Patent Publication Number: US-2023142787-A1

Title: Negative tone photoresist for euv lithography

Description:
CROSS-REFERENCES TO RELATED APPLICATION 
     This application is a Continuation Application of U.S. application Ser. No. 16/810,002, filed Mar. 5, 2020, now U.S. Pat. No. 11,550,220, issued on Jan. 10, 2023, which claims priority to U.S. Provisional Patent Application Ser. No. 62/928,226, filed Oct. 30, 2019, all of which are herein incorporated by reference in their entireties. 
    
    
     BACKGROUND 
     The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC material and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. During the course of IC evolution, functional density (e.g., the number of interconnected devices per chip area) has generally increased while geometry size (e.g., the smallest component or line that can be created using an IC fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. However, such scaling down has also increased the complexity of processing and manufacturing ICs. 
     One example process used to manufacture the ICs is lithography. Lithography is a process that is used to transfer IC patterns to a semiconductor wafer. In an example lithography process, a resist film is coated on a surface of a wafer and is subsequently exposed and developed to form a resist pattern. The resist pattern is then used to etch the wafer to form an IC pattern in the wafer. The quality of the resist pattern can directly impact the quality of the final IC. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Aspects of the present disclosure are best understood from the following detailed description when read with the accompanying figures. It is noted that, in accordance with the standard practice in the industry, various features are not drawn to scale. In fact, the dimensions of the various features may be arbitrarily increased or reduced for clarity of discussion. 
         FIGS.  1 A- 1 F  are partial cross-sectional views of a wafer at various stages of manufacture according to at least one embodiment of the present disclosure; 
         FIG.  2    illustrates example polymers used for a negative tone photoresist according to at least one embodiment of the present disclosure; 
         FIG.  3    illustrates examples of the photo acids formed from the example polymers according to at least one embodiment of the present disclosure; 
         FIG.  4    illustrates examples of cross-linked polymers according to at least one embodiment of the present disclosure; 
         FIG.  5    illustrates examples of dissolution inhibitors having an epoxy group according to at least one embodiment of the present disclosure; 
         FIG.  6    illustrates examples of dissolution inhibitors having a hydroxy-group according to at least one embodiment of the present disclosure; 
         FIG.  7    illustrates examples of dissolution inhibitors having a melamine group according to at least one embodiment of the present disclosure; 
         FIG.  8    illustrates examples of dissolution inhibitors having an alkene group according to at least one embodiment of the present disclosure; 
         FIG.  9    illustrates a flowchart of a method for developing a negative tone photoresist according to at least one embodiment of the present disclosure; and 
         FIG.  10    illustrates an example EUV lithography system according to at least one embodiment of the present disclosure. 
     
    
    
     DETAILED DESCRIPTION 
     The following disclosure provides many different embodiments, or examples, for implementing different features of the provided subject matter. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature over or on a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact. In addition, the present disclosure may repeat reference numerals and/or letters in the various examples. This repetition is for the purpose of simplicity and clarity and does not in itself dictate a relationship between the various embodiments and/or configurations discussed. 
     Further, spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature&#39;s relationship to another element(s) or feature(s) as illustrated in the figures. The spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. The apparatus may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein may likewise be interpreted accordingly. 
     The advanced lithography process, method, and materials described in the current disclosure can be used in many applications, including fin-type field effect transistors (FinFETs). For example, the fins may be patterned to produce a relatively close spacing between features, for which the above disclosure is well suited. In addition, spacers used in forming fins of FinFETs can be processed according to the above disclosure. 
     The present disclosure is related to various embodiments of a negative tone photoresist and methods for developing the same. In a lithography process, there may be two different types of processes for developing exposed resist films: a positive tone development (PTD) process and a negative tone development (NTD) process. 
     During the PTD process, the photoresist may be spun onto a wafer. A mask may be placed over the photoresist. The mask may include an IC pattern that is to be printed into the wafer. A radiation source (e.g., an ultraviolet light (UV) or extreme ultraviolet light (EUV) source) may be applied to the photoresist through the mask. Portions of the photoresist that are not covered by the mask may be exposed to the radiation source. 
