碳化硅单晶衬底超精密抛光关键技术研究

发布时间：2018-07-23 11:50

【摘要】：半导体产业的发展密切关系到我国国防、军事、航空航天、能源等重要科技领域。以碳化硅(SiC)单晶为代表的第三代半导体材料是一种重要的新型宽禁带半导体材料,通过外延可以作为生长氮化镓(GaN)、石墨烯的衬底材料。同时,它具有高杨氏模量、高硬度、耐高温、耐腐蚀等性质,可广泛用于制作高温、高频的大功率器件。尤其在军工方面,是新一代雷达、卫星通讯的核心,具有重要的应用价值和广阔的发展前景,已然经成为当今国际关注的焦点。由于硅(Si)电子元器件的开发已趋于极限,因此,研究第三代宽带隙半导体材料显得更加重要和尤为迫切;同时,它将引领第三次半导体产业革命。SiC单晶衬底的加工质量和精度直接影响器件的性能,故要求被加工表面超光滑、无缺陷、无损伤。超精密抛光技术是整个加工工艺的最后一步,分为机械抛光和化学机械抛光两道工艺。机械抛光对材料去除率和平坦度起到决定性作用,化学机械抛光是实现原子级表面粗糙度的核心。因此,超精密抛光技术是保证SiC单晶衬底高精度、高效率、低成本的关键。本文以3英寸SiC单晶衬底的表面粗糙度、平坦度和材料去除率为目标,对机械抛光和化学机械抛光的工艺和机理进行了研究。使用综合评分法来权衡表面粗糙度和材料去除率之间的关系,根据不同要求得到不同条件下的最佳工艺参数。从微观、宏观两个尺度出发,分析化学作用、机械作用以及化学机械耦合作用对SiC单晶衬底原子级去除机理的影响。具体的研究内容主要包括以下几个方面:(1)建立了无架行星式双面机械抛光二维几何模型,推导了 SiC单晶衬底和抛光垫上磨粒的相对运动轨迹方程。分析了磨粒分布半径、SiC衬底分布半径、齿圈与太阳轮转速比、抛光盘与太阳轮转速比对抛光轨迹和曲率的影响情况。构建抛光均匀性函数,使用统计学方法计算变异系数,研究了磨粒间隔半径、齿圈与太阳轮转速比、抛光盘与太阳轮转速比三个因素对SiC单晶衬底均匀抛光和抛光垫上磨粒磨损的影响规律。(2)建立了基于无架行星差动轮系的双面机械抛光机构的三维物理模型,分析了 3英寸SiC单晶衬底表面对称5点的位移、速度、加速度随时间变化曲线的重合情况,验证了理论模型的正确性和行星差动轮系参数的可行性。基于该模型设计了 3英寸SiC单晶衬底机械抛光正交试验,通过单因素分析法和综合分析法,研究了抛光压力、下抛光盘转速以及金刚石微粉直径三个因素对材料去除率、表面粗糙度和平坦度的影响规律,获得了最优工艺参数。(3)从微观尺度出发,建立了6H-SiC单晶晶胞模型,进行量子力学的计算,分析了晶胞模型分子动力学特性。根据密度泛函理论和第一性原理,使用CASTEP模块对能带结构、总态密度、电子密度以及电荷密度进行了分子动力学仿真。使用Forcite模块对(1 0 0)、(0 1 0)、(0 0 1)三个面的原子密度的相对浓度分布、结构无序化程度的径向分布函数、温度分布以及速度分布随位置的变化进行了研究,分析了晶胞势能、动能,非键合能,总能,总焓的变化规律。(4)建立了3英寸SiC单晶衬底化学机械抛光流固耦合模型,基于ANSYS分析了抛光液对SiC衬底被加工表面的单向流固耦合作用。分析了抛光液流量和抛光液底面转速对流固耦合界面的压力、应力、应变和应变能四个指标的影响情况,为化学机械抛光机理的研究提供理论指导。(5)研究了SiC衬底的Si面和C面的化学机械抛光的工艺参数对材料去除率和表面粗糙度的影响。首先,设计了化学机械抛光六因素五水平正交试验(抛光压力、抛光盘转速、磨粒直径、PH值、抛光液浓度和氧化剂浓度),通过极差、方差分析法确定了单因素的主次顺序,分别得到了材料去除率和表面粗糙度单目标的最优工艺参数。其次,通过综合评分法确定了材料去除率和表面粗糙度之间的权重系数,得到了多目标的最优工艺参数。然后,针对其中影响最大的三个因素(抛光压力、抛光盘转速和抛光液浓度),设计了三因子二次回归正交旋转试验,建立了回归模型的数学方程。通过曲面响应图分析了多因素之间的耦合作用对目标的影响规律,为实际加工过程中工艺参数的选择提供理论指导和借鉴,为下一步精密数字化控制提供保障。
[Abstract]:The development of the semiconductor industry is closely related to our national defense, military, aerospace, energy and other important fields of science and technology. The third generation of semiconductor materials, represented by silicon carbide (SiC) single crystal, are an important new type of wide band gap semiconductor material, which can be used as a substrate for the growth of gallium (GaN) and graphene by epitaxy. Young's modulus, high hardness, high temperature resistance and corrosion resistance can be widely used to make high temperature and high frequency high power devices. Especially in military industry, it is the core of new generation radar and satellite communication. It has important application value and broad development prospect. It has become the focus of international attention now. Because of the opening of silicon (Si) electronic components. Therefore, it is more important and urgent to study the third generation of broadband gap semiconductor materials. At the same time, it will lead the processing quality and precision of the third semiconductor industrial revolution.SiC single crystal substrate directly to influence the performance of the device, so that the machined surface is required to be super smooth, no defect and no damage. The last step of the processing technology is divided into two processes: mechanical polishing and chemical mechanical polishing. Mechanical polishing plays a decisive role in the material removal rate and the flatness. Chemical mechanical polishing is the core to realize the surface roughness of the atomic level. Therefore, the ultra precision polishing technology is the key to ensure high precision, high efficiency and low cost of SiC single crystal substrate. In this paper, the process and mechanism of mechanical polishing and chemical mechanical polishing are studied on the surface roughness, flatness and material removal rate of the 3 inch SiC single crystal substrate. The relationship between the surface roughness and the material removal rate is weighed by the comprehensive scoring method, and the optimum technological parameters under different conditions are obtained according to the different requirements. From the microcosmic and macro two scales, the effects of chemical, mechanical and chemical mechanical coupling on the atomic level removal mechanism of SiC single crystal substrate are analyzed. The main contents are as follows: (1) a two-dimensional geometric model of the non shelf planetary double-sided mechanical polishing is established, and the SiC single crystal substrate and the polishing pad are derived. The relative motion trajectory equation of the upper grinding particles, the distribution radius