Ion Implanter Beam Utilization via Scan Distance Optimization
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Solution Overview
Problem
Traditional single-wafer ion implanters face challenges in achieving uniformity and efficient beam utilization due to low beam currents and large system sizes, particularly with ribbon ion beams and 2D mechanical scan systems, which result in suboptimal dose distribution and beam irradiation area.
Innovation Solution
The method involves calculating a selected scan distance based on implant beam size and intensity, determining a relative velocity profile, and adjusting the scan distance to achieve dose uniformity, using a raster-like pattern and iterative simulations to optimize beam scanning across the wafer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If a 2D mechanical scan system is used to scan the wafer completely out of the beam in both directions, then dose uniformity is achieved, but beam utilization efficiency deteriorates because the total beam irradiating area is much greater than the wafer surface area
Solution Approach 1:
The patent applies parameter changes by optimizing the scan distance parameter to be less than the sum of beam height and wafer diameter, and by using a velocity profile that varies during the scan. This allows the beam to be concentrated more effectively on the wafer surface while still achieving uniform dose distribution, thereby improving beam utilization efficiency without sacrificing dose uniformity
Solution Approach 2:
The patent implements dynamics by using a velocity profile that changes during the scanning process. The wafer or beam scanning velocity is adjusted dynamically - moving slower when the beam is over the wafer and faster when moving between scan lines. This dynamic velocity adjustment ensures uniform dose distribution while minimizing the total area irradiated by the beam, thus improving beam utilization
2Loss of energy
If the scan distance is reduced to improve beam utilization, then beam irradiating area is reduced, but dose uniformity deteriorates due to overlapping beam paths
Solution Approach 1:
The patent employs feedback through an iterative simulation process. The system calculates dose distribution based on the current scan distance and velocity profile, evaluates the uniformity, and adjusts the parameters accordingly. This feedback loop continues until optimal parameters are found that achieve both good beam utilization and dose uniformity, resolving the contradiction between these two parameters
3Volume of stationary object
If traditional single-wafer scanning is used with beam scanning in one axis, then system size is reduced, but beam current becomes too low for high-dose implantation
Solution Approach 1:
The patent applies dimensionality change by introducing a second mechanical scanning dimension. Instead of scanning the beam in one axis only, the system scans the wafer in a raster pattern with motion in both x and y directions. This allows the use of a smaller, more focused beam while still achieving complete wafer coverage through the combined scanning motions, thereby maintaining high beam current capability in a compact system
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 enhances beam utilization and dose uniformity, improving the efficiency of ion implantation processes by optimizing the scan distance and velocity profile, leading to more precise and uniform dopant distribution on silicon wafers.
Implementation Method 1
ion implanter for introducing dopant materials into silicon wafers
Implementation Method 2
individual wafer(s) are mounted on the surface of an electrostatic chuck
Data Source
AI summary
To select a scan distance to be used in scanning a wafer with an implant beam, a dose distribution along a first direction is calculated based on size or intensity of the implant beam and a scan distance. The scan distance is the distance measured in the first direction between a first path and a final path of the implant beam scanning the wafer along a second direction in multiple paths. A relative velocity profile along the second direction is determined based on the dose distribution. Dose uniformity on the wafer is calculated based on the wafer being scanned using the relative velocity profile and the determined dose distribution. The scan distance is adjusted and the preceding steps are repeated until the calculated dose uniformity meets one or more uniformity criteria.