Ablation of poly(2-hydroxyethyl methacrylate) by 193-nm excimer laser radiation

Data on the ablation of poly(2-hydroxyethyl methacrylate) (PHEMA) by 193-nm radiation pulses, produced by an ArF excimer laser, are presented for the first time and are compared with the data for poly(methyl methacrylate) (PMMA). The ablation rate of PHEMA is lower than that of PMMA and some possible explanations are advanced. The other features of the etch curves are similar and confirm a predicted ablative behavior of the addition polymers susceptible to depolymerization. Geometric aspects of the ablated polymer's surface, and the influence of inhomogeneities in the material, are also presented and discussed.     

A negative resist for KrF excimer laser lithography

The design and preparation of a series of negative resists for KrF excimer laser lithography are described. Each resist is composed of poly(hydroxystyrene) and an aromatic azide. The base resin shows high transmittance of 62%/μm at 248 nm, when p-ethylphenyl p-azidophenylsulfonate. 4-azido-4α-methoxy-chalcone, 1-(4 azidobenzylidene)-3-(α-hydroxy-4-azidobenzyl)-indene, 4,4α-diazido-3,3α-dimethoxybiphenyl, or 1-(4-azidostyryl)-5, 5-dimethyl-2-cyclohexen-1-one is employed as a sensitizer. These azides are obtained by red-shifting the absorption maxima to lower energy regions than the exposing wavelength of 248 nm. Transmittance of resists can be controlled from 10 to 30%. The resist is exposed with a KrF excimer laser stepper and developed in an alkaline solution. Sensitivities of about 15 mJ/cm² are observed. A good, subhalf-micron resist profile is achieved. The photochemical reaction mechanisms of poly(hydroxystyrene) and 4,4α-diazido-3,3α-dimethoxybiphenyl were studied at 248 nm and 313 nm exposure. Quantum yield for photodecomposition at 248 nm is seven times larger than that at 313 nm, but dissolution-inhibition effects are larger at 313 nm exposure. Consequently, the resist shows higher sensitivity at 313 nm than at 248 nm.     

Positive excimer laser resists prepared with aliphatic diazoketones

A new class of alkali-developable positive excimer laser (KrF) resists is described. Novel α-diazoacetoacetates derived from aliphatic polyfunctional alcohols were synthesized. These compounds undergo photolysis upon deep UV exposure to yield carboxylic acids, and exhibit excellent bleaching effects. Some of them, especially those having steroid skeletons, act as effective dissolution inhibitors. The composites prepared from these compounds and poly(p-hydroxybenzylsilsesquioxane) were used as alkali-developable positive deep UV resists, whose sensitivities depend on the number of photoactive groups in one photoactive molecule. Imaging results of KrF excimer laser projection printing are presented.     

Novel positive deep UV resist for KrF excimer laser lithography

A novel positive deep UV resist for KrF excimer laser lithography has been developed. The resist is composed of 1,7-bis(4-chlorosulfonyl phenyl)-4-diazo-3,5-heptanedione as the alkaline dissolution inhibitor and an alkali-soluble sytrene polymer as the main-polymer. 1,7-bis(4-chlorosulfonyl phenyl)-4-diazo-3,5-heptanedione has great capability of alkaline dissolution inhibition. High thermal stability and excellent photobleachability at 248 nm of the compound are also characterized. The alkali-soluble styrene polymer has a high transmittance of 70% in 1.0 μm thickness at 248 nm. The novel positive resist had an excellent property for dissolution kinetics and photobleaching. We achieved high aspect ratio half-micron pattern fabrication in 1.0 μm thickness using the new resist.     

