SiC籽晶上生长AlN单晶的杂质组成及处理

采用物理气相传输法在SiC异质籽晶上制备了AlN单晶。通过Raman光谱仪、X射线衍射仪、二次离子质谱仪和X射线光电子能谱研究了AlN单晶的结晶质量和杂质成分,针对不同的杂质成分提出了相应的处理方式。结果表明:C、O为AlN单晶中的主要杂质元素,其中C元素为非故意掺杂,与AlN单晶的生长环境密切相关,随着生长晶体厚度的增加,C杂质元素的含量逐渐降低。而O元素除了源粉和生长系统中吸附氧外,还与抛光过程中形成的氧化物层有关;经腐蚀和退火处理,AlN表面氧化物的含量大幅降低,N/Al摩尔比接近1;经杂质处理后的AlN单晶片可作为同质生长的籽晶。     

不同粒径磨料对蓝宝石晶片及其抛光过程的影响EI北大核心CSCD

采用不同粒径的W28和W7碳化硼（B4C）磨料对蓝宝石晶片进行研磨和化学机械抛光。研究了不同粒径的B4C磨料对蓝宝石晶片研磨和化学机械抛光后的移除率、粗糙度、平坦度、弯曲度、翘曲度等参数的影响。结果表明：W28和W7的磨料有不同的研磨和抛光性能,在相同的加工条件下,使用W28的B4C磨料,移除速率较快,但研磨所得蓝宝石晶片的损伤层较深,单面抛光20μm不足以去除其损伤层,抛光后表面划痕较多,粗糙度较大（Ra=1.319 nm,Rt=2.584 nm）,表面有明显起伏;而W7磨料的移除速率慢,研磨时间长,在单面抛光移除20μm后其损伤层全部移除,抛光所得蓝宝石晶片平坦度略佳,抛光表面平整,粗糙度较小（Ra=0.194 nm,Rt=0.361 nm）,无明显起伏,表面质量相对较高,适于精修平坦度。     

不同粒径磨料对蓝宝石晶片及其抛光过程的影响

采用不同粒径的W28和W7碳化硼(B_4C)磨料对蓝宝石晶片进行研磨和化学机械抛光。研究了不同粒径的B_4C磨料对蓝宝石晶片研磨和化学机械抛光后的移除率、粗糙度、平坦度、弯曲度、翘曲度等参数的影响。结果表明:W28和W7的磨料有不同的研磨和抛光性能,在相同的加工条件下,使用W28的B_4C磨料,移除速率较快,但研磨所得蓝宝石晶片的损伤层较深,单面抛光20μm不足以去除其损伤层,抛光后表面划痕较多,粗糙度较大(R_a=1.319 nm,R_t=2.584 nm),表面有明显起伏;而W7磨料的移除速率慢,研磨时间长,在单面抛光移除20μm后其损伤层全部移除,抛光所得蓝宝石晶片平坦度略佳,抛光表面平整,粗糙度较小(R_a=0.194 nm,R_t=0.361 nm),无明显起伏,表面质量相对较高,适于精修平坦度。     

掺镁近化学计量比LiTaO3晶体的生长及光学性能

在同成分LiTaO3熔体中掺入一定剂量的K2O,采用顶部籽晶提拉法生长掺镁近化学计量比LiTaO3晶体.对晶体分别进行光谱分析,畴结构和抗光损伤阈值的测定.结果表明:与同成分掺镁LiTaO3晶体相比较,其紫外吸收边出现明显蓝移,红外吸收峰变弱.腐蚀晶片的晶相显微镜观察结果表明:掺镁近化学剂量比晶体的畴结构是较为规则的六边形;晶体的抗光致散射能力明显提高.     

Li_2Ti_3O_7晶体的生长、相变和物性

用提拉法生长了定向的、亚稳态Li_2Ti_3O_7晶体,单晶的尺寸可达φ20×20mm,研究了籽晶取向、生长气氛和掺杂剂对晶体生长的影响及晶体的相变过程,并测量了晶体的光学和声学特性。     

生长方法对DKDP晶体生长习性及光学性能的影响

以KH2PO4作为原材料,从含85%(摩尔分数)氘的氘化溶液中分别由传统降温法和"点籽晶"快速生长法生长了磷酸二氘钾[(K(DxH1-x)2PO4,DKDP]晶体。对加工后的样品进行了光散射和透过性能测试,研究了不同生长方法对DKDP晶体的生长习性和光学性能的影响。结果表明:对于纯度较高原料(杂质金属离子浓度≤10-6),"点籽晶"快速生长法能有效避免晶体生长过程中杂晶的出现,且生长速率为传统降温法的10倍,但所得晶体存在严重的光散射,透过性能明显下降,另外,快速生长所得晶体柱面区域较锥面区域光学性能明显下降。     

6H-SiC单晶的生长与缺陷

采用升华法,在一定的温度、气体压力和流量的条件下,生长了尺寸ф50．8mm的6H—SiC单晶。利用光学显微术观察了原生晶体的表面形貌,发现了微管在晶体表面的露头点具有明显的多个螺位错成核特征。采用透射模式对抛光晶片进行观察,发现了SiC晶体内的典型缺陷,如：负晶、微管、碳颗粒等,并对它们的形成机理进行了讨论。     

