Bonded Silicon Wafer Polishing Torque Feedback Control
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Solution Overview
Problem
Existing methods for producing bonded silicon wafers with an oxygen ion implanted layer as a polishing stop face challenges in achieving high accuracy in polishing stop timing and preventing over-etching, leading to variations in active layer thickness.
Innovation Solution
The method involves forming an oxygen ion implanted layer on a silicon wafer for active layer, bonding it to a support layer, and polishing on a rotating platen with a polishing means to detect changes in physical properties, such as friction resistance, to accurately stop polishing before the layer is over-etched.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If chemical polishing with caustic solution is used to thin the active layer, then polishing efficiency is improved, but it becomes very difficult to judge whether the polishing reaches the oxygen ion implanted layer, leading to inaccurate polishing stop timing
Solution Approach 1:
The patent introduces an intermediary detection mechanism (torque sensor) that mediates between the polishing process and the control system. The torque sensor detects changes in rotational torque caused by the exposure of the oxygen ion implanted layer, providing an indirect but accurate signal for polishing stop timing without requiring direct visual inspection or breaking the polishing continuity.
Solution Approach 2:
The patent implements a feedback control system where the rotational torque signal from the torque sensor is fed back to the polishing control system. This feedback loop allows real-time monitoring of the polishing process and automatic termination when the predetermined torque value is detected, ensuring accurate polishing stop timing while maintaining high polishing efficiency.
2Manufacturing precision
If polishing continues to ensure thickness uniformity, then active layer thickness variation is reduced, but the oxygen ion implanted layer is over-etched by mechanical polishing action
Solution Approach 1:
The feedback control system using torque sensor detection prevents over-etching by automatically stopping the polishing process when the oxygen ion implanted layer is exposed. The predetermined torque value serves as a precise threshold that signals the optimal stop point, ensuring thickness uniformity is achieved without excessive polishing that would remove the implanted layer.
Solution Approach 2:
The patent performs preliminary action by establishing the oxygen ion implanted layer as a sacrificial stop layer before the actual polishing begins. This pre-positioned layer serves as a built-in reference that guides the polishing depth, allowing the process to achieve uniform thickness while automatically preventing penetration into the underlying structure.
3Measurement precision
If polishing is stopped once to measure thickness and calculate polishing rate, then polishing stop timing accuracy is improved, but productivity is reduced due to interrupted polishing process
Solution Approach 1:
The patent replaces the mechanical interruption approach (stopping to measure and calculate) with a continuous mechanical sensing system. The torque sensor provides continuous real-time feedback during polishing, eliminating the need to stop the process for measurements. This substitution maintains measurement precision while preserving productivity by keeping the polishing process uninterrupted.
Solution Approach 2:
The patent ensures continuity of useful action by maintaining the polishing process running continuously without interruptions. The torque-based detection system operates in real-time during polishing, allowing the process to proceed uninterrupted from start to finish, thereby maximizing productivity while maintaining accurate control through continuous monitoring.
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 allows for precise control of the polishing process, reducing variations in active layer thickness and preventing over-etching of the oxygen ion implanted layer, resulting in a bonded silicon wafer with improved thickness uniformity.
Implementation Method 1
a step of implanting oxygen ions from one surface of a silicon wafer for active layer to form an oxygen ion implanted layer
Implementation Method 2
stopping the polishing at a time of detecting change of physical properties on the rotating platen... such as friction resistance
Implementation Method 3
A part (silicon layer) of the wafer for active layer is polished by chemical polishing action with a caustic solution as a polishing solution. When etching is conducted with the caustic solution, the difference of etching rate between silicon and SiO2 is large
Data Source
AI summary
A bonded silicon wafer is produced by a method comprising a step of implanting oxygen ions from one surface of a silicon wafer for active layer to form an oxygen ion implanted layer, a step of bonding the one surface of the silicon wafer for active layer to one surface of a silicon wafer for support layer and then conducting a heat treatment for strengthening the bonding to form a silicon wafer composite, a step of polishing a silicon portion at a side of the silicon wafer for active layer in the silicon wafer composite on a rotating platen having a polishing means and stopping the polishing at a time of detecting change of physical properties on the rotating platen resulting from the exposure of at least a part of the oxygen ion implanted layer and a step of removing the oxygen ion implanted layer.