Bit-patterned media (BPM) is a candidate for high-density magnetic recording media. Directed self-assembly
(DSA) is expected to be a solution for the fabrication process of high-density BPM. A BPM with 20 nm-pitch
dot pattern is fabricated. A 100 nm-pitch triangle lattice dot pattern, which is fabricated by EB lithography, is
used as a guide post to order PS-PDMS self-assembled diblock co-polymer with 20 nm pitch. Dot-pitch
fluctuation and linearity of pseudo dot tracks are estimated. The standard deviation of the dot-pitch variation
including the post guide is 8% of the self-assembled dot pitch. The dot-position deviation is estimated to be
about 8% of the pseudo dot track pitch. In both cases, variation of the size and pitch of the post guides is
found to increase the dot-pitch fluctuation and dot-position deviation from pseudo dot-track.
Bit patterned media (BPM) is a promising candidate for next-generation magnetic recording media beyond 2.5 Tb/in2.
To realize such high-density patterned media, directed self-assembling (DSA) technology is a possible solution to form
fine dots. In order to read and write magnetic signals on a magnetic dot of magnetic media, the position of magnetic dots
must be controlled. We examined ordering of directed self-assembly of diblock copolymer dots with a variety of prepatterned
guides in some conditions and evaluated the ordering of the dots by using Delaunay triangulation and Voronoi diagram. Applying the optimized conditions, we obtained highly controlled dot pattern suitable for magnetic recording media.
Bit patterned media (BPM) is a promising candidate for high-density magnetic recording media beyond 2.5 Tb/in2. To
realize such a high-density BPM, directed self-assembling (DSA) technology is a possible solution. On the other hand,
from the viewpoint of low-cost production, nanoimprint lithography is a promising process for the mass-production of
such a high-density BPM. We examine the replication of the BPM etching mask by UV nanoimprint process. At first, the
BPM silicon master mold consisting of servo pattern with dot array is made by the DSA method using PS-PDMS. For
the 30-nm pitch corresponding to the density of 2.5 Tb/in2, the nickel stamper is replicated from the silicon master mold
by electroplating. The etching mask is transcribed by the UV nanoimprint process with the transparent mold replicated
from the nickel mother stamper. On the other hand, as for the DSA-BPM pattern of 17-nm pitch corresponding to the
density of 2.5 Tb/in2, we adopt an alternative process and confirm the replication possibility.
Bit patterned media (BPM) is a candidate for high-density magnetic recording. One of the critical issues
concerning high-density BPM is a fine pattern drawing process for an etching mask. A self-assembled polymer is a
solution for the fine etching mask material realizing a density of more than several Tb/in2. The remaining issue
concerning the self-assembled mask is servo pattern formation with the self-assembled dots. This paper reports
fabrication of a ridge-and-groove servo pattern with arrays of
35nm-pitch self-assembled CoPt magnetic dots and signal
properties of the servo pattern are estimated. Dot size and alignment was not uniform in the servo pattern because of the
deviation of the guide width and the taper at the guide edge. This feature will result in a distorted servo signal profile.
However, the numerical estimation based on the fabricated servo patterns revealed that the linearity of the position error
signal was fairly good. The distortion in waveform does not degrade the phase information of the servo signal, provided
the guide is positioned with high precision. Thus the
ridge-and-groove servo is suitable for self-assembled bit patterned
media.
Fabrication of 16 nm pitch L&S pattern was investigated by applying self-organizing material as etching mask. For the
purpose, diblock copolymer template composed of polystyrene-polyethyleneoxide (PS-PEO) and spin-on-glass (SOG)
was utilized. The material was prepared to form polystyrene cylinder phase in PEO phase. SOG was located in the
PEO phase, because of its hydrophilic property. After spin-coating on a Si wafer, film was baked at high temperature.
By the thermal treatment, PS cylinder phase was eliminated to form cavities in the cured SOG matrix. Using the cured
Si matrix pattern as etching mask, Si substrate was etched. When baking was carried out at 300° C, bridge-like defects
were observed on Si pattern. The thermogravimetric examination indicated the baking at 400° C could reduce the
defects. Applying the optimized process, 16nm pitch L&S pattern was transferred on Si substrate.
A low-cost fabrication method combining self-organized lithography and nanoimprint is proposed as a possible solution
for patterned media production for the memory density beyond 1 Tbpsi. For that purpose, imprint mold equipped with
30-nm-pitch pillar pattern was formed on a Si substrate using diblock copolymer template. Room-temperature imprint
and ion milling were applied to avoid thermal and chemical damage to magnetic film during a patterning process. The
obtained aspect ratio of the relief by room-temperature imprint was enhanced via pattern-inverse process. After ionmilling
treatment, 30-nm-pitch magnetic dot array with 20 nm height was observed. A nickel replica mold was formed
by electroforming applying the Si mold as an original master. These results indicate the possibility that
nanoimprinting is a practical method for 1 Tbpsi patterned media production.
