N and P-DIFFUSOL
For Solid State Silicon Devices, Transsistors, 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 life time 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-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¡É 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¡É.
Diffusion Constants (cm2/Sec) for N- and P-DIFFUSOL
1000¡É | 3.0 x 10-14 |
1100¡É | 3.5 x 10-13 |
1200¡É | 3.0 x 10-12 |
1300¡É | 1.5 x 10-11 |
INSTRUCTIONS
DIFFUSOL preparations are applied by paint-on technique suing camels hair brush with coverage within 1/16 inch of wafer edge. Application by spinning is also a useful technique. Allow to dry; N-DIFFUSOL dries more slowly and use of a heat lamp is desirable. The wafers should be stacked in a quartz boat, n-painted sides against each other. Likewise p-painted sides are stacked against each other. Simultaneous p- and n-diffusion may be performed using P-DIFFUSOL and N-DIFFUSOL on opposite sides of stacked wafers.
Diffusion temperature is a matter of choice - an effective operating temperature is 1275¡É in air ambient 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. For use in planar technology the diffusion temperature must be limited to a maximum of 1075¡É to protect oxide.
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 1.6mm 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-Diffusio preparation may be diluted when lower surface concentration fo 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¡É 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 contants 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 itseld.
Another useful technique is based on heating the separated, diffused wafers in an oxygen atmosphere at about 500¡É. The diffusant material on the silicon surface then becomes more readily soluble in HF.