Epitaxial SOI Substrate Fabrication via Selective Etching
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Solution Overview
Problem
The existing methods for forming thin semiconductor-on-insulator (SOI) wafers with device layer thicknesses less than 120 or 150 nanometers and total thickness variations (TTVs) less than 10 nanometers are costly and unsuitable for advanced MOS devices, such as fully-depleted and partially-depleted MOS devices, due to the high cost of hydrogen implantation and splitting processes.
Innovation Solution
A method involving the epitaxial formation of an etch stop layer on a sacrificial substrate, followed by the epitaxial growth of a device layer with a different crystalline lattice, bonding to a handle substrate, and selective etching using a hydrofluoric acid, hydrogen peroxide, and acetic acid etchant to minimize damage and achieve low TTVs, thereby forming a thin SOI substrate at a lower cost.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If hydrogen implantation and splitting processes are used to form thin SOI wafers, then device layer thickness and TTV control are improved, but manufacturing cost increases
Solution Approach 1:
The patent extracts and removes the expensive hydrogen implantation and splitting processes from the SOI wafer fabrication method. Instead, it uses a simplified approach with epitaxial growth of silicon germanium layers followed by selective chemical etching, thereby achieving the desired thin SOI structure without the costly conventional processes.
Solution Approach 2:
The patent introduces sacrificial silicon germanium layers that are intentionally designed to be temporary and removable. These sacrificial layers serve their purpose during fabrication (providing structural support and enabling precise thickness control) and then are completely removed through selective chemical etching, leaving only the desired thin SOI device layer without the need for expensive hydrogen implantation.
2Manufacturing precision
If hydrogen implantation and splitting processes are used to form thin SOI wafers, then device layer thickness and TTV control are improved, but process complexity increases
Solution Approach 1:
The patent replaces the mechanical and physical processes of hydrogen implantation and wafer splitting with a chemical-based approach. Specifically, it uses epitaxial growth to form precise layers and selective chemical etching (using solutions like HNA or TMAH) to remove sacrificial layers, thereby achieving precise TTV control through chemical means rather than mechanical manipulation.
Solution Approach 2:
The patent changes the fundamental parameters of the fabrication process by using epitaxial growth conditions (temperature, pressure, gas composition) to control layer thickness and composition precisely. The selective etching process also relies on parameter optimization (etchant composition, temperature, time) to achieve precise removal of sacrificial layers without damaging the device layer, thereby controlling TTV through parameter management rather than mechanical processes.
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 allows for the formation of thin SOI substrates with low TTVs and high crystalline quality, resulting in semiconductor devices with low leakage current, high power efficiency, and high speed, while reducing production costs by avoiding hydrogen implantation and splitting processes.
Implementation Method 1
performing an etch into the etch stop layer to remove the etch stop layer, wherein the etch is performed using an etchant including hydrofluoric acid, hydrogen peroxide, and acetic acid
Implementation Method 2
epitaxially forming an etch stop layer on a sacrificial substrate; epitaxially forming a device layer on the etch stop layer, wherein the device layer has a different crystalline lattice than the etch stop layer
Implementation Method 3
bonding the sacrificial substrate to a handle substrate, such that the device layer and the etch stop layer are between the sacrificial and handle substrates
Data Source
AI summary
Various embodiments of the present application are directed to a method for forming a thin semiconductor-on-insulator (SOI) substrate at low cost and with low total thickness variation (TTV). In some embodiments, an etch stop layer is epitaxially formed on a sacrificial substrate. A device layer is epitaxially formed on the etch stop layer and has a different crystalline lattice than the etch stop layer. The sacrificial substrate is bonded to a handle substrate, such that the device layer and the etch stop layer are between the sacrificial and handle substrates. The sacrificial substrate is removed. An etch is performed into the etch stop layer to remove the etch stop layer. The etch is performed using an etchant comprising hydrofluoric acid, hydrogen peroxide, and acetic acid.