Sensitive chlorine-containing resists for X-ray lithography

New resists containing chlorine to enhance absorption to Pd_Lα X-radiation at 4.37 Å have higher sensitivity than currently available high-speed electron resists when used in a high-throughput Pd_Lα X-ray exposure system developed by Maydan and coworkers. Of the three classes of materials examined the poly(chloroalkyl acrylates) have the best properties. The sensitivity and contrast of these negative resists are dependent on the amount of Cl present, the structure of the chloroalkyl side chain, the inclusion of reactive functional groups, and molecular weight. Contrast is found to decrease with increasing sensitivity achieved by either increasing molecular weight or incorporating more reactive glycidyl groups. We suggest that such behavior, which is not predicted by theories of radiationinduced crosslinking, has its origin in competitive formation of intramolecular crosslinks with the desired, intermolecular crosslinks. Poly(2, 3-dichloro-1-propyl acrylate) has been investigated in greatest detail. Samples of this polymer requiring a dose of 7 mJ/cm² for 50 percent of the initial resist thickness (2 min exposure) have been used successfully to wet etch 1 μm features into SiO₂, Al and Cr and 2 μm features into phosphosilicate glass. It has moderate resistance to ion milling and good resistance to plasma etching with Freon-based plasmas.     

Submicron patterns in substituted polystyrene resists by focused-ion-beam lithography

Submicron lines in negative working, substituted polystyrene resists by focused-ion-beam lithography were demonstrated. These features were transferred into an underlying molybdenum layer by plasma etching using the resist as an etch mask, with the minimum continuous line having a width of 0.20 μm.     

Electron irradiation of polymerisable langmuir-blodgett multilayers as model resists for electron-beam lithography

Amphiphilic molecules containing a polymerisable oxiran (epoxide) group have been assembled into Langmuir-Blodgett multilayers. Lines were drawn on the multilayers by exposure to an electron beam and subsequent development by rinsing in toluene. Line widths and heights were examined for various doses of electrons of energies 10, 5 and 2 kV. Generally, for the higher energies and shorter exposures, narrow well defined lines were obtained of height similar to the thickness of the original multilayers. Conversely, at lower energies and exposure times, troughs rather than lines were observed following incomplete development. The implications of these results are compared with theoretical predictions of bbnd forming and bond scission processes during electron irradiation of organic molecules.     

Poly(t-BOC-styrene sulfone)-based chemically amplified resists for deep-UV lithography

The unique ability of the tert-butoxycarbonyl protecting group (t-BOC) to be removed by a catalytic amount of strong acid has intensified the search towards new chemically amplified resist systems based on this chemistry. A series of new copolymers of t-BOC-styrene and sulfur dioxide have been prepared by free radical polymerization. These polysulfones function as chemical amplification positive resists for deep-UV lithography when mixed with either 2,6-dinitrobenzyl tosylate or triarylsulfonium salt acid precursors. The lithographic characteristics of 2:1 and 3:1 polysulfones have been evaluated. The new positive deep-UV photoresists are aqueous base developed and are capable of 0.5 μm resolution. Even though the photoresists containing 2,6-dinitrobenzyl tosylate are less sensitive than the onium salt formulations, they displayed greater contrast values. For example the poly(t-BOC-styrene sulfone) (2:1) 15 wt % tosylate resist formulation exhibits a sensitivity of 26 mJ/cm² and a contrast of ～20.     

Ultrafast deep UV lithography using excimer lasers

Various excimer laser wavelengths have been used, both in mid- and deep-UV regions—308 nanometers (nm) from XeCl, 249 nm from KrF and 222 nm from KrCl–to delineate images in a number of resists. The quality of the images obtained with the laser exposures, the absence of speckle, and the insignificant loss of resist reciprocity make excimer laser lithography an attractive technique. The ultrafast exposures possible with this method significantly lessen the sensitivity requirements on deep UV resists, making the choice of the resist more flexible.     

Study on organosilicon positive resist. III. Organosilicon positive excimer laser resist (OSPR-2016)

A new alkali-developable organosilicon positive excimer laser (KrF) resist (OSPR-2016) has been developed for a bilayer resist system. OSPR-2016 is composed of poly(p-hydroxybenzylsilsesquioxane) and methyl cholate-tris (α-diazoacetoacetate). The ratio is 72.5 : 27.5 w/w. A sample of 0.5-μ thick OSPR-2016 resolved 0.35 μ L&S patterns when exposed to a dose of 320 mJ/cm² from an excimer laser projection printer (NA = 0.37).     

