Patent Application
20140330031
The present invention relates to a first generation dendrimer (FGD) comprising a core group and a peripheral moiety linked to the core wherein peripheral moiety has a functional group which has been chemically modified for a resist application.
Potential applications of dendrimers are based on their molecular uniformity, multifunctional surface and presence of internal cavities. These properties make dendrimers suitable for a variety of high technology applications in in vitro diagnostics; as contrast agents for magnetic resonance; in the targeted delivery of therapeutic agents; as coating agents to protect or deliver drugs to specific sites in the body or as time-release vehicles for biologically active agents, as carriers in gene therapy and industrial applications such as catalysts or as resists in electron beam as well as optical lithography.
A photoresist is a light-sensitive material used in industrial processes, such as photolithography and photoengraving to form a patterned coating on a surface. The resists can be classified into two types namely negative resists and positive resists. A positive resist is one in which the portion of the photoresist that is exposed to light becomes soluble in the photoresist developer. The portion of the photoresist that is unexposed remains insoluble in the photoresist developer. On the contrary, a negative resist is a type of photoresist in which the portion of the photoresist that is exposed to light becomes insoluble in the photoresist developer. The unexposed portion of the photoresist is dissolved by the photoresist developer.
Use of low molecular weight resists such as dendrimers in electron beam lithography (EBL) is well known in the art. Most of the low molecular weight resists and dendrimers used for EBL contain free hydroxyl groups and reactive furan rings or Powderlink1174 (tetrakis(methoxylmethyl)-glycoluril. Crosslinking of these systems during post exposure bake (PEB) results in the generation of small gas molecules such as water vapor and methanol, which may lead to pattern deformation especially at lower feature sizes. It is therefore desirable to avoid crosslinking reactions which result in the release of low molecular weight products. The most widely used photoresist systems are based on the crosslinking of epoxy resins.
The crosslinking of negative photoresist containing epoxide groups is caused by the irradiation of a photoacid generator, which generates a reactive oxygen species that reacts with the epoxide moiety on a neighboring polymer chain, resulting in the formation of a cross-link and corresponding propagating cation. This chain reaction leads to highly sensitive resists with high cross-linking efficiencies (Argitis et al., 1998).
Negative photoresists based on the epoxy resins are used extensively in the electronics industry as they offer a unique combination of properties like high strength, thermal stability, moisture resistance, chemical and corrosion resistance, adhesion and requisite mechanical as well as electrical properties.
SU-8 is a negative tone epoxy photoresist, which provides good lithographic performance. It is extensively used for applications in lithography and for molding and packaging, however it suffers from certain limitations. The spin-coating of both thick and thin layers of SU-8 resist often does not result in homogenous films. Debonding after post-baking and development results from poor adhesion to substrate. Also cracking at the corners of the microstructures has been reported.
Conventional epoxy resin (SU-8) contains eight epoxide groups and has Tg 50° C. before crosslinking, which is enhanced to 200° C. or more when fully cross linked (Balakrishnan et al., 2006; Feng and Farris 2003). It is recognized that for negative photoresists, increase in Tg with crosslinking is desirable since increase in difference in Tg between the exposed and unexposed areas results in greater solubility difference, which can be expected to result in better resolution and contrast as well as low line edge roughness (LER). Bilenberg et al (2006) reported 24 nm features at a pitch 1:12.5 nm at 19.9 μC/cm2 using 100 kV beam energy. However, these resins suffer from brittleness, resulting from high cross link density, higher shrinkage and stress generated during crosslinking, which results in cracks and adhesion problems.
Apart from SU-8 negative tone photoresist, a number of polymeric negative photoresists have been used in the past. However, lithographic performance of polymeric resist is affected by many factors like high molecular weights, broad molecular weight distribution, chain entanglement which results in poor performance especially irregularity of patterns.
Efforts are therefore underway to develop newer epoxy based resist for EBL. The negative resist based on calix[4]arene bearing epoxide was reported by Sailer et at (2004). The resist was processed by EBL at 80 μC/cm2 and 30 kV beam energy. 25 nm lines and 35 nm dots were resolved when pitch was set more than 150 nm. But the contrast was low (2.1).
The crosslink density can be manipulated by the choice of the peripheral moiety and number of hydroxyl or epoxide groups. Haba et al., (1999) reported dendrimer based on Calix[4]resorcinarene containing 16-hydroxyl groups at the periphery for optical lithography.
