Plasma Processing Power Supply Using Zero-Cross SSRs
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Solution Overview
Problem
In plasma processing for semiconductor and FPD manufacturing, increasing the number of segments on the mounting table leads to variations in heater resistance values, limiting temperature control resolution and causing harmonic noise due to discontinuous current waveforms from thyristor switching.
Innovation Solution
A plasma processing apparatus with a power supply device using transformers and zero-cross control type solid state relays to control current supply to heaters, reducing harmonic noise and enhancing temperature control resolution by stepping down voltage and controlling ON/OFF switching at zero voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the number of segments on the mounting table is increased to improve temperature control resolution, then temperature control precision is improved, but heater resistance values vary across segments causing control variations
Solution Approach 1:
The patent applies local quality by providing different resistance values to heaters in different segments of the mounting table. Each segment's heater is designed with a resistance value specifically tailored to compensate for the nonuniform heat input characteristics in that region, enabling uniform temperature distribution across the workpiece surface despite spatial variations in heating requirements.
2Ease of operation
If thyristor phase control is used to control current to heaters, then power adjustment is achieved, but discontinuous current waveforms generate harmonic noise
Solution Approach 1:
The patent eliminates the discontinuous current waveform problem by using zero-cross control type solid state relays that switch only at voltage zero-crossings. This ensures continuous and smooth current supply to the heaters without the abrupt on/off transitions characteristic of phase control, thereby preventing generation of harmonic noise while maintaining power control capability.
Solution Approach 2:
The patent replaces the thyristor-based phase control mechanism with a zero-cross control type solid state relay system. This substitution changes the control mechanism from one that creates discontinuous waveforms to one that maintains continuity by switching only at zero-voltage points, thereby eliminating harmonic noise generation.
3Ease of manufacture
If multiple heaters are connected in parallel to share wires, then wire arrangement becomes feasible, but combined resistance decreases causing large current supply requirements
Solution Approach 1:
The patent applies local quality by assigning different resistance values to heaters in different segments. When heaters are connected in parallel, their different resistance values result in unequal current distribution, which compensates for the area differences between segments. This allows feasible wire arrangement while maintaining appropriate power delivery to each segment without requiring excessively large total current.
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 configuration achieves high temperature control resolution while reducing harmonic noise, allowing precise temperature control of workpiece regions and improving manufacturing yield.
Implementation Method 1
A power supply device includes a plurality of transformers and a plurality of zero-cross control type solid state relays. The plurality of transformers step down a voltage from an alternating-current power source.
Implementation Method 2
a heater, which is a resistive heating element, is incorporated into the mounting table as the temperature control function in order to control the temperature of the mounting table and the temperature of the workpiece
Data Source
AI summary
A plasma processing apparatus according to an embodiment includes a processing container, a mounting table, a plurality of heaters, and a power supply device. The mounting table is provided in the processing container. The plurality of heaters are provided in the mounting table. The power supply device supplies electric power to the plurality of heaters. The power supply device includes a plurality of transformers and a plurality of zero-cross control type solid state relays (SSRs). The plurality of transformers are configured to step down a voltage from an alternating-current power source. Each of the plurality of transformers includes a primary coil and a secondary coil. The primary coil is connected to the alternating-current power source. Each of the plurality of SSRs is provided between one corresponding heater among the plurality of heaters and the secondary coil of one corresponding transformer among the plurality of transformers.