Monitoring sputtering rate

When argon is used as the plasma gas, the sputtering rate measured by the deposition rate of aluminum on a quartz crystal thickness monitor was found to be linearly proportional to Wjp as depicted in Figure 9.9 [15]. In the domain of glow discharge, W increases by the increase of current at nearly constant discharge voltage, and Wjp could replace Vjp. 

Depth-profile analysis is also possible, as the sample is ablated layer-by-layer with a penetration rate of 1 - 3 pm/min. Here, the intensities of the analyte lines are measured as a function of time. However, the sputtering rates of alloys with varying composition must be known to convert the time scale into a depth scale. The intensities must be related to concentrations, which can be done by using theoretical models and sputtering constants [291]. The power of detection may be quite good and depth resolution is of the order of 5 nm, when elemental concentrations >0.1% are monitored. Depth profile analysis is now a main field of application of glow discharge emission spectrometry in the metals industry (Fig. 42) [291]. 

An almost equally valuable ability of AES/SAM is the ease by which sputter-depth profiles can be obtained. These and other methods to derive depth distribution information will be discussed in Section 3.3. In this procedure, the surface is slowly milled away by inert ion bombardment and AES is used to monitor the composition as a function of time. Although this can also be done with small spot XPS, AES is more commonly used because of its smaller analysis area which permits a smaller sputtered area and, hence, a faster sputter rate, its faster data-acquisition rate, and its compatibility with the higher pressures in the analysis chambers needed for sputtering with older models of ion guns. 

If the primary ion beam is used to continuously remove material from the surface of a specimen in a given area, the analytical zone is advanced into the sample as a function of the sputtering time. By monitoring the secondary ion count rates of selected... 

Figure 9.9 Sputtering on the discharge parameter W/p the aluminum sputtering is measured by the deposition onto the thickness monitor sensor in the glow discharge of argon, flow rate (cm sTP /min) , 2.3 O, 5.6 A, 12.4 A, 23.3. Adapted from Ref. 15.

The online mass spectrometric analysis of the evolving gas under open-circuit conditions and at different electrode potentials was carried out using nickel film sputter deposited onto a thin Teflon film as a working electrode, which was interfaced to the inlet of the mass spectrometer. Deuterium labeling allowed the rate of partial reactions (19.11) and (19.12) and the isotopic composition of the evolving gas to be monitored as a function of the electrode potential in parallel to faradaic current measurements, providing a solid evidence of the electrochemical mechanism of (electro) catalytic hypophosphite oxidation. 

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

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