Silicon Si (P-type) Evaporation Process Notes

Silicon is one of the most extensively used elements in the world. It is dark gray and semi-metallic with a bluish tinge. It has a melting point of 1,410°C, a density of 2.32 g/cc, and a vapor pressure of 10^-4 Torr at 1,337°C. It is a brittle metalloid which can chip easily. Silicon is a semiconductor which is heavily utilized in the electronics and computer industries. It is often doped with arsenic, phosphorus, or boron depending on the application. It is evaporated under vacuum for circuit device, data storage device, and battery fabrication.

Silicon Si (P-type) Specifications

Material Type	Silicon (P-type)
Symbol	Si (P-type)
Atomic Weight	28.0855
Atomic Number	14
Color/Appearance	Dark Gray with a Bluish Tinge, Semi-Metallic
Thermal Conductivity	150 W/m.K
Melting Point (°C)	1,410
Bulk Resistivity	0.005-0.020 OHM-CM
Coefficient of Thermal Expansion	2.6 x 10-6/K
Theoretical Density (g/cc)	2.32
Sputter	DC, RF
Max Power Density (Watts/Square Inch)	40*

Type of Bond	Indium, Elastomer
Dopant	Boron
Z Ratio	0.712
E-Beam	Fair
E-Beam Crucible Liner Material	FABMATE^®‡, Tantalum
Temp. (°C) for Given Vap. Press. (Torr)	10^-8: 992 10^-6: 1,147 10^-4: 1,337

* This is a recommendation based on our experience running these materials in KJLC guns. The ratings are based on unbonded targets and are material specific. Bonded targets should be run at lower powers to prevent bonding failures. Bonded targets should be run at 20 Watts/Square Inch or lower, depending on the material.

Thermal Evaporation of Silicon (Si (P-type))

Thermally evaporating silicon is difficult, if not, impossible.

We refer to a material's evaporation temperature as the temperature required to achieve a vapor pressure of 10^-2 Torr. At this vapor pressure, a high deposition rate is possible in a system that has a normal source-to-substrate geometry. In order to reach this vapor pressure, silicon must be heated to ~1,600°C. Because this temperature is higher than its melting point (1,410°C), silicon will evaporate from liquid form.

However, liquid silicon reacts with refractory metals. We have attempted to thermally evaporate silicon from a thick-gauged tungsten boat (0.025" thickness) with little success. The liquid silicon wet and alloyed with the boat, causing it to fail before a reasonable layer could be deposited. We also attempted to use a shielded crucible heater with a graphite crucible. This approach failed as well because the liquid silicon reacted with the crucible.

As it stands, we do not have a good source recommendation for thermally evaporating silicon and generally recommend e-beam evaporation or sputtering for depositing silicon films. However, the e-beam evaporation process can be complicated as well.

E-beam Evaporation of Silicon (Si (P-type))

Silicon is rated as fair for e-beam evaporation.

We recommend using either a FABMATE^® or tantalum crucible liner for e-beam evaporating silicon. Crucible liners will need to be replaced fairly often because liquid silicon has the tendency to damage liners. When silicon melts, it will mechanically bond to the inner walls of the crucible liner. Upon cooling or re-heating, the difference in thermal expansion/contraction of the silicon in contact with the liner can produce enough stress to break the liner. We also find that the melt level of a material in the crucible directly affects the success of the crucible liner. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth. The outcome is cracking in the crucible. This is the most common cause of crucible liner failure. Placing too little material in the crucible or evaporating too much material before refilling can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage. Our recommendation is to maintain a melt level between 30-80% and slowly ramp power up and down to prevent these complications. However, even when following these guidelines, the liners will still need to be replaced frequently.

It is important to note that the FABMATE^® liners will likely survive only one evaporation run. It is possible to get multiple runs from tantalum liners. However, tantalum liners are generally more expensive than the FABMATE^® ones. Users will need to consider the extra life of the tantalum liner versus the extra cost to determine if it is more economical to purchase additional FABMATE^® liners and replace after each run.

E-beam Crucible Liner Fill Rate Calculator

Instructions for use:
Input the Crucible Liner Volume, Select Material (if not available in menu, manually input Material Density in g/cm³), and input fill rate %.

KJLC recommends a fill rate between 67-75%. Overfilling the crucible will cause the material to spill over and create an electrical short between the liner and the hearth causing the crucible to crack. Placing too little material in the crucible or allowing the melt level to get too low can be detrimental to the process as well. When the melt level is below 30%, the e-beam is likely to strike the bottom or walls of the crucible which immediately results in breakage.

The fill rate above assumes that the material is fully melted and does not take into account packing density. It should be noted that the crucible liner may need to be loaded multiple times, pre-melted, and topped off in order to achieve the final desired melt level/fill rate. When loading the crucible, do not load more than 80% of the height of the crucible liner.

This calculator is for estimation purposes only.

Crucible Liner Volume (in cc):

Material:

- or -
Density of the material in g/cm³:

Fill Rate %:

Result

See highlighted results that match your result in the table below.

Material Needed to Deposit a 1 Micron Film Calculator

Instructions for use:
Select source type, input distance from source to substrate and Select Material (if not available in menu, manually input Material Density in kg/m³).

This calculator is for estimation purposes only. The estimated mass is that needed to produce a desired film thickness (1 micron in this case) on a flat substrate at a point directly above the source, accounting for the approximate plume distribution of the selected source type. It does not account for any expected nonuniformity in thickness over a larger substrate area. More complex geometries, e.g. those with offset and/or tilted sources, may have higher material requirements. The estimated mass is for the film deposition only; additional margin should be included to account for loss during ramp-up, burn-in, stabilisation and ramp-down.

Source:

Distance of source to substrate (in cm):

Material:

- or -
Density of the material in kg/m³:

Multiplier:

Mass for 1 micron layer

Silicon Si (P-type) Evaporation Process Notes

Silicon Si (P-type) Specifications

Z-Factors

Thermal Evaporation of Silicon (Si (P-type))

E-beam Evaporation of Silicon (Si (P-type))