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Cylindrical Sleeve Technique for Improved Single Wafer Uniformity in LPCVD Processes

IP.com Disclosure Number: IPCOM000041551D
Original Publication Date: 1984-Feb-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 3 page(s) / 52K

Publishing Venue

IBM

Related People

Barbee, SG: AUTHOR [+3]

Abstract

Low pressure chemical vapor deposition (LPCVD) processes accomplish large batch size depositions by closely packing wafers such that they approximate an annular cylinder in the reaction tube. For many processes, this configuration is adequate for uniform film thicknesses across each wafer. However, certain reactions result in severe radial thickness nonuniformities across the wafers. This has been attributed to inter-wafer radial diffusion-caused reactant depletion. Examples of such processes are: 1. Arsenic or phosphorous, in-situ doped polysilicon using SiH4 with AsH3 or PH3; 2. Si3N4 by SiH4/NH3; 3. SiO2 by SiH4/O2; and 4. Phosphosilicate glass or arsenosilicate glass by SiH4/O2/PH3 or AsH3; tetraethoxysilane TEOS/PH3 or AsH3.

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Cylindrical Sleeve Technique for Improved Single Wafer Uniformity in LPCVD Processes

Low pressure chemical vapor deposition (LPCVD) processes accomplish large batch size depositions by closely packing wafers such that they approximate an annular cylinder in the reaction tube. For many processes, this configuration is adequate for uniform film thicknesses across each wafer. However, certain reactions result in severe radial thickness nonuniformities across the wafers. This has been attributed to inter-wafer radial diffusion-caused reactant depletion. Examples of such processes are: 1. Arsenic or phosphorous, in-situ doped polysilicon using SiH4 with AsH3 or PH3; 2. Si3N4 by SiH4/NH3; 3. SiO2 by SiH4/O2; and 4. Phosphosilicate glass or arsenosilicate glass by SiH4/O2/PH3 or AsH3; tetraethoxysilane TEOS/PH3 or AsH3. Since variations of process parameters, such as partial and total pressures, gas flow, and temperature, have not yet resulted in radially uniform films for these processes, various clever quartz-ware modifications have been used which inexplicably result in improvements in single-wafer uniformity. Among these designs are: 1. Modular "cages" consisting of axial rods connected together, enclosing the "wafer cylinder"; and 2. Enclosures which force gas-flow directly across each wafer. These designs are of delicate and fragile

construction with many critical dimensions,

causing their construction and replacement expense

to be high. A hollow cylinder enclosing the "wafer cylinder" is used to overcome these problems, as seen in the figure. The important design features are: 1. The material and thickness of the cylindrical sleeve 10; 2. The distance between the sleeve's inner surface and the edge of wafer 12; and 3. The length of the sleeve(s). For best radial uniformity, the sleeve thickness should be maximum, the sleeve-to-wafer perimetry distance minimum, and the length minimum to alleviate downstream depletion. For example, a
91.44 cm long quartz sleeve 10 with an I.D. of 9.75 cm and an O.D. of 11.1 cm may be used. This was placed in a 12.85 cm LPCVD tube 1...