基于PDMS图案化印章的Micro-LED巨量转移

本论文围绕Micro-LED的巨量转移问题，以如何实现高精度转移、高分辨率显示为目标，开展多方面研究工作。通过对比不同转移手段实现的难度和优缺点，选择了无限制器件尺寸的弹性印章法进行研究。

在前期的准备工作中进行了PDMS印章的制备测试和250 μm大颗粒LED的蓝膜转移实验，验证了技术路线的可行性。进入正式实验，着手准备制作转移工具和转移物，利用CAD工具设计了设计高密度排布的PDMS图案化印章和最小尺寸为10 μm的Micro-LED独立器件阵列。通过光刻、刻蚀、沉积等半导体工艺，成功制备出了多种尺寸的超分辨网格阵列印章，多种图案的掩膜获得了不同的形貌特征，最小图案线宽达到1 μm。在Micro-LED芯片制备上，优化了多层结构的制备流程和工艺参数，特别是由p-GaN和n-GaN的台阶差引起的深隔离槽刻蚀偏差问题，最终获取品质较佳的Micro-LED器件阵列。根据不同尺寸的芯片，还设计和制备了对应结构的指叉电路。结合制成的图案化印章和Micro-LED芯片，开展巨量转移实验。

巨量转移要实现把大量的Micro-LED器件从硬质的蓝宝石生长衬底转移到其他材质基板上，激光扫描虽然能分离外延层却不能保证不受破坏，在反复尝试了多种液态、固态介质材料后，总结出成功固定从衬底上脱落的器件的关键是使用大范围可调粘度的材料作为临时基板，能显著提高转移的成功率，而PDMS印章并不适用于转移当前设计的Micro-LED芯片。最后，通过UV膜-UV膜的两次转移实现了对11.5×13 mm²面积的36万颗10 μm的Micro-LED芯片的巨量转移，且平均良率达到99.90%，整体均匀度达98.44%，达到了对Micro-LED巨量转移的目的。

This thesis focuses research on the mass transfer of Micro-LED, aiming to achieve high-precision transfer and high-resolution display. After comparing the difficulties and strengths of various transfer approaches, the elastic stamp method with no device size requirement was selected. 
In the preliminary work, PDMS stamps were prepared and tested, and the blue film transfer experiment of 250-μm large-sized LEDs was carried out to verify the feasibility of the technical route. Then, transfer tools and objects were fabricated, and a CAD tool was used to design PDMS patterned stamps in a high-density arrangement and standalone Micro-LED arrays with a minimum size of 10 μm. Utilizing semiconductor fabrication processes such as photolithography, etching, and deposition, various sizes of super-resolution grid array stamps were successfully fabricated, and different morphological features were obtained with a 1 μm line width. In the preparation of Micro-LED chips, the process parameters of the multilayer structure were optimized, especially the deviation problem of deep isolation groove etching caused by the pGaN-nGaN step difference. Micro-LED arrays with better quality were finally obtained. Different finger circuits were also designed and fabricated. Combining the patterned stamps and Micro-LED chips, mass transfer experiments were prepared to carry out.
Mass transfer requires the transfer of tremendous Micro-LED devices from sapphire to other materials. Although laser scanning could separate the epitaxial layer, it may also bring damage. After various liquid and solid materials were investigated, the conclusion was reached to choose a temporary substrate with a wide range of adjustable viscosity which it the key to improve the success rate, while PDMS stamp was found no longer suitable for transferring the current desire. Finally, through two times of UV film-UV film transfer, the mass transfer of an 11.5×13 mm2 Micro-LEDs chip with 360k 10μm devices was achieved reaching an average yield of 99.90% and an overall uniformity of 98.44%.

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