Optical Characterization in Microelectronics Manufacturing

Texas Instruments, Inc., Dallas, TX 75243 To successfully construct semiconductor devices, the semiconductor industry must measure fundamental material parameters, especially when developing new materials; measure the quality of the material as it is grown; accutate\y determine the details of thin films, quantum wells, and other microstructures that control or affect device performance; and measure properties of the devices themselves. Properties that need to be determined, therefore, include basic band structure and transport parameters, such as energy gap values and carrier scattering times; the presence and concentration of impurities and defects; alloy parameters; layer thicknesses; the distribution of materials in complex structures; and many others. This process of determining a wide range of material, structural, and device parameters is called characterization. The semiconductor industry uses many characterization methods which draw on electrical, chemical, and other approaches. Among these, optical characterization techniques, defined as those using electromagnetic radiation from the ultraviolet to the far infrared, stand out because they are nondestructive and require minimal sample preparation since no contacts are needed. These features are of great importance for production use or to examine finished devices. Another benefit is that, unlike electrical methods which require fixed contacts, optical techniques can give twoor three-dimensional maps of properties over the extent of a semiconductor wafer. The six techniques described in this paper (ellipsomctry, infrared spcctroscopy, microscopy, modulation spectroscopy, photoluminesccncc, and Raman scattering) were chosen because they arc currently or potentially widely used in the industry; they measure a broad array of semiconductor parameters; and they operate in different regions of the electromagnetic .spectrum. The di.scussion of each technique indicates the basic semiconductor quantities measured, gives the scientific basis of the technique, and indicates how the measurement is made. Illustrative examples from the literature arc discussed in detail, showing applications to important semiconductor materials. More information can be obtained from the detailed list of references included.