Design and synthesis of new photoresist materials for ArF lithography

A new class of photoresist matrix polymers based on vinyl ether–maleic anhydride (VEMA) alternating copolymers was developed for ArF single‐layer lithography. These polymers were synthesized by copolymerization of alkyl vinyl ether and maleic anhydride alternating copolymers with acrylate derivatives containing bulky alicyclic acid‐labile protecting groups. The resulting polymers showed good control of polymerization and high transmittance. Also, these resists exhibited good adhesion to the substrate, high dry‐etching resistance against CF₄ mixture gas (1.02 times the etching rate of deep UV resist), and high selectivity to silicon oxide etching. Using an ArF excimer laser exposure system with 0.6 NA, 120‐nm L/S patterns were resolved under conventional illumination. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 165–170, 2004     

Photoresist development by plasma

Over the past several years the semiconductor industry has placed major efforts into replacing wet processes with dry processes in fabricating electronic devices. Plasma photoresist stripping, plasma cleaning, and other dry etching techniques have replaced wet methods in many product lines. One area that has received little mention but which is vital toward achieving a totally dry manufacturing process is the dry development of photoresist. One production applicable plasma developable photoresist (PDF) process, using a proprietary resist formulation, is reported. Plasma process characterization, such as end point detection, development latitude, and mechanism are discussed. Included also are development temperature, batch film uniformity, and resolution currently obtainable with the PDF process.     

A polymer complex as a new type of electron beam resist for dry development

Polymer complex of poly (4-vinylpyrldine) and malonic acid was investigated as a new type of electron beam (EB) resist for dry development, as malonic acid was decomposed by EB irradiation. It was found that the polymer complex could be developed with O₂ plasma etching and that the positive resist patterns with high resolution could be obtained. The mechanism for this lithography process was studied by means of IR and ESCA spectra.     

Plasma developable photoresist containing electronic excitation energy quenching system

A dry developable negative working resist composition comprised of poly(methyl isopropenyl ketone) (PMIPK) and 4-methyl-2,6-di(4′-azido-benzylidene) cyclohexanone-1 was examined. The main photochemical product formed in the resist pattern was found to be a secondary amine which crosslinks PMIPK. Post-annealing forms a hydrogen-bonded product which shows a powerful electronic excitation energy quenching effect. The quencher is more powerful than the aromatic compound arising from the azide by post-annealing only. The residual resist thickness of the negative pattern is about 80 percent of the initial thickness of the coating in spite of all the azide compound remaining in the resist coating. The obtained dry developed resist pattern has a high dry etch resistance. Etchings of Si and SiO₂ were performed by plasma and reactive ion etching, respectively.     

Study on organosilicon positive resist. II. Organosilicon positive photoresist (OSPR–1334) and its application to bilayer resist system

A new alkali-developable organosilicon positive photoresist (OSPR–1334) and a bilayer resist process with OSPR–1334 has been developed. OSPR–1334 is composed of poly(p-hydroxybenzylsilsesquioxane) and naphthoquinone diazide. The sensitivity and the resolution are almost the same as those of conventional novolac-based resists when aqueous tetrakis (2-hydroxyethyl) ammonium hydroxide is used as a developer. Also, OSPR–1334 has excellent resistance to O₂RIE. The etching rate is 3.6 nm/min, while that of polyimide resins or hard-baked novolac-based resists is 100 nm/min. OSPR–1334 is suitable for use as the top layer of the bilayer resist system. OSPR–1334, after O₂RIE, can be eliminated by dissolving an unchanged layer followed by spinning out or filtrating a changed surface layer. Submicron patterns with a high aspect ratio can easily be obtained with this bilayer resist process.     

Organosilicon polymers for lithographic applications

Linear polymers of silicone gums (polysiloxanes) have many attributes that make them attractive for lithographic applications, such as oxidative and thermal stability, good adhesion properties, solubility in common solvents, and resistance to etching in an oxygen plasma. When polysiloxanes are used as the top imaging layer (～2000Å) in a two-layer resist system, the developed negative siloxane images act as a high resolution etch mask for the oxygen plasma etching of the bottom planarizing polymer layer. Commercially available polysiloxanes have been evaluated for their deep UV sensitivity at 2537Å, and have been found to have very high resolution capabilities (～0.5μ) and high contrast (γ = 4). The negative images do not swell in the developer, and the line width is therefore independent of development time. The combination of high resolution, sensitivity, and ease of processing make this a simple multilayer system for deep UV and e-beam applications.     

