Multilayer Systems with Widely Different Sputter Rates - Sample Preparation for TEM

Application Note for Leica EM RES102 - Industrial Manufacturing

December 16, 2016

The multilayer system to be prepared in cross-section consists of a Si substrate, a TiN layer with a thickness of a few nm and a 500 nm W layer. All these components have extreme differences in their hardness, their atomic weight and in their sputter rates.

A preparation of this kind of samples with sample rotation would lead to a wall overlying the area of the layers. The reason for that is the different milling rate of the materials. In order to achieve an even thinning of all components, a flat milling angle (≤6°) is necessary. In addition, ion milling parallel to the adhesive joint of the cross-sectional sample must be avoided.

In case of the Leica EM RES102, an oscillating movement can be used in addition to the sample rotation. In doing this, both the zero point and the angle of the oscillation can be adjusted. The zero point should be set up so that the incidence of the ion beam is vertical with respect to the adhesive joint. If the sample is oscillating and the milling angle is flat, the layers with lower milling rate protect the layers with higher milling rate. That results in a uniform milling of the entire sample.

Preparation Conditions
Mechanical pre-preparation: Double sided polishing with diamond foils: 15 µm, 9 µm, 6 µm, 3 µm, 1 µm and 0.5 µm until the final sample thickness of 60 µm.

Ion milling

Sample holder:Quick-clamp-holder
Acceleration voltage:7 kV
Milling angle:
Sample movement:Oscillation (±45°)

 

Final step

Sample holder:Quick-clamp-holder
Acceleration voltage:2 kV
Milling angle:±4° (alternating with one ion gun)
Sample movement:Oscillation (±45°)


Results
The multilayer system, the preparation of which needs to be carefully, could be evenly thinned despite the wide difference in the sputter rates. All components are uniform electron transparent over a length of several 100 µm. An examination of the layers and their interfaces in high resolution is possible.

Fig.1: TEM cross-sectional image of a multilayer system consisting of Si substrate /TiN/ W
Fig.2: TEM cross-sectional image of a multilayer system consisting of Si substrate /TiN/ W

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