Fabrication technologies - Micromixers Fundamentals Design and Fabrication - page 118

Table 4.1 Chemical Reactions used in CVD of Different Material Films (After [3] )

Material Chemical Reactions

Silicon SiH 4 / Si þ 2H 2 [

SiH 2 Cl 2 / SiCl 2 þ 2H 2 [

SiCl 2 þ H 2 / Si þ 2HCl [

630 C; 60 Pa

Polysilicon SiH 4 ! Si þ 2 H 2 [

430 C

; 1 bar

Silicon dioxide SiH 4 þ O 2 ! SiO 2 þ 2 H 2 [

430 C; 40 Pa

SiH 4 þ O 2 ! SiO 2 þ 2 H 2 [

700 C; 40 Pa

Si ð OC 2 H 5 Þ 4 ! SiO 2 þ Gas [

400 C

; 0 : 5 bar

Si ð OC 2 H 5 Þ 4 þ O 2 ! SiO 2 þ Gas [

900 C; 40 Pa

SiH 2 Cl 2 þ 2 N 2 O ! SiO 2 þ Gas [

350 C;plasma; 40 Pa

SiH 4 þ 4 N 2 O ! SiO 2 þ Gas[

750 C

; 30 Pa

Silicon nitride SiH 2 Cl 2 þ 4 NH 3 ! Si 3 N 4 þ Gas [

700 C;Plasma; 30 Pa

SiH 4 þ 4 NH 3 ! Si 3 N 4 þ Gas [

3

300 C

; Plamsa ; 30 Pa

3 Si þ 4 NH 3 ! Si 3 N 4 þ 6 H 2 [

400 C

; 30 Pa

Silicide SiH 4 þ 2 WF 6 ! WSi 2 þ 12 HF [ þ 2 H 2 [

4 2

600 C; 60 Pa

SiH 2 Cl 2 þ 2 TaCl 5 ! TaSi 2 þ 18 HCl [

4 2

450 C

; plasma ; 30 Pa

2 SiH 4 þ TiCl 4 ! 2 TiSi 2 þ 4 HCl[ þ 2 H 2 [

Evaporation deposits a thin film on a substrate by sublimation of a heated source material in
a vacuum. According to the different heating techniques, evaporation can be categorized as vacuum
thermal evaporation (VTA), electron beam evaporation (EBE), molecular beam epitaxy (MBE), or
reactive evaporation (RE). The first two methods are the most common. Resistive heating, laser
heating, or magnetic induction is used in VTA. EBE utilizes an electron beam focusing on the target.
Alloys can be deposited with evaporation using two or more material sources. However, sputtering is
more stable than evaporation in the case of alloy deposition.
Sputtering utilizes a strong electromagnetic field to ionize a chemically inert gas, such as argon,
and makes it become a plasma. The positively charged argon atoms are accelerated and bombard the
target material. The bombardment knocks out target atoms, which are then condensed on the substrate
surface as a thin film. Sputtering can deposit all types of materials, such as alloys, insulators, or
piezoelectric ceramics. Sputtering is less directional than EBE but has higher deposition rates.

4.1.1.5 Spin coating
Spin coating is the simplest method for fabricating a film on a substrate. Thin-resist layers for
photolithography are coated with this technique. The spin-coating process starts with the dilution of
the material to be deposited in a solvent. The solution is subsequently dispensed on the substrate
surface. The wafer is then spun at a high speed. The thickness of the film is determined by the spinning
speed, surface tension, and viscosity of the solution. The solvent is removed partly during the spinning