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The layout dependence of the silicon-germanium source/drain {[Si.sub.1-x][Ge.sub.x] S/D} technology is studied for the 45-nm technology node and beyond. The nested transistor, where other gates surround a polygate and isolated transistors, where the active area is completely surrounded by isolation oxide are two technologically important configurations investigated.

The authors present a study on the layout dependence of the silicon—germanium source/drain (Si1-xGex S/D) technology. Experimental results on Si1-x Gex S/D transistors with various active-area sizes and polylengths are combined with stress simulations. Two technologically important configurations are investigated: the nested transistor, where a polygate is surrounded by other gates, and isolated transistors, where the active area is completely surrounded by isolation oxide. The channel stress, caused by epitaxial Si1-x Gex is reduced substantially when the active area is decreased from a large size towards typical values for advanced CMOS technology nodes. Nested transistors with longer gate lengths are more sensitive towards layout scaling than shorter gates, increasing recess depth and germanium concentration gives larger channel stress, bull does not change layout sensitivity. Increased lateral etching leads to higher stress, as well as to reduced layout sensitivity. In small-size transistors, there exists an optimal recess depth, beyond which the stress in the channel will not increase further. For isolated transistor structures, the interaction between Si1-x Gex and the isolating oxide can even lead to stress reduction when the recess depth is increased. When technology advances, active-area dimensions will be scaled together with gate lengths and widths. For typical sizes of advanced silicon CMOS Si1-x Gex S/D transistors, simulations indicate that the channel stress can be maintained in future technology nodes. [ABSTRACT FROM AUTHOR]

Recessed Si0.8Ge0.2 source/drain (S/D) and a compressive contact etch-stop layer have been successfully integrated resulting in nearly 200% improvement in hole mobility. This is the largest reported process-induced hole mobility enhancement to the authors' knowledge. This letter demonstrates that a drive-current improvement from recessed Si0.8Ge0.2 plus the compressive nitride layer are in fact additive. Furthermore, it shows that the mobility enhancement is a superlinear function of stress, leading to larger than additive gains in the drive current when combining several stress sources. [ABSTRACT FROM AUTHOR]

Hole mobility is found to more than double in fabricated p-MOSFETs with SiGe source/drain due to longitudinal compressive stress in the channel exceeding 1 GPa. The maximum observed low-field mobility enhancement is 140% at a simulated stress level of 1.45 GPa. The mobility enhancement is approximately linear with stress at moderate levels but becomes super-linear above 1 GPa. An important consequence of this behavior is that for moderate stress levels, an average channel stress can be used to estimate the performance of transistors with a nonuniform stress distribution across the channel width. Two alternative approaches to model stress-enhanced hole mobility are suggested. Analysis of the physical effects behind the experimental observations reveals the relative roles of band repopulation and mass modulation. In addition, previously published wafer bending experiments with compressive stress levels below 400 MPa are used to implicitly verify the accuracy of the stress simulations. [ABSTRACT FROM AUTHOR]

Physician assistants (PAs) have been making history for 50 years. For the past 15 years, the PA History (PAHx) Society has been working to make sure this history is not lost. The Society began in 2002 as a membership organization based at Duke University and since 2011 has been a supporting organization of the National Commission on Certification of Physician Assistants (NCCPA). Highly visible and active in the PA community, the Society encourages all PAs to understand their professional history and embrace it as a part of their professional identity. The Society, through the work of its board of trustees, historians, and staff, tells the story of the collective efforts of physicians, PAs, nurses, lawyers, educators, and policy makers to create a human innovation that has changed how medicine is practiced in the United States and, more recently, in other countries. The Society provides PA faculty and students access to a growing collection of historically relevant and primary source materials that can be used for educational, research, and literary purposes.