2.1  Mechanical Systems

A semiconductor device is a complex piece of engineering. Its concept and operation span through electronics, optics, materials science, and several other fields of science. A proper understanding and control of such technology demands a multidisciplinary approach. For instance, using strained semiconductors is a relatively old field – but still very active – in which the main goal is to understand how stress and strain impact the carriers’ mobility in the device. In order to have full comprehension of strained devices, one should consider a combined knowledge from electronics, mechanics, and materials science. The overlap between disciplines in semiconductor research and development is quite common. Therefore, mechanics in microelectronics requires a different approach by the engineer who must consider the interaction between several physical and chemical phenomena.

Mechanical stress in microelectronics arises mainly from two sources: intrinsic stress of films and thermal stress. Those effects are present in front-end of line (FEOL) processes, back-end of line (BEOL) processes, packaging, and device operation [37]. The device is under stress during its entire lifetime and the invention of a technology which neglects it is quite unlikely. Thus, one can only try to manage the stress, either by taking advantage of it or limiting its effects in order to prevent damage to the device.

To control the stress, engineers use the structural geometry of the device, material properties, thermal management, and different manufacturing techniques. However, stress management is a difficult task, especially in microelectronics. The small scale of layers and components invalidate some aspects of classical mechanics theory. Additionally, materials’ microstructural effects play a significant role in such dimensions and cannot be neglected. Even material properties can be different when comparing thin films and bulk films with the same material composition [38]. Well documented bulk material properties cannot be used freely in small structures. Sometimes a relationship can be traced between them, but this is not always the case. Naturally, experimental procedures are used to extract material properties, but to complete this task, experimentalists face challenges of their own. In summary, mechanics in microelectronics is a multiscale physical problem, where at small dimensions, the modification of material properties gives rise to new physical effects.