Flow rate sensor implementing a plurality of inner tubes located within a sensor tube

Abstract

There is provided a flow rate sensor comprising: a pair of heating resistors operable to heat a sensor tube; a temperature sensor operable to control respective temperatures of the heating resistors; and a case operable to hold the heating resistors and the temperature sensor. The flow rate sensor is adapted to detect a flow rate of a fluid flowing in the sensor tube based on variations of voltages applied to the heating resistors, wherein the variations occur according to the flow rate of the fluid. The flow rate sensor further comprises a voltage applying device operable to arbitrarily set an increase in temperature of each of the heating resistors. The sensor tube has opposite ends thereof thermally connected to the case. The temperature sensor is positioned to be equidistant from the opposite ends of the sensor.

Description

BACKGROUND OF THE INVENTION[0001]The present invention relates to a flow rate sensor capable of conducting measurement of a fluid flow rate with high sensitivity, without the need to heat the fluid to a high temperature.[0002]In a process for manufacturing semiconductors, a flow rate sensor is used as a flow rate controller for stably supplying a liquid material, such as TEOS (tetraethyl orthosilicate), a copper (I) compound, DMAH (dymethyl aluminum hydride) or the like. For use as such a flow rate sensor, in many cases, a thermal type flow rate sensor has been conventionally used. A thermal type flow rate sensor applies heat to a fluid flowing through a sensor tube and detects a quantity of heat carried away by the flowing fluid.[0003]In a conventional thermal type flow rate sensor, a heating temperature for the sensor tube is higher than room temperature by several tens of degrees Celsius. However, some types of liquid materials for semiconductors are extremely unstable relative t...

AI Technical Summary

Benefits of technology

The present invention provides a flow rate sensor that overcomes the problems of conventional thermal type flow rate sensors and can measure fluid flow rate at a low heating temperature for the sensor tube. The sensor comprises a pair of heating resistors, a temperature sensor, and a case. The sensor detects flow rate variations by monitoring the heating resistors' voltage variations caused by the fluid flow. The sensor tube is thermally connected to the case, and the temperature sensor is positioned equidistant from the opposite ends of the sensor tube. The heating resistors' temperature increase should be 5°C or less. The sensor tube may have a U-shaped configuration and be at least partially covered with a material having high heat conductivity. Narrow inner tubes may be provided within the sensor tube, and a sensor tube guide made of a material with high heat conductivity may be provided on the sensor tube. The sensor tube guide may enclose the sensor tube and be removable. The heating resistors may comprise metallic thin films.

Problems solved by technology

However, some types of liquid materials for semiconductors are extremely unstable relative to heat and form reaction products as a result of heat applied to the sensor tube.

Further, as a result of heat applied to the sensor tube, a convection current is generated in air outside the sensor tube, so that a tilt error due to the direction of mounting of the sensor occurs.

Further, when a liquid flows in the sensor tube, air bubbles are likely to be formed in the liquid as a result of heat applied to the sensor tube.

The formation of air bubbles can result in large measurement errors.

However, such a sensor tube is too large and is unsuitable for practical use.

However, in a flow rate sensor of this type, the inner diameter of the sensor tube is small, so that the flow rate which can be measured by the sensor is limited.

This necessitates use of a complicated sensor, and errors arising from the use of a divided flow can result.

Further, when the bypass portion is clogged, a large measurement error is likely to occur.

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