Photochemically combined mechanical polishing of N-type gallium nitride wafer in high efficiency
Photochemically combined mechanical polishing of N-type gallium nitride wafer in high efficiency
复制标题
N型氮化镓晶片的高效光化学联合机械抛光
DOI：
10.1016/j.precisioneng.2018.08.002
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发表时间：
2019-01-01
影响因子：
3.6
通讯作者：
Shi, Kang
中科院分区：
文献类型：
--
作者：
Ou, Li -Wei;Wang, Ya-Hui;Shi, Kang
传统的化学机械抛光（CMP）技术在超惰性N型氮化镓（GaN）晶片上的应用存在材料去除率（MRR）低的问题。在这项工作中，我们描述并测试了光化学结合机械抛光（PCMP）的策略，以促进MRR以下的光辅助（PA）氧化机制。利用紫外（UV）光照射GaN产生电子-空穴对，而使用适当的氧化剂提取导带（CB）电子导致价带（VB）空穴能够氧化GaN。通过自行设计的PCMP样机，研究了合适的氧化剂的特性，并阐明了影响MRR和表面粗糙度Ra的关键问题。结果表明，PCMP产生比CMP高得多的MRR，但需要某些特殊的氧化剂，因为常见的氧化还原氧化剂，如H2 O2，优先被VB孔氧化。当抛光液（pH = 1.5-13.5）中含有0.1M的K_2S_2O_8氧化剂和2wt%SiO_2磨料时，MRR可达180- 254.7nm/h，Ra最低可达0.76nm（5 × 5 μ m ~（2））。虽然GaN晶片本身的光腐蚀可能会导致表面粗糙化，但机械抛光工艺对MRR的增强可以降低Ra，揭示了PCMP系统和设备进一步优化的关键因素。总之，本研究证实了PCMP是高效抛光GaN晶片的一种很有前途的方法。
The application of conventional chemical mechanical polishing (CMP) to super inert N-type gallium nitride (GaN) wafer suffers from low material removal rate (MRR). In this work, we described and tested a photo-chemically combined mechanical polishing (PCMP) strategy to promote the MRR following a photo-assisted (PA) oxidation mechanism. The utilization of ultraviolet (UV)-light to irradiate GaN generates electron-hole pairs, while the use of proper oxidants to extract the conduction band (CB) electrons leads the valence band (VB) holes to be able to oxidize GaN. By means of the PCMP prototype we designed, the features of proper oxidants were investigated and the key issues on MRR and surface roughness (Ra) were clarified. Results show that PCMP generates much higher MRR than CMP, but requires certain special oxidants because common redox oxidants, such as H2O2, are preferentially oxidized by the VB holes. When polishing solution (pH = 1.5-13.5) includes 0.1 M K2S2O8 oxidants and 2 wt% SiO2 abrasives, the MRR reaches 180-254.7 nm/h and the lowest Ra attains 0.76 nm (5 x 5 mu m(2)). Although the photo-corrosion of GaN wafer itself may cause the surface roughening, the enhancement of the mechanical polishing process to MRR can decrease Ra, revealing a key factor in the further optimization of the PCMP system and equipment. In conclusion, the present study confirms that PCMP is a promising approach in polishing GaN wafer in high efficiency.