AC Power Supply Arc Discharge Prevention in Sputtering
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Solution Overview
Problem
Existing AC power supplies for sputtering apparatuses face issues with arc discharges due to rapid current rises and overvoltages when polarity is reversed, leading to poor film formation and potential target melting.
Innovation Solution
Incorporating an inductor with higher inductance than the plasma load and a snubber circuit with a diode, capacitor, and resistor in parallel to the bridge circuit, which limits current rise and suppresses overvoltages, preventing arc discharges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If an inductor with larger inductance than plasma is added to make the output have constant-current characteristic, then current rise at arc discharge is suppressed, but spike-like overvoltage is generated at polarity reversal
Solution Approach 1:
A snubber circuit is introduced as an intermediary component between the inductor and the bridge circuit. This snubber circuit absorbs the spike-like overvoltage generated during polarity reversal, preventing it from inducing arc discharges while allowing the inductor to maintain its current-limiting function.
Solution Approach 2:
The snubber circuit is configured in parallel with the bridge circuit inputs to provide beforehand cushioning against overvoltage spikes. By being positioned in advance, it can absorb and dampen voltage transients before they reach the switching elements and potentially cause arc discharges.
2Device complexity
If DC electric power supply source with constant voltage characteristic is used, then simple power supply structure is achieved, but rapid current rise occurs at arc discharge
Solution Approach 1:
The invention changes the electrical characteristic parameter of the power supply output by adding an inductor with inductance larger than that of the plasma load. This transforms the output from constant voltage characteristic to constant current characteristic, thereby suppressing rapid current rises during arc discharge while maintaining reasonable structural complexity.
3Reliability
If inductor is added to suppress current rise, then arc discharge is prevented, but switching element stress increases due to overvoltage
Solution Approach 1:
The snubber circuit serves as a protective intermediary that shields the switching elements from overvoltage stress. By absorbing voltage spikes during polarity reversal, it prevents direct stress on the switching elements while preserving the inductor's arc discharge prevention capability.
Solution Approach 2:
The snubber circuit provides beforehand cushioning to the switching elements against overvoltage transients. This protective measure is positioned in advance to absorb stress before it reaches the switching elements, thereby extending their operational life and reliability.
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
Effectively suppresses overvoltages and prevents arc discharges, ensuring stable film formation and reducing switching element stress, thereby improving the efficiency and durability of the AC power supply.
Implementation Method 1
an inductor having an inductance value larger than that of the plasma, the inductor being disposed in at least one of the positive and the negative DC outputs from the DC electric power supply source to the bridge circuit
Implementation Method 2
a snubber circuit in parallel with inputs to the bridge circuit
Implementation Method 3
a snubber circuit in parallel with inputs to the bridge circuit
Implementation Method 4
a bridge circuit made up of four switching elements (MOSFETs) disposed between a DC electric power supply source and a load. When each of the switching elements of the bridge circuit is appropriately operated to apply an arbitrary pulsed voltage to a couple of targets, which are output terminals (electrodes), with the polarity of the pulsed voltage alternately reversed at a predetermined frequency
Implementation Method 5
the plasma load has an inductance component, and a current rapidly flows into the plasma load at the time of reversing the polarity of each electrode. A spike-like overvoltage is consequently generated at that time
Data Source
AI summary
There is provided an AC power supply for a sputtering apparatus in which the AC power supply can prevent the induction of an arc discharge by suppressing an overvoltage to be generated when the polarity of each electrode is reversed. A bridge circuit made up of a plurality of switching transistors SW1-SW4 is disposed between positive and negative DC current output lines from a DC electric power supply source. An inductor DCL which makes a DC output to have a constant-current characteristic is disposed in at least one of the positive and the negative DC output lines from the DC electric power supply source to the bridge circuit, and a snubber circuit is disposed in parallel with inputs of the bridge circuit.