Process for suppressing the nucleation and/or growth of interstitial type defects by controlling the cooling rate through nucleation

#The present invention generally relates to the preparation of semiconductor grade single crystal silicon which is used in the manufacture of electronic components. More particularly, the present invention relates to the preparation of single crystal silicon ingots and wafers having an axially symmetric region of vacancy or interstitial dominated material which is devoid of agglomerated intrinsic point defects, and a process for the preparation thereof.

#Single crystal silicon, which is the starting material for most processes for the fabrication of semiconductor electronic components, is commonly prepared by the so-called Czochralski (“Cz”) method. In this method, polycrystalline silicon (“polysilicon”) is charged to a crucible and melted, a seed crystal is brought into contact with the molten silicon and a single crystal is grown by slow extraction. After formation of a neck is complete, the diameter of the crystal is enlarged by decreasing the pulling rate and/or the melt temperature until the desired or target diameter is reached. The cylindrical main body of the crystal which has an approximately constant diameter is then grown by controlling the pull rate and the melt temperature while compensating for the decreasing melt level. Near the end of the growth process but before the crucible is emptied of molten silicon, the crystal diameter must be reduced gradually to form an end-cone. Typically, the end-cone is formed by increasing the crystal pull rate and heat supplied to the crucible. When the diameter becomes small enough, the crystal is then separated from the melt.

#In recent years, it has been recognized that a number of defects in single crystal silicon form in the crystal growth chamber as the crystal cools after solidification. Such defects arise, in part, due to the presence of an excess (i.e. a concentration above the solubility limit) of intrinsic point defects, which are known as vacancies and self-interstitials. Silicon crystals grown from a melt are typically grown with an excess of one or the other type of intrinsic point defect, either crystal lattice vacancies (“V”) or silicon self-interstitials (“I”). It has been suggested that the type and initial concentration of these point defects in the silicon are determined at the time of solidification and, if these concentrations reach a level of critical supersaturation in the system and the mobility of the point defects is sufficiently high, a reaction, or an agglomeration event, will likely occur. Agglomerated intrinsic point defects in silicon can severely impact the yield potential of the material in the production of complex and highly integrated circuits.

#FIG. 1 is a graph which shows an example of how ΔGI, the change in free energy required for the formation of agglomerated interstitial defects, increases as the temperature, T, decreases, for a given initial concentration of self-interstitials, [I].

#FIG. 2 is a longitudinal, cross-sectional view of a single crystal silicon ingot showing, in detail, an axially symmetric region of a constant diameter portion of the ingot.

#FIG. 3 is a cross-sectional image of an ingot prepared as discussed in Example 1.

#In accordance with the present invention, it has been discovered that the reactions in which vacancies and silicon self-interstitial atoms react to produce agglomerated intrinsic point defects can be suppressed by rapidly cooling the single crystal silicon through the temperature of nucleation for these defects. Without being bound to any particular theory, it is believed that rapid cooling, sometimes referred to as quenching herein, prevents the reaction from progressing by freezing the reactants, i.e., the intrinsic point defects, in place.

#In general, the change in system free energy available to drive the reaction in which agglomerated vacancy defects are formed from vacancy point defects or in which agglomerated interstitial defects are formed from self-interstitial atoms in single crystal silicon is governed by Equation (1): 1 Δ ⁢ ⁢ G V / I = kT ⁢ ⁢ ln ⁡ ( [ V / I ] [ V / I ] eq ) ( 1 )

#wherein