利用纳米压入仪对Si片上的多晶Cu膜进行压入蠕变研究。实验结果显示晶粒尺寸大于200 nm时，应力指数对晶粒尺寸不敏感。当晶粒尺寸小于200 nm时，因压头底部更多的晶粒参与变形, 应力指数随晶粒尺寸的降低而增大.认为薄膜材料存在一个对应力指数不敏感的最小临界晶粒尺寸lc。Cu膜的应力指数随保载载荷增大而增大，其主要原因在于高载荷下位错强化机制使蠕变率降低。
The effects of grain size and holding load on creep properties of polycrystalline Cu thin films were investigated using nanoindentation instrument. The results show that when grain size of polycrystalline Cu thin films is between 200 nm to 1500 nm, the stress exponent is insensitive to grain size. However, when the grain size is reduced below 200 nm, the stress exponents increases with decreasing grain size, implying that there is a critical grain size for stress exponents in nanoindentation tests. The stress exponent also increases with the increase of holding load. The above phenomena result from more grains to be involved and the creep rate decrease due to dislocation strengthening the plastic zone under the indenter tip.
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