CN110660651A - Method of forming a semiconductor structure - Google Patents

Abstract

The method includes forming an underlayer on a semiconductor substrate, where the underlayer includes a polymer bonded to a first crosslinker and a second crosslinker, the first crosslinker configured to be ultraviolet activated and the second crosslinker configured to be thermally activated at a first temperature. The method then exposes the bottom layer to an ultraviolet source to activate the first crosslinker, thereby forming an exposed bottom layer. The method further includes baking the exposed underlayer, wherein the baking step activates the second crosslinker.

Description

Method of forming a semiconductor structure

technical field

Embodiments of the present invention generally relate to methods of forming integrated circuit devices, and more particularly, to methods and materials for forming photoresist bottom layers.

Background technique

The semiconductor integrated circuit industry has experienced rapid growth. Technological advances in body circuit materials and design have enabled each generation of integrated circuits to have smaller and more complex circuits than the previous generation. These advances, however, increase the complexity of processing and forming integrated circuits. To achieve these advances, methods of processing and forming integrated circuits need to evolve similarly. In the evolution of integrated circuits, functional density (the number of interconnected devices per chip area) typically increases as the geometry (the smallest component that can be produced by the manufacturing process employed) shrinks. As the size of photolithographic structures shrinks, a higher number of aperture processes are required to overcome resolution limitations.

The photolithographic three-layer structure has a photosensitive top layer formed on at least one bottom layer, which is used to solve some problems related to the photolithographic patterning process. Although the formation method of the three-layer structure is applicable to general applications, it is still not fully applicable to all aspects. For example, a light source that does not fully cure the bottom layer may result in inconsistent etch rates when transferring the final pattern of the bottom layer to the underlying substrate. Therefore, there is still a need to improve this aspect.

SUMMARY OF THE INVENTION

An embodiment of the present invention provides a method for forming a semiconductor structure, comprising: forming a bottom layer on a semiconductor substrate, wherein the bottom layer includes a polymer bonded to a first cross-linking agent and a second cross-linking agent, wherein the first cross-linking agent is provided thermal activation for ultraviolet activation, wherein the second crosslinking agent is set to a first temperature; exposing the base layer to a source of ultraviolet light to form an exposed base layer, wherein the step of exposing the base layer to ultraviolet light activates the first crosslinking agent; and baking The exposed bottom layer is baked to activate the second crosslinker.

An embodiment of the present invention provides a method comprising: spin-coating a material layer on a semiconductor substrate, wherein the material layer includes a polymer linked to at least one ultraviolet cross-linking agent and at least one thermal cross-linking agent, and wherein the material in the material layer The amount of ultraviolet crosslinking is greater than the amount of thermal crosslinking in the material layer; exposing the material layer to a first ultraviolet source having a first wavelength to form an exposed material layer, wherein the step of exposing the material layer to the first ultraviolet source induces ultraviolet crosslinking crosslinking of the linking agent; thermally curing the exposed material layer to form a cured material layer, wherein the step of thermally curing induces crosslinking of the thermal crosslinking agent; and forming a photoresist layer on the cured material layer.

An embodiment of the present invention provides a method, comprising: forming an underlayer on a semiconductor substrate, and the underlayer includes a polymer, a first crosslinking agent configured to crosslink when exposed to ultraviolet rays, and a heat source configured to be exposed to a first temperature a cross-linked second cross-linking agent, wherein the first cross-linking agent and the second cross-linking agent are bonded to the polymer; exposing the base layer to a first heat source at a second temperature, and the second temperature is lower than the first temperature; in After exposing the base layer to the first heat source, exposing the base layer to ultraviolet light and inducing crosslinking of the first crosslinking agent to form an exposed base layer; exposing the base layer to a second heat source at a third temperature to form a cured base layer, wherein The third temperature is higher than the first temperature; an intermediate layer is formed on the cured bottom layer; and a photoresist layer is formed on the intermediate layer.

Description of drawings

1A and 1B are flowcharts of a method of fabricating a semiconductor device according to various embodiments of the present invention.

2, 3, 4, 5, 9, 10, 11, 12, 13, 14A, and 14B are cross-sectional views of semiconductor devices at various steps of the method of FIGS. 1A and 1B in accordance with various embodiments of the present invention.

Figures 6, 7, and 8 are chemical structures in various embodiments of the present invention.

Description of reference numerals

100 ways

102, 104, 106, 108, 110, 112, 114, 116, 118, 120 steps

200 workpieces

202 substrate

204, 204A, 204B, 204C Bottom

206 Intermediate layer

208 photoresist layer

212 Exposure area

214 Unexposed area

216 Rays

218 Patterns

220 Photomask

222 Developer

230, 234 Baking process

232 UV exposure process

300 polymers

304, 306, 308 Crosslinker

320 polymer backbone

330 Polymer Network.

Detailed ways

It will be appreciated that the following description provides different embodiments or examples that may implement different structures of the invention. The following examples of specific components and arrangements are presented to simplify the present disclosure and not to limit the present disclosure. For example, the description of forming the first member on the second member includes an embodiment in which the two are in direct contact, or an embodiment in which other additional members are spaced between them without direct contact. In addition, the structures of the embodiments of the present invention may be formed on, connected to, and/or coupled to another structure, the structures may directly contact another structure, or additional structures may be formed within the structure and the other structure Between structures (ie, structures do not touch another structure). In addition, the same reference numerals may be used repeatedly in various examples of the present invention for brevity, but components with the same reference numerals in the various embodiments and/or arrangements do not necessarily have the same corresponding relationship.

