Bulletin of the American Physical Society
66th Annual Gaseous Electronics Conference
Volume 58, Number 8
Monday–Friday, September 30–October 4 2013; Princeton, New Jersey
Session LW1: Plasma Etching |
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Chair: Vincent Donnelly, University of Houston Room: Ballroom I |
Wednesday, October 2, 2013 3:30PM - 4:00PM |
LW1.00001: Challenges in the Plasma Etch Process Development in the sub-20nm Technology Nodes Invited Speaker: Kaushik Kumar For multiple generations of semiconductor technologies, RF plasmas have provided a reliable platform for critical and non-critical patterning applications. The electron temperature of processes in a RF plasma is typically several electron volts. A substantial portion of the electron population is within the energy range accessible for different types of electron collision processes, such as electron collision dissociation and dissociative electron attachment. When these electron processes occur within a small distance above the wafer, the neutral species, radicals and excited molecules, generated from these processes take part in etching reactions impacting selectivity, ARDE and micro-loading. The introduction of finFET devices at 22nm technology node at Intel marks the transition of planar devices to 3-dimensional devices, which add to the challenges to etch process in fabricating such devices. In the sub-32nm technology node, Back-end-of-the-line made a change with the implementation of Trench First Metal Hard Mask (TFMHM) integration scheme, which has hence gained traction and become the preferred integration of low-k materials for BEOL. This integration scheme also enables Self-Aligned Via (SAV) patterning which prevents via CD growth and confines via by line trenches to better control via to line spacing. In addition to this, lack of scaling of 193nm Lithography and non-availability of EUV based lithography beyond concept, has placed focus on novel multiple patterning schemes. This added complexity has resulted in multiple etch schemes to enable technology scaling below 80nm Pitches, as shown by the memory manufacturers. Double-Patterning and Quad-Patterning have become increasingly used techniques to achieve 64nm, 56nm and 45nm Pitch technologies in Back-end-of-the-line. Challenges associated in the plasma etching of these multiple integration schemes will be discussed in the presentation.\\[4pt] In collaboration with A. Ranjan, TEL Technology Center, America, LLC, 255 Fuller Rd., Suite 244, Albany, New York, 12203. [Preview Abstract] |
Wednesday, October 2, 2013 4:00PM - 4:15PM |
LW1.00002: Photo-assisted etching of silicon in halogen-containing plasmas Shyam Sridhar, Weiye Zhu, Lei Liu, Demetre Economou, Vincent Donnelly Cl$_{2}$, Br$_{2}$, HBr, and HBr/Cl$_{2}$ feed gases diluted in Ar were used to study etching of p-type Si(100) in a RF inductively coupled, Faraday-shielded plasma. Etching rates were measured as a function of ion energy. Etching at ion energies below the threshold for ion-assisted etching was observed in all cases, with Br$_{2}$/Ar and HBr/Cl$_{2}$/Ar plasmas having the lowest and highest sub-threshold etching rates, respectively. Sub-threshold etching rates scaled with the product of surface halogen coverage (measured by XPS) and Ar emission intensity (7504{\AA}). Etching rates measured under MgF$_{2}$, quartz, and opaque windows, or biased grids, showed that sub-threshold etching is due to photon-stimulated processes on the surface, with VUV photons being much more effective than longer wavelengths. Scanning electron and atomic force microscopy (SEM and AFM) revealed that photo-etched surfaces were very rough, quite likely due to the inability of the photo-assisted process to remove contaminants from the surface. Photo-assisted etching in Cl$_{2}$/Ar plasmas resulted in the formation of 4-sided pyramidal features with bases that form an angle of 45$^{\circ}$ with respect to \textless 110\textgreater\ cleavage planes, suggesting that the photo-assisted etching process is sensitive to crystal orientation, at least for chlorine. [Preview Abstract] |
