TECHNICAL BULLETIN

MOLDED NitroSil® OPAQUE COIL COVERS

DEVELOPED BY PYROMATICS

FOR USE IN

GEMINI EPITAXIAL REACTOR SYSTEMS

The following information is a compilation of data from companies engaged in high production epitaxy. The data represent a comparison of performance between NitroSil opaque fused quartz coil covers and conventional sandblasted fabricated coil covers. Information was obtained from production runs using Gemini I, Gemini II, Gemini III and Concept Systems Design encapsulated RF coil atmospheric epitaxial reactors.

  1. POWER SAVINGS: Power required to heat the graphite susceptors to process temperature was noticeably reduced.  NitroSil coil covers reflected IR radiation back into the susceptors which resulted in a 10 to 15 % power savings.
  2. "O" RING PROTECTION: NitroSil coil covers prevented IR radiation from reaching the RF feedthrough and burning the Teflon "O" rings.
  3. REDUCES "EPI" SPIKES: NitroSil coil covers lowered the heat load to the base plate thus reducing the rate at which deposits form there. Loose deposits are a source of particulates that cause "EPI" spikes. Further "up time" benefits resulted because the decrease in deposits increased the run time before cleaning of the base plate was required.
  4. PROFILE STABILITY: NitroSil coil covers exhibited unchanging reflectivity after wet chemical etching. The old clear style sandblasted covers became more transparent with each wet etch. This clearing condition caused the radial temperature profile to change as a function of an increasing transparency.
  5. EASY CLEANING: NitroSil coil covers reduced deposits on the RF coil copper weldment. Further, the weldment was easier to clean because the deposits remained soft and were easily removed by wiping down with a wetted towel. This meant that little pressure was needed during cleaning. (Less likely to disturb the temperature profile during cleaning). With sandblasted clear covers the deposit is a loose powder on top of a hard crust. These powder particles can become embedded in the deposited layer as spikes.
  6. LESS OUT-GASSING: NitroSil coil covers protected the coil hardware better. This reduced out-gassing and early breakdown of the coil adjusters thus diminishing particle generation.
  7. STOPS WATER LEAKS: The NitroSil molded opaque coil cover prevented most of the heat from entering the reactor base plate. With the old style sandblasted clear covers, the base plate was heated and would flex causing stresses on the water jacket welds, which frequently resulted in failure and water leaks.
  8. MORE DURABLE: The one piece molded NitroSil covers were structurally stronger and less likely to be damaged or broken by handling during wet etch cleaning.
  9. CLEANER CHAMBER HOUSING: Direct replacement of CSD encapsulated coil covers with NitroSil coil covers maintained a cleaner chamber housing due to the elimination of reactor gas leakage. The previous CSD encapsulated coil cover was a two part assembly in which the top disk sits on a bottom ring by stacking one on top of the other. Through operator handling during cleaning and installation, the mating edges of each part were susceptible to chipping which allowed reactor gasses to readily migrate in and out of the chipped chamber housing assembly (the copper coil weldment). This results in unwanted deposits both within and without the chamber.
  10. REDUCED SILICON BUILD UP: When NitroSil coil covers were used to replace two part cover assemblies, the silicon build up inside the bell jar was noticeably reduced.
  11. EASE OF ALIGNMENT: The inherent difficulty of aligning a two part assembly was eliminated with the use of molded one piece NitroSil coil covers.

This information is not to be taken as a warranty or representation for which we assume legal responsibility nor as permission or recommendation to practice any patented invention without a license.  It is offered solely for your consideration, investigation and verification.
August, 1997

 

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