Bulletin of the American Physical Society
61st Annual Gaseous Electronics Conference
Volume 53, Number 10
Monday–Friday, October 13–17, 2008; Dallas, Texas
Session QR1: Fluorocarbon Plasmas II |
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Chair: J-P Booth, LPTP Ecole Polytechnique, France, and MJ Brunger, Flinders University, SA, Australia Room: Salon E |
Thursday, October 16, 2008 10:00AM - 10:30AM |
QR1.00001: Control of Fluorocarbon Plasmas for Next-Generation ULSI Devices Invited Speaker: Fluorocarbon (C-F) plasma is widely used in the etching of dielectric materials (SiO2, Si3N4, and SiOCH). Models for controlling C-F plasma [1] and controlling the surface reaction during etching [2] have been proposed. Using these models, good etching results can be obtained after optimizing the absolute densities of reactive species as well as the ion energies. However, next-generation ULSI devices will have smaller pattern sizes, so we need to reduce the pattern-width variation and the degradation thickness of each stacked film to within several nanometers. Even small plasma fluctuations can severely degrade device properties. Furthermore, the densities of reactive species (CFx, O, H, etc.) are sensitive to the surface condition of the chamber wall. The etching properties, therefore, can be shifted by changes in chamber parts, dry cleaning, and/or polymer or metal deposition on chamber walls. To suppress fluctuations in etching performance, we need to understand and completely control the plasma-wall reactions. Using an equipment engineering system (EES) is one way to predict plasma conditions in real time. (An EES is a tool for statistical calculation of etching properties that uses all signals from an etching system, such as flow rate, power, capacitance of matching network, etc.) We analyzed results of plasma-wall reactions and improved the prediction method of etch rate fluctuation using an EES. The simultaneous use of a physical model (supported by in-situ signal monitoring of plasma parameters) and a statistical model is promising for suppressing plasma fluctuation in mass production. \newline \newline [1] T. Tatsumi et al, Jpn. J. Appl. Phys., Part 1 37 (1998) 2394. \newline [2] T. Tatsumi, Applied Surface Science, 253 (2007) 6716. [Preview Abstract] |
Thursday, October 16, 2008 10:30AM - 11:00AM |
QR1.00002: New insights into fundamental ion-surface interactions Invited Speaker: Collisions of ions with surfaces at low energy ($<$1 keV) are important in reactive ion etching of semiconductors, dielectrics, and metals. For example, ion bombardment strongly influences etch rates, anisotropy, and selectivity through physical sputtering, momentum-assisted product removal, and modification of reaction rates. Fundamental understanding of these issues requires detailed information about scattering dynamics. We report results from beam scattering experiments involving mass-filtered ions (F$^{+}$ and CF$_{x}^{+})$ with tunable energy (50-1000 eV) and high flux off several surfaces (Si, Al, Ag). Topics to be discussed include: (1) electronic excitations in hard collision events (inelastic losses and F$^{++}$ formation); (2) pre-collision fragmentation of CF$_{x}^{+}$ ions which result in fast exit products such as C$^{+}$, F$^{-}$, and CF$^{-}$; (3) high yields of fast F$^{-}$; and (4) F$_{2}^{-}$ formation via an Eley-Rideal mechanism. For instance, energy losses for single-scatter events of F$^{+}$ off Si and Al show that F$^{++}$ can be formed through double electron promotion which ``turns-on'' above a critical collision energy. Velocity analysis of daughter fragments from CF$_{3}^{+}$ impact on Si and Ag point to projectile fragmentation before the hard collision step. Finally, energy spectra of F$^{+}$, F$^{-}$, and F$_{2}^{-}$ leaving Si and Ag show three distinct scattering channels: single-scatter binary-like elastic events, another at low energy that cannot be explained as simple sputtering, and still another where fast F$_{2}^{-}$ is formed via abstraction. These results illustrate that product species can suffer significant inelastic losses as well as show faster-than-SIMS behavior which may have dramatic effects on profile evolution in plasma etching. [Preview Abstract] |
Thursday, October 16, 2008 11:00AM - 11:30AM |
QR1.00003: Electron Scattering from Fluorocarbons and Their Radicals Invited Speaker: In spite of their importance to industry, experimental studies of electron interactions with highly-reactive CF$_x$ radicals are seldom reported in the literature. A crossed electron-molecular beam experiment, featuring a skimmed nozzle beam with pyrolytic radical production, has been used to measured absolute cross sections for electron scattering from the CF$_2$ molecule. A new technique for placing measured cross sections on an absolute scale is applied for molecular beams formed as skimmed supersonic jets. Absolute differential cross sections for CF$_2$ are reported for incident electron energies of 3-50 eV and over an angular range of 15-135 degrees. Integral cross sections are subsequently derived from those data. The present data are compared to theoretical predictions for the differential and integral scattering cross sections. [Preview Abstract] |
Thursday, October 16, 2008 11:30AM - 12:00PM |
QR1.00004: Molecular dynamics simulations of blanket and small feature etching in fluorocarbon- and fluorine-containing plasmas Invited Speaker: As device scale-down continues, fundamental understanding of etch mechanisms at very small dimensions ($<$10 nm) is becoming increasingly important for the development and control of future plasma processing steps. We utilize molecular dynamics (MD) simulations to examine the interactions of representative plasma species from typical fluorocarbon (FC) and F containing etch systems on Si substrates. Our current MD work examines the etching of very small ($<$ 5 nm) features. By using an amorphous C masking layer (or confined beams of the desired dimension with no masking layer), ions (Ar$^{+}$, CF$_{x}^{+})$ and radicals (CF$_{x}$ and F) were used to fabricate trenches and holes in Si substrates. The nature and formation of the feature sidewalls are examined in detail, and the limitations of hole size are explored, including the collapse of the masking layer at very small dimensions ($\sim $2 nm) and the transport of etchants and products into and out of the feature. For the maskless confined beam experiments, etch limitations are primarily transport related as depth increases. In order to maintain pattern transfer fidelity and limit mask collapse, `pulsed' etching was simulated by alternating bombardment of the surface with CF$_{x}$ radicals and Ar$^{+}$ or Ar$^{+}$/F. The chemistries for this scheme were chosen to optimize selectivity between the C mask and the Si substrate. We compare the small feature simulations to our previous MD studies of blanket etching of Si with various FC/F/Ar$^{+}$ ratios. These simulations established a clear relationship between FC layer thickness and the Si etch yield at steady-state and showed semi-quantitative agreement with plasma experiments in the literature. We discuss how these effects translate to the Si yields in small feature etching, in relation to the surface compositions along the sidewalls and bottoms of the features. [Preview Abstract] |
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