Developer-soluble bottom anti-reflective coating (DBARC) BSI.W09008 has provided promising lithography results
with five different 193-nm photoresists, with the accomplishments including 120-nm L/S (1:1) and 130-nm L/S
through-pitch (i.e., 1:1, 1:3, and isolated line). This DBARC is not inherently light sensitive and depends on diffusing
photoacid from the exposed photoresist for development. With undercutting being an issue for the PAG-less DBARC
with some resists, the shapes of 130-nm lines (both dense and isolated) were improved by either a) incorporating a small
amount of a base additive in the BSI.W09008 formulation or b) altering the structure of the DBARC's binder polymer.
With selected photoresist(s) and/or resist processing conditions, either photoacid diffusion or photoacid activity is
inadequate to give DBARC clearance and BSI.W09008 performs more as a dry BARC. The post-development residue
obtained from BSI.W09008 on a silicon substrate is much less dependent on the initial DBARC film thickness and the
exposure dose than for earlier-generation photosensitive (PS)-DBARC BSI.W07327A, using the same photoresist.
BSI.W09008 also gives less post-development residue than BSI.W07327A using the same resist on a silicon nitride
substrate at exposure doses of 14-25 mJ/cm2.
As the semiconductor industry approaches smaller and smaller features, applications that previously used top antireflective
coatings have now begun using developer-soluble bottom anti-reflective coatings (BARCs). However, there
are several drawbacks to a wholly developer-soluble system, mainly because many of these systems exhibit isotropic
development, which makes through-pitch and topography performance unsatisfactory. To solve this problem, we have
developed several photosensitive BARC (PS BARC) systems that achieve anisotropic development. One issue with the
PS BARC, as with traditional dry BARCs, is resist compatibility. This effect is compounded with the photosensitive
nature of our materials. The acid diffusion and quenching nature of the resists has been shown to have a significant
effect on the performance of the acid-sensitive PS BARC. Some resists contain a highly diffusive acid that travels to the
PS BARC during the post-exposure bake and aids in clearance. Others show the opposite effect, and the same PS BARC
formulation is not able to clear completely. To address the lack of compatibility and to further improve the PS BARC,
we have developed a solution that properly matches PS BARC and photoresist performance.
Many approaches to double patterning have been devised, of which most have been designed to reduce the number of
process steps. The litho-freeze-litho-etch process (LFLE) is one such technique that eliminates the first etch step from
the standard litho-etch litho-etch (LELE) process. The resist freeze material chemically modifies the patterned
photoresist, as well as potentially the layer beneath, which may result in a performance change at the second lithography
step. Another approach, litho-process-litho-etch (LPLE) does not involve the use of a chemical freeze material, instead
relying on a thermal treatment to remove excess solvent from the polymer and differential energy of activation between
two resists to create a double-patterned image. Finally, double patterning using negative-tone development of a positiveacting
photoresist is another approach in consideration. In this paper, we present the results of several double-patterning
processes on organic bottom anti-reflective coatings (BARCs) and spin-on multilayer stacks consisting of a silicon
hardmask on top of a carbon underlayer. Pattern profiles of the first and second lithography steps are compared.
In a search for improved resolution and processing latitude for a family of light-sensitive developer-soluble bottom antireflective
coatings (BARCs), the structure of the binder terpolymer was altered by incorporating acid-cleavable
adamantyl methacrylates. Contrast curves and 193-nm microlithography were then used as tools in developing a novel
developer-soluble adamantyl BARC which does not include a photoacid generator (PAG) or quencher, but instead
depends on acid diffusing from the exposed resist for development. This formulation eliminates concern about PAG or
quencher leaching out of the BARC during application of the photoresist. Resolution for a resist A and the new BARC
was 150-nm L/S (1:1) for both 38-nm and 54- to 55-nm BARC thicknesses. Resolution and line shape were comparable
to that of the non-adamantyl control BARC with same resist at 55-nm BARC thickness, with both BARCs giving some
undercutting using an AmphibianTM XIS interferometer for the 193-nm exposures. Light-sensitive adamantyl BARCs
that do require inclusion of a PAG for optimum lithography with resist A are also described in this paper. The series of
developer-soluble adamantyl BARCs were solution and spin-bowl compatible. The 193-nm optical parameters (n and
k) for all adamantyl BARCs were 1.7 and 0.5-0.6, respectively.
A photosensitive developer-soluble bottom anti-reflective coating (DBARC) system is described for KrF and ArF lithographic applications. The system contains an acid-degradable branched polymer that is self-crosslinked into a polymeric film after spin coating and baking at high temperature, rendering a solvent-insoluble coating. The DBARC coating is tunable in terms having the appropriate light absorption (k value) and thickness for desirable reflection control. After the exposure of the resist, the DBARC layer decrosslinks into developer-soluble small molecules in the presence of photoacid generator (PAG). Thus the DBARC layer is removed simultaneously with the photoresist in the development process, instead of being etched away in a plasma-etching chamber in the case of traditional BARC layers. The etch budget is significantly improved so that a thin resist can be used for better resolution. Alternatively, the etch step can be omitted in the case of the formation of layers that may be damaged by exposure to plasma.
