Transmission Electron Microscope Studies of O, C, N Precipitation in Crystalline Silicon
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TRANSMISSION ELECTRON MICROSCOPE STUDIES OF 0, C, N PRECIPITATION IN CRYSTALLINE SILICON A. BOURRET DRF/Service de Physique/S, CEN Grenoble, 85 X, 38041 Grenoble C~dex, France
ABSTRACT The understanding of the precipitation phenomena of light non dopant Impurities has been recently improved thanks to high resolution electron microscopy and microanalysis. After a one-step annealing in Czochralski silicon long coesite (802) ribbons are formed between 485o and 7500 C ; amorphous platelets (Sl1 x with x = 1. 2 to 2) are formed between 6500 C - 10500 C. Silicon Interstitlals generated during the precipitation partly relax the strain energy associated with the volume change. These Interstltlals are also able to precipitate In various forms. After a two-step annealing both platelets and/or octahedra containing amorphous SIOx are formed. The role of carbon on oxygen precipitation Is important : It changes the nucleation parameters and gives a retardation phenomena In a two-step annealing treatment. Similar phenomena are observed in oxygen implanted silicon. The nucleation and growth process able to explain these observations is far from being well understood. The S10 2 polymorphism, the Important role of SI Interstitials and the mutual attraction between oxygen and carbon are some of the ingredients which explain this complexity. INTRODUCTION Since the last review on oxygen aggregation in silicon [E) several new observations have been made using transmission electron microscopy (2-4). The precipitation phenomena associated with oxygen in silicon are still not well understood.
It should be noted that the main emphasis is now given to a good
understanding of the complete nucleation and growth process. Several attempts to directly apply the classical theory of nucleation [5] were unsuccessfull or applied to a small temperature range. It Is now commonly admitted that oxygen precipitation Is governed by the thermal history of the wafers. and a good knowledge of the thermal behaviour of microdefects at low temperature is Indispensable If one wants to understand the complete nucleation and growth mechanism. Therefore In addition to the conventionnal annealing technique (one step heat treatment), a series of double-step annealing treatment have been reported. The aim was to clarify the nucleation stage and the role of additionnal impurities such as carbon. On the other hand the necessity of making buried oxygen or nitrogen layers for device manufacturing has induced new structural studies in a range of very high supersaturation. It has the further advantage of providing a way to Independantly vary the ratio of two Impurity concentrations. The purpose of this paper Is to review the new data and to point out the main progress obtained In the past two years as well as the remaining uncertainties. A brief account of the capabilities of transmission electron microscopy will also be given. in order to define the progress which can be made In the near future. CAPABILITIES OF THE TRANSMISSION ELECTRON MICROSCOPE Linear or planar defect
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