Triphenylsulfonium salt methacrylate bound polymer resist for electron beam lithography

A new photoacid generator (PAG) bound polymer containing triphenylsulfonium salt methacrylate (TPSMA) was synthesized and characterized. The PAG bound polymer was employed to improve electron beam lithographic performance, including sensitivity and resolution. The PAG bound polymer resist exhibited a higher sensitivity (120 μC/cm²) than the PAG blend polymer resist (300 μC/cm²). Eliminating the post exposure baking process during development improved the resolution due to decreased acid diffusion. A high-resolution pattern fabricated by electron beam lithography had a line width of 15 nm and a high aspect ratio. The newly developed patterns functioned well as masks for transferring patterns on Si substrates by reactive ion etching.     

Polystyrene negative resist for high-resolution electron beam lithography

We studied the exposure behavior of low molecular weight polystyrene as a negative tone electron beam lithography (EBL) resist, with the goal of finding the ultimate achievable resolution. It demonstrated fairly well-defined patterning of a 20-nm period line array and a 15-nm period dot array, which are the densest patterns ever achieved using organic EBL resists. Such dense patterns can be achieved both at 20 and 5 keV beam energies using different developers. In addition to its ultra-high resolution capability, polystyrene is a simple and low-cost resist with easy process control and practically unlimited shelf life. It is also considerably more resistant to dry etching than PMMA. With a low sensitivity, it would find applications where negative resist is desired and throughput is not a major concern.     

Silicon containing photoresists for half micron lithography

Several silicon containing topresists for bilayer oxygen reactive ion etching systems were developed and examined. Each topresist consists of a silicon containing alkaline soluble copolymer and a 2-diazo-1-naphthalenone-4-sulphonic acid ester photoactive compond (PAC). Half micron structures in the topresist were obtained with two different resist systems through deep-UV (257 nm) or iline exposure. The etch rate ratios (planarizing layer:copolymer) vary between 7:1 and 13:1 under anisotropic etching conditions. Linewidth loss during oxygen RIE (reactive ion etching) pattern transfer is a problem for resists containing about 10% silicon, but equal lines and spaces after etching can be obtained through the use of thick topresists or linewidth bias in the topresist prior to etching.     

The role of the latent image in a new dual image,aqueous developable,thermally stable photoresist

A new dual image, aqueous developable photoresist can be processed to yield either positive or negative images that are crosslinked and thermally stable to temperatures >300°C. Positive images have similar resolution and processing parameters to conventional positive novolak resists. Negative resists from this system have a number of new and interesting properties that surpass the capabilities of their positive counterparts. In addition to producing highly resolved submicron images, thick coatings of resist can be used to form images with high aspect ratios. By adjusting the exposure of the resist, images with inward sloping wall profiles can be realized. As a result of the images being crosslinked and Insoluble in the resist coating solution, images can be recoated and new images formed over the top of existing patterns to form structures. A hypothetical mechanism that suggests that resist defects caused by dust on the mask or photoresist surface can be reduced In negative mode processing is also presented.     

Recent resist developments in Japan—a review

Several kinds of resist materials for microlithography have been developed in Japan. Poly(4-vinyl phenol) sensitized with 3,3′-diazidodiphenyl sulfone has been proved to be a high resolution negative deep UV resist with high sensitivity and good resistance to dry etching. The use of this resist enables a 1:1 projection printer to replicate fine patterns with 1 micrometer (μm) minimum feature size at the rate of 90 wafers per hour. Poly(methyl isopropenyl ketone) (PMIPK) has been investigated as a positive deep UV resist. Several resists composed of PMIPK with or without sensitizers are commercially available. Dry-developable photo- and deep UV resists comprising PMIPK and aromatic bisazides have been developed. Poly(glycidyl methacrylate) having the sensitivity of 0.4 micro Coulomb (μC)/per square centimeter (cm²) is now being routinely used as a negative electron beam resist in the fabrication of chromium masks. Recently, aromatic polymers such as chloromethylated polystyrene, iodinated polystyrene, chloromethylated poly(α-methylstyrene), poly(vinylnaphthalene) and its copolymers have been investigated as dry-etching resistant electron beam resists.     

