| 摘要: | 碳化矽做為第三代半導體的核心材料，相較於目前使用率最高的矽晶圓，在熱導率、帶隙、擊穿電壓等，有更加優異的特性，可作為高溫、高壓、高頻與高功率元件的半導體材料。但碳化矽除了高帶隙外，其材料特性包含高化學穩定性、高硬度等，使得碳化矽晶圓的生產過程繁複且困難，其中如何提升切割、研磨、拋光效率仍是極具挑戰性。本研究以飛秒雷射加工線切割後的Semi 4H-SiC，試圖將其表面上的缺陷及線鋸痕去除，同時探討碳化矽不同極性面，碳面與矽面的加工差異。本研究首先觀察線切割所造成的表面缺陷及內部微裂痕，再以不同雷射參數進行表面處理測試，在能量密度(Fluence, F) 3.51 J/cm2與脈衝重疊率 (Pulse Overlapping, PO) 96.96%下，透過研磨結果顯示，可獲得粗糙度Ra為0.002 m、高差Rz為0.124 m的表面形貌，相比起未加工試片Ra為0.134 m、高差Rz為3.661 m差異極大。本研究也發現於不同掃描重疊率下，試片粗糙度及高差並無明顯變化，因此可選用低掃描重疊率進一步提升加工效率及降低材料損耗。而本研究也發現雷射加工不同極性面時，其研磨後形貌差異很大，推測是加工過程中兩極性面的氧化程度不同所致。使用不同的雷射加工參數，無論是改變掃描次數或是改變能量密度，碳面的氧化物沉積層皆厚於矽面，且隨著雷射削蝕能量的上升，兩極性面的差距也隨之擴大，較薄的氧化沉積層厚度使得矽面加工後坑洞較碳面深，因而矽面無法在相同研磨條件下獲得與碳面相同的奈米級、低粗糙度表面。;As one of the core materials of the third-generation semiconductor, silicon carbide (SiC) has several unique properties such as high thermal conductivity, wide band gap, and large breakdown voltage. These excellent characteristics make it to be very promising for high-frequency and high-power components. However, its extreme chemical stability and high hardness also pose great challenges in the fabrication of SiC wafers. This study uses a femtosecond laser to remove the remained defects and marks on the Semi 4H-SiC surface after the wire saw cutting process. At the same time, the differences in laser machining characteristics of different SiC polar surfaces, the carbon face and the silicon face, were also studied. First, the wire-sawed surface defects and internal micro-cracks were observed, and then the results of the machined surface were examined with different laser processing parameters. Under the process parameters of laser fluence (F) of 3.51 J/cm2 and the pulse overlapping (PO) of 96.96%, the grinding results showed that a good surface morphology, with a roughness of Ra of 0.002 m and a height difference of Rz of 0.124 m, could be achieved. When compared with that of the unprocessed specimens, where the Ra was 0.134 m and Rz was 3.661 m, there was a significant improvement in grinding performance. This study also showed that both Ra and Rz did not change significantly under different POs. Therefore, a lower PO can be employed to further improve processing efficiency and reduce material loss. It was also observed that when laser processing different polar surfaces, the morphology after grinding was very different. It is speculated this was due to the different oxidation degrees of the two polar faces after laser processing. Using different laser processing parameters, regardless of changing the scanning cycles or varying the fluence, the oxide deposition layer on the carbon face was thicker than that on the silicon face, and with the increase of laser fluence, the morphology difference of the two faces also expanded. The thinner oxide deposition layer made the silicon face have deeper pits than that of the carbon face after laser processing. Therefore, under the same grinding conditions, the silicon face could not achieve the same nano-scale, low-roughness surface as that of the carbon face. |
