piece of cake
no nuptials are in the works, the chefs at Sematech's front-end processes
division have cooked up something that is cause for celebration among
those struggling with certain electrical measurements.
A specially processed wafer called a "terraced oxide substrate"
used to measure work function on a single wafer has taken on the moniker
"the wedding cake" because of how the stacked series of four wide, concentric
circles or terraces look when viewed and magnified from the side.
cake features a stairstep-like pattern of oxide thicknesses (produced
in a spin-processor etcher), 20–100-Å deep, lodged in those
concentric circles. A high-k/metal
stack can be deposited on the entire cake, and then the work function
(which relates to the ability to turn a transistor on and off) can be
measured on the resulting array of oxide-and-metal stacks.
can achieve process uniformity on a single wafer that you can't across
several wafers, because with one wafer, the process remains the same
across the oxide layers," says the division's associate director, Larry
Larson. The "standard work function monitor structure" will ease the
search for a high-k gate metal that will ape the ability of silicon
to be tuned to two different work functions, which are required to accommodate
the negative and positive channels in circuitry, he adds.
Which is another way of saying
that engineers might have their cake and eat it too.