Diffusants

Solid Diffusants
N & P Diffusol

Solid Diffusants

For Semiconductor Technology

Semiconductor grade phosphorus and boron diffusants for semiconductor devices.

DONOR TYPE

Phosphorus Pentoxide (P2O5) granular

ACCEPTOR TYPES

Boric Anhydride (Boron Trioxide B2O3) granular
Boric Acid (H3BO3) powder

SOLID DIFFUSANTS for Semiconductor Technology
DESCRIPTION

Transene diffusants are hyper-pure semiconductor grade chemicals, dispensed in convenient unit quantities for solid state diffusion processes. Transene diffusants are moisture free with purity far exceeding A.C.S. specifications for chemically pure reagent grade materials. Types offered include boric acid, boric anhydride (acceptor types) and phosphorus pentoxide (donor type) packaged in dry nitrogen.

Transene diffusants function as primary materials for the introduction of impurity atoms by diffusion processes in group IV elemental semiconductors. The uniform particle size of Transene diffusants insures a controllable concentration of diffusant in the carrier gas flowing through the diffusion apparatus. The solid state diffusion processes depend upon chemical reaction of silicon (or germanium) with the vapors of boron and phosphorus compounds occurring at high temperatures. A film formed on the semiconductor surface becomes an infinite diffusion source for boron or phosphorus. Controls for these diffusion processes are easily regulated to obtain p-n junctions and ohmic contacts.

Transene diffusants are used in the manufacture of planar transistors, field-effect devices, diodes, rectifiers, and other silicon and germanium devices. The use of Transene high purity diffusants will assure high reliability and excellent quality of semiconductor devices made by diffusion technology.

Physical Properties of Transene Diffusants (99.9% Minimum Purity)

Properties Boric Acid Boric Anhydride Phosphorus Pentoxide
Mol. Formula H3BO3 B2O3 P2O5
M.P. 61.84 64.69 141.96
Heat of Vap. (Kcal./Mole) 22.7 (P2O5)
Ratio Tetrahedral Radii
B/Si or P/Si
0.75 0.75 0.93
Impurity Level
(In germanium)
(In silicon)
0.0104
0.045
0.0104
0.045
0.0120
0.050
Activation Energy (Kcal./Mole)
(In germanium)
(In silicon)
105
85
105
85
57
85
Preexpon. Diff. Coef.,Do(cm2/Sec)
In germanium
In silicon
1.6 x 109
10.5
1.6 x 109
10.5
2.5
10.5
Diffusion Constant (cm2/sec)
In silicon
In germanium
8.7 x 10-15@ 950 °C
6.4 x 10-12@ 1275 °C
.4 x 10-12@ 850 °C
7.7 x 10-15@ 950 °C
5.0 x 10-12@ 1235 °C
8 x 10=11@ 900 °C
Surface Conc. (atoms/cm3)
In silicon
8 x 1021 @ 950 °C
1 x 1021 @ 1275 °C
2.5 x 1021 @ 950 °C
6 x 1020 @ 1235 °C

N and P-Diffusol

For Semiconductor Technology

For Solid State Silicon Devices, Transistors, Rectifiers, Diodes

N-DIFFUSOL®

A new n-type diffusant preparation for making n+ contacts and p-n junctions in silicon.

P-DIFFUSOL®
A p-type diffusant preparation for making p-n junctions and p+ contacts.

SPECIAL FEATURES

  • Uniform diffusion, spiking eliminated
  • Preserves silicon lifetime characteristics
  • Yields high surface concentration [N s]
  • Produces low resistance ohmic contacts
  • Permits simultaneous p and n diffusions
  • Simplifies diffusion technology
  • Ready to use – allows stacking of wafers during diffusion – at air ambient -lowest cost.

N- and P-DIFFUSOL®
DESCRIPTION

N-DIFFUSOL is a stabilized liquid preparation containing an n-type diffusant with a diffusion coefficient similar to that of elemental phosphorus. Diffusion occurs at elevated temperature up to 1300 °C in air. The diffusion is extremely uniform. An adjunct component serves to neutralize trapping centers in the silicon crystal lattice during the diffusion process. Degradation of lifetime characteristics of silicon is thus avoided.

P-DIFFUSOL is a stable liquid preparation containing a p-type diffusant with a diffusion coefficient, which approximates that of N-DIFFUSOL. Uniform diffusion occurs in air up to 1300 °C.

Diffusion Constants (cm2/sec) for N- and P-DIFFUSOL

1000 °C 3.0 x 10-14
1100 °C 3.5 X 10-13
1200 °C 3.0 X 10-12
1300 °C 1.5 X 10-11

INSTRUCTIONS

APPLICATION
N-Diffusol should be mixed well before using. If necessary, use a glass rod to disperse sediment which may form.

Diffusol preparations are applied by paint-on technique using camel’s hair brush with coverage within 1.6 mm of the edge of the wafer. Allow to dry. N-Diffusol dries more slowly, and use of a heat lamp is desirable. Wafers should be stacked horizontally in a quartz boat, n-painted sides against each other. Likewise, p-painted sides are stacked against each other. Simultaneous n- and p-diffusion may be performed using N-Diffusol and P-Diffusol on opposite sides of stacked wafers.

When applicable, Diffusol preparations may be applied by dipping.

It is important that the silicon used for diffusion be pre-cleaned. Soak in HF prior to application of N- or P-Diffusol is recommended.

N- and P- Diffusol preparations may be diluted when lower surface concentration of diffusants is desired. Methyl alcohol may be used to dilute P-Diffusol, and ethylene glycol monoethyl ether may be used to dilute N-Diffusol.

DIFFUSION
Diffusion temperature is a matter of choice. An effective operating temperature is 1275-1300 °C with time determined by device requirements. An open, alundum furnace tube with ends blocked off with quartz wool is recommended for the high temperature diffusion process.

Diffusion constants provided in the data sheet for N- and P-Diffusol may be used to calculate junction depth for exact conditions used in diffusion. N- and P-Diffusol applied to silicon serves an infinite diffusant source.

After diffusion, the stacked wafers are separated by a prolonged soak in hydrofluoric acid (HF) for at least 24 hours.

REMOVAL OF EXCESS DIFFUSOL
After completion of diffusion, excess Diffusol preparations are removed from the silicon surfaces by prolonged soaking in HF. The removal of excess Diffusol when deep diffusions are used may also be accomplished by light lapping, preferably with the use of an S.S. White abrasive unit employing dolomite (CaCO3) as the abrasive material. The latter process removes material on the surface without removal of silicon itself.

Another useful technique is based on heating the separated, diffused wafers in an oxygen atmosphere at about 500 °C. The diffusant material on the silicon surface then becomes more readily soluble in HF.