Gas Flow and Properties: Standards and Models for Flow Metering Semiconductor Gases at Flows from 10 μL/min to 1 L/min

Summary

Numerous gases are used in the production of semiconductor chips, and the accurate metering of these gases into the process chamber is critical for maximizing device throughput and yield. Many of these gases are hazardous, and flow standards for hazardous gases do not exist. Therefore, the semiconductor industry relies on approximate “meter factors” to extrapolate a meter calibration.

This project will provide standards for the metering of hazardous gases and enable higher chip throughput and yield.

Grand Challenge 1: Metrology for Materials Purity, Properties, and Provenance

Description

This project will develop a primary flow standard and gas property data that can be used to determine MFC performance for industrially relevant gases. This should result in better semiconductor manufacturing process control. 

Credit: NIST

Today the control of process gases in semiconductor fabrication is highly empirical. The process is based on “recipes” for each step. The development of these recipes is a time-consuming process of trial and error, and each day in development can translate to many millions of dollars of lost production. 

Through the process, each gas precursor is measured and delivered by a meter called a mass flow controller (MFC). Because MFCs do not provide sufficient flow accuracy, manufacturers must develop recipes by trial and error to achieve the correct stoichiometric ratio. The iterative process is both resource-intensive and time-intensive. As semiconductor manufacturing advances, the requirements on MFC performance get tighter because any process variation can reduce device throughput and yield. 

Currently, manufacturers correct the measured MFC flow relative to nitrogen for many process gases. However, the correction method lacks standardization and SI traceability, and introduces significant errors depending on the flow and the gas type. A national flow standard will remove bias between different meter manufacturers, resulting in more accurate MFCs. 

This project will develop physics-based and experimentally verified models of the flow meters, measure gas properties to state-of-the-art accuracy, and validate the resulting calibration chain with flow measurements on a variety of industrially relevant process gases.