Cleaning and liquid contact with solids – Processes – For metallic – siliceous – or calcareous basework – including...
Reexamination Certificate
2000-10-16
2003-07-01
Gulakowski, Randy (Department: 1746)
Cleaning and liquid contact with solids
Processes
For metallic, siliceous, or calcareous basework, including...
C134S002000, C134S010000, C134S034000, C252S079100, C252S079500, C252S182280, C252S182280
Reexamination Certificate
active
06585825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to compositions useful in the microelectronics industry for cleaning semiconductor wafer substrates. Particularly, this invention relates to alkaline stripping or cleaning compositions containing bath stabilizing agents that are used for cleaning wafers having metal lines and vias by removing metallic and organic contamination without damaging the integrated circuits.
2. Description of the Prior Art
An integral part of microelectronic fabrication is the use of photoresists to transfer an image from a mask or reticle to the desired circuit layer. After the desired image transfer has been achieved, an etching process is used to form the desired structures. The most common structures formed in this way are metal lines and vias.
The metal lines are used to form electrical connections between various parts of the integrated circuit that lie in the same fabrication layer. The vias are holes that are etched through dielectric layers and later filled with a conductive metal. These are used to make electrical connections between different vertical layers of the integrated circuit. A halogen containing gas is generally used in the processes used for forming metal lines and vias.
After the etching process has been completed, the bulk of the photoresist may be removed by either a chemical stripper solution or by an oxygen plasma ashing process. The problem is that these etching processes produce highly insoluble metal-containing residues that may not be removed by common chemical stripper solutions. Also, during an ashing process the metal-containing residues are oxidized and made even more difficult to remove, particularly in the case of aluminum-based integrated circuits. See, “Managing Etch and Implant Residue,”
Semiconductor International
, August 1997, pages 56-63.
An example of such an etching process is the patterning of metal lines on an integrated circuit. In this process, a photoresist coating is applied over a metal film then imaged through a mask or reticle to selectively expose a pattern in the photoresist coating. The coating is developed to remove either exposed or unexposed photoresist, depending on the tone of the photoresist used, and produce a photoresist on the metal pattern. The remaining photoresist is usually hard-baked at high temperature to remove solvents and optionally to cross-link the polymer matrix. The actual metal etching step is then performed. This etching step removes metal not covered by photoresist through the action of a gaseous plasma. Removal of such metal transfers the pattern from the photoresist layer to the metal layer. The remaining photoresist is then removed (“stripped”) with an organic stripper solution or with an oxygen plasma ashing procedure. The ashing procedure is often followed by a rinsing step that uses a liquid organic stripper solution. However, the stripper solutions currently available, usually alkaline stripper solutions, leave insoluble metal oxides and other metal-containing residues on the integrated circuit.
Another example of such an etching process is the patterning of vias (interconnect holes) on an integrated circuit. In this process, a photoresist coating is applied over a dielectric film then imaged through a mask or reticle to selectively expose a pattern in the photoresist coating. The coating is developed to remove either exposed or unexposed photoresist, depending on the tone of the photoresist used, and produce a photoresist on the metal pattern. The remaining photoresist is usually hard-baked at high temperature to remove solvents and optionally to cross-link the polymer matrix. The actual dielectric etching step is then performned. This etching step removes dielectric not covered by photoresist through the action of a gaseous plasma. Removal of such dielectric transfers the pattern from the photoresist layer to the dielectric layer. The remaining photoresist is then removed (“stripped”) with an organic stripper solution or with an oxygen plasma ashing procedure. Typically, the dielectric is etched to a point where the underlying metal layer is exposed. A titanium or titanium nitride anti-reflective or diffusion barrier layer is typically present at the metal/dielectric boundary. This boundary layer is usually etched through to expose the underlying metal. It has been found that the action of etching through the titanium or titanium nitride layer causes titanium to be incorporated into the etching residues formed inside of the via. Oxygen plasma ashing oxidizes these via residues making them more difficult to remove.
The use of alkaline strippers on microcircuit containing metal films has not always produced quality circuits, particularly when used with metal films containing aluminum or various combinations or alloys of active metals such as aluminum or titanium with more electropositive metals such as copper or tungsten. Various types of metal corrosion, such as corrosion whiskers, pitting, notching of metal lines, have been observed due, at least in part, to reaction of the metals with alkaline strippers. Further it has been shown, by Lee et al., Proc. Interface '89, pp. 137-149, that very little corrosive action takes place until the water rinsing step that is required to remove the organic stripper from the wafer. The corrosion is evidently a result of contacting the metals with the strongly alkaline aqueous solution that is present during rinsing. Aluminum metal is known to corrode rapidly under such conditions, Ambat et al., Corrosion Science, Vol. 33 (5), p. 684. 1992.
Prior methods used to avoid this corrosion problem employed intermediate rinses with non-alkaline organic solvents such as isopropyl alcohol. However, such methods are expensive and have unwanted safety, chemical hygiene, and environmental consequences.
The prior art discloses several organic strippers used to remove bulk photoresist after the etching process. U.S. Pat. Nos. 4,765,844, 5,102,777 and 5,308,745 disclose photoresist strippers comprising various combinations of organic solvents. These strippers, however. are not very effective on wafers that have been “ashed” with oxygen plasmas as described above. Some photoresist strippers attempt to address this problem by adding additional water and an organic corrosion inhibitor such as catechol. Such compositions are disclosed in U.S. Pat. Nos. 5,482,566, 5,279,771, 5,381,807, 5,334,332, 5,709,756, 5,707,947, and 5,419,779 and in WO 9800244. In some cases, the hydrazine derivative, hydroxylamine, is added as well. The use of catechol or hydroxylamine in stripping compositions gives rise to various environmental, safety, and health concerns.
In U.S. Pat. No. 5,817,610 and EP 829,768 the use of a quaternary ammonium silicate, quaternary ammonium hydroxide and water is disclosed for use in removing plasma etch residues. In U.S. Pat. No. 5,759,973 and EP 828,197 the use of a quaternary ammonium silicate, an amine compound, water and optionally an organic polar solvent is disclosed for use as a stripping and cleaning composition. In WO 9960448, many silicate containing compositions are described that effectively remove metal-containing ash residues without causing corrosion.
The use of a quaternary ammonium hydroxide in photoresist strippers is disclosed in U.S. Pat. No. 4,776,892, U.S. Pat. No. 5,563,119; JP 09319098 A2; EP 578507 A2; WO 9117484 A1 and U.S. Pat. No. 4,744,834. The use of chelating and complexing agents to sequester metals in various cleaners has also been reported in WO 9705228, U.S. Pat. No. 5,466,389, U.S. Pat. No. 5,498,293, EP 812011, U.S. Pat. No. 5,561,105, JP 06216098, JP 0641773, JP 06250400 and GB 1,573,206.
U.S. Pat. No. 5,466,389 discloses an aqueous alkaline containing cleaning solution for microelectronics substrates that contains a quaternary ammonium hydroxide and optional metal chelating agents and is useful for a pH range of about 8 to 10. In the present invention, a pH greater than 10 is required to effect the desired residue removal.
U.S. Pat. No. 5,498,293 discloses a proce
Gulakowski Randy
Mallinckrodt Inc
Winter Gentle E.
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