Semiconductor device manufacturing: process – Chemical etching – Vapor phase etching
Reexamination Certificate
1995-12-04
2001-02-27
Beck, Shrive (Department: 1763)
Semiconductor device manufacturing: process
Chemical etching
Vapor phase etching
C438S714000, C438S743000, C438S744000, C438S723000, C438S724000, C438S696000
Reexamination Certificate
active
06194325
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to an oxide etch process which is highly selective to nitride. More particularly, this invention relates to an oxide etch process with high selectivity to nitride which can be used on surfaces of uneven topology.
2. Description of the Related Art
A significant challenge in semiconductor fabrication is to etch an oxide such as a silicon oxide, in the presence of a nitride, such as a silicon nitride, without also etching the nitride, i.e., while maintaining a high selectivity to the nitride. An example of such could be where an oxide layer to be etched is located over a nitride layer. Since both oxide and nitride materials generally etch at the same rate in a typical fluorocarbon chemistry etch plasma commonly used for etching oxide, a process of providing additional selectivity must be found.
When a fluorine-substituted hydrocarbon, such as C
3
F
8
, is used as an etchant, the fluorocarbon radicals react in the plasma to form a passivating coating of a carbon-fluorine polymer which forms over the materials being etched, e.g., by exposed oxide and nitride surfaces on a substrate. However, this polymer is dissociated by oxide atoms formed during the etch of the exposed oxide portions. Thus, as the oxide, e.g., silicon oxide, continues to etch, the nitride portions etches at a much slower rate due to the presence of the passivating coating thereon. However, the passivating layer is also attacked by free fluorine atoms present in the plasma, and thus the nitride also continues to be etched. Thus, a selectivity over about 8:1 of silicon nitride to silicon oxide was not achievable with such prior art etch processes due to the presence of such free fluorine atoms in the plasma. Since for state of the art devices having submicron dimensions, i.e., VLSI and ULSI devices, selectivity of over 10:1 and even 30:1 are required, an etch process for etching oxide in preference to nitride with a selectivity of over 10:1 would be highly desirable.
In U.S. Pat. No. 5,423,945, the subject matter of which is hereby incorporated by reference, we described and claimed the provision of a scavenger for fluorine such as a source of silicon or carbon. This scavenger for fluorine, when used in combination with such fluorine-substituted hydrocarbon etch gases, results in the formation of a carbon-rich polymer which does not dissociate over nitride surfaces, apparently due to either the reduced free fluorine content in the plasma, or the reduced fluorine content in the polymer, or both. In any event, this use of a scavenger for fluorine in combination with fluorine-substituted hydrocarbon etch gases results in an oxide etch having a selectivity to nitride, i.e., a preference for oxide etching over nitride etching, of over 10:1, and up to as high as approaching infinity.
However, more recently an additional problem has been discovered where at least the nitride surfaces of the nitride/oxide structure being etched are not flat, as for example, the sidewalls of a slot or on raised steps such as, for example, nitride-coated polysilicon lines. This type of structure is illustrated in
FIG. 1
wherein raised polysilicon lines
10
and
12
, formed over a substrate
2
, are coated with a conformal layer
20
of nitride, over which is formed an oxide layer
30
and a photoresist mask
40
.
When oxide layer
30
is etched, through mask opening
42
in photoresist mask
40
, down to conformal nitride layer
20
, nitride portions
22
on the sidewalls of raised polysilicon lines
10
and
12
are also at least partially etched, indicating that the above-described protective polymer is either not forming on such generally vertical surfaces (surfaces generally perpendicular to, or at least not planar with, the underlying substrate), or the protective polymer is being more readily attacked by the etchant gases on such nonplanar surfaces than the corresponding polymer portions formed on horizontal surfaces, i.e., surfaces generally planar to the underlying substrate, such as nitride portion
26
between raised lines
10
and
12
.
It would, therefore, be desirable to provide an oxide etch process highly selective to nitride which is suitable for use on surfaces of uneven topography wherein nitride surfaces which are not planar to the underlying substrate, including sidewalls on slots or raised portions, will be resistant to etching by the oxide etch process.
