LPCVD Gas Injection Ramps
Original Publication Date: 1987-Mar-01
Included in the Prior Art Database: 2005-Feb-01
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).