Wafer Edge Measurement Using Capacitive Sensors
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Solution Overview
Problem
Existing semiconductor fabrication processes face challenges in precisely positioning and rotating substrates during thermal processes like RTP, where uneven heating and optical sensor reliability issues arise due to direct contact and harsh conditions, leading to positioning errors.
Innovation Solution
A method and apparatus using capacitive sensors and a control system to support and rotate substrates without direct contact, measuring and controlling position and rotation using sensors positioned on the same X-Y plane, with a rotation sensor to monitor and adjust the substrate's non-uniform features, ensuring they do not pass through the sensors' field of view, thereby reducing disruptions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If direct contact wafer handling is used, then wafer rotation control is simplified, but heating uniformity deteriorates due to contact with support components
Solution Approach 1:
The patent introduces an optical field as an intermediary between the wafer and sensors. Optical sensors detect wafer position and rotation through non-contact optical measurement, eliminating the need for direct mechanical contact while maintaining precise rotation control. This resolves the contradiction by using light as a mediator to achieve both heating uniformity (no contact) and rotation control (precise measurement).
Solution Approach 2:
The patent replaces mechanical contact-based rotation control with optical field-based detection and control. Instead of using mechanical features that require direct contact, the system uses optical sensors to detect wafer position and a control system to adjust wafer rotation, substituting mechanical systems with optical and electronic systems to achieve both contactless operation and precise control.
2Measurement precision
If optical sensors are used in harsh chamber conditions, then wafer position monitoring is achieved, but sensor reliability deteriorates due to high temperature and process gas deposits
Solution Approach 1:
The patent positions optical sensors outside the harsh processing chamber environment, using optical fields that can penetrate chamber walls or windows. The optical field serves as an intermediary that allows position monitoring without exposing sensitive sensors to high temperatures and corrosive process gases, thereby maintaining both measurement precision and sensor reliability.
Solution Approach 2:
The patent replaces direct physical sensing within the harsh environment with remote optical sensing. By using optical fields that can transmit through chamber boundaries, the system achieves position monitoring without mechanical or physical contact between sensors and the harsh environment, preserving sensor reliability while maintaining measurement capability.
3Ease of operation
If notched wafers are used for orientation, then wafer positioning is simplified, but measurement accuracy deteriorates when the notch passes through optical sensor field of view
Solution Approach 1:
The patent implements preliminary action by having the control system predict when the notch will enter the sensor field of view based on wafer rotation direction and speed. Before the notch obscures the measurement, the system pre-adjusts the wafer position or modifies the measurement timing, ensuring continuous accurate measurement without interruption when the notch passes through the field of view.
Solution Approach 2:
The patent uses feedback control to continuously monitor wafer position and rotation, detecting when the notch approaches the sensor field of view. The control system then provides real-time adjustments to wafer positioning or measurement timing based on this feedback, maintaining measurement precision despite the presence of the notch feature that simplifies orientation.
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 enables precise, reliable positioning and rotation of substrates with improved heating uniformity and reduced particle contamination, enhancing processing accuracy and throughput by avoiding direct contact and harsh environment limitations.
Implementation Method 1
a first capacitive sensor positioned to detect a location of an edge of the substrate
Implementation Method 2
RTP chambers subject substrates to highly controlled thermal cycles, such as heating a substrate to over 1000° C. in less than ten seconds
Data Source
AI summary
Devices and methods are provided for positioning and/or rotating a substrate without solid contact, such as by floating the wafer on a thin layer of gas. Since there is no solid contact with components of a processing chamber, features on the wafer are used to determine wafer position and rotational speed. Closed loop control systems are provided with capacitive sensors to monitor the position of the edge of the wafer in a horizontal plane. Control systems may also monitor the position of a wafer feature as it rotates, such as a notch in the edge of the wafer. Because the presence of a notch can disrupt sensors facing the edge of the wafer, methods and devices to reduce or eliminate this disruption are also provided.