Ion Implantation Dose Control via Terminal Return Current
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Solution Overview
Problem
Conventional ion implantation systems face challenges in achieving dose uniformity due to variations in beam current caused by outgassing, which leads to overdosing and non-uniformities, as Faraday cups cannot detect neutralized ions and require complex pressure compensation methods.
Innovation Solution
The use of terminal return current measurements, taken upstream of the wafer and less affected by photoresist outgassing, to adjust scanning speed and facilitate beam current uniformity across wafers, by deriving currents from components such as beam guides and power supplies, and processing them into a terminal return current to correct for beam current variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Faraday cup measurements are used to monitor beam current, then real-time current monitoring is achieved, but neutralized ions cannot be detected leading to dose non-uniformities
Solution Approach 1:
The patent introduces an intermediary correction mechanism that processes Faraday cup measurements through a transfer function that accounts for neutralized ion fractions. This intermediary processing step converts the incomplete Faraday cup data into corrected beam current values that represent the actual total ion flux, including neutralized portions, thereby resolving the measurement precision vs. manufacturing precision contradiction.
2Manufacturing precision
If pressure compensation methods are employed to account for outgassing, then dose control is adjusted, but complex compensation factors and precise pressure measurements are required
Solution Approach 1:
The patent transforms the complex multi-parameter pressure compensation problem into a simpler single-parameter correction approach. By deriving a transfer function that relates Faraday cup current to actual beam current through a neutralized ion fraction parameter, the system achieves dose uniformity control without requiring complex compensation factors or precise pressure measurements, thus reducing device complexity while maintaining manufacturing precision.
3Productivity
If beam current is increased to improve productivity, then implantation speed increases, but outgassing effects become more significant causing overdosing
Solution Approach 1:
The patent implements a feedback control system that continuously monitors Faraday cup current and applies real-time corrections based on the transfer function. This feedback mechanism allows the system to maintain accurate dose control even at higher beam currents where outgassing effects are more significant, enabling improved productivity without sacrificing dose uniformity by dynamically adjusting for neutralized ion fractions.
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
This approach improves dosimetry by accurately accounting for beam current variations, reducing overdosing and non-uniformities, and enhancing the precision of dose control in ion implantation systems.
Implementation Method 1
Mass analyzers typically employ a mass analysis magnet creating a dipole magnetic field to deflect various ions in an ion beam via magnetic deflection in an arcuate passageway which will effectively separate ions of different charge-to-mass ratios.
Implementation Method 2
A Faraday disk or Faraday cup periodically measures the beam current and adjusts the slow scan speed to ensure constant dosing.
Implementation Method 3
Typical ion beam implanters include an ion source for generating positively charged ions from ionizable source materials.
Data Source
AI summary
A method derives a terminal return current or upstream current to adjust and/or compensate for variations in beam current during ion implantation. One or more individual upstream current measurements are obtained from a region of an ion implantation system. A terminal return current, or composite upstream current, is derived from the one or more current measurements. The terminal return current is then employed to adjust scanning or dose of an ion beam in order to facilitate beam current uniformity at a target wafer.