Fabrication mechanism of friction-induced selective etching on Si(100) surface

As a maskless nanofabrication technique, friction-induced selective etching can easily produce nanopatterns on a Si(100) surface. Experimental results indicated that the height of the nanopatterns increased with the KOH etching time, while their width increased with the scratching load. It has also found that a contact pressure of 6.3 GPa is enough to fabricate a mask layer on the Si(100) surface. To understand the mechanism involved, the cross-sectional microstructure of a scratched area was examined, and the mask ability of the tip-disturbed silicon layer was studied. Transmission electron microscope observation and scanning Auger nanoprobe analysis suggested that the scratched area was covered by a thin superficial oxidation layer followed by a thick distorted (amorphous and deformed) layer in the subsurface. After the surface oxidation layer was removed by HF etching, the residual amorphous and deformed silicon layer on the scratched area can still serve as an etching mask in KOH solution. The results may help to develop a low-destructive, low-cost, and flexible nanofabrication technique suitable for machining of micro-mold and prototype fabrication in micro-systems.     

A Fast Thermal-Curing Nanoimprint Resist Based on Cationic Polymerizable Epoxysiloxane

ABSTRACT: We synthesized a series of epoxysiloxane oligomers with controllable viscosity and polarity, and developed upon them a thermal-curable nanoimprint resist that was crosslinked in air at 110 oC within 30 seconds if pre-exposed to ultraviolet (UV) light. The oligomers were designed and synthesized via hydrosilylation of 4-vinyl-cyclohexane-1,2-epoxide with poly(methylhydrosiloxane) with tunable viscosity, polarity and crosslinking density. The resist exhibits excellent chemical and physical properties such as insensitivity toward oxygen, strong mechanical strength and high etching resistance. Using this resist, nanoscale patterns of different geometries with feature sizes as small as 30 nm were fabricated via a nanoimprint process based on UV-assisted thermal curing. The curing time for the resist was on the order of 10s of seconds at a moderate temperature with the help of UV light pre-exposure. This fast thermal curing speed was attributed to the large number of active cations generated upon UV exposure that facilitated the thermal polymerization process.     

Molecular transport through nanoporous silicon nitride membranes produced from self-assembling block copolymers

To achieve fast and selective molecular filtration, membrane materials must ideally exhibit a thin porous skin and a high density of pores with a narrow size distribution. Here, we report the fabrication of nanoporous silicon nitride membranes (NSiMs) at the full wafer scale using a versatile process combining block copolymer (BCP) self-assembly and conventional photolithography/etching techniques. In our method, self-assembled BCP micelles are used as templates for creating sub-100 nm nanopores in a thin low-stress silicon nitride layer, which is then released from the underlying silicon wafer by etching. The process yields 100 nm thick free-standing NSiMs of various lateral dimensions (up to a few mm(2)). We show that the membranes exhibit a high pore density, while still retaining excellent mechanical strength. Permeation experiments reveal that the molecular transport rate across NSiMs is up to 16-fold faster than that of commercial polymeric membranes. Moreover, using dextran molecules of various molecular weights, we also demonstrate that size-based separation can be achieved with a very good selectivity. These new silicon nanosieves offer a relevant technological alternative to commercially available ultra- and microfiltration membranes for conducting high resolution biomolecular separations at small scales.     

Excimer laser projection patterning with and without resists

Projection imaging with the deep-UV (193 nm) and VUV (157 nm) output of an excimer laser has been applied to submicrometer patterning of thin films by injected-defect, surface-chemical, and solid-transformation processing. The methods have been designed to take advantage of the short-wavelength, high-peak-intensity pulsed radiation from these sources. Examples are described of pattern definition by exposure of multilayer organic resists, by maskless etching and doping of solids in reactive vapors, and by solid-state chemical transformations in inorganic Al/0 films. Well-resolved 0.4-μm lines and spaces have been achieved. Required doses, between 0.04 and 1 J/cm², are compatible with single- or multi-pulse step-and-repeat projection patterning with a small excimer laser.     

