利用维氏和玻氏压头表征半导体材料断裂韧性
STUDY ON FRACTURE TOUGHNESS OF SEMICONDUCTOR MATERIAL USING VICKERS AND BERKOVICH INDENTERS
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摘要: 压痕法是测量材料断裂韧性 (K_\rm IC) 的常用方法之一, 如何根据不同的材料、不同的压头选择适合的公式, 是当前面临的一大问题. 因此,在不同载荷下对单晶硅 (111) 和碳化硅 (4H-SiC, 0001面) 这两种半导体材料进行了维氏微米硬度和玻氏纳米压痕实验, 对实验产生的裂纹长度c进行了统计分析, 并采用13个压痕公式计算材料的K_\rm IC, 开展了微米划痕实验, 验证压痕法评估半导体材料K_\rm IC的适用性. 研究结果表明: 为了消除维氏压痕实验产生的c的固有离散性, 需要多次测量取平均值; 裂纹长度与压痕尺寸的比值随压痕载荷的增大而增大; 材料的裂纹类型与载荷相关且低载荷下表现为巴氏裂纹, 高载荷下表现为中位裂纹; 与微米划痕实验得到的单晶硅和碳化硅材料的K_\rm IC平均值 (分别为0.96 MPa,\cdot,\sqrt\rm m和2.89 MPa,\cdot,\sqrt\rm m) 相比, 在同一压头下无法从13个公式中获得同时适用于单晶硅和碳化硅材料的压痕公式,但在同一材料下可以获得同时适用于维氏和玻氏压头的K_\rm IC计算公式; 基于中位裂纹系统发展而来的压痕公式更适合用于评估半导体材料的K_\rm IC, 且维氏压头下的K_\rm IC与玻氏压头下K_\rm IC的关系不是理论上的1.073倍, 应为1.13\pm 0.01.Abstract: The indentation method is one of the commonly used methods to determine fracture toughness (K_\rm IC) of brittle materials. One of the challenges is to obtain a suitable equation of the materials from various equations according to different materials and indenters. Therefore, fracture toughness tests with pyramid indenters (Vickers indenter and Berkovich indenter) were conducted on Si (111) and 4H-SiC (0001) under various loads. The crack length c generated in the Vickers indentation experiments were statistically analyzed, and thirteen equations were selected to calculate the fracture toughness of semiconductor materials at room temperature. The applicability of the indentation test was evaluated, based on a comparative analysis with the results of the scratch test. The results show that to eliminate the inherent discreteness of crack length c generated in the Vickers indentation experiment, multiple indentation tests (at least thirty tests) need to be conducted. The ratio of crack length c over the indentation diagonal length a increases with an increase in the applied load P. The crack types of the materials depend on P: Palmqvist crack system appears for low loads and Median crack system appears for high loads. Compared with the average fracture toughness (0.96~MPa,\cdot,\sqrt\rm m and 2.89~MPa,\cdot,\sqrt\rm m, respectively) of Si (111) and 4H-SiC (0001) obtained by micro scratch test, based on linear elastic fracture mechanics (LEFM), the appropriate equations was obtained for both Vickers and Berkovich indenters for the same as material, but which can not be obtained for both Si (111) and 4H-SiC (0001) under the same as indenter from thirteen equations. The fracture toughness of semiconductor materials are best calculated by an expression develope from the Median crack system, and the relationship between fracture toughness being obtained with Vickers indenter and that of with Berkovich indenter is not theoretically 1.073 times, which should be 1.13\pm 0.01.