退火工艺对Al离子注入的4H-SiC表面形貌的影响

通过应用多次Al离子注入和CVD中的高温退火技术,在SiC片表面形成了p型层。p型层中各深度下Al的浓度均为110¹⁹cm^-3,层厚为550nm。本文应用三种不同的退火工艺对注入后的SiC进行退火。通过测量和比较表面粗糙度,发现通过石墨层覆盖来保护表面的退火工艺可以很好的阻止SiC表面在高温退火下的粗化,粗糙度保持在3.8nm。通过其他两种(在氩气保护下、在SiC保护片的覆盖下)退火工艺退火所得到的表面有明显的台阶,粗糙度分别为12.2nm和6.6nm。     

Surface roughening in ion implanted 4H-silicon carbide

Silicon carbide (SiC) devices have the potential to yield new components with functional capabilities that far exceed components based on silicon devices. Selective doping of SiC by ion implantation is an important fabrication technology that must be completely understood if SiC devices are to achieve their potential. One major problem with ion implantation into SiC is the surface roughening that results from annealing SiC at the high temperatures which are needed to activate implanted acceptor ions, boron or aluminum. This paper examines the causes and possible solutions to surface roughening of implanted and annealed 4H-SiC. Samples consisting of n-type epilayers (5 × 10¹⁵ cm⁻³, 4 μm thick) on 4H-SiC substrates were implanted with B or Al to a total dose of 4 × 10¹⁴ cm⁻² or 2 × 10¹⁵ cm⁻², respectively. Roughness measurements were made using atomic force microscopy. From the variation of root mean square (rms) roughness with annealing temperature, apparent activation energies for roughening following implantation with Al and B were 1.1 and 2.2 eV, respectively, when annealed in argon. Time-dependent activation and surface morphology analyses show a sublinear dependence of implant activation on time; activation percentages after a 5 min anneal following boron implantation are about a factor of two less than after a 40 min anneal. The rms surface roughness remained relatively constant with time for anneals in argon at 1750°C. Roughness values at this temperature were approximately 8.0 nm. Annealing experiments performed in different ambients demonstrated the benefits of using silane to maintain good surface morphology. Roughnesses were 1.0 nm (rms) when boron or aluminum implants were annealed in silane at 1700°C, but were about 8 and 11 nm for B and Al, respectively, when annealed in argon at the same temperature.     

磨料特性对InP晶片集群磁流变抛光效果的影响

对InP晶片进行了集群磁流变抛光实验,研究了抛光过程中磨料参数(类型、质量分数和粒径)对InP材料去除速率和表面粗糙度的影响。实验结果表明,InP晶片的去除速率随磨料硬度的增加而变大,表面粗糙度受磨料硬度和密度的综合影响;在选取的金刚石、SiC、Al2O3和SiO2等4种磨料中,使用金刚石磨料的InP去除速率最高,使用SiC磨料的InP抛光后的表面质量最好。随着SiC质量分数的增加,InP去除速率逐渐增加,但表面粗糙度先减小后增大。当使用质量分数4%、粒径3μm的SiC磨料对InP晶片进行抛光时,InP去除速率达到2.38μm/h,表面粗糙度从原始的33 nm降低到0.84 nm。     

Low threading dislocation density Ge deposited on Si (1 0 0) using RPCVD

Epitaxial Ge layer growth of low threading dislocation density (TDD) and low surface roughness on Si (1 0 0) surface is investigated using a single wafer reduced pressure chemical vapor deposition (RPCVD) system. Thin seed Ge layer is deposited at 300 °C at first to form two-dimensional Ge surface followed by thick Ge growth at 550 °C. Root mean square of roughness (RMS) of ∼0.45 nm is achieved. As-deposited Ge layers show high TDD of e.g. ∼4 × 10⁸ cm⁻² for a 4.7 μm thick Ge layer thickness. The TDD is decreasing with increasing Ge thickness. By applying a postannealing process at 800 °C, the TDD is decreased by one order of magnitude. By introducing several cycle of annealing during the Ge growth interrupting the Ge deposition, TDD as low as ∼7 × 10⁵ cm⁻² is achieved for 4.7 μm Ge thick layer. Surface roughness of the Ge sample with the cyclic annealing process is in the same level as without annealing process (RMS of ∼0.44 nm). The Ge layers are tensile strained as a result of a higher thermal expansion coefficient of Ge compared to Si in the cooling process down to room temperature. Enhanced Si diffusion was observed for annealed Ge samples. Direct band-to-band luminescence of the Ge layer grown on Si is demonstrated.     

