Peter P. Longo

MARS: Femtosecond laser mask advanced repair system in manufacturing

Presently available nanosecond laser based tools for removing Cr defects from photomasks have proven inadequate to the task due to the thermal nature of the ablation process which produces metal splatter, haze, reduced transmission, and pitting of the quartz substrate. These problems are virtually nonexistent when employing femtosecond pulses of light to ablate Cr defects in a nonthermal process. Photomasks repaired with ultrashort light pulses exhibit transmission approaching 100%, no observable glass damage, and exceptional spatial resolution. We have built a femtosecond pulsed laser mask repair system which is presently operating successfully in a manufacturing environment.

Implementation and performance of a femtosecond laser mask repair system in manufacturing

Current laser based tools for removing Cr defects are fundamentally limited due to the thermal nature of ablation carried out with nanosecond pulses. Conversely, ablation carried out with femtosecond pulses of light removes Cr in a non-thermal process. As a result, the problems of metal splatter, haze, reduced transmission and pitting of the underlying quartz common to nanosecond ablation are virtually nonexistent with femtosecond ablation of Cr. In this paper we describe a femtosecond pulsed laser mask repair system which is presently operating successfully in a manufacturing environment.

Femtosecond laser ablation and deposition of metal films on transparent substrates with applications in photomask repair

We describe experiments using ultrashort pulses of laser light to ablatively remove opaque and partially transmitting materials from transparent substrates. Pulses of 100 femtosecond duration at a wavelength of 266 nm were used to repair defects on photomasks used in lithographic printing of integrated circuits, with better than 100 nm spatial resolution. Details of the development and implementation of a photomask repair tool, presently operating in manufacturing, which exploits the advantages of ablation with femtosecond pulses, are presented. We further describe experiments where pulses of 400 nm light were used to photolytically deposit Cr metal with better than 200 nm resolution. Finally we describe a gas phase 35 femtosecond laser source used to extend this approach to ablative mask repair at 193 nm.

MARS2: an advanced femtosecond laser mask repair tool

Femtosecond pulsed lasers offer fundamental advantages over other techniques for repairing lithographic masks. Since the femtosecond ablation process is non-thermal, the spatial resolution is not degraded by thermal diffusion and is therefore limited only by optical diffraction. In addition, metal splatter, gallium staining, reduced optical transmission, beam induced charging, quartz damage, and phase errors inherent in other repair methods are eliminated. A second generation femtosecond laser repair tool is described. The tool utilizes DUV optics which allow ~100nm mask features to be imaged. The laser beam is focused to a round, gaussian spot. This gaussian spot is scanned over the defect, thus allowing arbitrarily shaped repairs to be performed with a spatial resolution of ~100nm. Since the mask is not degraded in any way during the repair process, repairs can be performed iteratively by ablating small slices of the defect. Mask features can be trimmed to an RMS precision of ~5nm. The system is also highly automated: masks are loaded into the tool from a SMIF pod via a robot and the tool is controlled from a single screen operator interface. This new tool has been operating successfully in the IBM Burlington mask house since late 2001, and is currently IBMs primary repair tool for 248 and 193nm chrome on glass and phase shift masks.

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 resolution material ablation and deposition with femtosecond lasers and applications to photomask repair

Abstract We describe experiments using 100 femtosecond pulses of 266 nm light to ablate Cr defects from photomasks with resolution below 100 nm. In addition to the ablative removal of Cr, experiments were carried out to deposit Cr metal onto fused silica substrates using 100 fs, 400 nm light at atmospheric pressure. Multiphoton dissociation of Cr(CO)6 adsorbed on fused silica substrates initiates Cr deposition. The mechanisms for deposition on both transparent (fused silica) and absorbing (Cr metal) substrates are discussed. Finally we describe initial experiments to ablate Cr metal at wavelengths below 200 nm using light generated by frequency mixing of ultrashort, 30 fs pulses in an Ar filled capillary.

Focused Ion Beam Metrology

A focused ion beam metrology device and method are disclosed. A focused ion beam is used to measure dimensions of semiconductor features, such as top-down linewidth measurement. Low intensity focused ion beams form top view images of the semiconductor. High intensity focused ion beams etch the semiconductor in the presence of etch-enhancing material. A crater is etched to expose a cross-section the of semiconductor. The cross-section is imaged by directing low intensity focused ion beams toward the cross-section. This may be achieved by tilting the semiconductor. A three dimensional profile of a feature may be formed by successively etching the feature top surface and forming a top view image thereof. Overlaying the successive top view images forms the three dimensional profile.