boxylates and/or alkoxides. In another embodiment, L’ is a  dianion selected from the group consisting of oxalate  (C$_{2}$O$_{4 }$- 2 ), lactate, (C $_{3}$H$_{4}$O$_{3 }$ - 2 ), glycolate (C $_{2}$H$_{2}$O$_{3 }$ - 2 ), and  combinations thereof. In another embodiment, C’ is ammo› nium (NH$_{4}$ +).  Non-limiting examples of peroxo complexes of formula  (2) and/or formula (3) include [NH$_{4}$ ] $_{3}$[Ta(O$_{2}$MC$_{2}$O$_{4}$ )] and  [Ti(O$_{2}$)iC$_{2}$O$_{4}$)]. The peroxo complexes can be used in com› bination. The charges on the different ligands and counterion  are not shown.  The schematic layer diagrams of FIGS.  lA to lE  illustrate  a method of forming a lithographically patterned layered  structure utilizing a photoresist composition comprising at  least a peroxo complex and a solvent. The photoresist com› position is disposed on surface  12  of substrate  10  (FIG.  lA)  followed by removal of the solvent to form photoresist layer  22  of structure  20  (FIG.  1B).  Photoresist layer  22  can be  treated with an optional post-application bake (PAB) and/or  an optional solvent rinse under suitable conditions of time and  temperature before exposure. Pattern-wise exposure of pho› toresist layer  22  is performed preferably using EUV and/or  e-beam, resulting in exposed photoresist layer  32  of structure  30  (FIG.  lC).  Photoresist layer  32  is composed ofregions of  exposed photoresist  34  and regions of non-exposed photore› sist  36.  Photoresist layer  32  can be treated with an optional  post-exposure bake (PEB) and/or an optional solvent rinse  under suitable conditions of time and temperature before  development. The exposed photoresist  34  has less solubility  in a developer compared to non-exposed photoresist  36.  Con› sequently, aqueous development affords a negative-tone  image by removing regions of non-exposed photoresist  36.  The PAB, PEB and/or solvent rinse(s) can enhance solubility  differences of the exposed and non-exposed photoresist in a  given developer. Development in a developer produces lay› ered structure  40  comprising patterned photoresist layer  42  (FIG.  lD).  Patterned photoresist layer  42  is a topographical  relief pattern comprising photoresist features  44  composed of  exposed photoresist  34.  Photoresist features  44  are disposed  on surface  46  of substrate  10  and have top surface  48  and  sidewall  50.  Substrate surface  52  is in contact with air. The  topographical relief pattern of patterned photoresist layer  42  can be transferred to substrate  10  by known methods (e.g.,  oxygen ion etching) followed by removal of photoresist fea› tures  44,  resulting in structure  60  (FIG.  lE).  Structure  60  comprises a transferred topographical pattern  62  within sub› strate  10,  whose features  66  comprise bottom surface  64,  sidewall surface  68,  and top surface  70  of substrate  10.  The photoresist layer can be rinsed before or after the  exposure, the PAB, and/or the PEB with a solvent ( e.g., water,  aqueous solutions, including water/alcohol mixtures, and  organic solvents) to remove excess ligand or to promote par› tial condensation. Typically, the rinse is performed after the  PAB. Rinses can be performed at or near room temperature  ( e.g., 10°  C. to 50°  C.) for a period of 1 second to 1 hour.  Optionally, the pre-developed photoresist layer and/or  post-developed photoresist layer can be treated with water  vapor and/or alcohol vapor either at room temperature or at  elevated temperature on a time scale of 1 minute to 5 hours.  Such a treatment after exposure and PEB can be conducted,  for example, to promote additional crosslinking or to modify  the functional group distribution of the metal oxide matrix.  The term "substrate" refers to all underlying layers of a  structure on which the photoresist layer is disposed. The  substrate can have one or more layers arranged in a stack. In  a multi-layered substrate, the layer directly below and in  contact with the photoresist layer is the top-most layer of the  substrate, also referred to as "the underlayer" to the photore- Without being bound by theory, the photoresist composi› tions herein are believed to operate by a crosslinking and/or a  polarity switching mechanism as a result of chemical changes  in the film cast from the peroxo complex induced by the  exposure. The optional baking (PAB and/or PEB) treatments  and/or optional rinsing treatments can enhance the solubility  difference of the exposed photoresist compared to the non› exposed photoresist. Decreased solubility of the exposed  photoresist can result from a morphological change in struc› ture (e.g., a crystalline to amorphous phase transition of the  peroxo complex, or vice versa) and/or a change in the chemi- When referring to the chemical components, reactivity,  solubility and/or surface properties of the photoresist layer, it  is understood that such reference is directed only to the pho- toresist layer and not to the substrate or the substrate surface,  unless otherwise stated. Likewise, when referring to the  chemical components, chemical reactivity, solubility and/or  surface properties of the substrate surface or substrate layers,  such reference is directed only to the substrate surface or  substrate layer(s) and not to the photoresist layer, unless  otherwise stated.  It is understood that in some cases ( e.g., when forming  dense, high resolution patterns) all of the photoresist layer can  receive some dose of radiation exposure. "Non-exposed pho› toresist" refers to photoresist that has received insufficient  dose to switch the solubility of the photoresist in a given  developer compared to the pre-exposed photoresist, includ› ing pre-exposed photoresist that has been treated with an  optional bake and/or optional rinse. "Exposed photoresist"  has received sufficient exposure to switch the solubility of the  photoresist in a given developer compared to the pre-exposed  photoresist.  "Negative-tone development" means the non-exposed  areas of the photoresist layer are removed during develop› ment. "Positive-tone development" means the exposed areas  of the photoresist layer are removed during development.  A "negative-working" photoresist becomes less soluble in  a given developer when exposed to a radiation, typically due  to a crosslinking reaction or some other chemical change  induced by the exposure, which lowers the solubility of the  photoresist in the developer. The photoresist compositions  herein are negative-working.  Herein, a "positive-working" photoresist is a photoresist  that becomes more soluble in a given developer when  exposed to a radiation, typically by a non-crosslinking chemi- cal reaction induced by the exposure.  The term "casting" refers to forming a layer of a material  by disposing a solution of the material dissolved in a solvent  on a surface of another layer, and removing the solvent.  The term "disposed" refers to a layer in contact with a  surface of another layer. "Disposing" and "applying" refer to  forming a layer to be in contact with a surface of another layer,  without limitation as to the method employed unless other› wise stated, providing the desirable properties of the disposed  or applied layer are not adversely affected (e.g., uniformity  and thickness).  sist layer. The terms "surface" or "underlying surface" refer,  unless otherwise stated, to the substrate surface on which the  photoresist layer is disposed. As non-limiting examples, the  photoresist layer can be disposed on the surface of a silicon  wafer or a metal foil, or more particularly on the surface of an  anti-reflection layer (ARC) of a multi-layer substrate, where  the ARC layer is the top-most layer. In this example, the ARC  layer is also the underlay er of the photoresist layer. In another  example, the ARC layer has a polymer brush layer attached to  the top surface. In this example, the polymer brush layer is  also the underlayer of the photoresist layer.  8  7  US 8,703,386  B2 