Ion Beam Scanning Waveform for Implant Uniformity
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Solution Overview
Problem
Ion implantation systems face non-uniformity issues during photoresist outgassing, particularly in the fast scan direction, which existing methods fail to correct effectively due to rapid pressure changes.
Innovation Solution
A method involving the generation of a main scan waveform with a constant slope and a compensation waveform, specifically a quadratic waveform, is used to form a beam scanning waveform with a non-constant slope, allowing for adjustments in the mixture ratio based on instantaneous vacuum pressure readings to correct dose non-uniformities along the fast scan direction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a constant velocity scan waveform is used to move the ion beam across the wafer, then the implantation process is simple and fast, but implant uniformity deteriorates during photoresist outgassing due to pressure variations
Solution Approach 1:
The patent applies dynamics by transitioning from a static constant velocity scan waveform to a dynamic variable velocity scan waveform. The scan waveform is continuously adjusted based on real-time pressure feedback from the vacuum system, allowing the beam velocity to adapt to changing outgassing conditions during the implantation process, thereby maintaining implant uniformity despite pressure variations
Solution Approach 2:
The patent implements feedback control by monitoring vacuum pressure variations in real-time and using this information to dynamically adjust the scan waveform. The feedback loop compares the actual pressure conditions against reference values and modifies the beam velocity accordingly, ensuring that implant uniformity is maintained even when photoresist outgassing causes pressure fluctuations
2Manufacturing precision
If the scan waveform is dynamically adjusted to compensate for pressure changes, then implant uniformity is improved, but the system complexity increases due to additional control mechanisms
Solution Approach 1:
The patent uses an intermediary approach by introducing a pressure-dependent correction factor or lookup table that maps pressure conditions to appropriate waveform adjustments. This intermediary mechanism simplifies the control system architecture by avoiding complex real-time calculations, instead using pre-computed correction data to adjust the scan waveform based on measured pressure conditions
Solution Approach 2:
The patent changes the parameter of scan velocity dynamically based on pressure conditions. By modifying the velocity parameter in response to pressure measurements, the system achieves improved implant uniformity without requiring fundamental changes to the scanner hardware, thereby limiting the increase in system complexity to software/control parameter adjustments
3Manufacturing precision
If the beam velocity is reduced to maintain uniformity during outgassing, then implant uniformity is improved, but the processing time increases
Solution Approach 1:
The patent applies periodic action by implementing velocity adjustments that are synchronized with the characteristic time scale of outgassing events. Rather than maintaining reduced velocity throughout the entire scan, the system periodically modulates velocity in response to detected pressure changes, allowing fast scanning during stable pressure conditions and slower scanning only when outgassing occurs, thus minimizing overall processing time while maintaining uniformity
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 dynamically adjusts the ion beam's velocity to account for pressure changes, ensuring uniform implantation across the workpiece by modifying the beam scanning waveform in real-time, thereby improving implant uniformity during photoresist outgassing.
Implementation Method 1
an ion source configured to generate positively charged ions from ionizable source material
Implementation Method 2
a scanning system may comprise a pair of scan plates (or a scanning electromagnet for electromagnetic scanning) positioned to deflect an ion beam and a scan waveform generator configured to apply voltages, associated with a scan waveform, to the scan plates (or to apply currents to the scanning electromagnet for electromagnetic scanning). The voltages produce a time varying electric or magnetic field between the plates to deflect or scan a beam
Data Source
AI summary
A method and apparatus is provided for improving implant uniformity of an ion beam experiencing pressure increase along the beam line. The method comprises generating a main scan waveform that moves an ion beam at a substantially constant velocity across a workpiece. A compensation waveform (e.g., quadratic waveform), having a fixed height and waveform, is also generated and mixed with the main scan waveform (e.g., through a variable mixer) to form a beam scanning waveform. The mixture ratio may be adjusted by an instantaneous vacuum pressure signal, which can be performed at much higher speed and ease than continuously modifying scan waveform. The mixture provides a beam scanning waveform comprising a non-constant slope that changes an ion beam's velocity as it moves across a workpiece. Therefore, the resultant beam scanning waveform, with a non-constant slope, is able to account for pressure non-uniformities in dose along the fast scan direction.