电化学刻蚀增强机械抛光氮化镓的加工工艺及机理研究

PROCESS AND MECHANISM STUDY OF ELECTROCHEMICAL ETCHING-ENHANCED CMP PROCESS OF GAN

张临风

11749144

硕士

机械工程

邓辉

2019-06-04

2019-06-28

哈尔滨工业大学

深圳

氮化镓（GaN）具有优良电学性能和稳定的化学性质，被认为是一种极具发展前景的宽禁带半导体材料，也是制造高性能电子和光电器件的主要材料。一个光滑没有损伤的表面对于器件性能是至关重要的，而目前的表面平坦化方法均无法兼顾较好的表面质量与较高的材料去除速率。为解决传统化学机械抛光（CMP）工艺效率低下的问题，本文提出了一种电化学刻蚀增强CMP工艺，并实现了氮化镓的高效、无损伤抛光。在此工艺过程中，首先采用电化学刻蚀高效率去除磨削或研磨引起的损伤层，然后采用CMP对刻蚀后的表面进行平坦化处理。使用氢氧化钠（NaOH）溶液作为电解质溶液刻蚀氮化镓，其材料去除速率可以达到1.462 μm/min，证明电化学刻蚀可以实现氮化镓材料的高效去除。采用分步观察的方法，对电化学刻蚀的产生和扩展机理展开研究。结果显示，刻蚀优先发生在损伤区域，对材料的高低起伏没有明显的选择性，然后在整个表面上独立地发生，并逐渐连结为同一区域。电势是影响电化学刻蚀反应的一个重要因素，电势直接决定了材料去除速率与刻蚀后的表面形貌。为提高工艺效率，通过调节刻蚀电势以实现材料去除速率和表面粗糙度的平衡，最终选择20 V或30 V作为刻蚀电势。对采用碳化硅磨粒研磨后的氮化镓样品刻蚀20分钟后，再进行化学机械抛光，表面粗糙度Sa由77.5 nm降低到0.641 nm。用光致发光光谱（PL）对样品的亚表面损伤情况进行评价。结果表明，采用电化学刻蚀增强CMP工艺处理后的样品具有较好的表面粗糙度和较小的亚表面损伤（SSD）层。由于电化学刻蚀能够有效去除前道工序引入的裂纹和亚表面损伤层，后续CMP工艺所需的时间被大幅度缩短，最终可以获得无裂纹、无损伤、光滑的氮化镓表面。

Gallium nitride (GaN) is a wide bandgap semiconductor material with excellent electrical and chemical properties and is considered as a promising material for fabrication of electronic and optoelectronic devices. To overcome the bad efficiency problem in conventional chemical mechanical polishing (CMP) process and realize the highly efficient and damage-free finishing of GaN, an electrochemical etching-enhanced CMP process was proposed. In this process, electrochemical etching is first used to remove the damaged layer induced by grinding or lapping, and CMP is then conducted to flatten the etched surface. It was found that the etching rate can reach 1.462 μm/min using NaOH solution as the electrolyte demonstrating that electrochemical etching is a highly efficient process for material removal of GaN. Subsequent investigation of the initiation and development mechanism of etching process indicated that etching occurs preferentially in damaged areas, and then occurs independently on the entire surface and unites gradually. The applied potential was found to be a significant factor affecting the electrochemical etching process and the etching rate and surface roughness can be balanced by adjusting the applied potential. After 20 min of etching, CMP was carried out on a SiC-lapped GaN sample for 60 min. The surface roughness was reduced from Sa77.5 nm to Sa0.641 nm. Subsurface damage was also evaluated by PL and the sample processed by electrochemical etching-enhanced CMP had a sharper and stronger emission which indicates a desirable surface quality. Owing to the efficient removal of cracks and subsurface damage (SSD) layer by electrochemical etching, the required duration of the subsequent CMP process can be greatly shortened to obtain a crack-free, damage-free and smooth GaN surface.

电化学刻蚀 氮化镓 化学机械抛光 分步观察 亚表面损伤层

electrochemical etching GaN CMP in-situ observation damaged layer

中文

联合培养

南方科技大学

张临风. 电化学刻蚀增强机械抛光氮化镓的加工工艺及机理研究[D]. 深圳. 哈尔滨工业大学,2019.