Observation of Localized Breakdown Spots in Thin SiO[sub 2] Films Using Scanning Capacitance Microscopy

Abstract

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. ...

Implanted and irradiated SiO2∕Si structure electrical properties at the nanoscale

“…[18][19][20][21][22][23][24][25][26][27][28][29][30][31] The main characteristic of an AFM is that, when working on a MOS structure without gate electrode, the tip of the AFM plays the role of the metal electrode, defining a MOS capacitor with an area equal to the contact area between the tip and the sample. However, due to the extremely local nature of the damage induced in the oxide during the irradiation/implantation ͑related to the ion impact͒, atomic force microscope ͑AFM͒ related techniques can provide information hidden at device level thanks to their nanometer resolution.…”