Effect Of Hydrogen Annealing On Oxygen Precipitation And Void In Czochralski Silicon

Czochralski (CZ) silicon crystal has been and will be the dominant material in the semiconductor industry. The requirements on the silicon wafer are becoming increasingly stringent along with the ever-smaller feature size of ultra-large-scale integrated (ULSI) circuits. In recent years, it has been proved that the high temperature hydrogen annealing can well annihilated the void defects located in the near-surface region of silicon wafer and, moreover, reduce the surface micro-roughness of silicon wafer. As a consequence, the gate oxide integrity of MOS device is effectively improved. On the other hand, internal gettering (IG) is crucial for the silicon wafer used for ULSI circuits. For the contemporary silicon wafers in which the initial interstitial oxygen concentration ([O_i]) is being lowered, how to increase the IG capability is a matter of importance. In this thesis, the effects of high temperature hydrogen annealing on the out-diffusion of oxygen, IG and void defects in silicon wafer have been experimentally investigated. List below are the significant results obtained in this work.The out-diffusion of oxygen in silicon wafer annealed at high temperatures (1000 and 1200℃) under argon or hydrogen ambient was investigated. It was found that the hydrogen annealing facilitated oxygen out-diffusion and thus reducing the [Oi] in the near-surface region in comparison with the argon annealing.The variation of [Oi] during the oxygen growth anneal at 1000℃ following the nucleation anneal at different temperatures of 450-850℃ in the silicon wafers subjected to the prior high temperature (1000 and 1200℃ ) annealing under argon or hydrogen ambient was investigated. It was revealed that the hydrogen impurity induced into the silicon wafer by the hydrogen annealing could enhance the nucleation of oxygen precipitates with and without the assistance of vacancy. It is believed that the hydrogen enhancement of oxygen precipitation can be ascribed to two possible reasons: 1. the induced hydrogen facilitates the oxygen diffusion during the oxygen nucleation anneal;2. the heterogeneous oxygen precipitate nuclei are formed through the interaction of hydrogen and oxygen.The formation of denuded zone (DZ) in silicon wafers subjected to the low-high two-step anneal following the high temperature anneal under hydrogen or argon ambient was investigated. It was found that the prior hydrogen annealing not only enabled the formation of wider DZ but also facilitated the formation of denser bulk miro-defects due to the hydrogen enhancement of oxygen precipitation as mentioned above.The effect of high temperature hydrogen annealing on the bulk void defects which is commonly delineated as flow pattern defects (FPDs) in heavily boron-doped (HB) CZ silicon wafer was investigated. A modified Secco etchant recipe and optimum etching time were obtained by trial and error to delineate the FPDs in HB CZ silicon wafer. Based on this, the densities of FPDs in HB CZ silicon wafers before and after high temperature hydrogen annealing were compared. It was consequently found no notable difference between the two densities, indicating that the bulk voids in HB CZ silicon wafer could not be annihilated by the high temperature hydrogen annealing, which is also the case for the lightly-doped CZ silicon wafer.