thin Insulation Polyimide Films for High-Temperature Power Module Applications

This paper deals with thermal endurance tests carried out on thin polyimide (PI) films widely used in high-temperature power electronics applications. Specimens deposited on stainless steel supports are aged in an oven in air at four different temperatures up to the glass transition temperature (between 250

Suitable Characterization Methods and Insulating Materials for Devices Operating above 200 °C

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Study of Polyimide Films as Passivation for High Temperature High Voltage Silicon Carbide Devices

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Investigation of Thermo-Oxidative Polyimide Thin Film Aging at High Temperature

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Characterization of Polyimide Dielectric Layer for the Passivation of High Electric Field and High Temperature Silicon Carbide Power Devices

). Dielectric strength is measured at different aging times as an indicator of PI films endurance. In this paper, in addition to this property, other properties are measured during aging, such as dc conductivity at low field, film thickness, and film morphology. The evolution of these parameters is correlated to the breakdown voltage of the films to establish more accurate endpoint criteria. The results show that the breakdown voltage decreased during aging but not likewise over the whole aging period, because of the effect of the initial surface degradation. This might lead to an underestimation of the lifetime of the films. The thickness degradation rate is constant over the rest of the aging period, making it a suitable endpoint criterion. However, the low field dielectric properties show an improvement during the aging making them an unsuitable aging marker.

High Electrical Activation of Aluminium and Nitrogen Implanted in 6H-SiC at Room Temperature by RF Annealing

Two characterization techniques, the steady-state Conduction Current (CC) and the low frequency Dielectric Spectroscopy (DS) are reviewed and compared to each other in order to choose the most suitable method for evaluating the static electrical conductivity (σDC) of an insulating material. In the case of polymeric materials operating above 200°C, the DS appears as being better suited. These techniques are applied for insulating materials identified as good candidates for high temperature (HT) applications and new results are presented. HT polyimide, parylene films and silicon nitride substrates are studied. These examples highlight the σDC magnitudes for temperatures up to 400 °C, as well as other relevant parameters to be taken into account for practical applications.

Stoichiometric Disturbances in Ion Implanted Silicon Carbide

Characterizations of Al/Polyimide/Al capacitors in a temperature range extended up to 400°C are presented. The aim is to determine the retained BPDA/PPD polyimide (PI) intrinsic dielectric and conduction properties, as a first stage in the evaluation of its ability to be applied as a passivation material for high temperature operating silicon carbide power devices. The dielectric constant, dielectric loss factor, and the static leakage current of the “as-prepared” Al/PI/Al structures are strongly affected above 175°C, reaching critical values at 400°C with regard to the aimed application. However, an evolution of these characteristics after the sample exposure at high temperature is observed, resulting in a very good and stabilized electrical behavior even at 400°C.

Improved Annealing Process for 6H-SiC p+-n Junction Creation by Al Implantation

Polyimides (PIs) are widely used in electronics wherein high temperature (HT) insulating layers are needed. Like other polymers used in HT and in ambient atmosphere, polyimides are subject to the thermal and thermo-oxidative degradations. The thermo-oxidative aging can lead to the material dielectric properties degradation and then to the device failure. Therefore, it is important to study the thermo-oxidative aging effect on the dielectric properties of PI thin films, in order to predict their lifetime. During the thermo-oxidative aging of PI films deposited on stainless steel substrate at 300 °C in air, electrical (dielectric loss, DC conductivity, breakdown voltage), physical (thickness and surface profile) and physicochemical (FTIR) properties, have been monitored for different film thicknesses. Results are analyzed and discussed in order to choose the suitable life end point criterion, and to estimate the mean time to reach it in such aging conditions.