Multilayer Diamond Composites for Heat Spreaders in Electronic Packaging

9522659 Kasichainula本项目解决了高频功率器件对高效散热器的需求。研究方法是利用金刚石的高导热性，通过生长多层复合涂层来防止金刚石层从基体上剥离的常见故障。复合涂层由金刚石、氮化铝或碳化硅层组成。采用热丝化学气相沉积或微波等离子体化学气相沉积的方法，在铜或钼或氮化硅衬底上生长不连续的金刚石晶体层。通过激光物理气相沉积沉积氮化铝或碳化硅层的插入层，金刚石晶体进一步嵌入并锚定在衬底上。第二层和连续的金刚石层沉积在表面光滑的顶部。在多靶高真空室中，采用激光物理气相沉积的方法对金刚石层进行金属化，并沉积薄层钽和钨或铬阻挡层以防止钛与金-锡共晶焊料的相互作用。散热器将使用金锡或金硅共晶合金焊接到器件晶圆上，该合金可承受高达500K的温度。选择性沉积金刚石多层结构以吸收器件的热量，最大化接触面积以增加热流密度，以及金刚石外延生长和插入层以降低复合层中界面的热阻是本研究的重要目标。为了获得最高的导热系数和良好的附着力，将对金刚石和中间层的厚度、微观结构和外延生长进行优化。由于高频热循环产生的应力导致的抗破坏能力的提高是该项目的预期效益。为了量化效益，将通过将新型和传统散热器置于激光脉冲辐射或高功率热球辐射下确定其失效机制，并通过测量剥落时的能量密度来量化其失效机制。垂直于薄膜的有效导热系数将由闪蒸法测定。利用红外探测器件不同区域的温度，研究了新型散热片对功率器件的热冷却规律。多层结构的导热系数和热应力的建模将分别通过非线性热方程的数值解和有限元分析进行。随着电子设备体积的缩小和单位面积信息量的增加，以及频率的提高和信息处理速度的提高，局部加热成为主要问题。有效冷却这些设备的能力成为进一步发展的技术障碍。随着金刚石涂层技术的出现，利用其高导热性来散热的机会出现了。然而，金刚石的另一个特性，即不粘性，使得它很难作为粘附涂层使用。这个问题的成功解决方案在这个项目中可能会对电子工业产生重大影响。

9522659 Kasichainula This project addresses the need for higher efficiency heat spreaders for high frequency power devices. The research approach is to take advantage of high thermal conductivity of diamond by growing a multilayer composite coating to prevent the common failure of delamination of the diamond layer from the substrate. The composite coatings are designed to consist of diamond, aluminum nitride or silicon carbide layers. A discontinuous layer of diamond crystallites is grown on copper or molybdenum or silicon nitride substrates either by hot filament chemical vapor deposition or microwave plasma chemical vapor deposition. The diamond crystallities are further embedded and anchored to the substrate by deposition of an interposing layer of aluminum nitride or silicon carbide layer by laser physical vapor depostion. A second and continuous layer of diamond is deposited on the top with a smooth surface. Metallization of diamond layer with deposition of thin layer of tatanium and a barrier layer of tungsten or chromium to prevent interaction of titanium with the gold-tin eutectic solder will also be carried out in-situ by laser physical vapor deposition in the multi-target high vacuum chamber. The heat spreaders will be soldered to the device wafer using a eutectic alloy of gold-tin or gold-silicon that can withstand temperatures up to 500K. Selective deposition of diamond multilayer structure to absorb heat from the devices, maximization of contact area to increase the heat flux, and epitaxial growth of diamond and interposing layers to reduce the thermal resistance of the interfaces in the composite layers are the important goals of this research. The thickness of the interposing layers, the microstructure and the epitaxial growth of the diamond and the interposing layers will be optimized to give the highest thermal conductivity and good adhesion. Improvement in resistance against failure from stresses generated due to high frequency thermal cycling is the expected bene fit of this project. In an attempt to quantify the benefit, the failure mechanisms of the new and conventional heat spreaders will be determined by subjecting them to laser pulse radiation or high power heat bulb radiation and quantified by measuring the energy density at which peeling takes place. The effective thermal conductivity perpendicular to the film will be determined by the Flash method. Thermal cooling pattern of the power devices with the new heat spreaders will be investigated using the infrared detection of the temperature of different regions of the device. Modeling of the thermal conductivity and thermal stresses in the multilayer structure will be carried out by numerical solution of the non-linear heat equation and finite element analysis, respectively. As electronic devices shrink in size while packing more information per unit area and frequencies increase to speed information processing, local heating becomes a major problem. The ability to effectively cool these devices becomes the technical barrier to further progress. With the advent of diamond coating technology, an opportunity arises to use its high thermal conductivity to dissipate the heat. However, another property of diamond, non-stickiness makes it difficult to apply as an adherent coating. Successful solution of this problem as addressed in this project may have a major impact on the electronics industry.