Since the solubility of this dendrimer in aqueous tetramethyl ammonium hydroxide solutions was very high, only a very dilute solution could be used as a developer. To overcome this problem another dendrimer containing 6-hydroxyl groups at the periphery was used (Kamimura et al., 2005). Decreasing peripheral hydroxyl groups from 16 to 6, enabled reduce the feature size from 3 μm to 1 μm.
Inspite of these developments there is a need in the art to design photoresists that can overcome the limitation of the dendrimers reported in the past for the lithographic application and enable fabrication of patterns upto 30 nm and a pitch 1:1, that can be used for EBL applications.
In accordance with the above, in one aspect, the present invention provides first generation dendrimers having 1,3,5-trisbromo methylbenzene as a core using different rigid groups such as bisphenol, trisphenol (1, 1, 1-tris (4-hydroxyphenyl) ethane) and 1, 5 dihydroxy naphthalene as peripheral groups to manipulate Tg from 38 to 85° C.
According to the invention, the choice of peripheral groups allows number of the peripheral hydroxyl groups to be varied. In case of bisphenol and naphthalene based dendrimers three hydroxyl groups are present on the periphery, while in the case of 1, 1, 1-tris (4-hydroxyphenyl) ethane) six hydroxyl groups are present on the periphery. Polar ether linkage is introduced between the core and the peripheral groups to enhance adhesion.
Terminal hydroxyl groups on the periphery were subsequently reacted with epichlorohydrin to obtain epoxy function and yield a negative photoresist or conjugated with t-BOC to yield positive photoresists viz. G1-Tris-t-BOC, G1-Bis-t-BOC and G1-Dhn-t-BOC.
In another aspect, the FGDs prepared according to the invention are evaluated for their applications as negative as well as positive tone electron beam resist.
In an embodiment the present invention provides a first generation dendrimers comprising 1,3,5-trisbromo-methylbenzene as the core and dense, bulky, rigid units selected from Trisphenol (1, 1, 1-tris-p-4-hydroxyphenyl ethane), bisphenol-A and 1,5-dihydroxy naphthalene units at the periphery, wherein the peripheral aromatic rigid molecules are connected to the central core through an ether linkage.
In another embodiment the present invention provides a first generation dendrimers wherein the dendrimers based on trisphenol (1, 1, 1-tris-p-4-hydroxyphenyl ethane) comprise six hydroxyls at the periphery.
In another embodiment the present invention provides a first generation dendrimers wherein the dendrimers based on bisphenol-A and 1,5-dihydroxy naphthalene comprise three hydroxyl at the periphery.
In yet another embodiment the present invention provides a first generation dendrimers wherein the dendrimers are further conjugated with either epoxide or with tert-BOC to obtain negative or positive photoresists respectively.
In yet another embodiment the present invention provides a first generation dendrimers wherein the negative photoresists are selected from the group consisting of G1-Tris-epoxide, G1-Bis-epoxide and G1-Dhn-epoxide.
In yet another embodiment the present invention provides a first generation dendrimers wherein positive photoresists are selected from the group consisting of G1-Tris-t-BOC-100, G1-Tris-t-BOC-80, G1-Tris-t-BOC-60, G1-Tris-t-BOC-50, G1-Bis-t-BOC-100, BOC-80, G1-Bis-t-BOC-60, G1-Bis-t-BOC-50, G1-Dhn-t-BOC-100, G1-Dhn-t-BOC-80, G1-Dhn-t-BOC-60 and G1-Dhn-t-BOC-50.
In yet another embodiment the present invention provides a first generation dendrimers wherein the yield of positive photoresist is obtained in order of ≧65%.
In yet another embodiment the present invention provides a first generation dendrimers wherein glass transition temperature of positive photoresists is in the range of 45° C. to 130° C.
In yet another embodiment the present invention provides a first generation dendrimers wherein the molecular weights of the positive photoresists are in the range of 700 to 1700.
In yet another embodiment the present invention provides a first generation dendrimers wherein (G1-Tris-t-BOC 80), (G1-Bis-t-BOC 80) and (G1-Dhn-t-BOC 80) having contrast γ=2.50, γ=2.09 and γ=1.66 respectively in presence of 10 wt % PAG.
In a further embodiment the present invention provides a first generation dendrimers wherein (G1-Tris-t-BOC 80), (G1-Bis-t-BOC 80) and (G1-Dhn-t-BOC 80) having sensitivity 50 μC/cm2; 60 μC/cm2 and 80 μC/cm2 respectively at 20 keV electron beam acceleration.
