Plasma Chamber Electrode Power Tuning Across the LF RF Cycle
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Solution Overview
Problem
High reflected power in plasma chambers leads to inefficient wafer processing, as the power provided to the plasma chamber is not optimally delivered, resulting in suboptimal processing efficiency.
Innovation Solution
The system employs very high frequency (VHF) frequency tuning by dividing the low frequency (LF) RF period into multiple time intervals, aligning a central time interval with the LF RF period's positive crossover, and adjusting frequency offsets for each interval to optimize power delivery. This involves controlling the impedance matching network and high-frequency RF generator to minimize reflected power and maximize delivery to the plasma chamber.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If power is provided to the plasma chamber using conventional RF generation, then the plasma chamber can operate, but high reflected power is generated causing inefficient wafer processing
Solution Approach 1:
The patent applies dynamics by making the VHF frequency adjustable and time-dependent rather than fixed. The frequency is dynamically tuned during each LF RF period based on real-time impedance conditions, allowing the system to adapt to changing plasma conditions and maximize power transfer efficiency while minimizing reflected power
Solution Approach 2:
The patent changes the frequency parameter of the HF RFG dynamically. By varying the VHF frequency according to the instantaneous impedance of the plasma chamber and the timing within the LF RF period, the system optimizes power delivery and reduces reflected power, directly addressing the efficiency problem
2Power
If the impedance matching network is used to deliver power to the plasma chamber, then power transfer is enabled, but reflected power remains high reducing processing efficiency
Solution Approach 1:
The patent implements feedback by continuously monitoring the impedance conditions of the plasma chamber and using this information to adjust the VHF frequency in real-time. The system measures the actual power transfer efficiency and reflected power levels, then modifies the frequency accordingly to maintain optimal operation, creating a closed-loop control system that maximizes processing efficiency
3Reliability
If conventional RF power delivery is used, then the plasma chamber operates, but equipment size, weight, and cost are high
Solution Approach 1:
The patent employs periodic action by dividing the LF RF period into multiple time intervals and applying VHF frequency tuning at specific phases within each period. This periodic modulation approach allows the system to achieve efficient power transfer in discrete steps throughout the RF cycle, enabling reliable plasma operation while using a more compact and cost-effective implementation than continuous high-power systems
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.