CsI：Tl晶体生长中存在的问题及其解决途径

用Ｂｒｉｄｇｍａｎ方法制备了掺铊的碘化铯晶体，样品经过切割，研磨和抛光，观察了它们的缺限，测定其光学性质，结果表明，气泡，包裹体和局部开裂严重地影响晶体的光学质量和完整性，通过使用高纯试剂，惰性气氛生长，分段和均匀掺杂，窄的熔区和合适的温度梯度，能够明业改善晶体的性质和质量。     

快速扩大KDP(KH_2PO_4)晶体(xy)截面的生长方法

本文提出快速扩大KDP晶体(xy)截面的生长方法。籽晶用四块z 90°切或z 45°切的晶片彼此平行地拼接而成,经过淘汰拼锥,已生长出截面为80×80mm的KDP晶体。     

金刚石生长的驱动力

籽晶方法生长金刚石采用温度梯度技术,金刚石晶体生长驱动力来源于腔体内构造的温度梯度。工业上采用自发成核生长金刚石技术,金刚石生长的驱动力来源于金刚石晶体与石墨温度差。     

Efficient and slurryless ultrasonic vibration assisted electrochemical mechanical polishing for 4H–SiC wafers

This paper proposes a slurryless, highly efficient polishing method called ultrasonic vibration assisted electrochemical mechanical polishing (UAECMP) to realize 4H–SiC wafers with subnanometer surface roughness. UAECMP involves using ultrasonic vibration to simultaneously assist anodic oxidation of the SiC surface and mechanical removal of the generated oxide layer. The performance of UAECMP was evaluated by experiments and theoretical analyses. For a 4H–SiC (0001) surface, UAECMP achieved a material removal rate (MRR) of 14.54 μm/h, which was 4.5 times greater than that of ordinary electrochemical mechanical polishing (ECMP) and 290 times greater than that of mechanical polishing. Ultrasonic vibration increased the anodic oxidation rate by introducing local transient strain to the SiC surface and increasing the temperatures of the polishing area and electrolyte. The effect increased with the amplitude of the ultrasonic vibration. However, increasing the ultrasonic vibration amplitude also increased the surface roughness due to the large fluctuations of polishing marks caused by the grinding stone and SiC surface impact and the increasing residual oxide. Therefore, we propose a high-efficiency and -quality polishing process for SiC wafers that combines UAECMP and ECMP. The proposed polishing process may help simplify the existing manufacturing process for SiC wafers.     

Molecular dynamics simulation of SiC removal mechanism in a fixed abrasive polishing process

Precision polishing of mono-crystalline SiC wafers on a fixed abrasive pad is investigated by double-nano-abrasives cutting at micro/nano scale in this report. Prior to this report, a single abrasive approach in molecular dynamics simulation had been employed to illustrate the material removal mechanism in SiC polishing process, which is quite different from the real situation of the fixed abrasive polishing process. Cutting depth and spacing of abrasive particles in a fixed abrasive pads were tested to gain insights on phase transformation, subsurface damage, surface quality, material removal and friction characteristics of polished SiC wafers by molecular dynamics simulation. By following the coordination number and radial distribution function, we clearly see that the number of phase transformation atoms caused by cutting and abrasion increases with the cutting depth of nano-abrasives on the surface of SiC workpiece. Simulation results also suggest that the phase transformation of the SiC crystal phase increases with the lateral spacing of abrasive particles in pads, while does not change much with the increase of the longitudinal spacing. It is also found that the deeper the abrasive cutting depth, the deeper subsurface damage, resulting more materials’ removal from SiC workpiece. The lateral and longitudinal abrasive spacings lead to little change the depth of subsurface damage on the wafer in MD simulation for a fixed double abrasive polishing. The surface roughness is better with the larger lateral abrasive spacing, but no clear correlation with the longitudinal abrasive spacing.     

Plasma-activated direct bonding of diamond-on-insulator wafers to thermal oxide grown silicon wafers

Diamond-on-insulator (DOI) wafers featuring ultrananocrystalline diamond are studied via atomic force microscopy, profilometer and wafer bow measurements. Plasma-activated direct bonding of DOI wafers to thermal oxide grown silicon wafers is investigated under vacuum. DOI wafer with chemical mechanical polishing (CMP) on the diamond surface makes a poor bonding to silicon wafers with thermal oxide. Our results show that plasma enhanced chemical vapor deposition of silicon dioxide on top of the DOI wafer, CMP of the oxide layer and annealing are essential to achieve very high quality direct bonding to thermal oxide grown on silicon wafers. Plasma activation results in the formation of high quality bonds without exceeding 550 °C in the direct wafer bonding process.     