In a further embodiment the present invention provides a process for synthesis of negative photoresists according to claim 3, comprises reacting phenols/naphthols with 1,3,5-tris-bromomethylbenzene in the presence of potassium carbonate in DMF; conjugating the peripheral hydroxyls with epichlorohydrin using KOH as a base and PEG-400 as a phase transfer catalyst.
In a further embodiment the present invention provides a process wherein the molecular weights of the negative photoresists are in the range of 750-1400.
In a further embodiment the present invention provides a process wherein the glass transition temperature of negative photoresists is in the range of 60° C. to 90° C.
In a still further embodiment the present invention provides a process wherein the yield of negative photoresist is obtained in the order of >90%.
In a still further embodiment the present invention provides a process wherein the negative photoresists with 10 wt % PAG content shows a sensitivity of 35 μC/cm2.
In a still further embodiment the present invention provides a process wherein negative photoresists having resist etching rate in the range of 0.23 to 0.30.
In accordance with the need, the instant invention provides first generation dendrimers starting with 1,3,5-trisbromo-methylbenzene as the core and dense, bulky, rigid units selected from Trisphenol (1, 1, 1-tris-p-4-hydroxyphenyl ethane), bisphenol-A and 1,5-dihydroxy naphthalene units at the periphery. The peripheral aromatic rigid molecules are connected to the central core through an ether linkage.
Accordingly, in one embodiment, first generation dendrimer (FGD) based on trisphenol has six hydroxyls at the periphery.
In another embodiment, first generation dendrimers based on bisphenol-A and 1,5-dihydroxy naphthalene have three hydroxyl at the periphery. This variation at the periphery helps to vary crosslink density. Also, Tg could be manipulated by the choice of the peripheral aromatic group.
In another embodiment, the terminal hydroxyls in both the cases were reacted with epichlorohydrin to yield negative resists which were processed by EBL. These negative tone e-beam resists can be used to fabricate structures upto 30 nm width at a pitch 1:1.
Accordingly, in the instant invention ether functionality on the benzene core as shown in
The molecular weights of the negative photoresists were found to be in the range of 750-1400; whereas the glass transition temperature of negative photoresists was measured in the range of 60° C. to 90° C.
Further the yield of negative photoresists synthesiszed by the said process was obtained in the order of >90%.
In another preferred embodiment, the terminal hydroxyls in all the three cases were conjugated with t-BOC using procedures reported in literature (Hansen and Riggs, 1998) to yield positive photoresists viz. G1-Tris-t-BOC, G1-Bis-t-BOC and G1-Dhn-t-BOC. Degree of conjugation was controlled by controlling the amount t-BOC in the feed. The molecular weights of the FGDs are summarized in Table 2.
The molecular weights of the positive photoresists were found to be in the range of 700 to 1700, whereas glass transition temperature of positive photoresists was measured in the range of 45° C. to 130° C.
Further the yield of positive photoresists disclosed in Table 2 was obtained in order of ≧65%.
In yet another preferred embodiment, the first generation dendrimers prepared according to the invention have been evaluated for their negative as well as positive tone electron beam resist as well as negative for optical resist.
The resists based on 1, 1, 1-tris-p-4-hydroxyphenyl ethane and bisphenol-A evaluated as negative photoresist could resolve 30 nm lines at a pitch 1:1. The negative tone resists based on FGDs were evaluated for optical lithography. Reliable reproduction of structures with minimum feature size of 4.3 μm was possible using FGDs. An RIE process was used to check resist stability and the RIE results based on FGDs show greater stability compared to SU-8.
Further, low molecular weights FGDs varying in t-BOC functionality have been demonstrated to function as positive electron beam resist. Sensitivity of 50 μC/cm2 and contrast γ=2.5 in electron beam lithography in thin layers (70 nm) with dendrimer based on trisphenol has been demonstrated. Patterning of 30 nm lines with 30 nm pitch on silicon substrate was achieved successfully.
Following examples are given by way of illustration and therefore should not be construed to limit the scope of the invention.
Trisphenol 47 g (0.156 moles) was dissolved in 400 ml DMF, 97 g (0.702 moles) of anhydrous potassium carbonate was added and stirred for 30 min and maintained at 65° C., 2.8 g (7.8×10−3 moles) of 1, 3, 5-trisbromomethyl benzene in 20 ml DMF was added drop wise over 40 min. After the addition was complete, stirring was maintained for 12 h. DMF was recovered on rotary evaporator and reaction mixture was extracted with ethyl acetate. The solvent was evaporated and the G1-Tris formed was purified by column chromatography, using petroleum ether and ethyl acetate (70:30 v/v) as elutant.G1-Tris yield was 8.50 g (85%).
