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- 

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. 

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). 

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. 

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. 

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. 

"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. 

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. 

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. 

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- 

