1、ABSTRACTA novel method of ion implantation surface modication for cutting single crystal silicon is proposed. This method modies the mechanical properties of the materials surface layer, which provides a possibility to reduce surface fractures, prolong tool life and increase the machining efciency d
2、uring the cutting process. The mechanism of both implantation surface modication and nanometric cutting is studied using transmission electron microscopy, Raman spectroscopy, nano-indentation and molecular dynamics simulation. Experiments including taper cutting, face turning and aspheric surface ge
3、neration are conducted to verify the method. The results prove that the method is viable to fabricate complex silicon surface geometry and prolong tool life.本文提出了一种离子注入辅助切削单晶硅表面的新方法。这种方法改变材料表面层的机械性能，提供了减少表面断裂，延长刀具寿命一届增加切削过程中的加工效率的可能性。本文用透射电镜（TEM） ，拉曼光谱，纳米压痕和分子动力学仿真的方法，研究表面注入和纳米级切削的机制。包括锥形切削，表面车削和非球面
4、生成的实验旨在核实这种方法。结果证明，这种方法可以完成复杂几何表面的硅加工并延长工具寿命。1. IntroductionSingle crystal silicon is widely used in infrared optics and electronic applications 1. However, its brittle nature at ambient temperature 2 prevents it from producing intricate features and optical quality surfaces. Traditionally, single c
5、rystal silicon is manufactured through processes such as grinding, polishing and lapping. Ultra-precision cutting with diamond tools has been suggested as a replacement which can make the production of silicon components with nanometric surface nish and sub-micron level geometry accuracy possible 3.
6、Mirror surfaces on single crystal silicon have been achieved by ductile cutting under certain parameters 4,5. However, the short tool life and surface fractures are still the serious problems to be solved in achieving nanometric surfaces of silicon components. Ion implantation surface modication of
7、single crystal silicon has attracted signicant interests recently 6.It modies the mechanical properties of the surface layer of the workpiece, which provides a possibility to prolong the tool life, reduce surface fracture and increase the efciency of the silicon machining process. In this paper, a n
8、ovel method of ion implantation surface modication for nanometric cutting of single crystal silicon is proposed. The mechanism of both implantation surface modica- tion and nanometric cutting is studied using Transmission electron microscope (TEM), Raman spectroscopy, nano-indentation and Molecular
9、Dynamics (MD) simulations. The method shows that it is possible for diamond cutting of single crystal silicon in an efcient way. To verify the method, taper cutting, face turning and aspheric mirror generation experiments are conducted. The results show that nanometric surfaces can be generated with
10、out fracture and longer tool life is achieved.（和 abstract 一个意思）单晶硅在红外光学和电子应用中被广泛的使用。然而，它受周围环境影响的易碎性质阻止生产复杂的产品和光学特性表面。一般来说，单晶硅用磨削，研磨，抛光等过程加工。用金刚石刀具超精密切削替代的方法，被认为能够使含硅产品达到纳米级表面和亚微米级几何精度成为可能。特定参数下的柔性切削完成了单晶硅的镜面曲面。但是，短暂的刀具寿命和表面断层仍然是达成纳米级表面的含硅工件中亟待解决的问题。近来，单晶硅的离子注入表面改质引起了特别的关注。它修饰工件表层的机械性能，这使延长刀具寿命，减少表面断
11、裂和增加加工硅的效率成为可能。这篇论文提出了一种离子注入表面改质切削单晶硅表面的新方法。表面移植和纳米级切削的机制都用传动电子显微镜，拉曼光谱，纳米压痕和分子动力学仿真研究。结果表明金刚石可以有效地切割单晶硅。为了核实这种方法，（作者）进行了锥形切削，表面切削和非球面生成的实验。2. Mechanism2.1. Mechanism of ion implantation surface modificationIon implantation surface modification of single crystal silicon is the result of a critical b
12、alance between the damage generation and its annihilation 6. Ion bombardment and cascade collision generate different damage mechanisms from point defects (vacancies and interstitials) to point defect clusters.Fig. 1 shows the implantation results using F ion with 10.0 MeV energy and 1 1014 ion/cm 2
13、 fluence. Cross-sectional transmission electron microscopy (TEM) samples of the implantation layer were prepared using Nova 200 FIB-SEM dual-beam system equipped with an in situ Kleindiek rotational nanomotor. High-energy ions bombard the silicon surface and initiate defects production. When fluence
