Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
1999-05-03
2001-06-19
Gupta, Yogendra (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S175000, C510S449000, C510S505000, C134S001300
Reexamination Certificate
active
06248704
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a semiaqueous cleaning composition that is particularly useful for cleaning organic and inorganic compounds or “polymers” (post etch residues) from a semiconductor substrate. As used herein, the term “semiaqueous” refers to a mixture of water and organic solvent. The invention also includes methods of using this composition to clean residues from semiconductor substrates. More particularly, the invention describes a semiaqueous cleaning composition and processes for its use. The solutions are organoammoniun compound and amine carboxylate compound free and contain fluoride compounds, water, and solvent and optionally contain corrosion inhibitors, chelating agents, surfactants, acids and bases.
2. Description of Related Art
Fluoride containing chemistries have been used for many years to clean prime silicon wafers (wafers that have not yet undergone ion implantation or device construction) in the semiconductor industry. Normally the fluoride chemistry (usually dilute hydrofluoric acid) is used as the last process step in the sequence called “RCA rinses”. The substrate is often contaminated from previous process steps with monolayer amounts of metal, anions and/or organic contaminants or surface residues (particles). These contaminants have been shown to have significant impact on the electrical integrity of simple test device structures and they need to be efficiently cleaned without impairing their integrity. Such cleaning methods could include techniques discussed in the technical literature, for example, Int. Conf. On Solid State Devices and Materials, 1991, pp. 484-486 or Kujime, T. et al., Proc. of the 1996 Semi. Pure Water and Chemicals, pp. 245-256 and Singer, P.
Semi. International
, p.88, October 1995.
Patents that teach methods for cleaning prime wafers with low pH solutions include U.S. Pat. No. 5,560,857 and 5,645,737; 5,181,985; 5,603,849; 5,705,089.
Using fluoride chemistries (usually HF) as a final RCA cleaning step will cause the silicon wafer surface to be in a hydrophobic state (the surface is covered with Si—H groups) which will repel water. During this cleaning step a certain proportion of the wafer surface is dissolved (removed). Unless the cleaning conditions are carefully monitored (time, temperature, solution composition) the substrates can be damaged, as reported by Rafols, C. et al.,
J. Electroanalytic Chem
. 433, pp. 77-83, 1997. Numerous compositions combine water and organic solvents. The water concentration in these HF solutions is very critical. Silica oxide has an etch rate of 21 Å/min (@ 25° C.) in HF/water, but in isobutanol the rate was reduced to 2.14 Å/min and even lower in acetone (an aprotic solvent) the rate was only 0.12 Å/min, as reported at NSF/SRC Eng. Res. Center, Environmentally Benign Semiconductor Manufacturing, Aug. 5-7, 1998, Stanford University.
After the Front End of Line (FEOL) cleaning process the wafer proceeds to the typical Back End of Line (BEOL) manufacturing process for a semiconductor devices, in which the devices might be dynamic random access memories (DRAMs), static random access memories (SRAMs), logic, electrically programmable read only memories (EPROMs), complementary metal on silicon (CMOS), and the like. Etching fabrication technology using chemical reactions (liquid or plasma) has been used as a method of forming a wiring structure on such semiconductor substrates.
A photoresist film is deposited on the wafer to form a mask, then a substrate design is imaged on the film layer, baked, and the undeveloped image is removed with a photoresist cleaner. The remaining image is then transferred to the underlying material (either a dielectric or metal) with reactive etching gases promoted with plasma energy. The etchant gases selectively attack the unprotected area of the substrate. Liquid etching chemistries, usually containing fluoride chemistries have been used extensively over the years to etch metals (Al) and dielectrics. The fluoride chemistries can be very aggressive and can result in isotropic etching (etching equally in all directions). Isotropic etching effects cannot be tolerated with today's needs for tight critical dimension control, though there have been attempts to control the isotropic etch through statistical process control techniques, as reported by Taylor, D.,
Solid State Technology
, July 1998, p. 119.
The usual plasma etching process involves anisotropic (unidirectional) etching while at the same time the byproducts (composed of photoresist, etching gasses and etched materials) are deposited on the sidewall of etched openings as residues.
A disadvantage of forming this protective sidewall deposit is that it can be very difficult to remove the residue after the etching procedure. If the components in these residues are not removed or neutralized in some manner then the residues will absorb moisture and form acidic species that can corrode the metal structures. The resultant acid corrodes wiring materials to bring about an adverse effect such as an increase in electrical resistance and wire disconnection. Such problems frequently occur, in particular in aluminum and aluminum alloys generally used as wiring material. The wafer substrate in contact with acidic materials, if not controlled, can destroy the metal structures.
Following completion of the etching operation it is necessary that the resist mask be removed from the protective surface to permit finishing operations. It is desirable to develop an improved cleaning composition to remove the organic polymeric substance from a coated inorganic substrate without corroding, dissolving or dulling the metal circuitry or chemically altering the wafer substrate.
Cleaning compositions used for removing photoresist coatings if not already ashed and other substrates have for the most part been highly flammable, generally hazardous to both humans and the environment, and comprise reactive solvent mixtures exhibiting an undesirable degree of toxicity. Moreover, these cleaning compositions are not only toxic, but their disposal is costly since they might have to be disposed of as a hazardous waste. In addition, these compositions generally have severely limited bath life and, for the most part, are not recyclable or reusable.
Side wall residues have been removed with either acidic organic solvents or alkaline organic solvents. The acidic solvents are generally composed of phenolic compounds or chloro-solvent and/or an aromatic hydrocarbon and/or alkylbenzenesulfonic acids. These formulations generally need to be used at temperatures up to and beyond 100IC. These chemistries normally need to be rinsed with isopropanol.
Dilute hydrofluoric acid solutions can under certain conditions remove the sidewall polymers by aggressively attacking the via sidewall of the dielectric and therefore changing the dimensions of the device, as taught by Ireland, P.,
Thin Solid Films
, 304, pp. 1-12 (1997), and possibly the dielectric constant. Previous chemistries that contain HF, nitric acid, water and hydroxylamine are aggressive enough to etch silicon, as taught by U.S. Pat. No. 3,592,773 issued to A. Muller. Recent information also indicates that the dilute HF solutions can be ineffective for cleaning the newer CF
x
etch residues, as taught by K. Ueno et al., “Cleaning of CHF
3
Plasma-Etched SiO
2
/SiN/Cu Via Structures with Dilute Hydrofluoric Acid Solutions,”
J. Electrochem. Soc
., vol. 144, (7) 1997. Contact holes opened on to the TiSi
2
have also been difficult to clean with HF solutions since there appears to be an attack of the underlying TiSi
2
layer. There may also be difficulty with mass transport of the chemicals in the narrow hydrophilic contact holes, as taught by Baklanov, M. R. et al.,
Proc. Electrochem. Soc
., 1998, 97-35, pp. 602-609.
The photoresist around the contact hole of common interlayer dielectrics, TEOS (tetraethylorthosilicate) and boron phosphosilicate glass (BPSG), which are commonly used in ultra large scale integration (ULSI
Cheng Jun
Maw Taishih
Small Robert J.
EKC Technology, Inc.
Gupta Yogendra
Pennie & Edmonds LLP
Webb Gregory E.
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