【作者】 张菲；

【导师】 曾晓雁； 段军；

【作者基本信息】 华中科技大学 ， 物理电子学， 2012， 博士

【摘要】 紫外激光因波长短、部分特定材料吸收率高、热影响区小、可聚焦光斑尺寸小等特点,微加工时容易获得较高的加工精度和质量,已引起电子半导体制造和通讯工程、生物和医学、精密机械、航空航天、国防等领域工程技术人员的高度重视。特别是近十年来迅速发展起来的高功率全固态紫外激光器,电光转换效率高、重复频率高、性能可靠、运行成本低、体积小、光束质量好、功率稳定,在微电子和半导体工业精密制造和微细加工领域中占有重要地位。因此,研制具有自主知识产权的紫外激光微加工设备,特别是研究紫外激光微加工技术、机理和建模对提升我国在微制造领域中的技术水平和核心竞争力具有十分重要的意义。首先,针对现有紫外激光微加工装备采用振镜扫描加工作台运动或静态聚焦加工作台运动的方式,不能同时满足电子行业和半导体行业精密制造和微加工的多功能、高效率、高精度和大幅面要求的现状,本论文研发了一种多功能紫外激光微加工设备,兼有振镜快速扫描和静态短聚焦两种加工方式。根据两种加工方式刻蚀单晶硅片得到的刻缝宽度和深度的标准差对设备稳定性进行了评估,结果表明,多功能紫外激光微加工设备振镜快速扫描加工系统和静态短聚焦加工系统均能稳定工作,能够胜任工业应用的要求。其次,针对传统同心圆扫描或螺旋线扫描钻盲孔加工方法容易产生盲孔底部表面高度不均匀的问题,首次提出了定点—同心圆扫描结合加工方式,即盲孔中心区域采用激光定点钻孔方式去除材料,盲孔周边区域采用同心圆扫描方式去除材料。通过对PI(聚酰亚胺)和铜材料的单脉冲激光刻蚀率和扫描光斑等效脉冲数理论计算,得出了采用定点—同心圆扫描结合方式加工FPC(柔性线路板)盲孔时激光脉冲能量密度、激光频率、扫描速度与同心圆扫描间距之间的关系式。根据该关系式对多层FPC钻—阶盲孔参数进行了优化设置,获得了底部整洁光泽、锥度小、结构理想的盲孔(直径200μm),测得盲孔底面最大高度差为7.16μtm,孔底表面粗糙度Ra为1.06μm,符合电子行业要求。再次,采用355nmNd:YVO4激光器和1064nmNd:YAG激光器对CCL(覆铜箔层压板)和FPC进行了刻蚀、切割加工对比实验,比较了不同波长激光对加工质量的影响,分析了紫外激光能量密度和扫描速度对FPC主要材料铜、PI刻缝宽度、深度的影响,并对紫外激光切割FPC金手指进行了研究。然后,对纳秒脉冲紫外激光刻蚀铜材料的去除过程进行了有限元模拟和实验对比研究,模拟过程中首次采用将激光脉宽作用时间分段计算,并且将激光功率密度始终加载在已形成的盲孔或凹槽表面的方式,这种方式比目前ANSYS模拟激光去除加工研究中普遍采用的根据加载激光能量一段时间后的温度场分布进行材料去除的方式更符合实际情况,使得模拟结果更准确。将不同能量密度下刻蚀铜模拟值与实验值比较得出,刻缝宽度和深度的误差最大值分别为4.5μm和2μm；对不同扫描速度的情况模拟时,刻缝宽度和深度的误差最大值分别为2μm和3.5μm；不同扫描次数条件下,当扫描速度分别为100mm/s和200mm/s时模拟刻缝深度的误差最大值分别为1μtm和2μm。实验结果表明该数学模型的模拟结果具有较高的准确性,可对紫外激光刻蚀铜进行预测和理论指导。激光扫描刻蚀FPC材料时,模拟铜和PI的刻蚀宽度以及铜刻蚀深度较为准确,误差值分别为0.1μm、0.6μtm和1μm；但对PI的刻蚀深度误差较大,其原因是PI材料与紫外激光相互作用机理复杂且热物理性质参数尚不完善。最后,采用紫外激光精密切割和化学腐蚀相结合的方法研究了一种125μm厚超薄A1203陶瓷微势阱芯片基底层的制备技术。利用正交实验获得了A1203陶瓷激光精密切割的关键影响因素和优化参数,研究分析了关键影响因素对精密切割尺寸精度和切口边缘质量的影响规律以及高温浓硫酸对激光切缝周围残余颗粒和刻缝侧壁表面重熔层的相互作用机理。实验结果表明,采用紫外激光精密切割和化学腐蚀相结合的方法,不但可以获得高精度激光加工尺寸,而且还可获得刻缝侧壁表面无重熔层、表面粗糙度可达0.16μm的高质量超薄A1203陶瓷微结构,完全满足后续金属沉积工艺要求。更多还原

