Defects in Silicon Crystals Point Defects Stacking Fault Dislocation Precipitate Various types of defects can exist in crystal or can be created by processing steps. Point defects: 。 Impurity related defect Native point defect Vacancy (a missing atom),Interstitial(an extra atom) Equilibrium concentration increases with T:1012-1015cm3@1000C
Defects in Silicon Crystals Point Defects V Stacking Fault – I Dislocation Precipitate Point defects: Various types of defects can exist in crystal or can be created by processing steps. Point defects: • Impurity related defect • Native point defect Vacancy (a missing atom), Interstitial (an extra atom) Equilibrium concentration increases with T: 1012-1015cm-3 @ 1000 o C
Defects in Silicon Crystals Dislocations 0000000000000 00000000000 Intrinsic point defects in 00000000000 O0O000O0O000 a crystal N and N o0000o0000ooo increase with T 业 0000000000000 0000000000000 o0o0900888000oo00 oooO 00O 88808888088899008 00000O00O0000 ●●●●●●●●● Agglomeration of 0000000000000 000000000000o6008 00008000000000000 Interstitials 号 Extrinsic-type dislocation loop. 0000000009908 90980o00o9800 O000 HOOOO o088600008886 collapse 0000000000000 Sequence of intrinsic-type dislocation loop formation. One-dimensional defects (dislocations): 。 Edge dislocation,dislocation loop Macroscopic edge dislocations stress in silicon after high temperature processes (LOCOS);temperature gradients during processing Microscopic dislocation loops agglomeration of V I during a cooling process (not enough time for V&I recombination) Dislocations can move when subjected to stresses or when excess point defects are present
Defects in Silicon Crystals – Dislocations Intrinsic point defects in a crystal N v and NI increase with T Agglomeration of Interstitials collapse One-dimensional defects (dislocations): • Edge dislocation, dislocation loop • Macroscopic edge dislocations Macroscopic edge dislocations Å stress in silicon after high temperature processes stress in silicon after high temperature processes (LOCOS); temperature gradients during processing • Microscopic dislocation loops Å agglomeration of V & I during a cooling process (not enough time for V & I recombination) • Di l i h bj d h i d f islocations can move w hen subjecte d to stresses or w hen excess point d e fects are present
Propagation of Dislocations by Climb Climb motion in an edge dislocation 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 ● 0000099/000 00000000000 0000000000 b 00000●00000 Shift 00000100000 00000●00000 0000000000 。。00010.00。 0000000000 0000000000 00000000c0 0000000000 Negative climb by absorbing self-interstitials 00000000000 00000000000 00000000000 00000000000 00000000000 00000000000 00000000.000 0000000°，°00 00000006000 b 00 00000●6000 00000 00●00 Shift 00000●60000 0000000000 00000100000 0000000000 0000000000 0000000000 0000000000 .0000000000 Positive climb by capturing vacancies
Propagation of Dislocations by Climb Climb motion in an edge dislocation Shift Negative climb by absorbing self-interstitials Shift Positive climb by capturing vacancies
Motion of Dislocations by Glide Movement of a dislocation by glide in response to shear stress Shear Stress Easy motion of Stress induced by dislocations Mismatch of thermal expansion coefficients Temperature gradient AT g=aY△T
Motion of Dislocations by Glide Movement of a dislocation by glide in response to shear stress St i d d b Easy motion of dislocations Stress in duce d by • Mismatch of thermal expansion coefficients • Tem p g erature gradient ∆ T σ = αY∆ T
Defects in Silicon Crystals Stacking Faults 【111 [001 A A.B.C:three different a b [1i1 (111)planes B b' Perfect stacking c c B Stacking of(111)planes viewed along [110]in the diamond structure ESF Induced by oxidation ISF Missing(111)plane B [111】 001] SFs bound by →[i011 dislocations Two-dimensional defects(stacking faults): Along {111)planes Intrinsic:removal of part of a plane of atoms in {111)directions Extrinsic:addition of a partial plane of atoms in (111)directions Oxidation induced stacking faults(OISF):stacking faults grow during oxidation due to absorption of more I
Defects in Silicon Crystals – Stacking Faults A, B, C: three different Perfect stacking (111) planes Induced by oxidation Missing (111) plane SFs bound by dislocations Two-di i l d f t ( t ki f lt ) dimensional d e fects (stacking fault s): • Along {111} planes • Intrinsic: removal of part of a plane of atoms in {111} directions • Extrinsic: addition of a p p {} artial plane of atoms in {111} directions • Oxidation induced stacking faults (OISF): stacking faults grow during oxidation due to absorption of more I