【作者】 郑伟；

【导师】 何新波；

【作者基本信息】 北京科技大学 ， 材料科学与工程， 2019， 博士

【摘要】 随着大规模集成电路的发展,高性能电子封装材料日益受到人们的重视。其中,金刚石/碳化硅复合材料是一种很有潜力的电子封装材料。它具有高导热、低热膨胀、高抗弯强度和高硬度等许多优点。现有的金刚石/碳化硅复合材料存在着制备成本高、工艺不稳定的缺点。针对这种情况,本文采用硅蒸气渗透法,制备了高致密度的金刚石/碳化硅复合材料。这种方法成本低,操作简便,可控性强。但是,作为一种制备金刚石/碳化硅复合材料的新方法,硅蒸气渗透法在制备工艺及致密化机理方面尚存在许多不清楚的地方。本文在硅蒸气渗透法制备金刚石/碳化硅复合材料的基础上,优化了渗透过程的工艺参数,重点研究了复合材料的致密化机理。同时,对复合材料的显微组织、界面特征及热导率、热膨胀系数、抗热冲击性等性能进行了研究,并且通过理论模型计算,合理预测了复合材料的热物理性能。研究表明:随着压制压力的增大,试样的平均孔径及孔隙率逐渐减小。对不同的工艺阶段,孔隙率从热解坯、预制坯到渗透样品,逐渐减小,而平均孔径,则从预制坯、热解坯到渗透样品,逐渐减小。复合材料中的硅会向金刚石中扩散,且扩散深度随渗透温度升高逐渐加深。当渗透温度达到1700℃,金刚石表面会产生轻微石墨化。要实现复合材料的完全致密化,预制坯的压制压力应为50～60 MPa,硅蒸气渗透过程中当样品放置高度距离硅表面不超过4 mm,渗透温度保持在1550～1700℃之间,同时渗透时间应在30 min以上。最终制备的金刚石/碳化硅复合材料,其致密度可达到97%以上。复合材料的致密化是硅蒸气渗透沉积和碳化硅反应烧结共同作用的结果。其中,碳化硅主要由石墨和金刚石与硅的反应得到。由石墨与硅反应得到的碳化硅含量高,颗粒大,而由金刚石与硅反应得到的碳化硅含量低,颗粒小。石墨和硅反应生成碳化硅的过程主要通过石墨在硅中的溶解-析出进行,而金刚石和硅反应生成碳化硅的过程主要通过硅和碳在碳化硅中的固相扩散进行。硅蒸气渗透沉积包括硅熔化、硅蒸气压的形成、硅蒸气在孔道内部的扩散及硅蒸气在碳化硅表面凝聚沉积四个步骤。随着金刚石粒径增大、碳化硅含量增加及渗透温度升高,复合材料的热导率升高。破碎金刚石更容易与硅反应生成碳化硅,从而降低界面热阻,提高金刚石/碳化硅复合材料的热导率。当渗透温度为650℃,碳化硅含量为35%,110μm破碎金刚石体积含量50%,复合材料的热导率达到最大值518 W·m-1·K-1。当渗透温度为1700℃时,金刚石表面发生石墨化,导致复合材料的热导率严重下降。利用已有的热导率模型对复合材料的热导率进行检测。结果显示,当金刚石体积含量小于30%,复合材料的热导率变化与H-J模型相匹配,而当金刚石含量大于30%,复合材料的热导率介于H-J模型和Agari模型预测值之间,需要通过对两种模型进行复合处理,从而得到可靠的热导率预测值。大粒径破碎金刚石、高体积分数碳化硅以及高的渗透温度,会导致复合材料的热膨胀系数的增大。采用拉曼光谱法,对不同渗透温度下复合材料中金刚石进行峰值测试。结果显示,金刚石峰的偏移随渗透温度升高而变大,这也意味着,复合材料中残余应力随渗透温度升高而增大。结合已有的热膨胀系数模型对复合材料热膨胀系数进行预测,结果显示,在较低温度范围(50～150℃)下,热膨胀系数值与Turner模型的预测值吻合较好,而在较高温度(250～400℃)范围内,热膨胀系数实测值与下限Schapery模型吻合较好。另外,复合材料显示出良好的抗热冲击性。其抗弯强度可达到300 MPa以上,且随复合材料中碳化硅含量增加而变大。当金刚石体积含量从10%增大到60%,复合材料HRA硬度在84～92.8。本研究制备的金刚石/碳化硅复合材料具有工艺简单、成本低、可一次性制备多种不同形状的样品的优势。相比于其他类型的金刚石增强复合材料,本材料表现出致密度和热导率高、热膨胀系数低、抗热冲击性好、抗弯强度高的优异性能。更多还原