In addition, the structures of the embodiments of the present invention may be formed on, connected to, and/or coupled to another structure, the structures may directly contact another structure, or additional structures may be formed within the structure and the other structure between structures. In addition, spatially relative terms such as "below," "below," "lower," "above," "above," or similar terms may be used to simplify the description of one component relative to another in the icon relation. Spatial relative terminology can be extended to components used in other orientations and is not limited to the illustrated orientation. Further, when a value or a range of values is described with "about," "approximately," or similar terms, it includes +/- 10% of the stated value unless specifically stated otherwise. For example, the term "about 5 nm" includes a size range between 4.5 nm and 5.5 nm.

Embodiments of the present invention generally relate to methods of forming integrated circuit devices, and more particularly, to methods and materials for forming photoresist bottom layers. Many photoresists used to pattern semiconductor substrates are multilayer structures that include at least a bottom layer (eg, a bottom antireflective coating) on the substrate, and a top layer (eg, a photosensitive top layer) on the bottom layer. The photoresist may optionally further include layers of other materials, such as at least one intermediate layer (eg, a hard mask layer) between the bottom layer and the top layer. The use of multilayer photoresists in photolithographic processes has proven advantages, such as minimizing substrate reflection from radiation sources (eg, light) and improving etch selectivity among various underlying layers. However, many aspects of multilayer photoresists still need to be improved for advanced patterning processes. For example, it has been discovered that UV crosslinking of polymeric materials to form a primer layer may result in inconsistent curing (eg, crosslinking) upon UV exposure. The effect of non-uniform curing is particularly prevalent when semiconductor substrates contain structures (eg, conductive structures, spacers, cores, or the like) that have spaces smaller than the wavelength of ultraviolet light. As a result, after the patterned and photoresist top layer is formed and the pattern is transferred to the bottom layer, the uncured portion of the bottom layer may not be properly etched, resulting in a loss of pattern quality. As described in the following examples, combining a UV-activated crosslinker with a heat-activated crosslinker in the primer layer can improve the cure of the primer layer after exposing the primer layer to UV light and heat that activate the individual crosslinkers.

1A and 1B are flowcharts of a method 100 for processing a workpiece 200 in some embodiments of the present invention. The method 100 is only used to illustrate and not to limit the present invention to what is not actually recited in the claims. Additional steps may be provided before, during, and after method 100, and additional embodiments of the process may replace, omit, or exchange some of the steps. The intermediate steps of the method 100 will be described in conjunction with the cross-sectional views of the workpiece 200 shown in FIGS. 2-5 and 9-14B , while the chemical structures and reactions are shown in FIGS. 6-8 . To simplify the description, some elements in the drawings may be simplified.

As shown in FIGS. 1A and 2 , step 102 of method 100 provides a substrate 202 . Substrate 202 may comprise semiconductor elements (single elements) such as crystalline structure silicon and/or crystalline structure germanium; semiconductor compounds such as silicon carbide, gallium arsenide, gallium phosphide, indium phosphide, indium arsenide, and/or antimonide Indium; semiconductor alloys such as silicon germanium, gallium arsenide phosphide, aluminum indium arsenide, aluminum gallium arsenide, indium gallium arsenide, indium gallium phosphide, and/or indium gallium arsenide phosphide; non-semiconductor materials such as soda lime glass, Fused silica, fused silica, and/or calcium fluoride; and/or combinations of the foregoing.

Substrate 202 may be a single layer of material having a consistent composition. In other embodiments, the substrate 202 may include multiple layers of materials having similar or different compositions, which are suitable for forming integrated circuit devices. In one example, the substrate 202 may be a silicon-on-insulator substrate having a semiconductor silicon layer formed on a silicon oxide layer. In another example, the substrate 202 may include conductive layers, semiconductor layers, dielectric layers, other layers, and/or combinations thereof. In some embodiments, the substrate 202 may be a silicon wafer having a substantially flat surface. In some embodiments, the substrate 202 may include structures such as spacers or cores, which may be patterned and removed in subsequent steps to include additional process steps.

The substrate 202 may include various circuit structures formed thereon or in it, such as field effect transistors, metal oxide semiconductor field effect transistors, complementary metal oxide semiconductor transistors, high voltage transistors, high frequency transistors, bipolar junction transistors , diodes, resistors, capacitors, inductors, varactor diodes, other suitable devices, and/or combinations of the foregoing. In some examples, the substrate 202 may include multiple three-dimensional active regions or fins, multiple gate structures, and/or multiple spacers or cores.

