Polishing Device Retainer Ring and Membrane Sheet
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Solution Overview
Problem
Conventional polishing devices for semiconductor wafers experience reduced polishing rates and within-wafer uniformity due to insufficient downward pressure at the periphery, leading to degraded product yield.
Innovation Solution
A polishing device design featuring a retainer ring with a first retainer member of equal thickness to the wafer and a second retainer member, along with a membrane sheet of larger diameter that presses the inner edge of the first retainer member, ensuring uniform pressure distribution across the wafer by adjusting air pressure in closed spaces to effectively press the wafer's periphery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If the membrane sheet periphery is aligned with the wafer periphery, then the structure is simple, but insufficient downward pressure occurs at the wafer periphery
Solution Approach 1:
The membrane sheet is designed with different functional zones: the peripheral portion extends beyond the wafer to provide localized downward pressure at the wafer periphery through the retainer member, while the central portion covers the wafer surface for uniform pressure distribution. This local differentiation resolves the contradiction by providing enhanced pressure where needed without complicating the overall structure.
Solution Approach 2:
The retainer member acts as an intermediary between the membrane sheet periphery and the wafer periphery. It transfers and concentrates the downward force from the membrane sheet to the wafer edge, enabling sufficient peripheral pressure while maintaining the simple alignment structure. The retainer member mediates the force transmission without requiring complex mechanical linkages.
2Force
If high-pressure air is supplied to expand the membrane sheet, then the wafer is pressed against the polishing pad, but the membrane sheet deforms to convex shape causing pressure loss at periphery
Solution Approach 1:
The membrane sheet is designed with differentiated zones where the peripheral portion provides localized support and pressure at the wafer edge, while the central portion maintains uniform pressure distribution. This local quality differentiation compensates for the convex deformation by ensuring the peripheral zone maintains contact and pressure transmission even when the central area loses uniformity.
Solution Approach 2:
The membrane sheet function is segmented into distinct zones: a peripheral portion for edge pressure and support, and a central portion for general wafer contact. This segmentation allows each zone to perform its specific function independently, so that convex deformation in the central area does not completely compromise the pressure distribution, as the peripheral zone maintains effectiveness.
3Ease of operation
If the retainer ring inner edge abuts the wafer periphery, then the wafer is retained in-plane, but the membrane sheet cannot press the wafer periphery effectively
Solution Approach 1:
The retainer member serves as an intermediary element between the membrane sheet and the wafer periphery. It has a first surface that contacts the membrane sheet and a second surface that contacts the wafer, thereby mediating the force transmission. This allows the membrane sheet to apply downward pressure effectively at the wafer periphery while the retainer member maintains in-plane retention, resolving the contradiction between retention and pressure application.
Solution Approach 2:
The retainer member is designed with a thickness dimension that allows it to bridge the gap between the membrane sheet and the wafer surface. By extending in the vertical dimension, it can simultaneously maintain in-plane retention through its outer edge and transmit downward pressure to the wafer periphery through its inner surface, effectively operating in multiple dimensional spaces.
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 design enhances the polishing rate and within-wafer uniformity by maintaining consistent pressure across the wafer's surface, reducing variation in the polished amount to ±5% compared to ±10% in conventional devices, thereby improving product quality.
Implementation Method 1
a membrane sheet for pressing the wafer against the polishing pad
Implementation Method 2
High-pressure air is supplied into the closed space 18 to thereby expand the membrane sheet 17, which presses the wafer 12 against the polishing pad 11
Data Source
AI summary
A polishing device includes a polishing pad for polishing a wafer and a polishing head for holding the wafer. The polishing head has a retainer ring for retaining the wafer in the in-plane direction of the wafer, a membrane sheet for pressing the wafer against the polishing pad, and a head body for supporting the retainer ring and the membrane sheet. The retainer ring has a subordinate retainer member having a ring portion and a plurality of fins extending from the ring portion to retain the peripheral surface of the wafer. The subordinate retainer member has a thickness equal to the thickness of the wafer. The membrane sheet has a diameter larger than the wafer, and presses the wafer and the vicinity of the inner edge of the subordinate retainer member.