Annealing of ion-implanted defects in diamond by MeV ion-beam irradiation
Annealing of ion-implanted defects in diamond by MeV ion-beam irradiation
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DOI：
10.1103/physrevb.60.2747
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发表时间：
1999-07
影响因子：
3.7
通讯作者：
J. Nakata
中科院分区：
文献类型：
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作者：
J. Nakata
在一定剂量的C或P离子注入下形成的Ib型金刚石中的缺陷和非晶态C层或团簇在750℃的热退火过程中或在750兆电子伏特(MeV)的离子束辐照过程中外延晶化或明显退火或外延晶化。注入的P原子在MeV离子束辐照下完全晶化后进入替代位。用卢瑟福背向散射光谱沟道方法证实了这一点。对于$1\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$剂量，在50keV能量下，C离子注入形成了相当数量的缺陷或无定形团簇。然而，只使用750℃的热退火或750℃的MeV离子束辐照，它们就会外延到晶体钻石上，在$2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$C剂量以上，在衬底内部形成连续的非晶层，外延结晶同时从晶体衬底和晶体表面区域进行。此外，在相同温度下，用MeV-离子束辐照的退火比热退火的晶化速度快。然而，即使热处理时间或辐照剂量增加，内部非晶层的外延晶化在热退火和MeV-离子束辐照中都停止了。这可能是由于非晶态C在热退火或MeV-离子束辐照过程中转变为石墨层所致。As注入样品在退火前也观察到了石墨的形成。从$2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$剂量和$3\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$剂量下样品之间的沟道产额差异给出了石墨形成的直接证据，清楚地表明了{2}$(石墨)和${3}$(钻石)键合之间的阻止能力差异。与硅衬底非晶化所需的剂量相比，碳离子注入金刚石中的非晶层的剂量要小一个数量级以上。计算出每次入射C离子在硅中产生的空位数大于在钻石中产生的空位数。然而，钻石的非晶化速度比硅快。提出了金刚石中非晶层的形成机制。这包括非弹性电子散射引起的断键过程和离子注入引起的无反冲的弹性核散射辅助下的C原子断键后的运动过程。提出并讨论了离子束诱导外延结晶(IBIEC)和超高真空化学气相沉积形成的注入非晶化外延硅层的低温晶化的原子模型，特别强调了入射MeV离子束的核和电子散射的作用。在此原子IBIEC模型的基础上，提出了一个类似于将注入的P原子包含在替代位中的原子模型。
Defects and amorphous C layers or clusters in a type-Ib diamond formed by C- or P-ion implantation under certain doses are clearly annealed or epitaxially crystallized during thermal annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C or during mega-electron-volt (MeV) ion-beam irradiation at 750 \ifmmode^\circ\else\textdegree\fi{}C. Implanted P atoms are incorporated into substitutional sites after complete crystallization by using MeV-ion-beam irradiation. This is confirmed by using the Rutherford-backscattering-spectroscopy channeling method. A considerable amount of defects or amorphous clusters are formed by C-ion implantation at a 50-keV energy for a $1\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose. However, they are crystallized epitaxially to the crystalline diamond by using only thermal annealing at 750 \ifmmode^\circ\else\textdegree\fi{}C or by using MeV-ion-beam irradiation at 750 \ifmmode^\circ\else\textdegree\fi{}C. Above $2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ C doses, continuous amorphous layers are formed internally in the substrate and epitaxial crystallizations proceed from both the crystalline substrate and the crystalline-surface region. Moreover, the rate of crystallization is higher for annealing with MeV-ion-beam irradiation than for thermal annealing at the same temperature. Epitaxial crystallization of the internal amorphous layer, however, stops in both thermal annealing and MeV-ion-beam irradiation, even if annealing time or irradiation dose increases. This is probably due to amorphous C changing into the graphite layers that occurs during thermal annealing or MeV-ion-beam irradiation. Graphite formation is also observed for the as implanted sample before annealing. Direct evidence of graphite formation is given from the channeling yield difference between samples for a $2\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose and for a $3\ifmmode\times\else\texttimes\fi{}{10}^{15}/{\mathrm{cm}}^{2}$ dose, showing clearly the stopping power difference between ${\mathrm{sp}}^{2}$ (graphite) and ${\mathrm{sp}}^{3}$ (diamond) bonding. Amorphous layers in diamond can be formed by C-ion implantation at a more than one order of magnitude smaller amount of doses, compared with those needed for the amorphization of the Si substrates. A calculated number of vacancies created per incident C ion in Si is larger than in diamond. Nevertheless, diamond is amorphized faster than Si. A mechanism is proposed for forming the amorphous layer in diamond. This consists of a bond-breaking process due to inelastic electronic scattering and the movement process of C atoms after bond breaking with the assistance of elastic nuclear scattering without recoil, induced by ion implantation. Atomistic models for ion-beam-induced epitaxial crystallization (IBIEC) and for low-temperature crystallization of implantation-amorphized epitaxial Si layer formed by ultrahigh vacuum chemical-vapor deposition are proposed and discussed, putting particular emphasis on the role of both nuclear and electronic scattering of incident MeV-ion beam. A similar atomistic model for the inclusion of implanted P atoms into substitutional sites is also proposed, based on this atomistic IBIEC model.