Bulletin of the American Physical Society
60th Gaseous Electronics Conference
Volume 52, Number 9
Tuesday–Friday, October 2–5, 2007; Arlington, Virginia
Session VF1: Materials Processing in Low Pressure Plasmas II: Etching, deposition, new materials |
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Chair: Evgeniya Lock, Naval Research Laboratory Room: Doubletree Crystal City Crystal Ballroom A |
Friday, October 5, 2007 8:00AM - 8:30AM |
VF1.00001: Reaction of Fluorocarbon Species with Si and SiO$_{2}$ Surfaces Invited Speaker: Highly-selective high-aspect-ratio etching of SiO$_{2}$/Si is an indispensable key issue in the ULSI manufacturing processes. Furthermore, recent etching technology utilizes high density plasmas and requires complex fluorocarbon molecules such as C$_{4}$F$_{6}$ or C$_{5}$F$_{8}$ to achieve high etching speed and high etching selectivity. To improve etching performance, precise control of fluorocarbon plasmas based on deep understanding of radical reactions on SiO$_{2}$ and Si surfaces is required. Well-defined beam experiments in ultra-high vacuum are powerful for basic study of surface reactions. This paper shows elementary surface processes of fluorocarbon etching process, especially focused on the unique chemical reactivity of C$_{5}$F$_{8}$ molecule under co-incidence of Ar ion. The device was specially designed so as to enable \textit{in situ} measurements of etching yield and etched surfaces. Namely, Ar$^{+}$ beam at energies from 50 to 400 eV and various kinds of fluorocarbon neutral species (C$_{5}$F$_{8}$, C$_{4}$F$_{8}$, CF$_{2})$ are co-incident on a clean SiO$_{2}$ surface at a controlled flux. Etching yield of beam-incident surface is measured by profilometer while \textit{in-vacuuo} X-ray photoelectron spectroscopy (XPS) analysis reveals a time evolution of atomic composition of surface layer during the etching. In the case of C$_{4}$F$_{8}$/Ar$^{+}$, surface atomic composition after SiO$_{2}$ etching was almost similar to that of pure Ar$^{+}$ sputtering except for a small amount of F component. In the case of C$_{5}$F$_{8}$/Ar$^{+}$, however, formation of fluorocarbon layer after SiO$_{2}$ removal was observed as in the case of CF$_{2}$/Ar$^{+}$. The SiO$_{2}$ etching yield monotonically increased with the Ar$^{+}$ incident energy above 400 eV, and the etching yield of 2.4 was obtained at an Ar$^{+}$ incident energy of 900 eV with C$_{5}$F$_{8}$ co-incidence, which was about 3 and 1.5 times larger compared with pure Ar$^{+}$ sputtering and CF$_{2}$/Ar$^{+}$ co-incidence, respectively. These results suggest that fluorocarbon molecules themselves are important species in fluorocarbon etching plasma. [Preview Abstract] |
Friday, October 5, 2007 8:30AM - 8:45AM |
VF1.00002: Modeling high aspect ratio contact etch of SiO$_{2}$ Phillip Stout A Monte Carlo based feature scale model has been applied to the high aspect ratio contact etch of a dielectric stack. The model includes physical effects of transport to surface, specular and diffusive reflection within the feature, adsorption, surface diffusion, deposition and etching. Discussed will be 3D feature modeling of an etch sequence through an anti reflective coating / amorphous carbon / SiO$_{2}$ / SiN material stack. The effect of passivation, off normal ion angular distributions, and feature opening geometry on the etched profile will be discussed. The etch rate decreases as the aspect ratio of the contact increases due to the shadowing of etchant reactants from the etch front. The passivant buildup at the contact opening over the course of the etch also plays a role in the reduced etch rate with time. The passivant buildup can also reflect incident ions off normal into the feature contributing to a bowed etch profile. The amount of polymer (i.e. passivant) in the etch chemistry can transition profiles from bowed to tapered to etch stop. Off normal ion incidence can increase the etch rate due to off angle yield peaks and cause tilting of the etched profile. [Preview Abstract] |
Friday, October 5, 2007 8:45AM - 9:00AM |
VF1.00003: Time dependence analysis of the 3D profile charging during $SiO_2$ etching in $Ar^{+}$/$CF_4$ plasma Branislav Radjenovic, Marija Radmilovic-Radjenovic, Zoran Petrovic Damage to integrated circuits (ICs) during manufacturing as a result of charging of the dielectrics during finalization of interconnects is both reducing the profitability and reducing the ability to reach large sizes of microchips and make complex system integration on a single chip. The ability to simulate feature charging was added to the 3D level set profile evolution simulator. The ion and electron fluxes were computed along the feature using a Monte Carlo method. The surface potential profiles and electric field for the entire feature were generated by solving Laplace equation using finite elements method. Calculations were performed in the case of simplified model of $Ar^{+}$/$CF_4$ non-equilibrium plasma etching of $SiO_2$. The time necessary for the electric field in the feature to reach its steady-state value is potentially very important for the orderliness of the whole simulation cycle. Since the calculations show that this time is about several milliseconds, which is very short comparing to the etching time step (during which we assume that the etching rate is constant), it is reasonable to calculate steady-state values of the electric field in the beginning of every Monte-Carlo step and use this field subsequently, instead of devising a complex and computationally costly scheme for the recalculation of the field during particle fluxes calculations. [Preview Abstract] |
Friday, October 5, 2007 9:00AM - 9:15AM |