14、 is sufficient, ca transformation even occurred (Fig. 1(b) and (c). In this process, the modification layer was formed. Ions lost energy in collision, and finally rest in the certain depth of about 4.5 mm in the substrate shown in Fig. 1(a). Laser micro-Raman spectroscopy of the modification results
15、 is shown in Fig. 2. Renishaw inVia Raman microscope with a laser wavelength of 514 nm was used to characterize the material structural changes. The peak at 521 cm 1 was reduced by half and the intensity curves were different in several places, which demonstrate that the crystalline silicon has been
16、 transformed.单晶硅的离子注入表面改质是破环产生和消失的临界平衡。离子轰击和联级碰撞产生了从点缺陷（空位）到点缺陷从的不同损坏结构。图 1 显示了 10.0 MeV 和 1014 ion/cm 2 下的 F 离子的注入结果。用 Nova200 FIB-SEM 双光束系统与原位 Kleindiek 回转纳米马达产生了代表性的 TEM 注入层样品。高能离子轰击硅表面并。激光光谱学的修改结果图 2 所示。拉曼显微镜 以激光波长为 514 nm 描述材料的结构变化。521 厘米 A1 的峰值减少了一半，强度曲线几个地方有所不同,这表明晶体硅已经改变了。2.2. Mechanism of n
17、anometric cutting of modified siliconIn nanometric cutting, tool extrusion caused by negative effective rake angle, produces hydrostatic pressure on the work-piece 7. Single crystal silicon has perfect diamond lattice at ambient temperature. The hydrostatic pressure generates lattice slip and lattic
18、e disorder, which could be seen in Fig. 3. Defect-free atoms in the workpiece are minimized for visualization, and lattice defects can be observed. When the tool imposes force onto the workpiece, the hydrostatic pressure induced by tool extrusion leads to lattice slip. Layer by layer, lattice-slip e
19、xtents to the scale of the cutting depth. When lattice slip extents to the threshold, the material is conveyed at the lattice slip layer, and dislocation carries out underneath the tool cutting edge. As the cutting process steps into an equilibrant state, lattice deformation only exists at the tool
20、edge. The lattice disorder and atom flow, which contributes to small scale cutting force vibration, form the cutting chip and finished surface.在纳米级切削中，负前角导致的刀具产生对工件的压力。单晶硅在环境温度下有完美的金刚石晶格。流体静力压导致晶格滑动和晶格混乱，在图 3 中可以看到。工件中没有缺陷的原子被缩小至可观察,可以看到和晶格缺陷。当工具强加力到工件上,刀具推动引起的流体静力导致晶格滑动。晶格滑动一层一层地延伸至切削深度的规模。当晶格滑动达到临
21、界值，材料传递到晶格滑动层，从工具切削边缘被带出。当切削过程达到平衡状态，晶格变形只在工具边缘存在。晶格滑动和原子流动使小尺度切削力颤动After ion implantation, the lattice structure of the surface layer of the single crystal silicon has been transformed due to the ion bombardment. The silicon atoms are no longer arranged in an ordered structure. The internal damage
22、created by ion implantation acts as the core to absorb the tool induced energy and expands during the cutting process which prevents lattice-slip and dislocation from going further. As the cutting comes into the equilibrant state, all the damage inside the workpiece disappeared due to the self-relax
23、ation. The lattice deformation also only occurs at the tool edge. The process is shown in Fig. 4. The ion implanted silicon reduces the resistance against load. The brittleness is reduced and the elasticity is enhanced. It is beneficial for prolonging the diamond tool life and generating an optical
24、and damage-free surface finish.在离子注入之后，单晶硅表面的晶格结构因离子轰击而改变。硅原子不再排列为一个有序结构。在阻止晶格滑动和混乱进一步扩大的切削过程中，离子注入产生的内部损坏担当了吸收刀具导致的能量和扩张的核心。当切削达到平衡状态，工具内部的所有损坏因自我松弛而消失。晶格变形同样发生在刀具边缘。其过程如图 4 所示。经离子注入的硅减少了与负载相对的阻力。其脆性减小，弹性增加。这对延长金刚石刀具寿命，以及产生光学无损坏表面抛光有利。3.1. Molecular dynamics analysisMolecular dynamic analysis is an
25、 effective way 7,8 for studying the mechanism of ion implantation and modified surface cutting when the changes are in nanometric scale. The simulation model for ion implantation and nanometric cutting is shown in Fig. 5. Details of the workpiece and simulation conditions are summarized in Table 1.