     In one embodiment, the photoresist in the PTD process may include a polymer (e.g., poly hydroxystyrene (PHS)) in amounts between 20 weight per cent (wt %) to 40 wt %. The polymer may include an acid labile group (ALG) that may leave the polymer during exposure to the radiation source. When the ALG group leaves the polymer, the portions of the photoresist that are exposed to the radiation source may be become more hydrophilic than the portions of the photoresist that are not exposed to the radiation source. This allows the exposed portions of the photoresist to be soluble in a positive tone developer, such as a solution of tetra methylammonium hydroxide (TMAH), and easily removed by the TMAH solution. 
     It may be desirable to reduce the amount of energy applied by the radiation source to make the process to develop the photoresist more efficient. PHS is a weak acid and as the ratio of the PHS increases in the photoresist, the photoresist may be more sensitive to the radiation source. However, for the PTD process, adding more PHS may cause the solubility of the photoresist to be enhanced and dissolve more easily when exposed to the TMAH solution. Thus, the TMAH solution may develop too much of the photoresist, which can degrade the lithography performance (e.g., line width roughness, local critical dimension uniformity, and the like). 
     The present disclosure takes the disadvantage caused by the increase of the polymer ratio in the photoresist in the PTD process to improve the NTD process. For example, the increased sensitivity due to the increase in the ratio of polymer in the photoresist may allow lower amounts of energy (e.g., 20 milli-Joules (mJ) to 30 mJ as opposed to 40 MJ or more that are currently used) to be applied to the exposed portions of the photoresist. 
       FIGS.  1 A- 1 F  illustrate partial cross-sectional views of a wafer at various stages of a NTD process according to at least one embodiment of the present disclosure. It should be noted that additional operations can be provided before, during, or after each stage of the operation illustrated in  FIGS.  1 A- 1 F . 
       FIG.  1 A  illustrates a cross-sectional view of a semiconductor device  100 . The semiconductor device  100  may be an intermediate device fabricated during processing of an IC, or a portion thereof. The semiconductor device may comprise static random access memory (SRAM) and/or logic circuits, passive components such as resistors, capacitors, and inductors, and active components such as p-type field effect transistors (PFETS), n-type FETs (NFETs), fin-like FETs (FinFETs), other multi-gate FETs, complementary metal-oxide semiconductor (CMOS) transistors, bipolar transistors, high voltage transistors, high frequency transistors, other active devices, and combinations thereof. 
     In one embodiment, the semiconductor device  100  may include a substrate  102 . The substrate  102  may include one more layers of material or composition. In one embodiment, the substrate  102  may be a semiconductor substrate (e.g., a wafer). In one embodiment, the substrate  102  may include silicon in a crystalline structure. In one embodiment, the substrate  102  may include other elementary semiconductors such as germanium, a compound semiconductor such as silicon carbide, gallium arsenide, indium arsenide, indium phosphide, or an alloy semiconductor such as silicon germanium carbide, gallium arsenic phosphide, gallium indium phosphide, and the like. In one embodiment, the substrate  102  may include a silicon on insulator (SOI) substrate, be strained and/or stressed for performance enhancement, include epitaxial regions, include isolation regions, include doped regions, include one or more semiconductor devices or portions thereof, include conductive and/or non-conductive layers, or any other suitable features. 
     In one embodiment, the substrate  102  may include a patterning layer  104 . In one embodiment, the patterning layer  104  may be a hard mask layer that includes materials such as silicon, silicon oxide, silicon nitride, silicon oxynitride, silicon carbon nitride, silicon carbide, titanium nitride, and the like. The patterning layer  104  may include a high-k dielectric layer, a gate layer, a hard mask layer, an interfacial layer, a capping layer, a diffusion/barrier layer, a dielectric layer, a conductive layer, and the like. 
