US 20020025762 A1
Compounds containing both a sulfur and a nitrogen in a five-membered ring structure are used as biocides in polishing solutions and slurries.
1. An aqueous solution, for use in CMP of semiconductor wafers wherein a fixed abrasive polishing pad is used, which contains essentially no abrasive particles and which is protected from bacterial and fungal activity by means of a biocide comprising an organic compound with a five membered ring containing both a sulfur and a nitrogen group in said ring.
2. An aqueous slurry, for use in CMP of semiconductor wafers, which contains abrasive particles and which is protected from bacterial and fungal activity by means of a biocide comprising an organic compound with a five membered ring containing both a sulfur and a nitrogen group in said ring.
3. The solution of
4. The slurry of
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7. A method of polishing a semiconductor wafer comprising: applying a solution at a polishing interface between a fixed abrasive polishing pad and said wafer, said solution comprising essentially no abrasive particles and which is protected from bacterial and fungal activity by means of a biocide comprising an organic compound with a five membered ring containing both a sulfur and a nitrogen group in said ring.
8. A method of polishing a semiconductor wafer comprising: applying a slurry at a polishing interface between a polishing pad and said wafer, said solution comprising abrasive particles and which is protected from bacterial and fungal activity by means of a biocide comprising an organic compound with a five membered ring containing both a sulfur and a nitrogen group in said ring.
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 This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/182,960 filed Feb. 16, 2000.
 This invention relates to the protection of polishing slurries and silica dispersions from the proliferation of bacteria and/or fungi by means of biocides.
 The problem of bacterial and fungal growth in silica polishing slurries is addressed in U.S. Pat. No. 5,230,833 (Romberger et al.). It includes a thorough summary of the early related art. Bactericides disclosed in '833 are tetramethylammonium chloride, tetraethylammonium chloride, tetrapropylammonium chloride, alkylbenzyldimethylammonium chloride, and alkylbenzyldimethylammonium hydroxide, wherein the alkyl chaim ranges from 1 to about 20 carbon atoms. Also, the preferred biocide is sodium chlorite or sodium hypochlorite. The preferred fungicide is sodium OMADINE® (pyrithone).
 U.S. Pat. No. 3,377,275 discloses a synergistic blend of 3,5-di-methyl tetrahydro 1,3,5,2H-thiadiazine-2-thione in combination with formaldehyde as a microbiocide for aqueous colloidal silica sols.
 It has been found in recent years that the above chemicals are not always compatible with abrasive slurries used for chemical-mechanical polishing (CMP) of semiconductor wafers and with abrasive free slurries used with fixed abrasive polishing pads for semiconductor wafer polishing. It is the object of this invention to provide biocides which are not detrimental to the polishing of semiconductor wafers. Embodiments of the invention will now be described by way of example, with reference to the following detailed description.
 It has been found that a five membered organic ring compound containing both a sulfur and a nitrogen in the ring provide biocide protection of CMP slurries without affecting polishing performance. Examples of such compounds are 5-chloro-2-methyl-4-isothiazolin-3-one and 2-methyl-4-isothiazolin-3-one.
 A class of biocides has been found which do not significantly affect the polishing performance of both particle-free solutions for use with fixed abrasive pads and slurries comprising metal oxide abrasives such as alumina, ceria, zirconia, and silica. These biocides comprise a five-membered organic ring compound containing both a sulfur and a nitrogen in the ring.
 A chemical polishing solution for use with a fixed abrasive pad was made up with the following components: ammonium hydrogen phosphate, iminodiacetic acid, 5-methyl-1H-benzotriazole, surfactant, and hydrogen peroxide. Removal rates were determined using a Strasbaugh 6DS-SP Planarizer and a 3M fixed abrasive matrix MRW64 pad. The process was fixed at 4 psi downforce, 60 rpm platen speed, and 40 rpm carrier speed. Biocide 1 (Kathon CGICP II available from Rohn and Haas Company, Philadelphia, Pa.) and Biocide 2 (Neolone M50 available from Rohm and Haas Company, Philadelphia, Pa.) were added at a concentration of 0.15% by weight to solution batches. The active ingredients in these biocides are 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one. Results of polishing patterned wafers are shown in Table 1.
 These results show little or no effect from adding the biocide to the particle-free solutions. Similar solutions were prepared and evaluated using a challenge test with the intentional additions of bacteria and fungi.
 A polishing slurry comprising as major components iodic acid, lactic acid, potassium hydrogen phthalate, and metal oxide abrasive (a mixture of alumina and titania) was made up as slurry A. To a portion of this slurry was added 0.10% by weight of Kathon® CGICP biocide (active ingredients 2-methyl-4-isothiazolin-3-one and 5-chloro-2-methyl-4-isothiazolin-3-one). This slurry was designated slurry B.
 Wafers comprising tungsten (W), titanium (Ti), and silicon dioxide (Ox) were polished on a standard CMP polishing machine using slurry A and slurry B. Results of the polishing are shown in Table 3.
 A CMP slurry was made up with the following major components: Klebosol 1498-50 (silica sol), citric acid (complexing agent), benzotriazol (corrosion inhibitor), and a surfactant. Addition of a small amount (about 0.1%) of Neolone® (available from Rohm and Haas Company) gave adequate biocide protection to the CMP slurry while the slurry provided slightly improved surface quality when the slurry was used as a second step slurry for polishing semiconductor wafers comprising copper.
 It is obvious from the above results that the addition of a biocide comprised of 2-methyl-4-isothiazolin-3-one and/or 5-chloro-2-methyl-4-isothiazolin-3-one in an amount sufficient to provide antibacterial and antifungal protection to the slurry does not adversely affect the polishing performance of a slurry. It performs particularly well on slurries which comprise Klebosol® silica sol as an ingredient. A sufficient amount of biocide is in the range of 0.01% to 1% by weight of the CMP solution or slurry.