Wednesday, October 2, 2013 4:15PM - 4:30PM |
LW1.00003: Effect of TCP Pulsing in Photon Induced Sub-threshold Etching of Si Juline Shoeb, Saravanapriyan Sriraman, Tom Kamp, Alex Paterson With decrease in device sizes, plasma damage minimization of Si becomes very important. During over-etch processes a passivation layer protects Si from ions. Even below etching threshold energy, UV photons can cleave Si-Si bonds that acts as a precursor for Si etching. In HBr/He/O$_{2}$ plasmas, 58.4nm photons from He(2$^{\mathrm{1}}$p) and 130nm photons from O(3s) can result in sub-threshold etching of Si by Si-Si bond cleaving followed by Si etching as volatile SiBr$_{4}$.\footnote{J. Shoeb, S. Sriraman, T. Kamp, and A. Paterson, 65$^{\mathrm{th}}$ GEC, Austin TX, (2012).} Literature reports reduction in UV damage with ICP power pulsing.\footnote{C. P. Etienne, et. al., J. Vac. Sci. Technol. B \textbf{31(1)}, (2012).} During pulse-off period, electron temperature drops thereby reducing meta-stable densities responsible for photon emission. Reducing radical and ion density and photon fluxes, pulsed plasmas possibly can reduce sub-threshold Si etching.\footnote{Ibid.} In this talk, a comparison of sub-threshold damage of Si between continuous and pulsed HBr/He/O$_{2}$ plasmas using modeling and experiments will be presented. [Preview Abstract] |
Wednesday, October 2, 2013 4:30PM - 4:45PM |
LW1.00004: Vacuum ultraviolet photon fluxes in argon-containing inductively coupled plasmas S.B. Radovanov, H.M. Persing, S. Wang, C.L. Culver, J.B. Boffard, C.C. Lin, A.E. Wendt Vacuum ultraviolet (VUV) photons emitted from excited atomic states are ubiquitous in material processing plasmas. Damage of materials is induced by energy transfer from the VUV photons to the surface, causing disorder in the surface region, surface reactions, and affecting bonds in the material bulk. Monitoring of the surface flux of VUV photons from inductively coupled plasmas (ICP) and its dependence on discharge parameters is thus highly desirable. Results of non-invasive, direct windowless VUV detection using a photosensitive diode will be presented. Relative VUV fluxes were also obtained using a sodium salicylate coating on the inside of a vacuum window, converting VUV into visible light detected through the vacuum window. The coating is sensitive to wavelengths in the range 80-300 nm, while the photodiode is only sensitive to wavelengths below 120 nm. In argon the VUV emissions are primarily produced by spontaneous decay from $3p^54s$ resonance levels (1s$_2$,1s$_4$) and may be reabsorbed by ground state atoms. Real-time resonance level concentrations were measured [1] and used to predict the VUV photon flux at the detector for a range of different ICP pressures, powers, and for various admixtures of Ar with N$_2$, and H$_2$.\\[4pt] [1] JVSTA \textbf{31} (2013), 021303. [Preview Abstract] |
Wednesday, October 2, 2013 4:45PM - 5:00PM |
LW1.00005: Reduction Mechanism of Surface Roughness on ArF-Photoresist Using C$_{5}$HF$_{7}$ Gas Plasma Yudai Miyawaki, Keigo Takeda, Hiroki Kondo, Kenji Ishikawa, Makoto Sekine, Azumi Ito, Hirokazu Matsumoto, Masaru Hori Fluorocarbon (FC) plasmas have been used in reactive ion etch processes for the fabrication of high-aspect-ratio-contact-hole on SiO$_{2}$. There are some needs, such as high selectivity over photoresist (PR), Si$_{3}$N$_{4}$ and Si, avoiding surface roughness formation on ArF- PR. C$_{5}$F$_{8}$ gas is known to improve the SiO$_{2}$ selectivity compared with C$_{4}$F$_{8}$ and conventional gas chemistries. Recently, we achieved that highly selective etching of SiO$_{2}$ against PR, Si$_{3}$N$_{4}$ and Si using a newly-designed gas, C$_{5}$HF$_{7}$, and O$_{2}$, Ar gas mixture. So far, we have investigated the etch performances and its mechanism using C$_{5}$HF$_{7}$ gas chemistry through comparison with