SOI Substrate Annealing for Surface Roughness and Oxide Uniformity
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Solution Overview
Problem
Existing processes for fabricating silicon on insulator (SOI) substrates with silicon surface layers thinner than 200 nanometers face challenges in achieving uniform thickness and minimizing the dissolution of the buried oxide layer, particularly at high annealing temperatures, leading to non-homogeneous results and poor thickness control.
Innovation Solution
A process involving the formation of a weakened zone in a semiconductor donor substrate, bonding it to a receiver substrate with an oxide layer, detaching the donor substrate, and subsequent long annealing in a hydrogen or argon atmosphere to achieve a thin silicon layer with a thickness of 150 nanometers or less, while maintaining uniformity and reducing surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Shape
If annealing is carried out at high temperatures (1100-1350°C) to reduce surface roughness, then surface roughness is reduced, but the buried oxide layer dissolves and thickness uniformity deteriorates
Solution Approach 1:
The patent applies preliminary action by performing sacrificial oxidation before the high-temperature annealing step. An oxide layer is grown on the silicon active layer surface prior to annealing, which then serves as an oxygen reservoir during subsequent high-temperature processing. This preliminary oxidation prevents oxygen depletion from the buried oxide layer during annealing, thereby maintaining buried oxide thickness uniformity while still achieving surface roughness reduction through the high-temperature annealing step.
2Stability of the object's composition
If annealing time is extended to achieve homogeneous roughness reduction, then surface uniformity improves, but oxide layer dissolution increases
Solution Approach 1:
The patent applies parameter changes by modifying the chemical composition of the atmosphere during annealing. Specifically, hydrogen gas is introduced into the annealing atmosphere, which chemically reacts with oxygen that would otherwise diffuse from the buried oxide layer. This parameter change (adding hydrogen to the atmosphere) allows for extended annealing times to achieve homogeneous surface roughness reduction while preventing buried oxide layer dissolution by suppressing oxygen diffusion from the buried oxide.
3Loss of time
If temperature is increased above 1200°C to accelerate the annealing process, then annealing time is reduced, but oxygen solubility in silicon increases causing dissolution in bulk substrate
Solution Approach 1:
The patent applies the inert atmosphere principle by using a hydrogen-rich or inert gas atmosphere during high-temperature annealing. This controlled atmosphere environment prevents unwanted chemical reactions and oxygen diffusion into the bulk silicon substrate. The hydrogen atmosphere specifically suppresses oxygen solubility in silicon at high temperatures, allowing rapid thermal annealing above 1200°C to be performed without excessive oxygen dissolution in the bulk substrate and silicon active layer.
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 process effectively produces SOI substrates with a buried oxide layer thickness uniformity of less than 20% and an ultrathin silicon layer with reduced surface roughness, overcoming the limitations of prior art by ensuring consistent thickness and reduced oxide layer dissolution.
Implementation Method 1
a finishing annealing operation is then carried out in an atmosphere containing hydrogen, an inert gas, or a mixture of the two gases, at a temperature between 1100° C. and 1350° C.
Implementation Method 2
the dissolution phenomenon is also linked with the increase in solubility of oxygen in silicon and consequently its dissolution in the bulk substrate and the silicon active layer
Implementation Method 3
This substrate is then bonded to a support and then an annealing operation is carried out at temperatures between 400° C. and 600° C. to detach a portion of the substrate
Data Source
AI summary
A process for fabricating a silicon on insulator (SOI) substrate by forming a weakened zone within a semiconductor donor substrate to define a thick layer having a thickness of greater 150 nm and form a boundary between the thick layer and a remainder of the donor substrate, bonding the donor substrate to a semiconductor receiver substrate, with one of the substrates including an oxide layer that is present between the donor and receiver substrates after bonding; detaching a remainder of the donor substrate along the weakened zone to obtain a semifinished SOI substrate comprising the receiver substrate, the oxide layer and the thick layer; and finishing the semifinished SOI substrate by thinning the thick layer to obtain a silicon layer having a thickness is less than that of the thick layer but greater than 150 nm; long annealing the semifinished SOI substrate in a gaseous atmosphere comprising hydrogen and/or argon; and thinning the thin layer to obtain an ultrathin layer with a thickness of 150 nm or less and the finished substrate.