极紫外光学元件表面碳污染模型的建立

Carbon Contamination Modeling on Extreme Ultraviolet Optic Surfaces

为有效评估和预测在极紫外光辐照下，极紫外光刻机中残留的碳氢化合物气体在多层膜光学元件表面造成的碳污染状况，建立了光学元件表面碳沉积的复杂理论模型，描述了残留碳氢化合物在光学表面的传输，在极紫外光子和二次电子激发下引起的分子分解，并在光学表面形成碳沉积层的过程。模型预测结果和实验数据吻合得很好。理论分析表明引起碳氢化合物分解的主要原因是光子分解而不是二次电子分解。碳层的增长依赖于碳氢化合物气体偏压和极紫外光强，具有较轻分子量的碳氢化合物（〈～100 amu）对污染的贡献很小。同时当基底温度适度增加时（～30 ℃），能够加速表面碳氢化合物分子的解吸附，可有效减少碳污染。

In order to estimate and predict the carbonaceous contamination of extreme ultraviolet （EUV） multilayer optical element surfaces caused by EUV irradiation in the presence of residual hydrocarbon gases, a comprehensive model of radiation-induced carbon growth on EUV optic surfaces is presented. The model describes the transport of residual hydrocarbons to the irradiated area and the subsequent dissociation of the hydrocarbon by both EUV ionization and secondary electron excitation. The dissociated hydrocarbons are reactive and form a carbonaceous film. Model predictions fit experimental data quite well. Theoretical analysis indicates that the primary cause of hydrocarbon dissociation is bond breaking by direct photon absorption rather than by secondary electrons. Calculations also demonstrate that the growth of carbon film depends on various conditions of hydrocarbon partial pressure and EUV power. The model successfully predicts that light hydrocarbons （〈～100 amu） pose a negligible risk to EUV optics and modest increases in substrate temperature （-30 ℃）, which will substantially reduce optic contamination by increasing hydrocarbon desorption from the surface.