Formulation and Multilayer Jet Printing of Ceramic Inks

This paper describes the preparation of ceramic inks for forming ceramic components by multilayer printing using a continuous-ink-jet printer. The selection of appropriate binders and dispersants combined with high shear and ultrasonic mixing has enabled zirconia-containing inks to be printed successfully to produce 2.5 mm thick bars. Printing trials show that the method of dispersion of the ceramic powder in the ink is decisive for accurate ink droplet positioning. The quality of the vertical walls and the top surface of the bars are related closely to the rate of drying of each printed layer. Inks with higher ceramic volume loadings (up to 10%) were also studied and produced useful information for further investigations.     

Evaluation of poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) as negative electron-beam resist

Poly(allyl methacrylate)-co-(hydroxyethyl methacrylate) has been evaluated as a high-sensitivity, high-resolution, high temperature-resistant negative electron resist. The effects of molecular weight and polydispersity of the copolymer on its lithographic performance as an E-beam resist were studied. The sensitivity of the copolymer is nearly constant in the weight-average-molecular-weight range of 50,000 to 75,000, and it gradually decreases with a decrease in molecular weight. As expected for a negative resist, the resist contrast increases as the polydispersity is decreased. The sensitivity curve shape of the polymer was independent of the prebake temperature, which varied from 70 to 110°C, and of the various developers used. The exposed coating requires vacuum curing for image optimization. Resolution of 0.5 μm line/space pairs was obtained from a 0.6 μm thick resist by exposing the resist to 10 keV electrons with either a raster-scan-type or vector-scan-type electron-beam exposure machine. After postbaking at 170°C, the resist had good resistance to both chemical etching and dry etching. The plasma-etch resistance was about twice that of PMMA.     

Maskless and low-destructive nanofabrication on quartz by friction-induced selective etching

A low-destructive friction-induced nanofabrication method is proposed to produce three-dimensional nanostructures on a quartz surface. Without any template, nanofabrication can be achieved by low-destructive scanning on a target area and post-etching in a KOH solution. Various nanostructures, such as slopes, hierarchical stages and chessboard-like patterns, can be fabricated on the quartz surface. Although the rise of etching temperature can improve fabrication efficiency, fabrication depth is dependent only upon contact pressure and scanning cycles. With the increase of contact pressure during scanning, selective etching thickness of the scanned area increases from 0 to 2.9 nm before the yield of the quartz surface and then tends to stabilise after the appearance of a wear. Refabrication on existing nanostructures can be realised to produce deeper structures on the quartz surface. Based on Arrhenius fitting of the etching rate and transmission electron microscopy characterization of the nanostructure, fabrication mechanism could be attributed to the selective etching of the friction-induced amorphous layer on the quartz surface. As a maskless and low-destructive technique, the proposed friction-induced method will open up new possibilities for further nanofabrication.     

Organosilicon deep UV positive resist consisting of poly(p-disilanylenephenylene)

A new class of positive deep ultravoilet (UV) resists consisting of poly(p-disilanylenephenylene)s was developed, in which a disilanylene unit and a phenylene unit are connected alternatively in the polymer main chain. These resists had very high etching resistance against oxygen plasma. The lithographic applications of a double-layer resist system in which the poly(p-disilanylenephenylene) film was used as the top imaging layer were examined. As a result, very high resolution and high contrast were attained. The double-layer resist technique using organosilicon deep UV positive resist appears very promising for lithographic applications.     

Solution patterning of ultrafine ITO and ZnRh₂O₄ nanowire array below 20 nm without etching process

Transparent conductive patterns have significant applications in various optoelectronic devices. A low cost solution process to directly fabricate transparent conductive oxide nanopatterns was developed without a conventional lithographic or etching process. A uniform and high density array of ITO and ZnRh(2)O(4) nanopatterns was fabricated with block copolymer self-assembly and spin coating technology. A low resistivity of about 3-9 × 10(-4)Ω cm and high transmission of 90% in the visible spectrum region was demonstrated with uniform ITO nanopatterns with feature size of 24 nm. The first p-type ZnRh(2)O(4) nanopattern was also fabricated with low resistivity and small feature size of 15 nm. This cost-efficient and large area scalable process can fabricate patterns with feature size down to sub-20 nm, providing a faster patterning capability compared to conventional photolithography and etching processes.