This paper describes a new surface cleaning approach for photomask cleaning. This non-conventional cleaning method uses momentum transfer between aerosolized, frozen, CO2 particles and the contaminants for effective removal from surface. The purity of CO2 used is an important component in the determination of cleaning efficiency. The authors will present two methods developed to analyze hydrocarbon contamination in CO2. These analytical methods were used to compare different grades of CO2 including Ultra High Pure (UHP) grade developed for sub-micron particle removal from photomasks. Using the UHP grade CO2, it was shown that greater than 99% particle removal efficiency is possible from silicon wafer surfaces, with higher removal efficiency of sub-micron particles compared to larger size range. This particular characteristic of particle removal by cryogenic aerosol method is theoretically derived in an earlier paper. In this paper results of CO2 cryogenic aerosol cleaning with respect to electrostatic discharges on two different binary masks are presented. The paper also shows the removal of 99.9% of the progressive defects such as haze of 0.5 to 1.0 μm size. Cleaning characterization of attenuating phase shift masks with MoSiON films indicate 0.04% change in transmission and 0.37% change in phase angle after 16 cleaning cycles, suggesting that cryogenic cleaning has minimal effect on transmission and phase of att-PSM.
This paper describes the mechanism and cleaning results of a dry cleaning technology using CO2 cryogenic aerosols. The cleaning mechanism relies on momentum transfer from the aerosol particles to overcome the force of adhesion of the contaminant particles on the surface. Particle removal is possible without degradation or etching of underlying film or the need for drying with IPA as in wet cleaning. A theoretical model of particle removal based on momentum transfer is described, predicting higher removal efficiency for sub-micron particles compared to larger particles. Experimental results with Si3N4 particles on silicon wafers show that removal of sub-micron particles is 10% higher than larger particles up to 30 μm, as predicted by the model. The paper also shows experimental results of various types of contaminant particle removal in photomask cleaning. Results of post mechanical repair cleaning of photomasks show effective removal of the quartz particles without damage to the adjacent chrome lines. Inorganic contaminants such as ammonium sulphate, commonly known as "haze", is removed by cryogenic aerosol cleaning with 99% efficiency as seen using optical inspection tool. The effect of cleaning on the phase and transmission of the mask is measured with multiple cleaning. The results show that over 16 cleaning cycles, the change in transmission is 0.04% an the change in phase is 0.37°. Thus a non-invasive cleaning for sub-micron particles from photomasks is possible with CO2 cryogenic aerosols.
The utilization of visible laser diodes for laser printing is discussed. First, the characteristics of a multiple- element array of single-mode, individually-addressed red (AlGaInP) laser diodes is described. The benefit of shorter- wavelength blue lasers is then evaluated. Finally, towards the realization of a blue laser diode, we describe results for AlGaInN and its heterostructures, which have been grown by OMVPE and characterized, including electrical injection and optical pumping of InGaN/AlGaN heterostructures.
Progress in the development of surface emitting distributed feedback lasers and arrays is reported. Single devices have been demonstrated with as much as 8 percent net power efficiency, 250 mW CW output power, and 5000 hours of reliable CW operation. Continuous wave operation of arrays has been demonstrated with as much as 3 W of output power. Silicon microchannel heat sinks can achieve a much lower thermal resistance than predicted by an idealized analysis due to finite size effects and lateral heat flow in the sink package. Techniques for feeding in large electrical currents are discussed.
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