High Etch Resistance Research Articles

Aluminum oxides as imaging materials for 193-nm excimer laser lithography

Aluminum oxide films deposited over amorphous carbon(a-C:H) planarizing layers have been investigated as imaging layers for 193-nm excimer laser lithography. The AlOx films were deposited by ion beam deposition, e-beam evaporation, or sputter deposition. The films have been analyzed by Auger electron spectroscopy and x-ray photoelectron spectroscopy. Depending on the deposition conditions, AlOx films with compositions varying from metallic to fully oxidized Al can be formed. The optical appearance of these films varies from highly reflective for metallic Al to highly transparent for fully oxidized layers. Using pulsed 193-nm radiation from an ArF excimer laser, the single-pulse self-development threshold energy is similar for films with different compositions when the film reflectivity is taken into account. It was found that pure Al films and highly oxidized Al films do not provide good adhesion on a-C:H layers and have a tendency to peel during laser exposure. In contrast, films with intermediate compositions consisting of a mixture of Al and aluminum oxides provide good adhesion, high etch resistance during O2 reactive ion etching, and submicrometer resolution when exposed with the 193-nm excimer laser. Features as small as 0.1 μm have been patterned on these films in projection, and can be transferred through a 1-μm-thick a-C:H planarizing layer with vertical profiles.

Submicron pattern transfer with newly designed siloxane e-beam resist and Bias-ECR etcher

Submicron pattern transfer was achieved using a newly designed siloxane resist and Bias-ECR plasma stream etcher. The newly developed micro-resinoid siloxane resist for use in electron beam lithography exhibits high resolution, excellent thermal stability, and high dry etch resistance against O 2 RIE. Resist patterns of under 0.1 um for point-beams and 0.2 um for variable-shaped beams were obtained by optimizing the resist structure and its molecular weight. A Bias-ECR plasma stream etcher was applied to realize high speed and high aspect etching, and 0.3 um bilayer resist patterns were obtained.

Resolution characteristics of a novel silicone-based positive photoresist

A novel silicone-based positive photoresist (SPP) is developed for a two-layer resist system. SPP is composed of an alkali-soluble silicone polymer (APSQ) and a diazonaphthoquinone compound as a sensitizer. APSQ is newly synthesized by means of acetylation of polyphenylsilsesquioxane (PSQ). A fine SPP pattern below 0.5 μm can be fabricated with a g-line stepper (NA=0.6) using a two-layer resist system. Moreover, a 0.4 μm line/space pattern is successfully fabricated at a defocus of ±0.4 μm. The high oxygen reactive ion etching (O2RIE) resistance of SPP makes possible the fabrication of a submicron pattern with a high aspect ratio in a two-layer system. Pattern width loss can be negligible during O2RIE of a 2 μm thick bottom resist when a 0.6 μm thick SPP is used as the top imaging layer.

Oxygen plasma etching resistance of plasma polymerized organometallic film

The oxygen plasma etching resistance of plasma polymerized organometalic film was measured. The films were deposited by downstream plasma deposition using gaseous mixtures of an organic monomer (C3H6) and a metal-containing monomer tetramethyltin or tetramethylsilane. By changing the flow-rate ratio of both monomers, the metal content of the film was reproducibly varied from 0% to 27%. It was found that the O2 reactive ion etching rate depended on metal content in polymer, discharge power density, and oxygen gas pressure. High oxygen plasma etching resistance was obtained for films which contained even a few percent of metal. From the results of electron spectroscopy for chemical analysis and Auger electron spectroscopy measurements, it was observed that the metal-oxidized layer was formed on the surface during oxygen plasma etching.

Study on a positive photoresist with high dry etching resistance.

Study on a positive photoresist with high dry etching resistance.

