SOI Wafer Bonding Barrier for Dopant Diffusion Suppression
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Solution Overview
Problem
The existing methods for manufacturing SOI wafers face challenges with dopant contamination and warpage, particularly due to autodoping and solid phase diffusion from the buried oxide film, which affect the conductivity type and resistivity of the SOI layer.
Innovation Solution
A method involving a base wafer with a dopant concentration of 1×1017 atoms/cm3 or more, where a CVD insulator film and a barrier silicon layer with a lower dopant concentration are formed on the base wafer before thermal oxidation, creating a barrier silicon oxide film to prevent dopant diffusion during bonding and subsequent heat treatments, thereby suppressing autodoping and solid phase diffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a thick oxide film is formed on the base wafer to bond the base wafer to the bond wafer, then bonding strength is improved, but boron contained in the thermal oxide film diffuses outward to contaminate the SOI layer
Solution Approach 1:
A CVD insulator film is introduced as an intermediary layer between the base wafer and the bond wafer. This CVD film acts as a barrier that prevents boron diffusion from the thermal oxide film to the SOI layer, while still allowing the bonding interface to function properly. The CVD insulator film mediates between the conflicting requirements of strong bonding and dopant prevention.
Solution Approach 2:
The CVD insulator film is formed on the base wafer surface before the bonding process. This preliminary action creates a protective barrier in advance that prevents boron diffusion during subsequent bonding heat treatment and flattening heat treatment processes, eliminating the need for post-bonding corrections.
2Stability of the object's composition
If base wafers heavily-doped with boron are used to suppress warpage and increase gettering capability, then mechanical stability is improved, but autodoping occurs during heat treatment contaminating the SOI layer
Solution Approach 1:
The CVD insulator film serves as a mediator between the heavily-doped base wafer and the bond wafer/SOI layer. It allows the base wafer to maintain its heavy doping for mechanical stability and gettering capability, while simultaneously blocking the autodoping effect during heat treatment processes.
3Manufacturing precision
If ion implantation delamination method is used to thin the bond wafer, then thickness uniformity of the SOI layer is improved, but extremely large energy for ion implantation is required when thick oxide films are formed
Solution Approach 1:
The CVD insulator film is formed preliminarily on the base wafer before bonding. This preliminary formation of a thin CVD film (rather than a thick thermal oxide film) reduces the ion implantation energy required for delamination while still providing sufficient barrier function to prevent boron diffusion.
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 effectively prevents dopant contamination and warpage, maintaining the integrity of the SOI layer's conductivity type and resistivity, and provides an excellent gettering effect while suppressing secondary contamination from furnace components.
Implementation Method 1
forming a CVD insulator film on a second main surface of the base wafer
Implementation Method 2
the barrier silicon layer is thermally oxidized to form a barrier silicon oxide film
Implementation Method 3
suppressing solid phase diffusion from the buried oxide film
Data Source
AI summary
A method for manufacturing an SOI wafer including: a step of forming a silicon oxide film by thermal oxidation on an entire surface of a base wafer containing a dopant; and bonding a main surface of a bond wafer to a first main surface via the silicon oxide film, wherein, prior to the thermal oxidation step, a step of forming a CVD insulator film on a second main surface; and a step of forming, on the first main surface, a barrier silicon layer containing a dopant at a lower concentration than a dopant concentration of the base wafer, and in the thermal oxidation step, the barrier silicon layer is thermally oxidized to produce a barrier silicon oxide film, and in the bonding step, the bond wafer is bonded to the base wafer via the barrier silicon oxide film as a part of the silicon oxide film.