【作者】 宋崇富；

【导师】 李全新； 屠兢；

【作者基本信息】 中国科学技术大学 ， 化学物理， 2008， 博士

【摘要】 薄膜材料的制备及其性能研究是材料化学和材料物理领域的重要研究课题之一。氟负离子在半导体蚀刻、薄膜材料的制备及其改性、大气化学、生物化学和负离子质谱技术等领域具有重要的应用背景。本论文合成了氟负离子存储.发射功能材料[Ca₂₄Al₂₈O₆₄]⁴⁺·（F^-）_3.36(O^（2-）_0.32（缩写成C12A7-F^-）;首次研究了该材料的结构特征、负离子存储特性、负离子发射特性、高纯氟负离子源的建立技术;深入研究了C12A7-F^-材料的负离子存储-发射机理;利用该功能材料和建立的高纯氟负离子源,进行了F^-离子对硅和二氧化硅蚀刻应用研究。主要的研究结果如下:（1）C12A7-F^-的制备和结构特征。1350℃时,在氩气气氛下高温焙烧CaCO₃、γ-Al₂O₃和CaF₂,然后在780℃和氟气气氛下退火处理来制得C12A7-F^-材料。场发射扫描电子显微镜（FESEM）、BET-孔径分析和X射线衍射（XRD）测试表明C12A7-F^-材料的属于I（?）3d空间群,晶格常数为1.1969±0.0002 nm。比表面和平均孔径分别为1.073 m²/g和42.6（?）。另外经长时间发射后结构并没有发生明显变化。（2）F^-离子发射特性。利用时间飞行质谱测量了C12A7-F^-材料的发射特性,包括温度效应,引出场效应,发射分支比,表观活化能的计算和发射稳定性等内容。实验结果显示,F^-离子为最主要的发射离子,其强度随着温度和引出场的增加而增加.得到的各离子的表观活化能随着电场的增加而下降,并基本符合肖特基公式。（3）F^-离子存储特性。采用电子顺磁共振（EPR）、离子色谱（IC）和喇曼谱（RS）等方法表征C12A7-F^-材料的存储特性,表明该材料中的负离子物种主要是F^-负离子(（1.96±0.25）×10²¹cm^-3),伴随少量的O^2-和极少量的O^-和O₂^-,这也与TOF检测的C12A7-F^-材料表面负离子发射情况基本吻合。（4）F^-离子形成和发射机理。C12A7-F^-材料中的F^-离子是在焙烧过程中初步生成,然后在退火处理中经电荷交换反应进一步增强。在发射过程中,内部的F^-离子通过电场增强的热扩散过程迁移到样品表面,然后再脱附到气相中。实验中观测到的少量的O^-离子和电子发射主要来源于O^2-离子的解离.（5）F^-离子束。测量了C12A7-F^-材料的绝对发射电流密度。利用TOF质谱实时校正得到的发射分支比和总电流,计算各种离子的绝对电流。其中,F^-离子的绝对发射电流密度可以达到μA/cm²量级。在样品背面注入氟气的情况下,C12A7-F^-材料可以持续稳定地发射μA/cm²量级的F^-离子流.（6）F^-离子束对硅和二氧化硅的蚀刻。利用该功能材料和建立的高纯氟负离子源,进行了F^-离子对硅和二氧化硅蚀刻应用研究。同时利用FESEM和X射线光电子能谱（XPS）等表征方法对蚀刻前后样品表面形貌和组分变化进行了测试。表明F^-离子束对硅片和二氧化硅具良好的蚀刻效果。研究表明,该负离子存储-发射功能材料C12A7-F^-具有高选择性存储氟负离子,高纯度发射氟负离子的能力;在电催化注入时所发射的高纯和高稳定性的氟负离子束可用来建立高纯氟负离子源。另外,该氟负离子束有望用于蚀刻和材料表面改性等领域。更多还原

【Abstract】 Atomic fluorine anion（F^-） is a monovalent anion（or monovalent negative ion） through the attachment of an electron to atomic fluorine.As one of the important chemical intermediates,atomic fluorine anion is potentially useful in many fields such as semiconductor etching,filming,and material modifications,etc.This dissertation presents the synthesized of F^- anions storage-emission material [Ca₂₄Al₂₈O₆₄]⁴⁺.（F^-）_3.36(O^2-)_0.32（C12A7-F^-）.Its structural characteristics,anion storage and emission characteristics were observed.C12A7-F^- can be used as a high pure F^- anion source.The anion storage-emission mechanisms of C12A7-F^- was further revealed.The high pure F^- anion source was found to be useful for the etching of Si and SiO₂.The major conclusions have been summarized as follows:（1） Synthesis and structure characterization of C12A7-F^-.The C12A7-F^- sample synthesized by sintering CaF₂,CaCO₃ andγ-Al₂O₃ at 1350℃for 8 hours under flowing Ar atmosphere,then annealing at 780℃under flowing F₂/Ar mixture （F₂:Ar=5:95） atmosphere for 10 hours.The field emission scanning electron microscopy（FESEM）,BET and X-ray diffraction（XRD） measurements indicated that C12A7-F^- belongs to I（?）3d space group with a lattice constant of 11.969±0.002（?）.The BET surface area and average pore diameter are about 1.073 m²/g and 42.6（?）,respectively.No obvious structural damage was found after running the emission.（2） Anions emission feature.The emission features of C12A7-F^-,including temperature effects,the applied extraction field effects,the emission branch ratio and the apparent activation energy,the emission stability have been investigated by using time-of-flight mass spectrometry.It is showed that the F^- is the dominating emitted anion,and its emission intensity increases with the increase of the temperature and the extraction field.The apparent activation energies of anions decrease with the increase of the extraction field which can be approximately described Schottky formula.（3） Anions storage feature.The ion chromatography（IC）,electron paramagnetic resonance（EPR） and Raman spectroscopy（RS） measurements indicated that the anionic species stored in the C 12A7-F^- material was dominated by the F^- anions (（1.96±0.25）×10²¹ cm^-3),accompanied by small amount of oxygen-containing anions,which also agrees with the distribution of the emitted anions via the TOF observations.The chemical formula of present material is approximately described as[Ca₂₄Al₂₈O₆₄]⁴⁺·（F^-）_3.36(O^2-)_0.32（abbreviated as C12A7-F^-）.（4） Anions emission mechanism.In the sintered process,the encaged F^- and O^2- anions are formed simultaneously and the concentration of the encaged F^- anions are enhanced by substituting the F^- anions for O^2- anions during the subsequent annealing process.The F^- emission is attributed to the encaged F^- anions in C12A7-F^- migrating from the bulk onto the sample surface by field-enhanced thermal diffusion,and then desorbing to the gas phase.The minor O^- and electron emission are mainly generated from the dissociation of residual O^2-.（5） F^- emission current.The emission current densities from the C12A7-F^- sample are also measured.With the emission branch ration obtained by TOF-MS spectra, the emission current densities of different anions are estimated.The F^- emission current density could reach aμA/cm² level.When supplying fluorine gas and electrons,a sustainable and stable F- emission beam can be obtained.（6） Etching of Si and SiO₂ by F^-.Particularly,the atomic fluorine anions were found to be useful for the etching of Si and SiO₂,evaluated by the morphological alterations via a field emission scanning electron microscope（FESEM）,the surface composition’s changes using X-ray photoelectron spectroscopy（XPS）.It could be concluded that C12A7-F^- can be used as a good F^- anions storage and emitter material for its stability and the ability to emit high-pure F^- flux,which is useful for the etching or surface modification for the semiconductor materials or other materials.更多还原