This invention
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relates to a photoresist composition that has a polymer containing esters of tertiary -butyl acrylate as acid-labile groups to produce high resolution photoresist patterns.
Photoresists containing copolymers of tertiary -butyl acrylate or methacrylate and hydroxy styrene groups
are well known.
tertiary- Butyl acrylate
retards the alkaline solubility of the resist film in the unexposed area.
photogenerated acid and heat
causes hydrolysis of the ester group, enhancing the alkaline solubility of the exposed area of the film.
some lithographic properties, such as shape of the profile, linked to alkaline solubility
improve as the amount of tertiary- butyl acrylate in the copolymer increases, other properties such as plasma-etch resistance suffer as the amount of hydroxy styrene is decreased.
the objective of this invention
is to provide novel polymers suitable for sub-0.18 &#; m lithography. These polymers have improved photosensitivity, line-edge roughness, PEB and PED sensitivity.
the polymers of this invention
are useful in photoresist/radiation-sensitive compositions that include a photoacid generator, a solvent, and optionally, a basic compound.
the polymers of this invention
are tertiary -butyl acrylate polymers comprising the monomeric units: where 0.5 &#; a &#; 0.7, 0.15 &#; b &#; 0.3, 0.1 &#; c &#; 0.2, 0.3 &#; b + c &#; 0.5;
R
is H or a C 1 -C 4 alkyl group;
R 1
is H, methyl or CH 2 OR 2 ; each R 3 is independently H, methyl, CH 2 OR 2 , CH 2 CN, CH 2 X, or CH 2 COOR 4 where X is Cl, I, Br or F;
R 2
is H or a C 1 -C 4 alkyl group;
R 4
is C 1 -C 4 alkyl group;
R 5
is an isobornyl, cyclohexyl methyl, cyclohexyl ethyl, benzyl, phenethyl or tetrahydrofurfural group.
a
is from 0.60 to 0.65; b is from 0.20 to 0.25; c is from 0.10 to 0.20; and b+c is from 0.35 to 0.40; R is H, R 1 is H, R 2 is H; each R 3 is independently H or methyl; and R 5 is an isobornyl group.
Examples of the monomeric unit
include, but are not limited to, hydroxy styrene and &#; -methyl hydroxy styrene.
Examples of the monomeric unit
include, but are not limited to, tertiary -butyl acrylate, tertiary -butyl methacrylate, di-tertiary -butyl itaconate, and tertiary -butyl hydroxymethylacrylate.
Examples of the monomeric unit
include, but are not limited to, cyclohexyl methyl (meth)acrylate, cyclohexyl ethyl (meth)acrylate, phenethyl (meth)acrylate, benzyl (meth)acrylate, isobornyl (meth)acrylate and tetrahydrofurfural (meth)acrylate.
novel polymers of this invention
can be employed in photoresist compositions, especially for compositions that are intended for use in dep UV photolithography.
the photoresist composition
will include a photoacid generator (PAG).
PAG
photoacid generator
the function of the PAG
is to produce an acid upon exposure to radiation/photolysis, thereby increasing alkali solubility of the polymer in a chemically amplified resist by removing acid-labile groups, thus generating an alkali soluble moiety.
photoacid generator compound
may be used in the photoresist composition.
the photoacid generator compound
may be, for example, onium salts such as diazonium, sulfonium, sulfoxonium and iodonium salts, and sulfone compounds, sulfonate compounds, sulfonimide compounds, diazomethane compounds, and disulfones.
suitable photoacid generator compounds
are disclosed in US-A-, US-A- , US-A-, US-A- and US-A- which are incorporated herein by reference.
the photoacid generator
is gererally used at about 0.5 parts to 20 parts by weight per 100 parts of polymer.
the photoresist composition of this invention
also includes a solvent.
the solvent
should be inert, should dissolve all components in the composition, should not undergo reaction with other components, and should be removed on drying after coating.
Suitable solvents
include, but are not limited to organic solvents, such as 1-methoxy-2-propanol acetate (PMA), 2-methoxy-1-propylene acetate, N-methylpyrrolidone (NMP), &#; butyrolactone (GBL), dimethyl-2-piperidone, diglyme, tetrahydrofuran (THF), propylene glycol monomethyl etheracetate (PGMEA), propylene glycol monomethylether (PGME), methyl ethyl ketone, methyl isobutyl ketone, 2-heptanone, cyclopentanone, cyclehexanone, 2-methoxyethanol, 2-ethoxyothanol, 2-ethoxyethyl acetate, I-methoxy-2-propyl a
the solvent
is generally about 100 to parts by weight per 100 parts by weight of polymer in the photoresist composition.
the composition of the present invention
may include a basic compound.
the basic compound
functions to scavenge protons present in the radiation sensitive composition prior to being irradiated by the actinic radiation.
the base
prevents attack and cleavage of the acid labile groups by the undesirable acids thereby increasing the performance and stability of the resist.
