Using scanning capacitance microscopy (SCM), we have studied the photovoltaic effect on differential capacitance (dC/dV) signals of low-energy-BF2+-implanted silicon wafers. The surface photovoltage induced by the stray light of the atomic force microscope laser beam leads to distorted dC/dV profiles and hence perturbs the contrast of SCM images. Due to the photovoltaic effect on the junction region, the observed junction image also exhibits a narrower junction width. According to this study, the photovoltaic effect not only significantly affects the dC/dV signals but also deteriorates the accuracy of junction characterization, in particular for ultrashallow junctions and lower band-gap semiconductors.
This letter reports on the investigation of p+–n junction variation produced by various annealing sequences. With well-controlled photoperturbation, we have employed scanning capacitance microscopy to directly observe the junction narrowing induced by post-spike furnace annealing. For p+–n junctions, it is revealed that post-spike furnace annealing may degrade the electrical activation of boron atoms, leading to junction narrowing without significant boron diffusion. The mechanism and the stability of electrical junctions formed by spike annealing are also discussed. The experimental results also clearly show that furnace annealing followed by spike annealing can result in junction broadening with a more concentrated boron profile.
We have selectively grown carbon nanotubes on the probe tip of an atomic force microscope by microwave plasma chemical vapor deposition. The catalyst domain was defined on the tip apex of an Si based scanning probe by local electric field induced oxidation of a TiN cap layer, under which the cobalt catalyst layer was predeposited on the probe surface. High resolution atomic force microscopy images of an SiO2 trench pattern are demonstrated using the carbon nanotube tip. The nanotube tip fabrication method is simple and compatible with existing thin film process technology.
Scanning capacitance microscopy ͑SCM͒ is employed to study defect distribution induced by iron contamination on p-type silicon wafers. For slightly contaminated samples, SCM reveals that iron contamination induces interface traps in the defect region. Interface traps perturb significantly the depletion behavior of the silicon surface. Iron contamination also decreases the lifetime and increases the density of minority carriers in the defect region. The defects induced by iron contamination exhibit an obvious bias-dependent SCM contrast. By differential capacitance images, one can examine the defect density distribution. The influence of these microscale defects on the electrical characteristics of the metal oxide semiconductor ͑MOS͒ capacitor cannot be observed by conventional capacitance-voltage measurement.
Scanning capacitance microscopy ͑SCM͒, combined with atomic force microscopy ͑AFM͒, was employed to investigate the dielectric breakdown phenomena in thin SiO 2 films. The localized breakdown spots can be clearly imaged by the SCM technique. The spots exhibit signals with low differential capacitance ͑dC/dV͒ due to high conductivity. The diameters of these breakdown spots were approximately from 6 to 13.5 nm. Moreover, according to the corresponding AFM images, their surface morphology showed little change after the occurrence of oxide breakdown.Due to the continuous scaling down of metal-oxidesemiconductor field-effect transistors ͑MOSFETs͒, the quality of the thin-gate oxide has become more and more important. Currently, oxide breakdown ͑OBD͒ is one of the most critical concerns for integrated circuit device reliability. 1,2 The OBD phenomenon can be divided into three stages. 3 First, many defects are generated within localized regions in the oxide layer. This is called the wearout phase. Percolation paths then occur, which allow currents to leak through the oxide. Finally, large currents cause thermal damage and may induce OBD propagation. This OBD process is thought to be a local phenomenon within the nano-scale region, not occurring throughout the total oxide area. 3,4 However, the conventional electrical measurements, made through MOS capacitors, can only detect general information about the whole oxide area under the electrode, and the localized OBD behavior is not mentioned. To characterize the localized OBD evens in detail, highly sensitive measurement tools with a good spatial resolution are necessary.Due to its ability to measure two-dimensional ͑2-D͒ carrier concentration profiles with a nanometer-scale resolution, scanning capacitance microscopy ͑SCM͒ can be employed to determine the effective channel length and interface defects distributions of MOSFETs. 5-7 In addition, SCM has also been used to study local charge trapping in gate oxides and dynamic device operation images. 8,9 SCM combined with atomic force microscopy ͑AFM͒ is a powerful way to synchronously measure the differential capacitance ͑dC/dV͒ images and the corresponding topographic images of thin films. Thus, in this work, we demonstrate a technique for mapping OBD spots using SCM with corresponding AFM images. The results show that these localized OBD spots exhibit low dC/dV signals but the surface morphology does not change after the occurrence of OBD. ExperimentalFour inch diameter single-crystal ͑100͒ oriented p-type silicon wafers were used in this study. The wafers were chemically cleaned using standard RCA cleaning procedure, followed by wet oxidation in an atmospheric pressure furnace to form a 500 nm thick oxide layer. The active regions were defined by photolithography and wetchemical-etching. After a standard RCA cleaning process, a 40 Å thick SiO 2 layer was grown at 900°C in diluted O 2 ambient ͑N 2 :O 2 = 10:1͒. Then, a 150 nm thick poly-Si film was deposited using a low-pressure chemical vapor deposition ͑LPCVD͒ system. ...
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