SUMMARY OF THE INVENTION
We have found that the addition of one or more hydrogen-containing gases, preferably one or more hydrofluorocarbon gases, to one or more fluorine-substituted hydrocarbon etch gases and a scavenger for fluorine, in a plasma etch process for etching oxide in preference to nitride, results in a high selectivity to nitride which is preserved regardless of the topography of the nitride portions of the substrate surface. In a preferred embodiment, one or more oxygen-bearing gases are also added to reduce the overall rate of polymer deposition on the chamber surfaces and on the surfaces to be etched, which polymer deposition can otherwise, respectively, reduce the etch rate, and cause excessive polymer deposition on the chamber surfaces.
REFERENCES:
patent: 4350578 (1982-09-01), Frieser et al.
patent: 4368092 (1983-01-01), Steinberg et al.
patent: 4377438 (1983-03-01), Moriya et al.
patent: 4401054 (1983-08-01), Matsuo et al.
patent: 4492620 (1985-01-01), Matsuo et al.
patent: 4511430 (1985-04-01), Chen et al.
patent: 4675073 (1987-06-01), Douglas
patent: 4778561 (1988-10-01), Ghanbari
patent: 4807016 (1989-02-01), Douglas
patent: 4810935 (1989-03-01), Boswell
patent: 4918031 (1990-04-01), Flamm et al.
patent: 4948458 (1990-08-01), Ogle
patent: 5286344 (1994-02-01), Blalock et al.
patent: 5423945 (1995-06-01), Marks et al.
patent: 0 552 490 (1992-12-01), None
patent: 0644584 (1994-09-01), None
patent: 0651434 (1994-10-01), None
patent: 57-210631 (1982-12-01), None
patent: 64-15928 (1989-01-01), None
patent: 2-062038 (1990-03-01), None
patent: 2-62038 (1990-03-01), None
“Selective Reactive Ion Etch for Silicon Oxide—over Silicon Nitride, Using Carbon Tetra: Fluoride and Methylene Tri:Fluoride as Etel Gases”; RD-301059-A; May 10, 1989; Anonymous; Abstract only.
Anonymous, “Selective Reactive Ion Etch for Silicon Oxide over Silicon Nitride”,Research Disclosure, No. 301, May 1989, p. 340.
Becker, David S., et al., “A Method of Obtaining High Oxide to Nitride Selectivity in an MERIE Reactor”,Extended Abstracts, vol. 93, No. 1, May 21, 1993, pp. 367-368.
Bondur, J.A., et al., “Gas Mixing to Prevent Polymer Formation During Reactive Ion Etching”,IBM Technical Disclosure Bulletin, vol. 21, No. 10, Mar. 1979, p. 4016.
Plasma Etching, Chemistry of the Semiconductor Industry, 1987, pp. 374-378.
D'Agostino, Riccardo, “Summary Abstract: Mechanisms of Polymerization in Discharges of Fluorocarbons”,J. Vac. Sci. Technol. A, vol. 3, No. 6, Nov.-Dec. 1985, pp. 2627-2628.
Moss, S.J., et al., eds,The Chemistry of the Semiconductor Industry, New York: Blackie & Son Ltd., 1987, pp. 374-378.
Riley, Paul E., et al., “Comparison of Etch Rates of Silicon Nitride, Silicon Dioxide, and Polycrystalline Silicon upon O2Dilution of CF4Plasmas”,J. Vac. Sci. Technol. B, vol. 7, No. 6, Nov.-Dec. 1989, pp. 1352-1356.
Machida, Katsuyuki, et al., “SiO2Planarization Technology with Biasing and Electron Cyclotron Resonance Plasma Deposition for Submicron Interconnections”,J.Vac. Sci.Technol.B, vol. 4, No. 4, Jul./Aug., 1986, pp. 818-821.
Bright Nicolas
Collins Kenneth S.
Groechel David
Keswick Peter
Marks Jeffrey
Applied Materials Inc.
Beck Shrive
Goudreau George
Morris Birgit
LandOfFree
Oxide etch process with high selectivity to nitride suitable... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Oxide etch process with high selectivity to nitride suitable..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Oxide etch process with high selectivity to nitride suitable... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2582897