Effect Of Dopants On Grown-in And Thermal Induced Defects In Czochralski Silicon

The silicon epitaxial wafers using heavily doped n-type silicon have been widely used in fabrication of integrated circuits and power devices. To improve the yield of devices, the silicon epitaxial wafers and therefore indeed the silicon substrate are required to have an excellent internal gettering (IG) ability, which is determined by the formation of oxygen precipitates and their induced defects during the device manufacturing. In the past decade, rapid thermal processing (RTP) has been proved to be an efficient strategy to enhance oxygen precipitation (OP) in Cz silicon. However, most of the studies on the impact of high temperature RTP on OP are focused on lightly doped silicon. Therefore, an in-depth understanding on the effect of high temperature RTP on OP in heavily doped n-type silicon is of practically importance for improving the IG capability of silicon epitaxial wafers.In the past two decades, the co-doped Cz silicon crystals have been attached incremental importance. Among them, germanium (Ge) co-doped Cz silicon has been paid special attention due to its high mechanical strength and IG capability. Void is a type of primary grown-in defect in Cz silicon, being able to deteriorate the gate oxide integrity of MOS devices thus reducing the yield. The effect of Ge-doping on the formation of voids in Cz silicon is yet to be substantially investigated.In this dissertation the effects of heavily n-type dopoing on the formation of cacancy-containing complexes and oxygen precipitates with prior high temperature RTP have been studied. Moreover, using the non-destructively Scanning Infrared Microscopy (SIRM), the influence of Ge-doing and heavy n-type doping on the formation of void defects in Cz silicon have been addressed. The most important results achieved in this pissertation are listed below.(1) The impact of RTP on resistivity in heavily As, P or Sb doped Cz silicon has been investigated. It is found that after RTP at1000,1150or1250℃for90s, resistivity in all the specimens increased. After subsequent anneals at low temperature from300to650℃, resistivity gradually recover to their original value. As RTP at high temperature can introduce vacancies with high concentration, the cause of resistivity change is ascribed to the formation of DV (D=As, P, Sb) complexes. The DV complexes can deactivate dopant atoms leading to the increase of resistivity after RTP pretreatment. During subsequent anneals at300-650℃the DV complexes will decompose, leading to the recovery of resistivity. It is an effective method to estimate the injected vacancy concentration by the change of resistivity. For heavily P, As and Sb doped silicon, the injected vacancy concentrations are about1018cm-3,(2-3)×1017cm-3and (2-5)x1016cm-3separately.(2) Oxide precipitate nucleation at300℃in heavily As or Sb doped Cz silicon with and without prior rapid thermal processing (RTP) has been investegated. With the prior RTP, a subsequent nucleation anneal even at300℃, leads to a high oxide precipitate density after a precipitation anneal at1000℃. As this is not observed without prior RTP, the effect is assumed to be related to the introduction of vacancies by the prior RTP. As and Sb are deactivated by the formation of Asx-V or Sbx-V complexes. The reduction of free carriers causes an increase of resistivity corresponding with a few times1017cm-3deactivated dopant atoms suggesting that about1017cm-3vacancies are frozen-in after the RTP. During subsequent annealing at300℃, the resistivity recovers to its original value due to the release of vacancies that can facilitate oxide precipitate nucleation by forming VO2and AsVO or SbVO complexes acting as heterogeneous nucleation centers that will grow during subsequent anneals.(3) A comparative investigation is performed on the effects of vacancies induced by RTP on oxygen precipitation behavior in heavily As-and Sb-doped silicon crystals. It is found that vacancy-assisted oxide precipitate nucleation occurs at800,900,1000℃in the Sb-doped wafers, while it only occurs at800℃in the As-doped ones. Density functional theory (DFT) calculations indicate that it is energetically favorable to form AsVO and SbVO complexes in As-and Sb-doped silicon crystals, respectively. These complexes might act as the precursors for oxide precipitate nucleation under appropriate conditions. The difference between the effects of RTP induced vacancies on oxide precipitate nucleation in the heavily As-and Sb-doped Cz silicon is tentatively elucidated based on DFT calculations which reveal the difference in binding energies of AsVO and SbVO complexes.(4) The assumed impact of Ge doping with low concentration on void formation during Cz-growth of silicon single crystals has been first studied using scanning infrared microscopy. The present study reveals only a marginal-if any-effect of Ge doping on grown-in single void size and density. The limited effect of Ge doping on single void formation is in agreement with earlier findings that Ge atoms are only a weak trap for vacancies at higher temperatures and therefore should have a smaller impact on the vacancy thermal equilibrium concentration and on single void nucleation. Double and multiple void formation however is suppressed partially by heavily Ge doping.(5) The impact of heavy doping of Sb, As and P on the formation of void defects in Cz silicon have been investigated by SIRM. It is found that:(1) in heavily Sb doped silicon ([D]≈(1.6-3.4)×1018cm-3), void formation is significantly enhanced;(2) in heavily As doped silicon, void formation is enhanced in the seed end of the crystal ([D]≈1.9×1019cm-3) but it is suppressed in the tang-end of the crystal ([D]≈3.8×1019cm-3);(3) in heavily P doped silicon([D]≈4.6×1019cm-3), the void formation is much more significantly suppressed so that SIRM can not detect the voids. Such results have been tentatively explained in terms of the effects of heavy doping of Sb, As and P on the formation and evolution of vacancies in silicon.