测量了Mo/Si多层膜在250 ℃下经历不同时间退火后的掠入射X射线反射谱，从中提取出特定级次衍射峰在退火过程中的相对移位，通过布拉格公式拟合，得到了Mo/Si多层膜周期厚度皮米级别的相对变化。采用扩散控制模型来描述Mo/Si多层膜界面扩散，界面厚度的平方随时间线性增加，由此拟合得到Mo和Si间的扩散系数为0.33×10-22 cm2/s。采用四层模型，对掠入射X射线反射谱进行全谱拟合，得到了Mo，Si和扩散层MoSi2的密度分别为9.3，2.5和5.4 g/cm3，据此对Mo和Si间扩散系数进行修正，最终得到在250 ℃下，Mo/Si多层膜中Mo和Si间的扩散系数为1.88×10-22 cm2/s，从而为研究Mo/Si多层膜的热稳定性提供了定量依据。

The grazing incidence X-ray reflection spectra of a Mo/Si multilayer annealing at a temperature of 250 ℃ at different time are measured and the relative shifts in Bragg peak positions are extracted, from which the relative period thickness changes of the Mo/Si multilayer at pm-accuracy are calculated by fitting Bragg formula. A diffusion limited model is applied to account for the growing interfaces between Mo and Si, which states that the thickness of a compound interface grows quadratically over time. From this model the diffusion constant figures out to be 0.33×10-22 cm2/s. Then the grazing incidence X-ray reflection spectra are fitted by genetic algorithm using four-layer model, with the densities of Mo, Si and MoSi2 determined to be 9.3, 2.5 and 5.4 g/cm3. Accordingly, the diffusion constant is modified to be 1.88×10-22 cm2/s, which gives a quantitative criterion for investigating the thermal stability of the Mo/Si multilayer.