目的 针对异质外延生长的GaN晶片表面粗糙度高、亚表面损伤大等问题,通过优化平面研磨工艺,实现单晶GaN的高效率、高质量平面研磨加工。方法 采用游离磨料对GaN表面进行单因素研磨实验,研究磨料种类、磨料粒径、研磨液流量、研磨盘转速、研磨压力、研磨时间和研磨盘材质等对研磨效果的影响规律,通过图像分割识别法对已加工表面脆塑性域去除面积进行精准识别分割,研究工艺参数对脆塑域去除面积的影响规律。结果 单晶GaN的材料去除速率（Material Removal Rate,MRR）和表面形貌受多种因素的影响。粒径为W3的金刚石磨料最适合GaN的研磨加工,与其他磨料和粒径相比其表面粗糙度和材料脆性域去除面积占比最小。随研磨液流量的增大,MRR先增大后减小,表面粗糙度Ra和材料脆性域去除面积占比逐渐减小。随研磨盘转速和研磨压力的增大,材料去除速率不断增大,表面粗糙度和材料脆性域去除面积占比先减小后增大。在工艺参数为1%（质量分数）W3金刚石磨料、合成铜盘、研磨液流量8 mL/min、研磨转速40 r/min、研磨压力166 kPa条件下研磨12 min后,表面粗糙度从Ra 190 nm下降到Ra 20 nm,材料去除速率为3.61 μm/min,材料脆性域去除面积占比仅为7.66%。结论 采用优化工艺进行单晶GaN游离磨料研磨能有效降低表面粗糙度,采用图像分割识别法能快速精准识别材料的脆塑性域去除面积,用于指导工艺参数优化。
Abstract
To solve the problems of high surface roughness and large subsurface damage of heteroepitaxial GaN wafer surfaces, the work aims to achieve high-quality planar lapping of single-crystal GaN by optimizing the planar lapping process. Single-factor lapping experiments on the Ga face of single-crystal GaN were conducted with free abrasives to study the effects of abrasive type, abrasive particle size, lapping fluid flow rate, lapping speed, lapping pressure, lapping time, and lapping disk material on the lapping results. A Python-based image processing method was used to perform color recognition and image segmentation on the colored surface morphology maps of the processed surfaces to accurately identify the brittle-plastic domain removal area and study the effect of process parameters on the brittle-plastic domain removal area. The material removal rate and surface morphology of single-crystal GaN are affected by multiple factors. Diamond abrasives with a particle size of W3 are most suitable for GaN lapping, with the smallest surface roughness and brittle domain removal area ratio compared to other abrasives and particle sizes. As the lapping fluid flow rate increases, the material removal rate firstly increases and then decreases, while the surface roughness and brittle domain removal area ratio gradually decrease. The maximum material removal rate is 4.39 μm/min, the minimum Ra is 36 nm, and the minimum brittle domain removal area ratio is 12.88%. As the lapping speed increases, the material removal rate continuously increases, while the surface roughness and brittle domain removal area ratio firstly decrease and then increase. The maximum material removal rate is 7.78 μm/min, the minimum Ra is 44 nm, and the minimum brittle domain removal area is 17.60%. As the lapping pressure increases, the material removal rate continuously increases, while the surface roughness and brittle domain removal area ratio firstly decrease and then increase. The maximum material removal rate is 10.15 μm/min, the minimum Ra is 36 nm, and the minimum brittle domain removal area is 14.68%. As the lapping time increases, the surface roughness and brittle domain removal area ratio firstly gradually decrease and then stabilize. After 12 minutes of lapping on a cast iron disk, the Ra is 40 nm and the brittle domain removal area ratio is 13.33%. After 12 minutes of lapping on a synthetic copper disk, the Ra is 20 nm and the brittle domain removal area ratio is 7.66%. In the cast iron disk, the material removal modes are mainly two-body plastic removal, two-body brittle removal, and three-body brittle removal. In the synthetic copper disk, the material removal modes are mainly two-body plastic removal and three-body brittle removal. The synthetic copper disk is more suitable for single-crystal GaN lapping. Under the process parameters of 1wt.% W3 diamond abrasives, synthetic copper disk, lapping fluid flow rate of 8 mL/min, lapping pressure of 166 kPa, and rotation speed of 40 r/min after 12 minutes of lapping, the surface roughness decreases from Ra 190 nm to Ra 20 nm, the material removal rate is 3.61 μm/min, and the brittle domain removal area ratio is only 7.66%. The optimized process for single-crystal GaN free abrasive lapping can effectively reduce surface roughness, and the image segmentation recognition method can quickly and accurately identify the brittle-plastic domain removal area, which can be used to guide the optimization of process parameters.
关键词
单晶GaN /
平面研磨 /
材料去除 /
表面粗糙度 /
脆性域去除
Key words
single-crystal GaN /
planar lapping /
material removal /
surface roughness /
brittle domain removal
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基金
江西省自然科学基金（20224BAB214054,20242BAB25267,20232BAB214057）; 国家自然科学基金项目（52405486）; 江西省教育厅科学技术研究项目（GJJ2201116）; 南昌航空大学研究生创新专项资金项目（YC2024-009）
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