Patterned Silicon Wafers Improved with Quartz Gas-Line Heat

Baking out a chamber with the existing heater is designed to remove surface contaminants that are adsorbed to the material. However using the chamber heater is not efficient enough in removing such dislodged contaminants from the vacuum chambers’ inside surfaces. This is due to a reabsorption process that happens when molecules, desorbed by baking, become adsorbed in another area of the chamber due to the random path the desorbed molecules take prior to leaving the chamber. In addition, there is just not enough energy created by the chamber heater to remove all the absorbed particulates.

SOLUTION

An ultra-pure non-metallic gas flow heater is required for efficient purging of the vacuum chamber at temperatures from 90ºC to 250ºC. The heated gas flow will sweep through the chamber essentially preventing the contaminant molecules from being re-adsorbed on the inside surfaces of the chamber. Furthermore, the flow of gas walks the contaminant molecules to the exit door of the chamber with minimal opportunity for reabsorption.

The problem becomes what is an ultra-pure gas flow heater? Obviously not a gas line heater with metalic delivery system in the stream of the gas flow (see Figure A). The heater must utilize a quartz ID with the ability to heat fast enough in order to get to the 90º to 250ºC outlet temperatures.

Flow rates would be at a minimum of 5 standard cubic centimeters per second (sccm) into a chamber of 5 liters on up to 150 sccm. A higher flow would ensure a sufficient flow of gas for the sweeping of desorbed contaminants. However, higher flow means potentially lower temperature, there needs to be a balance. Make sure the wattage calculations are correct as well as using the preferred purging gas of argon with gases such as nitrogen and neon being secondary sources.