14  US 7,049,044 B2  13  cally contains a sulfonium group, but other photoacid gen› erating compounds, such as iodonium are encompassed by  this invention.  When present in the chemically amplified resist, the  polyhedral oligosilsequioxane component is present from  about 1 % to about 35% by weight in the polymer, typically  from about 10% to about 32% by weight in the polymer.  Additionally, the photoacid generating component is present  from about 2% to about 25% by weight in the polymer,  typically from about 5% to about 20% by weight in the  polymer. Polymers prepared according to this invention are  typically characterized by a weight-average molecular  weights  (Mw)  varying from 20,000 to 100,000 g/mol and a  polydispersity index between 1 and about 2, although those  polymers outside these ranges are encompassed by the  present invention.  In one embodiment of this invention, the CA resist  comprises methyl methacrylate, t-butyl methacrylate, meth› acrylic acid, 3-(3,5, 7,9, 11,13, 15-heptacyclopentylpentacy› clo-[9.5.1.13•9 .1 5 • 15  .l 7•$^{13}$]-octasiloxane-1-yl)propyl  meth- acrylate,  and  [p-CH$_{2}$ -C(CH 3 )C(O)OC$_{6}$H$_{4}$ SMe$_{2}$ ]  OSO$_{2}$CF  3 . In another embodiment, this invention includes a  dissolution promoter, and therefore comprises methyl meth› acrylate, t-butyl methacrylate, methacrylic acid, itaconic  anhydride, 3-(3,5, 7,9, 11, 13, 15-heptacyclopentylpentacyclo› [9 .5. l.13•9 .1 5 • 15  .l 7•$^{13}$]-octasiloxane-1-yl)propyl  methacry› late, and [p-CH$_{2}$-C(CH 3 )C(O)OC$_{6}$H$_{4}$ SMe$_{2}$]---0SO$_{2}$CF 3 .  To evaluate the lithographic properties of the resists, thin  films were cast on silicon wafers to a typical film thickness  of about 0.3 to about 0.5 µm. All resists samples had  excellent film formation behavior. No pinholes were  observed even with a film thickness of below 100 nm. This  observation behavior could be attributed to the absence of  phase separation frequently observed for CA resists contain› ing a high percentage of small-molecule PAGs that are not  incorporated directly into the polymeric resist chains as part  of the polymeric unit.  Table 3 presents the relative weight percents of compo- nents loaded into the mixture to be polymerized, and the  percent composition of that component in the resulting  polymer, for three representative resist samples with various  PAG and POSS content. Table 4 also presents the weight- average molecular weights  (Mw)  and polydispersity indices  (PDI) of each polymer sample.  An illustration or schematic of the micro structure of one  embodiment of this invention, viz. a copolymer containing  methyl methacrylate (MMA), t-butyl methacrylate (TBMA),  the polyhedral oligosilsesquioxane propyl methacrylate  POSS, itaconic anhydride, and the PAG group [p-CH$_{2 }$-C  (CH 3 )C(O)OC$_{6}$H$_{4}$ SMe$_{2}$]OSO$_{2}$CF 3  is presented in FIG.  2.  The resist films of this invention were first exposed on an  EX7 DUY 248 nm Excimer Laser stepper at a wavelength  of 248 nm. Typical processing conditions are presented in  Example 9 and details of the imaging experiments for this  type photoresist are provided in Example 10. High resolu› tion SEM micrographs of patterns obtained for samples at a  dose of 5 mJ/cm 2  were compared for those samples that  incorporated itaconic anhydride and those that did not.  Itaconic anhydride (IA) functions as a dissolution promoter  in TMAH solutions, and samples containing IA developed  properly in either 0.21 or 0.26 N TMAH solutions. In  contrast, samples that contained no IA dissolution promoter  developed equally well in 0.26 N TMAH, most probably due  to high conversion of tert-butyl group into an acid  (-COOH) group.  All resist samples had a wide processing window in terms  of post-exposure-bake (PEB) temperatures under both 248  nm deep UV and electron beam exposures. A series of PEB  temperatures, namely 110, 120, 125 and 130° C. were  applied, while maintaining the other processing parameters  One embodiment of the present invention optionally  incorporates a POSS component with a polymerizable group  for incorporation into the resist polymeric chaim, as illus› trated in Example 7. When present, the polyhedral oli› gosilsequioxane component is typically selected from 3-(3,  5,7,9,11, 13,15-heptacyclopentylpentacyclo[9.5.1.1 3 • 9  .1 5 •  1s.1 7 • $^{13}$]octasiloxane-l-yl)propyl methacrylate; 3-[(3,5,7,9,  11,13,15-heptacyclopentylpentacyclo-[9.5.l .1 3 • 9 .1 5 • 15  .1 7 •  13 ]-octasiloxan-l -y loxy )dimethy lsily l]propy 1 methacry late;  1,3,5, 7,9, 11, 13-heptacyclopentyl-15-vinylpentacyclo- [9 .5.1.1 3 • 9 .1 5 • 15  .1 7 • $^{13}$]octasiloxane, or combinations thereof.  However, other silica cage compounds that contain poly› merizable groups are encompasses by the present invention.  In one embodiment, the chemically amplified resist of the  present invention further comprises a dissolution promoter.  While a range of promoters are envisioned, itaconic anhy› dride (IA) is one preferred dissolution promoter, which  functions effectively in tetramethylammonium hydroxide  solutions.  OH  6  DMSO/HCl  Methanol,< 10°  C.  ci› OH  ¢  Acetone  NaOH  Methanol  CH3-S+-CH3  CF3S03- o-Na+  ¢  CH3-S+-CH3  Methacryloyl chloride  Acctonitrile, RT 