1H-NMR spectrum of G1-Tris in acetone-4 indicate complete disappearance of the peak at 4.50 ppm corresponding to methylene in 1, 3, 5-trisbromomethyl benzene and appearance of the peak at 5.11 ppm confirms formation of G1-Tris. Peak at 9.28 ppm corresponds to the aromatic hydroxyl functionality of Trisphenol unit and at 7.52 ppm to the aromatic protons of central benzene unit, which confirms conjugation of trisphenol and benzyl groups. It was thus concluded that, all benzyl bromide groups were converted to corresponding hydroxyl groups of G1-Tris.
25.5 g (0.112 moles) bisphenol-A, 47g (0.336 moles) of K2CO3 in 150 ml DMF and 2 g (5.6×10−3moles) of 1, 3, 5-trisbromomethyl benzene in 20 ml DMF were reacted as described above. G1-Bis yield was 5.00 g (87%).
1H NMR (DMSO-d6): 8.19 δ(3H, -OH), 6.7-7.19 (24H, phenolic protons), 7.56 (3H, benzylic protons), 5.13 (6H, Ph-CH2), 1.62 (18H, —CH3).
18 g (0.112 moles) 1, 5-Dhn, 47 g (0.336 moles) of K2CO3 in 150 ml DMF and 2 g (5.6×10−3 moles) of 1, 3, 5-trisbromomethyl benzene in 20 ml DMF were reacted as described above G1-Dhn yield was 3.80 g (81%).
1H NMR (DMSO-d6): 9.10 δ(3H, —OH), 6.94-7.85 (18H, naphthalene ring protons), 7.88 (3H, benzylic protons), 5.42 (6H, Ph-CH2).
5 g (5×10−3 moles) G1-Tris, 0.05 g polyethylene glycol (PEG-400) as a phase transfer catalyst and 50 ml epichlorohydrin were added to a 100 ml two necked flask equipped with a stirrer. The contents were heated to 70° C. for 1 h. To this reaction mixture dilute aqueous potassium hydroxide solution (KOH) 1.70 g (3×10−2 moles) in 10 ml water was added drop wise over 40 min. After addition of alkali was complete, the reaction was continued at 60° C. for further 2 h. The reaction mixture was filtered and the organic phase was washed with water three times and dried over anhydrous sodium sulphate. Excess epichlorohydrin was recovered over rotary evaporator under vacuum to yield a semisolid mass, which was then precipitated from pet ether. The product was purified by dissolving it in THF and reprecipitated from pet ether to recover a colorless product. The yield of G1-Tris-epoxide was 7.50 g (97%).
1H-NMR spectrum of G1-Tris-epoxide in CDCl3 shows that peak at 9.28 ppm corresponding to the aromatic hydroxyl is replaced by peaks corresponding to epoxide ring protons (2.72-4.2 ppm), and confirms conjugation of epoxide groups.
The compound was prepared by the same method used for G1-Tris-epoxide using 2 g (2.5×10−3 moles) G1-Bis, 0.02 g polyethylene glycol (PEG-400) as a phase transfer catalyst, 20 ml epichlorohydrin and potassium hydroxide 0.63 g (1.1×10−2 moles) in 4 ml water. G1-Bis-epoxide yield was 3.30 g (98%).
1H NMR (CDCl3-d6); δ [ppm]: 6.79-7.15 (24H, phenolic protons), 7.44 (3H, benzylic protons), 5.04 (6H, Ph-CH2), 1.63 (18H, —CH3), 2.72 to 2.92 ppm (6H, multiplet, protons of methylene in the oxirane ring), 3.43 ppm (3H, multiplet, protons of methine in the oxirane ring), 3.89 to 4.19 ppm (6H, multiplet, protons of methylene connecting the phenoxy and the oxirane ring),
G1-Dhn-epoxide was prepared from, 2 g (3.36×10−3moles) G1-Dhn, 0.02 g polyethylene glycol (PEG-400) as a phase transfer catalyst and 20 ml epichlorohydrin and potassium hydroxide 0.85 g (1.5×10−2 moles) in 5 ml water. G1-Dhn-epoxide yield was 2.60 g (93%).
