SiGe Substrate Amorphization Recrystallization Dislocation Control
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Solution Overview
Problem
Existing processes for manufacturing substrates with a top layer of relaxed SiGe or Ge and an underlying Si layer suffer from high dislocation densities and surface roughness issues, known as crosshatching, which affect the crystalline structure and quality of the top layer.
Innovation Solution
A process involving amorphisation and recrystallisation stages to create a network of defects at the interface between the top layer and the underlying layer, using ion implantation or pulsed laser exposure for amorphisation and thermal treatment for recrystallisation, to contain dislocations and reduce surface roughness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If a transition layer with continuous lattice parameter change is used between relaxed SiGe/Ge top layer and Si underlying layer, then lattice mismatch is accommodated, but dislocation defects and pile-ups occur in the top layer
Solution Approach 1:
The patent applies preliminary amorphisation to the top layer before final crystallisation. By amorphising the top layer after growing it on the transition layer, the lattice is reset and subsequent crystallisation occurs from a defect-free amorphous state, preventing dislocation propagation from the transition layer while maintaining the beneficial lattice parameter gradient.
Solution Approach 2:
The patent utilizes phase transition by converting the crystalline top layer to amorphous phase through ion implantation or laser irradiation, then recrystallising it in a controlled manner. This phase transition eliminates existing dislocations and allows reformation of the crystalline structure without inheriting defects from the transition layer interface.
2Ease of manufacture
If the top layer is grown with constant Ge concentration, then material composition is simplified, but surface crosshatching and roughness occur due to internal stresses
Solution Approach 1:
The amorphisation step is performed as a preliminary action after the top layer is grown with constant Ge concentration. This preliminary amorphisation relieves internal stresses frozen in during growth, and subsequent controlled crystallisation produces a flat, defect-free surface without requiring complex compositional gradients.
Solution Approach 2:
The patent changes the physical state parameter of the top layer from crystalline to amorphous and back to crystalline. This parameter change (phase transition) allows the layer to retain its simple constant-composition structure while eliminating stress-induced surface roughness through the amorphisation-relief-recrystallisation cycle.
3Manufacturing precision
If CMP polishing is used to reduce surface roughness, then crosshatching is removed, but dislocation pile-ups are not eliminated and may reappear
Solution Approach 1:
Instead of mechanical CMP polishing, the patent uses phase transition (amorphisation followed by recrystallisation) to simultaneously address both surface flatness and dislocation elimination. The amorphisation process removes dislocations by dissolving the crystalline order, and controlled recrystallisation produces a flat surface without re-forming dislocation pile-ups.
Solution Approach 2:
The patent replaces the mechanical CMP polishing process with a physico-chemical phase transition process. Instead of mechanically removing material to flatten the surface, the amorphisation-recrystallisation cycle chemically transforms the material state to eliminate both surface roughness and subsurface dislocations in a unified process.
4Stability of the object's composition
If annealing at high temperature is applied to stabilise the substrate, then residual stress is dissipated, but surface roughness increases and requires subsequent CMP treatment
Solution Approach 1:
The patent performs amorphisation as a preliminary action before any stabilisation annealing. By amorphising the top layer first, subsequent thermal treatments recrystallise the layer in a controlled manner that simultaneously achieves stress relief and surface flattening, avoiding the roughness problem that occurs when annealing is applied to already-formed crystalline layers.
Solution Approach 2:
The patent changes the crystalline state to amorphous before applying thermal stabilisation. This parameter change allows the thermal treatment to proceed without causing surface roughness, as the amorphous phase can relax stresses uniformly without forming stress-induced surface topography that plagues crystalline materials during annealing.
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 reduces dislocation densities and surface roughness, achieving dislocation densities of a few units/cm² and crosshatching values of 2.4 angstroms RMS and 17 angstroms PV, thereby improving the crystalline structure and quality of the top layer.
Implementation Method 1
the said amorphisation is effected by the implantation of species in the said top layer
Implementation Method 2
a stage for recrystallisation of the said amorphised region
Implementation Method 3
the recrystallisation stage includes a thermal treatment of the top layer
Implementation Method 4
the said amorphisation is achieved by exposure of the said top layer to a pulsed laser beam
Data Source
AI summary
A process for the manufacture of a substrate having a top layer of a first material and an underlying layer of a second material whose lattice parameter is different from that of the first material. The process includes the steps of conducting an amorphization of the top layer to create an amorphous region in the top layer lying between an exposed surface and an amorphization interface, with that portion of the top layer below the interface being shielded from the amorphization and remaining as a crystalline structure; recrystallizing the amorphous region while also creating a network of defects at the interface, wherein the network forms a boundary for dislocations from the crystalline structure of the top layer, and containing the dislocations in the portion of the top layer that is located below the interface. Also, the substrates obtained by the method.