Ion Implantation Beam Bending Element for Uniform Dose Control
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Solution Overview
Problem
Ion implantation systems face challenges in maintaining uniform dosimetry control due to charge exchange reactions, especially when high-speed ions interact with photoresist-coated semiconductor wafers, leading to vacuum degradation and inaccurate measurement of dopant particles, resulting in potential overdosing of workpieces.
Innovation Solution
The system incorporates a beam bending element and Faraday cups positioned at the exit opening to measure beam current accurately, with slits to limit ion acceptance angles and electronic gating to filter out charge-exchanged ions, ensuring precise dosimetry control by averaging beam currents from multiple cups and using a conductance limiter to reduce outgas influx.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Faraday cup is positioned close to workpiece to measure actual beam current, then dosimetry measurement precision is improved, but measurement accuracy deteriorates due to charge exchange reactions with outgassed molecules
Solution Approach 1:
A conductance limiter is introduced as an intermediary component between the process chamber and the Faraday cup chamber. This conductance limiter restricts the flow of outgassed molecules from the process chamber into the Faraday cup chamber, thereby reducing charge exchange reactions while still allowing the Faraday cup to measure beam current accurately. The conductance limiter acts as a mediator that protects the measurement system from adverse conditions.
2Reliability
If vacuum pressure is reduced to prevent charge exchange reactions, then measurement accuracy is improved, but productivity deteriorates due to longer pumping time required
Solution Approach 1:
The system is divided into two separate chambers: a process chamber for wafer implantation and a separate Faraday cup chamber for beam current measurement. Each chamber can be independently evacuated and pressurized. This segmentation allows the process chamber to maintain higher pressure for productivity while the Faraday cup chamber maintains low pressure for accurate measurements, eliminating the need to compromise either parameter.
3Extent of automation
If beam current is measured at Faraday cup located near workpiece, then dosimetry control responsiveness is improved, but measurement reliability deteriorates due to charge exchange reactions
Solution Approach 1:
The conductance limiter serves as an intermediary that enables the Faraday cup to be positioned in a separate chamber with controlled vacuum conditions. This arrangement maintains the responsiveness of dosimetry control by keeping the Faraday cup close to the beam path while protecting it from charge exchange reactions through the conductance limiter, thereby ensuring measurement reliability.
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 configuration enhances dosimetry control by accurately measuring the actual ion particle flux at the workpiece surface, reducing overdosing and maintaining uniform doping density despite fluctuations in ion beam intensity and vacuum pressure.
Implementation Method 1
a beam bending element configured to receive the ribbon shaped ion beam having a first direction, and bend the ribbon shaped ion beam to travel in a second direction
Implementation Method 2
a beam current measurement system located at an exit opening of the beam bending element that is configured to measure a beam current of the ribbon shaped ion beam at the exit opening of the beam bending element
Implementation Method 3
with slits to limit ion acceptance angles
Data Source
AI summary
An ion implantation system and associated method includes a scanner configured to scan a pencil shaped ion beam into a ribbon shaped ion beam, and a beam bending element configured to receive the ribbon shaped ion beam having a first direction, and bend the ribbon shaped ion beam to travel in a second direction. The system further includes an end station positioned downstream of the beam bending element, wherein the end station is configured to receive the ribbon shaped ion beam traveling in the second direction, and secure a workpiece for implantation thereof. In addition, the system includes a beam current measurement system located at an exit opening of the beam bending element that is configured to measure a beam current of the ribbon shaped ion beam at the exit opening of the beam bending element.