Sputter coating typically occurs at pressures in the mTorr range, specifically from 0.5 mTorr to 100 mTorr.
This pressure range is necessary to facilitate the sputtering process.
In this process, a target material is bombarded by ions from a plasma, usually argon.
This causes atoms from the target to be ejected and deposited onto a substrate.
What Pressure is Sputter Coating? (4 Key Factors Explained)
1. Base Pressure and Gas Introduction
Before the sputtering process begins, the vacuum chamber is evacuated to a base pressure.
This base pressure is typically in the range of 10^-6 mbar or lower.
This high vacuum environment ensures clean surfaces and minimal contamination from residual gas molecules.
After achieving the base pressure, a sputtering gas, commonly argon, is introduced into the chamber.
The gas flow can vary significantly, from a few sccm in research settings to several thousand sccm in production environments.
2. Operating Pressure During Sputtering
The pressure during the sputtering process is controlled and maintained in the mTorr range.
This range is equivalent to 10^-3 to 10^-2 mbar.
This pressure is crucial as it affects the mean free path of the gas molecules and the efficiency of the sputtering process.
At these pressures, the mean free path is relatively short, around 5 centimeters.
This influences the angle and energy with which the sputtered atoms reach the substrate.
3. Influence of Pressure on Deposition
The high density of the process gas at these pressures leads to numerous collisions between the sputtered atoms and the gas molecules.
This causes the atoms to arrive at the substrate at random angles.
This contrasts with thermal evaporation, where atoms typically approach the substrate at normal angles.
The presence of the process gas near the substrate can also lead to gas absorption into the growing film.
This can potentially cause microstructural defects.
4. Electrical Conditions
During the sputtering process, a DC electrical current is applied to the target material, which acts as the cathode.
This current, typically between -2 to -5 kV, helps in ionizing the argon gas and accelerating the ions towards the target.
Simultaneously, a positive charge is applied to the substrate, which acts as the anode.
This attracts the sputtered atoms and facilitates their deposition.
In summary, the pressure during sputter coating is carefully controlled to be in the mTorr range.
This optimizes the sputtering process for efficient and effective deposition of materials onto substrates.
This pressure control is essential for managing the interactions between the sputtered atoms and the process gas.
It ensures the quality and properties of the deposited film.
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