Double-Side Wafer Polishing Feedback Control
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Solution Overview
Problem
Existing double-side polishing methods for wafers face variations in GBIR values between batches due to wear of carrier plates and polishing pads, as well as changes in polishing slurry concentration, leading to wafers being out of specifications.
Innovation Solution
A method of double-side polishing that calculates polishing time based on a formula incorporating the center thickness and GBIR values of previous batches, with coefficients A1, A2, and A3, to maintain target GBIR values and reduce batch-to-batch variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Extent of automation
If polishing amount is controlled based on torque fluctuation of drive mechanism, then polishing process can be automated, but GBIR values vary between batches due to wear of carrier plate and polishing pads
Solution Approach 1:
The patent implements feedback control by measuring the actual GBIR value of polished wafers and using this measurement to adjust the polishing time for subsequent batches. The control unit calculates the difference between the actual GBIR value and the target GBIR value, then modifies the polishing time accordingly to compensate for variations caused by wear of carrier plates and polishing pads, thereby maintaining consistent GBIR values across batches.
Solution Approach 2:
The patent changes the control parameter from torque-based automated control to time-based control with feedback adjustment. By measuring GBIR values and using this data to dynamically adjust polishing time, the system adapts to wear of components and maintains manufacturing precision while preserving automation.
2Manufacturing precision
If polishing time is extended to compensate for wear, then GBIR values can be maintained, but productivity decreases
Solution Approach 1:
The patent dynamically adjusts the polishing time parameter based on measured GBIR values and wear characteristics. Rather than using a fixed extended polishing time, the system calculates the precise adjustment needed, thereby maintaining GBIR control while minimizing the impact on productivity by avoiding unnecessary extended polishing cycles.
3Shape
If polishing amount is increased to account for wear, then flatness can be maintained, but material removal exceeds specifications
Solution Approach 1:
The patent uses feedback from GBIR measurements to precisely control the amount of material removal. By measuring the actual GBIR value and adjusting polishing time based on the difference from the target value, the system removes only the necessary amount of material to achieve the desired flatness and shape, avoiding excessive material removal while accounting for wear of polishing components.
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 variations in GBIR values between batches, ensuring wafers meet specifications by adjusting polishing time based on previous batch data.
Implementation Method 1
a polishing pad is attached to each of an undersurface of the upper plate and a top surface of the lower plate... both surfaces of the wafer are polished
Data Source
AI summary
Provided is a method of double-side polishing a wafer by which variations of the GBIR values of polished wafers between batches can be reduced. In the method of double-side polishing a wafer, a current batch includes measuring the center thickness of the wafer before polishing (S100); setting a target GBIR value within a predetermined range (S110); calculating a polishing time of the current batch based on Formula (1) (S120); and polishing both surfaces of the wafer for the calculated polishing time (S130).Polishing time of current batch=polishing time of previous batch+A1×(center thickness of wafer before polishing in previous batch−center thickness of wafer before polishing in current batch)+A2×(GBIR value of wafer after polishing in previous batch−target GBIR value)+A3 (1),where A1, A2, and A3 are predetermined coefficients.