Vacuum Inductive Sensor Layout for In-Situ Wafer Layer Measurement
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Solution Overview
Problem
Eddy current sensors are not suitable for direct layer characterization in high vacuum cluster tool process chambers due to space constraints, integration issues, and thermal interference, leading to inaccurate and delayed measurements.
Innovation Solution
A measuring device with inductive sensors is designed to operate outside the vacuum chamber, using transmitting and receiving coils encapsulated in non-conductive materials, with signal processing units outside the vacuum, allowing for large distance measurements and avoiding heat-generating components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If eddy current sensors are integrated inside the vacuum chamber, then measurements can be performed in vacuum, but the vacuum chamber requires large space and thermal drifts occur due to heat dissipation limitations
Solution Approach 1:
The measuring device is divided into two separate parts: a sensor head containing the inductive sensor that can be positioned in vacuum, and a separate evaluation unit that processes signals outside the vacuum chamber. This segmentation allows the vacuum chamber to be compact while maintaining measurement capability through vacuum-compatible sensor design.
Solution Approach 2:
A vacuum-compatible cable connection serves as an intermediary to transmit measurement signals between the sensor head in vacuum and the evaluation unit outside vacuum. This intermediary enables signal transmission without requiring the evaluation unit to be physically inside the vacuum chamber, resolving the space contradiction.
2Reliability
If signal amplifier and processing unit are placed inside vacuum chamber, then measurements can be performed, but heat dissipation is limited and thermal drifts distort measurement results
Solution Approach 1:
The signal amplifier and processing unit are extracted from the vacuum chamber and positioned outside in the atmospheric environment. This extraction eliminates the thermal drift problem caused by limited heat dissipation in vacuum, as the evaluation unit can now dissipate heat effectively in atmospheric conditions while maintaining vacuum integrity through the sensor head design.
3Measurement precision
If test wafers are used for layer characterization, then measurements can be performed, but system capacity is lost and process errors are discovered late
Solution Approach 1:
The inductive sensor enables direct measurement of layer characteristics on production wafers themselves, eliminating the need for separate test wafers. The sensor can measure layer thickness and resistance directly during the deposition process, allowing production wafers to serve both as product and as measurement objects, thereby maintaining system capacity and enabling real-time process monitoring.
4Loss of time
If inductive sensors are used for layer characterization, then real-time measurements are possible, but integration in vacuum cluster tools is complex and space-consuming
Solution Approach 1:
The measuring device is segmented into a compact sensor head that integrates the inductive sensor and a separate evaluation unit. This segmentation reduces the integration complexity in vacuum cluster tools by allowing the sensor head to be independently designed and installed in vacuum-compatible locations, while the evaluation unit is positioned externally.
Solution Approach 2:
Vacuum-compatible cable connections serve as intermediaries to link the sensor head in vacuum with the evaluation unit outside vacuum. This intermediary solution simplifies integration by providing a standard interface for signal transmission, avoiding the need for complex integrated electronics within the vacuum chamber.
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
Enables accurate, real-time, and collision-free measurements of layer thickness and resistance on production wafers without interrupting the vacuum, reducing system downtime and costs by eliminating the need for test wafers and improving process control.
Implementation Method 1
an alternating current is applied to a transmitting or induction coil in a sensor head of the eddy current sensor, thus generating an alternating electromagnetic field or primary field. The primary field induces eddy currents in a measurement object to be characterized. The eddy current flowing in the measurement object generates an electromagnetic secondary field which is opposite the primary field generated by the coil
Implementation Method 2
The change in the total field can be detected by means of inductive sensors, e.g. a coil. The field changes depend, for example, on the material as well as on the position of the measurement object in the overall field or on the volume of the material of the measurement object.
Data Source
AI summary
A measuring device for characterizing a measurement object in a vacuum includes at least one inductive sensor having at least one transmitting coil for generating an alternating electromagnetic field, a receiving coil for detecting an impedance change, and a signal amplifier and/or a signal processing unit for evaluating measurement signals. The measuring device can be integrated in a vacuum system with minimal additional space requirements and enables a measurement with high accuracy and high spatial resolution with precise repeatability on a static measurement object and/or a measurement object guided past the measuring device. Both the transmitting and receiving coils as well as the signal amplifier and/or the signal processing unit are arranged outside a vacuum region. The transmitting and receiving coils can each be inserted into a capsule, and the capsules are configured as an integral part of a chamber wall of a vacuum chamber and project into the vacuum.