Micron Patterns Research Articles

Investigations on Reaction Mechanisms in a Surface Modification Resist Process Using Chemical Vapor Deposition of Polysiloxane

A surface modification resist process (SMR), in which polysiloxane is formed on the exposed resist surface by chemical vapor deposition, was studied for subquarter micron pattern fabrication. This paper describes the microscopic and macroscopic reaction mechanisms in SMR when methyltriethoxysilane is used as the chemical vapor deposition gas. Hydrolysis and condensation reactions occurring in acid‐catalyzed polysiloxane formation were investigated through Fourier transform infrared spectroscopy. It was demonstrated that the hydrolysis is the dominant reaction rather than the condensation, and is dependent on the generated acid catalyst and sorbed water. Polysiloxane layer growth at the near resist surface was observed by Rutherford backscattering spectroscopy and from cross‐sectional views of the polysiloxane layer. The polysiloxane layer initially grows in the resist film because of the dominant diffusion of methyltriethoxysilane molecules. Afterward the diffusion is prevented due to the excessive networking of the polysiloxane so that the polysiloxane layer grows on the resist surface. Furthermore, 0.20 μm pattern fabrication was demonstrated by applying SMR to KrF excimer laser lithography with an alternating phase‐shifting mask.

ArF surface modification resist process with enhanced water sorption ability

Surface modification resist (SMR) process, which gives negative-tone image owing to the polysiloxane formation in the exposed resist surface using chemical vapor deposition, was studied for subquarter micron pattern fabrication. SMR was based on the hydrolysis of alkoxysilane and the subsequent condensation reaction in the presence of an acid catalyst and water. This article describes the application of SMR to ArF excimer laser lithography with enhanced water sorption ability. We propose the copolymer of propylideneimino p-styrenesulfonate (PPISS) and methyl methacrylate with enhanced water sorption ability in order to improve the selectivity of the polysiloxane formation. PPISS generates sulfonic acid and acetone which acts as the diffusion promoter of water molecules. It was demonstrated that the hydrolysis reaction was promoted and the polysiloxane was more selectively formed with high sensitivity by using the proposed polymer. The influence of PPISS units ratio for the selectivity of polysiloxane formation and dry etch durability was investigated. Below 0.2 μm patterns fabrication was demonstrated by optimizing the ratio of the PPISS unit which functioned as the selective generation of acid and acetone.

Realisation of irregular quarter-micron patterns in thick resists using an advanced e-beam sensitive TSI process

The TSI process enables a high resolution of lines and spaces in thick resists by e-beam direct writing. The realisation of irregular patterns requires the compensation of the pattern-related backscattering by a proximity correction. The scattering parameters were determined by a new method. The non-complete elimination of the flow effect by an aqueous presilylation development and the pattern-dependent deposited energy cause variable silicon profile angles and impede the accurate CD realisation of irregular patterns. We developed guidelines for the choice of the process parameters enabling the compensation of CD deviations and the preparation of irregular quarter micron patterns in 1.2μm thick resist.

Chemically Amplified Resists Using 1,2‐Naphthoquinone Diazide‐4‐sulfonates as Photoacid Generators

A novel positive chemically amplified resist containing partially t‐butoxycarbonylmethylated poly(4‐hydroxystyrene)s and 1,2‐naphthoquinone‐4‐sulfonates (NQ4)s was investigated. The resists are effective for a wide region of UV lights including i‐line and excimer laser lights. The NQ4s photodecompose to form sulfonic acids which accelerate the decomposition of t‐butyl moieties of the polymers to form carboxylic acid. Only a few % of NQ4s realize the chemically amplified resists. NQ4s having electron‐withdrawing groups give resists with high sensitivities which provide excellent subhalf micron patterns when exposed to either i‐line light or excimer laser.

