This paper highlights and experimentally verifies a new source of random threshold-voltage (V_th) fluctuation in emerging metal-gate transistors and proposes a statistical framework to investigate its device and circuit-level implications. The new source of variability, christened work-function (WF) variation (WFV), is caused by the dependence of metal WF on the orientation of its grains. The experimentally measured data reported in this paper confirm the existence of such variations in both planar and nonplanar high-k metal-gate transistors. As a result of WFV, the WFs of metal gates are statistical distributions instead of deterministic values. In this paper, the key parameters of such WF distributions are analytically modeled by identifying the physical dimensions of the devices and properties of materials used in the fabrication. It is shown that WFV can be modeled by a multinomial distribution where the key parameters of its probability distribution function can be calculated in terms of the aforementioned parameters. The analysis reveals that WFV will contribute a key source of V_th variability in emerging generations of metal-gate devices. Using the proposed framework, one can investigate the implications of WFV for process, device, and circuit design, which are discussed in Part II.

Fluorinated amorphous carbon films were proposed as low dielectric constant interlayer dielectrics for ultralarge scale integration circuits. The films were deposited by plasma enhanced chemical vapor deposition with CH4 and CF4 in a parallel plate rf (13.56 MHz) reactor. The dielectric constant of the amorphous carbon films deposited with CH4 was increased with increases in rf power. The addition of CF4 to CH4 raised the deposition rate and reduced the dielectric constant. At an rf power of 200 W, and at a flow rate of 47 sccm for CF4 and 3 sccm for CH4, the dielectric constant of the fluorinated amorphous carbon films was 2.1.

Fluorinated amorphous carbon thin films (a-C:F) for use as low-dielectric-constant interlayer dielectrics are deposited by helicon-wave plasma enhanced chemical vapor deposition. To improve their thermal stability, the feasibility of adjusting the fluorine-to-carbon (F/C) ratio by changing the deposition pressure was investigated. Decreasing the pressure increased the dissociation of a source fluorocarbon material in the plasma and decreased the F/C ratio of the deposited film. Both the thermal stability and the dielectric constant of the a-C:F films were increased as the F/C ratio was decreased. Thus, there is a tradeoff relationship between a low dielectric constant and high thermal stability and the tradeoff could be optimized by the pressure during deposition. The mechanism of the pressure dependency of the dielectric constant of a-C:F films was investigated by quantifying the contribution of each polarization and found that a decrease in the dielectric constant of a-C:F films can be attributed to decreases in the orientational and electronic polarizations.

This paper describes a comprehensive study on the threshold voltage (V/sub th/) controllability of four-terminal-driven double-gate (DG) MOSFETs (4T-XMOSFETs) with independently switched DGs. Two types of 4T-XMOSFETs (fin and vertical) are experimentally demonstrated and their V/sub th/ controllability is thoroughly investigated in relation to the initial V/sub th/ in the DG-mode based on comprehensible modeling of the devices. Based on the investigation and simulated predictions, device design guidelines for 4T-XMOSFETs are proposed. Decreasing the workfunction of the DGs and increasing the oxide thickness of the second gate (T/sub ox2/) are preferable for improving the performance of the 4T-XMOSFET. The optimum workfunction of DGs for attaining low I/sub off(stand-by)/ and high I/sub on(active)/ under the limited V/sub g2/ condition is also proposed.

This work introduces an analytical approach to model the random threshold voltage (V_th) fluctuations in emerging high-k/metal-gate devices caused by the dependency of metal work-function (WF) on its grain orientations. It is shown that such variations can be modeled by a multi-nomial distribution where the key parameters of its probability distribution function (pdf) can be calculated in terms of the physical dimensions of the devices and properties of the materials. It is highlighted for the first time that such variations can have significant implications for the performance and reliability of minimum sized circuits such as SRAM cells.

Fluorinated amorphous carbon thin films (a‐C:F) for interlayer dielectrics are grown by helicon plasma enhanced chemical vapor deposition. The source gases are CH₄, CF₄, C₂F₆ and their H₂mixtures. a‐C:F films can be fabricated without adding hydrogen using the helicon reactor, while in the previously reported parallel‐plate reactor, no film grows unless a hydrogen source is added. The films grown in the helicon reactor have no hydrogen content. The growth rate of the films reaches 0.3 μm/min (C₂F₆) and 0.15 μm/min (CF₄). The thickness of the films deposited with C₂F₆ does not decrease on heating to 300 °C, while the films with CF₄ shrink. The dielectric constants of the films deposited from C₂F₆ and CF₄ are 2.4 and 2.3 respectively at 1 MHz. The dielectric loss tangent of these films is 0.01 at 1 MHz.