Monitoring deposition rates

Deposition rate monitoring and control are relatively easy... 

The deposition rate is often an important processing variable in PVD processing. Not only can the rate affect the film growth along with the deposition time, it is often used to determine the total amount of material deposited. The quartz crystal deposition rate monitor (QCM) is the most commonly used in situ, real-time deposition rate monitor for PVD processing. 

Ionization deposition rate monitors are commercially available but are not commonly used. Ionization rate monitors compare the collected ionization currents in a reference ionizing chamber and an ionizing chamber through which the vapor flux is passing. By calibration, the differential in gauge outputs can be used as a deposition rate monitor. In e-beam evaporation, the ions that are formed above the molten pool can be collected and used to monitor the vaporization rate. The optical emission of the excited species above the vaporization source can be used for rate monitoring.f ... 

Some deposition rate monitors use optical atomic absorption spectrometry (AAS) of the vapor as a non-intrusive rate monitoring technique (Sec. 7.8.8). 

A simple single-beam atomic absorption deposition rate monitor is shown in Figure 7.12. 

Figure 7.12 An Atomic Absorption Spectrometer (AAS) Sputtering/Deposition Rate Monitor...

Ionization deposition rate monitor (PVD technology) A deposition rate monitor that compares the collected ionization current in a reference ionizing chamber to the collected ion current from an ionizing chamber through which the vapor flux of the film material is passing. 

Deposition rate monitors include devices such as quartz crystal monitors and RHEED tools that measure the rate of deposition of a film on a surface and... 

In films that grow 2D for many layers, intensity oscillations have been observed for certain growth conditions using RHEED and LEED. Observation is made by monitoring the intensity of a diffracted beam as a function of time during growth. The period of an oscillation corresponds to the time it takes to deposit a monolayer. In practice, oscillations are ffequendy used to calibrate deposition rates. 

Chordal thermocouples are special sections of boiler tube containing thermocouples that are used to monitor increases in tube wall temperature due to the buildup of deposit. Calibration relating to the quantification of deposit rate buildup may be difficult... 

Supported model catalysts are frequently prepared by thermally evaporating metal atoms onto a planar oxide surface in UHV. The morphology and growth of supported metal clusters depend on a number of factors such as substrate morphology, the deposition rate, and the surface temperature. For a controlled synthesis of supported model catalysts, it is necessary to monitor the growth kinetics of supported metal... 

Coke builds up on the catalyst since the start up of operation. In the first weeks of operation, an amount between 5% and 8% of coke accumulates on the catalyst. The rate of deposition decreases with time on stream, a careful monitoring of temperature and of feed/H2 ratio is the basis for controlling deposition. Coke deposition primarily affects the hydrogenation reactions (and so denitrogenation), but the deposition rate determines the catalyst life. As mentioned above, deactivation is compensated by an increase in temperature (and some times in pressure, when denitrogenation has to be adjusted, as well). However, increasing severity, increases coke deposition and shorten catalyst life. 

The organic deposition sources are made of a variety of materials including ceramics (e.g., boron nitride, aluminum oxide, and quartz) or metallic boats (e.g., tantalum or molybdenum). Deposition is carried out in high vacuum at a base pressure of around 10-7 torr. The vacuum conditions under which OLEDs are fabricated are extremely important [41] and evaporation rates, monitored using quartz oscillators, are typically in the range 0.01 0.5 nm/s in research and development tools. In manufacturing, higher rates or multiple sources may be used to reduce tact times. 

Thickness controllability (Table 9.1, no. 6) and reproducibility in OVPD is achieved by accurate adjustment of the flow of carrier gas by means of mass-flow controllers whereas in VTE quartz crystal monitors are used to control the rate of deposition by adjustment of the evaporation temperature. In VTE small deviations of the evaporation temperature are known to affect the stability of the deposition rate and consequently the layer thickness, which may also affect the roughness and morphology of the VTE-deposited layer. 

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