Micrometer patterning of phthalocyanine derivatives by selective chemical vapor deposition method

Selective chemical vapor deposition was achieved to produce copper phthalocyanine thin films on the copper microelectrodes on insulating and optically transparent materials. By thermally annealing the fabricated films at 500 °C under vacuum, their quality was greatly improved and the conductivity of the modified copper microelectrodes became high.

Silylation Process for Quarter Micron Lithography.

Silylation process is one of the most attractive surface imaging techniques for deep-UV lithography. We demonstrate the quarter micron pattern fabrication by using KrF excimer laser (248nm) lithography with surface imaging such as silylation process. Furthermore, by combining silylation process with the phase-shifting mask, it can be expected that the excellent resolution and focus latitude are obtained. In fact, experimental results exhibit below quarter micron pattern resolution with large depth of focus. The developed surface imaging technology is very promising for the fabrication of 256MDRAM.

Micrometer patterning of phthalocyanines by selective chemical vapor deposition

Micrometer size patterns of copper phthalocyanine derivatives were fabricated from 1,2,4,5-tetracyanobenzene (TCNB) by a selective chemical vapor deposition method. Copper films were patterned on silicon wafers by photolithography and wet etching techniques, sealed in a glass tube with TCNB, and heated at different temperatures. Controlling the treatment temperature, selective chemical vapor deposition was achieved to produce copper phthalocyanine thin films on the copper patterns. After thermal annealing of the deposited film in vacuum, the films were converted to a polymer of the copper phthalocyanines.

An overview of x-ray lithography for use in semiconductor device preparation

Different aspects of X-ray lithography with a proven capability for the fabrication of 0.1 μm lines and 0.5 μm devices such as ULSI and multi-megabit memory are discussed. The technical, dimensional and economic features of modern X-ray sources such as synchrotron with classical, normal and superconducting storage rings, have been compared. Materials fully transparent or opaque to X-rays do not exist and so the choice of X-ray mask substrate and patterning of absorber on it are rather critical. EBL, FIBL, RIE, XRL and other techniques used for preparing submicron masks have been dealt with. The sensitivity and resolution of 16 positive and negative X-ray resists vis-à-vis specific sources and characteristic features of 7 XRL systems are compared. Alignment schemes using laser controlled stage and visible lights are discussed. R&D as well as commercial systems and results like quarter micron patterns, 0.5 μm CMOS, SAW BPF and large aspect ratio grooves are demonstrated.

Directional etching of Si with perfect selectivity to SiO2 using an ultraclean electron cyclotron resonance plasma

Using a newly developed ultraclean electron cyclotron resonance plasma etcher, Si wafers masked by SiO2 were etched with a chlorine plasma at pressures of 0.6–4.0 mTorr with a microwave power of 300–700 W. Ultraclean processing under a low ion energy condition at high pressures has revealed that there is an induction period during which time there is no SiO2 etching. This is not observed with Si. During the induction period, perfectly selective etching for Si to SiO2 has been achieved. Under this perfectly selective condition, anisotropic tenth micron patterns of polycrystalline silicon have been obtained with little undercut.

Process compatibility using high sensitivity resist for KrF excimer laser lithography-ASKA.

The current state of the art g-line and i-line photolithography using conventional novolac based resists will be able to pattern 0.5-0.6micron devices adequately, however beyond 0.5micron, an alternative lithography will be required. KrF excimer laser lithography is one of the leading candidates for sub-half micron VLSI lithography. This technology will be able to take advantage of the higher resolution and wider depth of focus possible with the smaller wavelength. One of the major technical barriers for application of this technology to mass production is the low sensitivity of commercially available resists. New non-novolac based resist have been introduced with high sensitivity to meet this requirement. By using chemical means, Ito [1] was able to achieve quantum efficiencies much greater than one resulting in very sensitive resist systems. In this paper we describe our work to develop ASKA, Alkaline Soluble Kinetics using Acid Generator, positive resist. This resist has sensitivity greater than 25mJ/cm2 which is sufficient for a controllable manufacturing process. ASKA resist also has very good lithographic characteristics with resolution to 0.40micron and near vertical resist profiles. Process characterization of ASKA resist is also reported. Post exposure bake (PEB) is a critical step that controls performance of this resist. ASKA resist has excellent stability and linewidth control and is not dependent on the time between exposure and PEB. The resist has wide exposure latitude up to +-15% for 10% variation in linewidth. ASKA has mask linearity down to 0.40micron lines where at 0.35micron the linewidth begins to deviate from linearity. Depth of focus for 0.40micron lines is about +-1.0micron. Etch resistance is evaluated and reported for silicon dioxide, nitride and polysilicon layers. ASKA was successfully applied to actual device wafers. KrF excimer laser lithography using ASKA resist can fabricate sub-half micron patterns for 64M DRAM.

