Development of in-situ measurement method of sub-nm size particles in processing plasmas

了解等离子体过程中粒子的生长动力学是很重要的，因为它们对电子器件的制造是有害的，而且作为新材料也很有前途。然而，由于缺乏对尺寸小于10 nm的颗粒的检测方法，有关此类颗粒生长的信息非常有限。在这项研究中，我们发展了一种光子计数激光光散射(PCLLS)方法和一种将阈值光电发射方法与微波干涉测量相结合的方法(TPE-MI方法)，该方法可以检测到尺寸在1-10 nm、密度在10-6 cm-3以上的可检测颗粒。通过这些方法，我们揭示了在所谓的器件质量条件下硅烷射频等离子体中粒子的生长：1)亚纳米粒子的密度比等离子体正离子密度高一个数量级，并且大部分粒子是中性的；2)粒子在等离子体/鞘边界附近成核和生长，在那里产生了活跃的自由基；3)在粒子生长的初始阶段，由于短寿命SiH_2自由基的聚合物种的沉积，粒子生长。

It is important to understand growth kinetics of particles in processing plasmas, because they are harmful for fabrication of electronic devices and also promising as new materials. However, information on growth of particles below 10 nm in size is very limited because of lack of detection methods of such particles. In this study, we have developed a photon-counting laser-light-scattering (PCLLS) method detectable particles in 1-10 nm size and above 10^6cm^<-3> in density and a method (TPE-MI method), which is combined a threshold photoemission method with the microwave interferometry, detectable particles below a few rim in size and above 10^9cm^<-3> in density. By using these methods, we have revealed the following results regarding growth of particles in silane rf plasmas under so-called device-quality conditions : 1) density of sub-nm particles is by more than one order higher than the plasma positive ion density and most of the particles are neutral, 2) particles nucleate and grow around the plasma/sheath boundary where radicals are produced actively, 3) in the initial growth phase of particles, they grow due to deposition of polymerized species, which are originated from short lifetime SiH_2 radicals.