Optical emission spectroscopy as a tool for studying, optimizing, and monitoring plasma-assisted atomic layer deposition processes
(Color online) (a) Schematic representation of the Oxford Instruments FlexAL reactor for plasma-assisted atomic layer deposition (Ref. 24) on which the OES equipment is implemented. The optical emission signal can either be obtained at the top of the plasma source (as indicated in the figure) or in the downstream region. (b) Photograph of the upper part of the FlexAL reactor showing the ICP plasma source, the top of the chamber, and the gate valve in between the chamber and the plasma source. The OES spectrometer (Ocean Optics USB4000, bottom left) is connected with an optical fiber to a window installed on a vacuum port in the downstream region.
(Color online) Emission spectra from (a) an plasma, (b) a plasma, (c) a plasma, (d) a plasma from a (10:1) mixture, and (e) a plasma. All spectra have been measured on the FlexAL reactor with plasma powers, gas flows, and pressures in the range of , , and , respectively. The most important spectral features have been identified in the figures. Some of the emission lines in the figures are in saturation.
(Color online) (a) Emission spectrum from a steady-state plasma and a spectrum of an plasma exposure during a plasma-assisted ALD cycle of . The latter spectrum was recorded after an dosing step during the first of plasma exposure, whereas the steady-state plasma spectrum was recorded well after the plasma half-reaction reached saturation. (b) Time-resolved intensities of emission lines related to plasma species and reaction products after an dose had preceded. The plasma was ignited at time .
(Color online) (a) Emission spectrum from a steady-state plasma and a spectrum of an plasma exposure during a plasma-assisted ALD cycle of . The latter spectrum was recorded after a dosing step during the first of plasma exposure. (b) Time-resolved intensities of emission lines of plasma species and reaction products after a dose had preceded. The plasma was ignited at time .
(Color online) (a) Emission spectrum from a steady-state plasma and a spectrum of a plasma exposure during a plasma-assisted ALD cycle of TaN. The latter spectrum was recorded after a dosing step during the first of plasma exposure. The inset shows the emission spectra around in more detail. (b) Time-resolved emission intensity at during the plasma exposure step for an ALD cycle with and without dosing step. The plasma was ignited at time .
(Color online) (a) Time-integrated emission intensity at , related to CN emission, as a function of the exposure time during plasma-assisted ALD of TaN. The emission intensity for zero exposure time is due to emission from the plasma. (b) Time-integrated emission intensities of O plasma species and H and CO reaction products as a function of the number of consecutive doses in the plasma-assisted ALD cycle. The lines serve as guides to the eye.
(Color online) (a) Time-resolved emission intensity recorded at related to atomic oxygen during plasma-assisted ALD of . Failures of plasma ignition can be observed for the fourth and sixth ALD cycles. (b) Time-resolved emission intensities recorded during plasma-assisted ALD of TiN in which a plasma is employed. The dashed line indicates the point at which the gas flow fails.
(Color online) (a) Evolution of the emission intensity at related to atomic hydrogen recorded during plasma-assisted ALD of TiN without reactor wall conditioning prior to deposition. (b) Integrated emission intensities per cycle at as a function of cycle number for plasma-assisted ALD of TiN in a reactor in which the reactor wall was conditioned by various procedures.
Overview of plasma-assisted ALD deposition processes for which optical emission spectroscopy results are reported in this work.
Overview of spectral lines that can be used for time-resolved OES measurements to investigate and monitor plasma-assisted ALD processes (Refs. 31 and 32). The most intense spectral line of the emission systems has been selected unless the most intense spectral line overlaps with other emission lines or is too intense to measure conveniently.
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