REG: Engineering Research Equipment: A Mass Spectrometer with Ion Monitoring Capability for Measuring Ions and Molecular Species in Plasma Discharges

射频等离子体放电在半导体工业中用于等离子体沉积和等离子体蚀刻。在一个典型的反应堆中，在真空室中两个平行电极之间施加0.01到10托的射频电压。产生的电场将电子加速到非常高的能级。这些电子与分子发生碰撞，产生更多的电子、离子和高活性的中性自由基。然后，根据特定的应用，这些化学物质相互之间和固体表面发生反应。由于产生的气相组成将影响蚀刻或沉积的速率和质量，因此通过一个小孔对质量分析仪取样气体组成是有用的。除了中性反应物质的作用外，离子对固体（晶圆）表面的轰击也很重要。由于等离子体中电子和离子的电相互作用，在任何固体表面附近都会形成等离子体“护套”。这个鞘层包含一个电场，可以排斥电子，并将它们更好地控制在等离子体的中心。同样的电场会加速正离子向固体表面移动。因此，离子以巨大的能量（平均能量在几eV到几百eV之间）被定向到表面。这种定向高能离子轰击固体表面，在等离子体刻蚀应用中产生定向刻蚀，它可以改变等离子体辅助化学气相沉积（CVD）薄膜的薄膜性能。由于离子的重要作用，PI计划对离子轰击进行采样，随后分析离子能量分布和离子流的组成。质谱法是一种测定这些取样的中性物质或离子组成的技术。在采样不带电分子的情况下，这些分子首先通过电离室，在那里它们被具有足够能量的电子轰击以电离大部分分子。对于直接从等离子体中采样离子，不需要这一步。一旦离子产生或取样，它们就会通过一个质量过滤器（四极杆），该过滤器允许原子质量与电荷比（m/q）的范围很窄的离子通过。然后用法拉第笼或电子倍增器收集并测量以该m/q通过过滤器的离子通量。因此，通过在m/q范围内调谐，可以测量具有特定m/q的离子的分布。这是一项研究设备拨款（REG），用于购买具有离子监测能力的四极杆质谱仪，用于检查等离子体放电和化学气相沉积反应器中的中性分子和离子。

Radio-frequency plasma discharges are used in the semiconductor industry for plasma deposition and plasma etching. In a typical reactor, a radio-frequency (RF) voltage is applied between two parallel electrodes inside a vacuum chamber at 0.01 to 10 Torr. The electric fields created accelerate electrons to very high energy levels. These electrons collide with molecules to produce more electrons, ions, and highly reactive neutral radical species. These chemical species then react with each other and solid surfaces according to the particular application. Because the resultant composition of the gas phase will affect the rates and qualities of the etching or deposition, it is useful to sample the gas composition through a small orifice to a mass analyzer. Besides the role of neutral reactive species, the bombardment of the solid (wafer) surface by ions is also important. Because of the electrical interaction of electrons and ions in the plasma, a plasma "sheath" is formed near any solid surface. This sheath contains an electric field that repels electrons and keeps them better contained within the center of the plasma. The same electric field will accelerate positive ions towards the solid surface. Therefore, the ions are directed to the surface with substantial energy (mean energies of a few eV to several hundred eV). This directed, high- energy ion bombardment at solid surfaces produces directional etching in plasma etching applications, and it can alter film properties in plasma assisted chemical vapor deposition (CVD) of thin films. Because of this important role of ions, the PI plans to sample this ion bombardment with subsequent analysis of the ion energy distribution and the composition of this ion stream. Mass spectrometry is a technique to determine the composition of either of these sampled neutral species or ions. In the case of sampling uncharged molecules, these molecules first pass through an ionizing chamber where they are bombarded by electrons with sufficient energy to ionize a substantial fraction of the molecules. For sampling the ions directly from the plasma, this step is not needed. Once the ions are created or sampled, they pass through a mass filter (quadrupole) that allows ions with a narrow range of atomic mass to electrical charge ration (m/q) to pass through. The flux of ions that pass through the filter at this m/q are then collected and measured with a Faraday cage or electron multiplier. Thus by tuning through a range of m/q, the distribution of ions with particular m/q is measured. This is a Research Equipment Grant (REG) to purchase a quadrupole mass spectrometer with ion monitoring capabilities which will be used to examine the neutral molecular species and ionic species from plasma discharges and a chemical vapor deposition reactor.