高体份SiC/Al反射镜在空间光学应用可行性的分析

简述了空间遥感器设计中反射镜材料选择的重要性及影响。对SiC和SiC/Al复合材料与常用光学材料的空间应用综合品质因子进行了比较,SiC材料的综合品质因子为8072.92,高体分SiC/Al复合材料的综合品质因子为1 687.50。并对高体分SiC/Al复合材料应用在反射镜上的光学性能进行了检测。检测结果得出材料的表面粗糙度能够达到1.49 nm,小于5 nm;反射率达到95%以上,能够满足反射镜的性能要求。对采用高体分SiC/Al复合材料作为反射镜和背板材料的相机结构进行分析。分析结果得出整体结构前三阶模态为115 Hz,120 Hz,203 Hz,满足空间遥感器大于100 Hz的技术要求,各反射镜的面形精度满足RMS≤1/50λ(λ=632.8 nm)的技术要求。各项测试数据和有限元分析结果表明,高体份SiC/Al复合材料作为反射镜在空间光学中应用是可行的。     

Dopant activation and surface morphology of ion implanted 4H- and 6H-silicon carbide

The activation of ion-implanted B into 4H-SiC, and B, and Al into 6H-SiC is investigated. Complete activation of B implants into 4H-SiC is achieved by annealing at 1750°C for 40 min in an Ar environment. Significant activation (>10%) is not achieved unless the annealing temperature is 1600°C or greater. Sheet resistances of Al-implanted 6H-SiC annealed at 1800°C are 32.2 kΩ/□, indicating high activation of Al at this temperature. Annealing conditions which result in good acceptor activation are shown to be damaging to the surface of either 4H- or 6H-SiC. Atomic force microscopy and Nomarski differential interference contrast optical microscopy are applied to characterize the surfaces of these polytypes. Roughening of the surfaces is observed following annealing in Ar, with measured roughnesses as large as 10.1 nm for B-implanted 4H-SiC annealed at 1700°C for 40 min. Based on data obtained from these techniques, a model is proposed to describe the roughening phenomenon. The premise of the model is that SiC sublimation and mobile molecules enable the surface to reconfigure itself into an equilibrium form.     

Comparison of Solid-State Microwave Annealing with Conventional Furnace Annealing of Ion-Implanted SiC

Rapid solid-state microwave annealing was performed for the first time on N⁺-, Al⁺-, and B⁺-implanted SiC, and the results were compared with the conventional furnace annealing. For microwave annealing, temperatures up to 2,000 °C were attained with heating rates exceeding 600 °C/s. An 1,850 °C/35 s microwave anneal yielded a root-mean-square (RMS) surface roughness of 2 nm, which is lower than the 6 nm obtained for 1,500 °C/15 min conventional furnace annealing. For the Al implants, a minimum room-temperature sheet resistance (R _s ) of 7 kΩ/□ was measured upon microwave annealing. For the microwave annealing, Rutherford backscattering (RBS) measurements indicated a better structural quality, and secondary-ion-mass-spectrometry (SIMS) boron implant depth profiles showed reduced boron redistribution compared to the corresponding results of the furnace annealing.     

Al-N共掺杂ZnO:Mn稀磁半导体薄膜的结构与性能

采用反应磁控溅射法在室温下沉积前驱体氮化物,在大气环境、500℃下氧化退火30min后获得了Al-N共掺杂ZnO:Mn薄膜。研究了直流与射频反应磁控溅射对氧化退火薄膜结构和性能的影响。结果表明:两种工艺制备的退火薄膜均具有ZnO纤锌矿结构,且均为n型导电。射频溅射退火样品具有很好的c-轴择优取向,其表面光滑平整,表面粗糙度RMS值为1.2nm,且具有室温铁磁性,饱和磁化强度(Ms)和矫顽力(Hc)分别为46.8A·m–1和4.9×103A·m–1;而直流溅射退火样品表面凹凸不平,RMS值为25.8nm,室温下是反铁磁性的。     

Vanadium-based ohmic contacts to n-type Al<Subscript>0.6</Subscript>Ga<Subscript>0.4</Subscript>N

Four vanadium-based contacts to n-type Al_0.6Ga_0.4N were compared in this work. Both V/Al/Pd/Au and V/Al/V/Au contacts with optimized layer thicknesses provided lower specific-contact resistances than did the previously reported V/Al/Pt/Au ohmic contact. Specific contact resistances of the V/Al/Pd/Au (15 nm/85 nm/20 nm/95 nm) and V/Al/V/Au (15 nm/85 nm/20 nm/95 nm) contacts were 3×10⁻⁶ Ω·cm² and 4×10⁻⁶ Ω·cm², respectively. On the other hand, an analogous V/Al/Mo/Au contact never became ohmic, even after it was annealed at 900°C for 30 sec. Compared to the V/Al/Pd/Au contact, the V/Al/V/Au contact required a less severe annealing condition (30 sec at 700°C instead of 850°C). The V/Al/V/Au contact also provided a smoother surface, with a root-mean-square (RMS) roughness of 39 nm.     

