PolarisMirror Mount

We recommend thermally evaporating zinc sulfide from a tantalum boat such as our EVS8B005TA. A tantalum baffle box like our EVSSO22 may also be used. Thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain using this method.

MotorizedGimbal mount

Due to the high vapor pressures of both zinc and sulfur at low temperatures, zinc sulfide is usually deposited in a dedicated vacuum chamber.

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.

LaserMirror Mount

Zinc sulfide can be e-beam evaporated from a tantalum or molybdenum crucible liner. However, thermal evaporation is more commonly used for depositing optical films because stoichiometric films are easier to obtain using this method.

Zinc sulfide is an inorganic chemical compound with a chemical formula of ZnS. It is white in appearance with a melting point of 1,700°C, a density of 3.98 g/cc, and a vapor pressure of 10-4 Torr at ~800°C. It is often used as a phosphor and can emit various colors depending on the element introduced as an activator. It is evaporated under vacuum for infrared optical coatings, more specifically, night vision optical coatings.

Motorizedmirror mount

Another key process note is to consider the fill volume in the e-beam application because we 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 fill the crucible between 2/3 and 3/4 full to prevent these difficulties.

Another alternative is to change crystals frequently and ignore the error. The graph below shows the % Error in Rate/Thickness from using the wrong Z Factor. For a crystal with 90% life, the error is negligible for even large errors in the programmed versus actual Z Factor.

Unfortunately, Z Factor and Shear Modulus are not readily available for many materials. In this case, the Z-Factor can also be determined empirically using the following method:

NewportMirror Mount

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.

Due to the high vapor pressures of both zinc and sulfur at low temperatures, zinc sulfide is usually deposited in a dedicated vacuum chamber.

We recommend to sweep the e-beam at low power to uniformly melt the material and avoid hole drilling. Evaporating at a low e-beam power will also help to avoid material dissociation. Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power. With an evaporation temperature of ~800°C, we anticipate a deposition rate of 10-15 angstroms per second. It is important to note that zinc sulfide decomposes at the source and recombines at the substrate only if the substrate temperature is adequate and nucleation occurs. Substrate surface cleaning is required for good adhesion. Yttrium oxide (Y2O3), hafnium oxide (HfO2), or fluorides can be used as a thin adhesion layer if necessary.

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 %.

Gimbal Mountboat

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.

* 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.

Pressure should be monitored to ensure outgassing is at an acceptable level before increasing power. With an evaporation temperature of ~800°C and a base pressure of 10-6 Torr, we anticipate a deposition rate of 10-15 angstroms per second. It is important to note that zinc sulfide decomposes at the source and recombines at the substrate only if the substrate temperature is adequate and nucleation occurs.

The Kurt J. Lesker Company is a Woman-Owned and Operated ISO 9001:2015 certified company. Copyright ©1996-2024 Kurt J. Lesker Company® All rights reserved.

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).