Dangling bonds stick up from the surface when sausage-like silicon crystals are sliced into wafers. Ordinarily bonded to four other silicon atoms, many silicon atoms at a cut surface find themselves bereft of a bond or two. When the first CMOS transistors were invented, those hungry bonds spoiled the performance of the devices. Then, in 1958, a group of scientists at Bell Telephone Laboratories found that growing a thin layer of silicon dioxide on the surface fulfilled the bonds. D.C. Yet in some ways, those new dielectrics leave semiconductor specialists pining for silicon dioxide.
Troubles arise at the silicon-dielectric boundary, for instance.
Researchers find lower-k compounds forming there, silicon dioxide itself or byproducts of reactions between silicon and the new partner materials. Huff notes also that none of the leading high-k candidates can tolerate the heat of the current process for fabricating circuits. The industry should be cautious not to jump prematurely into major, costly changes to manufacturing to accommodate the materials, he says. It may be wiser to cope with circuit leakage by counteracting it with power-conserving designs and more judicious placement of the thinnest silicon dioxide layers. Realizing the change may turn out to be necessary, however, Huff helps lead a Sematech team that is rushing to meet a June deadline.