单晶硅放电加工蚀除机理及试验研究
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摘要
随着科技的迅速发展,单晶硅作为最常用的半导体材料在许多高技术领域中具有不可替代的作用,但单晶硅由于其脆性造成了在机械加工中出现加工效率低、表面完整性差、加工成本高及加工损伤等制造难题。本课题组利用电火花技术进行了加工试验,发现单晶硅在蚀除机理上与金属有很大不同。本文基于仿真和加工试验,提出单晶硅放电加工蚀除机理,并在此机理的基础上,开展单晶硅放电加工表面粗糙度和相对电极损耗的研究。
主要研究内容如下:
(1)在工艺试验的基础上,提出了单晶硅电火花加工蚀除机理假设,确立热应力在其放电蚀除过程中占主要作用,利用ANSYS进行仿真,并用试验进行了验证。建立了单晶硅放电模型,利用有限元法模拟了单脉冲放电下的温度场及热应力场分布,计算出其在温度场和热应力场作用下的蚀除量,并与实际放电切割蚀除量对比,结果表明实际蚀除量近似等于其在模拟的温度场与热应力场蚀除量之和,验证了单晶硅放电加工蚀除机理的假设;并利用仿真对蚀除凹坑的深径比和相对电极损耗进行了研究。
(2)表面粗糙度是评估加工表面质量的重要特征参数,蚀除凹坑深径比的变化规律与表面粗糙度的变化规律一致。本文利用正交试验在WEDM机床上对单晶硅放电加工的表面粗糙度进行了研究,采用正交试验一方面可以得到各个参数对表面粗糙度的影响规律,与仿真进行对比,仿真和试验结果得到了很好的吻合,另一方面可以得到一组最佳工作参数,使得工件的表面粗糙度达到最低。
(3)在电火花成型加工过程中,工具电极的损耗是影响工件几何形状精度的主要因素之一。在自主开发的电火花加工装置上采用铜电极和钼电极进行了金属铜和单晶硅的放电加工试验,发现单晶硅的相对电极损耗远远低于金属铜,说明可以进行电极低损耗甚至无损耗研究;并研究了电压、脉宽、占空比、是否冲液等几个因素对单晶硅放电加工相对电极损耗的影响规律。
With the rapid development of science and technology, single crystal silicon, as the commonest semiconductor material, plays an irreplaceable role in frontier technology field. But for its brittleness, many manufacturing problems such as low productive efficiency, poor surface integrity, high processing costs and machining damage have caused during processing. Our team had tried to process Si by WEDM and had learned that its erosion mechanism was different from metal. In this paper, the erosion mechanism of single crystal silicon in EDM was proposed from the respect of simulation and testing, then the surface roughness and relative electrode wear of single crystal silicon in EDM had been studied based on this mechanism.
Following are main research work:
(1)Assumption of erosion mechanism of EDM on single crystal silicon was proposed from testing. It was considered that thermal stress played the leading role during the erosion process. Use ANSYS to simulation and tests to validate. Discharge model of single pulse was established on EDM, the temperature field and the thermal stress field of single-pulse discharge condition was analyzed based on finite element method. Theoretical amount of erosion of the silicon was calculated under the temperature field and thermal stress field, and was compared with the actual amount of erosion in tests. Results show that erosion process of the single crystal silicon EDM machining can be described by this assumption of erosion mechanism. The depth-diameter ratio of erosion pits and relative electrode wear were also studied by simulation.
(2)Surface roughness is the key evaluation characteristic parameter of Processed surface quality. The change rule of erosion pits is coincident with surface roughness. In this paper, the surface roughness of single crystal silicon in EDM was studied by orthogonal experiment in WEDM Machine. Based on orthogonal experiment, on the one hand, the influence of each parameter on surface roughness was got, which well tallied with simulation after being compared; on the other hand, a set of optimum operating parameters was found, making minimum surface roughness of the workpiece.
(3)In EDM process, tool wear is one of the primary factors that affect geometrical precision of workpiece. The EDM process rule of different doping types of silicon material with different process parameters was researched and compared with the machining process law of copper by copper electrode and silicon electrode. The relative electrode wear when machining silicon is far lower than copper, indicating that low electrode wear and even no electrode wear can be researched of silicon in EDM. The influence of voltage, pulse width, duty cycle, fluid flushing and other several factors on the electrode wear of silicon in EDM were also studied .
