新一代半导体材料氧化镓单晶的制备方法及其超精密加工技术研究进展

氧化镓(β-Ga2O3)单晶是继碳化硅(SiC)和氮化镓(GaN)之后,制造超高压功率器件、深紫外光电子器件、高亮度LED等高性能半导体器件的新一代半导体材料,大尺寸低缺陷氧化镓单晶的制备方法以及高表面质量氧化镓晶片的超精密加工技术是实现氧化镓半导体器件工业应用的瓶颈之一.针对易产生结构缺陷的氧化镓单晶的制备,系统阐述焰熔法、提拉法、光浮区法、导模法、布里奇曼法等氧化镓单晶制备方法的国内外研究进展,通过对比不同方法制备氧化镓单晶的晶体生长速度、晶体尺寸和内部缺陷等,分析不同制备方法的优缺点,指出大尺寸低缺陷氧化镓单晶制备方法的未来发展趋势;针对硬度高、脆性大、各向异性大、极易解理破碎的氧化镓晶片的超精密加工技术,详细介绍国内外在超精密加工氧化镓晶片的表面材料去除机理、亚表面损伤产生机理与演变规律,以及氧化镓晶片超精密磨削、研磨和抛光工艺等方面的研究进展,分析氧化镓晶片在加工过程中极易解理破碎的原因和目前采用游离磨料研磨工艺加工氧化镓晶片的局限性,提出未来实现大尺寸氧化镓晶片高效率高表面质量加工的工艺方法.分析表明,在氧化镓单晶制备方面,导模法将是未来批量化制备大尺寸低缺陷氧化镓单晶的最佳方法,但生长过程中气氛的选择与调控、不同缺陷的产生机理与抑制方法以及p型氧化镓单晶的掺杂方法等问题亟需解决.在氧化镓晶片超精密加工方面,基于工件旋转磨削原理的金刚石砂轮超精密磨削技术将是实现大尺寸氧化镓晶片高效高表面质量加工的有效方法,但氧化镓单晶延性域去除和解理破碎的临界磨削条件、表面质量和加工效率约束下的砂轮参数和磨削参数的选择等问题还亟待系统研究,才能为氧化镓晶片的超精密磨削加工提供理论指导.     

GaN 用衬底材料 LiGaO2 晶体超精密抛光的初步实验

主要介绍了作为发光半导体GaN衬底材料的LiGaO₂单晶超精密抛光方法及初步结果。利用聚氨酯抛光盘配合SiO₂悬浮液,采用机械化学抛光方法,已加工出表面粗糙度优于0.1mm,的超光滑表面。     

《2018-2019机械工程学科发展报告(机械制造)》——机械制造学科标志性研究进展

正在精密与超精密加工领域,清华大学路新春等建立了大尺寸表面纳米级平坦化的加工原理与方法,发明了系列大尺寸超薄硅片纳米级无损伤抛光关键技术,研制开发出12英寸"干进干出"化学机械抛光(CMP)装备与成套工艺,实现了IC制造大尺寸晶圆表面的纳米级平坦化及纳米级缺陷控制。整体技术达到国际先进水平,已在中芯国际等企业实现批量应用,打破了国外高端微电子超精密抛光装备长期垄断的局面。     

光学脆性材料的金刚石切削加工

重点对脆性材料的超精密研磨、抛光加工技术及超精密磨削加工技术和超精密切削加工技术进行了分析研究。分析表明,硬脆材料光学元件主要应进行超精密研磨、抛光及超精密磨削加工;软脆材料光学元件主要应进行金刚石切削加工。对软脆材料金刚石切削进行了试验设计,指出了光学脆性材料的金刚石切削加工过程不同于金属加工过程,通过控制切削条件可以实现脆性材料塑性域加工,提高光学脆性材料的表面加工质量。     

