Recently, several researchers have been able to measure precisely the contribution of the Casimir force to the dynamics of micro-electromechanical devices. Thus there is no doubt of the importance of these physics at the nanometer scale in metallic films. However, almost twenty years ago, it was estimated that the ratio of the Casimir energy to the Coulomb energy stored by a production, metal-oxide-semiconductor field effect transistor (MOSFET), having a gate oxide thickness of 50 nm, in a state of charge inversion should be of order 10%. Yet today's production MOSFET technologies are engineered with gate oxide thickness on the order of 2 nm, implying a Casimir-to-Coulomb energy ratio of well over 100% by using the original calculation. If this were correct, the Casimir effect would of necessity be a major factor in the design and in the resulting performance of current MOS technologies. This does not appear to be the case. In this light, the purpose of this paper is twofold: 1) To demonstrate that by including more precise physics the original estimate was too high, and 2) To propose a practicable method of measuring the strength of the Casimir effect in the MOS system.
Perhaps never before in semiconductor microlithography has there been such an interest in the accuracy of measurement. This interest places new demands on our in-line metrology systems as well as the supporting metrology for verification. This also puts a burden on the users and suppliers of new measurement tools, which both challenge and complement existing manufacturing metrology. The metrology community needs to respond to these challenges by using new methods to assess the fab metrologies. An important part of this assessment process is the ability to obtain accepted reference measurements as a way of determining the accuracy and Total Measurement Uncertainty (TMU) of an in-line critical dimension (CD). In this paper, CD can mean any critical dimension including, for example, such measures as feature height or sidewall angle. This paper describes the trade-offs of in-line metrology systems as well as the limitations of Reference Measurement Systems (RMS). Many factors influence each application such as feature shape, material properties, proximity, sampling, and critical dimension. These factors, along with the metrology probe size, interaction volume, and probe type such as e-beam, optical beam, and mechanical probe, are considered. As the size of features shrinks below 100nm some of the stalwarts of reference metrology come into question, such as the electrically determined transistor gate length. The concept of the RMS is expanded to show how multiple metrologies are needed to achieve the right balance of accuracy and sampling. This is also demonstrated for manufacturing metrology. Various comparisons of CDSEM, scatterometry, AFM, cross section SEM, electrically determined CDs, and TEM are shown. An example is given which demonstrates the importance in obtaining TMU by balancing accuracy and precision for selecting manufacturing measurement strategy and optimizing manufacturing metrology. It is also demonstrated how the necessary supporting metrology will bring together formerly unlinked technology fields requiring new measurement science. The emphasis on accuracy will increase the importance and role of NIST and similar metrology organizations in supporting the semiconductor industry in this effort.