ABSTRACT

Adding surface grooves to arc and sputter targets can extend the process life. The normal end of life (EOL) failure modes can be delayed.

INTRODUCTION

The normal cause of sputter target EOL is a rise in voltage beyond the capacity of the power supply, target thinning, uniformity degradation, or a rise in product defects. Soleras has discovered that minor grooves placed in the initial target surface can broaden the erosion trench. This delays the cause of EOL, and extends the functional life of the target. The principle is to initiate secondary plasma sites at the sides of the current trench. All sputter sites trend to the same end point. The primary erosion proceeds as normal, however the secondary side sputter sites proceed to the same point by eroding the sides of the previous trench walls. The result is a wider overall trench. The broader trench keeps the plasma impedance within the limits of the power supply, maintains distribution, and reduces both thinning and product defects. The percentage of gain in sputtered target material depends upon the severity of the original trenching, however the normal benefits are 10% to 50%. Where the magnetic field is high and narrow, gains have been over 100%. The groove size is in single digits for depth and width in mm. The location is dependent on the original EOL trench profile. The technique can be initiated with very small dimensions and proceed to the optimum.

Figure 1. Target "A" represents a normal, non-grooved target erosion pattern. Target "B" represents a grooved target.

CONCLUSION

This is a simple technique of extending target life. The theory is complex, however an empirical evaluation can be had with little design work or risk. The effect is seen in both sputter and arc deposition. The purpose in the arc application is often to divert the arc away from insulators and toward under utilized target material. The use of the technique is different for arc deposition.