A family of dye-filled developer-soluble bottom anti-reflective coatings (BARCs) has been developed for use in 193-nm
microlithography. This new dye-filled chemical platform easily provides products covering a wide range of optical
properties. The light-sensitive and positive-working BARCs use a transparent polymeric binder and a polymeric dye in
a thermally crosslinking formulation, with the cured products then being photochemically decrosslinked prior to
development. The cured BARC films are imaged and removed with developer in the same steps as the covering
photoresist. Two dye-filled BARCs with differing optical properties were developed via a series of DOEs and then used
as a dual-layer BARC stack. Lithography with this BARC stack, using a 193-nm resist, gave 150-nm L/S (1:1). A
193-nm dual-layer BARC stack (gradient optical properties) from the well-established dye-attached family of light-sensitive
BARCs also gave 150-nm L/S (1:1) with the same resist. However, the latter provided much improved line
shape with no scumming. The targeted application for light-sensitive dual-layer BARCs is high-numerical aperture
(NA) immersion lithography where a single-layer BARC will not afford the requisite reflection control.
New bottom anti-reflective coatings (BARCs) have been developed that can be incorporated into multiple patterning
schemes utilizing scanner-track-only processes. The BARCs have modifiable optical properties and can be removed
during the resist development step. Several dual patterning schemes were investigated for trench printing. The most
promising process produced 110 nm trenches with approximately 1:1 space ratios. The etch characteristics of these
BARCs under fluorinated and oxygenated gases were determined.
A novel approach to developer-soluble bottom anti-reflective coatings (BARCs) for 248-nm lithography
was demonstrated. The BARC formulations are photosensitive, dye-filled systems incorporated with a
polymer binder. The films are generated by thermally crosslinking the polymer matrix, and are then
photochemically decrosslinked in order to render them soluble in developer solutions. The BARCs are
compatible with solvents commonly used in the industry. Easy modification of the films with regard to
optical properties for potential use with various substrates was also demonstrated. The BARCs exhibit
anisotropic development in aqueous tetramethylammonium hydroxide (TMAH) solutions subsequent to
simulated photoresist application, exposure, and post-exposure bake.
This paper describes the chemistry and performance of a new family of wet-developable (wet) bottom anti-reflective coatings (BARCs) that have been developed for 193-nm implant layer applications. These BARCs, which are light sensitive and positive working, are imaged and developed in the same steps as the covering 193-nm photoresist. The BARCs are spin coated from organic solvents and then insolubilized during a hot plate bake step. The resulting cured films exhibit minimal solubility in numerous organic solvents. Resolution of a photoresist A and light-sensitive BARC I at optimum exposure (Eop) on a silicon substrate was 150-nm L/S (1:1), with good sidewall angle and no scumming. These best-case results utilize a first reflectivity minimum BARC thickness and meet the desired resolution goals for noncritical implant layers. BARC optical parameters can easily be adjusted by altering the polymeric binder. PROLITHTM modeling shows that near zero reflectance can be achieved on a silicon substrate for both a first and a second reflectivity minimum BARC thickness. The light-sensitive, wet BARCs are both spin-bowl and solution compatible with most industry standard solvents. A selected BARC from this family of wet products was shown to be stable, providing reproducible film properties over several months of ambient storage conditions.
Thermally curable hybrid high refractive index polymer solutions have been developed. These solutions are stable up to 6 months under room temperature storage conditions and can be easily spin-coated onto a desired substrate. When cured at elevated temperature, the hybrid polymer coating decomposes to form a metal oxide-rich film that has a high refractive index. The resulting films have refractive indices higher than 1.90 in the entire visible region and achieve film thicknesses of 300-900 nm depending on the level of metal oxide loading, cure temperature being used, and number of coatings. The formed films show greater than 90% internal transmission in the visible wavelength (400-700 nm). These hybrid high refractive index films are mechanically robust, are stable upon exposure to both heat and UV radiation, and are currently being investigated for microlithographic patterning potential.
The performance of optoelectronic devices can be increased by incorporating a high refractive index layer into the system. This paper describes several potential high refractive index resin candidates. Our materials include the added advantages over other systems because the new materials are cationically photocurable and free flowing, have low shrinkage upon cure, have no (or little) volatile organic components, are applicable by a variety of methods (dip coating, roller coating, injection molding, or film casting), can be applied in a variety of thicknesses (10-100 m), are fast-curing, and possess robust physical properties. Particular attention focuses on the refractive index in the visible spectrum, light transmission, and formulation viscosity.
