KEYWORDS: Annealing, Thin films, Luminescence, Solar energy, Thin film solar cells, Photovoltaics, Temperature metrology, Solar cells, Pulsed laser operation, Thin film devices
In this study, Cu2ZnSn(S,Se)4 (CZTSSe) thin films are subjected to long, low-temperature annealing treatments which have been suggested to bring the material through an “order/disorder” transition. The samples are then characterized by intensity-dependence photoluminescence measurements at low temperature. We observe that annealing the films at 150°C for 1 day causes a shift in the sub-band gap (Eg) states towards higher photon energies. One week of annealing appears to result in a similar electronic structure as 1 day of annealing, and therefore the measurements performed after 1 day roughly represents the equilibrium (kinetically-limited) defect structure for this temperature. Importantly, all samples measured in this study display strong recombination through deep states up to ~330 meV below the band gap. Therefore, while some improvements are observed to occur after long low-temperature annealing, we find that this approach does not fully remedy the band tailing states found to limit the Voc in CZTSSe thin film photovoltaics.
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.
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 IBM's primary repair tool for 248 and 193nm chrome on glass and phase shift masks.
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.
Conference Committee Involvement (1)
Laser Applications in Microelectronic and Optoelectronic Manufacturing XI
23 January 2006 | San Jose, California, United States
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