1H NMR (CDCl3); δ [ppm]: 6.79-7.15 (24H, naphthalene ring protons), 7.44 (3H, benzylic protons), 5.29 (6H, Ph-CH2), 2.83 to 2.99 ppm (6H, multiplet, protons of methylene in the oxirane ring), 3.47 ppm (3H, multiplet, protons of methine in the oxirane ring), 3.86 to 4.41 ppm (6H, multiplet, protons of methylene connecting the naphthalene and the oxirane ring).
3 g (2.9×10−3 moles) of G1-Tris and 3.2 g (2.6 10−2 moles) DMAP were dissolved in 25 ml NMP and stirred for 20 min. A solution of di-t-BOC 5.7 g (2.6×10−2 moles) in 10 ml NMP was then added drop wise to the solution at 0-5° C. After complete addition, the mixture was stirred for 24 h at room temperature. The product was precipitated from methanol. White powder was obtained after drying the product in a vacuum oven at 45° C. G1-Tris-t-BOC-100 was obtained in good yield, 3.7 g (78%).
1H NMR in CDCl3 shows that after conjugation with t-BOC peak at 9.28 ppm corresponding to aromatic hydroxyls, was replaced by the peak at 1.54 ppm corresponding to the methyl protons of t-BOC units. All phenolic hydroxyl groups at the periphery were converted to corresponding t-BOC group.
The compound was prepared by same method used for G1-Tris-t-BOC100 dendrimer from, 3 g (3×10−3 moles) of G1-Tris and 2.64 g (0.216 moles) DMAP, 25 ml NMP and di-t-BOC 6.16 g (2.8×10−2 moles) in 10 ml NMP. Yield 3.3 g (75%).
1H NMR (DMSO-d6); δ [ppm]: 6.64-7.09 (36H, aromatic protons), 7.49 (3H, benzylic protons), 5.09 (6H, Ph-CH2), 2.08 (9H, —CH3), 1.47 (40H, —CH3), 9.30 (2H, Ph-OH).
The compound was prepared by same method used for G1-Tris-t-BOC100 dendrimer from, 3 g (3×10−3 moles) of G1-Tris and 1.98 g (0.135 moles) DMAP, 25 ml NMP and di-t-BOC 4.62 (2.1×10−2 moles) in 10 ml NMP. Yield 2.98 g (73%).
1H NMR (DMSO-d6); δ [ppm]: 6.65-7.08 (36H, aromatic protons), 7.50 (3H, benzylic protons), 5.10 (6H, Ph-CH2), 2.09 (9H, —CH3), 1.48 (29H, —CH3), 9.25 (2.5H, Ph-OH).
The compound was prepared by same method used for G1-Tris-t-BOC-100 dendrimer from, 3 g (3×10−3 moles) of G1-Tris and 1.65 g (0.162 moles) DMAP, 25 ml NMP and di-t-BOC 3.85 (1.75×10−2 moles) in 10 ml NMP. Yield 2.96 g (76%).
1H NMR (DMSO-d6); δ [ppm]: 6.61-7.09 (36H, aromatic protons), 7.49 (3H, benzylic proton), 5.09 (6H, Ph-CH2), 2.08 (9H, —CH3), 1.47 (26H, —CH3), 9.25 (3H, Ph-OH).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (3.75×10−3 moles) of G1-Bis and 2 g (1.65×10−2 moles) DMAP, 25 ml NMP and di-t-BOC 5 g (2.27×10−2 moles) in 10 ml NMP. Yield 3.27 g (79%).
1H NMR (DMSO-d6); δ [ppm]: 6.90-7.24 (24H, aromatic protons), 7.47 (3H, benzylic protons), 5.08 (6H, Ph-CH2), 1.60 (18H, —CH3), 1.47 (27H, —CH3).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (3.75×10−3 moles) of G1-Bis and 1.6 g (1.32×10−2 moles) DMAP, 25 ml NMP and di-t-BOC 4 g (1.81×10−2 moles) in 10 ml NMP. Yield 2.97 g (76%).
1H NMR (DMSO-d6); δ [ppm]: 6.90-7.19 (24H, aromatic protons), 7.47 (3H, benzylic protons), 5.07 (6H, Ph-CH2), 1.60 (18H, —CH3), 1.47 (14 H, —CH3) 9.17 (1.5H, Ph-OH).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (3.75×10−3 moles) of G1-Bis and 1.2 g (9.9×10−3 moles) DMAP, 25 ml NMP and di-t-BOC 3 g (1.36×10−2 moles) in 10 ml NMP. Yield 2.65 g (72%).
