等离子体监测with Modular, High-resolution Spectroscopy

Background

等离子体是一种通电的气体状状态，其中已经激发或电离以形成游离电子和离子的一部分原子。当激励中性的电子返回到地状态时，等离子体发射特异于等离子体中的原子的波长的光。发射光的光谱分布用于确定等离子体的组成。使用一系列高能量方法形成等离子体，以电离包括热，高功率激光器，微波，电力和射频的原子。

Plasma is used in industries includingsemiconductor manufacturingfor applications including elemental analysis, film deposition, plasma etching and surface cleaning. Precise monitoring of plasma-based processes can help to minimize wafer contamination, improve quality and optimize production yields.

等离子体监测

通过对等离子体样品测量的发射光谱的等离子体监测可以提供详细的元素分析和测定控制基于等离子体的过程所需的临界等离子体参数。排放线的波长识别等离子体中存在的元件，发射线强度用于实时定量粒子和电子密度进行过程控制。

包括气体混合物，等离子体温度和颗粒密度的参数对于控制等离子体工艺至关重要。通过将各种气体或颗粒引入等离子体室的各种气体或颗粒的改变将改变等离子体特性，影响等离子体衬底相互作用。实时监测和控制等离子体的能力导致改进的过程和结果。

例如，等离子体监测对于基于等离子体的蚀刻过程中的过程控制很重要。在半导体工业中，使用光刻技术制造和操纵晶片。蚀刻是该过程的主要部分，其中材料可以层叠成非常具体的厚度。当在晶片表面上蚀刻层时，等离子体监测用于通过晶片层遵循蚀刻，并确定何时等离子体已完全蚀刻特定层并达到接下来。通过监测蚀刻期间等离子体产生的发射线，可以精确地遵循蚀刻工艺。该端点检测对于使用半导体材料的生产至关重要plasma-based etching processes.

等离子体监测设置

可以使用像这样的高分辨率光谱仪使用灵活的模块化设置来管理等离子体监控HR系列orMaya2000 Profrom Ocean Insight (the latter is a popular option for UV gases). For a modular setup, an HR spectrometer can be combined withsolarization-resistant optical fiber从等离子体f获得定性排放数据ormed in a chamber. If quantitative measurements are required, users can add a third-party spectral library against which to compare data and quickly identify unknown emission lines, peaks and bands.

An important consideration when monitoring plasma formed in a vacuum chamber is the interface to the chamber. Instrument components can be introduced into a vacuum chamber or set up to view the plasma through a viewport.Vacuum feedthrough assembliesor custom fibers designed to withstand the harsh conditions in the chamber can be used to couple components into the plasma chamber.

为了通过视口监测等离词，根据要测量的等离子体场的尺寸，可能需要像余弦校正器或准直透镜等采样附件。没有采样配件，距光纤到等离子体的距离将决定成像区域。使用准直镜头进行更加局部的收集区域，或在180°视场上的光收集余弦校正器。

Measurement Conditions

HR系列高分辨率光谱仪用于测量氩等离子体发射的变化，因为将其它气体引入等离子体室。利用光谱仪，光纤和余弦校正器收集封闭反应室中包含的等离子体的等离子体通过腔室外的小窗口收集光谱数据（图1）。

Figure 1: A modular spectrometer setup can be configured for plasma measurement in a vacuum chamber.

An HR2000+ high resolution spectrometer (~1.1 nm FWHM optical resolution) configured to measure emission from 200-1100 nm (Grating HC-1, SLIT-25) was coupled to a cosine corrector (CC-3-UV) using a solarization-resistant fiber (QP400-1-SR-BX fiber). ACC-3-UV余弦校正器选择采样配件被选择从等离子体室获取数据，并解决测量窗口的等离子体强度和不均匀污垢的差异。其他采样选项包括准直镜片和真空馈通。

结果

通过等离子体室的窗口测量的氩等离子体的光谱如图2所示。来自690-900nm的强光谱线是来自中性氩（Ar i）的排放线，其较低强度从400-650nm引起的单电离氩原子（AR II）。图2中所示的发射光谱是测量用于等离子体发射的富光谱数据的一个很好的例子。该光谱信息可用于确定半导体制造期间用于监视和控制基于等离子体的过程的一系列关键参数。

Figure 2: Emission of argon plasma is measured through a vacuum chamber window.

Hydrogen gas is a secondary gas that can be added to argon plasma to change its properties. In Figure 3, the effect of adding hydrogen gas to argon plasma is shown as increasing concentrations of hydrogen gas are added to the chamber. The ability of the hydrogen gas to change the characteristics of the argon plasma is clearly shown by a decrease in the intensity of the argon lines between 700-900 nm while the increasing concentration of hydrogen gas is reflected in the appearance of hydrogen lines between 350-450 nm. These spectra demonstrate the power of measuring plasma emission in real time to assess the impact of a secondary gas on plasma properties. The spectral changes observed could be used to ensure optimal amounts of secondary gases are added to the chamber to achieve the desired plasma characteristics.

Figure 3: Adding hydrogen gas to the argon plasma changes its spectral properties.

In Figures 4-5, emission spectra measured for the plasma before and after the addition of sheath gas to the chamber are shown. Sheath gas is used to decrease contact between the sample injector and the sample to reduce problems due to sample deposition and carryover. In Figure 4, the argon plasma emission spectrum is shown before the addition of sheath gas. The emission spectrum measured after sheath gas addition is shown in Figure 5. The addition of sheath gas leads to changes in the argon emission spectrum as seen in the loss of the broad spectral lines just below 400 nm and at ~520 nm.

Figure 4: Argon plasma emission is measured in the vacuum chamber before the addition of sheath gas.

图5：随着鞘气的添加，氩气发射特性明显不同，低于400nm和〜520nm。

结论

m UV-Vis-NIR光谱学是一个功能强大的方法easuring plasma emission to enable elemental analysis and precise control of plasma-based processes. The data shown here illustrate the power of the modular spectroscopy approach for plasma monitoring. The HR2000+ high resolution spectrometer and modular spectroscopy approach worked well to measure plasma emission spectra through the window of a plasma chamber as chamber conditions were adjusted.

Additional plasma monitoring options are available, including the Maya2000 Pro, which has excellent response in the UV. Also, spectrometers and subsystems can be integrated into other devices and combined with machine learning tools for even more sophisticated control of plasma chamber conditions.

Download a complete version of this application note as a PDF.