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tetramethylol urea compounds having 1 to 4 methylol groups methoxymethylated and mixtures thereof, and tetramethoxyethyl urea. 

Suitable isocyanate compounds include tolylene diisocya› nate, diphenylmethane diisocyanate, hexamethylene diiso› cyanate and cyclohexane diisocyanate. Suitable azide com› pounds include 1,1 ’-biphenyl-4,4’-bisazide, 4,4’› methylidenebisazide, and 4,4’-oxybisazide. Examples of the alkenyl ether group-containing compound include ethylene glycol divinyl ether, triethylene glycol divinyl ether, 1,2- propanediol divinyl ether, 1,4-butanediol divinyl ether, tetramethylene glycol divinyl ether, neopentyl glycol divinyl ether, trimethylol propane trivinyl ether, hexanediol divinyl ether, 1,4-cyclohexanediol divinyl ether, pentaerythritol trivinyl ether, pentaerythritol tetravinyl ether, sorbitol tet› ravinyl ether, sorbitol pentavinyl ether, and trimethylol propane trivinyl ether. 

In the negative resist composition, the crosslinker is preferably added in an amount of 0.1 to 50 parts, more preferably 1 to 40 parts by weight per 100 parts by weight of the base polymer. 

In the resist composition of the invention, a quencher may be blended. The quencher is typically selected from con› ventional basic compounds. Conventional basic compounds include primary, secondary, and tertiary aliphatic amines, mixed amines, aromatic amines, heterocyclic amines, nitro› gen-containing compounds with carboxyl group, nitrogen› containing compounds with sulfonyl group, nitrogen-con› taining compounds with hydroxyl group, nitrogen› containing compounds with hydroxyphenyl group, alcoholic nitrogen-containing compounds, amide derivatives, imide derivatives, and carbamate derivatives. Also included are primary, secondary, and tertiary amine compounds, specifi› cally amine compounds having a hydroxyl, ether, ester, lactone ring, cyano, or sulfonic acid ester group as described in JP-A 2008-111103, paragraphs [0146]-[0164], and com› pounds having a carbamate group as described in JP 3 790649. Addition of a basic compound may be effective for further suppressing the diffusion rate of acid in the resist film or correcting the pattern profile. 

Onium salts such as sulfonium salts, iodonium salts and ammonium salts of sulfonic acids which are not fluorinated at a-position may also be used as the quencher. While an a-fluorinated sulfonic acid, imide acid, and methide acid are necessary to deprotect the acid labile group of carboxylic acid ester, an a-non-fluorinated sulfonic acid or a carboxylic acid is released by salt exchange with an a-non-fluorinated onium salt. An a-non-fluorinated sulfonic acid and a car› boxylic acid function as a quencher because they do not induce deprotection reaction. 

Another useful quencher is an onium salt of carboxylic acid having the formula ( 4): 

wherein R 4 " is a C $_{1 }$-C$_{40 }$ straight, branched or cyclic mon› ovalent hydrocarbon group which may contain a heteroa› tom, and MA+ is an onium ion which is typically a sulfo› nium, iodonium or ammonium ion. 

The preferred anion moiety of the carboxylic acid onium salt has the formula (5): 

<img src='content_image/909163.jpg'>

wherein R 402 and R 403 are each independently hydrogen, fluorine or trifluoromethyl, and R$^{404 }$is hydrogen, hydroxyl, a C$_{1 }$-C$_{35 }$ straight, branched or cyclic monovalent hydrocar› bon group which may contain a heteroatom, or a substituted or unsubstituted CcC$_{30 }$ aryl group. 

Also useful are quenchers of polymer type as described in U.S. Pat. No. 7,598,016 (JP-A2008-239918). The polymeric quencher segregates at the resist surface after coating and thus enhances the rectangularity of resist pattern. When a protective film is applied as is often the case in the immer› sion lithography, the polymeric quencher is also effective for preventing a film thickness loss of resist pattern or rounding of pattern top. 

The quencher is preferably added in an amount of 0 to 5 parts, more preferably Oto 4 parts by weight per 100 parts by weight of the base polymer. 

To the resist composition, a polymeric additive (or water repellency improver) may also be added for improving the water repellency on surface of a resist film as spin coated. The water repellency improver may be used in the topcoat› less immersion lithography. Suitable water repellency improvers include polymers having a fluoroalkyl group and polymers having a specific structure with a 1,1,1,3,3,3- hexafluoro-2-propanol residue and are described in JP-A 2007-297590 and JP-A 2008-111103, for example. The water repellency improver to be added to the resist compo› sition should be soluble in the organic solvent as the developer. The water repellency improver of specific struc› ture with a 1,1,1,3,3,3-hexafluoro-2-propanol residue is well soluble in the developer. A polymer having an amino group or amine salt copolymerized as recurring units may serve as the water repellent additive and is effective for preventing evaporation of acid during PEB, thus preventing any hole pattern opening failure after development. An appropriate amount of the water repellency improver is 0 to 20 parts, preferably 0.5 to 10 parts by weight per 100 parts by weight of the base polymer. 

Also, an acetylene alcohol may be blended in the resist composition. Suitable acetylene alcohols are described in JP-A 2008-122932, paragraphs [0179]-[0182]. An appropri› ate amount of the acetylene alcohol blended is 0 to 5 parts by weight per 100 parts by weight of the base polymer. Process 

The resist composition is used in the fabrication of various integrated circuits. Pattern formation using the resist composition may be performed by well-known lithography processes. The process generally involves coating, prebak› ing, exposure, post-exposure baking (PEB), and develop- ment. If necessary, any additional steps may be added. 

For example, the resist composition is first applied onto a substrate on which an integrated circuit is to be formed ( e.g., Si, SiO$_{2}$ , SiN, SiON, TiN, WSi, BPSG, SOG, or organic antireflective coating) or a substrate on which a mask circuit is to be formed (e.g., Cr, CrO, CrON, M0Si$_{2}$ , or SiO$_{2}$ ) by a suitable coating technique such as spin coating, roll coating, flow coating, dipping, spraying or doctor coating. The coating is prebaked on a hot plate at a temperature of 60 to 150° C. for 10 seconds to 30 minutes, preferably at 80 to 120° C. for 30 seconds to 20 minutes. The resulting resist film is generally 0.01 to 2.0 µm thick. 

The resist film is then exposed to a desired pattern of high-energy radiation such as UV, deep-UV, EB, EUV, x-ray, soft x-ray, excimer laser light, y-ray or synchrotron radia› tion, directly or through a mask. The exposure dose is preferably about 1 to 200 mJ/cm 2 , more preferably about 10 to 100 mJ/cm 2 , or about 0.1 to 100 µC/cm 2 , more preferably about 0.5 to 50 µC/cm 2 . The resist film is further baked 

