Dependence of Mechanical Strength of Czochralski Silicon Wafers on the Temperature of Oxygen Precipitation Annealing

Abstract

Dependence of mechanical strength of Czochralski silicon (CZ‐Si) wafers on the temperature of oxygen precipitation annealing has been studied both experimentally and theoretically. Thermal stress was applied to CZ‐Si wafers after oxygen precipitation annealing at 1100°C or 1000°C after preannealing at 800°C. The warpages and the densities of slip dislocations in the wafers annealed at 1100°C are much higher than those in the wafers annealed at 1000°C, nevertheless each precipitate density is almost equal. Transmission electron microscopy observations of the 1100°C samples showed that both platelet and polyhedral precipitates were generated, but very few of these precipitates actually generated punched‐out dislocations. In contrast, in the 1000°C samples, only platelet precipitates were generated, many of which generated punched‐out dislocations. Further studies showed that slip dislocations formed only from platelets which did not punch out dislocations, i.e., slip dislocations formed only in the 1100°C samples. The mechanism of the generation of slip dislocation by oxide precipitates is discussed with calculated results of the system energy change due to slip dislocation generation.

Transition from a punched-out dislocation to a slip dislocation revealed by electron tomography

“…Therefore segments labeled (iv) are sessile, as the line direction and Burgers vector define the slip plane as (011) and not the accepted (111). In a previous study, 9 all segments of this kind of dislocation were considered to be on the identical {111} slip plane, which left the origin of the large dislocation loop ambiguous. It is also still ambiguous whether the dislocation loop can be a new dislocation source or not.…”

“…It has been reported that the precipitates affect not only the optical properties but also the mechanical properties. [3][4][5][6][7][8][9] For example, the yield stress of silicon with precipitates can be up to 33% lower than that of silicon with no precipitates. 5 The magnitude of the decrease is dependent on the precipitate size.…”

X-ray diffractometry and topography of lattice plane curvature in thermally deformed Si wafer

“…Wafer warpage owing to thermal stress in a very large scale integrated-circuit fabrication is a rediscovered issue of concern at each step of Si wafer enlargement (Hu, 1973;Leroy & Plougonven, 1980;Widmer & Rehwald, 1986;Sueoka et al, 1997;Fischer et al, 2000). Extensive efforts have been devoted to elucidate the onset mechanism of wafer warpage with an emphasis on the distribution of thermal stress within a wafer (Hu et al, 1976;Bentini et al, 1984) and/or on the effect of oxygen precipitates that are incorporated by the precipitation treatments (Leroy & Plougonven, 1980;Fukuda & Moizuka, 1992;Chiou et al, 1994).…”

Distribution of slip dislocations in thermally deformed silicon wafers

“…It is known that many slip dislocations are generated in the compressed region of CZ silicon and that precipitates produce the nucleation sites for the slip dislocations [2,4]. During the growth of oxide precipitates, SiO x precipitates expand in the silicon matrix.…”

“…Thermal stress generated during the cooling or heating of wafers is the highest at the center of the wafers, and thus, slip dislocations are initiated exclusively from that area, resulting in cup-shaped deformation [2,3]. As this takes place, dislocations are preferentially introduced in the concave side (compressed region) of the cup-shaped silicon wafer.…”