Grinding Apparatus Wafer Thickness Control
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Solution Overview
Problem
Grinding apparatuses often produce slight arcuate irregularities on ground wafers due to cyclic variations in thickness, which can negatively impact devices formed on the wafers.
Innovation Solution
A grinding apparatus with a chuck table, table rotating mechanism, grinding unit, spindle rotating mechanism, noncontact thickness measuring instrument, and rotation controlling section, where the rotation controlling section adjusts the rotational speed of the chuck table relative to the spindle to minimize cyclic variations in thickness, shifting the rotational speed ratio from an integer if the maximum thicknesswise difference exceeds a tolerance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If the chuck table rotates at a constant speed during grinding, then the grinding process is simple and stable, but cyclic variations in thickness occur along the direction of rotation, causing arcuate irregularities on the ground surface
Solution Approach 1:
The patent applies dynamics by transitioning from constant rotation to variable rotation speed. The rotation speed of the chuck table is dynamically adjusted during the grinding process based on real-time thickness measurements, allowing the system to adapt to varying material removal rates and prevent cyclic thickness variations that cause arcuate irregularities.
Solution Approach 2:
The patent implements feedback control by continuously measuring the thickness of the workpiece during grinding and using this information to adjust the rotation speed of the chuck table. The thickness measurement unit provides real-time feedback to the control unit, which then modifies the rotation speed to maintain uniform thickness and eliminate cyclic variations.
2Manufacturing precision
If the rotational speed ratio between spindle and chuck table is an integer, then the grinding process is stable and easy to control, but maximum thicknesswise differences are amplified, creating significant arcuate irregularities
Solution Approach 1:
The patent applies parameter changes by modifying the rotational speed ratio between the spindle and chuck table. Instead of maintaining a fixed integer ratio, the system dynamically adjusts the rotation speed of the chuck table to achieve a non-integer ratio that minimizes thicknesswise variations. This parameter adjustment prevents the amplification of cyclic variations that occurs with integer ratios.
3Manufacturing precision
If real-time thickness measurement and rotation speed adjustment are implemented, then arcuate irregularities are suppressed and surface planarity is improved, but the control system becomes more complex and requires additional sensors and processing
Solution Approach 1:
The patent implements feedback control by continuously measuring the thickness of the workpiece during grinding and using this information to adjust the rotation speed of the chuck table. The thickness measurement unit provides real-time feedback to the control unit, which then modifies the rotation speed to maintain uniform thickness and eliminate cyclic variations.
Solution Approach 2:
The patent replaces mechanical control methods with automated sensor-based control. Instead of relying on mechanical timing devices or manual adjustment mechanisms, the system uses electronic sensors to measure thickness and electronic control systems to adjust rotation speed, reducing mechanical complexity while improving precision.
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 effectively reduces cyclic variations and planarizes the ground surface of the wafer, suppressing the formation of slight arcuate irregularities.
Implementation Method 1
a noncontact thickness measuring instrument for measuring a thickness of the wafer held on the holding surface, in a noncontact manner
Data Source
AI summary
A rotation controlling section of a control unit calculates a maximum thicknesswise difference in a wafer by using a noncontact thickness measuring instrument, and if the maximum thicknesswise difference exceeds a tolerance, relatively changes a rotational speed of a chuck table relative to a rotational speed of a spindle. This can shift a rotational speed ratio, which is a ratio between the rotational speed of the spindle and the rotational speed of the chuck table, from an integer. Therefore, the maximum thicknesswise difference can be made small through spark-out processing. As a result, cyclic variations in thickness value of the wafer are reduced, enabling planarization of a ground surface of the wafer.