Measurements of Metal Alkylamide Density during Atomic Layer Deposition Using a Mid-Infrared Light-Emitting Diode (LED) Source

Abstract

A nondispersive infrared (NDIR) gas analyzer that utilizes a mid-infrared light emitting diode (LED) source was demonstrated for monitoring the metal alkylamide compound tetrakis(dimethylamido) titanium (TDMAT), Ti[N(CH3)2]4. This NDIR gas analyzer was based on direct absorption measurement of TDMAT vapor in the C-H stretching spectral region, a spectral region accessed using a LED with a nominal emission center wavelength of 3.65 μm. The sensitivity of this technique to TDMAT was determined by comparing the absorbance measured using this technique to the TDMAT density as determined using in situ Fourier transform IR (FT-IR) spectroscopy. Fourier transform IR spectroscopy was employed because this technique could be used to (1) quantify TDMAT density in the presence of a carrier gas (the presence of which precludes the use of a capacitance manometer to establish TDMAT density) and (2) distinguish between TDMAT and other gas-phase species containing IR-active C-H stretching modes (allowing separation of the signal from the LED-based optical system into fractions due to TDMAT and other species, when necessary). During TDMAT-only delivery, i.e., in the absence of co-reactants and deposition products, TDMAT minimum detectable molecular densities as low as ≈4 × 10(12) cm(-3) were demonstrated, with short measurement times and appropriate signal averaging. Reactions involving TDMAT often result in the evolution of the reaction product dimethylamine (DMA), both as a thermal decomposition product in a TDMAT ampoule and as a deposition reaction product in the deposition chamber. Hence, the presence of DMA represents a significant potential interference for this technique, and therefore, the sensitivity of this technique to DMA was also determined by measuring DMA absorbance as a function of pressure. The ratio of the TDMAT sensitivity to the DMA sensitivity was determined to be ≈6.0. To further examine the selectivity of this technique, measurements were also performed during atomic layer deposition (ALD) of titanium dioxide using TDMAT and water. During ALD, potential interferences were expected from the evolution of DMA due to deposition reactions and the deposition on the windows of species containing IR-active C-H stretching modes. It was found that the interfering effects of the evolution of DMA and deposition of species on the windows corresponded to a maximum of only ≈6% of the total observed TDMAT density. However, this level of interference likely is relatively low compared to a typical chemical vapor deposition process in which co-reactants are introduced into the chamber at the same time.

Nondispersive Infrared Gas Analyzer for Vapor Density Measurements of a Carbonyl-Containing Organometallic Cobalt Precursor

“…71 The deviation from a linear relationship increases with density, but the relationship may appear linear at sufficiently low molar density. A linear relationship between measured absorbance and molar density was previously shown for a NDIR gas analyzer for the organometallic compound tetrakis(dimethylamido) titanium (TDMAT), 53 although the optical configuration and molar density range in that work were somewhat different than in this report. In that work, the maximum TDMAT molar density was ≈6.4 × 10 –4 mole/m 3 .…”

“…Infrared laser-based methods 16,47,48 can provide data acquisition rates with high spatial resolution, but compensation for long-term measurement instability can increase system complexity. Non-dispersive IR (NDIR) gas analyzers have been utilized more recently to investigate metalorganic precursor delivery and deposition reactions, 37,49–53 with at least one such NDIR design being commercially available. 49 Nondispersive IR gas analyzers can provide rapid, stable precursor concentration measurements but have not been demonstrated for a large range of metalorganic precursors.…”

“…49 Nondispersive IR gas analyzers can provide rapid, stable precursor concentration measurements but have not been demonstrated for a large range of metalorganic precursors. Current designs have involved isolating absorption modes in the C–H stretching spectral region 37,49,53 or in the fingerprint spectral region of bis-cyclopentadienyl magnesium 50 and two metal alkyamide compounds. 51,52 To date, no NDIR gas analyzers have been reported for monitoring carbonyl-containing metalorganic precursors.…”

Nondispersive Infrared Gas Analyzer for Partial Pressure Measurements of a Tantalum Alkylamide During Vapor Deposition Processes

“…NDIR gas analyzers have been shown to be capable of providing rapid, stable precursor concentration measurements for metalorganic compounds; however, these capabilities have been demonstrated only for a few compounds and in sometimes limited investigations. [20][21][22][23][24][25][26] Of these demonstrated NDIR gas analyzers, a number operate based on isolating absorption modes in the C-H stretching spectral region. 21,25,26 Since both PDMAT and DMA absorb in this spectral region, [27][28][29][30][31][32] the potential for strong spectral interference between the two species is high in this region, complicating data analysis.…”

“…[20][21][22][23][24][25][26] Of these demonstrated NDIR gas analyzers, a number operate based on isolating absorption modes in the C-H stretching spectral region. 21,25,26 Since both PDMAT and DMA absorb in this spectral region, [27][28][29][30][31][32] the potential for strong spectral interference between the two species is high in this region, complicating data analysis. To reduce the potential for interference between a metal alkylamide and the corresponding amine decomposition product, NDIR gas analyzers designed to monitor both species can be based on isolating absorption modes in the fingerprint spectral region.…”