SiC化学机械抛光技术的研究进展

介绍了半导体材料SiC抛光技术的发展及直接影响器件成品率的衬底材料几何参数和表面质量因素.讨论了SiC化学机械抛光方法(CMP),包括磨削、粗抛和精抛三个过程,其中粗抛又分重压和轻压两个过程,通过这种方法能够制造出平整度好,表面低损伤的SiC晶片的抛光片,切割线痕通过磨削和抛光可以有效地去除,最终达到表面粗糙度小于1 nm.分析了CMP的原理和相关工艺参数对抛光的影响,指出了其发展前景.     

单片集成GaAs增强／耗尽型赝配高电子迁移率晶体管

介绍了单片集成GaAs增强／耗尽型赝配高电子迁移率晶体管（PHEMT）工艺。借助栅金属的热处理过程,形成了热稳定性良好的Pt／Ti／Pt／Au栅。AFM照片结果表明Pt金属膜表面非常平整,2nm厚度膜的粗糙度RMS仅为0．172nm。通过实验,我们还得出第一层Pt金属膜的厚度和退火后的下沉深度比大概为1：2。制作的增强型／耗尽型PHEMT的闽值电压（定义于1mA／mm）、最大跨导、最大饱和漏电流密度、电流增益截止频率分别是＋0．185／-1．22V、381．2／317．5mS／mm、275／480mA／mm、38／34GHz。增强型器件在4英寸圆片上的阈值电压标准差为19mV。     

A comparison of graphite and AlN caps used for annealing ion-implanted SiC

The SiC wafers implanted with Al were capped with AlN, C, or AlN and C and were annealed at temperatures as high as 1700°C to examine their ability to act as annealing caps. As shown previously, the AlN film was effective up to 1600°C, as it protected the SiC surface, did not react with it, and could be removed selectively by a KOH etch. However, it evaporated too rapidly at the higher temperatures. Although the C did not evaporate, it was not a more effective cap because it did not prevent the out-diffusion of Si and crystallized at 1700°C. The crystalline film had to be ion milled off, as it could not be removed in a plasma asher, as the C films annealed at the lower temperatures were. A combined AlN/C cap also was not an effective cap for the 1700°C anneal as the N or Al vapor blew holes in it, and the SiC surface was rougher after the dual cap was removed than it was after annealing at the lower temperatures.     

磁存储器驱动电路界面平坦化研究

利用原子力显微镜（AFM）和扫描电镜（SEM）对磁存储器(MRAM)驱动电路与存储单元--磁性隧道结(MTJ)的连接界面的表面平坦化进行了研究. 原子力显微镜照片表明：磁控溅射沉积的金属铝膜的表面由尺寸约为300nm的颗粒组成，其表面粗糙度约为几十纳米的量级，用统计平均值（均方根值root mean square,RMS）描述约为10nm；在铝膜的表面沉积一层难溶金属Ti或Ta膜以后，可很好地改善过渡层金属表面的平坦化效果. 通过用化学机械平坦化设备(chemical mechanical planarization,CMP) 在小压力和低转速的条件下，可使过渡层金属表面的RMS值达到小于1nm的平坦化效果. 扫描电镜照片的结果也显示：利用光刻胶平坦化，然后通过调节反应离子刻蚀的条件，使刻蚀的过程中对氧化硅和光刻胶的刻蚀速率相等，去掉光刻胶，达到平坦化整个芯片表面的效果.     

SiC晶圆背面激光退火工艺研究

降低芯片背面金属-半导体欧姆接触电阻是有效提高器件性能的方式之一。采用650 V SiC肖特基势垒二极管(SBD)工艺,使用波长355 nm不同能量的脉冲激光进行退火实验,利用X射线衍射(XRD)和探针台对晶圆背面镍硅合金进行测量分析,得出最佳能量为3.6 J/cm²。退火后采用扫描电子显微镜(SEM)观察晶圆背面碳团簇,针对背面的碳团簇问题,在Ar;气氛下对晶圆进行了表面处理,使用SEM和探针台分别对两组样品的表面形貌和电压-电流特性进行了对比分析。实验结果表明,通过表面处理可以有效降低表面的碳含量,并且使器件正向压降均值降低了6%,利用圆形传输线模型(CTLM)测得芯片的比导通电阻为9.7×10^-6Ω·cm²。器件性能和均匀性都得到提高。     

