Strained Germanium Doping via Nanosecond Laser Melting
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Solution Overview
Problem
Conventional doping methods fail to achieve high active n+ carrier concentrations in germanium (Ge) due to the formation of negatively charged donor-vacancy clusters, limiting the development of Ge devices that require high n-type doping and tensile strain.
Innovation Solution
A method involving the deposition of a strained Ge film on a substrate, followed by co-implantation of electron-donating dopants like phosphorus and passivating dopants like fluorine, and subsequent exposure to nanosecond pulsed laser melting to recrystallize the film, achieving active n-type donor concentrations of up to 2×10^20 cm^-3 and tensile strain.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If conventional doping methods (in-situ, gas-phase, or conventional ion implantation with thermal annealing) are used, then the doping process is simple and well-established, but the active donor concentration cannot exceed about 5×10^19 cm^-3 due to formation of negatively charged donor-vacancy clusters
Solution Approach 1:
The patent changes the physical state and processing parameters by using nanosecond pulsed laser annealing instead of conventional thermal annealing. This rapid heating and cooling process modifies the thermal history of the material, preventing vacancy formation and enabling donor concentrations exceeding 10^20 cm^-3 without the harmful donor-vacancy cluster formation that limits conventional methods
Solution Approach 2:
The patent replaces the conventional thermal field (slow heating/cooling) with a nanosecond pulsed laser field (extremely rapid heating/cooling). This substitution of the energy delivery mechanism fundamentally changes the defect formation kinetics, eliminating the donor-vacancy cluster formation problem while achieving the desired high active donor concentration
2Reliability
If high active n+ carrier concentrations are achieved through doping, then Ohmic contact and low parasitic resistance n-MOSFETs can be formed, but the doping process becomes complex and requires advanced techniques beyond conventional methods
Solution Approach 1:
The patent combines ion implantation with nanosecond pulsed laser annealing in a single integrated process flow. This merging of doping and activation steps eliminates the need for separate, complex thermal annealing procedures and defect management steps, achieving high reliability Ohmic contacts through a streamlined process that reduces overall complexity
Solution Approach 2:
By changing the annealing parameter from conventional slow thermal processing to nanosecond pulsed laser processing, the patent achieves high active donor concentrations and reliable Ohmic contacts through a more controllable and precise process, reducing the need for multiple process steps and thereby reducing overall process complexity
3Quantity of substance
If high tensile strain is maintained in Ge films for desired electronic properties, then device performance is improved, but conventional doping processes cannot simultaneously achieve high n-type doping without compromising the strain
Solution Approach 1:
The patent replaces conventional thermal annealing with nanosecond pulsed laser annealing, which delivers energy so rapidly that it activates dopants and repairs implantation damage before thermal diffusion can occur. This substitution preserves the tensile strain in Ge films while achieving high n-type doping concentrations, as the ultrafast process prevents strain-relieving defect formation
4Quantity of substance
If multiple implantations and co-doping approaches are used to manage vacancies, then the doping process complexity increases, but active n+ carrier concentrations still cannot be significantly improved
Solution Approach 1:
The patent replaces multiple sequential implantation and thermal annealing steps with a single nanosecond pulsed laser annealing step following ion implantation. This substitution of the thermal processing mechanism achieves high active n+ carrier concentrations in one step, eliminating the need for complex multiple implantation sequences and co-doping strategies while fully managing vacancy issues through the ultrafast cooling rate
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 method successfully generates highly n-doped strained Ge films with active n-type donor concentrations and tensile strain, overcoming the limitations of conventional doping techniques and enabling applications such as low parasitic resistance n-MOSFETs and lasing emission.
Implementation Method 1
exposing the implanted Ge film to one or more laser pulses having a pulsewidth in a range of about 1 ns to about 100 ms so as to generate a substantially crystalline strained Ge film
Implementation Method 2
the pulses can cause substantial recrystallization of at least a portion of the implanted Ge film
Implementation Method 3
implanting at least one dopant, e.g., an electron-donating dopant, in the Ge film
Data Source
AI summary
In one aspect a method of fabricating an n-doped strained germanium (Ge) film is disclosed, which includes depositing a strained Ge film on an underlying substrate, implanting at least one electron-donating dopant in the Ge film, and exposing the implanted Ge film to one or more laser pulses having a pulsewidth in a range of about 1 ns to about 100 ms so as to generate a substantially crystalline strained Ge film. In some embodiments, the pulses can cause melting followed by substantial recrystallization of at least a portion of the implanted Ge film. In some embodiments, the resultant Ge film can have a thickness in a range of about 10 nm to about 1 microns.