     In  FIG.  1 B , a negative tone photoresist  106  of the present disclosure may be spun onto the patterning layer  104  of the substrate  102 . The negative tone photoresist  106  may be formed by spin-on coating the negative tone photoresist  106  onto the substrate  102 . In one embodiment, the negative tone photoresist  106  may be further processed or treated with a soft baking process, a hard baking process, or a combination thereof. 
     In one embodiment, the negative tone photoresist  106  of the present disclosure may contain large amounts of a photosensitive polymer. For example, the polymer may be a polymer with an ALG or a hydroxyl group. In one embodiment, the negative tone photoresist  106  may include over 40 wt % of the polymer to increase the sensitivity of the negative tone photoresist  106  to radiation. For example, the negative tone photoresist  106  may include approximately 40 wt % to 60 wt % of the polymer. 
     As discussed above, negative side effects may occur when too much of the polymer (e.g., greater than 40 wt %) is included in the positive tone photoresist for the PTD process. For example, the positive tone photoresist may become too developed (e.g., too much of the positive tone photoresist is removed by the developer) and create lithography issues. Thus, the amount of polymer that can be used in the positive tone photoresist may be limited, which may limit the amount of energy reduction for the PTD process. 
     In contrast, for the NTD process, the amount of polymer in the negative tone photoresist  106  can be increased to allow the portions of the negative tone photoresist  106  that will be developed to be more easily removed. As a result, a lower amount of radiation energy or UV light may be applied to develop the negative tone photoresist  106 . For example, instead of using up to 40 milli-Joules of energy, the negative tone photoresist  106  of the present disclosure can be developed with as little as 20 milli-Joules to 30 milli-Joules of radiation energy. 
     In addition, as noted above, the polymer (e.g., PHS) in the negative tone photoresist  106  may create a weak acid when exposed to the radiation energy. The higher the concentration of the polymer that is contained in the negative tone photoresist  106 , the greater the amount of weak acids that may be generated during exposure to the radiation energy. 
     The weak acids may react with dissolution inhibitors, or cross linking units, in the negative tone photoresist  106 . The cross-linking reactions may increase the molecular weight of the negative tone photoresist  106  and allow the exposed portions of the negative tone photoresist  106  to be more resistant to being developed. Thus, an increase in the amount of polymer in the negative tone photoresist  106  may also improve the contrast in addition to a reduction of the amount of energy that is used. 
     In one embodiment, the negative tone photoresist may include a polymer, a dissolution inhibitor, polyethylene glycol (PEG), and a quencher that is mixed in a solvent. The polymer may be any type of photo acid generator (PAG) that includes an acid labile group (ALG). When the PAG is exposed to radiation, the ALG may be cleaved from the backbone of the PAG to form weak acids. This may increase the solubility of the polymer in the developer. 
     In one embodiment, the polymer may comprise a hydroxyl group (OH).  FIG.  2    illustrates examples of polymers  202 ,  204 , and  206  that can be used for the negative tone photoresist  106 . For example, the polymer  202  may be poly hydroxystyrene (PHS), the polymer  204  may be poly benzoic acid (PBA), and the polymer  206  may be poly acrylic acid (PAA). It should be noted that the polymers  202 ,  204 , and  206  are a few examples, but any type of polymer that can be a PAG can create ALGs. 
     In one embodiment, the dissolution inhibitor may comprise cross-linking units that allow hydroxyl radicals formed from exposure of the polymers to a radiation source to cross-link to the cross-linking units. The cross-linking reactions may help increase the molecular weight of the portions of the negative tone photoresist  106  that are exposed to the radiation source such that the exposed portions are more resistant to the developer. 
     In one embodiment, the negative tone photoresist  106  may contain greater than 5 wt % of the dissolution inhibitor. For example, the negative tone photoresist  106  may contain 5-10 wt % of the dissolution inhibitor. Adding relatively large amounts of the dissolution inhibitor may improve the amount of cross-linking reactions that occur. The cross-linking reactions can improve the resistance of the exposed portions of the negative tone photoresist  106  to the developer. 
