US 10,303,056 B2  60  59  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.  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.  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.  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.  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.  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.  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. 