26、The workpiece in the model has been divided into three different layers, namely boundary, thermo layer and Newton layer. The implantation position for ions is randomly chosen. The three dimensional cutting tool in the simulation is modelled with 08 rake angle and 128 clearance angle. The tool is reg
27、arded as rigid body so that the atoms in the tool are fixed relatively to each other and with no interaction force between the tool atoms.分子动力学分析是研究离子注入和表面改质在纳米级尺度变化的机制的有效方式。离子注入和纳米级切削的仿真模型如图 5 所示。表 1 总结了工件和仿真条件的详情。模型中的工件被分为三层，也就是边界，热层和牛顿层。离子注入的位置随机。仿真中的刀具前角 08和后角 128。刀具被视为刚体，这样刀具的原子相对稳定，之间没有相互作用力。I
28、on implantation simulation results are shown in Fig. 6. High-energy ions bombard the single crystal silicon surface, sputtering away surface atoms, implanting into the substrate, and creating dislocations including vacancies, interstitials and defect clusters by direct bombardment and cascade collis
29、ion (Fig. 6(a). Fig. 6(b) shows the radial distribution function (RDF) measurements of the phase transition during implantation. During implantation, RDF value is broadened and exhibits various short peaks, indicating amorphization taking place. The workpiece experienced self-annealing after implant
30、ation, but the single-crystal structure has been destroyed as indicated by a wider RDF peak and a secondary peak.离子注入仿真结果如图 6 所示。高能离子轰击单晶硅表面，从表面原子喷出，注入基层，产生空穴，缺陷和缺陷从等位移。图 6 显示了植入过程中相变测量结果的径向分布函数。注入过程中，径向分布函数值扩大，展现了不同的短峰，表示无定形化发生。在植入后，工件发生了自退火，但是径向分布函数更宽的高峰和次峰值显示，单晶结构已被破坏。3D cutting simulations are c
31、arried out on both normal and implanted silicon. Fig. 7 shows the cutting forces with 2 nm cutting depth using a 2 nm cutting edge tool. Cutting force is expressed by the summation of the total force on all tool atoms. Cutting force curves follow the mechanism of nanometric cutting. The tapered sinu
32、soidal oscillation is greatly reduced while cutting the modified silicon. The oscillation is introduced by material shearing which caused by tool extrusion induced lattice slip extending to the threshold. Lattice distortion and atom flow at the adjacent region between the tool and the workpiece is t
33、he main reason for the small vibration.3D 切削仿真给出了正常硅和被注入的硅。图 7 显示 2nm 切削深度，2nm 刀具边缘的切削力。切削力以所有刀具原子所受的合力表达。切削力曲线根据纳米级切削的机制改变。在改善硅后，锥形正弦震荡减弱。刀具推挤引发晶格滑动至平衡点，这导致材料断裂，引起震荡。刀具和工件相邻区域的晶格扭曲和原子流动是切削力颤动的主要原因。3.2. Nano-indentation analysisNano indentation measurements were carried out with a MTS XP nano-indent
34、er using high-precision Berkovich diamond tip to measure the mechanical property changes (hardness and Youngs modulus) of the implanted material. Surface oxide layer was removed by hydrofluoric acid to exclude the influence. Tests were conducted under indentation penetration depth of 3 mm which is a
35、bout half of the mean projected ranges (Rp) to minimize the influence of the bulk material.使用高精度 Berkovich 金刚石尖端的 MTS XP nano-indente 测量被植入材料的机械性能（硬度和杨氏模量） ，给出纳米压痕测量结果。表面氧化层被氢氟酸去除以消除影响。实验在压痕贯穿深度低于 3mm，平均投影射程的一半的条件下进行，以减小疏松物质的影响。Fig. 8 shows the loaddisplacement curves of the indentation tests. With
36、the same displacements, normal silicon requires a larger load (up to 130 mN) to reach the identical penetration depth. Displacement discontinuity (pop-out) is observed in unloading curves of normal silicon, which is related to the density change caused by the high pressure phase transformation 9. Wh
37、ile implanted silicon exhibits a smooth curve, indicating no phase transformation occurs during unloading, as the phase transformation already took place during the implantation process.图 8 展示了压痕测试的加载-位移曲线。在相同的位移下，正常硅需要更大的加载（130mN） ，才能达到相同的穿透深度。间断位移出现在正常硅的无负载曲线，这与高压相位变化导致的密度变换有关。植入硅展示了一个平滑曲线，表明相位变化不
