ELEC 7730 02’

1. Analysis of etched low-k organic material surface Abstract authors: Keisuke Nakamura, Sumio Sekiyama, Hiroshi Yanazawa Presented by Yu-Chun Chen October 23, 2002 ELEC 7730 02’

2. Introduction • Low-k material: Interlayer dielectrics in order to reduce RC delay (ULSI) • Gas mixtures of N2 and H2: Commonly used for etching of low-k organic material • This paper: Characterized the surface of low-k organic materials after exposure to various etching plasma ELEC 7730 02'

3. Outline • NLD • Experimental process • XPS • TOF-SIMS • Conclusions ELEC 7730 02'

4. NLD(Neutral Loop Discharge) Set on a vacuum chamber RF antenna NL Substrate Schematic diagram of experimental apparatus Ref.: Keisuke Nakamura, Sumio Sekiyama, and Hiroshi Yanazawa, “Analysis of etched low-k organic material surface”. ELEC 7730 02'

5. Experimental Process • Reactor: Neutral-loop-discharge plasma • Etching sample: SiLKTM samples • Gas mixtures: 1. Pure N2 (150nm/min) 2. N2 and H2 (220nm/min) 3. Pure NH3 (280nm/min) • To analyze etched surface: 1. XPS 2. TOF-SIMS ELEC 7730 02'

6. SiLKTM • Dow chemical company • Features: 1. Aromatic hydrocarbon (Fluorine-free) 2. Low dielectric constant organic polymer 3. High heat resistance 4. Compatible with Cu dual-damascene process and Al gap-filling ELEC 7730 02'

7. SiLKTM • Characteristics: Ref.: www.hitachi-chem.co.jp, Hitachi chemical comapny ELEC 7730 02'

8. XPS(X-ray Photoelectron Spectroscopy) • Also called ESCA, electron spectroscopy for chemical analysis • Not sensitive to hydrogen or helium, capable of detecting all other materials Ref.: www.nrel.gov, National renewable energy laboratory ELEC 7730 02'

9. XPS(X-ray photoelectron spectroscopy) • For XPS, Al Kalpha (1486.6eV) or Mg Kalpha (1253.6eV) are often the photon energies of choice. The XPS technique is highly surface specific due to the short range of the photoelectrons that are excited from the solid. The energy of the photoelectrons leaving the sample are determined and will give a spectrum with a series of photoelectron peaks. The binding energy of the peaks are characteristic of each element.The peak areas can be used to determine the composition of the materials surface. The shape of each peak and the binding energy can be slightly altered by the chemical state of the emitting atoms. Ref.: www.uksaf.org, Surface science techniques ELEC 7730 02'

10. XPS Schematic diagram of a core electron ejected by X-rays to produce a photoelectron Ref.: Joseph Lambert, Charles McLaughlin, CatherineShawl, Liang Xue, “X-ray Photoelectron Spectroscopy and Archaeology” ELEC 7730 02'

11. XPS Survey of X-ray photoelectron spectroscopy: fluorspar bead (mid-western United States) Ref.: Lambert, J. B.; McLaughlin, C. D. Archaeometry 1976, 18, 169. ELEC 7730 02'

12. XPS XPS spectra of etched SiLKTM surface Ref.: Keisuke Nakamura, Sumio Sekiyama, and Hiroshi Yanazawa, “Analysis of etched low-k organic material surface”. ELEC 7730 02'

13. XPS spectra • A strong C1s peak and an O1s peak are shown in reference spectrum. • By etching: 1. a N1s peak appears. 2. an O1s peak becomes stronger ELEC 7730 02'

14. XPS results Atom concentration ratios calculated from XPS results: In the lower etch rate process, the more nitrogen atoms consist in surface region. Ref.: Keisuke Nakamura, Sumio Sekiyama, and Hiroshi Yanazawa, “Analysis of etched low-k organic material surface”. ELEC 7730 02'

15. TOF-SIMS • Time-Of-Flight Secondary Ion Mass Spectrometry • TOF-SIMS is a surface analytical technique that uses an ion beam to remove small numbers of atoms from the outermost atomic layer of a surface. A short pulse of primary ions strikes the surface, and the secondary ions produced in the sputtering process are extracted from the sample surface and into a time-of-flight mass spectro-meter. These secondary ions are dispersed in time according to their velocities. Ref.: www.uwo.ca/ssw/services, Surface science ELEC 7730 02'

16. Advantages of TOF-SIMS • The technique has ultra-high sensitivity to surface layers (one atomic thickness), and detection of atomic concentrations as low as 10 ppm. • Molecular fragmentation patterns are characteristic of the molecular or crystalline structure of the surface and its reaction products. • Distribution of organics and inorganics can be measured on a surface with a sub-micron lateral distribution. • Surface layers of insulating materials, including minerals, polymers, organic, and biological materials, can be analyzed readily. • TOF-SIMS produces secondary electron (SE) images down to a 50 nm lateral resolution, and back-scattered ion (BSI) images, and SIMS images with lateral resolution down to 100 nm for elements, or 0.5 mm for big molecules.  Ref.: www.uwo.ca/ssw/services, Surface science ELEC 7730 02'

17. TOF-SIMS TOF-SIMS provides spectroscopy for characterization of chemical composition, imaging for determining the distribution of chemical species, and depth profiling for thin film characterization. Ref.: www.phi.com, Physical electronics ELEC 7730 02'

18. TOF-SIMS results TOF-SIMS data focused on the fragments that consist of NH2- base: In the higher etch rate process, the more fragments consist of NH2-base are observed. Ref.: Keisuke Nakamura, Sumio Sekiyama, and Hiroshi Yanazawa, “Analysis of etched low-k organic material surface”. ELEC 7730 02'

19. Conclusion • N2: 1. Lower etch rate 2. N2 ions/molecules: Play an important role in etching reaction, and produce byproducts that have low volatility 3. These byproducts don’t desorb from the surface easily, and therefore nitrogen atom concentration ratio is higher in the surface region. ELEC 7730 02'

20. Conclusion • N2/H2 & NH3: 1. Higher etch rate 2. More NHX ions/molecules: Consist in those process plasmas 3. These ions/molecules produce volatile byproducts, and these byproducts desorb from the surface. Therefore nitrogen atom concentration ratio is lower in the surface region. ELEC 7730 02'