金刚石立铣刀的研究及应用

随着精密和超精密加工的发展和新材料的不断出现,金刚石刀具得到广泛的发展。大量文献都报道了车削的例子,铣削和钻削的很少。本文对单晶金刚石、聚晶金刚石、CVD金刚石在立铣刀中的应用进行了综述。     

CVD金刚石薄膜涂层轴承支撑器的制备和应用

轴承支撑器是轴承精密加工中的关键部件。本文采用热丝化学气相沉积(简称CVD)法,以丙酮和氢气为碳源,在WC-Co硬质合金轴承支撑器衬底上沉积金刚石薄膜,制备CVD金刚石薄膜涂层轴承支撑器,并应用于轴承的精密磨削加工。结果表明,合理控制衬底材料的预处理和CVD沉积工艺对金刚石薄膜质量、形貌、粗糙度和薄膜与衬底间的附着力有显著影响。与传统硬质合金轴承支撑器相比,CVD金刚石涂层轴承支撑器的耐用度和使用性能显著提高。     

非球面超精密抛光技术研究现状

非球面应用范围的拓展以及应用精度要求的不断提高对非球面元件的尺寸精度与表面质量提出了更高要求;作为终加工手段,非球面超精密抛光技术也越来越受到世界各国的重视。掌握非球面超精密抛光过程中的材料去除机理以及由此导致的亚表面损伤等特性对提高非球面抛光的精度与效率十分重要。对非球面抛光技术的发展进行回顾,并根据非球面超精密抛光技术的发展脉络,阐述当前主要非球面超精密抛光技术的加工原理及加工实例,随后从亚表面损伤、边缘效应等方面对几种非球面超精密抛光技术进行比较,并以提高抛光精度与效率为目标,对非球面超精密抛光技术的发展趋势进行预测。     

单晶金刚石刀具有新型加工方法

介绍了四种加工单晶金刚石刀具的新型工艺方法,这些加工方法可弥补传统机械加工方法的缺点,适用于金刚石刀具的超精密抛光加工。     

单晶蓝宝石基片抛光工艺研究进展

对目前抛光单晶蓝宝石基片的工艺方法,如游离磨料磨削、金刚石砂轮磨削、在线电解修整磨削(ELID)、化学机械抛光(CMP)、固结软磨料抛光、磁流变抛光(MRF)、超声振动辅助磨削的加工原理、方法和特点进行综述。分析了各方法的优势和不足以及最新研究成果存在的关键问题。其中游离磨料磨削、在线电解修整磨削、金刚石砂轮磨削的材料去除速率较高,化学机械抛光是抛光大面积基片的唯一方法,磁流变抛光后的基片表面不存在亚表面损伤。根据单晶蓝宝石基片的应用需求和目前抛光方法的不足,对后续研究的方向进行了预测。     

CVD金刚石膜抛光新技术

提出了一种新的CVD金刚石膜抛光技术。金刚石膜表面被预先涂覆一层导电金属，然后采用电蚀方法对该表面进行加工，使金刚石膜突起的尖峰被迅速去除，加工中金刚石表面的石墨化使电蚀加工得以不断延续。采用CVD金刚石膜抛光新技术，可以高效率地完成对CVD金刚石膜的粗抛光。     

A study of abrasive wear mechanisms using diamond and alumina scratch tests

Scratch tests using alumina (Al₂O₃) abrasive particles and Vickers diamond pyramids were employed to study material removal mechanisms in the abrasion of cobalt-base powder metallurgy alloys 6 and 19. The alloys were specially prepared to produce either fine or coarse carbides in order to study the effects of carbide size. Scanning electron microscopy was used to analyze the scratch grooves, the scratch tools and the wear debris particles.

Comparison of scratch tests with Al₂O₃ and diamond pyramids shows that many features produced by the extremely hard regularly shaped diamond tools are different from those produced by irregular Al₂O₃ particles. Except for differences produced by tool wear, multiple-pass Al₂O₃ scratch tests provide excellent reproduction of the material removal processes which occur in low stress Al₂O₃ abrasion. Al₂O₃ scratches produced both chip-like and fine irregular debris particles similar to those extracted from spent abrasive used in wear testing.

