Articles

Philippe Colomban

LA​DIR-UMR 7075 CNRS & Université P. & M. Curie, 2 rue Henry Dunant, 94320 Thiais, France

Moore’s law* dictates microelectronics researchers to make integrated circuit (IC) devices smaller and to put them as close to each other as possible on a chip. This results in a better performance and a larger functionality of the chips. However, these devices also require a good electrical isolation from each other. This is in general done by the formation of a thick local oxide in the “field region” between the devices. In 1970, researchers from Philips¹ invented the so-called LOCOS (LOCal Oxidation of Silicon) technique to achieve this isolation. Using a Si₃N₄ mask, the silicon is thermally oxidised in the nitride-free field regions. Figure 1 (left) shows a typical LOCOS structure. Although LOCOS seemed a perfect solution at that time, it came with a lot of problems, many of them related to mechanical stresses. Thermal oxidation of Si to SiO₂ occurs together with a 125% volume expansion. As a result, the oxide grown in the field region, called the “field oxide,” exerts large forces on the surrounding silicon. Another major drawback of this technique is the so-called “bird’s beak,” caused by the lateral growth of the oxide under the nitride mask. This bird’s beak not only affects the intended device length, it also introduces large local mechanical stresses in the silicon, because of volume expansion, and it also deforms the nitride film. These stresses often resulted in the generation of dislocations in the silicon, which are quite harmful for the devices.

The study of the mineralogical phases of archaeological ceramics may be very helpful in unravelling the history of an ancient sherd, particularly by means that investigate the process of its production. Micro-Raman spectroscopy offers advantages as a non-destructive, or even better, a non-sampling technique.