J. S. Luo, Y. H. Lu, P. Y. Chen, J. D. Russell, Inotera Memories, Inc., Taoyuan, Taiwan

Summary: The transmission electron microscope (TEM) plays a very important role in the ultra-thin film monitoring and material science analysis with high resolution as the device shrinkage, especially on atomic level crystal defect analysis. From our present observations, more and more device leakage problems are related to crystal defects, such as dislocation, dislocation loop and stacking faults. Especially, those defects appearing at P-N junction or around source and drain areas of transistors. Normally, these crystal defects were believed to be induced by the implantation process. In addition, it is well known that the device’s performance and characteristics are very dependent on the implanted dosage and resulting profile shape. For instance, the threshold voltage (Vth) of MOSFETs decreases as the channel length is shortened and also as the drain bias is increased. The influencing factors of Vth performance are device geometry, doping, gate oxide thickness and interface charge fluctuations. Secondary Ion Mass Spectrometry (SIMS) has the same sensitivity as the electrical test data of Vth on the dose variation. For deep trench (DT) type DRAM, As is used to be a dopant in poly-Si electrodes or Si substrate electrodes of memory cell for reducing the electrode’s resistance. The As distribution, which near the interface of AA and doped poly-Si, is very important. Because it might influence the drain implanted profile and channel, which cause Vth mis-matching, when As diffuses to the drain area. Furthermore, the micro-structure in doped poly-Si grains will also influence device performance. In this letter, we report several examples to carry out the applications of TEM and SIMS on crystal defects analysis and electronic characteristics of advanced 512M- bit DRAM.