       FIGS.  5 - 8    illustrate examples of the dissolution inhibitor that can be used. The dissolution inhibitors may include two or more cross-linking sites.  FIG.  5    illustrates dissolution inhibitors  502 ,  504 , and  506  that contain an epoxy-group. The dissolution inhibitor  502  may contain four cross-linking sites, the dissolution inhibitor  504  may contain three cross-linking sites, and the dissolution inhibitor  506  may contain two cross-linking sites. R1 in the dissolution inhibitors  502 ,  504 , and  506  may be a C2-C20 alkyl group, cycloalkyl group, hydroxylalkyl group, cycloalkyl carboxyl group, a carbon (C)2-C20 saturated or unsaturated hydrocarbon ring, or a C2-C20 heterocyclic group. The R1 chain may be rotatable to achieve a high cross-link reaction efficiency in the exposed areas of the negative tone photoresist  206 . 
       FIG.  6    illustrates dissolution inhibitors  602 ,  604 , and  606  that contain a hydroxy-group. The dissolution inhibitor  602  may contain four cross-linking sites, the dissolution inhibitor  604  may contain three cross-linking sites, and the dissolution inhibitor  606  may contain two cross-linking sites. R1 in the dissolution inhibitors  602 ,  604 , and  606  may be a C2-C20 alkyl group, cycloalkyl group, hydroxylalkyl group, cycloalkyl carboxyl group, a C2-C20 saturated or unsaturated hydrocarbon ring, or a C2-C20 heterocyclic group. The R1 chain may be rotatable to achieve a high cross-link reaction efficiency in the exposed areas of the negative tone photoresist  106 . Ra in the dissolution inhibitors  602 ,  604 , and  606  may be hydrogen (H) or C1-C8 alkyl group, cycloalkyl group, hydroxylalkyl group, cycloalkyl carboxyl group, a C1-C8 saturated or unsaturated hydrocarbon ring, or a C1-C8 heterocyclic group. 
       FIG.  7    illustrates dissolution inhibitors  702 ,  704 , and  706  that contain a melamine group. The dissolution inhibitor  702  may contain four cross-linking sites, the dissolution inhibitor  704  may contain three cross-linking sites, and the dissolution inhibitor  706  may contain two cross-linking sites. R1 in the dissolution inhibitors  702 ,  704 , and  706  may be a C2-C20 alkyl group, cycloalkyl group, hydroxylalkyl group, cycloalkyl carboxyl group, a C2-C20 saturated or unsaturated hydrocarbon ring, or a C2-C20 heterocyclic group. The R1 chain may be rotatable to achieve a high cross-link reaction efficiency in the exposed areas of the negative tone photoresist  106 . Ra in the dissolution inhibitors  702 ,  704 , and  706  may be hydrogen (H) or C1-C8 alkyl group, cycloalkyl group, hydroxylalkyl group, cycloalkyl carboxyl group, a C1-C8 saturated or unsaturated hydrocarbon ring, or a C1-C8 heterocyclic group. 
       FIG.  8    illustrates dissolution inhibitors  802 ,  804 , and  806  that contain an alkene group. The dissolution inhibitor  802  may contain four cross-linking sites, the dissolution inhibitor  804  may contain three cross-linking sites, and the dissolution inhibitor  806  may contain two cross-linking sites. R1 in the dissolution inhibitors  802 ,  804 , and  806  may be a C2-C20 alkyl group, cycloalkyl group, hydroxylalkyl group, cycloalkyl carboxyl group, a carbon (C)2-C20 saturated or unsaturated hydrocarbon ring, or a C2-C20 heterocyclic group. The R1 chain may be rotatable to achieve a high cross-link reaction efficiency in the exposed areas of the negative tone photoresist  106 . 
     The PEG may help provide adhesion of the negative tone photoresist  106  to the patterning layer  104 . The quencher may be a basic quencher that functions as a stoichiometric neutralizer of the PAG that is generated by the polymers. 
