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

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

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

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

In-situ Sensing using Mass-Spectrometry and its use for Run-to-Run Control on a

Abstract. A 300 amu closed-ion-source RGA (Leybold-Inficon Transpector 2) sampling gases directly from the reactor of an ULVAC ERA-1000 cluster tool has been used for real time process monitoring of a W CVD process. The process involves H 2 reduction of WF 6 at a total pressure of 67 Pa (0.5 torr) to produce W films on Si wafers heated at temperatures around 350° C. The normalized RGA signals for the H 2 reagent depletion and the HF product generation were correlated with the W film weight as measured post-process with an electronic microbalance for the establishment of thin-film weight (thickness) metrology. The metrology uncertainty (about 7% for the HF product) was limited primarily by the very low conversion efficiency of the W CVD process (around 2-3%). The HF metrology was then used to drive a robust run-to-run control algorithm, with the deposition time selected as the manipulated (or controlled) variable. For that purpose, during a 10 wafer run, a systematic process drift was introduced as a -5°C processing temperature change for each successive wafer, in an otherwise unchanged process recipe. Without adjustment of the deposition time the W film weight (thickness) would have declined by about 50% by the 10 th wafer. With the aid of the process control algorithm, an adjusted deposition time was computed so as to maintain constant HF sensing signal, resulting in weight (thickness) control comparable to the accuracy of the thickness metrology. These results suggest that in-situ chemical sensing, and particularly mass spectrometry, provide the basis for wafer state metrology as needed to achieve run-to-run control. Furthermore, since the control accuracy was consistent with the metrology accuracy, we anticipate significant improvements for processes as used in manufacturing, where conversion rates are much higher (40-50%) and corresponding signals for metrology will be much larger

Nanotubular metal–insulator–metal capacitor arrays for energy storage

Nanostructured devices have the potential to serve as the basis for next-generation energy systems that make use of densely packed interfaces and thin films1. One approach to making such devices is to build multilayer structures of large area inside the open volume of a nanostructured template. Here, we report the use of atomic layer deposition to fabricate arrays of metal–insulator–metal nanocapacitors in anodic aluminium oxide nanopores. These highly regular arrays have a capacitance per unit planar area of 10 F cm-2 for 1-m-thick anodic aluminium oxide and 100 F cm-2 for 10-m-thick anodic aluminium oxide, significantly exceeding previously reported values for metal–insulator–metal capacitors in porous templates2, 3, 4, 5, 6. It should be possible to scale devices fabricated with this approach to make viable energy storage systems that provide both high energy density and high power density