Susceptor Annular Step for Epitaxial Wafer Scratch Reduction
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Solution Overview
Problem
The existing methods for growing epitaxial films on semiconductor wafers result in scratches on the rear surface due to friction between the wafer and the susceptor, leading to particle generation during device processing, which reduces yield and affects the flatness of the epitaxial wafer.
Innovation Solution
A method and structure where the semiconductor wafer is supported by an annular step portion on the susceptor, allowing a predetermined range of the rear surface to be in surface or line contact, reducing friction-induced scratches and minimizing film formation on the rear surface, thereby preventing particle generation and achieving ultra-flatness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the wafer is supported by the susceptor in the boundary area with the chamfered surface, then the wafer can be stably positioned, but scratches are caused on the wafer rear surface due to friction between the wafer and susceptor
Solution Approach 1:
A wafer supporting projection is introduced as an intermediary element between the wafer and susceptor. The projection is made of a material softer than the wafer (such as silicon or silicon carbide with controlled hardness) to prevent scratch damage while maintaining stable positioning. The projection contacts the wafer rear surface in the boundary area with the chamfered surface, distributing the contact stress and eliminating direct friction between the hard susceptor and soft wafer.
Solution Approach 2:
The hardness parameter of the supporting structure is changed by using a material softer than the wafer for the wafer supporting projection. This parameter change allows the projection to deform slightly under load, reducing contact stress and preventing scratches on the wafer rear surface while maintaining stable positioning.
2Strength
If the wafer rear surface is in contact with the susceptor during epitaxial growth, then the wafer is securely held, but film formation occurs on the wafer rear surface affecting ultra-flatness
Solution Approach 1:
The wafer supporting projection is designed with specific dimensional parameters (height, diameter, and position) to create localized contact only in the boundary area with the chamfered surface. This local contact provides sufficient holding strength while minimizing the contact area to prevent film formation on the wafer rear surface, thus maintaining ultra-flatness of the epitaxial wafer.
Solution Approach 2:
Instead of providing full surface contact between the wafer rear surface and susceptor, only partial contact is provided through the wafer supporting projection in the boundary area. This partial action is sufficient to secure the wafer during epitaxial growth while preventing excessive film formation that would occur with broader contact areas.
3Temperature
If the susceptor material is silicon carbide for high temperature resistance, then the susceptor can withstand epitaxial growth temperatures, but the difference in thermal expansion coefficient causes increased friction and scratches
Solution Approach 1:
The wafer supporting projection acts as a mediator between the silicon carbide susceptor and the silicon wafer. The projection material has thermal expansion properties intermediate between SiC and Si, reducing the differential thermal expansion effect. This intermediary layer accommodates thermal expansion differences during heating and cooling cycles, minimizing friction and preventing scratches on the wafer rear surface.
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
The approach effectively reduces scratches and particle deposition on the front surface, enhancing device yield and achieving ultra-flatness of the epitaxial wafer by adjusting the supporting position and design of the susceptor's annular step portion.
Implementation Method 1
when being heated by a heater provided external to the reactor
Implementation Method 2
the susceptor has a higher coefficient of thermal expansion than the silicon wafer, as the coefficient of thermal expansion of SiC is 4.8×10−6/k and that of Si is 2.5×10−6/k
Implementation Method 3
an epitaxial film is grown on a front surface of a silicon wafer by vapor-phase epitaxial growth
Implementation Method 4
the silicon wafer is reacted with a variety of source gases (raw material gas and reactive gas), which pass through the reactor
Data Source
AI summary
An annular step portion provided to a periphery of a wafer housing portion is provided to an area with which an area of 1 to 6 mm from a boundary line with a chamfered surface of a wafer rear surface toward a wafer center comes in contact. As a result, it is possible to produce an epitaxial wafer having no scratch in a boundary area between the rear surface and the chamfered surface, and to eliminate particles generated due to a scratch in a device process.