Suitable examples of basic compounds
are, for example, 1,5-diazobicyclo[4.3.0]non-5-ene (DBN), 1,8-diazobicyclo[5.4.0]undec-7-ene (DBU), 2,4,5-triphenylimidazole, trimethylpropanetris(2-methyl-aziridinepropionate), 1-cyclohexyl-3-(2-morpholonoethyl)-2-thiourea, Troger's Base, 1-amino-4-piperazine, 4-(3-aminopropyl)morpholine, 2-(aminophenyl)-6-methylbenzothiazole, tribenzylamine, 1,1,4,7,10,10-hexamethyltriethylenetetramine, thiomorpholine, 1,3-bis(3-pyridylmethyl)-2-thiourea, 4,4"-tetramethylenedipiperidine, aniline, N-methylaniline, N,N-dimethylaniline,
the basic compound
may be included at generally about 2 to 50 parts by weight per 100 parts by weight of the photoacid generator used in the photoresist composition.
the present invention
may further include one or more other additives.
Suitable additives
are, for example, surfactants, adhesion promoters, leveling agents, dyes, mixtures thereof, and the like.
the present invention
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includes a process for forming a relief pattern using the composition of the present invention.
the process
comprises the steps of: (a) coating on a suitable substrate, a photoresist composition comprising a tertiary -butyl acrylate polymer of this invention, a photoacid generator, a solvent, and optionally a basic compound, forming a coated substrate; (b) drying the photoresist composition; (c) imagewise exposing the coated substrate to actinic radiation; (d) post exposure baking the coated substrate at an elevated temperature; (e) developing the coated substrate with an aqueous developer, forming an imaged coated substrate; and (f) rinsing the imaged coated substrate.
a copolymer containing 60 mole percent of hydroxy styrene and 40 mole percent of tertiary -butyl acrylate
was purchased from TriQuest, LP.
a 500 mL three necked flask
was fitted with a temperature probe attached to a temperature controller, an adaptor for nitrogen and a reflux condensor.
the flask
was placed in an oil bath over a magnetic stirrer.
20.83 G of isobornyl acrylate and 64.88 g of acetoxy styrene along with 60 g of p-dioxane and 200 g isopropyl alcohol
were charged into the flask. Nitrogen gas was bubbled through the monomer solution for 30 minutes. The contents were stirred and the temperature of the reaction mixture was raised to 60°C. 2.92 G of benzoyl peroxide was charged and the reaction temperature was gradually increased to 78°C.
the reaction contents
were allowed to cool to 24°C.
the copolymer formed
was isolated from its solution by precipitation in mL of de-ionized water.
the isolated polymer
was washed with 800 mL of de-ionized water, filtered and dried in a vacuum oven.
a 500 mL three-necked flask
was fitted with a temperature probe attached to a temperature controller, an adaptor for nitrogen and a Dean-Stark apparatus with reflux condensor.
85 G of the dried polymer
was suspended in 300 g of methanol.
5 G of 10% sodium methoxide solution in methanol
was added.
Temperature of the reaction mixture
was raised to 66°C.
Methyl acetate formed
was removed by azeotropic distillation with methanol. Conversion of acetoxy styrene to hydroxy styrene was monitored by disappearance of IR peak at cm-1.
the reaction mixture
was cooled to room temperature (19°C).
Base-catalyst
was removed by stirring the solution with 10 g of Amberlyst ion-exchange (A-15) resin for 2 hours. Ion-exchange resin was removed by filtration. Hydroxy styrene/isobornyl acrylate copolymer was isolated by precipitation in mL of de-ionized water. The isolated polymer was washed three times with mL de-ionized water, filtered and dried in a vacuum oven at 60°C for 24 hours.
the copolymer
contained 79 mole% of hydroxy styrene and 21 mole% of isobornyl acrylate, as determined by 1H- and 13C-NMR. This polymer had a Mw of 14,467.
the resist components
were blended in amber colored glass bottles. All the components are the same for all the formulation, unless, stated otherwise.