     The solvent may allow the components of the negative tone photoresist  106  to be coated or spun onto the patterning layer  104 . For example, the solvent may include 2-methoxy-1-methylethyl acetate (PGMEA), butyl acetate, ethyl lactate, and the like. 
     Referring back to  FIG.  1 B , additional process steps can be performed that are not shown. For example, prior to applying the negative tone photoresist  106  onto the patterning layer  104  an anti-reflective coating (ARC) layer may be formed over the patterning layer  104 . The ARC layer may be a nitrogen-free anti-reflective coating (NFARC) that includes a material such as silicon oxide (SiO 2 ), silicon oxygen carbide (SOC), plasma enhanced chemical vapor deposited silicon oxide (PECVD-SiO 2 ), other suitable materials, or any combination thereof. Additional layers may also be formed between the patterning layer  104  and the negative tone photoresist  106 . 
       FIG.  1 C  how the negative tone photoresist  106  is exposed to a radiation beam  110  (e.g., an ultraviolet (UV) light source, an extreme UV (EUV) light source, a laser, and the like) in a lithography system  1000 . The radiation beam  110  may be any type of light source or radiation source. For example, the radiation beam  110  may be an I-line (365 nanometers (nm)), a deep UV radiation such as KrF excimer laser (248 nm) or ArF excimer laser (193 nm), an EUV radiation (e.g., 13.8 nm), an e-beam, an x-ray, an ion beam, or other suitable radiations. 
     The operation illustrated in  FIG.  1 C  may be performed in air, in a liquid (immersion lithography), or in a vacuum (e.g., for EUV lithography and e-beam lithography). In an embodiment, the radiation beam  110  is patterned with a mask having IC patterns, such as a transmissive mask or a reflective mask, which may include resolution enhancement techniques such as phase-shifting and/or optical proximity correction (OPC). In another embodiment, the radiation beam  110  is directly modulated with IC patterns without using a mask (maskless lithography). In the present embodiment, the radiation beam  110  is an EUV radiation and the lithography system  1000  is an EUV lithography system. An embodiment of the EUV lithography system  1000  is shown in  FIG.  10   . 
     Referring to  FIG.  10   , the EUV lithography system  1000  includes a radiation source  1002  that produces the radiation beam  110 , condenser optics  1006 , a mask stage  1010  securing a mask  1008  thereon, projection optics  1012 , and a substrate stage  1014  securing the device  100  including the substrate  102  and the negative tone photoresist  106 . Other configurations and inclusion or omission of items may be possible. In the present disclosure, the EUV lithography system  1000  may be a stepper or a scanner. 
     The radiation source  1002  provides the radiation beam  110  having a wavelength in the EUV range, such as about 1-100 nm. In an embodiment, the radiation beam  110  has a wavelength of about 13.5 nm. As noted above, due to the composition of the negative tone photoresist  106  of the present disclosure, the negative tone photoresist  106  may be more sensitive to the radiation beam  110 . As a result, the amount of energy applied by the radiation source  1002  may be reduced. For example, the radiation source  1002  may apply approximately 20 milli-Joules-30 milli-Joules of energy instead of 40 milli-Joules or more that was previously used. 
     The condenser optics  1006  includes a multilayer coated collector and a plurality of grazing mirrors. The condenser optics  1006  is configured to collect and shape the radiation beam  110  and to provide a slit of the radiation beam  110  to the mask  1008 . The mask  1008 , also referred to as a photomask or a reticle, includes patterns of one or more target IC devices. The mask  1008  provides a patterned aerial image to the radiation beam  110 . The mask  1008  is a reflective mask in the present embodiment, and may incorporate resolution enhancement techniques such as phase-shifting techniques and/or optical proximity correction (OPC). The mask stage  1010  secures the mask  1008  thereon, such as by vacuum, and provides accurate position and movement of the mask  1008  during alignment, focus, leveling, and exposure operations in the EUV lithography system  1000 . 
