Microlithographic Applications Research Articles

Measuring of High Quality Optics for Lithography

AbstractHighly homogeneous glasses and crystalline materials such as CaF2 (calcium fluoride) are used in microlithographic applications. Inherent stresses in the material induced in manufacture lead to stress birefringence and thus to imaging errors, which is undesirable for semiconductor manufacture in view of the ever smaller structure sizes. Materials from which optical components for wafer steppers are manufactured must therefore also satisfy high requirements with regard to inherent stresses.

Surface assessment of CaF_2 deep-ultraviolet and vacuum-ultraviolet optical components by the quasi-Brewster angle technique

The requirements for optical components have drastically increased for the deep-ultraviolet and vacuum-ultraviolet spectral regions. Low optical loss, high laser damage threshold, and long lifetime fluoride optics are required for microlithographic applications. A nondestructive quasi-Brewster angle technique (qBAT) has been developed for evaluating the quality of optical surfaces including both top surface and subsurface information. By using effective medium approximation, the negative quasi-Brewster angle shift at wavelengths longer than 200 nm has been used to model the distribution of subsurface damage, whereas the positive quasi-Brewster angle shift for wavelengths shorter than 200 nm has been explained by subsurface contamination. The top surface roughness depicted by the qBAT is consistent with atomic force microscopy measurements. The depth and the microporous structure of the subsurface damage measured by the qBAT has been confirmed by magnetorheological finishing. The technique has been extended to evaluate both polished and antireflection-coated CaF(2) components.

Poly(ferrocenylsilanes) as etch barriers in nano and microlithographic applications

AbstractThin films of organic‐organometallic block copolymers are shown to be efficient self‐assembled templates for nanolithography. Block copolymers composed of organic blocks such as polyisoprene or polystyrene and a poly(ferrocenylsilane) block microphase separate to form a monolayer of densely packed organometallic spheres in an organic matrix. The high resistance of the organometallic phase to reactive ion etching enables the nanoscale patterns to be transferred into silicon substrates, forming nano structured surfaces. Electrostatic self‐assembly of poly(ferrocenylsilane) polyanions and polycations is discussed as a means to form laterally structured organometallic multilayer thin films by area‐selective adsorption onto chemically patterned substrates.

Polymers for microlithographic applications: new directions and challenges

Advances in the fabrication technologies associated with electronic devices have placed increasing demands on microlithography, the technology used to generate today's integrated circuits. Within the next few years, a new form of lithography will be required that routinely produces features of less than 0.1 μm. As the exposing wavelength of light decreases to facilitate higher resolution imaging, the opacity of traditional materials precludes their use; and major research efforts to develop alternate materials are underway. As a current example, lithography tools utilizing 193 nm light are now being introduced into the manufacturing environment. Through understanding of materials structure and its relationship to device process requirements and performance, a new class of cyclo-olefin based polymers was designed for these applications. In particular, alicyclic monomers such as norbornene are readily copolymerized with maleic anhydride and substituted acrylates to afford a wide range of alternative matrices that exhibit transparency at the exposing wavelength and aqueous base solubility. Materials properties must be carefully tailored to maximize lithographic performance with minimal sacrifice of other performance attributes. Further reduction in exposing wavelength to 157 nm introduces new challenges in polymer materials design. Efforts to address those challenges will be discussed.

Supramolecular Approaches to Nanoscale Dielectric Foams for Advanced Microelectronic Devices

The increasing demands of miniaturization in the microelectronics industry has forced continual improvement in the materials that are used in the fabrication of semiconductor devices. Advances in photoresists for microlithographic applications have reduced the feature size to 0.25 µm and below, and this drive to eversmaller features, coupled with the introduction of copper, has placed increasing demands on the dielectric material. Materials with lower dielectric constants (depicted in dark gray in Figure 1) are therefore required to more efficiently insulate these submicron features, such as the copper interconnect lines used to connect the transistors and memory cells in these advanced multilevel devices (Figure 1). This allows the minimization of crosstalk, signal delays, and power consumption. While vapor-deposited silicon dioxide and other derivatives are currently being employed, they suffer from unacceptably high dielectric constants (ε > 3.6) and are unacceptable for future generations of microelectronic devices.