VF1.00004: Plasma Modeling for Cu barrier/seed applications Prashanth Kothnur, Ananth Bhoj, Ron Kinder Ionized Metal Physical Vapor Deposition (IMPVD) enables barrier/seed layer deposition in high aspect ratio trenches and vias for microelectronics fabrication. As device sizes continue to shrink, the capability to predict bulk plasma dynamics coupled with feature-scale evolution on the surface of the trench or via is becoming increasingly important. The focus of this talk is to describe a methodology for modeling IMPVD Cu deposition using a combination of reactor scale and feature scale modeling. The Hybrid Plasma Equipment Model (HPEM) is used to simulate the bulk plasma in the chamber and compute the flux and energy distributions of species at the wafer. The Monte Carlo Feature Profile Model (MCFPM) predicts trench profiles using the species fluxes and energies obtained from the HPEM and a detailed set of surface sticking coefficients and sputtering yield curves. The choice of input parameters to the MCFPM is guided by a fast string-based feature evolution algorithm (Feature 2D). Surface properties on the trench such as neutral and ion sticking coefficients, and sputtering yield curves are deduced by comparing Feature 2D results with experimental profiles. The overall procedure provides a method to predict the Cu seed layer profile on the trench as a function of chamber operating conditions. Results are presented for typical processing conditions (argon plasma sputtering a Cu target at 1 -15 mTorr) and varying source power and rf bias. [Preview Abstract] |
Friday, October 5, 2007 9:15AM - 9:30AM |
VF1.00005: Spatial distributions of Cu particulates in high-pressure magnetron sputtering plasmas studied by laser light scattering N. Nafarizal, N. Takada, K. Sasaki, M. Ikeda, Y. Sago Ionized physical vapor deposition (IPVD) is a new technique to deposit barrier and seed layers on the surface of narrow trenches and holes. In our previous works, we have found that the ionization ratio of metal atoms in a conventional magnetron sputtering plasma increased with the discharge pressure. However, the high--pressure plasmas may have a risk of the formation of particulates. In the present work, we detected Cu particulates produced in high--pressure magnetron sputtering plasmas by laser light scattering. We observed the scattered laser light in the gas phase of the sputtering plasma when the discharge pressure was higher than 200 mTorr. Typically, particulates were concentrated at the boundary between the bright plasma and the dark region. The peak of the scattered intensity was located adjacent to the ring anode of the magnetron sputtering source. The scattered intensity varied with time after the initiation of the discharge. Since the intensity of the scattered laser light is dependent on the mean size and the density of particulates, this result indicates the temporal variations of the size and the density of particulates. In addition, it was found that the scattered intensity was very sensitive to the discharge power and the gas pressure. [Preview Abstract] |
Friday, October 5, 2007 9:30AM - 9:45AM |
VF1.00006: Multi-hollow discharge plasma CVD reactor with magnets for highly stable a-Si:H film deposition Kazunori Koga, William M. Nakamura, Hiroshi Satou, Hiroomi Miyahara, Masaharu Shiratani Incorporation of amorphous silicon nanoparticles (clusters) has been related to a-Si:H films' light induced degradation [1]. In the present work, we have developed a multi-hollow discharge plasma CVD reactor in which we introduced magnets into the electrode to produce a magnetic field (400 G) along the holes' axis to increase the confinement of electrons of low kinetic energy $<$10eV. Due to such selective confinement of electrons, the generation rate of SiH$_{3}$ radicals, which is the main precursor of good films, increases; while the generation rate of SiH$_{2}$, which forms clusters, is reduced. By applying the magnetic field, we have obtained a deposition rate 20-100{\%} higher than that without the magnetic field. Moreover, the volume fraction of clusters in films deposited in the downstream region is 14-80{\%} lower when applying the magnetic field. These results indicate that a-Si:H of high stability can be deposited at high rate by applying the magnetic field to the electrodes. \newline \newline [1] M. Shiratani, K. Koga, N. Kaguchi, K. Bando, and Y. Watanabe, Thin Solid Films, \textbf{506-507}, 17 (2006). [Preview Abstract] |
Friday, October 5, 2007 9:45AM - 10:00AM |
VF1.00007: Control of structures of Carbon Nanowalls in plasma enhanced CVD Wakana Takeuchi, Yutaka Tokuda, Mineo Hiramatsu, Hiroyuki Kano, Masaru Hori Carbon nanowalls (CNWs), two-dimensional carbon nanostructures consisting of graphite sheets standing vertically on the substrate, have attracted much attention for several applications. In view of the practical application of CNWs, it is necessary to control their structure and electronic properties. In this study, we focused on the control of CNW structures. CNWs were fabricated on the Si substrate by the fluorocarbon plasma-enhanced CVD with H radical injection. We investigated the influence of O$_{2}$ addition to the mixture of C$_{2}$F$_{6}$/H$_{2}$ on the morphology and structure of CNWs. Raman spectroscopy was used to evaluate the structure of CNWs. The morphology and crystallinity of CNWs were found to be controlled by the O$_{2}$ addition. Raman spectra for all samples have a strong peak at 1590 cm$^{-1}$ (G-band) indicating the formation of a graphitized structure and another peak at 1350 cm$^{-1}$ (D-band) corresponding to the disorder-induced phonon mode. As a result of O$_{2}$ addition, width and peak intensity ratio of D/G bands of CNWs decreased. Oxygen atom would play a role of etching of disorder carbon phase and contribute to the higher graphitization. [Preview Abstract] |
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