Plasma Chamber Electrode Power Tuning Across the LF RF Cycle
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Solution Overview
Problem
In plasma chambers, high reflected power during power delivery to the electrode leads to inefficient processing of wafers, as existing systems fail to effectively mitigate intermodulated frequency reflections.
Innovation Solution
The implementation of very high frequency (VHF) frequency tuning by dividing the low frequency (LF) RF period into multiple time intervals, with frequency offsets for the VHF generator adjusted based on the LF RF period, to optimize power delivery and reduce reflections, using a control scheme that varies the total range of frequency offsets in a non-random, trajectory-dependent manner.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If power is provided to the plasma chamber, then processing of the wafer is enabled, but reflected power is generated leading to inefficient processing
Solution Approach 1:
The patent applies dynamics by continuously adjusting the frequency of the RF generator in real-time during the RF period. The frequency is modulated based on the instantaneous voltage or current of the RF signal, transforming a static frequency system into a dynamic one that adapts to changing plasma conditions, thereby reducing reflected power and improving power transfer efficiency.
Solution Approach 2:
The patent changes the frequency parameter of the RF generator dynamically throughout the RF period. By varying the frequency according to the RF signal's voltage or current waveform, the system optimizes impedance matching conditions at different moments, reducing reflected power and enhancing wafer processing efficiency.
2Loss of energy
If frequency tuning is performed to reduce reflected power, then power delivery is optimized, but system complexity increases
Solution Approach 1:
The system performs self-service by using the RF generator's own output signal (voltage or current) to control its frequency modulation. The RF signal itself serves as the control input for the frequency tuner, creating a self-regulating system that reduces reflected power without requiring external sensing or complex control circuits.
Solution Approach 2:
The RF signal serves multiple functions simultaneously: it provides power to the plasma chamber, acts as the control signal for frequency modulation, and enables real-time optimization of power transfer. This multi-functionality reduces the need for separate control systems and simplifies the overall device architecture.
Data Source
AI summary
A method for optimizing delivery of power to a plasma chamber is described. The method includes dividing each cycle of a low frequency (LF) radio frequency generator (RFG) into multiple time intervals. During each of the time intervals, a frequency offset of a high frequency (HF) RFG is generated for which the delivery of power is maximized. The frequency offsets provide a substantially inverse relationship compared to a voltage signal of the LF RFG for each cycle of the voltage signal. The frequency offsets for the time intervals are multiples of the low frequency. The substantially inverse relationship facilitates an increase in the delivery of power to the electrode. A total range of the frequency offsets from a reference HF frequency over the LF RF cycle depends on a power ratio of power that is supplied by the LF RFG and power that is supplied by the HF RFG.