Contrast and sensitivity enhancement of resists for high-resolution lithography

Novolac based resists have received much attention in the submicron device fabrication area because of their high dry etch resistance. In high‐resolution device fabrication requirements novolac resists suffer from a lack in sensitivity and resolution capability. In order to make use of these high‐quality resists, approaches to improve the resolution capability and sensitivity of conventional positive resists have been a major interest of research. Development techniques such as two‐step and spray development techniques to improve resist contrast have been reported, but neither is well characterized and well understood. In this paper, we report an interrupted development technique which enhances the contrast of an electron beam (e‐beam) exposed diazonapthoquinone novolac, AZ‐type resist. As a result of this enhancement, submicron features varying in density can be controlled properly in size and in image profile. The resolution capability of this resist as a single‐layer system is extended to the one‐quarter micron regime with good linewidth control. In the optically exposed AZ resist, a smaller enhancement in contrast was observed and the resolution improvement is minimal. However, vertical sidewalls are readily obtained by employing appropriate interrupted development schemes on optically as well as e‐beam exposed AZ resists. This difference in response to interrupted development is related to the difference in the energy deposited in the resist film due to electron scattering. In the e‐beam exposed AZ film, the energy deposited in the resist gradually increases through the bulk of the film. On the other hand, because of the UV absorption characteristics of the novolac resist in optical lithography, the energy deposited is attenuated as it penetrates the resist. Sensitivity enhancement by this technique is on the order of 30% to 50%. A sulfone novolac resist with an inductive effect was examined to try to understand the mechanism of contrast enhancement of AZ resist by interrupted development. No response to interrupted development was observed. Possible mechanisms for the delayed lateral erosion of the AZ resist images are proposed, based on the studies of these resists anddeveloper interactions. Using this interrupted development technique on a single‐layer e‐beam exposed resist system, various profiles can be tailored to fit different applications in device processing requirements, namely an undercut profile for metal lift‐off, straight sidewalls for etch masks or ion implantation masks.

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.

Amorphous carbon films as resist masks with high reactive ion etching resistance for nanometer lithography

We propose the application of carbon films as resist masks for practical nanometer lithography involving reactive ion etching (RIE). Amorphous carbon films prepared by room-temperature plasma chemical vapor deposition show a very high resistance against RIE, the etching rates being less than 1/2 of that of a novolak-based conventional photoresist. The carbon films can be finely patterned by O2 RIE in a bilayer resist process using a high-resolution silicone-based negative resist. Nanometer patterns as small as 40 nm are fabricated on a thick solid substrate, and can be transferred into the substrate layer directly by RIE.

Plasma developable photoresist containing electronic excitation energy quenching system

AbstractA 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.

Application of chlorinated polymethylstyrene, CPMS, to electron beam lithography

Swelling behavior and resist performance of a series of chlorinated polymethylstyrenes, CPMS, were investigated. Measurements of swelling ratio and resolution of the CPMS resist coating in a wide variety of organic solvents disclosed that resolution depends on the swelling ratio. In addition, it was found that Cellosolve acetate or methyl isobutyl ketone was the most suitable developer, and that the critical swelling ratio might be 3.2 (=1.473) for screening of a developer. Functional testings on CPMS showed the resist had considerably high sensitivity as well as high contrast and dry etch resistance. The selectivity ratio of the resist to aluminum, when the resist was used in a dry etching process, was 1.5 times as high as that of the conventional Novolak-type positive-working photoresist.

Electron sensitive negative resists of vinylaromatic polymers

AbstractElectron resist properties of three vinylaromatic polymers, polystyrene, polyvinylcarbazole and poly(3‐bromo‐N‐vinylcarbazole) have been examined. Polystyrene and polyvinylcarbazole are high contrast resists of high dry etch resistance, but for adequate sensitivity (D ⩽ ca. 10 μC/cm2 at 25 kV) high molecular weights are needed (Mw ⩾ 106). Poly(3‐brotno‐N‐vinylearbazole) has a much higher sensitivity (D = ca. 2 μC/cm2) than the unsubstituted polymer. The sensitivity of polystyrene and polyvinylcarbazole is increased appreciably by addition of organic bisazides as crosslinking agents, e.g. a sensitivity increase of almost an order of magnitude was found upon addition of 3% 4, 4′‐diazidostilbene to polystyrene, high contrast being maintained.