Detection of Metal Segregation at the Oxide-Silicon Interface

Codegoni

Grasso

et al. 2015

Phys. Status Solidi A

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A few key techniques for the analysis of contamination in silicon are compared for their ability to detect different impurities. Both metal and organic contamination is included in this study. In addition, common contaminants and elements recently introduced in the fabrication process are considered. For what concerns metal contamination, it is shown that different approaches are required depending on the in‐depth distribution of the contaminant and hence on its diffusivity. Copper, iron, molybdenum, and tellurium are chosen as examples of contaminants with different diffusivity and solubility properties. Total reflection X‐ray fluorescence (TXRF), recombination and generation lifetime measurement techniques, deep level transient spectroscopy (DLTS) and capacitance versus voltage measurements are compared. The detection of slow diffusers is found to be very critical, because a very low dose may result in a non‐negligible concentration in the device region. As a consequence, the sensitivity per unit area required for these elements is difficult to reach with surface techniques such as TXRF. On the other hand, very fast diffusers such as copper can hardly be revealed in the solid solution in silicon. Copper in silicon can be revealed at the oxide–silicon interface by TOF‐SIMS measurements, or by surface generation velocity measurements with the Zerbst method. For what concerns organic contamination, surface recombination velocity and gate oxide integrity tests were compared. The most relevant effects of organic contamination were observed by electrical stress of the oxide. Indeed, the fraction of capacitors with degraded breakdown voltage increased dramatically in wafers with intentional organic contamination.

Section: Ironmentioning

confidence: 62%

A comparative analysis of different measurement techniques to monitor metal and organic contamination in silicon device processing

Codegoni

Grasso

et al. 2015

Phys. Status Solidi A

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“…In addition, in experiments about a fast diffuser (nickel) similar results were obtained by implantations at wafer frontside or at wafer back side. 11,12 On the other hand, the doses used in this experiment are lower than the typical threshold doses for defect formation. 13,14 After the implantation, the wafers were thermally treated by a Rapid Thermal Treatment (RTP) at 1100 • C for 3 min in an inert environment.…”

Section: Methodsmentioning

confidence: 88%

Analysis of Near-Surface Metal Contamination by Photoluminescence Measurements

ECS J. Solid State Sci. Technol.

Galbiati

Mica

et al. 2018

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In this work, molybdenum and tungsten-implanted wafers are analyzed by an innovative technique based upon photoluminescence measurements, with the aim to assess the ability of this technique to detect metal contamination in the near-surface region. Surface Photovoltage (SPV) measurements of carrier diffusion length are compared to the results of photoluminescence measurements. It is shown that molybdenum and tungsten contamination are easily detected by photoluminescence intensity measurements down to about 10 10 cm −2 contaminant dose. Vice versa, SPV has limited sensitivity to these elements (≥5 • 10 10 cm −2 ), because of their low diffusivity. Therefore, photoluminescence intensity measurement can be a valid alternative to conventional carrier diffusion length measurements for monitoring slow diffuser contamination.

“…In addition, in experiments about a fast diffuser (nickel) similar results were obtained by implantations at wafer frontside or at wafer back side. 31,32 To validate and calibrate carrier lifetime measurements for the detection and quantification of iron in silicon, p-type, 10 cm wafers were implanted with iron and annealed at 1100 • C for 2 min. Fig.…”

Section: Resultsmentioning

confidence: 99%

Review—Characterization of Metal-Contamination Effects in Silicon

ECS J. Solid State Sci. Technol.

Codegoni

Galbiati

et al. 2015

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Various measurement techniques are compared and the most suitable methods for contamination detection are identified. The results of this study show that it is not possible to define a unique recipe that can be applied in all cases. Concerning metal contaminants, the stratigraphic in-depth distribution and hence the diffusivity of contaminants determines the most effective approach. Iron and palladium are chosen as the examples of fast diffusers, molybdenum and tungsten as slow diffusers. Fast diffusers like iron and palladium diffuse through several hundred microns during an ordinary thermal treatment. Minority carrier lifetime measurements are probably the best choice to detect these contaminants. Molybdenum and tungsten do not diffuse deep enough to be efficiently revealed by recombination lifetime measurements, but are easily revealed in the silicon volume by DLTS. Because of their low diffusivity, a very small amount of these elements per unit surface may result in a significant concentration in the near-surface region where devices are built. Ion implantation is confirmed to be an important source of metal contamination. It is shown that ion implantation can be responsible both for iron contamination and for contamination by slow diffusers, such as molybdenum and tungsten. A procedure for monitoring molybdenum and tungsten contamination in ion implantation processes by DLTS is defined and calibrated. Finally, the efficiency of some gettering techniques in reducing iron, molybdenum and tungsten contamination is discussed. Gettering is found to be active at relatively high contaminant concentrations, but low contamination levels are not gettered under our experimental conditions. Carbon implantation showed partial efficiency in gettering molybdenum and tungsten, whereas gettering did not take place after silicon implantation.