Ohmic contacts to polycrystalline 3C–SiC films for extreme environment microdevices

Ohmic contact characteristics were studied under the surface treatments of poly 3C–SiC films heteroepitaxially grown on SiO₂/Si wafers by APCVD. The poly 3C–SiC surface was polished to remove submicron-sized roughness and to get flat and smooth surface using chemical–mechanical polishing (CMP) process. However, some scratching marks on the poly 3C–SiC have remained surface due to the mechanical defect of CMP process. To remove a part of subsurface damage and scratching marks, the polished surface was oxidized by wet-oxidation furnace and it has been etched by diluted HF solution. Titanium tungsten (TiW) thin film was deposited on the surface treated poly 3C–SiC using circular transmission line model as a metallization process and it was annealed through the rapid temperature annealing (RTA) process to improve interfacial adhesion. The contact resistivity of the treated 3C–SiC surface was measured as the lowest 1.2 × 10⁻⁵ Ω cm³ at 900 °C for 45 s.     

坩埚下降法生长铌酸锂晶体

采用坩埚下降法,生长了直径为5 cm的铌酸锂晶体.探讨了晶体生长工艺条件,测试了晶体的透过光谱.所得晶体呈浅茶色,分析认为主要是氧空位缺陷所致.铌酸锂晶体通常用作声表面波(surface acoustic wave,SAW)器件的基片,氧空位缺陷可增加基片的电导率,减少器件制造过程中晶片开裂,有利于提高SAW器件成品率.     

Improved electrical properties of SiC wafer with defects covered by free standing graphene

As a single crystal SiC is grown, defects and dislocations occur due to many reasons. In particular, defects such as micropipes and micropores that are generated during the growth of single crystal SiC ingot have irregular locations and sizes. These defects continue to exist after the manufacturing process and undermine the properties of single crystal SiC wafer. Moreover, they lower the electrical properties of the wafers and can even cause detrimental damages after being applied in devices.We combined single crystal SiC wafer and graphene with a floating method in order to use graphene as a bridge to connect the SiC bonding that is broken due to defects such as micropipes and micropores in single crystal SiC wafer. In this process, we characterized the layers of graphene needed, ranging from monolayer to multilayer, to cover micropipes and micropores of various sizes. As a result of measuring the thermoelectrical conductivity of single crystal SiC wafer combined with monolayer graphene up to temperatures of 400 °C, we observed electrical conductivity that was two or three orders higher than that of the SiC wafer alone. In addition, the connection between the SiC and the graphene was stable.     

锗酸铋晶体缺陷和小面生长

对坩埚下降法生长锗酸铋闪烁晶体的缺陷进行了研究，除使用通常研究透明晶体的光学方法，由于ＢＧＯ晶体在受到光辐照损伤对短波长光具有高的吸收系数，因此还采用近紫外光吸收形貌法研究晶体缺陷，以及缺陷与晶体小面之间的关系，并根据ＢＧＯ晶体的结晶习性和小面形成机理提出了减少和消除晶小面生长及缺陷的方法。     

Mechanistic difference between Si-face and C-face polishing of 4H–SiC substrates in aqueous and non-aqueous slurries

The traditional aqueous-based polishing slurries have been extensively used in the ultra-precision machining process of SiC substrates, but their processing efficiency remains a major challenge in making SiC wafers with high surface quality. SiC polishing slurries based on non-aqueous solvents have been explored and reported, however, the mechanism for the accelerated SiC material removal rate (MRR) remains unknown. In this work, the Si-face and C-face of the SiC wafer were polished with water and methanol as polishing liquid carriers, respectively. The MRR of Si-face using the methanol-based slurry, can reach 260.9 nm/h, and the polished Si-face surface roughness Ra reduces to 0.150 nm. In contrast, the MRR of Si-face by using the aqueous-based slurry, is 66.8 nm/h, the polished Si-face surface roughness Ra is 0.691 nm. However, the results of MRR and Ra for C-face are opposite. The reaction between the polishing liquid carriers and the atomic structures of Si-face and C-face lead to differences of the MRRs by analyzing contact angle, XPS, and molecular dynamics (MD) simulation results. The newly revealed polishing mechanisms shined light for speeding up the development of SiC polishing slurries based on the specific aspects of the polishing surface of SiC.     

Quality improvement of single crystal 4H SiC grown with a purified β-SiC powder source

In the processing of single crystal SiC using the PVT method, defects such as micropipes and dislocations occur due to various reasons, including growth rate, temperature gradient, seed quality, pressure change and the SiC source powder. Among these factors, the SiC source powder was investigated to reduce defects in single crystal SiC. β-SiC powder was used to reduce the growth temperature and change basic properties of the particle, including microstructure, particle size and chemical composition, through the purification process. The structure of the purified β-SiC particle was changed into a spherical structure and its particle size expanded. Chemical analysis revealed reduced free carbon, oxide phases such as silica (SiO₂), silicon oxycarbide and metallic impurities. Purified β-SiC powder showed increased particle size of 37 µm and showed improved purity. With this, we grew single crystal 4H SiC and compared the micropipe and dislocation density to that of single crystal 4H SiC grown with non-purified β-SiC powder. The experimental results confirmed that the 4H SiC wafer grown by purified β-SiC powder exhibited improved quality.