The substitution of Czochralski (CZ)-silicon (Si) wafers into p-(n-)/p-(n-) ( p- or n- layer on p- or n- Si substrate: resistivity of approximately 100 m Ω m) thin-film epitaxial Si wafers used as starting materials has been investigated with respect to application to metal-oxide-semiconductor (MOS) large-scale-integrated circuits (LSIs). The optimum epitaxial layer ( p-/p- structure) thickness for MOS-LSIs was determined to be approximately 1 µ m from the viewpoints of gate oxide integrity (GOI) improvement and cost effectiveness. With increasing epitaxial layer thickness from 0.1 to 0.3 µ m, the oxide defect density was greatly reduced and leveled off at approximately 1/30 that of a CZ-Si layer if the layer thickness is above 0.3 µ m. This is because microdefects in CZ-Si represented by crystal originated particles (COP) which cause weak spots in the gate oxide layer are covered by an excellent Si epitaxial layer on the CZ-Si surface. The p-/p- thin epitaxial structure results in very controlled resistivity for electrically active regions in the device, resulting in a lower cost of growth.
A new concept of epitaxial silicon (Si) wafers (NC epi.) in which p 0 (n 0 ) thin-film layers are grown on p 0 (n 0 ) Czochralski (CZ)-Si substrates (substrate resistivity: approximately 10 cm) is proposed for metal oxide semiconductor (MOS) ultra large-scale integrated circuits (ULSI's) as a starting material. A thickness of 0.3-1 m for the epitaxial layer (p 0 /p 0 structure) is shown to be sufficient for improving the gate oxide integrity for MOS-ULSI's. The epitaxial layer grown on Si substrate greatly reduces weak spots in the gate oxide layer by covering microdefects in the CZ-Si represented by crystal originated particle (COP). The p 0 /p 0 thin-film epitaxial structure results in very controlled resistivity for the electrically active region in the device, which in turn results in a lower growth cost and higher feasibility for use in current ULSI's. The features of NC epi. in combination with proximity gettering ispresented. An application of NC epi. in shallow-trench isolation processes discussed considering retrograde-type well-tub. The amenability of epitaxial wafers to wafer enlargement (over 300 mm) is discussed to eliminate bad effects of COP.
The resistance of precipitation-treated Czochralski-grown silicon wafers to warpage has been investigated using crystals containing oxygen at a concentration of 5.5-12.3×1017 atoms/cm3. The precipitation softening is effectively suppressed if the oxygen concentration is lower than a threshold value of about 8×1017 atoms/cm3. In wafers with oxygen concentrations of 5.5-8×1017 atoms/cm3, oxygen precipitation proceeds slowly, resulting in slow growth of bulk stacking faults and few dislocation sources. In MOS image-sensor devices, the wafers with such oxygen concentrations have few crystal defects within the area of the photodiodes after processing, which cause the fatal failure of white blemishes detected as white scratches on output pictures.
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