Material removal in the fine carbide alloys is facilitated by the direct removal of entire carbides within the volume of micromachining chips removed from the scratch groove. In coarse carbide alloys, machining chips from large carbides are observed, but the depth of cut in the carbide phase is less than that in the f.c.c. matrix and this leads to a decrease in the volume of material removed. Direct comparison of chips removed from fine and coarse carbide alloys by the same Al₂O₃ particle shows larger chips from the fine carbide material.

The effects of subsurface deformation and surface irregularities on material removal were studied by carrying out scratch tests on specimens subjected to prior abrasion and by investigating multiple-pass scratches in the same scratch groove.     

WEAR PERFORMANCE OF MULTILAYER-COATED CARBIDE TOOLS

Three multilayer-coated carbides [two trigon-shaped inserts: Ti(C,N)/TiC/Al₂O₃ (T1), Ti(C,N)/ Al₂O₃/TiN (T2) and one 80°-rhomboid shaped insert: TiC/Al₂O₃/TiN (T3)] were used to machine a martensitic stainless steel at various combinations of cutting speed and feed rate without coolant to assess their wear performance. Significant nose wear and chipping/fracture of the cutting edge were the predominant failure modes affecting tool performance at higher speed conditions. Plucking of tool materials was the main rake face wear phenomenon observed on T1 grade insert with alumina as the top-layer coating when machining at the lower speed conditions. Attrition and plastic flow were the main wear mechanisms observed on the ceramic coating layers, with dissolution-diffusion being the probable wear mechanism of the tool grades where tungsten carbide substrate had direct contact with the flowing chip. The fitted statistical wear models revealed T3 grade insert with 80°-rhomboid shape as having the highest speed-feed capability, resulting in the highest material removal rate relative to T1 and T2 grade inserts with trigon shapes.     

Effects of a second phase on the tribological properties of Al2O3 and ZrO2 ceramics

The tribological properties of four different materials are investigated, tetragonal zirconia (Y-ZTP), Al₂O₃ dispersed in Y-TZP (ADZ), ZrO₂ dispersed in Al₂O₃ (ZTA) and Al₂O₃ (with 300 ppm MgO). These materials are used as a cylinder sliding against a plate of Y-TZP (TZ-3Y)). Compared to Y-TZP, the wear resistance of ADZ composites is increased by a factor of 4–10. At a contact pressure of 230 MPa, a wear transition for Y-TZP is observed from plastic deformation to microchipping and microfracture due to the high interfacial temperature (450°C–550°C) generated by frictional heating. Because of the higher elastic modulus, hardness and fracture toughness at high temperature, ADZ composites show better wear resistance and a higher transition contact pressure (over 400 MPa) under the present conditions. For Al₂O₃, the transition from mild to severe wear occurs when the contact pressure is changed from 250 to 400 MPa. For ZTA ceramics, the wear behaviour does not change because of the presence of a compressive layer due to the zirconia phase transformation during sliding.

In water the wear resistance for ADZ and ZY5 is almost two orders of magnitude higher than the results under dry conditions. Reduction of the interfacial temperature by using water and the formation of a hydroxide layer at the contact surface by the tribochemical reaction of water with the ceramic, as observed by XPS, gives a positive effect on wear resistance.     

Feasibility study of plasma sprayed Al2O3 coatings as diffusion barrier on CFC components

Carbon fibre reinforced carbon (CFC) materials are increasingly applied as sample carriers in modern furnaces. Only their tendency to react with different metals at high temperatures by C-diffusion is a disadvantage, which can be solved by application of diffusion barriers. Within this study the feasibility of plasma sprayed Al₂O₃ coatings as diffusion barrier was studied. Al₂O₃ coatings were prepared by air plasma spraying (APS). The coatings were investigated in terms of their microstructure, bonding to CFC substrates and thermal stability. The results showed that Al₂O₃ could be well deposited onto CFC substrates. The coatings had a good bonding and thermal shock behavior at 1060°C. At higher temperature of 1270°C, crack network formed within the coating, showing that the plasma sprayed Al₂O₃ coatings are limited regarding to their application temperatures as diffusion barrier on CFC components.     