In some embodiments where the substrate 202 includes field effect transistors, various doped regions such as source/drain regions may be formed in or on the substrate 202 . The doped regions can be doped with n-type dopants such as phosphorus or arsenic, and/or p-type dopants such as boron or boron difluoride, depending on design requirements. The doped regions can be planar or non-planar (such as in FinFETs), and can be formed directly on the substrate 202, in p-well structures, in n-well structures, in dual wells In the structure, or using a raised structure. The doped regions may be formed by implanting dopant atoms, in-situ doped epitaxial growth, and/or other suitable techniques.

As shown in FIGS. 1A and 2 , step 104 of method 100 forms a bottom layer 204 (or first layer) on substrate 202 . In many embodiments, the bottom layer 204 is a bottom antireflective coating material that is composed to minimize reflections from the radiation source when exposing a subsequently formed photoresist layer (such as photoresist layer 208 in FIG. 4). As shown in FIG. 6, the bottom layer 204 comprises a polymer 300 having a polymer backbone 320 bonded to a plurality of cross-linking components (hereinafter referred to as cross-linking agents 304, 306, and/or 308). Cross-linking agents 304, 306, and/or 308 are activatable in response to one or more external stimuli to cross-link with adjacent cross-linking agents. In many embodiments, polymer 300 includes cross-linking agent 304 bonded to polymer backbone 320 and includes one or both of cross-linking agents 306 and 308 .

In particular, the polymer backbone 320 may comprise an acrylate-based polymer, a copolymer of norbornene and maleic anhydride, a polyhydroxystyrene-based polymer, other suitable polymers, or the foregoing In combination, it has any number of functional groups to facilitate one or more subsequent exposure and development processes. In one example, the functional group may comprise a lithographically sensitive group (sensitizer) such as phenol, styrene, fluoride, and/or other suitable groups. In many embodiments, the functional substrate contains acid-sensitive groups that are configured to be cleaved from the polymer backbone by acidic components.

The cross-linking agent 304 is a UV-activated cross-linking agent configured to be activated by a UV source. In other words, the cross-linking agent can be cross-linked with another cross-linking agent when irradiated with an ultraviolet source with a wavelength between about 160 nm and about 300 nm, and the above-mentioned ultraviolet light is set to initiate the cross-linking reaction of the cross-linking agent 304 . It will be appreciated that these wavelength ranges are not so limited and depend on the chemical composition of the crosslinking agent 304, and that other wavelengths of ultraviolet light sources may be employed. In some embodiments, once the cross-linking agent 304 is exposed to ultraviolet light, it can be cross-linked with another cross-linking agent that is similar. In other embodiments, once the cross-linking agent 304 is irradiated with ultraviolet light, it can be cross-linked with a different cross-linking agent.

The cross-linking agent 304 may comprise the following structure: H ₂ C=CH-R-, where R refers to the portion of the cross-linking agent bonded to the polymer backbone 320 . In many embodiments, R is a [pi] bond-containing functional group configured to be conjugated to _H2C =CH-. Non-limiting examples of R include -(C=O)-, -(C=O)-O-, -CH=CH-, phenyl, phenol, other suitable functional groups, or combinations thereof. In many embodiments, the wavelength of the ultraviolet source can activate the crosslinking agent 304, depending on the chemical composition of R in the crosslinking agent 304. As such, the choice of chemical composition of the crosslinking agent 304 depends on the available stable UV wavelengths. Conversely, the selection of the UV source depends on the chemical composition of R in the one or more crosslinkers 304 bound to the polymer backbone 320 . Once irradiated with UV light, the _H2C =CH- moiety of the crosslinker 304 forms -H2C- _CH- via an addition reaction with another similar or different crosslinker bonded to a different polymer backbone 320 (eg carbon-carbon covalent bonds) to form a carbon-based network of polymer backbone 320 linked by cross-linking agent 304.

Cross-linking agent 306 is different from cross-linking agent 304 and is a thermally activated cross-linking agent (configured as a cross-linking agent activated by a heat source). In other words, the crosslinking agent 306 can crosslink with another crosslinking agent when exposed to a heat source. The crosslinking agent 306 is configured to activate upon reaching a critical temperature, depending on its specific chemical composition. If the temperature is below the critical temperature, the thermal energy applied to the crosslinking agent 306 is not sufficient to initiate the breaking and formation of chemical bonds. The cross-linking agent 306 can be cross-linked with another cross-linking agent of similar chemical composition. In other embodiments, the crosslinking agent 306 can be crosslinked with another crosslinking agent of a different chemical composition. The crosslinker 306 may comprise any suitable functional group such as phenyl, alkyl substituted phenyl, epoxy, hydroxyl, ether, ester, phenolic, other suitable functional groups, or a combination of the foregoing. In some examples, the critical temperature of the cross-linking agent 306 may be between about 150° C. and about 250° C., depending on the specific chemical properties of the cross-linking agent 306 . Embodiments of the present invention may also implement other critical temperatures, depending on the specific chemical properties of the crosslinking agent 306 .