Photoresist formulations
are described in Table 2: Formul ation type Polymer (amount) PAG used (amount) Base used (amount) Solvent (amount) I 13.2 g Triphenylsulfonium 2,4,6-triisopropyl benzenesulfonate (0.27 g) 2,4,5-triphenyl imidazole (0.018 g) PGMEA (86.5 g) II 12.94 g Triphenylsulfonium 2,4,6-triisopropyl benzenesulfonate (0.54 g) 1,5-diazobi-cyclo [4.3.0]non-5-ene (0.019 g) PGMEA (86.5 g) III 12.88g Triphenylsufonium-dodecylbenzene sulfonate (0.61 g
the wafers
were spin coated by applying 3 mL of photoresist formulations to the static six-inch wafers. The wafer was then spun to give a uniform film thickness of around &#; . These photoresist coated wafers were then baked (SB) at 140°C (unless otherwise stated) for 60 seconds to remove the residual solvents. The softbaked photoresist coated wafers were then exposed using 248 nm wavelength light on an ISI XLS 0.53 NA stepper. After completion of exposure, the wafers were subjected to a post exposure bake (PEB) at 140°C (unless otherwise stated) for 60 seconds.
PEB
post exposure bake
the wafers
were puddle or spray-developed using a 0.262 N tetramethylammonium hydroxide, aqueous developer.
a deionized water rinse
was applied for 20 seconds while spinning , followed by dry nitrogen gas to dry the wafer.
Dissolution rate data
were generated by static immersion development in 0.26 N TMAH using a Perkin Elmer, multiple channel Development Rate Monitor (DRM). Sixteen separate open frame exposures (zones) ranging from unexposed to 60 mJ/cm 2 were printed. The 256 channel raw data were reduced to 16 zones using DREAMS PC software. The results of DRM data are shown in Table 3.
DRM
Development Rate Monitor
Resist formulation type
I (see Table 2); SB/PEB: 130/135 °C for 60 seconds
Example Polymer
Example Polymer Composition Dark Film Erosion ( &#; ) 1 P1 Hydroxy styrene (60) t-butyl acrylate (40) 460 2 P10 Hydroxy styrene (71) isobornyl methacrylate(9) t-butyl acrylate (20) 491 3 P11 Hydroxy styrene (7-1) isobornyl acrylate (10) t-butyl acrylate (19) 848 4 P9 ) Hydroxy styrene (62) Isobornyl methacrylate(13) t-butyl acrylate (25) 100 5 P12 Hydroxy styrene (66) Isobornyl methacrylate(15) t-butyl acrylate (19) 120 6 P13 Hydroxy styrene (63) Isobornyl acrylate(12) t-butyl
the desirable, low dark film erosion
could be obtained with terpolymers containing hydroxy styrene 60-66% and isobornyl acrylate or isobornyl methacrylate levels of 12-15%.
Resist formulation type
I (see Table 2); SB/PEB: 130/135 °C for 60 seconds
Example Polymer
Example Polymer Example Polymer Composition E0 (mJ /cm 2 ) E0 pt (mJ/ cm 2 ) 1 P2 Hydroxy styrene (79) Isobornyl acrylate (21) >100 - 2 P3 Hydroxy styrene (68) Isobornyl methacrylate(21) t-butyl acrylate (11) >68 - 3 P13 Hydroxy styrene (63) Isobornyl methacrylate(12) t-butyl acrylate (25) 18. 5 34 The desirable photosensitivity of &#; 40 mJ/cm 2 was achieved with example P13.
PED sensitivity
was determined by measuring the 0.17- &#; m line-space features after 20 minutes delay between exposure and post-exposure baking (PEB) and at zero time-delay. The results are tabulated in Table 5.
Resists based on P4 and P5 polymers
do not show any change in the CD of 0.17 &#; m line/space pair, indicating good PED stability.
Plasma etching studies
were carried out on a LAM TCP- etcher.
the etching conditions
were 700 W (source), -20°C; 200 sccm Ar, 8 sccm CF 4 , 12 sccm CHF 3 : pressure 700 m torr.
Substrate used
DUV-30 (Brewer Science); thickness: 60 nm on Poly-Si (100 nm)/ Resist formulation type (from Table 2): I; Resist thickness: variable; SB/PEB: 130/135 °C; Feature Type/Size: 0.25 &#; m isolated line. Results are shown in Table 6.
Resist based on P10
retains 9% more film after etching through 100 nm Poly-Si and 60 nm of BARC compared to resist based on P1.
Example Polymer
Example Energy to size 0.15 &#; m isolated line mJ/cm 2 ultimate Resolution &#; m Formul ation Type (from Table 2) SB/PEB (°C) DOF (0.15 &#; m isolated line) 1 P1 18 mJ (to size 0.18 &#; m) 0.15 I 130/135 0.6 &#; m (0.18 &#; m line) 2 P4 30 mJ 0.13 II 140/140 0.6 &#; m 3 P7 20 mJ 0.13 II 140/140 0.5 &#; m
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