Oxygen Scavenging Layer for Buried Oxide Dissolution in SOI Wafers
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Solution Overview
Problem
Existing methods for dissolving buried oxide in silicon-on-insulator (SOI) wafers are limited by the need for oxygen-tight furnaces, high temperatures, and thick silicon layers, leading to non-uniformity and inefficiency, especially when dealing with thin silicon layers, which can result in de-wetting or silicon ball-up phenomena.
Innovation Solution
A method involving the deposition of an oxygen scavenging layer on the silicon layer of the SOI wafer before annealing, allowing for BOX dissolution at lower temperatures and in standard furnaces, with the option of additional diffusion barrier layers to control oxygen diffusion, enabling faster and more uniform dissolution without the need for oxygen-controlled environments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If known BOX dissolution methods are used with oxygen-tight furnaces and high temperatures, then the buried oxide can be dissolved, but the process requires thick silicon layers (200 nm) to prevent de-wetting and ball-up phenomena
Solution Approach 1:
A thin silicon layer (10-150 nm) is deposited on the carrier substrate before the BOX dissolution process, replacing the conventional thick silicon layer approach. This preliminary thin layer configuration enables BOX dissolution without triggering de-wetting or ball-up phenomena, as the process conditions are optimized specifically for thin layer compatibility
Solution Approach 2:
The annealing temperature is reduced from conventional high temperatures (1150-1200°C) to a lower range (900-1100°C), and the atmosphere is modified to contain carbon-containing gases (CH4, C2H6, C2H4, CO, or CO2) at controlled partial pressures (10^-5 to 10^-1 atm). These parameter changes enable BOX dissolution while maintaining thin silicon layer integrity and preventing de-wetting
2Productivity
If high temperatures (1150-1200°C) are used for BOX dissolution, then the dissolution reaction proceeds, but the process requires oxygen-tight furnaces and results in non-uniformity due to oxygen diffusion
Solution Approach 1:
The process uses a carbon-containing atmosphere (CH4, C2H6, C2H4, CO, or CO2) instead of an oxygen-tight environment. The carbon-containing gas serves multiple functions: it prevents oxygen diffusion into the silicon layer, maintains a reducing environment that facilitates BOX dissolution, and eliminates the need for complex oxygen-tight furnace designs. The partial pressure of carbon-containing gas is controlled at 10^-5 to 10^-1 atm
Solution Approach 2:
Standard furnaces can be used instead of expensive oxygen-tight furnaces by introducing carbon-containing gases. The carbon-containing atmosphere acts as a protective medium that enables BOX dissolution in conventional equipment, eliminating the need for specialized expensive furnace systems
3Device complexity
If standard furnaces are used without oxygen control, then equipment complexity is reduced, but BOX dissolution cannot proceed due to oxygen presence preventing the reaction
Solution Approach 1:
Carbon-containing gases (CH4, C2H6, C2H4, CO, or CO2) are introduced into the furnace atmosphere at controlled partial pressures (10^-5 to 10^-1 atm). This creates a reducing environment that prevents oxygen from interfering with the BOX dissolution reaction, enabling standard furnaces to perform BOX dissolution effectively without requiring oxygen-tight designs
Solution Approach 2:
The carbon-containing gas acts as an intermediary medium that mediates between the oxygen-containing ambient environment and the BOX dissolution reaction. It consumes oxygen through carbon deposition reactions, maintaining a locally reducing environment at the wafer surface that enables BOX dissolution in standard furnaces
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 enables BOX dissolution in SOI wafers with silicon layers as thin as 10 nm, significantly reducing processing time and temperature requirements, improving uniformity, and allowing for simultaneous processing of wafers with different thicknesses in a standard furnace, while preventing de-wetting and ball-up phenomena.
Implementation Method 1
providing an oxygen scavenging layer on or over the silicon layer before the annealing step
Implementation Method 2
known BOX dissolution methods are limited by the diffusion of oxygen from the BOX layer through the silicon layer
Data Source
AI summary
A method for dissolving a buried oxide in a silicon-on-insulator wafer comprises providing a silicon-on-insulator wafer having a silicon layer attached to a carrier substrate via a buried oxide layer, and annealing the silicon-on-insulator wafer to at least partially dissolve the buried oxide layer. The method further comprises a step of providing an oxygen scavenging layer on or over the silicon layer before the annealing step.