Dual Controller Laser System for Thick Resist Focus Control
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Solution Overview
Problem
Lithographic apparatuses face challenges in maintaining focus over thick resist layers due to wafer bending and topography, leading to stress and alignment issues, particularly with 3D memory stacks where resists are several microns thick, and current solutions like adjusting wafer stage height and tilt cause local stress and alignment problems.
Innovation Solution
A control system for a laser that includes two controllers and a switch, allowing cyclic operation to adjust setpoint values based on sensor feedback, minimizing stress and enabling precise control of radiation sources, including pulsed lasers with multiple wavelengths, to optimize exposure across the full thickness of thick resist layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If wafer stage height and tilt are adjusted to optimize focus for thick resist, then focus is improved, but local stress and alignment problems occur
Solution Approach 1:
The patent divides the single wafer stage adjustment system into two separate controllers (first and second controllers), each managing different aspects of focus control. This segmentation allows independent optimization of focus parameters without coupled stress effects, resolving the contradiction between achieving focus and avoiding local stress/alignment issues.
Solution Approach 2:
The patent implements cyclic switching between two different setpoint values for focus control. By alternating between different parameter settings (first setpoint and second setpoint) in a cyclic manner, the system achieves sustained focus optimization while distributing mechanical stress over time, preventing the accumulation of local stress and alignment problems.
Data Source
AI summary
A control system for controlling a laser, comprising a sensor for sensing a physical value indicative of a characteristic of a laser beam emitted by the laser, a switch, a first controller and a second controller. Each controller is configured, to receive a further sensor value from the sensor, adjust a received setpoint value based on the received further sensor value to give an output value and cause the laser to operate in accordance with the output value. The switch is configured to switch between the controllers such that output values are provided from each controller in a cyclic fashion.