Semiconductor Wafer Lapping with Surface Reversal to Suppress Ring Patterns
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Solution Overview
Problem
Conventional lapping methods for semiconductor wafers result in ring-shaped patterns in nanotopography maps due to uneven pressing forces applied during the lapping process, which are not adequately removed by subsequent polishing steps, affecting the nanotopography quality of the wafers.
Innovation Solution
A method involving reversing the surfaces of the semiconductor wafer during lapping, specifically when the lapping amount reaches 40% to 60% of the target, to mitigate the machining-induced undulations, thereby preventing the formation of ring-shaped patterns in nanotopography maps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lapping methods are used with continuous pressing forces, then the lapping process is simple and efficient, but ring-shaped patterns are formed in nanotopography maps due to uneven pressing forces
Solution Approach 1:
The lapping process is divided into multiple stages with periodic reversal of the wafer. The method performs lapping for a first period, then reverses the wafer and continues lapping for a second period. This periodic action distributes the uneven pressing forces over time and prevents the accumulation of ring-shaped patterns that occur in continuous lapping processes.
Solution Approach 2:
The wafer is reversed between lapping stages, switching which surface faces the lapping plate. This inversion ensures that any localized uneven pressing forces affect different areas of the wafer in subsequent stages, preventing the formation of persistent ring-shaped patterns and improving overall nanotopography uniformity.
2Manufacturing precision
If lapping is performed for extended periods to remove machining undulations, then surface flatness improves, but ring-shaped patterns become more pronounced due to cumulative uneven pressing forces
Solution Approach 1:
By implementing periodic lapping with intermediate reversal, the process extends the total lapping time while preventing the cumulative effect of uneven pressing forces. The reversal interrupts the pattern formation mechanism, allowing extended lapping to achieve better surface flatness without exacerbating ring-shaped patterns.
Solution Approach 2:
The continuous lapping process is segmented into discrete stages with reversal in between. This segmentation breaks the cumulative effect of uneven pressing forces that would otherwise build up over extended lapping periods, allowing the process to achieve high surface flatness without generating harmful ring-shaped patterns.
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 suppresses the formation of ring-shaped patterns in nanotopography maps, ensuring improved nanotopography quality by reducing machining effects and allowing for better polishing results, with no ring patterns observed in the evaluation of mirror-polished surfaces.
Implementation Method 1
a solution containing abrasive grains (not shown) is supplied, the semiconductor wafers W are pressed by the upper plate 10A and the lower plate 10B, thus the front and back surfaces of the semiconductor wafers W are lapped
Implementation Method 2
each carrier plate 20 is made to perform planetary motion, thereby lapping a front surface and a back surface of the semiconductor wafer
Data Source
AI summary
Provided is a method of lapping a semiconductor wafer, which can suppress the formation of a ring-shaped pattern in a nanotopography map. The method of lapping a semiconductor wafer includes: a stopping step of stopping lapping of a semiconductor wafer; a reversing step of reversing surfaces of the semiconductor wafer facing a upper plate and a lower plate after the stopping step; and a resuming step of resuming lapping of the semiconductor wafer after the reversing step while maintaining the reversal of the surfaces facing the plates.