Ta PVD Target Racetrack Erosion Reduces Target Utilization - Functional Modeling
In the Ta PVD process, the sputtering target develops a deep erosion groove in the narrow racetrack region. As a result, the target must be replaced while a significant amount of expensive tantalum remains unused. This reduces target utilization, shortens target life, and increases manufacturing costs.
The erosion is believed to result from the magnetron magnetic field, which concentrates the plasma and Ar⁺ ion bombardment in a limited area. The same mechanism that enables efficient Ta deposition therefore causes localized target erosion. Reducing the deposition rate provides only minor improvement while decreasing throughput. Cause and Effect Chain Analysis will identify the fundamental causes of nonuniform erosion and determine where the chain can be broken without compromising deposition performance.
We learned that the PVD equipment does not provide uniform erosion of the Ta sputtering target.
The Ta PVD system consists of a vacuum chamber, Ta sputtering target, magnetron assembly behind the target, power supply, gas delivery system, wafer support, shields, and vacuum pumps. The wafer is positioned opposite the target. Argon is used as the process gas; nitrogen may be added for reactive TaN deposition.
Electrical power creates an Ar plasma. Ar⁺ ions bombard the Ta target and eject Ta atoms, which travel through the chamber and form a thin barrier film on the wafer. The magnetron’s magnetic field confines electrons near the target, increasing plasma density and sputtering efficiency, but also concentrating target erosion within the racetrack region.
Let’s define the Product. The Product is what the system is designed to create. In our case, the Ta PVD system is designed to deposit a Ta/TaN thin film.
Therefore, the deposited Ta/TaN thin film is the Product.
Operational Effectiveness – OE
Effective
Ineffective
OE 0.48
Operational Perfectness - OP
Basic functions
Components
Supersystems
OP 0.07
Ar+ ions | 15 60 |
Ta sputtering target | 10 |
Ta atoms | 10 |
Magnetron | 7 63 |
TaN | 6 |
Periphery of the target | 4 4 |
Nitrogen | 4 |
RaceTrack area | 4 4 |
Ar plasma | 3 |
Field | 3 |
Either compensate for magnetic-field non-uniformity with temperature, or compensate for magnetic-field non-uniformity with magnetic-field control or target-shape compensation.
If | Magnetron remains unchanged |
|---|---|
Then | Magnetron Creates Field |
But | Magnetron Splits Ar+ ions |
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