244  US 9,551,933 B2  243  (iii’) a step of developing the exposed film by using an  organic solvent-containing developer to form a negative  pattern.  The exposure in the step (ii) may be immersion exposure.  The pattern forming method of the present invention  preferably includes (iv) a heating step after the exposure step  (ii).  The antireflection film used may be either an inorganic  film type such as titanium, titanium dioxide, titanium nitride,  chromium oxide, carbon and amorphous silicon, or an  organic film type composed of a light absorber and a 40  polymer material. A commercially available organic antire› flection film such as DUV30 Series and DUV-40 Series  produced by Brewer Science, Inc. andAR-2, AR-3 andAR-5  produced by Shipley Co., Ltd. may be also used as the  organic antireflection film.  The pattern forming method of the present invention may  further include (v) a step of performing development by  using an alkali developer when the developer in the step (iii)  is an organic solvent-containing developer, and on the other  hand, may further include (v) a step of performing devel› opment by using an organic solvent-containing developer  when the developer in the step (iii) is an alkali developer.  In the pattern forming method of the present invention,  the exposure step (ii) may be performed a plurality of times.  In the pattern forming method of the present invention,  the heating step (v) may be performed a plurality of times.  The resist film is formed of the above-described actinic  ray-sensitive or radiation-sensitive resin composition of the  present invention and, more specifically, is preferably  formed on a substrate. In the pattern forming method of the  present invention, the step of forming a film on a substrate  by using the actinic ray-sensitive or radiation-sensitive resin  composition, the step of exposing the film, and the devel› opment step can be performed by generally known methods.  For example, the composition is coated on such a sub› strate as used in the production of a precision integrated  circuit device, an imprint mold or the like (e.g., silicon/  silicon dioxide-coated substrate, silicon nitride and chro- mium-deposited quartz substrate) by using a spinner, a  coater or the like. The coating is thereafter dried, whereby an  actinic ray-sensitive or radiation-sensitive film can be  formed.  Before forming the resist film, an antireflection film may  be previously provided by coating on the substrate.  The pattern forming method also preferably includes,  after film formation, a pre-baking step (PB) before entering  the exposure step.  Furthermore, the pattern forming method also preferably  includes a post-exposure baking step (PEB) after the expo› sure step but before the development step.  As for the heating temperature, both PB and PEB are  preferably performed at 70 to 120°  C., more preferably at 80  to 110°  C.  The heating time is preferably from 30 to 300 seconds,  more preferably from 30 to 180 seconds, still more prefer› ably from 30 to 90 seconds.  The heating can be performed using a device attached to  an ordinary exposure/developing machine or may be per› formed using a hot plate or the like.  The reaction in the exposed area is accelerated by the  baking and in turn, the sensitivity or pattern profile is  improved.  It is also preferred to include a heating step (post baking)  after the rinsing step. By the baking, the developer and  rinsing solution remaining between patterns as well as in the  inside of the pattern are removed.  Such an additive is preferably, for example, an aliphatic  alcohol having a refractive index substantially equal to that  of water, and specific examples thereof include methyl  alcohol, ethyl alcohol and isopropyl alcohol. By virtue of  adding an alcohol having a refractive index substantially  equal to that of water, even when the alcohol component in  water is evaporated and its content concentration is changed,  the change in the refractive index of the liquid as a whole can  be advantageously made very small.  In the case of using water, an additive (liquid) capable of  decreasing the surface tension of water and increasing the  interface activity may be added in a small ratio. This additive  is preferably an additive that does not dissolve the resist  layer on the wafer and at the same time, gives only a  negligible effect on the optical coat at the undersurface of the  lens element.  The immersion liquid is preferably a liquid being trans- parent to light at the exposure wavelength and having as  small a temperature coefficient of refractive index as pos› sible in order to minimize the distortion of an optical image  projected on the film. In particular, when the exposure light  source is ArF excimer laser (wavelength: 193 nm), water is  preferably used in view of easy availability and easy handle› ability in addition to the above-described aspects.  In the case of performing immersion exposure, a step of  washing the film surface with an aqueous chemical may be  performed (1) before the exposure step after forming the  film on a substrate and/or (2) after the step of exposing the  film through an immersion liquid but before the step of  baking the film.  That is, the effect of immersion is equal to use of an  exposure wavelength of 1/n. In other words, in the case of  a projection optical system having the same NA, the depth  of focus can be made n times larger by immersion. This is  effective for all pattern profiles and furthermore, can be  combined with the super-resolution technology under study  at present, such as phase-shift method and modified illumi› nation method.  Examples of the actinic ray or radiation include infrared  light, visible light, ultraviolet light, far ultraviolet light,  X-ray, and electron beam. An actinic ray or radiation having,  for example, a wavelength of 250 nm or less, particularly  220 nm or less, is preferred. Such an actinic ray or radiation  includes, for example, KrF excimer laser (248 nm), ArF  excimer laser (193 nm), F$_{2 }$ excimer laser (157 nm), X-ray,  and electron beam. The actinic ray or radiation is preferably,  for example, KrF excimer laser, ArF excimer laser, electron  beam, X-ray or EUV light, more preferably electron beam,  X-ray or EUV light.  In the present invention, an immersion exposure method  can be applied in the step of performing exposure.  The immersion exposure method is a technique to  increase the resolution, and this is a technique of performing  exposure by filling a space between the projection lens and  the sample with a high refractive-index liquid (hereinafter,  sometimes referred to as an "immersion liquid").  As for the "effect of immersion", assuming that  A$_{0 }$ is the  wavelength of exposure light in air, n is the refractive index  of the immersion liquid for air,  8  is the convergence half› angle of beam and NA$_{0}$=sin 8, the resolution and the depth  of focus in immersion can be expressed by the following  formulae. Here, k$_{1 }$ and k$_{2 }$ are coefficients related to the  process.  (Resolution)~k $_{1 }${Ar/n )/NA$_{0 }$ (Depth of focus)~–k$_{2}$•(Ar/n)INAa2 