Laminate Polishing Pad Structure for Wafer NT Flatness
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Solution Overview
Problem
The transfer of asperities from a hardened polishing pad to the wafer surface during single-side polishing, resulting in nanotopography (NT) degradation, is exacerbated by the deformation of detachable turntables due to vacuum suction, particularly with improved NT quality levels.
Innovation Solution
A polishing pad with a laminate structure comprising a polishing layer, a PET sheet layer, an elastic layer, and adhesive layers, providing a compressibility of 16% or more, absorbs deformations caused by vacuum suction grooves and maintains a flat polish-processing surface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If a hardened polishing pad with thickness of 0.8 mm or less is used to suppress creep deformation and enhance flatness quality, then flatness quality is improved, but nanotopography quality degrades due to asperity transfer to the wafer surface
Solution Approach 1:
The polishing pad is constructed as a composite structure combining a hard top layer (0.8 mm thick with Asker C 63 hardness) for maintaining flatness quality and a soft underlying layer (compressibility 18% or more) for absorbing deformations. This composite structure allows the hard top layer to suppress creep deformation while the soft underlying layer prevents asperity transfer to the wafer surface, thereby resolving the contradiction between flatness quality and nanotopography quality
Solution Approach 2:
The polishing pad exhibits local quality differentiation where the top layer (0.8 mm thick) has high hardness (Asker C 63) to maintain flatness, while the underlying layer has high compressibility (18% or more) to absorb deformations. This spatial differentiation of material properties allows each layer to perform its specific function: the hard top layer ensures flatness quality while the soft underlying layer protects nanotopography quality by preventing asperity transfer
2Ease of operation
If a detachable turntable with thickness of 20 mm or less is used for easy replacement and operation, then ease of operation is improved, but the turntable deforms under vacuum suction, transferring deformation to the wafer surface
Solution Approach 1:
The detachable turntable thickness is optimized to 20 mm or less (specifically 15-20 mm) to facilitate easy replacement and operation, while the hard top layer of the polishing pad (0.8 mm thick with Asker C 63 hardness) compensates for the turntable deformation by maintaining a stable polish-processing surface. The soft underlying layer (compressibility 18% or more) further absorbs residual deformations, allowing thin turntables to be used without compromising manufacturing precision
3Reliability
If vacuum suction is applied to immobilize the detachable turntable on the base turntable, then reliability of turntable fixation is improved, but the turntable and polishing pad deform following the groove paths, transferring asperity to the wafer
Solution Approach 1:
The polishing pad acts as an intermediary layer between the vacuum suction system and the wafer. The soft underlying layer (compressibility 18% or more) absorbs the deformation caused by vacuum suction, preventing it from being transferred to the wafer surface. Meanwhile, the hard top layer (0.8 mm thick with Asker C 63 hardness) maintains a stable polish-processing surface, thereby allowing reliable vacuum fixation without compromising nanotopography quality
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
The laminate structure effectively prevents NT quality degradation of polished wafers by absorbing deformations, maintaining the polish-processing surface flatness and reducing NT degradation to levels equivalent to pre-polishing conditions.
Implementation Method 1
the elastic layer absorbs deformations caused by vacuum suction grooves and maintains a flat polish-processing surface
Implementation Method 2
a detachable polishing turntable immobilized on the upper surface of the base turntable by vacuum suction
Data Source
AI summary
A single-side polishing apparatus including: a base turntable having a groove for vacuum suction; a detachable polishing turntable immobilized by vacuum suction; a polishing pad; and a polishing head configured to hold a wafer. The single-side polishing apparatus brings a surface of a wafer held by the polishing head into sliding contact with the polishing pad for polishing. The polishing pad includes a polishing layer configured to polish the wafer surface, a first adhesive layer, a PET sheet layer, a second adhesive layer, an elastic layer, and a third adhesive layer for attachment to the polishing turntable. The layers are sequentially stacked. The polishing pad has a compressibility of 16% or more.