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What Is Pre-Amorphization?
Pre amorphization implantation, or PAI, uses ion bombardment to turn the top layer of crystalline silicon into amorphous silicon before dopants such as boron are implanted.[11][12] The amorphous layer suppresses ion channeling, helping prevent some dopant ions from travelling too deeply and creating a long tail in t...
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Key takeaways
- Pre amorphization implantation, or PAI, uses ion bombardment to turn the top layer of crystalline silicon into amorphous silicon before dopants such as boron are implanted.[11][12]
- The amorphous layer suppresses ion channeling, helping prevent some dopant ions from travelling too deeply and creating a long tail in the implanted profile.[7][11][12]
- After implantation, annealing recrystallizes the silicon and activates dopants, but residual defects must be managed.[1][6]
- In Sentaurus Process, the pai option refers to a PAI related implantation model; it does not by itself prove that an additional germanium implant was run.[15]
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Pre-amorphization is a semiconductor-processing step performed before implanting the desired dopant, such as boron. Ions are first used to disrupt the orderly crystal structure near the silicon surface, creating a thin layer of amorphous silicon. The main purpose is to reduce channeling during the later dopant implant, so fewer dopant ions penetrate too deeply.11
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What does “amorphous” mean here?
- Single-crystal silicon has atoms arranged in a long-range, ordered lattice.
- Amorphous silicon has lost that long-range order, while remaining a solid. The silicon has not been melted.
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The word pre- simply means that this step occurs ahead of the target dopant implant. A common sequence, for example, is a germanium (Ge) pre-amorphization implant followed by a boron implant.11
Why deliberately disrupt the silicon lattice?
In single-crystal silicon, some crystallographic directions provide relatively open paths between atoms. Ions entering along those directions can experience fewer collisions and travel unusually far into the wafer. This is known as ion channeling. It can produce a long, deep tail in the implanted dopant profile.12
This is not the electrical channel in a MOSFET. It refers to ions moving through open directions in the crystal lattice.
By disrupting those ordered pathways in the near-surface region, pre-amorphization makes the subsequent dopant profile shallower and more controllable. That is especially useful in processes designed to form ultra-shallow junctions.7
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A simple analogy: an orderly forest may have straight paths that let someone travel a long way. Once the trees are scattered irregularly, it is much harder to move straight through.
Typical process sequence
- Pre-amorphization implant: Ge or Si ions are implanted to create sufficient lattice damage to amorphize the silicon surface layer.
- Dopant implant: The target impurity, such as boron, is implanted. The amorphous layer helps suppress deep channeling tails.
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- Annealing: Heat treatment recrystallizes the amorphous layer and helps activate the implanted dopants. Residual defects must still be controlled, so the disruption is not cost-free.
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PAI is therefore an intermediate processing state. The goal is not to leave the final transistor region permanently amorphous.
What does pai mean in an SProcess command?
Consider this command:
implant Boron energy=230 dose=1.0e13 tilt=0 rot=135 pai
Here, pai is an SProcess option associated with a pre-amorphization implantation model.15
However, an important distinction applies:
- PAI in a real fabrication flow means an earlier ion implant is physically carried out to form an amorphous layer.
paiin the command selects a related model for that implantation step. The keyword alone does not establish that the script automatically performed a separate Ge implant.15
The explicitly specified implanted species in this line is still Boron. Whether the simulated structure already contains an amorphous layer, how deep it is, and exactly how pai is handled depend on earlier implant steps and the model configuration in the specific software version. Those details cannot be determined from this line alone.
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What is the short answer to "What Is Pre-Amorphization?"?
Pre amorphization implantation, or PAI, uses ion bombardment to turn the top layer of crystalline silicon into amorphous silicon before dopants such as boron are implanted.[11][12]
What are the key points to validate first?
Pre amorphization implantation, or PAI, uses ion bombardment to turn the top layer of crystalline silicon into amorphous silicon before dopants such as boron are implanted.[11][12] The amorphous layer suppresses ion channeling, helping prevent some dopant ions from travelling too deeply and creating a long tail in the implanted profile.[7][11][12]
What should I do next in practice?
After implantation, annealing recrystallizes the silicon and activates dopants, but residual defects must be managed.[1][6]