Electron beam lithography of copolymeric resists containing styrenes and allyl acrylates

A series of electron beam sensitive negative resists based on styrene allyl methacrylate copolymers and substitutional modifications thereof were prepared and their resist characteristics were investigated. Depending on the molecular parameters, such as monomeric ratios, molecular weights and molecular weight distributions, the sensitivity to electron beam irradiation of the copolymer resist can vary from 10^?7 μC/cm² to 10^?6 μC/cm². A styrene allyl methacrylate copolymer having a 57/43 mol-percent and a molecular weight of 3.3 × 10⁵ shows a sensitivity of 1.4 μC/cm² (Dg^0.5) and a resolution of 1.10 μm line/space at 6000A remaining thickness.     

Synchrotron lithography: The way to sub-micron features with single layer resists

Soft X-ray radiation is affected neither by scattering in the resist nor by reflection from the substrate surface, so that a one-layer resist system can be maintained even in the sub-micron range. This holds primarily for the parallel synchrotron radiation avoiding all the geometrical distortions connected with X-ray tubes and even plasma sources. It has been shown that a minimum feature size of 0.2 μm can be achieved in this case. Different resist systems applicable in X-ray lithography have been tested regarding resolution, sensitivity, and etch stability. The optical resists Kodak ‘HPR 204’ shows very high process stability, good resolution, but low sensitivity. It is, therefore, suitable for an X-ray pilot process but not for high throughput production. The high sensitive X-ray resist TBM 120′ a fluorized poly(methyl methacrylate) which shows originally a very poor etch stability can be stabilized by post exposure with synchrotron radiation.     

An X-ray photoelectron spectroscopy study of poly(methyl methacrylate) surface modified by 193-nm laser radiation

Summary The swelling and equilibrium mechanical behaviour of networks of copolymers of acrylamide (AAm) with a ionic crosslinker — sodium salt of 2,2-bisacrylamidopropionic acid (I) in water-ethanol mixtures was investigated. Two series of networks were prepared. While in series 1 AAm and ionic crosslinker were copolymerized (mole fraction x _I=0.005 to 0.1), in series 2, AAm, ionic crosslinker and non-ionic crosslinker — methylenebisacrylamide (MBAAm) — were copolymerized in such way that x _I + x _MBAAm = 0.05 (x _I varied from 0 to 0.05). In the region x _I0.01 the phase transition was observed for both series. As expected, for networks of series 2 with constant crosslinker concentration the extent of transition (jumpwise change of the volume of the gel) increases with increasing charge concentration, x _I. On the other hand, for samples of series 1 this extent slightly decreases with x _I which means that the effect of increasing crosslinking density on the swelling is greater than that of increasing charge concentration. The critical ethanol concentration at which collapse takes place, e _c, increases with x _I in both series. The jumpwise change in the gel volume is accompanied by a similar change in the equilibrium modulus of the gel.     

Variable development response of resists using electron beam lithography: Methods and applications

In the manufacture of electronic devices for integrated circuits, reducing the number of resist steps is desirable for a variety of reasons. We describe some experiments on a process aimed at reducing the number of resist and registration steps in electron beam lithography. The process involves locally varying the electron dose in an electron sensitive resist (in this case poly[methyl methacrylate]) so that the different levels of exposure can be distinguished by subsequent developing. Reliable results have been achieved with three levels:

• (i) Strongly exposed (resist removed after short immersion in developer).
• (ii) Partially exposed or “metastable” (resist removed only after prolonged immersion in developer).
• (iii) Unexposed.

In strongly exposed regions, operations such as etching may take place while using the metastable and unexposed regions to protect the workpiece. Subsequently, the metastable region may be developed for further processing.     

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.     

Electron beam lithography — influence of molecular characteristics on the performance of positive resists

Polymers are widely used as resists in electron beam lithography. This paper is concerned with theoretical modelling of the electron beam lithographic process and establishing criteria which need to be satisfied for a polymer to behave as a good positive resist. The effects of molecular weight, tacticity, solvent selection and sequence structure are discussed. Criteria are presented upon which the design of a new resist material may be based.     