Crosslinking agent 308 is a UV-thermal hybrid crosslinking agent configured to be activated by a UV source, a heat source, or both a UV source and a heat source. In other words, the cross-linking agent 308 can cross-link with another cross-linking agent when irradiated with an ultraviolet source, and/or can cross-link with another cross-linking agent when the temperature is raised above the critical temperature of the cross-linking agent 308 . Thus, in such embodiments, the cross-linking agent 308 may be cross-linked with another cross-linking agent 308 , cross-linking agent 304 , or cross-linking agent 306 . For example, the cross-linking agent 308 is configured to bond with the cross-linking agent 304 (eg, a UV-activated cross-linking agent) during the UV exposure process. In other embodiments, the crosslinking agent 306 may be configured to bond with the crosslinking agent 306 (eg, a thermally activated crosslinking agent).

The crosslinking agent 308 may have the following structure:

wherein R may include -(C=O)-, -(C=O)-O-, -CH=CH-, phenyl, phenolic, other suitable functional groups, or a combination of the foregoing as previously described. X is set to the part that will be thermally activated. X can be an alkyl chain (eg ( _-CH2- ) _n , where n is between 2 and 6, other alkyl structures, or a combination of the above), an aromatic ring (eg, benzene, phenol, aniline, toluene, toluene, other aromatic structures, or a combination of the above), a heteroaromatic ring (eg, furan, thiophene, pyridine, indole, other heteroaromatic rings, or a combination of the above), other suitable functional groups, or a combination of the above. The crosslinker 308 can be activated by a UV source, and the wavelength (or range of wavelengths) of the UV light can initiate a chemical reaction in the _H2C =CH-R- portion of the crosslinker 308 (similar to the crosslinker 304). In additional or other embodiments, the cross-linking agent 308 may be activated by a heat source that is raised above the critical temperature of the cross-linking agent 308 to initiate a chemical reaction in the X portion of the cross-linking agent 308 .

Once the crosslinker 306 is thermally activated, it will form covalent bonds (eg, crosslinks) with another crosslinker, similar or different, bonded to a different polymer backbone 320, and may create one or more reaction by-products. Since these by-products (eg, evaporation by-products) can be eliminated from the bottom layer 204 once the cross-linking reaction is complete, the bottom layer 204 may shrink. For example, by-products include small molecular species such as methanol, ethanol, water, or the like, which evaporate during condensation-based cross-linking reactions, inducing shrinkage of the bottom layer 204. However, UV-activated cross-linking reactions, such as those associated with cross-linking agent 304, produce little or no by-products (very few as compared to cross-linking agent 306 reactions). Instead, it forms a carbon-carbon (eg, carbon single bond) network, which shrinks only slightly or not when the crosslinking reaction is completed. In summary, to avoid film collapse and/or lack of film thickness consistency, polymer 300 includes cross-linking agent 304 and/or 308 in an amount greater than cross-linking agent 306 . In one example, the amount of cross-linking agent 306 included in the bottom layer 204 may be between about 25% and about 67% of the amount of cross-linking agent 304 and/or cross-linking agent 308 . If the amount of cross-linking agent 306 is greater than about 67%, the film of bottom layer 204 may collapse. If the amount of crosslinking agent 306 is less than about 25%, the polymer 300 lacks UV exposure to fully cure its bottom.

As shown in FIGS. 1A and 2 , the bottom layer 204 may be formed by spin-coating the polymer 300 on the upper surface of the substrate 202 (or on the upper surface of the topmost material layer of the multilayer substrate 202 ). The spin coating process can use centrifugal force to disperse the polymer 300 in the liquid phase to a uniform thickness over the entire upper surface of the substrate 202 . The polymer 300 is soluble in a solvent in order to implement and apply the polymer 300. After removal of the solvent, a solid or semi-solid base layer 204 (eg, film) can be formed. The solvent can be one or more of the following: propylene glycol methyl ether acetate, propylene glycol monomethyl ether, gamma-butyrolactone, ethyl lactate, cyclohexanone, ethyl ketone, dimethylformamide, alcohols (such as iso propanol or ethanol), other suitable solvents, or a combination of the above. The solvent may be removed during part of the spin coating process, during the settling process, and/or during the subsequent bake process.

As shown in FIGS. 1A and 3 , step 106 of method 100 performs a bake process 230 on workpiece 200 to form baked bottom layer 204A. The temperature of the bake process 230 is below the critical temperature of the cross-linking agent 306 and/or the cross-linking agent 308, so that the cross-linking agent is not activated to form chemical bonds with adjacent cross-linking agents (or destroy adjacent cross-linking agents) chemical bonds of the agent). Conversely, the bake process 230 may be configured to reduce the stress and/or strain introduced during the spin coating process to facilitate thermal reflow to achieve planarity of the bottom layer 204 (eg, a smooth upper surface) and/or to facilitate The underlying layer 204 on the structure of the substrate 202 is filled (eg, interstitial). In one example, the temperature of the baking process 230 is between about 50°C and about 200°C. Other temperatures may also be used to implement the bake process 230 . For example, any temperature below about 50° C. may not provide sufficient thermal energy to polymer 300 to generate thermal reflow on the upper surface of bottom layer 204 . In some embodiments, the bake process 230 may be omitted, and the method 100 may perform the UV exposure process as described below.

