Patent Application: US-201113583518-A

Abstract:
the present invention relates to a method the synthesis and utilization of random , cross - linked , substituted polystyrene copolymers as polymeric cross - linked surface treatments to control the orientation of physical features of a block copolymer deposited over the first copolymer . such methods have many uses including multiple applications in the semi - conductor industry including production of templates for nanoimprint lithography .

Description:
in the course of our efforts to employ non - traditional monomers for bcs , we became interested in the effect of surface energy on bc orientation . films thicker than 15 nm of polymer 3 ( fig3 ) were spin - coated , heated to cross - link through the azide functionality , and thoroughly rinsed to remove any non - cross - linked materials . surface energies of these films were obtained by goniometry with water , glycerol , and diiodomethane contact angles . several measurements were made over the entire wafer , and the error was consistently +/− 2 dyne / cm . fig4 displays these data and shows that the substituents affect the surface energy of the film . additionally , the surface energies of non - cross - linked homopolymer films of ps and pmma and a wafer cleaned with piranha were measured , and these values are consistent with the literature [ 2 , 13 ]. in one embodiments , the invention relates to the ps - b - pmma films of various thicknesses were coated on the pxsts . these were annealed and investigated by afm . the afm images display very different process windows for perpendicular orientation of the pxsts . the cl - substituted pxst resulted in perpendicular cylinders for block film thicknesses of 30 to 35 nm , and the pxst with a br substituent had a process window from 23 to 41 nm ( fig5 ). these process window results are similar to other polymeric surface treatments reported by nealey [ 14 ] and hawker and russell [ 10 , 15 , 16 ]. this leads to the conclusion that a pxst need not consist of the same monomers as the bc being coated . it is not intended that the present invention be limited to specific block polymers . however , to illustrate the invention , examples of various copolymers are provided . in one embodiment , the invention relates to the synthesis of the polystyrene - containing block copolymer “ ps - b - pmma .” ps - b - pmma was anionically synthesized via standard schlenk line techniques ( fig1 ) [ 11 , 12 ]. 1 h - nmr showed the resulting polymer is 31 mol % pmma , which corresponds to a volume fraction of 0 . 27 [ 17 ]. this is within the range for cylinder morphology [ 1 ]. the mn of the ps aliquot was 45 . 8 kda with a pdi of 1 . 18 ; the total molecular weight was 65 . 6 kda with a pdi of 1 . 18 . fig2 shows gpc chromatograms of the ps aliquot and ps - b - pmma . in one embodiment , the invention relates to the synthesis of p ( sr )- r - p ( sbnaz ). in a procedure similar to hawker et al . [ 9 ], several commercially available styrene derivatives were radically copolymerized with vinyl benzyl chloride to investigate the role of substituents on the surface energy of ps . upon isolation of 2 , nucleophilic substitution of the chloride with azide ion led to cross - linkable polymers 3 ( fig3 ). the presence of the azide was confirmed by ir , and the resulting polymers are described in table 1 . all reagents were purchased from sigma - aldrich chemical co . and used without further purification unless otherwise noted . thf was purchased from jt baker . 100 mm silicon wafers were purchased from silicon quest international . all 1 h and 13 c nmr spectra were recorded on a varian unity plus 400 mhz instrument . all chemical shifts are reported in ppm downfield from tms using the residual protonated solvent as an internal standard ( cdcl 3 , 1 h 7 . 26 ppm and 13 c 77 . 0 ppm ). molecular weight and polydispersity data were measured using an agilent 1100 series isopump and autosampler and a viscotek model 302 tetra detector platfoiin with 3 i - series mixed bed high mw columns against polystyrene standards . polymer solutions were filtered with 0 . 