RF Power Divider Calibration for Plasma Chamber Uniformity
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Solution Overview
Problem
Inductively coupled plasma (ICP) sources face challenges in maintaining consistent power division between inner and outer RF coils due to variations in coil tolerances and RF matching networks, leading to wafer-to-wafer and chamber-to-chamber process variations, affecting uniformity and performance.
Innovation Solution
A method for calibrating RF power applied to RF coils by measuring and adjusting the power divider setpoint values to match reference ratios within a tolerance level, and determining calibration factors based on plasma characteristics and chamber pressure to ensure consistent power distribution between coils.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If power divider setpoint values are used to control RF power division between coils, then power distribution can be adjusted, but variations in coil tolerances and RF matching networks cause the actual power ratio to deviate from the intended setpoint value
Solution Approach 1:
The system measures the actual RF power ratio between coils and feeds this information back to adjust the power divider setpoint values. This closed-loop feedback mechanism compensates for deviations caused by component tolerances, ensuring the actual power ratio matches the intended setpoint value within acceptable tolerances.
Solution Approach 2:
The calibration process determines correction factors that modify the relationship between power divider setpoint values and actual RF power ratios. By changing the operational parameters (setpoint values) based on measured deviations, the system achieves accurate power distribution despite hardware variations.
2Device complexity
If standard power divider calibration is used, then device complexity is minimized, but wafer-to-wafer and chamber-to-chamber process variations occur
Solution Approach 1:
The system performs preliminary calibration measurements to determine correction factors before actual processing. By pre-characterizing each chamber's RF power distribution and storing correction factors, the system eliminates process variations without adding complex real-time adjustment mechanisms during production.
Solution Approach 2:
The calibration process creates a reference model (copy) of the ideal power distribution for each chamber. This reference is stored and used to guide power divider adjustments, allowing each chamber to replicate optimal performance without requiring identical hardware configurations.
3Productivity
If no calibration is performed, then the process is simpler and faster, but center-to-edge uniformity and chamber matching are degraded
Solution Approach 1:
Calibration is performed as a preliminary one-time setup procedure rather than a continuous process. The initial calibration measurements and correction factor determination are completed before production, minimizing impact on ongoing productivity while ensuring precise power distribution for center-to-edge uniformity.
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 improves wafer-to-wafer and chamber-to-chamber uniformity, particularly in advanced technology nodes below 40 nanometers, by accounting for hardware tolerances and chamber conditions, ensuring better chamber matching and reduced process variations.
Implementation Method 1
Inductively coupled plasma (ICP) sources can have RF currents flowing along concentric inner and outer coils to inductively couple RF energy into a process gas to form a plasma in a process chamber
Data Source
AI summary
Methods for calibrating RF power applied to a plurality of RF coils are provided. In some embodiments, a method of calibrating RF power applied to a first and second RF coil of a process chamber having a power divider to control a first ratio equal to a first magnitude of RF power provided to the first RF coil divided by a second magnitude of RF power provided to the second RF coil, may include measuring a plurality of first ratios over a range of setpoint values of the power divider, comparing the plurality of measured first ratios to a plurality of reference first ratios, and adjusting an actual value of the power divider at a given setpoint value such that the first ratio of the power divider at the given setpoint matches the corresponding reference first ratio to within a first tolerance level.