带有容性偏压的感性耦合放电的混合模拟方法及实验验证

Inductively coupled plasma (ICP) sources are being widely used in the semiconductor manufacturing industry, as they are characterized by several advantages, such as high plasma density at low gas pressure, relative simplicity, no requirement for external magnetic fields, and so on. For etching processes, it is important to control the plasma density and ion bombardment energy independently, which is difficult to be realized in purely inductive discharges. Therefore, a bias power is often employed and capacitively coupled to the substrate. In this discharge system, the plasma is generated by the ICP power, which controls the plasma density and ion flux, and the capacitive bias power is used to control the energy of the ions at the substrate. The bias power, which determines the ion energy distribution (IED) at the wafer, has a significant influence on the plasma properties and is, for instance, responsible for the etch rate. Hence, the bias power effect should be systematically investigated, in order to control the discharge process and to optimize the plasma for microelectronics applications. In this project, a hybrid model is developed to investigate the coupling effect between the ICP power and the bias power, especially in reactive gases. To validate the model prediction, the charged particle density, temperature and the ion energy and angle distribution functions are diagnosed by means of Langmuir probes and other diagnosis methods.

感性耦合等离子体源(Inductively coupled plasma，ICP)具有放电气压低、等离子体密度高、均匀性好、低介电损伤等优点，因此被广泛地用于刻蚀工艺中。在等离子体刻蚀过程中，等离子体组分以及轰击到基片表面的离子能量-角度分布，是影响刻蚀工艺的两个至关重要的因素。为了实现对等离子体组分及轰击到基片表面的离子能量-角度分布的独立控制，人们提出了在ICP源的基片台上施加一个容性偏压。本项目将针对工艺中使用的复杂反应性气体，建立一套面向整个系统（从外界射频电源、外界匹配网络，到放电腔室、基片台及偏压电源）的多物理、化学场的混合模型，较全面地考虑不同外界因素对实际放电过程的影响。通过采用不同类型的偏压波形，重点考察偏压源参数对等离子体特性的影响，为提高刻蚀过程的速率和选择性、优化刻蚀工艺提供科学依据。最后，将模拟结果与实验诊断相比较，进一步验证模型的可靠性。

本项目的主要工作是针对刻蚀工艺中采用的感性耦合等离子体源，建立了包含等离子体模块、电磁场模块、偏压鞘层模块、离子蒙特卡洛碰撞模块等的混合模型，实现了对带有偏压源的感性耦合放电过程的自恰模拟。尤其是在等离子体模块中，可根据模拟需求选择适合的模型，如整体模型、双极扩散模型、流体力学模型和流体/电子蒙特卡洛碰撞混合模型。采用上述混合模型，系统研究了不同的放电条件（如气压、线圈功率、气体组分等）下，偏压源参数（如频率、偏压幅值、相位角等）对等离子体加热过程、放电模式、等离子体组分、等离子体径向均匀性、基片表面的离子能量角度分布的调控。结果表明在不同的线圈功率下，偏压幅值对等离子体组分的调控作用有所不同。当采用双频偏压源时，通过改变相对相位角，离子通量小幅振荡，离子平均能量得到了显著调控。此外，基片表面的离子能量分布是不均匀的，即放电中心处的能峰宽度更宽。这主要是由于径向边缘处的等离子体密度较低，鞘层较厚，因此离子渡越鞘层的时间较长。偏压源不仅会影响基片表面的离子能量角度分布，还会调制等离子体的径向均匀性。结果表明随着偏压幅值的增加，腔室中心处的电子密度下降，而径向边缘处的电子密度上升，等离子体的径向均匀性变好。尤其是当偏压频率为27.12 MHz时，偏压源对等离子体空间分布的调制作用更加明显。部分模拟结果与实验测量数据进行了对比，验证了模型的可靠性。本项目所取得的研究成果可以为优化刻蚀工艺，提供理论依据。