19  US 2002/0111024 Al  Aug. 15,2002  [0213]  Ammonium Persulfate with Malonamide  [0214]  Ammonium persulfate combined with malonamide  (H$_{2}$NCOCH$_{2}$ CONH$_{2}$ )  shows W removal rates comparable  with those of Ammonium persulfate+malonic acid using the  Logitech PMS polisher (33 rpm, 12 inch IC 1000 pad, 2 psi)  on 3 inch wafers (10,000 A sputtered  W),  with 5% alumina  slurry (50 parts of 10% alumina +90% water slurry), chem› istry flow rate of 90 ml/min, and slurry flow rate of 20  ml/min, as shown below.  [0215]  Malonamide enhances the  W  removal rate when  combined with Ammonium persulfate in an aqueous system  over the  W  removal rate of Ammonium persulfate alone.  Removal rates increase with pH, and is particularly fast  between pH 7.9 and pH 9.  [0216]  As  with previous examples, the slurry pH may be  adjusted to any suitable value in order to give the desired  polishing performance. For example, the slurry  pH  may be  adjusted to a value of between about 1 to 10, and more  preferably to between about 6 to 9.  [0217]  Experiments with blanket  W  metal (10,000 A)  wafer showed that a 10 wt% ammonium persulfate solution  with a 5% alumina slurry removed 162  Nmm  of the metal  (pH  8), yet a 10 wt % ammonium persulfate mixed with a  2%  K.10$_{4 }$ with only a 5 wt% alumina slurry at a  pH  of 6.9  removed 637  Nmm.  When a 2 wt % potassium iodate  (K.1O$_{3}$ )  was substituted into the ammonium persulfate solu› tion, the polishing rate decreased to 246  Nmm.  Polishing  was done with a Logitech SM polisher with a Politex felt  cloth at 33 rpm and 2 psi pressure on the 3 inch wafer.  [0218]  The concentration of the ammonium persulfate  solution is preferably between about 2 to 20% by weight,  more preferably between about 5 to 15%, and most prefer› ably about 10 wt%. This relationship seems to hold for cases  where additional oxidizers are added also. The alumina  slurry is preferably between about 2 to 20% solids, more  preferably between about 2 to 10%, and most preferably  about 5%.  [0219]  Ammonium Persulfate with Periodic Acid  [0220]  In another aspect of the invention, a similar chem› istry to that of the previous aspect uses a synergism between  ammonium persulfate (Ammonium persulfate) and periodic  acid (rather than potassium periodate) for polishing tung› sten. There is a synergistic effect that enhances W removal  rate when Ammonium persulfate and periodic acid are used  together. The tungsten process appears to operate via the  tungstate (WO4-) anion.  [0221]  Periodic acid in water added to Ammonium per› sulfate increases the removal rate of W over Ammonium  persulfate alone at a pH of 1; increasing the amount of  [0222]  Periodic acid clearly improves the polishing rate of  Ammonium persulfate formulations when used on a tung› sten substrate. The Ammonium persulfate concentration is  preferably between about 2 to 20%, more preferably  between about 5 to 15%, and most preferably about 10%.  The concentration of the periodic acid solution is preferably  between about 0 to 10% by weight, more preferably between  about 0.2 to 5%, and most preferably about 2 wt %.  [0223]  The periodic acid can also be the primary oxidizer.  However, a 10% periodic acid and 2% Ammonium persul› fate formulation at the high  pH  of 8.2, added at 20 ml per  minute with 5%  LOGITECH  abrasive added at 20%, using  an  POLITEX  pad at 2 psi and 33 rpm on a 3"  IWS  substrate  the disappointing polishing rate of 56 Angstroms per minute.  A  similar test with 10% Ammonium persulfate and 3%  periodic acid at  pH  1.3 gave the surprisingly high etch rate  of 174 Angstroms per minute.  [0224]  Ammonium Persulfate with Lithium Periodate  [0225]  Ammonium persulfate can also be admixed with  lithium periodate. Lithium periodate in water added to  Ammonium persulfate increases the removal rate of  W  over  Ammonium persulfate alone. In tests using the Logitech  PMS polisher (33 rpm, 12 inch IClO00 pad, 2 psi), 3 inch  wafers (10,000 A sputtered  W),  5%  MOYCO  alumina (10  parts of 10% alumina+90% water slurry), and chemistry/  slurry addition rate of 100 ml/min, the lithium periodate  provided modest increases in the etching rate as shown  below.  periodic acid used with 10 parts Ammonium persulfate also  increases the W removal rate using the Logitech PMS  polisher (33 rpm, 12 inch IClO00 pad, 2 psi), 3 inch wafers  (10,000 A sputtered  W),  0-3 parts  NH$_{4}$0H  to adjust  pH,  1 %  alumina (10 parts of 10% alumina+90% water slurry), and  chemistry/slurry addition rate of 100 ml/min, as shown  below.  CMP with Ammonium persulfate - Malonamide Slurries  Ammonium  persulfate (wt.  %)  Malonamide (wt. %) pH  Removal Rate (A/mm)  10  0  8.0  162  10  2.0  7.9  210  10  1.0  9.0  429  10  2.5  8.9  385  10  2.0  7.9  250  10  0  7.9  198  CMP with Ammonium persulfate/Periodic acid Slurries  Ammonium  persulfate (wt.  %)  Periodic Acid (wt. %)  pH Removal Rate (A/mm)  0  2.0  1.5  130  10  2.0  1.1  386  10  0.5  3.5  118  10  2.0  5.2  388  10  0  6  112  CMP with Ammonium persulfate/Lithium Periodate Slurries  Ammonium  Removal Rate  persulfate (wt.  % )  Lithium Periodate (wt.  % )  pH  (A/mm)  0  0.4  7.4  38  8  0.3  6.4  112  10  0.3  2.7  202  10  0.4  5  196  10  0.4  5.5  298  10  0.4  8.5  473  10  0.1  7  177  10  0.3  7.5  237  10  0.3  7.7  301 