主要研究内容如下:
(1)在工艺试验的基础上,提出了单晶硅电火花加工蚀除机理假设,确立热应力在其放电蚀除过程中占主要作用,利用ANSYS进行仿真,并用试验进行了验证。建立了单晶硅放电模型,利用有限元法模拟了单脉冲放电下的温度场及热应力场分布,计算出其在温度场和热应力场作用下的蚀除量,并与实际放电切割蚀除量对比,结果表明实际蚀除量近似等于其在模拟的温度场与热应力场蚀除量之和,验证了单晶硅放电加工蚀除机理的假设;并利用仿真对蚀除凹坑的深径比和相对电极损耗进行了研究。
(2)表面粗糙度是评估加工表面质量的重要特征参数,蚀除凹坑深径比的变化规律与表面粗糙度的变化规律一致。本文利用正交试验在WEDM机床上对单晶硅放电加工的表面粗糙度进行了研究,采用正交试验一方面可以得到各个参数对表面粗糙度的影响规律,与仿真进行对比,仿真和试验结果得到了很好的吻合,另一方面可以得到一组最佳工作参数,使得工件的表面粗糙度达到最低。
(3)在电火花成型加工过程中,工具电极的损耗是影响工件几何形状精度的主要因素之一。在自主开发的电火花加工装置上采用铜电极和钼电极进行了金属铜和单晶硅的放电加工试验,发现单晶硅的相对电极损耗远远低于金属铜,说明可以进行电极低损耗甚至无损耗研究;并研究了电压、脉宽、占空比、是否冲液等几个因素对单晶硅放电加工相对电极损耗的影响规律。
With the rapid development of science and technology, single crystal silicon, as the commonest semiconductor material, plays an irreplaceable role in frontier technology field. But for its brittleness, many manufacturing problems such as low productive efficiency, poor surface integrity, high processing costs and machining damage have caused during processing. Our team had tried to process Si by WEDM and had learned that its erosion mechanism was different from metal. In this paper, the erosion mechanism of single crystal silicon in EDM was proposed from the respect of simulation and testing, then the surface roughness and relative electrode wear of single crystal silicon in EDM had been studied based on this mechanism.
Following are main research work:
(1)Assumption of erosion mechanism of EDM on single crystal silicon was proposed from testing. It was considered that thermal stress played the leading role during the erosion process. Use ANSYS to simulation and tests to validate. Discharge model of single pulse was established on EDM, the temperature field and the thermal stress field of single-pulse discharge condition was analyzed based on finite element method. Theoretical amount of erosion of the silicon was calculated under the temperature field and thermal stress field, and was compared with the actual amount of erosion in tests. Results show that erosion process of the single crystal silicon EDM machining can be described by this assumption of erosion mechanism. The depth-diameter ratio of erosion pits and relative electrode wear were also studied by simulation.
(2)Surface roughness is the key evaluation characteristic parameter of Processed surface quality. The change rule of erosion pits is coincident with surface roughness. In this paper, the surface roughness of single crystal silicon in EDM was studied by orthogonal experiment in WEDM Machine. Based on orthogonal experiment, on the one hand, the influence of each parameter on surface roughness was got, which well tallied with simulation after being compared; on the other hand, a set of optimum operating parameters was found, making minimum surface roughness of the workpiece.
(3)In EDM process, tool wear is one of the primary factors that affect geometrical precision of workpiece. The EDM process rule of different doping types of silicon material with different process parameters was researched and compared with the machining process law of copper by copper electrode and silicon electrode. The relative electrode wear when machining silicon is far lower than copper, indicating that low electrode wear and even no electrode wear can be researched of silicon in EDM. The influence of voltage, pulse width, duty cycle, fluid flushing and other several factors on the electrode wear of silicon in EDM were also studied .
引文
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[29]周勇,刘正埙.电火花放电加工中工具电极损耗理论研究[J].电加工, 1998(4): 1-3.
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[2]卢景霄,张宇翔,王海燕,等.硅太阳电池稳步走向薄膜化[J].太阳能学报, 2006, 27(5): 444-450.
[3]马春.世界半导体硅材料发展现状[J].上海有色金属, 2005, 26(3): 145-148.
[4] Panek P, Lipiński M, Dutkiewicz J. Texturization of multicrystalline silicon by wet chemical etching for silicon solar cells[J]. Journal of Materials Science, 2005, 40(6): 1459-1463.
[5] Willeke G P. Thin crystalline silicon solar cells[J]. Solar Energy Materials and Solar Cells, 2002, 72(1): 191-200.
[6]康仁科,田业冰,郭东明,等.大直径硅片超精密磨削技术的研究与应用现状[J].金刚石与磨料磨具工程, 2003(4): 13-18.
