Modeling of mechanical stress in silicon isolation technology and its influence on device characteristics

One of the challenges the semiconductor industry faces as it attempts and continues the scaling of silicon integrated circuits is understanding and control of mechanical strain resulting from silicon fabrication technology. High magnitudes of strain can be induced under standard fabrication conditions and may produce deleterious effects in device behavior, such as increased current leakage. Current leakage has been identified as a critical device characteristic for future sub-micron dynamic random access memory (DRAM) and complementary metal oxide semiconductor (CMOS) technologies, as it is a limiting factor for increasing switching speeds and decreasing power consumption. The following are various known sources of stress in silicon technology: thermal expansion mismatch, intrinsic stress, and oxidation volume dilation. This work results from an examination, by modeling, experiment, and simulation, of the contribution of stress due to these sources using the Florida Object-Oriented Process Simulator (FLOOPS).;The contributions of each source can be simulated using different models that represent or approximate the physics involved. After the models are described and presented, example applications are provided to distinguish the advantages and limitations for each model.;Coupling experiment along with process simulation then validates the results and allows for a better understanding of the problem. One such problem examined in this work is the strain induced by the shallow trench isolation (STI) process. STI has become an essential isolation scheme for present and future sub-micron processes. It consists of several sequential steps that exert stress in the silicon active area by each of the previously described sources. Scanning Kelvin probe force microscopy (SKPM) is then applied as a new technique to characterize the strain exerted from STI processes through measurements of strain-induced work function variations in silicon. Qualitative agreement is demonstrated between the SKPM measurements and the work function influence due to finite element based STI induced mechanical strain computations.;Finally, a wafer bending experiment is performed that quantifies the influence of tensile and compressive uniaxial stress on forward current of pn-junction devices. This effect is then modeled primarily through the strain influences in the silicon bandgap.