Susceptor Pocket Geometry for Epitaxial Wafer Flatness Uniformity
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing susceptors for epitaxial silicon wafer growth result in non-uniform thickness profiles due to growth rate orientation dependence, particularly affecting the circumferential flatness uniformity, especially at the wafer edge.
Innovation Solution
A susceptor design with a counterbore portion where the radial distance and counterbore depth vary at 90° periods, with elliptical arcs that minimize thickness profile variation, ensuring the circumferential thickness profile variation index is 0.75% or less.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a conventional susceptor with fixed radial distance and fixed counterbore depth is used, then the structure is simple and easy to manufacture, but the circumferential flatness uniformity deteriorates due to growth rate orientation dependence
Solution Approach 1:
The susceptor structure is designed with local variations: the radial distance from the center to the opening edge varies in the circumferential direction (describing an elliptical arc), and the counterbore depth varies at 90° periods. These local structural differences compensate for the growth rate orientation dependence of silicon crystal at different orientations, achieving uniform epitaxial layer thickness across the wafer circumference.
Solution Approach 2:
The patent changes the geometric parameters of the susceptor: the radial distance L varies circumferentially (minimum at 0°, 90°, 180°, 270° and maximum at 45°, 135°, 225°, 315°), and the counterbore depth H varies at 90° periods. These parameter variations are specifically designed to counterbalance the growth rate differences caused by crystal orientation, transforming a uniform structure into a non-uniform one that achieves uniform results.
2Manufacturing precision
If the radial distance and counterbore depth are varied to compensate for growth rate orientation dependence, then the circumferential flatness uniformity improves, but the manufacturing complexity increases
Solution Approach 1:
The susceptor employs asymmetric geometry where the opening edge describes an elliptical arc rather than a circle, and the counterbore depth varies periodically. This asymmetric design intentionally creates different radial distances and depths at different circumferential positions to compensate for the inherent asymmetry in silicon crystal growth rates at different orientations.
Solution Approach 2:
The counterbore depth H is designed to vary periodically at 90° intervals around the susceptor circumference. This periodic variation synchronizes with the periodic nature of silicon crystal orientation (which repeats every 90°), creating a matching pattern that effectively compensates for growth rate differences at different orientations.
3Manufacturing precision
If a fixed pocket width is used in the susceptor, then the structure is simple, but the growth rate orientation dependence causes non-uniform epitaxial layer thickness at the wafer edge
Solution Approach 1:
The pocket width (radial distance from center to opening edge) is designed to vary locally around the susceptor circumference, following an elliptical arc pattern. This creates minimum pocket widths at 0°, 90°, 180°, 270° and maximum pocket widths at 45°, 135°, 225°, 315°. These local variations in pocket width compensate for the growth rate orientation dependence, ensuring uniform epitaxial layer thickness particularly at the wafer edge where the effect is most pronounced.
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 significantly improves the circumferential flatness uniformity of epitaxial silicon wafers by effectively controlling growth rate orientation dependence, resulting in more uniform epitaxial layer thickness across the wafer.
Implementation Method 1
an epitaxial layer is grown on a surface of the silicon wafer by vapor deposition (epitaxial growth)
Implementation Method 2
an epitaxial layer is grown on a surface of the silicon wafer by vapor deposition (epitaxial growth)
Implementation Method 3
the difference H between the heights of the upper end (corresponding to the opening edge 110C) and the lower end of the inner wall surface 110A on the opening edge 110C side of the counterbore portion 110 (also referred to as 'counterbore depth') varies at 90° periods in the circumferential direction
Data Source
AI summary
Provided is a susceptor which makes it possible to increase the circumferential flatness uniformity of an epitaxial layer of an epitaxial silicon wafer. A susceptor 100 is provided with a concave counterbore portion on which a silicon wafer W is placed, and the radial distance L between the center of the susceptor and an opening edge of the counterbore portion varies at 90° periods in the circumferential direction. Meanwhile, when the angle at which the radial distance L is minimum is 0°, the radial distance L is a minimum value L1 at 90°, 180°, and 270°; and the radial distance L is a maximum value L2 at 45°, 135°, 225°, and 315°. Accordingly, the pocket width Lp also varies in conformance with the variations of the radial distance L. The opening edge 110C describes four elliptical arcs being convex radially outward when the susceptor 100 is viewed from above.