【Abstract】 With the development of large-scale integrated circuits,high-performance electronic packaging materials have attracted more and more attention.Among them,diamond/silicon carbide composites are potential electronic packaging materials.It has many advantages such as high thermal conductivity,low thermal expansion,high flexural strength and high hardness.The existing diamond/silicon carbide composites have the disadvantages of high cost and unstable process.In view of this situation,high density diamond/silicon carbide composites were prepared by silicon vapor infiltration method.This method has the advantages of low cost,simple operation and strong controllability.However,as a new method of preparing diamond/silicon carbide composites,there are still many unclear aspects in the preparation process and densification mechanism of silicon vapor infiltration method.Based on the preparation of diamond/silicon carbide composites by silicon vapor infiltration,the technological parameters of the infiltration process were optimized,and the densification mechanism of the composites was mainly studied.At the same time,the microstructures,interfacial characteristics and thermal conductivity,thermal expansion coefficient and thermal shock resistance of the composites were studied,and the thermophysical properties of the composites were reasonably predicted by theoretical model calculation.Research shows:With the increase of compression pressure,the average pore size and porosity of the sample decrease gradually.At different process stages,the porosity decreases gradually from pyrolysis billet,preform to permeation sample,while the average pore size decreases gradually from preform,pyrolysis billet to permeation sample.Silicon in composites will diffuse into diamond,and the diffusion depth will deepen with the increase of permeation temperature.When the permeation temperature reaches 1700℃,slight graphitization will occur on the surface of diamond.In order to achieve complete densification of the composites,the pressure of preform should be 50-60 MPa..During the silicon vapor infiltration,the sample should be placed at a height not more than 4 mm away from the silicon surface,and the infiltration temperature should be kept between 1550-1700℃,and also the infiltration time should be more than 30 mins.The densification degree of the diamond/silicon carbide composites can reach over 97%.Densification of composites is a simultaneous process of silicon vapor infiltration deposition and reaction sintering of silicon carbide.Among them,silicon carbide is mainly obtained by the reaction of graphite and diamond with silicon.The silicon carbide obtained by graphite reaction has high content and large particle size,while the silicon carbide obtained by diamond reaction has low content and small particle size.The reaction between graphite and silicon produces silicon carbide mainly through the dissolution-precipitation of graphite in silicon,while the reaction between diamond and silicon produces silicon carbide mainly through the solid diffusion of silicon and carbon in silicon carbide.In addition,silicon vapor osmotic deposition includes four steps:silicon melting,formation of silicon vapor pressure,diffusion of silicon vapor in the channel and condensation deposition of silicon vapor on the surface of silicon carbide.The thermal conductivity of the composites increases with the increase of diamond size,silicon carbide content and permeation temperature.The surface of broken diamond has good wettability,and it is easier to react with silicon to form silicon carbide,which reduces the interfacial thermal resistance and improves the thermal conductivity of diamond/silicon carbide composites.When the penetration temperature is 1650℃,the content of SiC is 35%,the volume content of broken diamond is 50%at 110 um,and the thermal conductivity of the composites has a maximum value of 518 W·m-1·K-1.When the temperature reaches 1700℃,the graphitization of the diamond surface leads to a serious decrease in the thermal conductivity of the composites.The thermal conductivity of the composites was measured by the second iteration method and the existing thermal conductivity model.The results show that when the volume fraction of diamond is less than 30%,the change of thermal conductivity of composites matches H-J model,and when the content of diamond is more than 30%,the thermal conductivity of composites is between H-J model and Agari model.It needs to be predicted by the combination of the two models.The thermal expansion coefficient of the composites is less than 4×10-6·K-1.Large particle size,broken diamond,high volume fraction of silicon carbide and high infiltration temperature will lead to the increase of thermal expansion coefficient of composites.The peak value of diamond in composites was measured by Raman spectroscopy at different infiltration temperatures.The results show that the peak shift of diamond increases with the increase of temperature,which also means that the thermal residual stress in composites increases with the increase of infiltration temperature.The thermal expansion coefficients of composites were predicted by the second iteration method and combined with the existing thermal expansion coefficient models.The results show that CTE values are in good agreement with the predicted values of Turner model at temperature(50～150℃),while the measured values of thermal expansion coefficients at higher temperature(250～400℃)are in good agreement with the lower bound Schapery model.In addition,the composites exhibit good thermal shock resistance,the flexural strength can reach more than 300 MPa.When the volume fraction of diamond increases from 10%to 60%,the HRA hardness of composites is 84-92.8.The diamond/silicon carbide composites prepared in this study have the advantages of simple process and low cost,and can be used to prepare a variety of samples with different shapes at one time.Compared with other types of diamond reinforced composites,this material has higher desification degree,higher thermal conductivity,lower thermal expansion coefficient,better thermal shock resistance and higher flexural strength.更多还原