Allen H. Gabor

Block and random copolymer resists designed for 193-nm lithography and environmentally friendly supercritical CO2 development

The concept of using block copolymers as resist materials is presented. Both the demonstrated enhancements of block copolymers, compared to random copolymer resists, as well as benefits still to be exploited are discussed. In our own research, block and random copolymer 193 nm resists were prepared using the monomers tert-butyl methacrylate (t-BMA) and 3- methacryloxypropylpenta-methyldisiloxane (SiMA). The resists have a high resistance to oxygen plasma reactive ion etching, making them suitable for the imageable layer of a bilevel resist system. Of particular interest is the development behavior of the copolymer resists. After exposure, the block copolymers develop better in aqueous base than the corresponding random copolymers. Thus, it appears that incorporating the hydrophobic (but etch resistant) siloxane component into the resist as a distinct block is an effective way of achieving aqueous base solubility with copolymers of t-BMA and SiMA. The copolymers with higher silicon- concentrations are also developable as negative tone resists using environmentally friendly supercritical carbon-dioxide. Thus, without using organic solvent, these resists are developable in both positive and negative tones. Some of the future benefits of using block copolymers that we envision include diffusion barriers for photo-generated acid and passivation of reactive substrates.

193 nm single layer resist strategies, concepts, and recent results

Matrix resins used in conventional resists are not suitable for use at 193 nm due to their opacity. Hence new materials that are functionally similar to but structurally different from novolac and poly(hydroxy styrene) are required for 193 nm lithography. We report on the use of alternating copolymers of cycloolefins with maleic anhydride as effective 193 nm matrix resins, with or without dissolution inhibitors based on polyfunctional cholates, for 193 nm lithography. Due to their structural diversity, the required high transparency and etch stability, compatibility with industry standard 0.262 N tetramethyl ammonium hydroxide (TMAH) can be built into the polymer by conventional free redical polymerization techniques. A correlation between the molecular properties of the resist components (matrix resin, dissolution inhibitor, photoacid generator, and base additive) and resist lithographic performance parameters is illustrated. The formulations containing dissolution inhibitors currently show 0.13 μm line/...

Silicon containing polymer in applications for 193 nm high NA lithography processes

The ability to extend 193 nm lithography resolution depends on increasing the numerical aperture (NA) of the exposure system, resulting in smaller depth of focus, which subsequently requires use of thinner photoresists. Bottom antireflective coatings (BARCs) are a necessity, but the organic composition of current 193 nm BARCs offers poor etch selectivity to the photoresist. As a result, image transfer with thin resists is becoming increasingly difficult. It is also more challenging to control reflectivity at high numerical apertures with a thin, single layer BARC. To address these issues, IBM has developed a new class of silicon containing BARCs. These materials exhibit high etch selectivity that will significantly improve the performance of high NA 193 nm lithography. The incorporation of silicon in the backbone of the polymers comprising these BARCS affords a high etch selectivity to conventional organic resists and therefore these polymers can be used as thick planarizing BARCs. The optical constants of these BARCs have been tuned to provide good reflectivity control at NA > 1.2 These materials can also be used as part of a dual layer BARC scheme composed of the thin organosilicon based BARC coated over a planarizing organic underlayer. This scheme has also been optically tuned to provide reflectivity suppression at high incident angles. By utilizing a thick BARC, a novel contact hole shrink process is enabled that allows tapering of the sidewall angle and controlling the post-etch critical dimension (CD) bias. Structures of the silicon containing polymer, formulation chemistry, optical tunability, lithography at high NA and RIE pattern transfer are reported.

Improving the power-performance of multicore processors through optimization of lithography and thermal processing

It is generally assumed that achieving a narrow distribution of physical gate length (Lpoly) for the poly conductor layer helps improve power performance metrics of modern integrated circuits. However, in advanced 90 nm technologies, there are other drivers of chip performance. In this paper we show that a global optimization of all variables is necessary to achieve the optimum performance at the lowest leakage. We will also describe how systematic physical gate-length variation can improve core matching in multicore designs.

Overlay improvement roadmap: strategies for scanner control and product disposition for 5-nm overlay

To keep pace with the overall dimensional shrink in the industry, overlay capability must also shrink proportionally. Unsurprisingly, overlay capability < 10 nm is already required for currently nodes in development, and the need for multi-patterned levels has accelerated the overlay roadmap requirements to the order of 5 nm. To achieve this, many improvements need to be implemented in all aspects of overlay measurement, control, and disposition. Given this difficult task, even improvements involving fractions of a nanometer need to be considered. These contributors can be divided into 5 categories: scanner, process, reticle, metrology, and APC. In terms of overlay metrology, the purpose is two-fold: To measure what the actual overlay error is on wafer, and to provide appropriate APC feedback to reduce overlay error for future incoming hardware. We show that with optimized field selection plan, as well as appropriate within-field sampling, both objectives can be met. For metrology field selection, an optimization algorithm has been employed to proportionately sample fields of different scan direction, as well as proportional spatial placement. In addition, intrafield sampling has been chosen to accurately represent overlay inside each field, rather than just at field corners. Regardless, the industry-wide use of multi-exposure patterning schemes has pushed scanner overlay capabilities to their limits. However, it is now clear that scanner contributions may no longer be the majority component in total overlay performance. The ability to control correctable overlay components is paramount to achieving desired performance. In addition, process (non-scanner) contributions to on-product overlay error need to be aggressively tackled, though we show that there also opportunities available in active scanner alignment schemes, where appropriate scanner alignment metrology and correction can reduce residuals on product. In tandem, all these elements need to be in place to achieve the necessary overlay roadmap capability for current development efforts.