The stability during the storage between EB exposure and post- exposure bake (PEB) of the chemically amplified resist containing diphenylamine (DPA) was discussed. The large dimension change of 0.15 micrometer L/S pattern with 14 (mu) C/cm2 EB dose was observed within 1 hour in a vacuum due to the deprotection reaction. The stability of the resist properties in an atmosphere before PEB (PED instability) depends on the time during which the exposed resist is stored in a vacuum. Keeping the exposed resist in a vacuum for more than about 20 minutes makes PED instability good. This seems to be caused by a dark reaction for about 20 minutes, which occurs in addition to the deprotection reaction and realizes equilibrium between DPA and acid generated by EB exposure. This mechanism by which DPA acts as a superior stabilizing base additive is supported by the time dependence of surface resistance for the resist in an atmosphere.
This paper focuses on the inhibition efficiency of t-Boc derivatives of bis-phenols. Several t- Boc derivatives of bis-phenols were synthesized and their inhibition effects were evaluated in novolac resin and poly (4-hydroxystyrene) (PHS). When the novolac resin was used as the matrix polymer, the inhibition effects were thought to be governed by both the hydrophobicity and molecular size of the inhibitors. On the other hand, in the case of PHS, the hydrophobicity of the inhibitor molecule was thought to be the dominant factor responsible for decreasing dissolution rates. In addition, the effects of the basic components of the developers were also investigated. Solutions of sodium hydroxide, tetramethylammonium hydroxide and tetraethylammonium hydroxide were employed as developers. The effects of the basic components on the dissolution rates of the resists varied with the matrix polymer of the resist. The dissolution rate of novolac resin was higher in NaOH solution than in the developers consisting of organic bases. However, the dissolution rates of novolac resin samples containing dissolution inhibitors were lower in NaOH solution than in developers consisting of organic bases. This phenomenon may be attributable to the hydrophilic properties of the cation of a developer.
Quantum chemical calculation is applied to investigate the reaction mechanism of sulfonyl acid generator and the transparency of the resist material. We have found that electron absorbed dimethylsulfone can be easily decomposed by relatively low energy (2.95 Kcal/mol), reaching to the decomposed status of methyl radical and methyl sulfonyl anion. This was thought to be an initial step in the electron acid generation reaction of the sulfonyl compounds. The total molecular energy of dimethyl sulfone anion was found to be higher than that of the neutral dimethylsulfone. On the other hand, sulfone derivatives with electron-withdrawing groups, such as methyl sulfonyl acetonitrile, usually have higher energy (about 41 kcal/mol) than those for their anion. This suggests that the electron withdrawing groups enhance the electron affinity of the sulfone compounds, which are also considered to increase the efficiency of acid generation. Additionally, another quantum chemical study was carried out in order to improve transparency of the aromatic species in resist for ArF excimer laser. Using configuration interaction (CI) methods of molecular orbital theory, the substituent effects of UV absorption in the aromatic compounds were investigated. As a result, significant red sifts in Amax were observed in the conjugated aromatic rings, which increases the transparency at 193 nm wavelength region.
This paper reports on a novel three-component chemical amplification positive resist system for EB lithography composed of a novolak resin, an acid generator, and a newly synthesized dissolution inhibitor. We synthesized a novel dissolution inhibitor named CP-TBOC (1), which contains a tert-butoxycarbonyl (t-BOC) group and a lactone ring, to obtain resist materials with high sensitivity and high contrast. The t-BOC group of this dissolution inhibitor effectively decomposed by an acid catalyzed thermal reaction as the other conventional dissolution inhibitors. In addition to this decomposition, the lactone ring of the decomposed product was spontaneously cleft in an aqueous base to generate carboxylic acid, further enhancing the solubility to alkaline developers. The subsequent cleavage in an aqueous developer was investigated by UV-visible spectroscopy. The highest EB sensitivity was obtained at a CP-TBOC concentration of approximately 4.7 X 10-4 mol/g.
Polyamic acid esters with phenol moieties (Ph-ES) were synthesized from diamines and dicarboxylic acids bonding to phenol moieties through ester linkage. To synthesize the dicarboxylic acids, 1 mol of BTDA was reacted with 2 mol of m-hydroxybenzyl alcohol in NMP. The resultant dicarboxylic acid are predominantly benzyl esters, not phenyl esters, was condensed with ODA, using DCC as condensing agent. The polyimide precursors Ph-ES was actually soluble in basic aqueous solutions. However, its dissolution rate was too low for binder resins used for resists. To increase the resist dissolution rate, polyamic acid PA, which is assumed to be more soluble in the base developer, was added to Ph-ES. The PA was synthesized from BTDA and ODA. Resists containing Ph-ES (60 wt%), PA (20 wt%) and naphthoquinone diazide (20 wt%) gave 4 micron line and space pattern with 5 micron thickness. There was no pattern deformation, even after the polyamic acid ester was heated at 320 degree(s)C to form the polyimides. The PA content was critical to the high resolution achievement. As the content of the PA to Ph-ES increases, the pattern shape of the resist deteriorated rapidly. At more than 40 wt% PA rate, patterns could not be obtained, because fine patterns peeled off form the silicon wafer substrate during the development. This proved that adjusting dissolution rates in basic aqueous solutions is one of the significant points for realizing fine resist patterns.
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