基于平板夹具的电子束蒸发沉积薄膜中的挖坑效应分析

Discussion on digging effect on thin flims deposited by electron beam evaporation with substrate held by plate jig

电阻加热具有比较好的加热均匀性，可以认为对于非升华性材料，具有比较理想的平面源发射特性n=1。而电子束加热时，通常n=2～3，甚至可以为6，发射特性参数的范围大，没有取值指导理论或规律，具有很大的不确定性，这对分析薄膜均匀性非常不利。采用细分蒸发源为无数个小的面蒸发源的思想，建立了镀膜材料出现挖坑效应时薄膜厚度均匀性的分析模型。分析结果表明电子束蒸发方法很难获得理想的平面蒸发源，不同程度的挖坑效应将使得n值不同程度地偏离n=1，挖坑效应越明显，n值越大。可以从镀膜机结构设计及薄膜沉积工艺选取两方面着手，降低挖坑效应带来的影响。该研究对认识蒸发源材料发射特性的物理含义具有重要意义，对实验工作同样具有指导性意义。

Resistance heating may be regarded as an ideal plane evaporation source of which the emissivity is assumed as n=1 for non-sublimable materials, because of its highly uniform heating property. However, n is equel to 2-3 even up to 6 for electron beam heating. It implies a great range of emissivity without theoretic explanation and with high uncertainty-- both are very unfavorable to analyzing the homogeneity of thin films. A new approach is therefore proposed that the evaporation source is divided into finite number of minimized surface evaporation sources so as to develop an analytic model for the uniformity of film thickness while the digging effect happends in coating material. The analysis showed that the electron beam evaporation process is hard to obtain an ideal plane evaporation source, and the digging effect will cause the n value to deviate from the value 1 to varying degrees, ie., the clearer the digging effect, the greater the n value. The influence due to digging effect can be weakened by improving the design of coater and selecting more appropriate film deposition process. The results from the discussion are highly meaningful to both the understanding of the physical implication of emissivity of the material used as evaporation source and the relevant experiments.