As shown in FIGS. 1A , 4 , and 7 , step 108 of method 100 performs a UV exposure process 232 on workpiece 200 to form exposed bottom layer 204B, which includes polymer network 330 . As shown in FIG. 7, once the UV exposure process 232 is performed, the crosslinkers 304 and 308 bound to one polymer backbone 320 (eg, their UV activated moieties) will interact with the crosslinkers 304 and 308 bound to a different polymer backbone 320. /or 308 cross-linking (eg forming covalent bonds). In other words, the crosslinking agents 304 and/or 308 crosslink the two polymer backbones 320 to form the polymer network 330 . In the embodiments of the present invention, covalent bonds are represented by dashed lines to distinguish them from chemical bonds between each crosslinking agent and its polymer backbone. In many embodiments, the cross-linking agent 304 may be cross-linked with another cross-linking agent 304, or instead with a cross-linking agent 308, such as a UV-activated portion thereof. Similarly, the cross-linking agent 308 can be cross-linked with another cross-linking agent 308, or with the cross-linking agent 304 instead.

The UV wavelength at which step 108 is performed may depend on the chemical composition of the crosslinking agent 304 and/or 308 . In particular, the composition of the functional groups R in the cross-linking agents 306 and/or 308 can determine the wavelength of the ultraviolet rays used in the step 108. In some embodiments, the wavelength range is between about 160 nm to about 300 nm. The stability of different UV sources used to generate different wavelengths can vary and can affect the quality of the exposure process. As such, in some embodiments, the wavelength corresponding to the stable UV source can be used as a parameter for selecting the specific functional group R contained in the crosslinking agent 304 and/or 308 .

In some instances, the UV exposure level may not be uniform throughout the thickness of the bottom layer 204B. For example, if the substrate 202 includes a structural space smaller than the UV wavelength, the UV-activated crosslinking agent in the bottom of the bottom layer 204B may not be sufficiently activated. Incomplete crosslinking (or curing) may affect the quality of the bottom layer 204B and subsequent steps of etching the bottom layer 204B. Methods provided by the present invention perform a thermal curing process after the UV exposure process 232 to provide additional crosslinking in the bottom layer 204B.

As shown in FIGS. 1A , 5 , and 8 , step 110 of method 100 performs a bake process 234 on workpiece 200 to thermally cure polymer network 330 to form bottom layer 204C. In many embodiments, the bake process 234 can thermally activate the crosslinker 306 included in the polymer network 330 . As shown in FIG. 8, during the baking process (or curing process) 234, the cross-linking agents 306 and 308 (eg, thermally activated portions thereof) bonded to a polymer backbone 320 may be bonded to different polymers Crosslinking agents 306 and/or 308 of backbone 320 crosslink (eg, form covalent bonds). In many embodiments, crosslinking agent 306 may be crosslinked with another crosslinking agent 306, or instead crosslinking with crosslinking agent 308 (the thermally activated portion thereof). Similarly, the cross-linking agent 308 can be cross-linked with another cross-linking agent 308, or with the cross-linking agent 306 instead. In some embodiments (although not shown here), the crosslinking agent 308 may form a UV-activated crosslink with the crosslinking agent 304 during the UV exposure process 232, and then may interact with the crosslinking agent 306 during the bake process 234. Heat activated crosslinks are formed. In some embodiments, the substrate 202 is heated to perform the bake process 234 such that the bottom of the bottom layer 204C near or in contact with the substrate 202 is heated to a greater degree than the top of the bottom layer 204C. As such, the bottom of the bottom layer 204C that is difficult to reach by UV curing in step 108 (since the UV irradiation is set from top to bottom) can be thermally cured, eg, cross-linked, to ensure that the extent of curing in the bottom layer 204C is maximized Even throughout the entire thickness area. In some embodiments, the bake process 234 is performed at a temperature above the critical temperature required to activate the thermally activated portion of the crosslinker 308 and/or the crosslinker 306 . In some examples, bake process 234 may be performed at a temperature between about 150° C. and about 250° C., depending on the specific chemical composition of cross-linking agent 306 and/or cross-linking agent 308 . In addition, other temperatures or other temperature ranges may also be used.

As shown in FIGS. 1B and 9 , step 112 of method 100 forms intermediate layer 206 (or second layer) on bottom layer 204 . The intermediate layer 206 may be a single-layer structure, or a multi-layer structure each having a different composition. In many embodiments, the composition of the intermediate layer 206 may provide the desired anti-reflection properties and/or hard mask properties for subsequent lithography processes. The intermediate layer 206 may be formed by spin coating a solution containing a suitable polymer dissolved in a solvent to form the intermediate layer 206 on the bottom layer 204 . This spin coating process can be similar to the spin coating process in the aforementioned step 104 . In some embodiments, step 112 may be omitted.

