Reactive Sputtering Target Surface State Control
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Solution Overview
Problem
High-power impulse magnetron sputtering (HiPIMS) processes face limitations due to target overheating and the formation of non-conductive layers when using high current densities, leading to rate drops and hysteresis in reactive gas pressure, restricting the use to electrically conducting materials and requiring pulse operation to manage target cooling.
Innovation Solution
The method involves operating the sputter discharge with high current densities starting from an intermediate state between poisoned and metallic states, using defined energy impulses to transition the target from a more poisoned to a more metallic state, with impulse durations between 50 μs and 100 ms, and maintaining continuous power supply between impulses to prevent target poisoning and ensure stable operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If high current density is used to increase ionization of sputtered material, then coating quality improves, but target overheating occurs
Solution Approach 1:
The patent applies periodic pulsed power instead of continuous power to the magnetron cathode. The power is supplied in pulses with duration 1-100 ms at frequencies 10-1000 Hz, allowing the target to cool between pulses while still achieving high ionization during the pulse when current density exceeds 0.5 A/cm². This resolves the contradiction by providing high current density intermittently rather than continuously.
2Manufacturing precision
If reactive gas flow is increased to form compounds with sputtered material, then reactive coating is achieved, but target surface becomes poisoned and coating rate drops
Solution Approach 1:
The pulsed power operation creates periodic cycles where the target surface alternates between poisoned state (during reactive gas flow) and metallic state (during power pulse when high current density cleans the surface). By controlling pulse parameters, the system spends more time in the poisoned state for compound formation while periodically restoring metallic state to maintain high sputtering rates, avoiding the permanent rate drop associated with continuous poisoning.
Solution Approach 2:
The patent changes the operational parameters by using high current density pulses (>0.5 A/cm²) that temporarily alter the target surface composition from poisoned to metallic state. This parameter change allows dynamic control of the target surface state, enabling the system to overcome the rate drop by periodically restoring high sputtering yields even in the presence of reactive gas.
3Temperature
If pulse operation is used to cool the target, then target overheating is prevented, but process continuity is interrupted
Solution Approach 1:
The patent uses pulsed power with frequencies of 10-1000 Hz, which creates sufficiently short cooling intervals that the target never loses its operating temperature entirely. The high thermal mass of the target combined with the frequent pulsing maintains process continuity while still allowing adequate cooling between pulses to prevent overheating.
Solution Approach 2:
By operating at pulse frequencies of 10-1000 Hz, the patent ensures that the sputtering process effectively continues without interruption. The averaging effect of high-frequency pulsing maintains steady-state coating deposition while the brief intervals between pulses provide sufficient cooling, thus achieving both temperature control and process continuity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach stabilizes the sputter discharge and reactive gas pressure, achieving high coating rates and ionization of sputtered particles without hysteresis, particularly in oxide sputtering processes like aluminum oxide production, allowing for continuous and reproducible power impulses without power interruptions.
Implementation Method 1
During sputtering, which is also known as cathodic sputtering, material is ejected by means of on bombardment from the surface of a solid body (target), which constitutes the cathode
Implementation Method 2
Impact ionization causes the atoms of the working gas to become ionized. During impact ionization, free electrons essentially collide with the atoms and ionize the latter, in this manner, a plasma is formed
Implementation Method 3
a magnet system is placed behind the cathode and whose magnetic field extends into the area above the target surface. This projecting part of the magnetic field, which is often executed as tunnel, forces the electrons onto a spiral path
Implementation Method 4
Because of the negative voltage applied to the cathode, the working gas ions are accelerated towards the latter. During the sputtering, a current flow is thus generated
Implementation Method 5
the degree of ionization of the material ejected from the target is very low. However, if using current densities greater than 0.5 A/cm2, the degree of ionization increases dramatically
Implementation Method 6
a reactive gas can be introduced into the process chamber during the sputtering, which then forms a bond with the sputtered material. the target surface, as a result of the reaction of the reactive gas with the target material, is covered with a non-conductive or poorly conductive layer
Data Source
AI summary
Reactive sputtering in which, by ion bombardment, material is ejected from the surface of a target and transitions to the gas phase. Negative voltage pulses are applied to the target to establish electric current having a current density greater than 0.5 A/cm2 at the target surface, such that the material transitioning to the gas phase is ionized. Reactive gas flow is established and reacts with the material of the target surface. Voltage pulse duration is such that, during the pulse, the target surface where the current flows is at least partly covered most of the time with a compound composed of reactive gas and target material and, consequently, the target surface is in a first intermediate state, and this covering is smaller at the end of the voltage pulse than at the start and, consequently, the target surface is in a second intermediate state at the end of the voltage pulse.