MICRO: TechEmergent

Alex Salnik, Lena Nicolaides, and Jon Ospal, combination of ion implantation and thermal annealing, which are both silicon surface modification methods, is a key production process in semiconductor manufacturing. Thermal-wave (TW) technology measures surface modification (i.e., "damage") induced by ion implantation. Based on modulated optical reflectance, which is also known as photomodulated reflectance, the technology is well established in wafer processing to characterize and control ion implant dose accuracy and uniformity. Advanced semiconductor fabrication uses low-energy ion implantation processes to achieve ultrashallow (<500-Å) implantation depths. Several types of annealing methods, including rapid thermal-spike anneals, laser annealing, and flash-lamp annealing, are known to minimize the diffusion of dopants, thus forming low-resistivity ultrashallow junctions (USJs). The implantation of B at low-energy, high-doping concentrations (~10 ) combined with rapid thermal-spike annealing (RTA) is currently the leading process used to fabricate USJs. Potential process problems in forming USJ layers lie in both the implant and the anneal procedures. While it is relatively easy to create a shallow layer using implantation, keeping the USJ profile abrupt and close to the surface after anneal is challenging. Junction depth (X ), profile abruptness, and resistivity (dopant activation) are the most critical parameters in the characterization of USJs. Nonuniformities associated with ion implantation and RTA or other types of anneal methods can result in residual damage areas on the wafer surface. Hence, monitoring is required to ensure process control. Typically, destructive analytical methods such as secondary ion mass spectroscopy (SIMS), transmission electron microscopy (TEM), and spreading resistance depth profiling (SRP) have been used to analyze USJs. While these methods can provide detailed USJ profile information, they do so at the expense of turnaround times that are measured in days or even weeks. The increasing need for a sensitive, rapid, and nondestructive technique for monitoring all key USJ profile parameters