Fishing – trapping – and vermin destroying
Patent
1993-01-26
1994-11-15
Hearn, Brian E.
Fishing, trapping, and vermin destroying
437231, 437978, 437982, 156630, H01L 2190
Patent
active
053648188
DESCRIPTION:
BRIEF SUMMARY
This invention relates generally to a process for applying spin-glass to a substrate, and more particularly to a process for the planarization of semiconductor wafers. The invention is especially applicable to inorganic spin-on glasses.
Spin-on glasses (SOG) are proprietary liquid solutions containing siloxane or silicate based monomers diluted in various kinds of solvents or alcohols. They are commonly used for the planarization of semiconductor wafers, i.e. the filling and levelling of the trenches formed between interconnect paths deposited on the wafer. On coating and curing of spin-on glasses, monomers are polymerized by condensation and release of water, solvent, and alcohol. The condensed material is a thin solid film having mechanical, chemical and electrical properties which depend on the starting solution, and the coating and curing process.
There are more than one hundred different SOG solutions currently available. These are classified into two major families:
The various components of a SOG solution (silicon containing oligomer, solvents mixture, and residual water) are in equilibrium in the liquid phase. Immediately after coating, volatile products (solvents and water) evaporate, and polymerization occurs due to the formation by condensation of silanol, Si--OH, bonds. These produce more water according to the following reaction (i): ##STR1##
Polymerization continues until the distance between neighbouring silanol groups, Si--OH, becomes too large or when too much by-product, such as water, blocks the condensation reaction. Heating is then required to permit further densification.
The properties of the films, such as higher density, reduced hydrogen content, higher coefficient of thermal expansion, better-flexibility and higher resistance to cracking, made from both types of SOG solution can be improved by incorporating phosphorus organometallic catalyst. In the SOG solution, the phosphorus organometallic molecules are generally not well bound to the silicon-containing compounds. Strong bonding generally occurs in the solid state when the film is exposed to relatively high temperatures. These organometallic molecules can nevertheless polymerize in the solution to form poorly bonded polymers that dissociate and form stable polymers during coating and condensation of the film. As an example, a Japanese SOG solution alloyed with a phosphorus organometallic molecule, P.sub.w O.sub.x (OH).sub.y (OC.sub.2 H.sub.5).sub.z, which is in dynamic equilibrium with the water and ethanol, C.sub.2 H.sub.5 OH behaves as shown in reaction (ii): ##STR2##
In theory, the phosphorus atom connects to the SiO.sub.2 network with three P.O.Si bonds. These bonds are formed by the condensation of --P.OH or --P.OC.sub.2 H.sub.5, and --Si.OH.
While the properties of the SOG films can be improved by alloying with phosphorus organometallic catalyst the presence of water H.sub.2 O hydrogen H.sup.+, hydroxyl OH.sup.-, hydronium H.sub.3 O.sup.+, lithium Li.sup.+, sodium Na.sup.+, and potassium K.sup.+ ions causes serious instabilities in MOS devices.
Some phosphorus bound in the dielectrics deposited in the upper levels of these sensitive ICs can eliminate such negative effects by acting as a getter. As an example, a 23 nm thick 6.0 mole % P.sub.2 O.sub.5 phosphosilicate glass protective layer increases by twelve orders of magnitude the resistance of a 100 nm SiO.sub.2 film against sodium, Na.sup.+, contamination at 80.degree. C. and 2.0 MV/cm electrical field [See for example, J. R. Davis, Instabilities in MOS Devices, Gordon and Breach, Science Publishers Inc., Electrocomponent Science Monographs, Vol 1, Chap. 4, pp. 65-81].
The mechanism for proton H.sup.+, lithium Li.sup.+, sodium Na.sup.+, and potassium K.sup.+ ion gettering as follows (iii): ##STR3##
The free proton, H.sup.+, lithium Li.sup.+, and potassium K.sup.+ ion, is trapped by the --P:O double bond. This results in the formation of a local positively charged centre with a certain orientation freedom; the formed --P.O.sup.+ charged centre can orient itself under an
REFERENCES:
patent: 5252515 (1993-10-01), Tsai
Chang J.
Hearn Brian E.
Mitel Corporation
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