TiO2
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TiO2 TEM specimens can be prepared by crushing bulk single crystals into fine fragments in an agate mortar, dispersing in ethyl alcohol and finally by putting drops of ethyl alcohol on a carbon-film grid. [1]

Figure 2071a shows several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive TiSi2 layer at the source, gate, and drain. When silicon and titanium are reacted, Ti and Si can diffuse laterally over the isolation regions and form thin filaments of TiSix that can electronically connect a gate electrode and source/drain regions and can cause failure of the device. This phenomenon is called "bridging". On the other hand, those by-products (TiSix, TiOx, and TiN) form over the isolation regions and cannot easily be etched in conventional salicide etching solutions. The use of a nitrogen atmosphere during thermal annealing is essential in preventing this failure mechanism [3] because nitrogen quickly diffuses into the grain boundaries and significantly suppresses any long-range silicon diffusion in the titanium layer. Furthermore, to avoid the by-product formation, the annealing temperature cannot be too high.

several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive SiTi2 layer

Figure 2071a. Several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive SiTi2 layer.

Table 2071b. Properties of main crystalline TiO2.

Structure
Rutile (Tetragonal)
Anatase (Tetragonal)
Brookite (Orthorhombic)
TiO2 (B)
TiO2, II
TiO2, (H)
Perovskite
Space group
P42/mnm I41/amd Pbca C2/m Pbcn I4/m Pnma
Lattice parameters (nm)
a = 0.459; c = 0.296 [1] a = 0.379; c = 0.951 a = 0.917; b = 0.546; c = 0.514 a = 1.216; b = 0.374; c = 0.651, β = 107.29° a = 0.452; b = 0.550; c = 0.494 a = 1.018; c = 0.297 a = 0.537; b = 0.764; c = 0.544
Unit cell
Anatase (Tetragonal)
Anatase (Tetragonal)
Anatase (Tetragonal)
Anatase (Tetragonal)
Brookite (Orthorhombic)
       
Density (g/cm3)
4.1 3.7 3.99 3.64 4.33 3.46 4.03
Specific weight
4.2 3.9 2.87-4.01        

Rockwell hardness

6 - 6.5 5.5 - 6 5.5 - 6        
Habitus

Ditetragonal bipyramidal

Tetragonal bipyramidal tabular Bipyramidal rhombic        

Existing condition

Stable: <1845 °C Metastable Metastable, rare        
Molecules per cell ( Z)
2 4 8        
6 6 6        
Ti-O distance (Å)
2 at 1.946
4 at 1.984
2 at 1.937
4 at 1.964
2 at 1.993
1 at 1.865
1 at 1.919
1 at 1.945
1 at 2.040
       
Ti: 0, 0, 0; 1/2, 1/2, 1/2.
O: 0.3, 0.3, 0; 0.8, 0.2, 1/2; 0.2, 0.8, 1/2; 0.7, 0.7, 0.
           

Melting point (°C)

1870            
Boiling point (°C)
2500-3000 2500-3000          
Model of stacking fault
Oxygen deficiencies [2]            
Relaxation width of lattice at stacking faults
1 nm [1]            
Displacement vector R of stacking faults in (-101) plane
-0.25±0.00, 0.00±0.03, -0.27±0.01            
Band gap (eV)
3.02 3.2          
  0          
Static dielectric constant
  80          
Absorption onset (nm)
410 380          
Molar mass
79.9 79.9          

Table 2071c. Example of compounds with similar structures to BCC.

 
TiO2 (Rutile)
Cu2O (Cuprite)
Space group Im-3m P42/mnm Pm-3m Pn-3m
Compounds α-Fe, W, Nb, Ta, Na, K, Mo, V GeO2, SnO2, PbO2 CsI, CsBr, CsCl Pb2O, Ag2O

Ti-O phase diagram

Figure 2071b. Ti-O phase diagram.

Table 2071d. Phases and space groups of TiOx.

Space group Phase : Composition (mass % O)
A2/m αTiO: 25; TiOx: 0.9 < x < 1.1
C2/m (12) αTi3O5: 35.8; Ti5O5
Cc (9) αTi3O5: 35.8
Im-3m (229) (βTi): 0 to 3
Imm2 (44) TiO1.20
Immm (71) Ti5O6
I222 (23) βTi1-xO: 29.5
I4/m (87) αTi1-xO: 29.5; Ti4O5
P63/mmc (194) (αTi): 0 to 13.5
P-3c1 (165) Ti3O: 8 ~ 13
P-3m1 (164) Ti2O: 10 ~ 14.4
Fm-3m (225) γTiO: 15 ~ 30; Ti90O90
P6/mmm (191) Ti3O2: 18
R-3c (167) βTi2O3: 33.2 ~ 33.6; αTi2O3: 33.2 ~ 33.6
P-1 (2) γTi5O9: 37.6; αTi4O7: 36.9; βTi4O7: 36.9; γTi4O7: 36.9; Ti7O13: 38.3; Ti9O17: 38.7
P42/mnm (136) Rutile TiO2, 40.1

Table 2071e. Other characteristics of TiO2 materials.

Most closed packed d-spacing and planes page1721

 

 

 

 

 

 

 

 

[1] Susumu Yamada and Michiyoshi Tanaka, Structure of a stacking fault in the (-101) plane of TiO2, Journal of Electron Microscopy 1: 67-74 (1997).
[2] Yamada S and Tanaka M (1995) Determination of the displacement vector at a stacking fault in TiO2 by convergent-beam electron diffraction. J. Electron Mkrosc 44: 212-218.
[3] C. K. Lau, “Method of Forming Titanium Disilicide,” U.S. Patent 4,545,116, 1985.

 

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