Arylazophosphonate containing polymers designed for XeCl excimer laser ablation

Applying the N‐P coupling technique, fifteen new poly(arylazophosphonate)s were synthesized by interfacial polycondensation from bifunctional diazonium salts and bifunctional phosphoric diesters. Because of their excellent film forming properties and absorption behaviour poly(arylazophosphonate)s are suitable materials for laser ablation experiments with XeCl excimer lasers (308 nm). A variety of ablated structures have been generated by irradiation of the polymer films with a commercially available pulsed XeCl excimer laser. Macro experiments indicate remarkable structures with sharp edges, clear contours, and flat bottoms. Moreover, various patterns with μm dimensions were generated by micro experiments and were characterized by means of scanning electron microscopy (SEM). The resolution of these structures indicate that poly(arylazophosphonate)s are suitable materials for applications in microtechnology.     

Prepare SiTiOC ceramic coatings by laser pyrolysis of titanium organosilicon compound

A SiTiOC ceramic coating with outstanding tribological performance was prepared by laser scanning the organosilicon coating with different laser power. The composition and structure of the obtained SiTiOC ceramic coatings were analyzed by scanning electron microscopy (SEM), infrared spectroscopy (FTIR), Raman spectra, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and transmission electron microscope (TEM). The tribological performance of the coatings was studied using a multi-functional reciprocating friction and wear tester. The results showed that the chemical structure (chemical bonding) of the coatings prepared at 0 W, 350 W, and 500 W laser powers included Si-O-Si, Si-C, and TiO₂, while that prepared at 800 W was mainly composed of amorphous SiO₂, indicating that the coating had higher ceramization. The SiTiOC ceramic coatings prepared by the present process effectively reduced the friction coefficient and wear volume of the steel substrate, which indicated that they had good anti-friction and wear resistance properties.     

Surface modification of synthetic fibers by excimer laser irradiation

It was attempted to improve the fiber/rubber adhesion by surface modification of fibers by excimer laser irradiation. The fibers were first treated with a glycidyl ether acrylate compound which is sensitive to UV rays, then cured with a KrF laser and treated with an ordinary RFL (resorcinol formalin rubber latex), and then cured in heat. For poly(ethylene terephthalate) (PET) and poly(p-phenylene-3,4′-oxydiphenylene terephthalamide) (PPODPTA) fibers, the adhesion performances were improved, whereas for poly(p-phenylene terephthalamide) (PPTA) fibers they were not. In PET fibers, the surface layer was converted into the amorphous state, and therefore the affinities for the treating agents were enhanced. As for the aramid fibers, the copolymer components of the PPODPTA fibers contain crystalline domains, independently, which are oriented sufficiently, leaving almost no amorphous state in which molecules remain relaxed, and are difficult to be fibrillated. On the other hand, the PPTA fibers comprise a skin layer and a core layer composed of fibrils stacked into blocks. Between the blocks, amorphous phases containing a relatively large number of molecular chain ends are present, facilitating the fibrillation. Probably, the molecules in the non-crystalline state of both of the fibers were relaxed differently, causing different susceptibilities to ablation. This might result in different affinities to the acrylate compound, or different adhesion performances, respectively.     

Focused laser spike (FLaSk) annealing of photoactivated chemically amplified resists for rapid hierarchical patterning

Lithographic alternatives to conventional layer-by-layer processes for the design of 3D structures such as photonic or phononic crystals often present a dichotomy: patterning control versus patterning area. We demonstrate a combined technique of large area interference lithography and local area direct write focused laser spike (FLaSk) annealing that can enable the microscale patterning of hierarchical structures defined in their morphology by the interference and defined in placement and shape by the direct write. This is accomplished by doping a commercial chemically amplified photoresist (SU-8) with an absorbing dye to provide thermal activation at a wavelength shifted from that causing UV crosslinking. In this way, the necessary post-exposure bake to complete the crosslinking of the resist is locally performed by the FLaSk laser, rather than globally on a hot plate. By utilizing the same experimental setup as used by a 3D direct write system, it is possible to integrate another level of patterning by enabling fully dense, arbitrarily written features on multiple length scales. Both experimental and simulated results of this novel processing method are shown.