1H NMR (DMSO-d6); δ [ppm]: 6.62-7.19 (24H, aromatic protons), 7.47 (3H, benzylic protons), 5.07 (6H, Ph-CH2), 1.55-1.60 (18H, —CH3), 1.47 (11 H, —CH3) 9.17 (1.7H, Ph-OH).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (3.75×10−3 moles) of G1-Bis and 1g (8.2×10−3 moles) DMAP, 25 ml NMP and di-t-BOC 2.5 g (1.13×10−2 moles) in 10 ml NMP. Yield 2.50 g (70%).
1H NMR (DMSO-d6); δ [ppm]: 6.62-7.19 (24H, aromatic protons), 7.47 (3H, benzylic protons), 5.07 (6H, Ph-CH2), 1.55-1.60 (18H, —CH3), 1.46 (9H, —CH3) 9.16 (2H, Ph-OH).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (4.5×10−3 moles) of G1-Dhn and 2.4 g (1.95×10−2 moles) DMAP, 25 ml NMP and di-t-BOC 5.85 g (2.7×10−2 moles) in 10 ml NMP. Yield 3.26 g (72%).
1H NMR (DMSO-d6); δ [ppm]: 8.16 (3H, protons on 8th carbon of naphthalene ring), 7.75 (3H, protons on 4th carbon of naphthalene ring), 6.59-7.19 (6H, protons on 2nd and 6th carbon of naphthalene ring), 7.63 (3H, protons on 3rd carbon of naphthalene ring), 7.34 (3H, protons on 7th carbon of naphthalene ring), 7.46 (3H, benzylic protons), 5.43 (6H, Ph-CH2), 1.52 (27H, CH3).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (4.5×10−3 moles) of G1-Dhn and 1.92 g (1.56×10−3 moles) DMAP, 25 ml NMP and di-t-BOC 4.68 g (2.1×10−3 moles) in 10 ml NMP. Yield 2.78 g (66%).
1H NMR (DMSO-d6); δ [ppm]: 6.59-8.12 (18H, naphthalene ring protons, same splitting of ring protons was observed as discussed in section 2.3.12), 7.46 (3H, benzylic protons), 5.42 (6H, Ph-CH2), 1.52 (17H, CH3), 10.11 (1H, hydroxyl proton of naphthalene).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (4.5×10−3 moles) of G1-Dhn and 1.44 g (1.17×10−2 moles) DMAP, 25 nil NMP and di-t-BOC 3.57 g (1.6×10−2 moles) in 10 ml NMP. Yield 2.66 g (67%).
1H NMR (DMSO-d6); δ [ppm]: 6.59-8.12 (18H, naphthalene ring protons), 7.46 (3H, benzylic protons), 5.42 (6H, Ph-CH2), 1.52 (14H, CH3), 10.11 (1.54H, hydroxyl protons of naphthalene).
The compound was prepared by same method used for G1-Tris-t-BOC dendrimer from, 3 g (4.5×10−3 moles) of G1-Dhn and 1.2 (9.7×10−3 moles) DMAP, 25 ml NMP and di-t-BOC 2.97 g (1.3×10−2 moles) in 10 ml NMP. Yield 2.44 g (65%).
1H NMR (DMSO-d6); δ [ppm]: 6.59-8.12 (18H, naphthalene ring protons), 7.46 (3H, benzylic protons), 5.42 (6H, Ph-CH2), 1.52 (12H, CH3), 10.11 (1.84H, hydroxyl protons of naphthalene).
Thermal stability of the FGDs was evaluated using TGA-7, Perkin Elmer at a heating rate 10° C./min under nitrogen atmosphere. The temperature Ts corresponding to 5 wt % loss was considered as the index of thermal stability (Table 1).
Tgs of FGDs were determined using TA Instruments DSC Q-10 in nitrogen atmosphere at a heating rate 10° C./min and the data are presented in Table 1.
The FGDs were dissolved in propylene glycol methyl ether acetate (PGMEA) to obtain a 5 wt. % solution. Commercially available triphenylsulfonium perfluoro-1-butanesulfonate (PAG) 5 wt. % and 10 wt. % on the basis of resist was used. The resulting solutions were filtered through a 200 nm filter and spin coated onto 2 inch oxidised silicon wafers (oxide thickness 200 nm) at 6000 rpm for 30 sec, leading to a film thickness of 66 nm for G1-Tris-epoxide, 63 nm for G1-Bis-epoxide and 62 nm for G1-Dhn-epoxide as measured by Raith-150Two SEM. This was subjected to prebaking at 70° C. for 5 min on hotplate and then exposed to e-beam using Raith-150Two. Post exposure baking was done at 90° C. for 60 sec on a hotplate. The wafers were then developed using propylene glycol methyl ether acetate (SU-8 developer) for 30 sec and rinsed with IPA for 10 sec and dried with a nitrogen blower.
