Chemistry: electrical and wave energy – Processes and products – Coating – forming or etching by sputtering
Patent
1993-06-21
1995-09-05
Breneman, R. Bruce
Chemistry: electrical and wave energy
Processes and products
Coating, forming or etching by sputtering
20419212, 20419222, 20419223, C23C 1410
Patent
active
054476135
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to the fabrication of semiconductor devices, and more particularly, but not exclusively, to a method of fabricating semiconductor wafers wherein spin-on glass (SOG) is applied to the semiconductor substrate as a planarization layer during the fabrication process.
Spin-on glasses (SOGs) are proprietary liquid solutions containing silicate (purely inorganic SOGs) or siloxane (quasi-inorganic SOGs) based monomers diluted in various kinds of solvents or alcohols. Such solutions are available from Allied Signal Inc., Milpitas, Calif. During coating and curing, the monomers are polymerized by condensation of silanol and ethoxy groups. Water vapour, ethyl alcohol, and other by-products such as ethylene, are released according to the following scheme: ##STR1##
Polymerization of the SOG solution stops when the distance between neighboring silanol groups, or ethoxy groups, becomes too large, or when too much condensation gas such as water vapour, ethyl alcohol, or its decomposition by-products, ethylene, and water vapour, blocks the condensation mechanism. Heating is then needed to eliminate these gases and permit further condensation, densification, and the fabrication of a hard purely inorganic or quasi-inorganic SOG film.
The final density of the obtained SOG films depends on many factors, but it is generally lower than the density of other inorganic or quasi-inorganic glasses deposited by other commonly used techniques such as LPCVD or PECVD. This lower density is due to the large number of pores in the SOG film, which cause high conductance paths between film surface and its bulk.
These pores permit readily adsorbed gas molecules present on SOG film surface to continuously and rapidly diffuse through the bulk of the film and rapidly physically connect to the glass by forming low energy (<0.3 eV) Van der Waals bonds ( . . . ). The gas molecules are rapidly physically absorbed by the SOG film network.
Some gases, such as water vapour, have molecules that can slowly form high energy (>0.5 eV) chemical bonds (.) with the SOG film network by forming a pair of silanol groups. Water vapour molecules are slowly chemically absorbed by the SOG film network as shown below: ##STR2##
This slow chemical absorption of water vapour by the SOG film is particularly efficient if the SOG solution contains phosphorus organometallic molecules, which provide very efficient water vapour gettering due to the presence of phosphorus-oxygen double bounds in the SOG film: ##STR3##
The gettering of water vapour by absorption can be verified by infrared spectroscopy by monitoring the behaviour of these P:O bonds and other bonds in presence of moisture. Infrared spectroscopy shows that readily adsorbed water vapour molecules rapidly diffuse in the pores of the SOG, rapidly become physically absorbed (3350 cm.sup.-1), and slowly become chemically absorbed by --P:O bonds (1280 cm.sup.-1) and --Si.O.Si--bonds (460, 810, 1070 and 1140 cm.sup.-1) to form respectively --P.OH (950 and 3700 cm.sup.-1) and --Si.OH (930 and 3650 cm.sup.-1) groups.
The rapid physical absorption is characterized by a t.sup.1/2 behaviour and the slow chemical absorption is characterized by a t.sup.1/4 behaviour.
The same mechanism is observed for glasses other than spin-on glasses and has been reported for very low temperature, thus very porous, LPCVD and PECVD silicates [See W. A. Pliskin, J. Vac. Sci. Technol., Vol. 14, p. 1064.; J. A. Theil, D. V. Tsu, G. Lucovsky, Journal of Electronic Materials, Vol. 19, No. 3, pp. 209-217].
It is believed that this mechanism is universal and should be observed for any type of porous glass. It is also believed that the lower the film porosity, which implies fewer pores and lower conductance from the film surface to its core, the slower the water vapour channeling, its physical absorption and chemical absorption.
Since the cure temperature of SOG used to smooth glasses in a non etch-back SOG multi-level interconnect process is limited to less than 550.degree. C., and since SOG
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Paul E. Riley and Attila Shelley, "Characterization of a Spin -Applied Dielectric for Use in Multilevel Metallization" May 1988 pp. 1207-1210.
Breneman R. Bruce
McDonald Rodney G.
Mitel Corporation
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