38、在无负载过程中发生，而在注入过程中就已经发生了。After the ion implantation, the structure of the single crystal silicons surface layer transforms due to the ion bombardment. The bonding force between atoms greatly reduced. Therefore, the modified silicon performs a different mechanical behavior, the resistance against load
39、 lowered, the brittleness reduced, and the elasticity enhanced. Fig. 9 shows the results of hardness and elastic modulus measurements. Depth-sensing indentation hardness was evaluated from the indentation loaddisplacement curve using the Oliver and Pharr method. Youngs modulus was deduced from the u
40、nloaddisplacement curve using a Poissons ration n = 0.25.离子注入发生后，单晶硅表层的结构因离子轰击而变化。原子之间结合力减小。因此，改善后的硅表现出不同的机械性能，抗加载阻力减小，脆性减小，弹性增加。图 9 显示了硬度和杨氏弹性模量的测量。Surface topography after nano-indentation was observed by SEM, and the results are shown in Fig. 10. After ion implantation, the pressure mark exhibits
41、 smoother surface and the indenting area shows smaller brittle cracking after indentation. From the results, it is predicted that ion implantation offers a possibility of reducing surface roughness and tool wear in micro-cutting.纳米压痕后的表面形貌被 SEM 检测，结果如图 10 所示。在离子注入之后，压痕展现了更加光滑的表面，压痕区域的脆性断裂更少。从结果中，我们可
42、以预计离子注入提供减小表面粗糙度和工具磨损的方法。4. Experimental verification and discussion4.1. Taper cuttingTaper cutting experiments with a continuous change in depth of cut were performed on ion implantation modified silicon to examine the ductilebrittle transition on the modified material. Depth of cut was changed fro
43、m 0 to 2 mm at a constant cutting speed of 400 mm/min. The experiments were carried out on Moore Nanotech 250UPL. Single crystal diamond tools were specified with a nose radius of 0.513 mm, a rake angle of 08 and clearance angle of 128. The taper-cut grooves were scanned by AFM. Topographic details
44、of ductilebrittle transition depth are measured in Fig. 11. Modified silicon performs a ductilebrittle transition point of 923.566 nm, much deeper than normal silicon of 236 nm 4.切削深度连续变化的锥形切削实验展示了离子注入对材料韧脆性的改变。4.2. Nanometric surface generation and tool wear experimentsExperiments were carried out
45、to generate nanometric surfaces and examine the tool wear for nanometric cutting of ion implantation modified silicon. The workpiece was pre-modified with F ions, implantation parameters are 1 1014ion/cm2 of ion fluence and 10 MeV of energy. Single crystal diamond tool is used. The machining paramet
46、ers of the depth of cut, feed rate and cutting speed are 1.0 mm, 1 mm/min, and 1500 rpm, respectively. The single crystal diamond tool has a rake angle of 08, a clearance angle of 128and a nose radius of 1.0 mm. Mirror surface finish was achieved, as shown in Fig. 12. Fig. 13(a) and (b) shows the ma
47、chined surface. The feed marks on the machined surface are clearly displayed, and there are no apparent fractures and micro cracks. The mean surface roughness Ra is measured to be 0.861 nm. The machined surface results demonstrate a ductile material removal mode.（作者）进行了产生纳米级表面和检验离子注入辅助纳米切削后刀具磨损情况的实验
48、。工件用 F 离子预先改质，注入的是 1014 个离子每平方厘米，10Mev 的离子。本实验使用单晶金刚石刀具。机械参数为：切削深度：1.0 mm,进给率：1 mm/min,切割速度：1500 rpm。单晶金刚石刀具前角 0 度，后角 12 度，刀尖半径为 1mm镜像曲面完成图如 12。图 13 展示的是加工过的表面。表面清晰地展示了走刀痕迹，没有明显的断裂和微裂。表面平均粗糙度 Ra 为 0.861nm。加工过的表面结果阐释了脆响材料去除模式。Fig. 13(c) is an SEM photograph of the cutting edge of the diamond tool aft
49、er ductile mode cutting of ion implantation surface modified silicon for 6.5 km. A 2 mm wide flank wear with micro grooves is formed. The flank wear is smooth and uniform along the entire cutting edge, indicating that the tool wear has been a stable and gradual process. The surface roughness kept almost constant at a low level during the 6.5 km cutting, which is much longer than cutting without ion implanted silicon图 13 是金刚石刀具的切削边缘。形成了 2mm 的有微型刀槽的侧面磨损。侧面磨损是一个稳定渐进的过程。6.5 千米的切割中，表面粗糙度几乎恒定在一个很低的水平。这比离子注入前的切割长许多。
