Silicon Nitride (Si3N4 & SixNy)
- Practical Electron Microscopy and Database -
- An Online Book -

http://www.globalsino.com/EM/  



 
This book (Practical Electron Microscopy and Database) is a reference for TEM and SEM students, operators, engineers, technicians, managers, and researchers.
 

=================================================================================

Table 2074a. Properties of silicon nitrides.

Properties
General
α-Si3N4
PECVD
LPCVD
Atomic property

Density (g/cm3)

2.4-2.7
2.9-3.3
Quality
Film quality
Poor
Excellent
Pinholes
Yes
No
Step coverage
Poor
Conformable

Particles

More
Less
Atom % H
20-25
4-8
Fabrication

Throughput

Low
High
Pressure (torr)
2.9

Deposition rate (nm/min)

120-170
Deposition temperature (°C)
250-400
700-800
Electrical property

Dielectric constant

7
6-9
6-7

Resistivity (Ω-cm)

106-1015
1016
Band gap energy (eV)
5.3
4-5
5
Dielectric strength (V/cm)
5 × 106
10 × 106
TCE (/°C)
1.6 × 10-6
Conduction band (CB) offset on Si (silicon) substrate
2.4
Optical property

Refractive index

1.8-2.4
2.0
Mechanical property

Poisson ratio

0.27
Young's modulus (GPa)
270
Residual stress
(dyn/cm2)
-2 × 109 (compressive) - +5 × 109 (tensile)
+1 × 109 (tensile)
Chemical property

Etch rate in high concentration HF (Å/min)

200 at 25 °C
Etch rate in BHF (Å/min)
5-10 at 25 °C
Etch rate in H3PO4 (Å/min)
100 at 180 °C

CF4-4% O2 plasma (Å/min)

250

Table 2074b. Chemical reactions used in CVD for Si3N4 film growth.

Chemical reactions used in CVD for Si film growth

                                                 * LPCVD: low pressure CVD; PECVD: plasma-enhanced CVD.

Figure 2074 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 [1] 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 2074. Several chemical reactions occurring during annealing of a transistor structure coated with Ti to form a low resistive SiTi2 layer.

Some phenomena related to Si3N4 are important in ICs. For instance, evidences show that the Cu/Si3N4 cap interface is the dominant electromigration path, [2,3].

In EELS, the silicon ‘metallic’ bulk plasmon is found at 17 eV, and it moves up to 23 eV for silicon nitride (Si3N4).

Table 2074c. Etchants used in semiconductor manufacturing.

Film
Etchant
SiO2(Silicon oxide)
Dilute hydrofluoric acid (DHF)
Buffered HF (BHF)
Polysilicon
Alkaline hydroxide + organic
Si3N4(silicon nitride)-selective to SiO2
Boiling phosphoric acid (H3PO4)
Si3N4/SiO2 (non-selective)
Hydrofluoric acid + organic

Table 2074d. Etching selectivity of Si3N4:SiO2:Si in various solutions.

Etching selectivity of Si3N4:SiO2:Si
BHF
1:200:0
40% HF
1:≥110:0.1
H3PO4
10:1:0.3
CF4-4% O2 plasma
3:2.5:17

Table 2074e. Color chart for Si3N4 films observed perpendicularly under daylight fluorescent lighting.

Film thickness (nm)
Color
Film thickness (nm)
Color

10

Very light brown

95

Light blue

17

Medium brown
105
Very light blue

25

Brown
115
Light blue - brownish
34
Brown-pink

125

Light brown-yellow

35

Pink-purple
135
Very light yellow

43

Intense purple
145
Light yellow
52.5
Intense dark blue

155

Light to medium yellow

60

Dark blue
165
Medium yellow
69
Medium blue
175
Intense yellow

 

 

 

 

 

 

[1] C. K. Lau, “Method of Forming Titanium Disilicide,” U.S. Patent 4,545,116, 1985.
[2] S. P. Hau-Riege, Appl. Phys. Lett. 91, 2014 (2002).
[3] C-K. Hu, L. Giganac, S. G. Malhotra, R. Rosenberg, and S. Boettcher, Appl. Phys. Lett. 78, 904 (2001).

 

 

 

 

=================================================================================

The book author (Yougui Liao) welcomes your comments, suggestions, and corrections, please click here for submission. If you let book author know once you have cited this book, the brief information of your publication will appear on the “Times Cited” page.