By the year 2000 electronics will probably be the basis of the largest industry in the world. Silicon microelectronics will continue to keep a dominant place covering 99% of the `semiconductor market'. The aim of this review article is to indicate for the next decade the domains in which research work in `physics' is needed for a technological advance towards increasing speed, complexity and density of silicon ultra large scale integration (ULSI) integrated circuits (ICs). By `physics' we mean here not only condensed matter physics but also the basic physical chemistry and thermodynamics. The review begins with a brief and general introduction in which we elucidate the current state of the art and the trends in silicon microelectronics. Afterwards we examine the involvement of physics in silicon microelectronics in the two main sections. The first section concerns the processes of fabrication of ICs: lithography, oxidation, diffusion, chemical and physical vapour deposition, rapid thermal processing, etching, interconnections, ultra-clean processing and microcontamination. The second section concerns the electrical operation of the ULSI devices. It defines the integration scales and points out the importance of the intermediate scale of integration which is the scale of the next generation of ICs. The emergence of cryomicroelectronics is also reviewed and an extended paragraph is dedicated to the problem of reliability and ageing of devices and ICs: hot carrier degradation, interdevice coupling and noise are considered. It is shown, during our analysis, that the next generation of silicon ICs needs mainly: (i) `scientific' fabrication and (ii) microscopic modelling and simulation of the electrical characteristics of the scaled down devices. To attain the above objectives a return to the `first principles' of physics as well as a recourse to nonlinear and non-equilibrium thermodynamics are mandatory. In the references we list numerous review papers and references of specialized colloquia proceedings so that a more detailed survey of the subject is possible for the reader.