High-NA swing curve effects

The periodic variations of dose-to-clear, reflection and CD with resist thickness are well known phenomena commonly known as swing curves. Proper process control dictates that the resist thickness is chosen at a swing extreme, so as to reduce dose variation. Swing curves are commonly calculated for normal incidence waves. The recent trends toward high NA optics and use of off-axis illumination introduce oblique waves into the swing curve problem. Significant shifts in the magnitude and the phase of the different swing curves are now possible, and these shifts depend on exposure illumination configuration. This paper will discuss the impact of oblique waves on the swing curve. Experimental swing curves for both 248 and 193nm resist processes will be compared with expectations from simulations.

Modeling influence of structural changes in photoacid generators on 193 nm single layer resist imaging

We present recent modeling work aimed at understanding the influence of structural changes in photoacid generators (PAGs) on acid generation efficiency, deprotection efficiency, and photoacid diffusion in 193 nm chemically amplified resists. An analytical model for the postexposure bake process is used to study the reaction and diffusion properties of the various acids generated by the PAGs. Fourier transfer infrared spectroscopy is used to monitor the generation of photoacid during exposure. Resist thickness loss after PEB as a function of exposure dose is related to the deprotection extent to extract the reaction rate parameters. The effects of the acid size and boiling point on process latitude, line end shortening, and line edge roughness are presented. Analytical model predictions of process latitude and line end shortening are also presented and compared to experimental data. In this study, the photogenerated acid with the smallest molar volume and highest boiling point temperature gave the best ove...

Resist outgassing as a function of differing photoadditives

The effect of different photoadditives in high and low activation energy resist resins on resist outgassing during lithographic exposure was studied by quartz microbalance and gas chromatography/mass spectroscopy techniques. The resist outgassing was analyzed both qualitatively and quantitatively and structure-property relationships were developed between resist outgassing and the molecular structure of photoacid generators and additives. The photoadditives examined include, aryl iodonium perfluoroalkylsulfonates, triarylsulfonium perfluoroakylsulfonates, photogenerators of sulfamic acids, 2-nitrobenzyl PAGs and doxyl derivatives.

193-nm single-layer photoresists based on alternating copolymers of cycloolefins: the use of photogenerators of sulfamic acids

Single layer resists for 193 nm based upon resins derived from alternating copolymers of cycloolefins and maleic anhydride will be discussed. Our past work has examined the effect of polymer structure and composition, dissolution inhibitor structure and loading as well as the effect of the photoacid generator on the resist dissolution properties. In this paper, we will report upon on some of our recent investigations aimed at improving performance by use of a new class of photoreactive additives, photogenerators of aminosulfonic acids. One example of these, bis(t- butylphenyl)iodonium cyclamate, will be shown in our high activation 193 nm single layer resist system as being a useful photodecomposable base additive capable of limiting acid diffusion and alleviating post exposure bake delay effects. Finally, we will describe the utility of these materials in low activation energy (acetal based) resist systems.

Smaller, smarter, faster, and more accurate: the new overlay metrology

With the introduction of double patterning, overlay capability below 5nm is required for optical lithography density scaling to the 22nm node and beyond. Commensurate overlay metrology must enable dense sampling of all patterned area to control single-nanometer systematic sources of error among an increasing number of device layers. This translates to the need for sub-second measurement of microscopic targets representing multiple layers within a metrology tool field of view, all while improving accuracy. Blossom (BLO) is the overlay metrology of record for the IBM 32nm technology. As we will describe here, the densely packed array of layers represented in a single BLO target has enabled us to conduct within-field in-line sampling on our most critical layers. We will also report the significant improvements to metrology performance that have resulted from our migration of BLO technology to a new measurement platform. In addition, as 22nm development proceeds, we are shrinking our overlay targets further. A target suitable for within-chip insertion, a 10μm square micro-Blossom (μBLO) target, can accommodate up to 8 layers. Correlation of μBLO to BLO measurements on a layer pair shows excellent agreement, and despite an approximately 10X area shrink relative to BLO, the μBLO measurement uncertainty remains comfortably below 0.5nm. Our paper presents details of our target layout, measurement, and analysis approach. In addition, we detail data representative of overlay variation in state-of-the-art lithographic processes, along with our outlook for overlay metrology implementation for future technologies.