OPTICAL CHARACTERIZATION IN MICROELECTRONICS MANUFACTURING

To successfully construct semiconductor devices, the semiconductor ind ustry must measure fundamental material parameters, especially when de veloping new materials; measure the quality of the material as it is g rown; accurately determine the details of thin films, quantum wells, a nd other microstructures that control of affect device performance; an d measure properties of the devices themselves. Properties that need t o be determined, therefore, include basic band structure and transport parameters, such as energy gap values and carrier scattering times; t he presence and concentration of impurities and defects; alloy paramet ers; layer thicknesses; the distribution of materials in complex struc tures; and many others. This process of determining a wide range of ma terial, structural, and device parameters is called characterization. The semiconductor industry uses many characterization methods which dr aw on electrical, chemical, and other approaches. Among these, optical characterization techniques, defined as those using electromagnetic r adiation from the ultraviolet to the far infrared, stand out because t hey are nondestructive and require minimal sample preparation since no contacts are needed. These features are of great importance for produ ction use or to examine finished devices. Another benefit is that, unl ike electrical methods which require fixed contacts, optical technique s can give two- or three-dimensional maps of properties over the exten t of a semiconductor wafer. The six techniques described in this paper (ellipsometry, infrared spectroscopy, microscopy, modulation spectros copy, photoluminescence, and Raman scattering) were chosen because the y are currently or potentially widely used in the industry; they measu re a broad array of semiconductor parameters; and they operate in diff erent regions of the electromagnetic spectrum. The discussion of each technique indicates the basic semiconductor quantities measured, gives the scientific basis of the technique, and indicates how the measurem ent is made. Illustrative examples from the literature are discussed i n detail, showing applications to important semiconductor materials. M ore information can be obtained from the detailed list of references i ncluded.