C$_{5}$F$_{8}$ gas. In this study, we focused on the mechanism of reducing the surface roughness formation on ArF-PR during SiO$_{2}$ etching in the C$_{5}$HF$_{7}$ gas chemistry. The plasma etching time dependency of surface morphology on ArF-PR was compared with the case of C$_{5}$F$_{8}$. For C$_{5}$F$_{8}$/O$_{2}$/Ar plasma, surface roughness increased. For C$_{5}$HF$_{7}$/O$_{2}$/Ar plasma, RMS roughness about 2 nm was formed on the PR surface at 5 sec. As the time elapsing, surface roughness stayed constant. The RMS roughness caused by C$_{5}$HF$_{7}$ gas chemistry was lower than that of C$_{5}$F$_{8}$. Since F atoms in FC film were reduced by hydrofluorocarbon species, CxHFy, the FC polymerization was enhanced selectively on PR to form a thicker FC film that protects the PR surface from ion bombardments, while keeping the high etch rate for SiO$_{2}$. [Preview Abstract] |
Wednesday, October 2, 2013 5:00PM - 5:15PM |
LW1.00006: Molecular Dynamics Analysis of Surface Reaction Kinetics during Si Etching in Cl-based Plasmas: Effects of Etch By-Products Ion Incidence Nobuya Nakazaki, Yoshinori Takao, Koji Eriguchi, Kouichi Ono Profile anomalies and surface roughness are critical issues to be resolved in plasma etching of nanometer-scale microelectronic devices, which in turn requires a better understanding of the effects of ion incident energy and angle on surface reaction kinetics. This paper presents a classical molecular dynamics (MD) simulation of Si etching by energetic Cl$^{+}$ and SiCl$_{x}^{+}$ ($x=$ 1--4) ion beams at normal incidence with different energies $E_{i}=$ 20--500 eV, where the improved Stillinger-Weber interatomic potential was used for Si/Cl system. Emphasis is placed on differences in the etching mechanisms between the etchant and etch by-products ion incidences. Numerical results indicated that in Cl$^{+}$ incidence, the Si etch yield increases with increasing $E_{i}$; on the other hand, in SiCl$^{\mathrm{+}}$ incidence, the deposition of Si atoms (or minus Si etch yield) occurs at lower $E_{i}\le $ 300 eV while the etching occurs at high $E_{i}$ \textgreater\ 300 eV. In addition, in Cl$^{+}$ incidence, the thickness of surface reaction layers and the coverage (or concentration) of Cl atoms therein increase with increasing $E_{i}$, while in SiCl$^{\mathrm{+}}$ incidence, the surface layer thickness and the Cl coverage are large at lower $E_{i}$ owing to deposition. [Preview Abstract] |
Wednesday, October 2, 2013 5:15PM - 5:30PM |
LW1.00007: Simulation of microwave pulsing in a radial line slot antenna etch process reactor Rochan Upadhyay, Kiyotaka Ishibashi, Laxminarayan Raja The radial line slot antenna reactor couples the microwave power to a process plasma through a slot antenna. This arrangement leads to efficient generation of plasma with high electron energy adjacent to the window and a lower energy near wafer surfaces. This arrangement is beneficial for low ion energy applications such as soft etching or thin film processing. With increased charge densities, charge-up damage of dielectric surfaces can be a problem that can be addressed though plasma pulsing strategies in electronegative feed gases. The periodic power-off cycle results in an afterglow where electron attachment forms large amounts of negative ions that when extracted to the wafer surface, reduces the effects of positive charge trapping on the surface. We use computational modeling to investigate the effect of microwave pulsing on the negative ion generation rates for high density HBr and CF4 plasmas. We discuss improvements to a plasma chemistry mechanism for the pulsed plasma regime. Our results verify much larger negative ion to electron density ratios compared to the continuous (un-pulsed) case for both HBr and CF4 gases. Results also indicate greater plasma uniformity due to diffusion of positive and negative ions during the power-off phase of the pulse. [Preview Abstract] |
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