As shown in FIGS. 1B and 10 , step 114 of method 100 forms a photoresist layer 208 on the interlayer 206 . The photoresist layer 208 can be a photosensitive layer that can be patterned by an exposure process that initiates a series of photochemical reactions in the photoresist layer 208 . The photoresist layer 208 may comprise any suitable photosensitive photoresist material, and in many embodiments the photoresist material included in the photoresist layer 208 is resistant to radiation sources (eg, ultraviolet, deep ultraviolet, and/or extreme ultraviolet) sensitive. However, the principles of the present invention are applicable to e-beam photoresist and other direct-write photoresist materials. The photoresist layer 208 may have a single-layer structure or a multi-layer structure. In many embodiments, the radiation-exposed regions of the photoresist layer 208 undergo a chemical reaction, eg, decomposition, so that the radiation-exposed regions in turn become soluble in the developing solution. In other embodiments, the exposed portions of the photoresist layer 208 undergo chemical reactions, such as polymerization and/or cross-linking, such that the exposed portions become insoluble in the developing solution.

In many embodiments, photoresist layer 208 comprises a polymer whose backbone (not shown) has a plurality of functional groups (not shown) attached to the backbone. The polymer backbone may comprise acrylate-based polymers, copolymers of norbornene and maleic anhydride, polyhydroxystyrene-based polymers, other suitable polymers, or combinations of the foregoing, with any of the above. number of functional groups to facilitate one or more subsequent exposure and development processes. In one example, the functional group may comprise a lithographically sensitive group (sensitizer) such as phenol, styrene, fluoride, and/or other suitable groups. In another example, the functional group may comprise an acid-sensitive group, which is provided as a group that can be cleaved from the polymer backbone by an acidic component.

In addition, the photoresist layer 208 may be implemented as a chemically amplified photoresist material, which includes a photosensitive component in the composition of the photoresist material. For example, photoresist layer 208 includes one or more photoacid generators, which can generate acidic components in response to radiation exposure. Non-limiting examples of suitable photoacid generators include sulfonium cation salts with sulfonates, iodonium ion salts with sulfonates, sulfone azomethane compounds, N-sulfoneoxyimide photoacid generators, benzoin Sulfonate photoacid generator, pyrogallol trisulfonate photoacid generator, nitrobenzylsulfonate photoacid generator, sulfone photoacid generator, glyoxime derivative, perfluorobutylsulfonic acid acid triphenylsulfonium salt, and/or other suitable photoacid generators now known or developed in the future. The photoresist layer 208 may additionally or alternatively contain other photosensitive components, such as photolytic bases, photobase generators, photolytic quenchers, other photosensitive components, or combinations thereof. The photoresist layer 208 may also contain various additives such as cross-linking agents (eg, tetramethylol glycoluril cross-linking agents or epoxy cross-linking agents), surfactants, chromophores, and/or solvents. The photoresist layer 208 may be applied by any suitable technique, such as the spin coating process previously described. Method 100 may implement a pre-exposure bake process to evaporate any solvent remaining during the spin coating process.

As shown in FIGS. 1B and 11 , step 116 of method 100 exposes photoresist layer 208 with radiation 216 . In many embodiments, the rays 216 may be I-line (approximately 365 nm wavelength), deep ultraviolet such as a krypton fluoride excimer laser (approximately 248 nm wavelength) or argon fluoride excimer laser (approximately 193 nm wavelength), extreme ultraviolet (approximately 193 nm wavelength) between about 1 nm and about 100 nm), x-rays, electron beams, ion beams, and/or other suitable radiation.

The exposure process of step 110 can be performed in the atmosphere, in a liquid (immersion lithography), or in a vacuum (eg, EUV lithography and electron beam lithography). In the described embodiment, the method 100 employs a photomask 220 to perform lithography, and the photomask 220 includes the pattern 218 . Photomask 220 may be a transmissive photomask or a reflective photomask, which may further each employ resolution enhancement techniques such as phase shifting, off-axis illumination, and/or optical proximity correction. In other embodiments, the rays 216 are directly adjusted in a predetermined pattern, such as an integrated circuit layout, without using a photomask 220 (eg, using an electron beam direct writer). In one embodiment, the radiation 216 is EUV, and the exposure process of step 110 is performed in an EUV lithography system. In contrast, a reflective photomask 220 may be used to pattern the photoresist layer 208 . In many embodiments, the wavelength of radiation 216 is different from the UV wavelength of UV exposure process 232 . In the embodiment in which the rays 216 are extreme ultraviolet rays, the wavelengths of the rays 216 are smaller than the wavelengths of the ultraviolet rays implemented in the ultraviolet exposure process in step 108 .

