Microwave Wafer Annealing for Selective Dopant Activation
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Solution Overview
Problem
Conventional annealing technologies, such as rapid thermal annealing and millisecond annealing, non-selectively heat both the lattice and dopants in semiconductor wafers, leading to inefficient dopant activation and increased resistivity due to dopant compensation and impurity scattering.
Innovation Solution
A system for selective heating of dopants or defect clusters with an electrical dipole moment, utilizing a chamber, a heating device, a microwave source, and an elongated waveguide to direct microwave energy at a predetermined frequency, intensity, and period, thereby activating dopants or breaking up defect clusters with minimal lattice heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thermal annealing (RTA/MSA) is used to activate dopants, then dopant activation occurs, but both lattice and dopant are heated non-selectively causing dopant diffusion and profile broadening
Solution Approach 1:
The patent segments the heating process into two distinct components: lattice heating (for dopant activation) and dopant heating (for profile control). By using separate heating mechanisms - conventional thermal fields for lattice and microwave fields for dopants - the process achieves selective heating that prevents unwanted dopant diffusion while maintaining activation efficiency
Solution Approach 2:
The invention applies different heating qualities to different targets: thermal heating is applied to the lattice structure while microwave heating is applied specifically to dopant atoms. This local differentiation in heating quality enables the lattice to reach activation temperatures without causing excessive dopant mobility, thereby preserving profile abruptness
2Quantity of substance
If heavy doping is used to increase free-electron concentration for scaling, then carrier mobility is enhanced through strain, but resistivity increases due to impurity scattering and dopant compensation
Solution Approach 1:
The patent changes the temperature parameter selectively - heating dopants to higher temperatures than the lattice to optimize activation without excessive diffusion. By controlling the dopant temperature independently through microwave heating, the process achieves optimal electrical activation that reduces resistivity while maintaining the heavy doping concentration needed for carrier mobility enhancement
3Quantity of substance
If in situ doping during epitaxial growth is used to reduce channel resistance, then doping concentration exceeds equilibrium solubility, but free-electron concentration saturates due to dopant compensation
Solution Approach 1:
The patent applies microwave heating before or during the annealing process to pre-activate dopants in heavily doped regions. This preliminary action ensures that dopants are optimally activated before subsequent processing steps, maximizing free-electron concentration from the heavy in situ doping without suffering from compensation effects that would occur with conventional thermal annealing alone
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 system achieves efficient and stable dopant activation in heavily doped semiconductor wafers with an abrupt dopant profile, reducing resistivity and preventing broadening of the dopant profile, as demonstrated by improved free electron concentration and junction abruptness compared to conventional annealing methods.
Implementation Method 1
a microwave source configured to direct microwave energy at a predetermined frequency to a first location within the chamber
Implementation Method 2
heating device configured to heat a substrate borne within the chamber during system operation; a microwave source configured to direct microwave energy
Data Source
AI summary
Technologies for microwave annealing include a chamber, a heating device configured to heat a substrate borne within the chamber during system operation, a microwave source configured to direct microwave energy at a predetermined frequency to a location within the chamber at which the substrate is disposed, and an elongated waveguide disposed within the chamber and extending between the microwave source and the location within the chamber at which the substrate is disposed. The substrate may be a semiconductor doped by ion implantation or epitaxial growth. During operation, the microwave energy activates a dopant and/or breaks up a defect cluster within the substrate.