Society critically depends on computers, cell phones and a myriad of specialized electrical circuits in nearly every technological product we use, from cars to door openers. What is not widely known is that these electrical circuits are largely contained in small semiconductor chips, that the dimensions of components of those circuits are approaching the size of atoms, and that the circuits are produced in machines containing the fourth state of matter ? plasma. Plasmas are ionized gases that can produce chemically reactive environments, and are composed of a mix of positive ions, negative ions, electrons and neutral atoms and molecules. Low pressure plasmas are essential to the fabrication of microelectronics devices by delivering fluxes of radicals and ions to a semiconductor wafer. These radicals and ions then etch (remove material), deposit (add material) and passivate (change surface composition) the wafer surface through many fabrication steps to create the devices. A voltage is also applied to the substrate holding the wafer to accelerate ions to high energies in order to activate these on-wafer processes. An important type of plasma used in microelectronics fabrication is an electronegative plasma in which the density of negative ions is much larger than electrons. These plasmas are very sensitive to operating conditions (such as power, pressure and gas mixture), with instabilities often. The quality of the devices being fabricated are sensitive to these instabilities and so tighter control of the plasma process is becoming more important. Pulsing the plasma (turning the power on-and-off) and pulsing the acceleration voltage results in higher precision components with smaller dimensions, whiich translates into more powerful electronics devices. Although pulsing provides many advantages, pulsing also produces instabilities. In order to optimize the plasma processes that are used to manufacture microelectronics devices, these instabilities in electronegative plasmas must be understood, controlled and, if possible, prevented.
In this project, experimental and computational investigations of pulsed electronegative plasmas are being conducted for the type of inductively coupled plasmas (ICPs) that are used for microelectronics fabrication. The goal is to quantify the interactions between the pulsed sources that produce the plasma and the pulsed biases that accelerate ions into the wafer, the onset of instabilities, and methods to control those instabilities. This investigation is being conducted in collaboration with our GOALI partner Lam Research Corp. We are making 3-dimensional, time dependent measurements of electron density, temperature, plasma potential, current density, magnetic fields and ion energy distributions using laser and electrical probe diagnostics. First principles modeling is being used to investigate fundamental plasma transport during pulsed transients, electrostatic-to-electromagnetic (E-H) transitions and interactions of pulsed sources and biases. The end result will be a greatly improved understanding of pulsed electronegative plasmas of the type used for materials processing, with this understanding being rapidly translated to practice by our GOALI partner.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
