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Chapter 1 Basic semiconductor properties What is a Semiconductor? • • • • Low resistivity : 106 104 cm => conductor High resistivity : 1010 1018 cm => insulator Intermediate resistivity: 104 108 cm => semiconductor The uniqueness of semiconductors is that their conductivity can be varied over a wide range, e.g. by – adding minute quantities of impurities – applying electric field – illumination • Simple 3-D Unit cells # of atoms per unit cells SCC : one atom BCC : two atoms FCC : four atoms Figure 1.2 Simple three-dimensional unit cell. (a) Simple cubic unit cell. (b) pedantically correct simple cubic unit cell including only the fractional portion (1/8) of each corner atom actually within the cell cube. (c) Body-centered cubic unit cell. (d) Face-centered cubic unit cell (After pierret.) Simple cubic lattice : packing density Simple cubic lattice : areal density Diamond FCC lattice for Si The Si Crystal • Each Si atom has 4 nearest neighbors • lattice constant = 5.431Å “diamond cubic” lattice How Many Silicon Atoms per cm-3? • Number of atoms in a unit cell: • 4 atoms completely inside cell • Each of the 8 atoms on corners are shared among cells count as 1 atom inside cell • Each of the 6 atoms on the faces are shared among 2 cells count as 3 atoms inside cell Total number inside the cell = 4 + 1 + 3 = 8 • Cell volume: (.543 nm)3 = 1.6 x 10-22 cm3 • Density of silicon atoms = (8 atoms) / (cell volume) = 5 x 1022 atoms/cm3 Specification of vectors normal to a particular plane! Table 1.6 Miller Convention Summary Example…. • Examples use of Miller indices – wafer surface orientation • Size : diameter : 300±0.2 mm • Thickness : 775±25㎛ • Surface orientation : ( 1 0 0 ) or ( 1 1 1 ) – wafer flats and notches Preparation of silicon wafers Polysilicon Seed crystal Crucible 6. Edge Rounding 1. Crystal Growth Heater 7. Lapping 2. Single Crystal Ingot 8. Wafer Etching 3. Crystal Trimming and Diamet er Grind Slurry 9. Polishing 4. Flat Grinding Polishing table 5. Wafer Slicing 10. Wafer Inspection Polishing he ad Fullman Company clients like MEMC and Mitsubishi Materials Silicon create raw polycrystalline silicon by mixing refined trichlorosilane with hydrogen gas in a reaction furnace and allowing the poly- silicon to grow on the surface of electrically heated tantalum hollow metal wicks. 웨이퍼 제조 공정 그림 6.2 쵸크랄스키 방법 그림 6.3 쵸크랄스키 방법으로 성장시킨 단결정 CZ crystal puller Crystal pull er and rotatio n mechanism Crystal seed Single cryst al silicon Molten pol ysilicon Quartz cruc ible Heat shield Carbon heating el ement Water jacket Silicon ingot grown by CZ method Photograph courtesy of Kayex Corp., 300 mm Si ingot – 실리콘 wafer
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