Gas Delivery System With Flow Restrictor For Square Wave Control
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Solution Overview
Problem
Commercially available mass flow controllers (MFCs) are slow to turn on and off, causing a bottleneck in semiconductor processing, particularly in atomic layer deposition (ALD) and three-dimensional integrated circuit (3DIC) processes, leading to undesirable initial spikes in gas flow due to pressure buildup and rapid release when switching between gas species.
Innovation Solution
A high impedance flow restrictor is added in series with the on-off valve to increase the time constant of gas flow, producing rapid square waves with minimal initial spike by regulating the flow out of the accumulation volume, ensuring consistent and reproducible gas delivery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If an on-off valve is used to rapidly switch gas flow, then the response speed is improved, but pressure buildup occurs behind the valve causing large initial flow spikes
Solution Approach 1:
A flow restrictor is introduced as an intermediary component between the on-off valve and the accumulation volume. This restrictor acts as a mediator that limits the rate at which pressure can build up behind the valve during the off cycle, thereby preventing the large initial flow spike that occurs when the valve opens. The restrictor allows the system to maintain fast response speed while eliminating the harmful pressure buildup effect.
Solution Approach 2:
The flow restrictor changes the flow resistance parameter in the system. By increasing the resistance to flow through the restrictor, the rate of pressure buildup behind the on-off valve is controlled. This parameter change allows the system to achieve rapid switching while maintaining consistent flow output without large spikes, as the restrictor dampens the pressure transient effects.
2Manufacturing precision
If mass flow controllers are used to control gas flow, then flow control precision is improved, but the response time becomes slow creating a bottleneck
Solution Approach 1:
The gas delivery system is segmented into two functional parts: an MFC that maintains steady state flow for precision control, and a separate on-off valve with accumulation volume that handles rapid switching. This segmentation allows each component to optimize its specific function - the MFC provides flow control precision while the valve assembly provides fast response time, eliminating the bottleneck effect.
Solution Approach 2:
The accumulation volume is pre-filled with process gas during the off cycle, preparing the gas supply in advance. When the on-off valve opens, this pre-positioned gas can flow immediately without waiting for the MFC to respond, thereby achieving fast response time while the MFC continues to provide precise flow control for the overall process.
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
The solution effectively reduces the initial spike and maintains a consistent gas flow magnitude during the on cycle, improving the reproducibility and reducing variations in semiconductor processing by significantly increasing the time constant of gas flow decay.
Implementation Method 1
A high impedance flow restrictor is added in series with the on-off valve to increase the time constant of gas flow
Data Source
AI summary
A wave generation component during an off cycle when the on-off valve is closed to build pressure from the process gas in an accumulation volume. During an on cycle when the on-off valve is open the wave generation component releases the process gas according to a time constant. A flow restrictor installed downstream in a throat of the on-off valve, outputs the rapid square waves to the conduit at a predefined magnitude. The flow restrictor is selected to have an impedance that is high enough to significantly raise the time constant during the on cycle such that pressure decay in each square wave pulse over the on cycle decreases to within a tolerance, wherein the time constant is at least in part a function of the flow restrictor impedance.