     The projection optics  1012  includes one or more lenses and a plurality of mirrors. The lens may have a magnification of less than one thereby reducing the patterned aerial image of the mask  1008  to the device  100 , particularly, to the negative tone photoresist  106 . The device  100  is secured by the substrate stage  1014  which provides accurate position and movement of the device  100  during alignment, focus, leveling, and exposing operations in the EUV lithography system  1000  such that the patterned aerial image of the mask  1008  is exposed onto the negative tone photoresist  106  in a repetitive fashion (though other lithography methods are possible). The exposed portions of the negative tone photoresist  106  become insoluble in a developer, while the unexposed portions are removed by the developer. 
     As shown in  FIG.  1 C , portions  106 B of the negative tone photoresist  106  may be exposed by the radiation beam  110 . As noted above, due to the large amounts of polymer (e.g., greater than 40 wt %) in the negative tone photoresist  106 , the negative tone photoresist may be more sensitive to the radiation beam  110 . As a result, a lower dosage or lower amount of energy can be applied by the radiation beam  110  to generate the weak acid from the polymers and create cross-linking reactions in the negative tone photoresist  106 . 
     For example, the exposure by the radiation beam  110  may create an acid and hydroxyl radical from the polymer contained in the negative tone photoresist  106  as shown in  FIG.  3   .  FIG.  3    illustrates the example hydroxyl radicals  302 ,  304  and  306  formed by exposure of the polymers  202 ,  204 , and  206  to the radiation beam  110 . In addition,  FIG.  3    illustrates the formation of an acid  308 ,  310 , and  312 . The acid  308 ,  310 , and  312  may be neutralized by the basic quencher contained in the negative tone photoresist  106 . 
     In one embodiment, the hydroxyl radicals  302 ,  304 , and  306  can then react with the dissolution inhibitors (e.g., the dissolution inhibitors illustrated in  FIGS.  5 - 8    and described above) or cross-linking units  408 ,  410 , and  412  illustrated in  FIG.  4   . For example, the hydroxyl radical  302  may react with the cross-linker  408  to form the cross-linked compound  402 . The hydroxyl radical  304  may react with the cross-linker  410  to form the cross-linked compound  404 . The hydroxyl radical  306  may react with the cross-linker  412  to form the cross-linked compound  406 . 
       FIG.  1 D  illustrates how the negative tone photoresist  106  may be developed. A developer  112  may be applied to both the exposed portions  106 B and the unexposed portions  106 A. In one embodiment, the developer may be TMAH. However, due to the composition of the negative tone photoresist  106  (e.g., an amount of greater than 40 wt % of the polymer) additional types of organic solvents may be used to develop the unexposed portions  106 A of the negative tone photoresist  106 . Additional types of organic solvents that can be used as the developer  112  may include butyl acetate, a mixture of 70 per cent glycol monomethylether and 30 per cent propylene glycol monomethylether acetate, and the like. 
     In one embodiment, the developer  112  may be applied in a developer tool. For example, the device  100  may be transferred to the developer tool. The device  100  may be secured on a stage or chuck of the developer tool. The device  100  may be held or spun while the developer  112  is sprayed onto the negative tone photoresist  106 . The developer  112  may be sprayed continuously or by other means such as a puddle developing process. After the negative tone photoresist  106  is developed, the remaining portions  106 B may be rinsed with deionized (DI) water to remove particles or residue. The remaining portions  106 B may also be subjected to a post-development baking (PDB) process to harden the remaining portions  106 B that form the resist pattern so as to increase its structural stability. 
       FIG.  1 E  illustrates a resulting resist pattern that is formed in the negative tone photoresist  106 . For example, after the developer  112  is applied, the exposed portions  106 B may remain on the patterning layer  104 . Due to the increased number of cross-linked reactions in the exposed portions  106 B, the remaining exposed portions  106 B may be resistant to the developer  112 . As a result, the remaining exposed portions  106 B may have very smooth edges and sidewalls (e.g., a low line edge roughness and a low line width roughness) and be well defined (e.g., have a high developing contrast). 
