Investigation Of A New Intrinsic Gettering Process For Large-diameter Czochralski Silicon Wafers

Semiconductor silicon is the fundamental material for the microelectronic industry. For the past decades, the manipulation and application of impurities and defects in the Czochralski (CZ) silicon crystal, i.e. so-called "defect engineering", has been intensively investigated. Internal gettering (IG) is an important area received intensive interests from both academia and industry. Recently, great efforts have been expended in simplifying IG process and reducing the thermal budget of IG processes. In this thesis, a new IG process has been presented. Listed below are the main results obtained.A new IG process, called "Low-High (L-H) Ramping IG", has been experimentally attempted. The basic idea underlying this process is as follows: through the ramping anneal from a low temperature to a high temperature and then soaking for a period of time, the grown-in oxygen precipitates in the bulk of silicon wafer grow up and therefore generating dense bulk micro-defects (BMDs) which act as the gettering sites, while, the grown-in defects in the near-surface region of silicon wafer are dissolved and the interstitial oxygen atoms out diffuse, thus forming a oxygen precipitates denuded zone (DZ). Compared with the traditional high-low-high (H-L-H) IG process, the L-H ramping IG process is simpler and more cost-effective due to lower thermal budget.Detailed investigation of L-H ramping IG process indicates that: 1) the density of BMDs increases with decreasing starting temperature and ramping rate, 2) the width of DZ is determined by the terminal high temperature of ramping anneal and the soaking time at high temperature, 3) the terminal temperature of ramping anneal should be high enough to produce DZ, 4) only the L-H ramping anneals under inert ambients produce substantial DZ. Furthermore, it has been proved that the L-H ramping IG process is more appropriate for the nitrogen-doped CZ silicon than for the conventional CZsilicon.Moreover, the effects of oxidizing protective ambient for different IG processes including H-L-H, L-H and L-H ramping anneals on the formation of DZ and oxygen precipitation have been tentatively investigated. It is indicated that the anneal under oxidizing ambient strongly affects the growth of oxygen precipitates while slightly exerts effects on the nucleation for oxygen precipitation. Furthermore, it is believed that for the traditional H-L-H IG process a better IG structure can be achieved through adjusting the protective ambients for each stage.