Afterwards, as shown in FIGS. 1B and 12 , the exposed regions 212 of the photoresist layer 208 undergo a photochemical reaction, while the unexposed regions of the photoresist layer 208 remain substantially the same as the photoresist material before exposure. In some embodiments, the material in the exposed area 212 decomposes and becomes soluble in the developing solution. In other embodiments, the material in the exposed regions 212 of the photoresist layer 208 polymerizes and/or cross-links and becomes insoluble in the developing solution. In this embodiment, the photoresist material prior to exposure is chemically amplified, so that the chemical reaction generated by the exposure process is initiated by one or more photoactive components, which then trigger subsequent reactions of the material in the exposed area.

As shown in FIGS. 1B and 13 , step 118 of method 100 performs a development process on workpiece 200 . The development process can dissolve or remove exposed areas 212 (shown in FIG. 14B ) or unexposed areas 214 (shown in FIG. 14A ), depending on the specific chemical changes that occur during the exposure process in step 110 and the nature of the developer. Suitable water-based developers include tetramethylammonium hydroxide, potassium hydroxide, sodium hydroxide, and/or other suitable solvents, and suitable organic solvent-based developers include solvents such as n-butyl acetate, ethanol , hexane, benzene, toluene, and/or other suitable solvents. The step of applying the developer 222 may include spraying the developer 222 on the photoresist layer 208 in a spin coating process. The development process of step 112 may start with a post-exposure bake process. The post-exposure bake process may catalyze the reaction between the polymer in the photoresist layer 208 and the reacted photosensitive components, depending on the polymer contained in the photoresist layer 208 .

As shown in FIG. 1B , additional fabrication processes performed in step 120 of method 100 may include transferring the pattern formed in photoresist layer 208 to underlying intermediate layer 206 and bottom layer 204C in one or more etching processes. The etching process may be performed by any suitable method, including a dry etching process, a wet etching process, other suitable etching processes, a reactive ion etching process, or a combination thereof. Then, the patterned bottom layer 204C can be used as a mask to process the substrate 202 . The processes performed on the substrate 202 can be any suitable method, including deposition processes, implantation processes, epitaxial growth processes, and/or any other fabrication processes. In one embodiment, the patterned bottom layer 204C is used as an etch mask and the substrate 202 is etched. However, embodiments of the present invention can be used for any fabrication process performed on the substrate 202 . In various examples, the patterned bottom layer 204C acts as a mask to fabricate gate stacks, interconnect structures, non-planar devices (eg, fins, which are fabricated by etching or epitaxial growth of fin material), and/or or other suitable structures in the substrate 202 . After processing the substrate 202 , the patterned photoresist layer 208 , the patterned intermediate layer 206 , and the patterned bottom layer 204C may be removed from the substrate 202 . In some embodiments, patterned bottom layer 204C may be removed together with patterned photoresist layer 208 and/or patterned intermediate layer 206 by any suitable process, such as plasma ashing or photoresist strip. In other embodiments, after the patterned photoresist layer 208 and the patterned intermediate layer 206 are removed from the workpiece 200 in a suitable manner, the patterned bottom layer 204C may be removed by an etching process, which may be a dry etching process , wet etching process, reactive ion etching process, and/or other suitable etching process.

In many embodiments, workpiece 200 may be used to fabricate integrated circuit chips, SoCs, and/or portions thereof after step 120, so that subsequent fabrication processes may form various passive and active microelectronic devices such as resistors, capacitors, Inductors, diodes, metal oxide semiconductor field effect transistors, complementary metal oxide semiconductor transistors, bipolar junction transistors, laterally diffused metal oxide semiconductor transistors, high power metal oxide semiconductor transistors, other kinds of transistors, and/or other circuit units.

One or more embodiments of the methods, apparatus, and compositions described herein have various advantages. The bottom layer (eg, bottom anti-reflection coating) provided by the embodiment of the present invention is formed on the substrate, and is arranged to facilitate the photolithographic patterning process. In particular, the bottom layer may comprise a polymer network having at least one UV crosslinking agent and at least one thermal crosslinking agent bound thereto. In some embodiments, the methods provided by the embodiments of the present invention expose the bottom layer to ultraviolet light to activate the ultraviolet crosslinking agent, and then expose the bottom layer to heat to activate the thermal crosslinking agent, prior to the photolithographic patterning process. The photolithographic patterning process involves exposing and developing a photosensitive top layer on top of the bottom layer. In many embodiments, the inclusion of both UV- and heat-activated cross-linking agents in the primer layer provides additional cross-linking sites in the polymer network before exposing the primer layer to UV light and heat to activate their respective cross-links After curing, the degree of curing can be improved.

In one embodiment of the present invention, the method includes forming an underlayer on the semiconductor substrate, wherein the underlayer includes a polymer bonded to a first cross-linking agent and a second cross-linking agent, the first cross-linking agent is configured to be UV-activated, and the first cross-linking agent is configured to be UV-activated. The thermal activation of the second crosslinking agent is set to the first temperature. The method also includes exposing the base layer to an ultraviolet source to form an exposed base layer, wherein exposing the base layer to the ultraviolet source activates the first crosslinking agent. The method also includes baking the exposed bottom layer, wherein the baking step activates the second crosslinking agent.