【Abstract】 UV laser, with the advantages of short wavelength, high absorptivity as well as small heat-affected zone and focusing spot size, has played an important role in the field of electronic semiconductor manufacturing and communications engineering, biotechnology and medical, precision mechanics, aerospace and national defense. Particularly, during the last decade, diode-pumped solid state (DPSS) lasers have been applied widely in semiconductor and electronics micro-fabrication industry due to the advantages of high efficiency, high frequency, low operating cost, good beam quality and flexibility as well as miniature size. It has great significance to enhance the technical level and core competitiveness in the field of micro-fabrication by developing UV laser micro-machining equipment with independent intellectual property and by studying UV laser microprocessing techniques, mechanisms and modeling.Fistly, a multi-functional UV laser microprocessing equipment, which had both short focus and scanning galvanometer processing methods, had been developed for the application in electronics and semiconductor industry in this dissertation. The stability of the equipment was tested according to the standard deviation of etched width and depth of silicon wafers. The results showed that both short focus and scanning galvanometer microprocessing methods had a higher machining stability, which was qualified for the requirements of industrial application.Secondly, an innovative method of drilling blind holes—percussion-concentric scanning drilling was proposed to solve the rugged bottom surface produced by the traditional concentric or spiral scanning drilling methods. The key point of the percussion-concentric scanning drilling method was that the laser percussion and concentric scanning drilling were taken respectively to remove the blind hole center and surrounding material. Based on the theoretical calculation of both single pulse etching rate and pulses canning etching rate, the relationships between laser etching parameters (such as laser fluence, frequency, scanning speed) and concentric circle spacing were achieved for this method drilling blind holes in PI and Cu materials and first-order blind holes (diameter of 200μm) with smooth bottom, small taper, and good structure in multi-layer FPC were obtained by calculating the optimal parameters. Measurement results showed that bottom surface roughness Ra and maximum height difference were 1.06μm and 7.16μm respectively, which could meet the needs of electronics industry.Thirdly, CCL and FPC cutting and etching experiments were carried out by using 355nm Nd:YVO4 laser and 1064nm Nd:YAG laser respectively to compare the impact of lasers with different wavelengths on microprocessing precision and quality. The resuts showed that no matter in the microprocessing accuary or quality, UV laser is better than IR laser. Therefore, the effects of UV laser fluence and scanning speed on etching width and depth of Cu and PI as well as cutting quality of FPC goldfingers were investigated and analyzed systematically.Next, a finite element simulation of nanosecond pulsed UV laser etching copper was carried out. The laser pulse duration was divided into several sub-pulse duration in simulation calculation process to calculate the removal of material at each sub-pulse duration. In this way, the simulation results were closer to the actual etching process, and made the simulation results more precision. Comparied with the experimental results of UV laser etching copper, the simulated maximum errors of both etching width and depth were 4.5μm and 2μm respectively under the conditions of different laser fluence and 2μm and 3.5μm respectively in the case of different scanning speed as well as 1μm and 2μm respectively at different scanning number when the scanning speeds were 100mm/s and 200mm/s respectively. The experimental results showed that the simulation results of the mathematical model has good accuracy, which could predict the results of UV pulse laser processing copper and guidance how to carry out the UV pulse laser microprocessing copper. When simulation on UV pulse laser scanning etching FPC, the maximum errors are 0.1μm in etching width of copper,0.6μm in etching width of PI and 1μm in etching depth of copper, which is more accurate than the simulation etching depth of PI due to very complex interaction mechanism between PI materials and UV laser and incomplete parameters in thermophysical properties of PI.Finally, a method combining UV laser cutting and post chemical etching was studied to fabricate a multi-layer microchip substrate of ultrathin ceramic plates (125μm). The effects of the key factors and optimized parameters on laser microprocessing accuracy and quality were investigated by means of a 4X4 orthogonal design. The key microprocessing parameters were determined and optimized to achieve a narrow kerf width and minimal Ra on the kerf sidewall under the conditions of keeping high production efficiency. Subsequent chemical etching on the laser processed areas was performed to remove debris on the kerf surface and recast layer on the kerf sidewall in order to reach the requirements of both size precision and post gilding treatment. The results showed that the combining UV laser cutting and post chemical corrosion method could get not only a higher laser processing size precision, but also a clean surface on both kerf top and sidewall surface with a roughness Ra of 0.16μm, which fully met the requirements of subsequent metal deposition process.更多还原