Wafer Pin Chuck Flatness Repair Using Toroidal Lapping
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Solution Overview
Problem
Conventional techniques face challenges in achieving and maintaining the required flatness and roughness on wafer chucks with plateaued surfaces, particularly due to non-uniform pin distribution and interference with abrasive media, which leads to localized pressure variations and difficulties in correcting mid and high spatial frequency errors.
Innovation Solution
The pins of the wafer chuck are engineered with an annular or pitted surface, and a toroidal-shaped lapping tool is used to impart and restore flatness and roughness, with the tool having a hardness similar to the wafer chuck material to effectively abrade and maintain the surface characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional lapping techniques are used on wafer chucks with plateaued surfaces, then the lapping process can be performed, but non-uniform pin distribution and interference with abrasive media lead to localized pressure variations and difficulties in correcting mid and high spatial frequency errors
Solution Approach 1:
The patent applies local quality by creating pins with non-uniform characteristics - specifically, pins with varying heights and/or radii rather than uniform dimensions. This local variation in pin properties allows different regions of the chuck surface to exert different forces on the wafer, enabling correction of localized flatness errors and interference with abrasive media during lapping. The non-uniform pin distribution and dimensions directly address the localized pressure variations mentioned in the contradiction.
2Device complexity
If pins are made uniform in height and distribution, then the chuck structure is simpler, but friction increases and wafer sticking occurs
Solution Approach 1:
The patent resolves this contradiction by implementing local quality through non-uniform pin characteristics. Instead of uniform pins that cause sticking, the invention uses pins with varying heights and/or radii. This local variation creates differences in contact pressure and friction characteristics across the chuck surface, preventing uniform sticking while maintaining structural simplicity. The non-uniform pin design allows some pins to have reduced friction characteristics while others provide structural support.
3Ease of manufacture
If the lapping tool is softer than the wafer chuck material, then the tool is easier to manufacture, but it cannot effectively abrade and maintain the surface characteristics
Solution Approach 1:
The patent applies parameter changes by selecting a lapping tool material with hardness similar to the wafer chuck material (silicon carbide). This parameter match in hardness enables the tool to effectively abrade and maintain the chuck surface characteristics. The parameter change from using softer, easier-to-manufacture materials to using equally hard materials is justified by the need to maintain precise surface flatness and roughness on the durable silicon carbide chuck.
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 reduces friction and non-repeatable clamping errors, maintains the required flatness and roughness, and allows for in-situ correction of worn surfaces, enhancing the precision and longevity of wafer chucks.
Implementation Method 1
a toroidal-shaped lapping tool is used to impart and restore flatness and roughness, with the tool having a hardness similar to the wafer chuck material to effectively abrade and maintain the surface characteristics
Implementation Method 2
The pins help in reducing the friction so that the wafer can move laterally across the mesas as it flattens out upon settling on the mesas
Data Source
AI summary
In a wafer chuck design featuring pins or “mesas” making up the support surface, engineering the pins to have an annular shape, or to contain holes or pits, minimizes sticking of the wafer, and improves wafer settling. In another aspect of the invention is a tool and method for imparting or restoring flatness and roughness to a surface, such as the support surface of a wafer chuck. The tool is shaped such that the contact to the surface being treated is a circle or annulus. The treatment method may take place in a dedicated apparatus, or in-situ in semiconductor fabrication apparatus. The tool is smaller than the diameter of the wafer pin chuck, and may be approximate to the spatial frequency of the high spots to be lapped. The movement of the tool relative to the support surface is such that all areas of the support surface may be processed by the tool, or only those areas needing correction.