Investigation of Czochralski Silicon Grown with Different Interstitial Oxygen Concentrations and Point Defect Populations

Abstract

Czochralski silicon crystals, grown with different interstitial oxygen concentrations ͑group I͒ or different types of intrinsic defects ͑group II͒, were analyzed by X-ray section topography, diffuse X-ray scattering, surface photovoltage, microwave photoconductive decay, and Fourier infrared spectroscopy. The samples of group I showed that the main factor influencing the X-ray section topography images is the amount of precipitated oxygen. The increase in this amount involves a decrease in size and an increase in density of the oxygen precipitates. A strong reduction in the minority carrier diffusion length is observed after precipitation. These effects seem to be dependent on the positions along the ingot axis at which the samples were taken, which would indicate the influence of the sample thermal history on the detectability of oxygen precipitates by means of these techniques. The samples of group II are characterized by vacancy-rich, interstitial-rich, and defect-free regions. After copper decoration, the different defects were observed to have different sizes, densities, shapes, and depth distributions. This feature allows one to clearly distinguish between crystal zones where vacancy or interstitial clusters prevail and where defects are absent. Minority carrier lifetime values are directly related to the defect volume densities. The combined use of different characterization techniques proved itself a powerful tool to study different defect types in Czochralski silicon.The study of crystalline defects in Czochralski ͑CZ͒ silicon ͑Si͒ has been an active area of research for decades. Far from decreasing, the interest of the scientific community in this field has increased considerably in the last years, as the rapid shrinking of ultralarge scale integrated device dimensions has put more stringent requirements on the crystalline perfection of the starting wafer. Investigations have focused on two main defect classes, particularly critical for achieving good device yields: oxygen precipitates and point defect clusters. Oxygen precipitates are formed because the interstitial oxygen present in the wafer is supersaturated at the typical temperatures of device processing. It is well known that oxygen precipitates can have both a harmful and a beneficial role for device yield: if present in the near-surface region where devices are fabricated, they can cause device failure. On the other hand, their presence in the wafer bulk is often desirable, in order to ensure a good intrinsic gettering for metallic impurities. Point defect ͑vacancy and interstitial͒ clusters in CZ grown Si have been studied since the early seventies. 1 At that time, they were called swirls or microdefects, and their nature ͑vacancy or interstitial͒ was not always clear. The recent discovery, in the early nineties, that vacancy clusters can give origin to pits on the surface of a polished wafer ͑crystal originated particle, COP 2 ͒ and cause degradation of the gate oxide integrity, 3 has renewed the interest for this subject and promoted huge ad...

Approaches in Wet Chemical Etching for Defect Delineation in Silicon-on-Insulator Substrates

“…This Si becomes fluorinated by HF and elemental hydrogen is developed which was proven by oxyhydrogen reaction. By further fluorination SiF 4 or SiF 6 2-is produced, which can be easily removed from the surface. Hydrogen development could also be proven during Secco etching, and it is assumed that its low solubility in the etching solution could explain the flow pattern formation on bulk silicon surfaces.…”

“…19 The sequence is completed with removal of the surface silicon atom as SiF 4 ͑Fig. 10i, part of the SiF 4 will finally form SiF 6 2-͒ and reentry of the H-terminated silicon in the oxidation/fluorination cycle ͑Fig. 10j͒.…”

Kinetics of Formation and Growth of Microdefects in Crystals

“…При таких термообработках может продолжаться развитие «ростовых» и образование новых микродефектов, обусловленное продолжением распада пересыщенного собственными точечными дефектами твердого раствора и коалесценцией микродефектов [5,21,24,36]. С другой стороны, возможен и процесс их обратного растворения в результате ухода собственных точечных дефектов или примесей, образующих микродефекты, на поверхность кристалла (пластины) [37,38].…”

“…В последние годы большое внимание уделяется методам внутреннего геттерирования, в которых геттер располагается внутри кремниевой пластины. Чаще всего в роли такого геттера выступают оксидные выделения и микродефекты, возникающие при термообработке выращенных по методу Чохральского монокристаллов с высоким содержанием кислорода ( 110 18 см 3 ) [32,33,37,38]. В этом случае в качестве активного слоя будущей приборной структуры выступает приповерхностный слой пластины, из которого с помощью специальной предварительной термообработки удаляют избыточный кислород [1,3,42].…”

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“…При таких термообработках может продолжаться развитие «ростовых» и образование новых микродефектов, обусловленное продолжением распада пересыщенного собственными точечными дефектами твердого раствора и коалесценцией микродефектов [5,21,24,36]. С другой стороны, возможен и процесс их обратного растворения в результате ухода собственных точечных дефектов или примесей, образующих микродефекты, на поверхность кристалла (пластины) [37,38].…”