Nanolithography for VLSI and ULSI

Lithography techniques hold the key to achieving ultra large-scale integration (ULSI) and they have been a major research subject. For fabrication of ULSI devices, a quarter micron or smaller pattern delineation with nanometer scale accuracy is required. Various techniques using electron, ion and photon beams have been investigated to fulfill these requirements. The present paper discusses the characteristics of several key lithography techniques and their limitations.

Resolution limits of optical methods for the defectinspection of lithography masks

The most advanced inspection machine available today detects 250nm defects in 500nm features, which matches the demand in the production of 5:1 and 10:1 optical masks. In the near future the microelectronic industry might need 1:1 x-ray masks for the printing of feature sizes below 500nm and may use 1:1 optical masks for one micron pattern. Both types of masks require the detection of minimum defect sizes below 150nm. This paper focuses on the detection of those defects by optical sampling. Measurements of the optical signal of edge defects on a chrome-glass-wafer are presented and the limitations to enhance the signal are discussed. Based on a simple model for the optical image, the false defect signals are calculated followed by a discussion of inspection strategies in order to find out about the minimum detectable defect signal. The results suggest a resolution limit at about 100nm defect size.

X-Ray Lithography Using Chlorinated Polymethylstyrene (CPMS) as a Negative X-Ray Resist

The development characteristics of chlorinated polymethylstyrene (CPMS) have been studied in order to form half micron patterns with X-ray lithography. The solubility and the swelling of CPMS are very sensitive to the chlorine content, especially in ethylcellosolve (EC); swelling has been reduced while maintaining a reasonable solubility in the development process of a CPMS (\\overlineMw=52×104, Cl%=21.8 wt%) using an EC as a developer. This CPMS has been called CPMS-HR. The resolution of CPMS-HR has been influenced by a resist shrinking procedure which is determined by the rinse sequence. EC development followed by the optimum rinse sequence has formed 0.4-µm wiring patterns of CPMS-HR with a thickness of 1.2 µm. The advantages of the X-ray lithography using a single CPMS-HR layer have been demonstrated through the application of the X-ray lithography to a VLSI fabrication process.

A Half-Micron Gate GaAs FET Fabricated by Chemical Dry Etching

A new microfabrication method is devised to make a submicron gate GaAs FET's. Ordinary photolithographic techniques are applied to duplicate a one micron pattern on the photoresist film deposited on a thick metal layer. Controlled undercutting of the metal by chemical dry etching produces a submicron contact with the semiconductor, leaving a wide metal top surface. This process gives experimentally confirmed advantages for reproducibility, accurate duplication, easiest lithography and minimal parasitic resistance. Half-micron gate GaAe FET's are fabricated by using this technique combined with triple layer (n«-n-buffer) epitaxial growth. The maximum frequency of oscillation observed is as high as 80 GHz and the noise figure as low as 3 dB at 12 GHz. The new technology has not resulted in any adverse effects and the high frequency performance is improved in direct proportion to the gate length.

Projection-type aligning and exposure device for micron patterns JUBPM50

Projection-type aligning and exposure device for micron patterns JUBPM50