[7] Takino H, Ichinohe T, Tanimoto K, et al. Contouring of polished single-crystal silicon plates by wire electrical discharge machining[J]. Precision Engineering, 2007, 31(4): 358-363.
[8] Green M A. Third generation photovoltaics: solar cells for 2020 and beyond[J]. Physica E: Low-dimensional Systems and Nanostructures, 2002, 14(1-2): 65-70.
[9]樊瑞新,卢焕明.切割单晶硅表面损伤的研究[J].材料科学与工程, 1999, 17(2): 55-57.
[10] Glunz S W. New concepts for high-efficiency silicon solar cells[J]. Solar Energy Materials and Solar Cells, 2006, 90(18-19): 3276-3284.
[11] Luo Y F, Chen C G, Tong Z F. Investigation of silicon wafering by wire EDM[J]. Journal of Materials Science, 1992, 27(21): 5805-5810.
[12] Peng W Y, Liao Y S. Study of electrical discharge machining technology for slicing silicon ingots[J]. Journal of Materials Processing Tech., 2003, 140(1-3): 274-279.
[13]汪炜,刘志东,田宗军,等.低电阻率单晶硅电火花/电解复合切割加工表面完整性研究[J].电加工与模具, 2007(6): 6-10.
[14]刘志东.快速走丝线切割多次切割特性及其可行性研究[J].电加工, 1990(5): 10-15.
[15]李明辉.电火花加工理论基础[M].国防工业出版社, 1989: 34-39.
[16] Singh A, Ghosh A. A thermo-electric model of material removal during electric discharge machining[J]. International Journal of Machine Tools and Manufacture, 1999, 39(4): 669-682.
[17] DiBitonto D D, Eubank P T, Patel M R, et al. Theoretical models of the electrical dischargemachining process. I. A simple cathode erosion model[J]. Journal of Applied Physics, 1989, 66(9): 4095-4103.
[18] Patel M R, Barrufet M A, Eubank P T, et al. Theoretical models of the electrical discharge machining process. II. The anode erosion model[J]. Journal of Applied Physics, 1989, 66(9): 4104-4111.
[19] Eubank P T, Patel M R, Barrufet M A, et al. Theoretical models of the electrical discharge machining process. III. The variable mass, cylindrical plasma model[J]. Journal of Applied Physics, 1993, 73(11): 7900-7909.
[20] Tamura T, Kobayashi Y. Measurement of impulsive forces and crater formation in impulse discharge[J]. Journal of Materials Processing Tech., 2004, 149(1-3): 212-216.
[21] Zingerman A S. Electric erosion of an anode as a function of interelectrode distance[J]. Sovient Physics, Technical Physics, 1958, (3): 361-367.
[22] Van Dijck F, Crookal J R, Heuvelman C J, et al. Some results of physical research in EDM[C], 1974.
[23] Motoki M, Hashiguchi K. Energy distribution at the gap in Electric Discharge Machining[J]. CIRP ANN, 1967, 14(4): 485-489.
[24] Koenig W, Weill R, Wertheim R, et al. The flow fields in the working gap with Electro-Discharge-Machining[J]. Annals of the CIRP, 1977, 26(1): 71–76.
[25] Obaciu G. A Theory for the physical mechanism of metal removal by Electro Discharge Machining[J]. Proc. ISEM 1980, (6): 79.
[26]陈湛清,李明辉.放电加工极间胶体系统[J].电加工与模具, 1979, (5).
[27]陆纪培,伍世荣.黑膜对电极损耗的影响[J].电加工, 1982, (5): 1-8.
[28]赵伟,任延华,任中根,等.电火花放电通道中带电粒子运动规律的研究[J].机械科学与技术2001, 20(5): 762-763.
[29]周勇,刘正埙.电火花放电加工中工具电极损耗理论研究[J].电加工, 1998(4): 1-3.
[30] Crookall J R. A theory of planar electrode-face wear in EDM[J]. Annals of the CIRP, 1979, 28(1): 125–129.
[31] Kunieda M, Yoshida M, Taniguchi N. Electrical discharge machining in gas[J]. ANNALS-CIRP, 1997, (46): 143-146.
[32] Shankar P, Jain V K, Sundararajan T. Analysis of spark profiles during EDM process[J]. Machining Science and Technology, 1997, 1(2): 195-217.
[33] Marafona J, Chousal J A G. A finite element model of EDM based on the Joule effect[J].International Journal of Machine Tools and Manufacture, 2006, 46(6): 595-602.
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