碳化硅表面硅改性层的特性研究

为了获得具有高质量光学表面的非球面碳化硅反射镜,需对碳化硅反射镜表面进行改性。介绍了离子束辅助沉积硅的碳化硅表面改性技术。对改性样片表面硅改性层的机械性能、光学加工性、表面粗糙度及反射率等特性进行研究。实验结果表明,碳化硅表面的硅改性层具有优良的机械性能和良好的光学加工性。光学抛光后,碳化硅表面硅改性层的表面粗糙度为0.85nm[均方根(RMS)值],在可见光波段反射率最高可达98.5%(镀银反射膜)。采用数控加工方法对口径为Ф600mm的表面改性离轴非球面碳化硅反射镜进行加工,最终反射镜面形精度的RMS值达到0.018λ(λ=0.6328μm),满足高精度空间非球面反射镜的技术指标要求。     

Deposition and crystallization of a-Si thin films by rapid thermal processing

The deposition and crystallization of a-Si thin films grown by rapid thermal processing have been studied, using transmission electron microscopy. The a-Si films were deposited in a rapid thermal processor at reduced pressures in the temperature range of 530–580°C, at different deposition pressures and silane flow rates and subsequently were annealed in-situ by high temperature rapid thermal annealing (RTA) or by a two-step annealing process involving low temperature furnace annealing (FA) followed by high temperature RTA. The activation energy of a-Si deposition was found to be approximately 1.7 eV, in reasonable agreement with the conventional LPCVD technique. It has been found that the deposition temperature and deposition rate have a strong effect on the grain size, which is attributed to the nucleation processes in the bulk of the films. The combination of low deposition temperature, high deposition rate and a two-step annealing process permits the low temperature growth of poly-Si films of 100 nm thickness, with large grains of 520 nm size, containing a low density of microtwins and characterized by very low surface roughness of 2.2 nm.     

SiO2/4H-SiC界面氮化退火

通过1 300℃高温干氧热氧化法在n型4H-SiC外延片上生长了厚度为60 nm的SiO2栅氧化层.为了开发适合于生长低界面态密度和高沟道载流子迁移率的SiC MOSFET器件产品的栅极氧化层退火条件,研究了不同退火条件下的SiO2/SiC界面电学特性参数.制作了MOS电容和横向MOSFET器件,通过表征SiO2栅氧化层C-V特性和MOSFET器件I-V特性,提取平带电压、C-V磁滞电压、SiO2/SiC界面态密度和载流子沟道迁移率等电学参数.实验结果表明,干氧氧化形成SiO2栅氧化层后,在1 300℃通入N2退火30 min,随后在相同温度下进行NO退火120 min,为最佳栅极氧化层退火条件,此时,SiO2/SiC界面态密度能够降低至2.07×1012 cm-2·eV-1@0.2 eV,SiC MOSFET沟道载流子迁移率达到17 cm2·V-1·s-1.     

碱性铜精抛液中表面活性剂ADS对平坦化效果的影响

研究了阴离子表面活性剂十二烷基硫酸铵(ADS)在弱碱性铜抛光液中对晶圆平坦化效果的影响.对不同质量分数的阴离子表面活性剂ADS下的抛光液表面张力、铜去除速率、抛光后铜膜的碟形坑高度、晶圆片内非均匀性和表面粗糙度进行了测试.实验结果表明,当阴离子表面活性剂ADS的质量分数为0.2％时,抛光液的表面张力降低,铜的去除速率为202.5 nm·min-1,去除速率片内非均匀性减小到4.15％,抛光后铜膜的碟形坑高度从132 nm降低到68.9 nm,表面粗糙度减小到1.06 nm.与未添加表面活性剂相比,晶圆表面的平坦化效果得到改善.     

光盘反射层纳米A1膜性能研究

利用原子力显微镜（AFM）和椭圆偏振仪研究了溅射条件对纳米Al薄膜性能的影响。研究表明，随溅射Ar气压的增大，纳米Al膜的表面粗糙度增加，折射率降低，反射率减小，这与薄膜的结构变化密切相关；随溅射功率的增大，纳米Al膜的表面粗糙度增加，而其光学常数的变化则不明显。     

Highly anisotropic, ultra-smooth patterning of GaN/SiC by low energy electron enhanced etching in DC plasma

Hetero-epitaxial films of GaN(OOOl), deposited on SiC(OOOl) by organometallic vapor phase epitaxy and masked by 200 nm of SiO₂, have been patterned by low energy electron enhanced etching (LE4) in hydrogen and chlorine dc plasmas at room temperature. Lines 2.0 μm wide showed highly anisotropic etching: straight side walls, no overcut, no trenching, and no “pedestal” at the base of the line. Root mean square (RMS) surface roughness of the films as grown was 8.5–10?; after LE4, RMS surface roughness of the etched surfaces was 2.5?.