ICMCTF2007 Session B8: In-Situ Characterization and Modelling of PVD Processes

Development new PVD processes and corresponding magnetron cathodes meeting ever growing customer requirements is increasingly costly when done only by experimental iterations. Examples of such customer requirements are: (1) high thickness uniformity over the substrate and (2) feature coverage in semiconductor wafer processing, (3) growing substrate size for flat panel displays, (4) high target utilization for optical and magnetic data storage applications, and (5) high rate reactive sputtering with uniform chemical composition in architecture glass coating.

Computer simulations help in reduction of development time and cost in these cases. A brief overview of well established simulation methods is given, including methods of computing magnetic field and resulting target erosion, transport of sputtered material to the substrate including interaction with inert and reactive gases, feature size modeling, and finally plasma simulation methods, such as Particle in Cell and fluid models.

Examples of successful deployment of the models (mostly resulting from development for Oerlikon Balzers Coating corporation) for the technologies mentioned are given.

Advances in development of the Direct Simulation Monte Carlo (DSMC) method used for neutral transport simulation in sputtering are described. An efficient 3D model of magnetron plasma based on movement of energetic electrons with Monte Carlo collisions is presented. Limitations and challenges of the available simulation methods are discussed, especially for pulsed magnetron sputtering technologies.

The sputter deposition of coatings onto capsules of polymer and oxide shells as well as solid metal spheres is accomplished using a chambered substrate platform. Oxides and metal coatings are sputter deposited through a screen-aperture array onto 0.3-1.2 mm diameter, solid spheres and hollow shells. Each capsule is contained within its own individual chamber within a larger array. Ultrasonic vibration is the method used to produce a random bounce of each capsule within each chamber, in order to produce a coating with uniform thickness. Characterization of thin aluminum-oxide coated, platinum solid spheres and thicker copper-gold layered coated, hollow capsules using cross-section microscopy techniques show that uniform coatings can be produced using a screen-aperture chambered, substrate platform. Potential advantages of this approach as compared to open-bounce pans include improved sample yield and reduced surface roughness from debris minimization. A process model for the coating growth on the capsules is developed to assess selection of the screen aperture based on the effects of sputter deposition parameters and the coating materials. A screen-aperture coefficient provides a direct link to model coating thickness on each chambered capsule. The deposition rate of a single material for each unique deposition condition experiment is found to be directly proportional to the screen-aperture coefficient which is logarithmically proportional to the material density. The modeled coating thickness values for the cases of the aluminum-oxide and copper-gold coatings are found to be within the range of experimental for measured values.

This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48.

Due to geometrical reasons the lateral magnetic field component across the racetrack of a rectangular magnetron is reduced in the curves in comparison to the side tracks. This causes a certain inhomogeneity of the charge carrier density in the plasma torus known as cross-corner effect (CCE) or - in similar form in case of a dual magnetron - cross-magnetron effect (CME). Recently, the CCE/CME attracted attention because of the inhomgeneous target erosion for magnetrons with strong magnetic fields.

We have investigated a pulsed reactive sputtering process for ITO films using a metallic In:Sn target. An arrangement of two identical rectangular magnetrons was applied which was powered either as a dual magnetron or as two separate conventional magnetrons. Plasma parameters (charge carrier density, electron temperature), heat flux towards the substrate, growth rate as well as film structure and properties (optical absorption, electrical resistivity) have been determined in dependence on the lateral position.

We found a distinct CCE/CME in terms of plasma inhomogeneity which, however, was not connected with a noticeable inhomogeneity of target erosion and growth rate. On the other hand, both film structure and properties exhibited a strong lateral inhomogeneity which cannot be neglected with respect to the deposition of films having low resistivity and low absorption at the same time over larger areas.

In the talk, special importance is attached to the dependence of film structure and properties on the plasma parameters. We found, that the formation of atomic oxygen, which is essentially determined by the plasma parameters, plays a crucial role in the ITO process. Considering the formation of atomic oxygen, both peculiarities of the process as a whole (depending on the mode of powering the targets) and lateral inhomogeneities within one process can be explained.