Press-patterning of polymers to yield optical structures is being pursued in optics and photonics to yield low-cost optical components. This is a promising technology for the low-cost and high-throughput fabrication of polymeric photonic components. The processing of such imprinted photonic components is usually done using a metallic shim where a pattern is generated on the shim by electroforming or electroplating. The shims are then used to replicate patterns on plastics and polymers under high temperatures and pressures. Under the correct conditions, the polymer flows and replicates a diffraction grating.
Polymeric diffraction gratings and holograms have applications in a multitude of photonic applications for diffractive optics. This requires materials that are transparent in the visible region, and preferably have relatively high refractive indices in order to achieve a high diffraction efficiency. In addition, in order to facilitate processing by the press-patterning method that will be further described in this paper, polymeric materials that are amenable to spin-coating and show good thermoplastic behavior are also desired.
Optically transparent, high-refractive index polyimides were tested for their ability to be processed and patterned using a press-patterning method. A process that allowed the materials to be patterned were developed, and measurements were taken to validate the results. Our initial results showed successful press-patterned polyimide films with grating structures having submicron line and trench widths and step heights of less than 0.5 microns.
A series of soluble, fully aromatic polyetherimides were prepared as candidate materials for optical coating applications. Most of the new polymer coatings possessed high transparency in the optical and near-infrared spectral regions at thicknesses ranging from 1 to 10 microns. The refractive indices obtained ranged from 1.60 to 1.80 at visible wavelengths, with the highest values generally being obtained near 400 nm followed by a gentle decline as wavelength increased to 700 nm and beyond. The refractive index values could be controlled by varying the dianhydride and diamine composition. All of the polyimides showed good thermal stability to 400°C and displayed glass transition temperatures above 220°C, making them excellent candidates for device applications where increased refractive index and high optical clarity are desired. The paper will discuss the preparation and physical and optical properties of the polymers and compare them to other high index coating systems.
The performance of many solid-state devices including emissive displays, optical sensors, integrated optical circuits, and light-emitting diodes can be improved by applying a transparent high refractive index coating (≥ 1.65) onto the light-emitting or light-sensing portion of the device. Ideally, the coating should combine the excellent durability and easy deposition of a spin-applied polymer coating with the high refractive index and optical clarity of a vacuum deposited metal oxide coating such as titanium dioxide or zirconium oxide. While some success has been achieved in combining these very dissimilar materials to form transparent hybrid coating systems, for example, using sol-gel or nanoparticle dispersion techniques, the resulting coating systems often require complicated manufacturing schemes and have limited storage stability and reliability.
We have demonstrated two new approaches to development of high refractive index polymer coatings. In the first approach, an organometallic polymer and a conventional organic polymer are combined to form a compatible coating. When cured at elevated temperatures, the organometallic polymer decomposes to form a highly dispersed metal oxide phase that imparts high index properties to the final hybrid coating. The new coatings are transparent and have
refractive indices ranging from 1.6 to as high as 1.9 depending on the metal oxide content.
The second approach utilizes our discovery that polyimide materials possess naturally high refractive indices in comparison to most polymer materials. Through careful molecular design, we have developed a new class of polyimide materials having refractive indices ranging from 1.60 to 1.78 at visible wavelengths and exhibiting excellent optical clarity. The new polyimides can be spin-applied to a layer thickness of more than 10 microns in a single coating step and form thermally stable films with good mechanical strength and adhesion to device substrates.
We are developing a set of dyed red, green, and blue color filter coatings for the fabrication of high resolution CCD and CMOS image sensor arrays. The resists contain photosensitive polymer binders and various curing agents, soluble organic dyes, and solvents. The new dyed photoresists are sensitive to i-line radiation, primarily at 365 nm, and are negative-working, requiring less than 500 mJ of exposure energy for patterning. The coatings are developed in standard Tetramethylammonium Hydroxide (TMAH) developers. Many dyes were examined in order to achieve the desired spectral properties as well as the meet the solvent solubility and thermal stability requirements. Computer modeling was utilized to determine the correct proportions of dye(s) in each resist, after which the modeling results were verified by actual formulation and testing. Thermal stability of the dyes was determined using isothermal. Thermogravimetric Analysis (TGA) at 200°C for 30 minutes. The dyes were evaluated in both traditional (free radical) and novel polymer systems to see if adequate sensitivity, resolution, and feature quality could be obtained. The studies showed that traditional free radical-based photochemistries are marginal at best for high resolution (1-2 micron) applications. To overcome this limitation, a new polymer system having photodimerizable functional units and acid functional groups was developed to impart photosensitivity and developer solubility, respectively. This system, which does not use free radical-initiated photopolymerization as a mechanism for patterning, shows low exposure dose requirements and is capable of resolving features less than 2 micron in size.