Accupak/VE Helps Optimize Semiconductor Process Instrumentation

Semiconductors are the foundation of the computer and communication systems that are an integral part of our lives and a growing industry boasting more than a hundred billion in yearly sales worldwide. Aiding in the manufacturing of these valuable devices are mechanisms such as the thermal mass flow control instrumentation designed by Paul Lucas at MKS Instruments, Inc., in Methuen, MA, with the help of Algor's Accupak/VE software.

Mr. Lucas optimized the design of this thermal mass flow control instrument, which is used in semiconductor manufacturing. The tube is sealed to the body of the instrument using ferrule compression, a common tube joining method which poses new challenges given the small scale of the instrument. Accupak/VE was used to analyze the joint between the tube and the body of the instrument to simulate the effects of the compression procedure. Mr. Lucas' objective was to optimize the metal used for sealing and location of the pressure that would seal the two components.

Control Instrument Components Sealed Using Ferrule Compression

The thermal mass flow control instrument is an electro-mechanical device which controls the flow of gasses which are being used to create semiconductors. The devices must carefully control the amount of gas flowing into the reaction so that the chemical process takes place properly. The thermal sensor is a tube which protrudes from the body of the instrument with windings around the outside that cool and heat.

Mr. Lucas' analyses were focused on joining this tube to the body of the instrument using ferrule compression. The technique was being investigated because it uses only metals, rather than a polymer or other kind of sealant, which does not corrode or permit gasses to permeate the seal and escape.

Compression is a common way of sealing a pipe to an object for many applications, but it is unique in the small scale being utilized in this design. A metal ring called a ferrule is placed on the outside of the tube. Pressure is applied to the ferrule, causing it to deform in and seal the tube to the body of the instrument.

Unexpected Conclusions from Analysis Results

Mr. Lucas modeled the tube and the ferrule with 2-D axisymmetric elements. Truss elements were used to simulate the body. Mr. Lucas performed a series of Accupak/VE analyses to optimize both the ideal location to apply pressure and the best material. Accupak/VE was chosen because it could analyze the assembly for large deformation, large strain and nonlinear material properties.

On both counts, analysis results ran counter to Mr. Lucas' initial guesses. He was especially surprised how the ferrule material strength related to the sealing capability. Test data confirmed accuracy of the Algor analysis results.

The final design was also analyzed using Fluid Flow to ensure that the seal would not negatively affect the flow sensing function of the tube.

About Algor

"The auto-load incrementation option (/autotm) was very useful," said Mr. Lucas. "By automatically decreasing the load increment, the analysis converged without restarting and I got very interesting results about the dynamic moments in the analysis. It was especially useful when I encountered buckling in one of the runs."

"With Superdraw III's automatic options, the meshing process flies without a problem," added Mr. Lucas.