Chapter 1 Basic semiconductor properties

What is a Semiconductor? Low resistivity : 10  6  10  4  cm => conductor High resistivity :   cm => insulator Intermediate resistivity: 10  4  10 8  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

 Moore’s Law a Self-Fulfilling Prophesy

 Device Sizes and Transport Concepts

Simple 3-D Unit cells 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.) # of atoms per unit cells SCC : one atom BCC : two atoms FCC : four atoms

Simple cubic lattice : packing density

Simple cubic lattice : areal density

Diamond FCC lattice for Si

“diamond cubic” lattice The Si Crystal Each Si atom has 4 nearest neighbors lattice constant = 5.431Å

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 = = 8 Cell volume: (.543 nm) 3 = 1.6 x cm 3 Density of silicon atoms = (8 atoms) / (cell volume) = 5 x atoms/cm 3

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 : ( ) or ( ) –wafer flats and notches

Preparation of silicon wafers 1.Crystal Growth 2.Single Crystal Ingot 3.Crystal Trimming and Diamet er Grind 4.Flat Grinding 5.Wafer Slicing 6.Edge Rounding 7.Lapping 8.Wafer Etching 9.Polishing 10.Wafer Inspection Slurry Polishing table Polishing he ad Polysilicon Seed crystal Heater Crucible

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

Crystal seed Molten poly silicon Heat shield Water jacket Single cryst al silicon Quartz cruci ble Carbon heating el ement Crystal pulle r and rotation mechanism CZ crystal puller

Silicon ingot grown by CZ method Photograph courtesy of Kayex Corp., 300 mm Si ingot

– 실리콘 wafer