Silicon Wafer Support Layout for Heat-Treatment Slip Suppression
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Solution Overview
Problem
Heat treatment of silicon wafers often results in slip generation due to thermal stress at the contact points with supporting elements, leading to reduced wafer yield, especially for larger diameters, as the stress varies with crystal orientation and is difficult to disperse evenly.
Innovation Solution
A method and jig that support silicon wafers with crystal orientations {100} or {110} by positioning the backside in fan-shaped regions between 40° to 60° relative to the reference direction, with additional supporting areas determined by 90° rotations, to minimize shear stress and suppress slip growth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If silicon wafers are supported at three or four points by conventional supporting elements, then the supporting structure is simple and easy to manufacture, but crystal defects called slip initiate from the contact points and grow under thermal stress, decreasing wafer yield
Solution Approach 1:
The patent applies local quality by making the supporting elements have different shapes and sizes at different locations. Specifically, the supporting elements include a flat portion and an inclined portion, where the flat portion contacts the wafer back surface to distribute stress, while the inclined portion provides structural support. This localized differentiation of support element geometry allows stress dispersion at contact points without compromising overall structural simplicity
Solution Approach 2:
The patent applies preliminary action by pre-configuring the supporting elements with specific geometric features (flat portions and inclined portions) before wafer placement. The flat portions are positioned to make contact with the wafer back surface in advance, creating predetermined stress distribution patterns that prevent slip initiation during subsequent thermal processing
2Reliability
If the contact area between wafer and supporting element is widened to disperse gravity stress, then wafer yield should improve, but machining accuracy variations in grooves cause stress concentration at specific points, acting as slip initiation points
Solution Approach 1:
The patent applies local quality by providing different supporting elements at different grooves rather than using uniform contact surfaces. Each supporting element is specifically designed with flat portions of appropriate sizes and orientations to compensate for groove machining variations, ensuring uniform stress distribution despite manufacturing tolerances in groove positions and dimensions
Solution Approach 2:
The patent applies parameter changes by varying the geometry parameters of supporting elements (flat portion area, inclined portion angle, element position) to optimize stress distribution. By adjusting these parameters, the patent compensates for groove machining accuracy variations and prevents stress concentration that would otherwise occur with uniform wide-contact supporting structures
3Device complexity
If conventional supporting elements are used, then the supporting device is simple, but thermal stress causes slip growth and extension, reducing wafer quality
Solution Approach 1:
The patent applies local quality by designing supporting elements with differentiated geometry where flat portions contact the wafer back surface to distribute thermal stress, while inclined portions provide structural support. This localized geometric differentiation enables effective stress dispersion during thermal processing without requiring complex overall device architecture
Solution Approach 2:
The patent applies the blessing in disguise principle by utilizing the inclined portions of the supporting elements to convert potentially harmful stress concentrations into beneficial stress distribution patterns. The inclined geometry transforms point-contact stress into distributed stress over the flat portions, converting the harmful effect of thermal stress into a beneficial stress dispersion mechanism
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 significantly reduces shear stress at contact points, effectively preventing slip growth and extension, thereby improving the yield of heat-treated silicon wafers by supporting the wafers in positions where maximum resolved shear stress is minimized.
Implementation Method 1
the stress (shear stress) contributing to slip extension varies depending on the crystal orientation
Implementation Method 2
such slip grows and develops under the influence of the thermal stress caused during heat treatment
Data Source
AI summary
Provided is a method applicable to the production of silicon wafers having crystal orientation <100> or <110> and consisting in specifying wafer-supporting positions on the occasion of heat treatment in a vertical heat treatment furnace as well as a heat treatment jig for use in carrying out that method. It becomes possible to suppress the shear stress which contributes to the extension of the slip generated at each wafer-supporting element contact point as an initiation, suppress slip growth and thus markedly improve the yield of heat-treated silicon wafers. The heat-treated wafer obtained by using the supporting method and the heat treatment jig has few slip, in particular has no long and large slip, and is high in quality.