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THE ELIMINATION OF AMMONIUM CHLORIDE DEPOSITION IN A LPCVD FORELINE

IP.com Disclosure Number: IPCOM000008181D
Original Publication Date: 1997-Jun-01
Included in the Prior Art Database: 2002-May-23
Document File: 3 page(s) / 110K

Publishing Venue

Motorola

Related People

Ivan Field: AUTHOR [+2]

Abstract

In a LPCVD system a problem exists due to deposition of the by-product Ammonium Chloride on the unheated foreline surface. Pumping and vent- ing the foreline caused the deposit to backstream into the furnace tube, resulting in high infilm particle counts affecting uptime and MTBF.

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@ MOTOROLA Technical Developments

THE ELIMINATION OF AMMONIUM CHLORIDE DEPOSITION IN A LPCVD FORELINE

by Ivan Field and Peter Donald

  In a LPCVD system a problem exists due to deposition of the by-product Ammonium Chloride on the unheated foreline surface. Pumping and vent- ing the foreline caused the deposit to backstream into the furnace tube, resulting in high infilm particle counts affecting uptime and MTBF.

  A heated foreline, using external heating jackets, is used to eliminate the Ammonium Chloride by- product from the rear flange to the heated gate valve. This, along with a cold trap down stream to collect this by-product, causes a great improvement of the uptime and the infilm particle data. Heating the foreline from the rear flange to the gate valve ensures that any build up of Ammonium Chloride is confined to the pump side of the valve. The cold trap is designed to collect the deposit in a crystalline form so that it does not flake into the process tube on pump down. An auto-soft flap valve is installed between the gate valve and the cold trap to minimize turbulence in the process tube on initial pump down. The external heating jackets are daisy chained to the LPCVD system via a relay so as to prevent operation if the chain is disconnected in any way. The foreline is made out of a single piece of piping to prevent deposits which would form at joints of separate pieces of pipe.

  The problem of Ammonium Chloride deposit causing the throttle valve to stick is overcome by using a heated throttle and gate valve. The cold trap is designed to be at ambient in order to remove most of the Ammonium Chloride before reaching

the pump. The heated gate valve and auto soft valve are protected by an extra heating jacket because the cold trap otherwise acts as a hea...