Ion Beam Scanner Magnetic Deflection System
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Solution Overview
Problem
Magnetic scanning techniques in ion implanters face challenges such as beam size fluctuations during zero field crossing, leading to non-uniform irradiation and increased power consumption, especially when handling larger wafers, and existing solutions either suffer from reactive power issues or ion optical deterioration.
Innovation Solution
A magnetic deflection system with ac and dc coils arranged to create a bipolar scanning magnetic field that never experiences zero field crossing, ensuring stable beam emittance and uniformity, using a configuration where ac coils extend parallel to the magnetic core and dc coils are orthogonal, with a collimator having polynomially varying pole faces to achieve precise ion collimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a magnetic scanning field approaches zero field crossing to enable beam scanning, then the beam can be scanned across the wafer, but beam size fluctuation occurs leading to non-uniform irradiation
Solution Approach 1:
The patent applies preliminary anti-action by introducing a DC magnetic field component that counteracts the zero field crossing effect before it can cause beam size fluctuation. The DC field is specifically designed to maintain a minimum magnetic field strength that prevents electron orbit expansion and maintains stable beam emittance throughout the scanning cycle.
Solution Approach 2:
The patent changes the magnetic field parameters by superimposing a DC field component onto the AC scanning field. This parameter change transforms the magnetic field from one that periodically approaches zero to one that maintains a minimum threshold, thereby eliminating beam size fluctuation while preserving scan functionality.
2Manufacturing precision
If a unipolar scanning magnetic field is used to avoid zero field crossing, then beam size stability is improved, but ac reactive power consumption increases significantly
Solution Approach 1:
The patent merges AC and DC magnetic field components into a unified scanning system. The AC field provides the scanning motion while the DC field prevents zero field crossing, creating a combined field solution that achieves beam stability without the excessive reactive power consumption of purely unipolar AC fields.
Solution Approach 2:
By changing the magnetic field parameters to include a DC offset component, the system achieves beam stability while optimizing power consumption. The DC component magnitude is specifically tuned to prevent zero field crossing without creating excessive reactive power demands.
3Manufacturing precision
If the magnetic field strength is increased to maintain beam stability, then beam emittance is stabilized, but the capital cost of the ion implanter increases
Solution Approach 1:
The patent applies partial action by using just enough DC magnetic field strength to prevent zero field crossing and stabilize beam emittance, rather than using excessive field strength. This optimized approach achieves the necessary beam stability without proportionally increasing the capital cost of the magnetic scanning system.
4Manufacturing precision
If a collimator magnet is used to form a parallel ribbon beam, then beam directionality is improved, but the system complexity and cost increase
Solution Approach 1:
The magnetic scanning system is designed to perform multiple functions: it scans the beam across the wafer while simultaneously maintaining beam directionality and forming a collimated ribbon beam. This multi-functional approach eliminates the need for separate collimator magnets, reducing system complexity and capital cost while maintaining beam precision.
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 achieves uniform beam spot characteristics, reduces ac reactive power consumption, and allows for higher scan frequencies and larger wafer diameters without increasing capital costs, while maintaining precise ion collimation and minimizing unwanted particle impingement on the substrate.
Implementation Method 1
an ac current source, coupled to said ac coils and adapted to apply to said ac coils an excitation current to generate an ac magnetic field component in said gap that substantially alternates in polarity as a function of time, to cause scanning of the ion beam
Implementation Method 2
a dc current source coupled to said dc coils, and adapted to apply to said dc coils a current that generates a dc magnetic field component in the gap
Implementation Method 3
Magnetic scanning techniques in ion implanters face challenges such as beam size fluctuations during zero field crossing
Data Source
AI summary
A magnetic system for uniformly scanning an ion beam across a semiconductor wafer comprises a magnetic scanner having ac and dc coil windings each of which extend linearly along internal pole faces of a magnetic core. The ac and dc coil windings are mutually orthogonal; a time dependent magnetic component causes ion beam scanning while a substantially static (dc) field component allows the ion beam to be bent in an orthogonal plane. The current density in the ac and dc coil windings is uniformly dispersed along the pole faces leading to an improved beam spot uniformity at the wafer. The magnetic system also includes a collimator having first and second mutually opposed symmetrical dipoles defining an aperture between them. The poles of each dipole have a pole face varying monotonically and polynomially in a direction perpendicular to a central axis of the collimator: an increasing pole gap is formed towards that central axis.