Mass Flow Controller Backpressure Adjustment for Low Flow Control

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Solution Overview

Problem

Mass flow controllers face challenges in achieving low fluid flow rates in backpressure environments, particularly in semiconductor manufacturing, where rapid reduction of flow rates is required without compromising precision and efficiency.

Innovation Solution

A mass flow control apparatus featuring a control module, variable control valves, solenoid valves, pressure sensors, and a flow restrictor system that dynamically adjusts fluid pressure and flow rates to maintain desired operating conditions, including a method for flow verification using pressure-volume-temperature measurements and a supervision function for calibration curve determination.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If a mass flow controller operates in a backpressure environment, then it can maintain stable pressure, but it becomes difficult to achieve low fluid flow rates

Engineering Contradiction:

Improvepressure stabilityVSAvoidlow flow rate capability

Core Design Contradiction:

ReliabilityVSProductivity

Solution Approach 1:

The patent implements a dynamically adjustable downstream valve that can modify its opening degree in real-time based on the required flow rate and backpressure conditions. This dynamic adjustment allows the system to overcome the backpressure effect by opening the valve wider when low flow rates are needed, thereby resolving the contradiction between maintaining pressure stability and achieving low flow rates.

Inventive Principle:

Principle #15Dynamics

2Productivity

If a variable control valve constricts to reduce flow rate, then low flow rates are achieved, but the pressure from the flow restrictor may become lower than backpressure from the tool

Engineering Contradiction:

Improveflow rate reductionVSAvoidpressure differential

Core Design Contradiction:

ProductivityVSStress or pressure

Solution Approach 1:

The patent employs a two-stage valve system where the downstream valve is adjusted first to establish appropriate backpressure, and then the upstream proportional valve is modulated to achieve the desired flow rate. This preliminary action ensures that the pressure differential across the flow restrictor remains positive even at low flow rates, preventing the restrictor pressure from dropping below tool backpressure.

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The system uses pressure sensors to continuously monitor the pressure at the flow restrictor and tool backpressure, feeding this information back to the control algorithm. The control algorithm dynamically adjusts both valves based on this feedback to maintain the required pressure differential, ensuring that restrictor pressure always exceeds tool backpressure even at minimal flow rates.

Inventive Principle:

Principle #23Feedback

3Ease of operation

If a traditional mass flow controller is used, then it can control fluid flow, but it lacks the capability for rapid reduction of flow rates

Engineering Contradiction:

Improveflow control capabilityVSAvoidflow rate reduction speed

Core Design Contradiction:

Ease of operationVSSpeed

Solution Approach 1:

The patent divides the single valve control into two separate valve stages: an upstream proportional valve for fine flow modulation and a downstream variable valve for rapid flow reduction. This segmentation allows each valve to specialize in different aspects of flow control, with the downstream valve providing fast response for rapid flow rate reduction while the upstream valve maintains precise flow control.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The control system implements a staged valve adjustment strategy where the downstream valve is adjusted in larger increments for rapid flow reduction, followed by finer adjustments of the upstream proportional valve for precise flow control. This periodic action with different adjustment granularities enables both rapid response and precision control.

Inventive Principle:

Principle #19Periodic action

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

Enables rapid and precise adjustment of flow rates, extending the useful operating range of mass flow controllers and ensuring accurate fluid delivery even under low flow and backpressure conditions, enhancing the performance in semiconductor manufacturing processes.

Implementation Method 1

A second pressure sensor located upstream from the variable control valve, the second pressure sensor configured to measure back pressure from the tool

Methodology Applied

Scientific EffectPressure sensing:

Implementation Method 2

providing provisions for measuring a reference temperature (T0) and a reference pressure (P0) of a fluid contained within a reference volume of the fluid pathway

Methodology Applied

Scientific EffectTemperature sensing:

Implementation Method 3

adjust the pressure to the flow restrictor such that the pressure drops across the flow restrictor to yield a flow rate that is equal to the second set point

Methodology Applied

Scientific EffectPressure drop: Pressure Drop

Data Source

PatentUS11467608B2Systems and methods for flow sensor back pressure adjustment for mass flow controller

Publication Date: 2022.10.11 FLOW DEVICES & SYST INC

AI summary

A mass flow control apparatus is capable of controlling a flow rate of a fluid to a tool. Pressure of the fluid is regulated by a solenoid valve, which receives signals from a control module. Various set points may be inputted to the control module, whereby control module receives pressure sensor signals from across a flow restrictor and adjusts the solenoid valve to control the fluid flow rate to equal a set point.