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Research on Chemo-Mechanical Grinding Process for Extremely-thin Si Wafer Used in Next Generation Power Devices

下一代功率器件用极薄硅片化学机械研磨工艺研究

基本信息

批准号：
16360061
负责人：
ZHOU Libo
金额：
$ 9.34万
依托单位：
Ibaraki University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2004
资助国家：
日本
起止时间：
2004 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-16360061/
关键词：
Extremely thin Si wafer Fixed abrasive technology Damaged layer Power devices Chemo-Mechanical Grinding Defect free Residual stress 固定砥流加工技術完全表面

项目摘要

After long term research and development, new energy sources like fuel cell, solar-electric power generation and wind force power generation are getting into the stage of practical use. The most essential driving force and enabling technology is the power electronics. Improvement in performance, function, reliability and miniaturization of power devices is increasingly demanded. Especially, the Field-Stop type IGBT (Insulated Gate Bipolar Transistor) is expected to make a technological break-through. Unlike the structure of conventional transistors, IGBT functions as the current flows across the thickness directions of the Si substrate. Since the switching resistance of IGBT is proportional to the thickness of the Si substrate, the current Punch-Through type IGBT is 350 μm thick and thus has a large energy loss. The problems encountered are the voltage drop and internal heat generation. The design for next-generation non-punch through type IGBT is 100 μm thick for automotive industry. … More Therefore, the Si wafer has to be thinned down to the diminished thickness.In addition, the miniaturization and high degree integration of system LSI (large scale integrated) circuit are increasingly demanded by mobile devices. As a cost effective solution, low-profile-package containing multi-layer chips is applied into the products like IC cards, mobile phones and digital music players. The Si wafers have to be thinned down to 50〜70 μm from 725μm for 8 inch wafer or from 800μm for 12 inch wafer, before being diced into individual chips. At the next stage when the new transfixed interconnection technology is available, the wafer thickness required is further down to 30〜50 μm.Backgrinding is the conventional method for reducing wafer to a diminished thickness suitable for the final packaging. The diamond wheels and process parameters are necessarily optimized to obtain minimal subsurface damage in grinding process. By use of the latest technologies in ultra precision engineering and the concept of ductile mode-machining, it is now able to control the cutting depth of each abrasive not to exceed the critical limit which causes the material fracture so that no crack remains on the surface after grinding. However, subsurface damage including plastic flow and residual stress are developed on the surface instead. As such kinds of defect degrade the wafer deflective strength, it is very difficult to thin wafer down below 150μm.In order to remove such defects, a further smaller processing unit, in which the interactive force/energy is small enough not to cause silicon plastic deformation, is preferable. Polishing is an available technology possible to produce a surface almost free of plastic flow, but this sacrifices the geometric accuracy. As an alternative solution, a fixed abrasive process offers better accuracy in geometry, requires fewer steps of the equipment/process and discharges less waste disposal. However, the damaged layer of several μm to several ten μm thick is the barrier to the use fixed abrasive technology, as it is intolerable for Si substrates as typical ICs are built in the layer of 2〜10 μm thick from the topmost surface. To achieve a defect-free surface by fixed abrasive only, this research has successfully developed a novel chemo-mechanical-grinding (CMG) process, by introducing chemical effect into the grinding process. The results achieved during the period of this project are summarized as follows;・A new grinding wheel which possesses solid-state chemical reaction with Si has been successfully developed.・With above CMG wheel, it is able generate a defect free surface on the Φ300 mm Si wafer at a dry condition.・The surface integrity of CMG is equivalent or better than that of commercial CMP wafer.・A on-machine instrument has been successfully developed to measure the geometry of ground wafers.・With the above instrument, it is able to get the 3 dimensional parameters including SFQR, GBIR, TTV and other geometric dimension necessary for control and evaluation of grinding operation.・A molecular dynamic simulation has been performed to verify the CMG mechanism.・The simulation results has revealed that the chemical aspect of CMG is based on the thermal-chemical reaction between Si and O_2, and the solid-state reaction between the CeO_2 abrasive and products of SiO_2, which forms a soft product in an amorphous complex and can be mechanically removed by relatively soft abrasives.・The final thickness of CMG wafer is 30 μm for 8 inch wafers and 100 μm for 12 inch wafers, and the TTV is within 0.2% of the final thickness.・The machining time including CMG is about 10 minutes for 8 inch wafers and 30 minutes for 12 inch wafers. Less

