Surface Morphology Evolution Induced by Multiple Femtosecond Laser Ablation on 4H-SiC Substrate and Its Application to CMP

Abstract

4H silicon carbide (SiC) substrates were processed by multiple femtosecond (fs) laser ablation. Its surface morphologies changed dramatically at different scanning pitches, different scanning velocities, different repetition rates and near-threshold fluence. The evolution of surface morphologies and the uniformity of rippled structures were respectively investigated and discussed. The overlapped zones of adjacent pulses were focused in discussion. In the case of high repetition rate, periodic ripples with average spatial periodicities ranging from 145 nm to 196 nm were induced; whereas in the case of lower repetition rate, coarse ripples (roughly 440 nm) and fine ripples (about 117 nm) were simultaneously formed. Large amount of agglomeration was fabricated in the case of scanning pitch 0.05 μm and scanning velocity ≤ 5 mm/s. At near-threshold fluence, 4H-SiC surface was partly ablated. When the rippled structures induced in Transverse Irradiation Mode were further ablated in Cross Scanning Mode, horizontal ripples changed into vertical ripples. X-ray diffraction and Raman spectra were utilized for surface analysis. Confirmatory experiment was carried out, demonstrating that chemical mechanical polishing (CMP) process could be promoted by fs laser ablation.

Experimental study on femtosecond laser ablation of 4H–SiC substrate

“…Wang et al optimized the ultrafast laser ablation process and further performed CMP on the processed silicon carbide surface. The results showed that the material removal efficiency was significantly improved and the surface roughness was improved, indicating that laser treatment of the silicon carbide surface can help improve the subsequent processing performance [23,24], Other researchers had also reached similar conclusions [25][26][27]. Zheng, Feng, and others used femtosecond laser to polish SiC ceramics under water.…”

SEM, AFM and TEM Studies for Repeated Irradiation Effect of Femtosecond Laser on 4H-SiC Surface Morphology at Near Threshold Fluence

“…After fs laser irradiation, discontinuous ablated zones were fabricated. More discontinuous zones were ablated with the increase of scan times, indicating that stronger accumulation of energy deposition caused by incubation effect 22 played an important role for the increase of ablation.…”

Defect-Engineered MnO2 as Catalyst for the Chemical Mechanical Polishing of Silicon Carbide Wafer

“…In recent years, huge amount of research effort has been devoted to the polishing of SiC wafer using various approaches, such as conventional CMP [11][12][13][14][15][16][17][18][19][20] and non-conventional CMP. Non-conventional CMP includes electrochemical assisted CMP, [21][22][23][24][25][26][27] catalyst assisted CMP, [28][29][30][31][32][33][34][35] plasma assisted CMP, [36][37][38][39][40] thermal oxidation assisted CMP, 41 ultrasonic vibration assisted CMP, 42,43 laser ablation assisted CMP, 44 and magnetorheological CMP, 45 which use different approaches to accelerate the oxidation rate of SiC wafer. Though effective in increasing MRR, these non-conventional CMP technologies usually require either the use of expensive equipment (like electrochemical assisted CMP, plasma assisted CMP, ultrasonic vibration assisted CMP, laser ablation assisted CMP) or complicated pre-treatments (thermal oxidation assisted CMP, laser ablation assisted CMP), which increase system cost and process complexity significantly and therefore hinder their commercial applications.…”