Temperature controlled degassification of deionized water...

Details Temperature controlled degassification of deionized water... Temperature controlled degassification of deionized water...

1999-05-25

2001-01-02

Gulakowski, Randy (Department: 1746)

Cleaning and liquid contact with solids

Processes

Including application of electrical radiant or wave energy...

C134S021000, C134S035000

Utility Patent

active

06167891

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a system, including a method and an apparatus arrangement, for temperature controlled degassification of deionized water for megasonic cleaning of semiconductor wafers, and more particularly, to such a system for preparing deionized water containing a substantially 100% saturated concentration of a non-reactive cleaning enhancing gas dissolved therein at a selective elevated cleaning temperature and selective attendant cleaning pressure for cleaning a semiconductor wafer, e.g., of silicon.
As used herein, “non-reactive” cleaning enhancing gas means any gaseous substance capable of being dissolved in deionized water for enhancing the cleaning of, e.g., particle, contaminants from a semiconductor wafer without reacting (i.e., being inert to chemical reaction) with any constituents present in the water or in or on the semiconductor wafer. Also, as used herein, “semiconductor wafer” means any microelectronic device, substrate, chip or the like, e.g., of silicon, used to provide an integrated circuit or other related circuitry structure subject to contaminant particle removal and cleaning chemistry procedures.
BACKGROUND OF THE INVENTION
In fabricating microelectronic semiconductor devices and the like on a wafer substrate or chip, e.g., of silicon, to form an integrated circuit (IC), etc., various metal layers and insulation layers are deposited in selective sequence. To maximize integration of device components in the available substrate area to fit more components in the same area, increased IC miniaturization is utilized. Reduced pitch dimensions are needed for denser packing of components per present day very large scale integration (VLSI), e.g., at sub-micron (below 1 micron, i.e., 1,000 nanometer or 10,000 angstrom) dimensions.
One type of wet chemical process used in the IC fabrication of a semiconductor wafer concerns the cleaning of the wafer to remove contaminant particles from its surface. This may be effected by immersing the wafer in a hot deionized water cleaning bath subjected to rapid agitation such as by applying non-reactive cleaning enhancing (bubble generating) gas, e.g., nitrogen (N
2
), and/or megasonic vibrations thereto.
For overall cleaning of the wafer, e.g., of silicon, a so-called “RCA clean” process has been used wherein the wafer is treated with two cleaning agents in sequence comprising an alkaline, so-called SC1 (standard clean 1), solution, e.g., of hydrogen peroxide (H
2
O
2
) and ammonium hydroxide (NH
4
OH) in deionized water, such as for removing organic and particulate contaminants, in a first step, and then an acidic, so-called SC2 (standard clean 2), solution, e.g., of hydrogen peroxide and hydrogen chloride (HCl) in deionized water, such as for removing metallic impurities, in a second step. Each treatment step is effected, e.g., for about 10-20 minutes at about 75-85° C., and is followed by a rinse step typically using hot deionized water. The wafer is usually dried in a drying step after the final rinse step.
For removing particles in particular, a traditional SC1 mixture of deionized H
2
O/H
2
O
2
/NH
4
OH at a volume ratio of about 5:1:1 has been used to clean the wafer such as at about 65° C. for about 10 minutes. The high concentrations of the SC1 chemicals in the solution and high temperature used cause removal of most particles by etching the wafer surface and the particles to some extent, thus reducing the particle adhesion forces with the wafer and promoting particle movement away from the wafer and into the bulk of the solution. The high pH of the SC1 solution also induces negative charges on the wafer and particles, providing a mutual repulsion tending to keep loosened particles from reattaching to the wafer surface. However, such traditional SC1 cleaning solution is expensive and too aggressive at many critical cleaning steps for use in currently available devices.
Recent introduction of megasonics assisting techniques into wafer cleaning processes has led to better particle removal efficiency with solutions substantially less aggressive and thus less harmful to the surface of the wafer, e.g., of silicon. The megasonic vibration assisting cleaning solutions are usually dilute versions of the traditional SC1 solution, and are used at widely varying temperatures depending on the effect sought. A typical dilute SC1 solution used in this regard is a mixture of deionized H
2
O/H
2
O
2
/NH
4
OH at a volume ratio of about 100:0.9:0.5, wherein 98+% (100/101.4=98.6) is deionized water and only about 1.4% constitutes the active chemicals. Because almost all of the solution is water, the amount of gases dissolved therein will dominate the total gas concentration of the dilute SC1 mixture.
The exact mechanism by which megasonics assisting techniques enhance the particle removal operation is not fully understood at this time. However, as noted below, it is clear that the amount of dissolved gases in the cleaning solution is critical for effective cleaning, i.e., particle removal, to occur.
Some examples of methods of cleaning semiconductor wafers are shown in the following prior art.
U.S. Pat. No. 5,464,480 (Matthews), issued Nov. 7, 1995, discloses removing organic material, e.g., photoresist, from a semiconductor wafer in a tank with sub-ambient or chilled (1-1 5° C.) deionized water in which ozone (O
3
) is diffused, and then rinsing the wafer with deionized water. While ozone has little solubility in deionized water at room temperature or higher temperature, it is stated to be sufficiently soluble therein at sub-ambient temperature to oxidize the organic material to insoluble gases. Megasonic transducers are used to agitate the ozonated deionized water in the tank.
For an RCA clean therein, the wafer is rinsed with deionized water, treated with ozonated deionized water in which ammonia (NH
3
) is diffused to form an SC1 solution, and rinsed again. Next, hot (70° C.) deionized water is used to raise the tank temperature. Then, the wafer is treated with deionized water in which ozone gas and hydrochloric (i.e., hydrogen chloride, HCl) gas are diffused to form an SC2 solution, whereupon the wafer is finally rinsed with deionized water.
U.S. Pat. No. 5,714,203 (Schellenberger et al.), issued Feb. 3, 1998, discloses dipping a silicon wafer in an aqueous cleaning bath containing hydrogen fluoride (HF), which renders the wafer surface hydrophobic, and removing the wafer therefrom while subjecting the bath surface, or alternatively the removed and dried wafer, to a gaseous flow of an oxygen/ozone (O
2
/O
3
) gas mixture alone or in a carrier gas chemically inactive thereto, such as air, i.e., nitrogen, oxygen and carbon dioxide (N
2
, O
2
and CO
2
), or carbon dioxide, helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe) or radon (Rn). When applied to the bath surface, the gaseous flow lowers the liquid surface tension to aid drying of the wafer, and when applied to the dried wafer, the gaseous flow hydrophilizes the wafer surface. The wafer surface is also hydrophilized if the cleaning bath contains ozone.
U.S. Pat. No. 5,569,330 (Schild et al.), issued Oct. 29,1996, discloses chemically treating a semiconductor wafer in sequence in the same container with a liquid bath containing HF which renders the wafer surface hydrophobic, then with a liquid bath containing ozone which renders the wafer surface hydrophilic, while applying megasonic vibrations thereto in both treating steps, and finally drying the wafer. The wafer may also be intermediately dried between the treating steps.
U.S. Pat. No. 5,520,744 (Fujikawa et al.), issued May 28, 1996, discloses treating a silicon wafer in a hermetically sealed chamber in sequence with three constant temperature heated (e.g., 60° C.) chemical baths of deionized water, respectively containing (1) hydrogen peroxide and ammonia, (2) HF, and (3) hydrogen peroxide and HCl, and also with a deionized water rinsing bath after each chemical bath treatment. A vapor of an inactive gas and an organic solvent, e.g., nitrogen and isopropyl alcohol,

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