Polishing Head with Movable Mid-Plate for Wafer Flatness
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Solution Overview
Problem
Current polishing heads face challenges in maintaining uniformity and preventing surface defects during semiconductor wafer polishing, particularly at the outer peripheral portions, due to variations in template thickness and pressure distribution, leading to issues like outer circumference sag and difficulty in detaching the workpiece from the polishing pad.
Innovation Solution
A polishing head with an annular rigid ring, an elastic film, and a movable mid-plate that adjusts the shape of the elastic film by controlling the incompressible fluid pressure within a sealed space, allowing for uniform polishing and preventing surface defects by adjusting the vertical position of the mid-plate to optimize the workpiece's attachment and detachment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a template assembly with a template attached to an elastic film is used to hold the workpiece, then the workpiece can be held without wax, but variation in thickness of the elastic film produces small pressure distribution resulting in waviness of the polished front surface
Solution Approach 1:
The patent changes the physical state of the fluid from compressible (gas) to incompressible (liquid) to eliminate pressure distribution variations. This parameter change ensures uniform pressure transmission across the elastic film, preventing waviness while maintaining the waxless holding capability.
Solution Approach 2:
The patent uses a rigid plate as a backup support that copies and reinforces the pressure distribution pattern. The rigid plate with its support portions provides a stable geometric reference that compensates for elastic film thickness variations, ensuring uniform pressure application.
2Force
If pressurized fluid is supplied to inflate the elastic film to press the workpiece against the polishing pad, then the workpiece can be held firmly, but the rubber film inflates largely at the gap between the template and workpiece causing excessive polishing at the outer peripheral portion
Solution Approach 1:
The patent changes the fluid from compressible gas to incompressible liquid, which fundamentally alters the pressure transmission characteristics. The incompressible fluid distributes pressure uniformly throughout the sealed space, preventing localized inflation at gaps and ensuring even pressure distribution across the workpiece surface.
Solution Approach 2:
The rigid plate acts as an intermediary between the fluid pressure and the workpiece. It receives the uniform pressure from the incompressible fluid and redistributes it through its support portions to the elastic film, mediating the pressure transmission to eliminate localized inflation effects.
3Reliability
If the template has an inner diameter larger than the outer diameter of the workpiece to prevent the workpiece from coming off, then the workpiece is secured, but there is a gap between the template and workpiece where the rubber film inflates causing outer circumference sag
Solution Approach 1:
The patent changes the fluid compressibility parameter from gas to liquid, which eliminates the inflation problem at the template-workpiece gap. The incompressible fluid maintains uniform pressure even in the presence of the gap, preventing rubber film distortion and outer circumference sag while retaining workpiece security.
Solution Approach 2:
The rigid plate serves multiple functions: it provides backup support for the elastic film, distributes fluid pressure uniformly, prevents localized inflation at gaps, and maintains the structural integrity of the polishing head assembly, making the system versatile and robust.
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 configuration ensures uniform polishing up to the outermost peripheral portion of the workpiece without surface defects and facilitates easy detachment from the polishing pad, enhancing the workpiece's flatness and process efficiency.
Implementation Method 1
an incompressible fluid 2 enclosed in a sealed space 6 defined by the rigid ring 4, the elastic film 3, and the mid-plate 5
Implementation Method 2
an elastic film 3 made of e.g., rubber, and bonded on a lower surface side of the rigid ring 4
Data Source
AI summary
The present invention provides a polishing head including: an annular rigid ring; an elastic film bonded to the rigid ring; and an upward and downward movable mid-plate, the mid-plate defining a first sealed space together with the rigid ring and the elastic film; an incompressible fluid enclosed in a sealed space; and a mid-plate positioning device for adjusting vertical position of the mid-plate, to hold a back surface of a workpiece on a lower surface of the elastic film and polish a front surface by bringing the front surface into contact with a polishing pad attached to a turn table, wherein the mid-plate can adjust a shape of the lower surface of the elastic film by adjusting the vertical position of the mid-plate. The polishing head polishes a workpiece without generating surface defects on the workpiece surface and easy detachment of the workpiece from a polishing pad after polishing.