Browse Prior Art Database

LPCVD Gas Injection Ramps

IP.com Disclosure Number: IPCOM000038872D
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
Document File: 2 page(s) / 38K

Publishing Venue

IBM

Related People

Deseez, C: AUTHOR [+6]

Abstract

When applying thin films by using the low pressure chemical vapor deposition (LPCVD) process, the reactive gases are currently injected at the front gate of the process tube through ordinary input ports. Under low pressure, the reactive molecules are driven along the tube from the front to the rear where they gradually decompose. This causes a progressive loss of the fresh reagent in the rear section of the process tube, which is to be compensated by establishing a positive gradient of temperature from the front to the rear. This allows a flat profile of thickness to be obtained. This thermal gradient allows films of different composition or structure to grow along the same load of wafers (the best known case is the one relating to polysilicon in which the size of the polycrystalline grains is an important parameter).

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LPCVD Gas Injection Ramps

When applying thin films by using the low pressure chemical vapor deposition (LPCVD) process, the reactive gases are currently injected at the front gate of the process tube through ordinary input ports. Under low pressure, the reactive molecules are driven along the tube from the front to the rear where they gradually decompose. This causes a progressive loss of the fresh reagent in the rear section of the process tube, which is to be compensated by establishing a positive gradient of temperature from the front to the rear. This allows a flat profile of thickness to be obtained. This thermal gradient allows films of different composition or structure to grow along the same load of wafers (the best known case is the one relating to polysilicon in which the size of the polycrystalline grains is an important parameter). The object of the invention is to combine a conventional injection of gas at the front of the tube with an injection directly distributed under the load of wafers to be deposited by means of injection ramps. The injection ramps go through the rear gate, up to the middle of the process tube, and allow the reactive species to be balanced in order to obtain directly a flat profile of thickness along the load without the need of a thermal gradient. The advantages of the injection ramp are as follows: - The possibility of the increasing the number of wafers

produced on each run (batch). - The possibility of using diluted gases w...