薄膜热膨胀系数测试技术研究

热膨胀系数是薄膜的重要热学性能参数,也是薄膜热应力和残余应力计算分析过程中的关键数据.文章基于热诱导弯曲原理,分别采用单基片法和双基片法对氮化钛(TiN)和铝(Al)薄膜的热膨胀系数进行测试,并着重对双基片法的测试误差和适用性进行了分析.研究结果表明,薄膜在不同材质基底上弹性模量的差异是影响双基片法薄膜热膨胀系数测试精度的重要因素.当不同材质基片上薄膜弹性模量差异较小时,双基片法测得的热膨胀系数与单基片法所获结果基本一致;而当不同材质基片上薄膜弹性模量相差较大时,双基片法将不再适用.此外,文章结合薄膜的形貌、结构和残余应力表征测试,对TiN和Al薄膜热膨胀系数与其块体材料的差异进行了分析,结果显示残余压应力会导致薄膜热膨胀系数增大,而残余拉应力则具有相反的效果.

The Study of the Testing Technique of Thermal Expansion Coefficient of Thin Films

The coefficient of thermal expansion (CTE) is an important thermal parameter for thin films, which is a critical issue in the calculation and analysis of the thermal stress and residual stress of thin films. In this paper, the CTEs of titanium nitride (TiN) and aluminum (Al) films were measured by single-substrate and dualsubstrate method based on the thermally induced bending principle, respectively. Feasibility and tolerance of the dual-substrate method were mainly investigated. The results show that difference in the elastic modulus of films is an important factor affects the calculation accuracy of CTEs tested by the dual-substrate method. When the difference of elastic modulus is small, the CTEs measured by the dual-substrate method agree well with the results by the single-substrate method. The dual-substrate method became inapplicable when there is big elasticmodulus difference of the films on different materials. In addition, the difference of CTE values between the thin film and bulk TiN and Al were also discussed according to the characterizations of the morphology, structure and residual stress of the films. The results also show that the compressive residual stress will increase the film CTE, while the tensile residual stress can decrease the film CTE.