of the abrasive particles, the distribution radius of the SiC substrate, the speed ratio of the ring and the sun rotation, the influence of the speed ratio of the disc and the sun wheel on the polishing trajectory and the curvature are analyzed. The polishing uniformity function is constructed. The coefficient of variation is calculated by the statistical method, and the radius of the abrasive spacing, the ring of the tooth and the sun wheel are studied. The influence of three factors on the rotational speed ratio and the speed ratio of the discs and the sun wheel on the uniform polishing of the SiC single crystal substrate and the abrasive wear on the polishing pad. (2) a three-dimensional physical model of the double-sided mechanical polishing mechanism based on the non shelf planetary differential gear system was established. The displacement, velocity and acceleration of the symmetrical 5 points on the surface of the 3 inch SiC single crystal substrate were analyzed. The correctness of the theoretical model and the feasibility of the planetary differential gear parameters are verified by the coincidence of the change curve. Based on this model, a 3 inch SiC single crystal substrate mechanical polishing orthogonal test is designed. The polishing pressure, the speed of the polishing disk and the diameter of the diamond micro powder are studied by the single factor analysis method and the comprehensive analysis method. The effect of material removal rate, surface roughness and flatness of surface roughness has been obtained. (3) from the microscopic scale, the 6H-SiC single crystal cell model is established, the quantum mechanics is calculated and the molecular dynamics characteristics of the cell model are analyzed. According to the density functional theory and the first principle, the energy band structure is used with the CASTEP module. The molecular dynamics simulation is carried out in the density of States, electron density and charge density. The relative concentration distribution of the atomic density of (100), (010), (001) three surface, the radial distribution function of the degree of disordering of structure, the distribution of temperature and the change of velocity distribution with the position are studied by using the Forcite module. The potential energy and kinetic energy of the cell are analyzed. The change law of non bonding energy, total energy and total enthalpy. (4) a fluid solid coupling model for chemical mechanical polishing of a 3 inch SiC single crystal substrate was established. The unidirectional fluid solid coupling effect of the polishing liquid on the machined surface of the SiC substrate was analyzed based on ANSYS. The pressure, stress, strain and strain of the convective solid coupling interface of the polishing fluid flow and the bottom speed of the polishing liquid were analyzed. It can provide theoretical guidance for the study of the mechanism of chemical mechanical polishing (5) the influence of the four indexes on the mechanism of chemical mechanical polishing. (5) the influence of the technological parameters of chemical mechanical polishing on the material removal rate and surface roughness of the SiC substrate is studied. First, the orthogonal test of six factors and five levels of chemical mechanical polishing (polishing pressure, rotating speed of discs, The particle diameter, pH, concentration of polishing liquid and the concentration of oxidant are determined. The order of the single factor is determined by the method of variance analysis. The optimal process parameters of the material removal rate and the surface roughness single target are obtained. Secondly, the weight coefficient between the removal rate of material and the surface roughness is determined by the comprehensive scoring method. Then, in view of the three factors (polishing pressure, disc speed and concentration of polishing liquid), the three factor two regression orthogonal rotation experiment was designed, and the mathematical equation of the regression model was established. The effect of coupling effect between multiple factors on the target was analyzed by the surface response map. The selection of process parameters in the actual processing process can provide theoretical guidance and reference for the next step of precision digital control.
【学位授予单位】：山东大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TQ127.2

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