Gate-to-channel parasitic capacitance minimization and source-drain leakage evaluation in germanium PMOS

This work studies the behavior of both gate-to-channel capacitance (CGC) and source-channel-drain/well leakage in metal-gate/high-κ/Ge PMOS technology (W = 10 μm and L = 10; 5; 1 μm) under development at IMEC. The hole drift-mobility of germanium is ~4X that of silicon, leading researchers to evaluate germanium as a possible channel material replacement for PMOS expected at the 32 nm technology node. In particular this study focuses on—but is not restricted to—(1) the presence of a parasitic gate-to-channel capacitance (CGC), the large non-ideal trap assisted conductance which contributes to it, and its function versus Ge-PMOS architecture and gate length; (2) the existence of C-V tool compensation error due to CGC measurement technique resulting in conductance measurement error; (3) the presence of large source-channel-drain/well leakages characterized using a new MOS gated-diode measurement technique; (4) extrinsic capacitance (CEXT), flatband voltage (VFB), and effective oxide thickness (EOT) parameter extraction with discussion on inversion layer quantization. This study found that excessive current leakages from the Ge-PMOS source-anddrain into the channel led to a chuck-dependent parasitic capacitance during CGC measurement. This excessive leakage is identified as a trap-assisted leakage through both AC and DC analysis. The chuck-dependent parasitic capacitance was an unexpected side effect of the PMOS architecture: namely the lack of N-Well isolation. The parasitic capacitance—dependent on both applied bias and frequency—was separated into two main capacitive components: a frequency-dependent source/well and drain/well trapassisted leakage capacitance (CPara_SD) and a frequency-voltage-dependent gate-induced iv junction leakage capacitance (CPara_GIJL). A third parasitic capacitance due to interface trap (IT) contribution (CIT) during channel depletion was also identified. This study also found that the new MOS gated-diode measurement technique designed to separate and evaluate the source, channel, and drain leakage components is superior to typical VGS versus IDS methods when attempting to quantify the CGC measurement. The MOS gated-diode configuration allowed for temperature-dependent analysis and activation energy extraction (EA), thereby providing a means to confirm individual leakage components: diffusion; Shockley-Read-Hall (SRH); trap-assisted leakage (TAL). TAL components include: Poole-Frenkel (PF); phonon-assisted tunneling (PAT); trap-to-band tunneling (TBT). In conclusion, it was found that the source-channel-drain/well leakages and hence parasitic capacitances of PMOS built on relaxed germanium-on-silicon can be minimized by reducing the source/drain area, reducing the source/drain-to-gate contact distance, while increasing both the gate length and measurement frequency. The dominance of SRH and TAL during Ge-PMOS operation disagrees with diffusion dominance predicted by theory and as a result opens the door for future research. Future research includes Ge- PMOS fabrication on substrates free of dislocations—to minimize SRH and TAL current leakage contributions—so as to compare leakage performance

Esaki Tunnel Diodes Formed by Proximity Rapid Thermal Diffusion

For the first time tunnel diodes have been fabricated by Proximity Rapid Thermal Diffusion (PRTD) using spin on sources and the AG Associates 610 Rapid Thermal Annealing Furnace (RTA) at RIT. Initial devices revealed a maximum peak-to-valley current ratio (PVCR) of 1.3 with a peak current density (Jp) of l6mA/cm2 at 300K. A second-generation design involving proximity diffusion of Boron and Phosphorous resulted in a higher Jp, of 3A/cm2 and an elevated PVCR of 1.97 at 300K. The increased performance is attributed to closer matching of the doping profiles via the phosphorous proximity anneal. This paper discusses the method of fabrication, key aspects of proximity diffusion, and lessons learned during evaluation

Direct Discharges of Domestic Wastewater are a Major Source of Phosphorus and Nitrogen to the Mediterranean Sea

Direct discharges of treated and untreated wastewater are important sources of nutrients to coastal marine ecosystems and contribute to their eutrophication. Here, we estimate the spatially distributed annual inputs of phosphorus (P) and nitrogen (N) associated with direct domestic wastewater discharges from coastal cities to the Mediterranean Sea (MS). According to our best estimates, in 2003 these inputs amounted to 0.9 × 10⁹ mol P yr-1 and 15 × 10⁹ mol N yr-1, that is, values on the same order of magnitude as riverine inputs of P and N to the MS. By 2050, in the absence of any mitigation, population growth plus higher per capita protein intake and increased connectivity to the sewer system are projected to increase P inputs to the MS via direct wastewater discharges by 254, 163, and 32% for South, East, and North Mediterranean countries, respectively. Complete conversion to tertiary wastewater treatment would reduce the 2050 inputs to below their 2003 levels, but at an estimated additional cost of over €2 billion yr-1. Management of coastal eutrophication may be best achieved by targeting tertiary treatment upgrades to the most affected near-shore areas, while simultaneously implementing legislation limiting P in detergents and increasing wastewater reuse across the entire basin