气体团簇离子束两步能量修形法的平坦化效应

本文提出采用气体团簇离子束的两步能量修形法来改善4H-SiC(1000)晶片表面形貌.先用15 keV的高能Ar团簇离子进行整体修形,再用5 keV的低能团簇离子优化表面.结果表明,在相同的团簇离子剂量下,与单一15 keV的高能团簇处理相比,两步法修形后的表面具有更低的均方根粗糙度,两者分别为1.05 nm和0.78 nm.本文还以原子级平坦表面为研究对象,揭示了载能团簇引起的半球形离子损伤(弧坑)与团簇能量的关系,及两步能量修形法在弧坑修复中的优势.在原子力显微镜表征的基础上,引入了二维功率谱密度函数,以直观全面地给出材料的表面形貌特征及其随波长(频率)的分布.结果表明,经任何能量的团簇离子轰击的表面,在0.05—0.20μm波长范围内,团簇轰击都能有效地降低粗糙度,而在0.02—0.05μm范围内,则出现了粗化效应,这是由于形成了半球形离子损伤,但第二步更低能量的团簇离子处理可以削弱这种粗化效应.

Double-step gas cluster ion beam smoothing

In this study we use the double step gas cluster ion beam treatment to improve smoothing process of mechanically polished 4H-SiC(1000)wafers and compare it with conventional single-step smoothing.The first step is a higher energy treatment with 15 keV Ar cluster ions,and the second step is a lower 5 keV treatment.Single-step treatments are performed at 15 and 5 keV.It is shown that single-step 15 keV smoothing as compared with lower 5 keV one is very effective for removing the initial surface morphological feature(scratches),however,cluster ions impacting on the surface can create larger craters,resulting in roughness Rq of 1.05 nm.Whereas,5 keV treatment at a selected fluence cannot remove initial scratches,which requires using higher fluences,i.e.such smoothing becomes time consuming.On the other hand,crater morphology with such a treatment is less developed,hence,the roughness slightly decreases to 0.9 nm.Using the double-step treatment,one can obtain the surface with lower Rq roughness of 0.78 nm as compared with single-step treatment,at the same total cluster ion fluence.Therefore,the double-step treatment combines the advantages of the effective smoothing of scratches at high energy and smaller crater morphology at low energy.To evaluate the contribution of the cluster morphology introduced by the accelerated clusters into the total roughness,the cluster ion beam treatment of an atomically smooth 4H-SiC(1000)surface is also carried out.It is shown that the crater diameter increases in a range of 15–30 nm with the cluster energy increasing.More detailed analysis of the smoothing process is carried out by using two-dimensional isotropic PSD function.It is shown that the cluster treatment of mechanically polished 4H-SiC wafers effectively reduces the roughness in a wavelength range of 0.05–0.20μm and the efficiency of smoothing is higher at higher cluster energy.In a range of 0.02–0.05μm,a roughening effect is observed,which is due to the formation of craters.This roughening effect can be effectively reduced by the subsequent lower energy step treatment,which can be shown by the PSD function analysis of the smooth SiC surface treated initially by cluster ion beam.