Discussion on the Figures of Merit of Identified Traps Located in the Si Film: Surface Versus Volume Trap Densities

• Main Authors: Cretu, Bogdan, Nafaa, Beya, Simoen, Eddy, Hellings, Geert, Linten, Dimitri, Claeys, Cor
• Format: Conference Proceeding
• Language: English
• Subjects: Engineering Sciences; Micro and nanotechnologies; Microelectronics
• ISSN: 2151-2043; 1091-8213; 2151-2035
• DOI: 10.1149/MA2020-01241372mtgabs

In this work a discussion on the estimated volume trap densities (N T ) compared to surface traps densities (N eff ) related to identified traps in the Si fin of Si/SiGe superlattice I/O n-channel FinFETs using low frequency noise spectroscopy is made. The investigated devices present a fin width of 10 nm, a fin height of 10 nm and four fins in parallel, leading to an equivalent channel width of 120 nm. The equivalent oxide thickness (EOT) is 5.6 nm. More details on the device fabrication and experimental setup may be found in [1,2]. The noise spectra and the estimated surface traps densities are provided in [3]. In this work, focus is only on the identified T4 trap, for which using the linear dependence that should exist between A 0i and t 0i related to the same trap, without any other assumption, a surface trap density of 2.8∙10 12 cm -2 is obtained [3]. It should be noted that from the 1/f flat-band noise level an interface trap density value of about 1.9∙10 18 eV -1 cm -3 is obtained at 300 K. However, as the traps in the Si film are related to a volume phenomenon, two methodologies to estimate the volume trap densities are employed: one using the relationship between the surface trap density and volume trap densitiy [4], where B is a coefficient estimated to be 1/3 [4,5]; and a second one from the temperature (T) evolution at fixed frequency of the Lorentzian plateau level associated to the same trap (from equation 34 in [4]). Using the first method leads to a volume trap density of T4 of about 1.7∙10 19 cm -3 . The second method consists to use the maximum of the measured S vg_Lor ( f 0 ,T) dependence with temperature. Indeed, the S vg_Lor ( f 0 ,T) of Lorentzians associated to the same trap are proportional with t i (T)/{1 + [2p f 0 t i (T)] 2 }. For a given frequency f 0 , if 2p f 0 t i (T) ≫ 1, S Vg_Lor ( f 0 ,T) ∝ t i (T)] -1 , and S Vg_Lor ( f 0 ,T) increases with increasing temperature because t i decreases. If 2p f 0 t i (T) ≪ 1, then S Vg_Lor ( f 0 ,T) ∝ t i (T) and S Vg_Lor ( f 0 ,T) decreases with increasing temperature, as explained in detail in [4]. The evolution of the S vg_Lor ( f 0 ,T)∙ f 0 in a temperature range where T4 traps are active is illustrated in Figure 1 and presents a bell-shaped behavior, as expected. Using this method, volume trap densities of about 1.25∙10 18 cm -3 for f 0 = 10 kHz and of about 1.1∙10 18 cm -3 for f 0 = 14 kHz are obtained. It may be observed that the estimated volume trap densities of the T4 defect are