Molecular Flow Module
New App: Ion Implanter Evaluator
This app examines the number density, pressure, and molecular flux inside an ion implantation device. The angle of the wafer, chemical composition, temperature, outgassing rate, and pump speeds are all inputs. Visual results include 3D plots of the number density, while analytic results give the average number density along the beamline.
Numerical Improvements for Faster Free Molecular Flow Calculations
The Free Molecular Flow interface is more efficiently parallelized, allowing more cores to be used effectively during the computation. The table below shows how much faster three tutorial models were run in COMSOL Multiphysics 5.1 compared to the previous version. A 10-core machine was used to run the simulations.
|Tutorial||CPU Time (5.0)||CPU Time (5.1)||Speedup|
|Evaporator||2h 24m 4s||18m 31s||7.8|
|Outgassing Pipes||2m 57s||45s||3.9|
|Ion Implanter||5m 15s||2m 1s||2.6|
Multiple Species for Molecular Flow
It is now possible to model multiple species in the Free Molecular Flow interface.
New Option for Specifying Outgassing Rate
The outgassing rate can now be specified in units of [(torr * l)/cm^2/s] or [(mbar * l)/cm^2/s] (the equivalent SI unit is W/m2). You can now use these units in the new Thermal desorption rate feature when the Outgassing wall option is chosen in the Wall boundary condition.
New Tutorial: Chemical Vapor Deposition at Ultra High Vacuum
Chemical vapor deposition (CVD) is a process often used in the semiconductor industry to grow layers of high-purity solid material on top of a wafer substrate. CVD is achieved using many different techniques and across a range of pressures, from atmospheric to ultra high vacuum (UHV/CVD). Since UHV/CVD is performed at pressures below 10-6 Pa (10-8 Torr), gas transport is achieved by molecular flow and it lacks any hydrodynamic effects such as boundary layers. In addition, with no gas-phase chemistry involved (due to the low frequency of molecular collisions), the growth rate will be determined by the number density of species and surface molecular decomposition processes.
This tutorial uses multiple species in the Free Molecular Flow interface to model the growth of silicon wafers from CVD. The effects of different pumping curves are explored after running an auxiliary sweep.
The plot shows the molecular flux fraction of SiH4 at the wafer cassette during Chemical Vapor Deposition at Ultra High Vacuum.