     The IC pattern from the remaining portions  106 B of the negative tone photoresist  106  may be transferred to patterning layer  104  of the substrate  102 . For example, the IC pattern may be transferred via an etching operation that uses the remaining portions  106 B as an etch mask. The etching operation may include a dry (plasma) etch, a wet etch, and/or any other etching methods. 
     For example, a dry etching process may implement an oxygen-containing gas, a fluorine-containing gas (e.g., CF 4 , SF 6 , CH 2 F 2 , CHF 3 , and/or C 2 F 6 ), a chlorine-containing gas (e.g., Cl 2 , CHCl 3 , CCl 4 , and/or BCl 3 ), a bromine-containing gas (e.g., HBr and/or CHBR 3 ), an iodine-containing gas, other suitable gases and/or plasmas, and/or combinations thereof. For example, a wet etching process may comprise etching in diluted hydrofluoric acid (DHF); potassium hydroxide (KOH) solution; ammonia; tetramethylammonium hydroxide (TMAH); a solution containing hydrofluoric acid (HF), nitric acid (HNO 3 ), and/or acetic acid (CH 3 COOH); or other suitable wet etchant. The remaining portion  106 B of the negative tone photoresist  106  may be partially or completely consumed during the etching of the patterning layer  104 . In an embodiment, any remaining portion of the remaining portion  106 B may be stripped off, leaving a patterned layer  104 B over the substrate  102 , as illustrated in  FIG.  1 F . 
     In one embodiment, the device  100  may proceed to final pattern or an IC device on the substrate  102 . In an embodiment, the substrate  102  is a semiconductor substrate and substrate  102  may proceed to additional processing to form fin field effect transistor (FinFET) structures. For example, a plurality of active fins may be formed in the semiconductor substrate  102 . The active fins have uniform critical dimension (CD), due to the low LER and LWR of the pattern formed by remaining portions  106 B of the negative tone photoresist  106 . 
     In another embodiment, the substrate  102  may proceed to operations to form a plurality of gate electrodes in the semiconductor substrate  102 . The gate electrodes have uniform gate length due to the smooth sidewalls of the pattern formed by remaining portions  106 B of the negative tone photoresist  106 . In another embodiment, a target pattern is to be formed as metal lines in a multilayer interconnection structure. For example, the metal lines may be formed in an inter-layer dielectric (ILD) layer of the substrate  102 , which has been etched by operation  110  to include a plurality of trenches. 
     The substrate  102  may then proceed to operations to fill the trenches with a conductive material, such as a metal; and polish the conductive material using a process such as chemical mechanical planarization (CMP) to expose the patterned ILD layer, thereby forming the metal lines in the ILD layer. The above are non-limiting examples of devices/structures that can be made and/or improved using the negative tone photoresist  106  of the present disclosure according to various aspects of the present disclosure. 
       FIG.  9    illustrates a flowchart of a method  900  of developing a negative tone photoresist according to at least one embodiment of the present disclosure. The method  900  may be performed via a lithography tool or developer under the control of a controller or processor. 
     While the method  900  is illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. 
     The method  900  begins at block  902 . At block  904 , the method  900  deposits the negative tone photoresist on a substrate. In one embodiment, the negative tone photoresist may be spun onto a patterning layer of the substrate. The negative tone photoresist may comprise a solvent, a dissolution inhibitor (e.g., cross-linking units), a polymer, PEG, and a basic quencher. In one embodiment, the polymer may be a polymer that includes a hydroxyl group. The polymer may be more than 40 wt % of the total amount of the negative tone photoresist. In one embodiment, the polymer may be approximately 40 wt % to 60 wt %. In one embodiment, the polymer may be PHS, PBA, PAA, and the like. 
