Ozone Cleaning of Carbon-Related Contaminants on Si Wafers and other Substrate Materials
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Figure 1 shows a schematic diagram of the
R
ozone jet generator system.
The mixture of 5% ozone in
oxygen (02) generated by
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an ozonizer is introduced
into the ozone vessel equipped with a cryocooler,
and ozone is liquefied and
pu rified therein by m ean s of vacuum distillation since
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compressor CrYocoolee oxygen has a much higher vapor pressure than that of ozone within the temperature range of 70 to 95 K. Fig. 1 Schematic diagram of pure ozone jet generator The main features of the generator are i) the flux of the pure ozone jet simply depends on the temperature of the ozone vessel, i.e., the equilibrium vapor pressure of ozone, and the conductance of the gas lines and that enables a steady handling. ii) the whole system is made of chemically treated materials that are inactive to ozone to prevent unexpected decomposition of ozone which might trigger an explosion. The pure ozone jet generator produces the pure ozone of lxl0-2 mol per hour at 85 K. The purity of the ozone thus accumulated is estimated to be more than 98 % and it goes up to nearly 100 % when accumulated at 95 K with the rate of 5x10- 3 mol per hour. The beam flux of the jet can be controlled within a range of 1016 to 1017 molecules per second by setting the ozone vessel temperature between 85 to 95 K. When the whole system for the gas introduction to the chamber is ozone-cleaned and stabilized, the purity of the introduced jet is estimated to be higher than 80 % with a beam fluctuation of less than 2.5 % in 1.5 hours which is longer than the life time of the ozone in the vessel at 90 K.
In-situ RHEED-beam-excited Auger electron spectroscopy Although there were some pioneers to observe the RHEED-beam-excited Auger electrons from the materials surfaces[3], we adopted the method to in-situ observation of the growing surface of oxide films in a strongly oxidizing atmosphere such as ozone. The detail of the system was reported elsewhere[4] and is briefly described here. The system consists of a conventional RHEED system and a specially designed compact energy analyzer module in a magnetic shield box. Inside the box, a sector-type energy analyzer (Comstock Model AC-900), an Einzel lens, and a dual microchannel plates (Galileo MCP-18) detector were packed and the box was differentially evacuated with a magnetic-bearing turbomolecular pump through the bottom hole in the box to prevent the analyzer module from exposing to oxidizing gases. The electrons emitted normal to the substrate surface entered into the module through a 2-mm aperture. The energy analyzer was operated with constant pass energy mode giving a resolution of 0.8 eV. The signal was detected with a lock-in amplifier applying a modulation frequency to the outer sector of the analyzer. XPS measurement of ozone cleaning Figure 2 shows the experimental set up for the ozone cleaning of
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