SPUTTERING FAQ #2:

Why is my sputtering yield too low? Why is my target overheating? Why did my target come debonded from the backing plate? Why did my target shatter during sputtering?
Note: some of the below suggestions appeared in the "Ask Stan" column in the January 2011 Vacuum & Coating Technology magazine:
Charles Albert, PhD
ACI Alloys, Inc.
4/29/11
1. Is there any chamber shielding? If so, is it getting a build-up? This can affect vacuum, effective power, etc. It may need replacing.
2. Chemically active materials (Al, etc.) may react with water to release H2, lowering power yield but not otherwise easily measurable. Try pumping
longer, or a mild bake, or water vapor pumping.
3. Change the water in your closed cycle cooler on the turbopump/sputter source.
The below information comes from the Gencoa.com faq:
4. What principles determine the maximum power I can apply to my target materials?
A: The main aspect to what power the target can withstand is down to the material itself and also the means of heat removal from the target or backing plate. For good thermal conductors such as Cu and Al which also have good mechanical properties, max power densities can be high (20-50 W/cm2).
If the target is bonded to a backing plate (as is the case for more fragile or soft materials), then the bond material maybe the point of weakness due to a low melting point (in the case of indium). There are higher melting-point bonds, but for the family of bonded targets the maximum power density is generally 10-20 W/cm2).
Thermal shock is also a problem. Brittle target materials will crack if the power is too high or the thermal heating and cooling cycle is too agressive. For these materials generally the maximum is 5-15 W/cm2.
For low melting point target materials, the heat removal will be the most important, and special high water flow magnetrons are recommended. Power levels for such materials are 5-20 w/cm2 depending upon the cooling mode, efficiency and the material.
Once the power density that the material can withstand has been assessed its important to always bear in mind the coating quality required. Even though high powers maybe possible, the demands of the product may limit the effective power that can applied.
5. What is the operating standard range of distances from target to substrate?
A. As a general rule, the target to substrate separation should be more than the target width / 2. So if its a 150mm wide target 80mm t-s is good. Any closer and the substrate will be in the magnetron plasma and could become charged electrically leading to substrate heating, arcs or thin film device damage. Further away and the uniformity drop-off starts at the ends starts to increase. Sometimes the distance is greater to reduce heating effects on temperature sensitive materials.

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