In some embodiments, the first crosslinking agent comprises _H2C =CH-R-, and wherein R comprises -(C=O)-, -(C=O)-O-, -CH=CH-, benzene base, phenol, or a combination of the above.

In some embodiments, the second crosslinking agent comprises phenyl, alkyl-substituted phenyl, epoxy, hydroxyl, ether, ester, phenolic resin, or a combination thereof.

In some embodiments, the baking step is a first baking process, and the method further includes performing a second baking process on the bottom layer before the step of exposing the bottom layer to ultraviolet light, and the second baking process is configured to expose the upper surface of the bottom layer to smooth.

In some embodiments, the temperature of the second baking process is lower than the first temperature.

In some embodiments, the temperature of the first baking process is higher than the first temperature.

In some embodiments, the polymer is bonded to a third crosslinking agent, wherein the third crosslinking agent is configured to be UV and thermally activated.

In some embodiments, the third crosslinking agent comprises _H2C =CH-(C=O)-O-X-, and X comprises an alkyl chain, an aromatic ring, a heteroaromatic ring, or a combination thereof.

Another embodiment of the present invention provides a method comprising spin coating a material layer on a semiconductor substrate, wherein the material layer includes a polymer linked to at least one UV crosslinking agent and at least one thermal crosslinking agent, and wherein the UV light in the material layer The amount of crosslinking is greater than the amount of thermal crosslinking in the material layer. The method includes exposing the material layer to a first ultraviolet source having a first wavelength to form an exposed material layer, wherein exposing the material layer to the first ultraviolet source induces crosslinking of the ultraviolet crosslinking agent. The exposed material layer is then thermally cured to form a cured material layer, wherein the step of thermally curing induces crosslinking of the thermal crosslinking agent. Next, a photoresist layer is formed on the cured material layer.

In some embodiments, the method further includes exposing the photoresist layer to a second ultraviolet light source having a second wavelength to form an exposed photoresist layer, wherein the second wavelength is different from the first wavelength; and developing the exposed light resist layer to form a pattern.

In some embodiments, the second wavelength is less than the first wavelength.

In some embodiments, the ratio of the amount of thermal crosslinking to the amount of UV crosslinking is at least about 25% but not greater than about 67%.

In some embodiments, the method further includes forming an intermediate layer on the cured material layer prior to forming the photoresist layer.

In some embodiments, the UV crosslinking agent includes a UV-activated functional group comprising -(C=O)-, -(C=O)-O-, -CH=CH-, phenyl, phenol, or the above The combination.

In some embodiments, the UV-activated functional group is attached to the polymer via an alkyl chain, an aromatic ring, a heteroaromatic ring, or a combination thereof.

In some embodiments, the UV crosslinking agent further includes a functional group configured to be thermally activated.

Yet another embodiment of the present invention provides a method comprising: forming an underlayer on a semiconductor substrate, and the underlayer includes a polymer, a first crosslinking agent configured to crosslink when exposed to ultraviolet light, and configured to be exposed to a heat source at a first temperature A crosslinked second crosslinking agent, wherein the first crosslinking agent and the second crosslinking agent are bonded to the polymer. The method then exposes the bottom layer to a first heat source at a second temperature, and the second temperature is lower than the first temperature. After exposing the base layer to the first heat source, the base layer is exposed to ultraviolet light and crosslinking of the first crosslinking agent is induced to form the exposed base layer. The exposed base layer is exposed to a second heat source at a third temperature to form a cured base layer, wherein the third temperature is higher than the first temperature. The method then follows forming an intermediate layer on the cured bottom layer; and forming a photoresist layer on the intermediate layer.

In some embodiments, the amount of the second crosslinking agent is less than the amount of the first crosslinking agent.

In some embodiments, the polymer further includes an acrylate-based polymer, a copolymer of norbornene and maleic anhydride, a polyhydroxystyrene-based polymer, or a combination thereof.

In some embodiments, the bottom layer further includes a third crosslinking agent configured to crosslink upon exposure to ultraviolet light and a heat source.

The features of the above-described embodiments are helpful for those skilled in the art to understand the present invention. It should be understood by those skilled in the art that other processes and structures can be designed and changed using the present invention as a basis to achieve the same purpose and/or the same advantages of the above embodiments. Those skilled in the art should also understand that these equivalent replacements do not depart from the spirit and scope of the present invention, and can be changed, replaced, or changed without departing from the spirit and scope of the present invention.

Claims (1)

1. A method of forming a semiconductor structure, comprising:

forming a bottom layer on a semiconductor substrate, wherein the bottom layer comprises a polymer bonded to a first cross-linking agent and a second cross-linking agent, wherein the first cross-linking agent is configured to be ultraviolet activated, and wherein the second cross-linking agent is configured to be thermally activated at a first temperature;

exposing the substrate to an ultraviolet source to activate the first crosslinker to form an exposed substrate; and

baking the exposed underlayer to activate the second crosslinker.

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