Real-time acoustic sensing and control of metalorganic chemical vapor deposition precursor concentrations delivered from solid phase sources

Abstract

We have investigated the performance and potential benefit of acoustic sensing for real-time monitoring and closed loop control of binary gas mixture compositions delivered from low vapor pressure metalorganic sources. Two solid phase sources were investigated in the presence of H 2 as a carrier gas: (1) trimethylindium (TMI) and (2) bis(cyclopentadienyl) magnesium ͑Cp 2 Mg͒, which have room temperature ͑25°C͒ vapor pressures of 2.5 and 0.04 Torr, respectively. An acoustic sensor was implemented on the gas feed line to measure the concentration-dependent speed of sound in the gas mixture. This enabled sensitivity and control at precursor levels as low as 0.6 ppm in H 2. Closed loop process control was implemented to maintain TMI and Cp 2 Mg concentration target in the presence of intentionally introduced long term temperature drifts. Despite induced variations of the precursor vapor pressure up to 50%, the delivered composition was controlled to within ±0.15% for TMI (at 0.5 mol% set point) and ±0.3% for Cp 2 Mg (at 0.01 mol% set point). Short term variability could also be substantially reduced by the control scheme. This work demonstrates the feasibility of sensor-driven control systems for stable delivery of low vapor pressure, normally problematic precursor materials. In turn, this opens the door to utilization of a broader range of species which can be synthesized as chemical precursors.

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

“…1–11 Schemes for improving control of precursor delivery in vapor deposition processes fall within two main categories: enhanced precursor delivery system design; 5,9,12–18 and closed loop control of precursor flux. 2–4,6,19–25 Metrologies that provide the time-dependent precursor concentration can contribute to both methods. In the case of delivery system design, precursor concentration measurement is desirable for efficient characterization of the flow system.…”

“…Acoustic methods are commercially available and have been utilized for decades. 2–4,6,9,17,18,21,23–31 However, these methods tend to be limited to pressures above ≈6.7 kPa (50 Torr), 30 making them unsuitable for many low-pressure CVD and ALD processes. A range of optical methods have been utilized that have the potential to operate at lower pressures and with more flexibility in the sampling configuration than acoustic methods.…”

Low-Pressure Metallorganic Chemical Vapor Deposition of Fe[sub 2]O[sub 3] Thin Films on Si(100) Using n-Butylferrocene and Oxygen

“…To overcome these difficulties with solid precursors, complex and expensive nonconventional delivery approaches, like using a separate heating zone within the reaction chamber, solvent-based direct liquid injection, and sublimation in a fluidized bed, have been employed. [12][13][14][15] While such solid precursor delivery techniques provide possible solutions, they also bring in additional parameters that increase the complexity of the MOCVD process compared to the use of liquid precursor delivery schemes.…”