Preparation of ultrafine α-AlO using precipitation-azeotropic distillation method

Ammonium aluminum carbonate hydroxide (AACH) was prepared by a precipitation-azeotropic distillation method, which uses aluminum sulfate as the Al source and ammonium carbonate as the precipitant. Then, AACH was calcined into ultrafine ?-Al₂O₃ powder. The factors that influence the dispersion property of ultrafine ?-Al₂O₃ powder are discussed in this paper, such as the methods of adding materials, surfactant, and drying methods. The changes of the structure and property of ultrafine alumina in the thermal treatment process are also studied. The morphological structure and properties of AACH are characterized by DTA/TGA, SEM, XRD, and ICP measurements. The results show that ultrafine ?-Al₂O₃ powder with a uniform particle size and well-distributed property can be synthesized only after aluminum sulfate atomizes into ammonium carbonate, proper amount of PEG1000 is added as the dispersant, and the product is treated by azeotropic distillation. The phase transformation of alumina during the calcination process can be described as amorphous Al₂O₃ → ?-Al₂O₃ → ?-Al₂O₃ → ?-Al₂O₃. The crystal grain size and density of ultrafine alumina powder increase with the increase of the calcination temperature. After AACH has been calcined at 1200°C for 2 h, the ultrafine ?-Al₂O₃ with uniform particle size, spherical shape, and more than 99.97% purity is obtained and its powder is well dispersed.     

Vibration monitoring in sliding wear of plasma sprayed ceramics

Dry frictional contact between two surfaces, one made of plasma sprayed ceramic coatings of Al₂O₃ and Al₂O₃---TiO₂ combination and the other made of steel, is analyzed. The experiments were conducted using a pin-on-disc set-up in the load range of 5–35 N and for sliding distances up to 14 km. The interactions between friction, wear and vibrations due to influence of normal load, sliding speed and system dynamics are investigated in the present paper. Two vibration parameters of pin in the load direction (vertical) are monitored, namely the r.m.s. acceleration and the kurtosis, which seem to be influenced considerably by the wear process and indicate correlation with wear mechanisms taking place such as stick-slip and grain pull-out, as evidenced by scanning electron microscopy of worn surfaces. The study shows that a range of frequency is to be utilized for vibration monitoring to include natural frequencis of the system consisting of pin in contact with disc. This could be estimated by a standard impulse hammer test. The pin acceleration decreases with increase in load and sliding distance, but with respect to sliding speed, the vibration level intially decreases but increases beyond the sliding speed of 1.5 m s⁻¹. Among the three ceramic coatings, TiO₂ is found to be most wear resistant, exhibiting the lowest friction coefficient and a low vibration level. Variation in kurtosis with run-in wear indicates smoothing of Al₂O₃ due to grain pull out.     

Adhesion, friction and wear of thin hard coatings

Chemically vapour-deposited and physically vapour-deposited coatings of hard and wear-resistant materials such as TiC, TiN, Ti(C, N), Cr₇C₃, Al₂O₃, SiO₂ and TiO₂ as well as other carbides, nitrides, borides, oxides and combinations thereof are increasingly used in industrial applications to protect metal, ceramic and in certain cases polymer parts against mechanical and chemical attack, sometimes with a decorative purpose also. Some relevant examples of coated products are cemented carbide throwaway cutting tips (TiC, TiN, Ti(C, N), Al₂O₃ etc.), high speed steel drills and milling cutters (TiN), hobs, deep drawing tools, ball-bearing elements, gears, machine elements, electrical contacts, body implants, surgical instruments and tools, cutlery, fuel pins and armatures especially for helium- and sodium-cooled nuclear reactors, low Z sputter-resistant protective coatings on parts (limiters, antennae etc.) and walls of the torus in fusion reactors (tokamak) and gold- or silver- or black-coloured watch cases and jewelry pieces. The life of such coated tools or machine elements as well as their performance are considerably increased, provided that the adhesive strength of the coating to the base material and the intrinsic cohesion of the coating are sufficient. Bad adhesion leads to flaking (adhesive failure) while poor cohesion causes chipping (cohesive failure).     

