Basic Properties of Silicon Crystals
Basic Properties of Silicon Crystals
Basic Properties of Crystals Type of crystals for silicon: Single Crystal Polycrystalline Amorphous periodic small crystals no long range arrangements order between of atoms atoms Crystal lattice is described by a unit cell with a base vector(distance between atoms) Types of unit cells Z Cubic BCC FCC Body Centered Cube Face Centered Cube
Basic Properties of Crystals Type of crystals for silicon: Single Crystal Polycrystalline Amorphous periodic small crystals no long range p y arrangements order between of atoms atoms Crystal lattice is described by a unit cell with a base vector (distance between atoms) Types of unit cells Types of unit cells Body Centered Cube Face Centered Cube
Directions and Planes in Crystals Directions (vector components:a single direction is expressed as [a set of 3 integers], equivalent directions(family)are expressed as a set of 3 integers> Planes:a single plane is expressed as(a set of 3 integers hk/=Miler indices)and equivalent planes are expressed as fa set of 3 integers Miler Indices:take x,y,z(multiple of basic vectors ex.x=4a,y=3a,z=2a) reciprocals(1/4,1/3,1/2)>common denominator(3/12,4/12,6/12)>the smallest numerators(3 4 6) [h k I]crystal direction is perpendicular lattice constant to (h k I)plane Z (100)plane a (110)plane [111] (111)plane [1001 X
Directions and Planes in Cr ystals Directions (vector components: a single direction is expressed as [a set of 3 integers], equivalent directions (family) are expressed as < a set of 3 integers > y equivalent directions (family) are expressed as < a set of 3 integers > Planes: a single plane is expressed as (a set of 3 integers h k l = Miler indices) and equivalent planes are expressed as {a set of 3 integers} Miler Indices: take x, y, z (multiple of basic vectors ex. x=4 a, y=3 a, z=2 a) reciprocals (1/4, 1/3, 1/2) Æ common denominator (3/12, 4/12, 6/12) Æ the smallest ( ) lattice constant numerators (3 4 6) [h k l] crystal direction is perpendicular to (h k l) plane
Silicon Crystal Structure Diamond lattice (Si,Ge,GaAs) Two interpenetrating FCC structures shifted by a/4 in all three directions All atoms in both FCCs ○inside one FCC O from the second lattice covalent bonding (100)Si for devices (111)Si not used-oxide chargest
Silicon Crystal Structure Diamond lattice (Si, Ge, GaAs) Two interpenetrating FCC structures shifted by a/4 in all three directions All t i b th FCC All atoms in both FCCs Diamond covalent bonding inside one FCC from the second lattice (100) Si for devices (111) Si not used - oxide charges
Silicon Surface Orientation (100) Devices are built on surface>surface orientation affects the electrical and physical properties Two commonly used crystal orientation in silicon (111)crystal plane Largest number of atoms per cm2, Oxidize fast 111) Higher density of interface states (defects) (100)crystal plane Superior electrical properties of the Lowest number of atoms per cm2 (100)Si/SiO,interface makes (100) Oxidize slow silicon dominant in manufacturing. Low density of interface states
Silicon Surface Orientation Devices are built on surface Æ surface orientation affects the electrical and physical properties (100) Two commonly used crystal orientation in silicon (111) crystal plane • Largest number of atoms per cm 2 , • Oxidize fast • Hi h d it f i t f t t (111) Hi g her density o f inter face states (defects) (100) cr ystal plane (111) ( )y p • Lowest number of atoms per cm 2 • Oxidize slow • Low density of interface states Superior electrical properties of the (100) Si/SiO 2 interface makes (100) silicon dominant in manufacturing