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EMULSITONE EMITTER DIFFUSION SOURCE N-250

Emulsitone Emitter Diffusion Source N-250 forms a phosphorous doped SiO₂ layer when applied as a thin film to a silicon wafer. In addition to phosphorous, a suitable concentration of arsenic is also contained in the SiO₂ layer. The arsenic to phosphorous ratio is precisely controlled to introduce sufficient arsenic in the emitter regions to compensate for the lattice strain caused by the high phosphorous surface concentration. Since the diffusion coefficient of arsenic in silicon is approximately an order of magnitude smaller than the phosphorus diffusion coefficient, the diffusion front of donor atoms consists of phosphorous, while at the surface there is a sufficient arsenic concentration to reduce lattice strain caused by the misfit of the phosphorous atom.

Application

The preferred method of applying Emitter Diffusion Source N-250 is by spinning. At a spin speed of 3000 rpm, a film 1500-1700 angstroms thick will result. After spinning for 5 to 10 seconds, the coated wafer should be baked at 150^o to 200^oC for 15 minutes to harden the film. Emitter Diffusion Source N-250 will flow easily over a suitably hydrophilic surface and will flow into emitter windows one micron wide or smaller. Surface treatments which produce hydrophilic surfaces are ammonium hydroxide-hydrogen peroxide mixtures, sulfuric acid-hydrogen peroxide solution, or simply heating the wafer to 300^oC for several minutes.

Diffusion Results

Table I display typical diffusion results at temperatures from 800^oC-1150^oC. The table lists the sheet resistivity, the penetration depth and the surface concentration for 15 minutes and 30 minutes heat treatments.

In addition, Table II shows data on the effect of atmosphere on the diffusion profile as well as the effect of prolonged diffusion time to determine the penetration depth for which the Emitter Diffusion Source N-250 behave as an infinite source producing and erfc profile.

Oxide Masking

The penetration of the donor atoms through a masking oxide has been determined for the temperature 1050^oC. Assuming the penetration of a thermal oxide by the donors in the Emitter Diffusion Source N-250 film is by a Ficks Law process, one computes a diffusion coefficient of 6 x 10-¹⁵ cm²/sec. for donor atom movement through the oxide. Approximately 2000 angstroms of thermal oxide will be sufficient to mask against donor penetration in the temperature range 1000^o to 1100^oC for 1 hour diffusion time.

Etch Rate Of Films Of Emitter Diffusion Source N-250

After diffusion, the doped oxide film of Emitter Diffusion Source N-250 will be removed in 2 minutes time in an aqueous 10% solution.

TABLE I

SHEET RESISTIVITY AND JUNCTION DEPTH vs. TEMPERATURE*

*Atmosphere: 90% N₂:10% O₂
"P" wafer 5 Ohm cm.
Spin Speed: 3000 rpm

TABLE II

EFFECT OF ATMOSPHERE ON DIFFUSION PROFILES OF EMULSITONE EMITTER DIFFUSION SOURCE N-250 AT 1100^oC

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