     In one embodiment, the negative tone photoresist may include greater than 5 wt % of the dissolution inhibitor. In one embodiment, the negative tone photoresist may include approximately 5-10 wt % of the dissolution inhibitor. The dissolution inhibitor may include two or more cross-linking sites. The dissolution inhibitor may include at least one rotatable chain of carbon atoms that allows a high cross-link reaction efficiency to be achieved in the exposed areas of the negative tone photoresist. The dissolution inhibitor may include an epoxy-group, a hydroxyl-group, a melamine-group or an alkene group, as illustrated in  FIGS.  5 - 8    and discussed above. 
     As discussed above, the high amount of polymers in the negative tone photoresist allows the negative tone photoresist to be more sensitive to radiation. As a result, a lower dose, and thereby lower amounts of energy, may be applied by the radiation source. The high amounts of negative tone photoresist may also create more acid and hydroxyl radicals. The large amount hydroxyl radicals with the larger amount of dissolution inhibitors can create more cross-linking reactions. The large amount of cross-linking reactions in the negative tone photoresist may allow the exposed portions of the negative tone photoresist to be more resistant to the developer. 
     At block  906 , the method  900  exposes a portion of the negative tone photoresist to a radiation source at a power of approximately 20 milli-Joules to 30 milli-Joules. As noted above, the large amount of polymer (e.g., greater than 40 wt %) in the negative tone photoresist may allow the negative tone photoresist to be more sensitive to the radiation. As a result, a lower dose or lower amount of energy may be applied to the negative tone photoresist. The radiation source may be a UV light, an EUV light, a laser, and the like. 
     At block  908 , the method  900  develops the negative tone photoresist with an organic solvent, such that the portion of the negative tone photoresist that is exposed remains and unexposed portions of the negative tone photoresist are removed. In one embodiment, due to the composition of the negative tone photoresist, additional types of organic solvents that were not previously used for the NTD process may be used. For example, the organic solvents may include TMAH, butyl acetate, a mixture of 70 per cent glycol monomethylether and 30 per cent propylene glycol monomethylether acetate, and the like. 
     After the negative tone photoresist is developed, a pattern formed by the negative tone photoresist may be used to transfer a pattern of ICs onto a substrate. The patterned negative tone photoresist may then be removed and the substrate may continue for additional processing to form the final IC device. At block  910 , the method  900  ends. 
     Therefore, the present disclosure relates to a negative tone photoresist and method for developing the same. In some embodiments, the present disclosure relates to a negative tone photoresist that uses less radiation energy. For example, the negative tone photoresist comprises a solvent, a dissolution inhibitor, and a polymer. The polymer may comprise a hydroxyl group. The polymer may comprise greater than 40 wt % of a total weight of the negative tone photoresist. 
     In other embodiments, the present disclosure relates to a negative tone photoresist that uses less radiation energy and improves the resistance of the exposed negative tone photoresist to a developer. The negative tone photoresist comprises a solvent, a dissolution inhibitor and a polymer. The dissolution inhibitor comprises greater than 5 weight per cent (wt %) of a total weight of the negative tone photoresist. The polymer comprises a hydroxyl group and comprises greater than 40 wt % of the total weight of the negative tone photoresist. 
     In yet other embodiments, the present disclosure relates to a method for developing a negative tone photoresist of the present disclosure. For example, the method comprises depositing the negative tone photoresist on a substrate. A portion of the negative tone photoresist is then exposed to a radiation source. The radiation source may be applied at a power of approximately 20 milli-Joules to 30 milli-Joules. After exposure, the negative tone photoresist is developed with an organic solvent. The portion of the negative tone photoresist that is exposed remains and the unexposed portions of the negative tone photoresist are removed. 
     The foregoing outlines features of several embodiments so that those skilled in the art may better understand the aspects of the present disclosure. Those skilled in the art should appreciate that they may readily use the present disclosure as a basis for designing or modifying other processes and structures for carrying out the same purposes and/or achieving the same advantages of the embodiments introduced herein. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the present disclosure, and that they may make various changes, substitutions, and alterations herein without departing from the spirit and scope of the present disclosure.