Ion beam sputter deposition is a process that is employed in a wide range of applications where high quality, high performance layer materials and precision film control are of great importance. However, this process has certain difficulties - for instance, when an ion beam is used to sputter a target material, it is difficult to control the beam shape and collimation so as to prevent any energetic ions following trajectories whereby they could sputter other materials other than the intended target material, such as surrounding fixtures and furniture.
This may possibly contaminate the depositing film with impurities. The impact of this on the performance of the deposited film will depend on the levels of impurities, on the specific application targeted, and on the nature of the impurities.
High Purity Thin Films
The traditional way to ensure high purity thin films in ion beam deposition has been to use a large vacuum chamber. The size of the chamber was crucial in reducing the effects of high energy particles reflected from the target surface sputtering chamber materials onto the substrate, and also enabled the use of large targets to prevent beam overspill onto the chamber furniture. For example, chambers above 1m3 have been utilized for depositing low loss dielectric mirrors.
A better understanding of re-sputtered material paths and beam trajectories has facilitated the deposition of thin films with extremely low metallic impurity content in a chamber volume less than 0.5m3. Figure 1 shows the progress made over the 6 month contamination reduction project for a round target of 8”.
Figure 1. Progress over the 6 month contamination reduction project for an 8” round target
By improving the target, substrate configuration and sputter ion source, and by assembling appropriate shielding made of suitable material in the process chamber, the contamination levels in the deposited films can be greatly reduced. With this improved arrangement of hardware, the parameters of the ion beam process can be optimised with regard to the ppm levels of contaminants determined in the films by SIMS analysis.
Figure 2. lonfab300Plus ion beam system
SiO2 is used as a standard material for impurity level determination and SIMS composition analysis. Using the deposition of SiO2 it has been shown that Oxford Instruments’ ion beam sputtering deposition tool (Figure 2) can be used for depositing films with contamination levels of less than 50ppm for the total of all metal impurities in the deposited films.
This information has been sourced, reviewed and adapted from materials provided by Oxford Instruments Plasma Technology.
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