The sensitivity curves for the negative tone resists on exposure to e-beam at 20 kV acceleration voltage, 20 μm aperture, resulting in a beam current of 170 pA are shown in
Resist sensitivity was calculated by measuring the thickness of the lines patterned at various dose rates using Raith 150Two SEM. Sensitivity was defined as the dose D1 at which thickness of the developed pattern was the same as that of spin coated film.
The resist containing 5 wt % PAG shows a sensitivity of 70 μC/cm2 for G1-Tris-epoxide, 85 μC/cm2 for G1-Bis-epoxide and 95 μC/cm2 for G1-Dhn-epoxide (
The contrast (γ) was calculated from the formula γ−1=log D1−log D0 where D0 is the highest dose where the resist is not crosslinked. D1 is the dose where the resist height after development is the same as the thickness of spin coated film. The resists show a sensitivity of 35 μC/cm2 and lines upto 30 nm and pitch 1:1 could be resolved with high contrast 3.3 at 20 kV. The results are summarized in Table 3.
Oxidised silicon wafers were used to enhance adhesion of photoresist to the substrate. Resists containing 5 wt. % FGDs and 10 wt. % triphenylsuiphonium-nanoflate (PAG) on the basis of FGDs were spin-coated onto two inch silicon wafers at 6000 rpm which formed 66 nm (G1-Tris-epoxide), 63 nm (G1-Bis-epoxide) and 62 nm (G1-Dhn-epoxide) thick films respectively. Soft baking of the coated films on the silicon wafer was carried out on hot plate at 70° C. for 5-min.The resists were patterned using e-beam at 20 kV acceleration voltage, 20 μm aperture and the dose 35 μC/cm2at beam current 170 pA. Post exposure bake (PEB) was carried out at 90° C. for one min. Post exposure baked films were developed with propylene glycol methyl ether acetate (SU-8 developer MicroChem) for 20 sec, followed by a 10 sec immersion in isopropyl alcohol.
LER was calculated using the formula reported by Leunissen et al., (2004) for feature size 100, 50 and 30 nm.
The LER values calculated are based on an average of 20 adjacent points along the lines and are summarized in Table 4.
The resists containing 14.4 wt % dendrimer (G1-Tris-epoxide, G1-Bis-epoxide and G1-Dhn-epoxide) solutions in PGMEA were used to match the composition of SU-8 (0.5).
Triarylsulphonium hexafluoroantimonate (PAG) which is also used in SU-8 (0.5), 10 wt % on the basis of FGDs was added. SU-8 (0.5) was used as resist for comparison. Standard RCA (Radioactive Corporation of America) cleaned 2-inch silicon wafers were used, which were cleaned by immersion in hydrofluoric acid (HF) and washed with water. Wet oxidation was carried out to grow 490 nm thick silicon dioxide layer. This was followed by spin-coating of resists at 6000 rpm. SU-8 (0.5) was first spin-coated onto the substrate to form resist layer 460 nm thick. The FGDs were spin-coated onto the silicon substrate to form a resist layers 200 nm thick for G1-Tris-epoxide, 150 nm for G1-Bis-epoxide and 110 nm for G1-Dhn-epoxide. Coated samples were processed using a standard procedure which involved pre-baking on a hotplate at 70° C. for 5 min and 90° C. for 1 min, followed by exposure using a soft-contact mask-aligner of 60 mJ/cm2 intensity at 365 nm wavelength for 5 sec. Post exposure bake (PEB) was carried out at 60° C. for 1 min and 95° C. for 1 min to accelerate cross linking of the exposed areas of the photoresist. The patterns were developed using PGMEA (SU-8 developer) at room temperature rinsed with isopropanol and dried with a nitrogen blower.
The FGDs based on trisphenol and bisphenol could resolve defect free features after development.
(A), 1:2 (B), and 1:1(C). Thus trisphenol as well as bisphenol based FGDs could be used to pattern features upto 30 nm at the pitch 1:1.
