A basic compound may be added to the resist composi› tion. The addition of the basic compound to the resist composition is effective, for example, for reducing the rate of acid diffusion in the resist film, thus contributing to a further improvement in resolution. Exemplary basic com- pounds include primary, secondary and tertiary amine com› pounds, specifically amine compounds having a hydroxyl, ether, ester, lactone, cyano or sulfonic ester group, as described in JP-A 2008-111103, paragraphs [0146]-[0164] (U.S. Pat. No. 7,537,880) and compounds having a carbam- ate group as described in JP 3790649. Also useful are quenchers of polymer type as described in JP-A 2008- 239918 (U.S. Pat. No. 7,598,016). The polymeric quencher segregates at the resist surface after coating and thus enhances the rectangularity of resist pattern. In the immer- sion lithography where a protective film is applied on the resist film, the polymeric quencher is also effective for preventing any film thickness loss of resist pattern or round› ing of pattern top. An appropriate amount of the basic compound added is Oto 100 parts, more preferably 0.001 to 50 parts by weight per 100 parts by weight of the base resin. 

A surfactant may be added to the resist composition. The addition of the surfactant to the resist composition is effec› tive for facilitating or controlling coating operation. Exem› plary surfactants are described in JP-A 2008-111103, para- graphs [0165]-[0166]. An appropriate amount of the surfactant added is Oto 10 parts, more preferably 0.0001 to 5 parts by weight per 100 parts by weight of the base resin. 

An acetylene alcohol may be added to the resist compo› sition. Exemplary acetylene alcohols are described in JP-A 2008-122932, paragraphs [0179]-[0182]. An appropriate amount of the acetylene alcohol added is 0 to 5 parts by weight per 100 parts by weight of the base resin. Process 

The positive resist composition may be 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, prebake, exposure, and development. If necessary, any additional steps may be added. 

Specifically, the positive 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 or MoSi$_{2}$ ) by a suitable coating technique such as spin coating, roll coating, flow coating, dip coating, spray coating or doctor coating. The coating is prebaked on a hot plate preferably at a temperature of 60 to 150° C. for 10 seconds to 30 minutes, more 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. 

If desired, a protective film may be formed on the resist film. The protective film is preferably formed of an alkaline developer-soluble composition so that both formation of a resist pattern and stripping of the protective film may be achieved during development. The protective film has the functions of restraining outgassing from the resist film, filtering or cutting off out-of-band (OOB) light having a wavelength of 140 to 300 nm emitted by the EUV laser (other than 13.5 nm), and preventing the resist film from assuming T-top profile or from losing its thickness under environmental impacts. 

The resist film is then exposed to a desired pattern of high-energy radiation such as UV, deep-UV, EUV (wave› length 3 to 15 nm), EB, x-ray, soft x-ray, excimer laser light, y-ray or synchrotron radiation 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 0.1 to 100 µC/cm 2 , more preferably 0.5 to 50 µC/cm 2 . The resist film may be further baked (PEB) on a hot plate preferably at 60 to 150° C. for 10 seconds to 30 minutes, more preferably at 80 to 120° C. for 30 seconds to 20 minutes. Notably PEB is optional. 

Thereafter the resist film is developed in a developer for 3 seconds to 3 minutes, preferably 5 seconds to 2 minutes by conventional techniques such as dip, puddle and spray techniques. The resist film in the exposed area is dissolved in the developer whereas the resist film in the unexposed area is not dissolved. In this way, the desired positive pattern is formed on the substrate. It is appreciated that the resist composition of the invention is best suited for micro› patterning using such high-energy radiation as EB, EUV, x-ray, soft x-ray, y-ray and synchrotron radiation among others. 

Suitable developers are 0.1 to 10 wt%, preferably 2 to 5 wt% aqueous solutions oftetramethylammonium hydroxide (TMAH), tetraethylammonium hydroxide (TEAH), tet› rapropylanimonium hydroxide (TPAH) and tetrabutylam› monium hydroxide (TBAH). Using the developer in the form of an alkaline aqueous solution, a positive resist pattern is formed. 

Although TMAH aqueous solution is generally used as the developer, TEAH, TPAH and TBAH having a longer alkyl chain are effective in inhibiting the resist film from being swollen during development and thus preventing pattern collapse. The TMAH developer is most often used as 2.38 wt% aqueous solution, which corresponds to 0.26N. The TEAH, TPAH, and TBAH aqueous solutions should preferably have an equivalent normality. The concentration of TEAH, TPAH, and TBAH that corresponds to 0.26N is 3.84 wt %, 5.31 wt %, and 6.78 wt %, respectively. 

When a pattern with a line size of32 nm or less is resolved by the EB and EUV lithography, there arises a phenomenon that lines become wavy, lines merge together, and merged lines collapse. It is believed that this phenomenon occurs because lines are swollen in the developer and the thus expanded lines merge together. Since the swollen lines containing liquid developer are as soft as sponge, they readily collapse under the stress of rinsing. For this reason, the developer using a long-chain alkyl developing agent is effective for preventing film swell and hence, pattern col- lapse. 

In another embodiment, an organic solvent is used as the developer. A negative pattern can be formed from the resist composition by organic solvent development. The developer used to this end is at least one solvent selected from among 2-octanone, 2-nonanone, 2-heptanone, 3-heptanone, 4-hep› tanone, 2-hexanone, 3-hexanone, diisobutyl ketone, meth› ylcyclohexanone, acetophenone, methylacetophenone, pro- pyl acetate, butyl acetate, isobutyl acetate, pentyl acetate, butenyl acetate, isopentyl acetate, propyl formate, butyl formate, isobutyl formate, pentyl formate, isopentyl for› mate, methyl valerate, methyl pentenoate, methyl crotonate, ethyl crotonate, methyl propionate, ethyl propionate, ethyl 3-ethoxypropionate, methyl lactate, ethyl lactate, propyl lactate, butyl lactate, isobutyl lactate, pentyl lactate, isopen› tyl lactate, methyl 2-hydroxylsobutyrate, ethyl 2-hydroxy› isobutyrate, methyl benzoate, ethyl benzoate, phenyl acetate, benzyl acetate, methyl phenylacetate, benzyl for- mate, phenylethyl formate, methyl 3-phenylpropionate, ben› zyl propionate, ethyl phenylacetate, and 2-phenylethyl acetate. 