20 μm ptfe filters prior to spin coating . films were spin coated and baked on a brewer cee 100cb spincoater & amp ; hotplate . film thicknesses were determined with a j . a . woollam co , inc . vb 400 vase ellipsometer using wavelengths from 382 to 984 nm with a 70 ° angle of incidence . contact angles were measured with a ramé - hart , inc . nrl c . a . goniometer ( model # 100 - 00 ). a heraeus vacutherm type vt 6060 p from kendro was used to thermally anneal the films under reduced pressure . a digital instruments dimension 3100 atomic force microscope with nchr pointprobe ® non - contact mode tips with a force constant of 42 n / m was used to collect afm images . ps - b - pmma was synthesized as previously reported by sequential anionic polymerization of styrene and methyl methacrylate in thf at − 78 ° c . under ar atmosphere via standard schlenk line techniques [ 11 ]. the initiator was sec - buli ; diphenyl ethylene was used to properly initiate mma , and licl was added to suppress side reactions during mma propagation [ 12 ]. in a procedure adopted from hawker et al . [ 9 ], a substituted styrene ( 20 mmol ) and vinyl benzyl chloride ( 0 . 62 mmol ) were radically copolymerized in refluxing thf ( 20 ml ) for 48 h with enough aibn to obtain a theoretical mw of 25 kda . once polymer 2 was precipitated in 0 ° c . meoh , filtered , and dried in vacuo , the mol ratio of substituted styrene to vinyl benzyl chloride was determined by 1 h - nmr . taking into account this ratio and the mn as determined by gpc , polymer 2 ( 1 . 0 g ) and sodium azide ( 3 equiv / bncl ) were dissolved in dmf ( 20 ml ) and stirred overnight at room temperature ( rt ). the polymer was precipitated in meoh , filtered , redissolved in thf ( 10 ml ), and stirred with h 2 o ( 1 ml ) to remove any unreacted salts . finally , the polymer was isolated by precipitation in 0 ° c . meoh , filtered , and dried in vacuo to yield white powder 3 . typical yields over these two steps were 50 %; ir ( kbr ) 2100 cm - 1 . complete characterization is shown in table 1 . a film of p ( sr )- r - p ( sbnaz ) was spin coated from a 1 . 0 wt % solution in toluene at 3770 rpm for 30 sec onto a wafer that had been rinsed with ipa and acetone . the wafer was immediately baked at 250 ° c . for 5 min to cross - link the film . the wafer was then submerged in toluene for 2 min , blown dry , submerged again for 2 min , and blown dry . typical film thicknesses as determined by ellipsometry were 15 - 20 nm . contact angles were measured with h 2 o , diiodomethane , and glycerol , and analyzed via the young - dupre equation ( eq 1 ) and the acid - base surface energy model ( eq 2 ) [ 18 ]. γ sv = γ sl + γ lv cos θ − π eq eq 1 γ sv is the surface energy of the solid - vapor interface , γ sl is the interfacial energy of the solid - liquid interface , γ lv is the surface tension of the fluid , θ is the angle between the solid and liquid , and π eq is the equilibrium spreading pressure , which is approximately zero for polymeric surfaces . − γ 2 cos θ = γ 2 lw − 2 ( γ 1 lw γ 2 lw ) 1 / 2 + 2 [( γ 2 p + γ 2 p − ) 1 / 2 −( γ 1 p + γ 2 p − ) 1 / 2 −( γ 1 p − γ 2 p + ) 1 / 2 ] eq 3 briefly , eq 2 describes the interfacial energy between two components ( γ 12 ) as the sum of the dispersion ( γ 12 lw ) and acid - base components ( γ 12 ab ). eq 3 relates the surface energy of the film and cosine of the contact angle (− γ 2 cos θ ) to the dispersion ( γ 2 lw ), lewis acid ( γ 2 p + ), and lewis base components ( γ 72 p − ). using literature values for h 2 o , diiodomethane , and glycerol , a system of equations was solved to obtain the surface energy of the pxst films . a clean , surface - treated wafer was spin coated with a film of ps - b - pmma from toluene at various speeds and concentrations to give 20 - 70 nm films as determined by ellipsometry . once cast , the wafer shards were annealed at 170 ° c . under reduced pressure for 12 - 18 h . 1 . bates , f . s ., and fredrickson , g . h . 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