Cleaning compositions for solid surfaces – auxiliary compositions – Cleaning compositions or processes of preparing – For cleaning a specific substrate or removing a specific...
Reexamination Certificate
2000-03-31
2002-04-16
Gupta, Yogendra N. (Department: 1751)
Cleaning compositions for solid surfaces, auxiliary compositions
Cleaning compositions or processes of preparing
For cleaning a specific substrate or removing a specific...
C510S407000, C510S411000, C510S512000, C510S415000, C510S506000, C252S571000, C252S580000, C252S079400, C252S364000, C252S372000, C438S745000
Reexamination Certificate
active
06372700
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to homogeneous non-aqueous compositions containing a fluorinated solvent, ozone, and optionally a co-solvent and the use of these compositions for cleaning and processing semiconductors and integrated circuits including silicon and Ga/As substrates.
BACKGROUND
The use of microelectronic devices, such as integrated circuits, flat panel displays and micro electromechanical systems, has burgeoned in new business and consumer electronic equipment, such as personal computers, cellular phones, and electronic calendars. Such devices have also become an integral part of more established consumer products such as televisions, stereo components and automobiles.
These devices in turn contain one or more very high quality semiconductor chips made from silicon wafers containing many layers of circuit patterns. Typically nearly 350 processing steps are required to convert a bare silicon wafer surface to a semiconductor chip of sufficient complexity and quality to be used, for example, in high performance logic devices found in today's personal computers. The most common processing step of semiconductor chip manufacture is wafer cleaning steps, accounting for over 10% of the total processing steps. These cleaning steps are normally one of two types: oxidative and etch. During oxidative cleaning steps, oxidative compositions are used to oxidize the silicon or polysilicon surface, typically by contacting the wafer with aqueous peroxide or ozone. During etch cleaning steps, etching compositions are used to remove native and deposited silicon oxide films and organic contaminants from the silicon or polysilicon surface before gate oxidation or epitaxial deposition, typically by contacting the wafer with aqueous acid. See, for example, L. A. Zazzera and J. F. Moulder,
J. Electrochem. Soc.,
136, No. 2, 484 (1989). The ultimate performance of the resulting semiconductor chip will depend greatly on how well each cleaning step has been conducted.
Microelectromechanical systems (MEMS) (also called micromachines or micromechanical devices) are small mechanical devices which can be made using traditional integrated circuit manufacturing techniques. Typical devices include motors, gears, accelerometers, pressure sensors, actuators, and mirrors. The manufacture of MEMS results in a chip, or die, which contains the moving pieces of the device made from silicon or polycrystalline silicon (polysilicon) encased in silicon oxide. The die can also contain the circuitry necessary to run the device.
The etch cleaning and drying of MEMS has similar issues to those for semiconductor chip manufacture. Particulate contamination on micromachines can hinder movement of the device and ultimately affect device performance or cause failure. Care is taken to rinse the device with deionized water followed by ethyl alcohol or isopropanol but has similar problems to the IC in that the particles are not easily removed from devices due to the polysilicon surface energy and intricate designs.
In addition to the problem of particulate contamination, drying of MEMS following DI water rinses or alcohol rinses can lead to a phenomenon known as stiction. Stiction can be described as the adhesion of two surfaces due to adhesives forces as well as frictional forces. Polysilicon devices are typically 0.2-4.0 &mgr;m, but can range up to hundreds of &mgr;m, with lateral dimensions anywhere from 1-500 &mgr;m. The high surface area of these structures along with the tight tolerances between structures makes stiction a very troublesome problem. Stiction of microdevices can occur during use of the device, as a result of capillary condensation from exposure to humid air, or as a result of capillary effects during the drying of the device following the release etch process. See, for example, R. Maboudian and R. T. Howe,
J. Vac. Sci. Technol. B,
15(1), 1-20 (1997). The high surface tensions of the aqueous or alcoholic rinses can greatly exacerbate the capillary effects and lead to a higher incidence of microstructure stiction following the release-etch and drying steps.
SUMMARY OF THE INVENTION
In one aspect, this invention relates to a cleaning composition useful in integrated circuit manufacture, the composition comprising a fluorinated solvent and ozone. The liquid cleaning composition may optionally contain a co-solvent to improve specific cleaning operations. Advantageously, the present invention provides substrate cleaning composition useful for oxidation of a substrate, removal of residues, rinsing and drying, but has an efficient rate of surface oxidation. The present composition may also be rendered non-flammable by appropriate selection of the fluorinated solvent. Substrates useful in the present invention include silicon, germanium, GaAs, InP and other III-V and II-VII compound semiconductors. It will be understood, due to the large number of processing steps involved in integrated circuit manufacture, that the substrate may include layers of silicon, polysilicon, metals and oxides thereof, resists, masks and dielectrics.
In yet another aspect, this invention relates to a cleaning process for substrates comprising contacting a substrate with a liquid cleaning composition comprising a fluorinated solvent and ozone; and then separating the cleaning composition from the processed substrate. The cleaning process makes more efficient use of the available ozone than conventional aqueous processes and achieves an oxidative cleaning rate comparable to that of conventional aqueous oxidative compositions. The present invention also improves safety by avoiding potentially hazardous “RCA” solutions that contain strong acids. The process and composition of this invention may also be used in the cleaning and etching of GaAs devices and substrates.
In yet another aspect, this invention relates to a cleaning process for silicon or polysilicon part in MEMS substrates with a homogeneous cleaning composition comprising a fluorinated solvent and ozone. The present invention provides silicon substrate cleaning composition that easily penetrates the intricate microstructures and wets surfaces on MEMS substrates. The cleaning composition is easily removed from MEMS and provides a dry, hydrophilic surface without residual water that would be present from an aqueous cleaning composition. Thus the present invention may avoid a drying step of the prior art, since contact with an aqueous solution is avoided.
In yet another aspect, this invention relates to a cleaning process for silicon or polysilicon part in MEMS chip with a homogeneous cleaning composition comprising a fluorinated solvent and ozone. Advantageously, the present invention provides a cleaning composition useful for oxidizing silicon or polysilicon surface in MEMS. The surface silicon oxide film is rendered hydrophilic thus reducing particle adhesion on the MEMS surfaces. The surface silanol groups present on the silicon oxide films of the treated silicon substrate are also available for reaction with surface modifying agents. The surface silicon oxide film also electrically isolates a silicon or polysilicon part in MEMS.
DETAILED DESCRIPTION
Compositions of this invention, comprising a fluorinated solvent and ozone are useful in the various cleaning steps of substrates required for subsequent operations. As used herein “cleaning” of silicon substrates will refer to any of oxidation of a substrate, removal of residues and/or particulates, rinsing and drying. As used herein “substrate” will refer to wafers or chips used in semiconductor manufacture, microelectromechanical devices, as well as glass surfaces. The compositions can effectively remove both inorganic particles, and organic residues, such as oils and greases, oxidize the silicon wafer surface to produce a hydrophilic silicon surface and additionally convert hydrophobic silicon hydrides to hydrophilic silicon oxides. As a result, many of these cleaning steps (e.g., oxidizing, rinsing and drying) can be combined into a single step.
The cleaning composition and method of this invention c
Behr Frederick E.
Parent Michael J.
Rajtar Paul E.
Zazerra Lawrence A.
3M Innovative Properties Company
Kokko Kent S.
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