经过长期的研究和开发，燃料电池、太阳能发电、风力发电等新能源已进入实用阶段。最重要的驱动力和使能技术是电力电子。对功率器件的性能、功能、可靠性和小型化的改进的需求日益增加。特别是场截止型IGBT（绝缘栅双极晶体管）有望取得技术突破。与传统晶体管的结构不同，IGBT的功能是电流流过Si衬底的厚度方向。由于IGBT的开关电阻与Si衬底的厚度成正比，因此目前的穿通型IGBT厚度为350 μm，因此具有较大的能量损耗。遇到的问题是电压降和内部发热。下一代非穿通型IGBT的设计厚度为100 μm，适用于汽车行业。 ...更多信息因此，硅晶片必须减薄到减小的厚度。另外，移动的设备对系统LSI（大规模集成）电路的小型化和高度集成化的要求越来越高。作为一种低成本的解决方案，包含多层芯片的低剖面封装被应用于IC卡、移动的电话和数字音乐播放器等产品中。在切割成单个芯片之前，Si晶片必须从8英寸晶片的725μm或12英寸晶片的800μ m减薄到50 ~ 70 μm。在下一阶段，当新的贯穿互连技术可用时，所需的晶片厚度进一步降低到30 - 50 μm。背面研磨是将晶片减小到适合于最终封装的减小的厚度的常规方法。为了使磨削过程中的亚表面损伤最小，必须对金刚石砂轮和工艺参数进行优化。通过使用超精密工程的最新技术和韧性模式加工的概念，现在可以控制每个磨料的切削深度不超过导致材料断裂的临界极限，从而使磨削后的表面不留下裂纹。然而，亚表面损伤，包括塑性流动和残余应力，而是在表面上发展。由于这种缺陷降低了晶片的偏转强度，因此很难将晶片减薄到150μm以下。为了去除这种缺陷，优选更小的处理单元，其中相互作用力/能量足够小，不会引起硅塑性变形。抛光是一种可以产生几乎没有塑性流动的表面的可用技术，但这牺牲了几何精度。作为替代解决方案，固定磨料工艺提供更好的几何精度，需要更少的设备/工艺步骤，并且排放更少的废物处理。然而，几μm到几十μm厚的损伤层是使用固定磨料技术的障碍，因为这对于Si衬底是不能容忍的，因为典型的IC构建在距离最顶表面2 μ m到10 μm厚的层中。为了实现无缺陷的表面，只有固定磨料，本研究成功地开发了一种新的化学机械磨削（CMG）工艺，通过引入化学效应的磨削过程。本项目期间取得的成果总结如下：·成功开发了一种与Si发生固态化学反应的新型砂轮。使用上述CMG砂轮，可在干燥条件下在Φ300 mm硅晶片上生成无缺陷表面。·CMG的表面完整性等同于或优于商业CMP晶圆。·已成功开发了一种用于测量研磨晶圆几何形状的机上仪器。·利用该仪器，可获得磨削操作控制和评价所需的三维参数，包括SFQR、GBIR、TTV和其他几何尺寸。·为了验证CMG机制，进行了分子动力学模拟。·模拟结果表明，CMG的化学性质是基于Si和O_2之间的热化学反应，以及CeO_2磨料和SiO_2产物之间的固相反应，SiO_2产物以非晶态复合物的形式形成软产物，可以被相对较软的磨料机械去除。CMG晶圆的最终厚度为30 μm（8英寸晶圆）和100 μm（12英寸晶圆），TTV在最终厚度的0.2%以内。·包括CMG的加工时间对于8英寸晶片为约10分钟，对于12英寸晶片为30分钟。少