To transfer the resist pattern into silicon, reactive ion etching process was conducted. The process was carried out for five minutes. Etch rates of resist and SiO2 was measured using SEM by measuring the resist thickness. In addition, etch rates of these resists were also examined with a standard AFM. Thickness of the oxide layer plus resist layer (C) was measured by SEM. The etch rate was calculated by the difference of the thickness before (C) and after (F) etching as shown in
The etch rate in resist and silicon oxide are described in Table 5
The RIE results were compared with SU-8.
A=Resist thickness before RIE (AFM measurements); B=Dioxide thickness before RIE (SEM measurements); C=Total thickness before RIE (A+B); D=Thickness after RIE (resist+dioxide) (AFM measurements); E=Dioxide thickness after RIE (SEM measurements); F=Total thickness after RIE (D+E); G=Resist etching rate (C−F); H=Dioxide etching rate (B−E).
Dendrimers and their t-BOC conjugates were evaluated usingTGA-7, Perkin Elmer at 10° C./min under nitrogen atmosphere. The plots in the
Tgs of dendrimers were determined by TA Instruments DSC Q-10 in nitrogen atmosphere at a heating rate 5° C./min and the data are presented in Table-6. The traces indicate no melting peak confirming amorphous nature of the materials.
Adhesion of polymers on the silicon substrate was evaluated by calculating work of adhesion (Wad) from the following eqn.
W
ad=2{(γpd·γsd)1/2+(γph·γsh)1/2} (1)
(Where γ: surface free energy, P: polymer, S: substrate, d: dispersion force, h: hydrogen bonding force). To solve this equation, the contact angles (θ) of water and diiodomethane were measured. The values of contact angle and work of adhesion for various t-BOCconjugated FGDs films on silicon wafer are given in Table-7.
The FGDs were dissolved in propylene glycol methyl ether acetate (PGMEA) making a 5 wt % solution. Commercially available triphenylsulfonium perfluoro-1-butanesulfonate (10 wt. % with respect to resist) was used as PAG. The resulting solutions were filtered through a 0.2 μm filter. Then, the solutions were spin coated onto a 2 inch silicon wafers at 6000 rpm, for 30 s. This was prebake at 70° C. for 5 min, and then exposed using e-beam radiation. After exposure, the wafer was baked at 90° C. for 60 seconds. Positive tone images were developed in an aqueous solution developer (0.26 N TMAH in DI water) for 80 seconds.
The sensitivity curves for the positive-tone dendrimeric resists on exposure to electron beam at 20 keV acceleration voltage, 20 μm aperture, resulting in a beam current of 157 pA (Pico ampere) are shown in
Resists containing 10 wt % PAG showed higher sensitivity 50 μC/cm2 (G1-Tris-t-BOC 80), 60 μC/cm2 (G1-Bis-t-BOC 80) and 80 μC/cm2 (G1-Dhn-t-BOC 80) at 20 keV electron beam acceleration. The contrast (γ) was calculated by using formula (γ1=log D1−log D0), where D0 is the maximum dose where the resist thickness before development is the same as after development D1 is minimum dose where the resist is washed out after development. Higher contrast obtained using 10 wt % PAG is γ=2.50 (G1-Tris-t-BOC 80), γ=2.09 (G1-Bis-t-BOC 80), γ=1.66 (G1-Dhn-t-BOC 80).
The evaluation of the system for EBL resist was performed using FGDs with 80% t-BOC conjugation. Oxidised silicon wafer was used to enhance adhesion of photoresist to the substrate.A 5 wt. % solution of 80% t-BOC conjugated FGDs (G1-Tris-t-BOC, G1-Bis-t-BOC, G1-Dhn-t-BOC) and 10 wt. % (with respect to dendrimer) PAG (triphenylsulphoniumnanoflate) was spin-coated onto a two inch silicon wafer at a 6000 rpm which form 70 nm, 64 and 61 nm thick films respectively. Prebaking of the coated film on the silicon wafer was carried out at 70° C. for 5-minutes. Positive-tone FGD systems were tested using e-beam exposure 20 kV at a dose 50 μC/cm2, 60 μtC/cm2and 80 μC/cm2 respectively. The post exposure bake (PEB) process, carried out at 90° C. for one minute. Post exposure baked film was developed with 0.26N TMAH for 85 seconds.
Measured LER values are given in Table-8.
| Number | Date | Country | Kind |
|---|---|---|---|
| 3496/DEL/2011 | Dec 2011 | IN | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IN2012/000792 | 12/6/2012 | WO | 00 | 6/5/2014 |