Precise Characterization of Resists and Thin Gate Dielectrics in the VUV Range for 157nm Lithography

AbstractSpectroscopic ellipsometry is one of the most important tools for thin film metrology. It is now intensively used in microelectronics and especially for the microlithographic applications. Instrumentation for the next generation of VUV lithography at 157nm requires special optical setup since oxygen and water are extremely absorbing below 190nm. Recently a new ellipsometer included in a purged glove box to reduce the oxygen and water contamination in the part per million range has been developed. In the VUV range, roughness and interface diffusion become critical since the layer thickness is generally reduced. An independent characterization technique like the grazing x-ray reflectance is then extremely complementary to ellipsometry in this wavelength region. The present paper presents recent results on up to date lithography samples combining the two characterization techniques. Photoresists and gate dielectrics are successively examined.

A New Purged UV Spectroscopic Ellipsometer to characterize 157nm nanolithographic materials

AbstractSpectroscopic ellipsometry has long been recognized as the technique of choice to characterize thin films and multilayers. It is now intensively used in microelectronics and especially for the microlithographic applications. Instrumentation for the next generation of UV lithography at 157nm requires special optical setup since oxygen and water are extremely absorbing below 190nm. The ellipsometer discussed in this paper works into a purged glove box to reduce the oxygen and water contamination in the part per million ranges. The optical setup has been especially studied for microlithographic applications. It includes for example a premonochromator in the polariser arm to avoid resist photobleaching. Technical details of the system and some first measurement results on substrates and thin films are reported hereafter.

Progress in the chemistry of organosilicon resists

AbstractRecent developments in the chemistry of organosilicon polymers for use as oxygen plasma‐resistant imaging materials in microlithography are reviewed. Various classes of resists, grouped according to molecular structure, are described with special emphasis on properties critical in microlithographic applications. In addition, several silylation schemes involving selective silylation of a non‐silicon‐containing resist material following patternwise exposure to actinic radiation are also described.

Conformations of poly(methyl methacrylate) and its degraded forms upon radiation

The radiation-induced decomposition of syndiotatic (st) and isostatic (it) poly(methyl methacrylate) (PMMA) to yield irradiation products (PMMA(d)) resulting from hydrogen abstraction from alpha-methyl or methylene groups to form main chain (M[double bond]) or side chain (S[double bond]) double bonds is studied by conformational analysis. Relative minimum energy conformations of the st- and it-isomers of PMMA as free molecules are studied. The isomers of PMMA(d) have relative minima in an overall linear (L) chain as well as a global minimum in a bent (B) form. The impact of the change of a tetrahedral C atom to a trigonal C atom upon double bond formation on the conformational energy is fundamental to the understanding of the results. The experimental results are explained by the following theoretical observations. In reactions involving only overall linear conformations, side chain double bond formation is favored because of the resulting large increase in steric repulsion between polymer units in main chain double bond formation. In reactions proceeding to bent conformations, however, the decreased steric interaction yields both main and side chain double bond formation within 6.3 kcal/mol for the st-PMMA(d) isomer and 2.2 kcal/mol for the it-PMMA(d) isomer. Reactions on surfaces are assumed to be constrained tomore » the overall linear conformation of the starting material, PMMA. Prevention of both M[double bond] and S[double bond] degradation products is desired for microlithographic applications. Increased solubility arising from main chain scission (MCS) is desired, and both M[double bond] and S[double bond] for that reason are undesirable with respect to resist sensitivity. It is proposed that the troublesome S[double bond] process can be attenuated or eliminated by replacing alpha-CH[sub 3] with alpha-CF[sub 3], thus enhancing the distribution of products toward MCS.« less

High performance acrylic polymers for chemically amplified photoresist applications

Chemically amplified resists have recently achieved importance as materials useful for high density microlithographic applications requiring submicron imaging. In an effort to extend the chemical amplification concept to applications requiring thick film resists, we have developed a family of acrylic polymers which provide high performance, aqueous developing positive resists when formulated with the appropriate photo-acid generators. The polymers were prepared from methyl methacrylate (MMA), t-butyl methacrylate (TBMA) and methacrylic acid (MAA), each of which serves a separate function in the formed terpolymer. An unusual degree of control over the aqueous development kinetics can be achieved by manipulation of the terpolymer composition. The lithographic properties of resist formulations based on these polymers have been examined employing optical exposure at wavelengths from 248 to 514 nm, and e-beam exposure.