Modeling Wafer Bias from RF Generator Output
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Solution Overview
Problem
The monitoring and control of plasma performance in plasma-based systems using voltage measurements are costly, time-consuming, and often unsatisfactory, particularly due to the expense and potential malfunctions of voltage probes, which may fail during manufacturing processes.
Innovation Solution
A method and system that utilize modeling to determine wafer bias by propagating complex voltage and current from an RF generator through models of RF transmission lines and impedance matching circuits, eliminating the need for direct voltage probe measurements, and using calibrated voltage and current probes to measure complex voltages and currents, providing more accurate wafer bias calculations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If voltage probes are used to monitor and control plasma performance, then plasma operation can be monitored, but the cost increases and the probes may malfunction during manufacturing processes
Solution Approach 1:
The patent creates an electrical model that replicates the electrical characteristics of the plasma system components (RF generator, impedance matching circuit, RF transmission line, electrostatic chuck). This virtual copy allows monitoring and control functions to be performed on the model rather than requiring physical voltage probes in the actual plasma system, thereby eliminating probe-related costs and malfunction risks while maintaining monitoring capability.
Solution Approach 2:
The patent replaces the physical voltage probe measurement system with an electrical modeling and computation system. Instead of using physical probes to measure voltage, the system uses an electrical model with computed complex voltage and current values to determine wafer bias, substituting mechanical/physical measurement with electrical computation.
2Loss of information
If voltage probes are used to measure plasma voltage, then plasma performance can be monitored, but the process becomes time-consuming
Solution Approach 1:
The patent performs preliminary actions by pre-establishing the electrical model of the plasma system components before actual plasma operation. The model includes pre-defined electrical characteristics and relationships. During operation, the system directly computes wafer bias using the pre-established model and measured generator output, eliminating the need for time-consuming voltage probe measurements and manual calculations.
3Measurement precision
If traditional voltage-based methods are used to determine wafer bias, then measurement can be performed, but accuracy is reduced compared to direct complex voltage and current measurement
Solution Approach 1:
The patent introduces an electrical model as an intermediary between the RF generator output measurements and the wafer bias determination. The model acts as a mediator that translates generator output complex voltage and current measurements into accurate wafer bias values by accounting for the electrical characteristics of intermediate components (impedance matching circuit, RF transmission line, electrostatic chuck), thereby achieving high accuracy without direct measurement at the wafer location.
Data Source
AI summary
Systems and methods for determining wafer bias are described. One of the methods includes detecting output of a generator to identify a generator output complex voltage and current (V&I). The generator is coupled to an impedance matching circuit and the impedance matching circuit is coupled to an electrostatic chuck (ESC). The method further includes determining from the generator output complex V&I a projected complex V&I at a point along a path between an output of a model of the impedance matching circuit and a model of the ESC. The operation of determining of the projected complex V&I is performed using a model for at least part of the path. The method includes applying the projected complex V&I as an input to a function to map the projected complex V&I to a wafer bias value at the ESC model.