Metallic contaminants on a wafer surface have been known to be a major source of performance failure in IC devices by increasing the p-n junction leakage, degradation of the oxide breakdown voltage and deteriorating the carrier lifetime. 1 With shrinking device geometries, the tolerance level of metallic contaminants is becoming more stringent. It has been reported that metallic contamination on a silicon surface needs to be suppressed to less than 1 × 10 10 atoms/cm 2 to manufacture a 64-Mbit DRAM in order to prevent the above-mentioned failures. 2 According to device development and an estimation of the research organization, this level should be down to 1 × 10 9 atoms/cm 2 in the future. With this tendency, analytical techniques used to measure ultratrace metallic contaminants on a silicon surface have also been developed.One of the most prevalent techniques used for measuring metallic contaminants is VPD-DC (vapor phase decompositiondroplet collection). During the VPD procedure, the wafer is exposed to hydrogen fluoride vapor in a closed container to decompose the surface oxide layer. The decomposition reaction of silicon oxide by hydrogen fluoride vapor is expressed by SiO2 + 6HF ⇔ H2SiF6 + 2H2O.(1)Metallic contaminants remain on the wafer surface after the decomposition of silicon oxide. In the DC procedure, these metallic contaminants are collected into a small amount of ultrahigh-purity liquid droplets by scanning the wafer surface. A liquid droplet prepared by VPD-DC is analyzed by different trace-element analysis techniques, such as atomic absorption spectrometry (VPD-AAS), 3-7 inductively coupled plasma-mass spectrometry (VPD-ICP-MS) 5,8-10 and total reflection X-ray fluorescence (VPD-TXRF). 4,[11][12][13] DC is a procedure used to collect and preconcentrate all impurities into liquid droplets. The composition of the collecting solution as well as the chemistry of the collected contaminants determine the collection efficiency. Morinaga et al. have reported that metallic contaminants deposit on a silicon wafer surface in a wet process depending on the type of metal element, the type of solution and the type of substrate. 14 Therefore, a chemical reaction of metal at the silicon surface during VPD-DC can influence the collection efficiency of a metallic contaminant. However, there have been few reports concerning the collection efficiency of the VPD-DC procedure. In this experiment, the collection efficiency of VPD-DC sample preparation was investigated for 14 elements (Na, Mg, Al, K, Ca, Cr, Fe, Mn, Co, Ni, Cu, Zn, Mo and Ti) on four types of silicon wafers. Standard solutions containing 7 elements in each solution were intentionally contaminated on a silicon wafer surface. The contaminated area was scanned with various collecting solutions in the VPD-DC procedure and a droplet containing metallic contaminants, collected from the silicon wafer surface, was measured by ICP-MS. The collection efficiency was determined as the ratio of the collected metallic concentration to the initial contamination conce...

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 upto 30 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% and the change in phase is 0.37°. Thus a non-invasive cleaning for sub-micron particles from photomasks is possible with CO2 cryogenic aerosols.

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