剪切增稠抛光磨料液的制备及其抛光特性

为了实现对工件的剪切增稠抛光(STP),采用机械混合与超声波分散法制备了一种Al2O3基STP磨料液,并研究了它们的抛光特性。利用应力控制流变仪考察其流变性能,通过扫描电镜和光学轮廓仪研究了单晶硅加工后表面显微组织的变化,并测量其表面粗糙度。结果表明:STP磨料液具有剪切变稀和可逆的剪切增稠特性,达到临界剪切速率后,会形成Al2O3"粒子簇";当剪切速率增大至1000s-1,储能模量,耗能模量和耗散因子都增至最大值,此时主要表现为类似固体的弹性行为,有利于形成类似"柔性固着磨具"。在STP加工单晶硅过程中,采用塑性去除的材料去除方式。随着抛光时间的延长,硅片去除速率先增大后减小;表面粗糙度不断减小并趋于稳定。实验显示,磨粒浓度不宜过高,否则会因剪切增稠效应造成黏度过大,导致流动性差而影响抛光质量。当Al2O3质量分数为23%时,抛光25min后,硅片表面粗糙度Ra由422.62nm降至2.46nm,去除速率达0.88μm/min,表明其能实现单晶硅片的高效精密抛光。     

LED蓝宝石衬底抛光表面原子台阶形貌及其周期性研究

LED蓝宝石衬底的表面质量会极大影响到后续外延质量,进而影响到LED器件性能。蓝宝石研磨片经Al2O3磨粒粗抛液、SiO2磨粒精抛液下进行化学机械抛光(CMP),最终表面经原子力显微镜(AFM)所测表面粗糙度达到0.101nm,获得亚纳米级粗糙度超光滑表面,并呈现出原子台阶形貌。同时,通过使用Zygo表面形貌仪、AFM观察蓝宝石从研磨片经Al2O3粗抛液、SiO2精抛液抛光后的表面变化,阐述蓝宝石表面原子台阶形貌的形成原因,提出蓝宝石原子级超光滑表面形成的CMP去除机理。通过控制蓝宝石抛光中的工艺条件,获得a-a型、a-b型两种不同周期规律性的台阶形貌表面,并探讨不同周期规律性台阶形貌的形成机理。     

The effects of iron particles on the friction and wear mechanisms of ceramics in ethanol

For the combinations of an Si₃N₄ pin and five kinds of ceramic disk (SiC, Si₃N₄, Al₂O₃, ZrO₂, TiC), a friction and wear test was carried out in ethanol and in ethanol containing iron particles (1 wt.%, average diameter d = 200 nm, D = 12 μm under cohered condition) under a load in the range 5.88–11.50 N, at a sliding velocity of 0.138–0.196 m s⁻¹. A topographical analysis was also performed on the microasperities of the wear surfaces to estimate the behavior of the iron particles, and the degree of surface damage. As a result, the following facts were found. (1) The addition of iron particles in ethanol decreased both the wear rates of SiC and TiC disks and the mating pins, and also decreased the wear rate of the Al₂O₃ disk but increased that of the mating pin. The addition increased the wear rates of both ZrO₂ and Si₃N₄ disks and the mating pins. (2) The average coefficients of friction with the addition of iron particles were greater than those without iron particles. (3) The wear rates of pin and disk depended on the topographies of wear surfaces and the wear index Γ.