Plasma Immersion Ion Implanter Control Method
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Solution Overview
Problem
In plasma immersion ion implantation, the growth of an ion sheath leads to a rapid decrease in implantation current, necessitating reinitialization, which results in undesirable side effects such as particle generation, heat delivery, metal contamination, and unstable acceleration voltage, particularly during the rising and falling voltage stages, and insufficient neutralization of positive charges on insulating substrate zones.
Innovation Solution
A method controlling the ion implanter with stages including implantation, neutralization, suppression, and expulsion, where the plasma is ignited during implantation and neutralization, extinguished during suppression and expulsion, with the expulsion stage lasting longer than 5 μs to remove negatively charged particles, and optionally using a recovery electrode for enhanced particle removal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the plasma is kept ignited during neutralization stage, then positive charges on the substrate are effectively neutralized, but negatively charged particles accumulate on the substrate surface
Solution Approach 1:
The method divides the plasma control into distinct temporal stages: implantation stage with plasma ignited, neutralization stage with plasma ignited, and expulsion stage with plasma extinguished. This segmentation allows independent optimization of each stage - plasma presence during neutralization for charge removal, and plasma absence during expulsion for particle removal
Solution Approach 2:
The plasma power supply operates in periodic pulses, being ignited during implantation and neutralization stages, then extinguished during expulsion stage. This periodic on/off action enables the system to alternately achieve charge neutralization and particle expulsion, resolving the contradiction between these two opposing requirements
2Object-affected harmful factors
If the plasma is extinguished during expulsion stage, then negatively charged particles are removed from the substrate, but the neutralization of positive charges is compromised
Solution Approach 1:
The neutralization stage is positioned before the expulsion stage, with plasma ignited during neutralization to remove positive charges from the substrate. By the time plasma is extinguished for the expulsion stage, the substrate has already been neutralized, so subsequent particle removal does not compromise charge balance
Solution Approach 2:
The plasma power supply uses periodic pulsing with specific timing: ignited during implantation and neutralization stages, then extinguished during expulsion stage. This temporal sequencing ensures that charge neutralization occurs while plasma is present, and particle expulsion occurs when plasma is absent, resolving the contradiction
3Productivity
If reinitialization is performed to reset the ion sheath, then implantation current is restored, but undesirable side effects occur including particle generation, heat delivery, and metal contamination
Solution Approach 1:
The harmful plasma effects are extracted and isolated to specific time periods. The plasma is extinguished during the expulsion stage and between pulses, removing the source of particle generation, heat delivery, and metal contamination from the enclosure walls, while maintaining plasma only during implantation and neutralization stages where it is beneficial
Solution Approach 2:
The plasma power supply operates in periodic pulses rather than continuously. During each pulse cycle, plasma is ignited for implantation and neutralization, then extinguished for expulsion and between pulses. This periodic action restores implantation current through controlled plasma presence while minimizing harmful effects through controlled plasma absence
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
Significantly reduces particle contamination and charge effects on the substrate, maintaining stable implantation conditions and minimizing arcing phenomena by effectively neutralizing positive and negative charges, and reducing dust accumulation through extended expulsion of negatively charged particles.
Implementation Method 1
an ion implanter which comprises a plasma power supply and a substrate power supply
Implementation Method 2
biasing it with a negative voltage lying in the range a few tens of volts to a few tens of kilovolts in order to create an electric field capable of accelerating the ions of the plasma towards the substrate
Implementation Method 3
an ion sheath is created around the substrate a few nanoseconds after the voltage is applied. The potential difference that is responsible for accelerating ions towards the substrate is thus located at the boundaries of the sheath
Implementation Method 4
It is also possible to make provision for a filament, but that tends to vaporize. It is also possible to make provision for an electron gun, but that constitutes additional equipment that is relatively expensive. It is therefore appropriate to facilitate neutralizing positive charges.
Implementation Method 5
an expulsion stage for expelling negatively charged particles from the substrate and during which the plasma is extinguished; which method is remarkable in that the duration of the expulsion stage is longer than 5 μs
Data Source
AI summary
A method of controlling an implanter operating in plasma immersion, the method including the steps of:an implantation stage (1) during which the plasma AP is ignited and the substrate is negatively biased S;a neutralization stage (2) during which the plasma AP is ignited and the substrate has a positive or zero bias S applied thereto;a suppression stage (3) during which the plasma AP is extinguished; andan expulsion stage (4) for expelling negatively charged particles from the substrate and during which the plasma AP is extinguished.The method is remarkable in that the duration of the expulsion stage is longer than 5 μs.The invention also provides a power supply for biasing an implanter.