Lithium (Li) Pieces Evaporation Materials

Lithium (Li) Pieces Overview

We sell these pellets and pieces by unit weight for evaporation use in deposition processes. These approximate materials prices are published to provide budgetary guidelines. Actual prices can vary and may be higher or lower, as determined by availability and market fluctuations. To speak to someone directly about current pricing, please click here .

Lithium (Li) General Information

Lithium is classified as an alkali metal on the Periodic Table. It is the least dense of all metals and one of only three other metals that can float on water. It is silvery-white in appearance and very soft with a density of 0.53 g/cc, a melting point of 181°C, and a vapor pressure of 10^-4 Torr at 407°C. Lithium is also highly flammable and easily oxidizes when exposed to air. While lithium and its compounds serve a variety of industries, it is mainly used to make rechargeable batteries which are found in smartphones, tablets, cars, and in many other products. Lithium, along with its alloys and compounds, is evaporated under vacuum to make batteries, fuel cells, and to form optical coatings.

Lithium (Li) Specifications

**** Suggestion based on previous experience but could vary by process. Contact local KJLC Sales Manager for further information

Z-Factors

Empirical Determination of 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:

• Deposit material until Crystal Life is near 50%, or near the end of life, whichever is sooner.
• Place a new substrate adjacent to the used quartz sensor.
• Set QCM Density to the calibrated value; Tooling to 100%
• Zero thickness
• Deposit approximately 1000 to 5000 A of material on the substrate.
• Use a profilometer or interferometer to measure the actual substrate film thickness.
• Adjust the Z Factor of the instrument until the correct thickness reading is shown.

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.

Thermal Evaporation of Lithium (Li)

The preferred method to deposit lithium films is by thermal evaporation. Depositing lithium via sputtering or e-beam evaporation is possible but the rate can be difficult to control due to the material's low melting point.

In order to successfully evaporate lithium, it is important that the material is not oxidized. Oxidized lithium will require more initial power to break through the oxide layer and then melt the metal. The power will then need to be brought down quickly as the oxide melts at a relatively high power causing the remaining lithium metal to flash evaporate quickly at that high power. To avoid oxidation, lithium should be kept either in oil or an argon inert atmosphere.

It is important to identify at what power the lithium melts. This can be done by manually ramping up the power and observing the material to determine when it melts. Once this power level is identified, it can be documented as the Ramp#1/Soak#1 set point in a recipe. Then, the power can be increased slowly until the desired deposition rate is reached. This power level becomes the Ramp#2/Soak#2 level in a recipe.

Suitable evaporation sources depend on the desired thickness of the lithium film. It is important to note that liquid lithium will eventually alloy and damage refractory metal coils and boats so the lifetime of these sources is limited. We have reported success in using tungsten coils to thermally evaporate lithium. As the power ramps up on the coils, the pellets melt and wet to the coils. With a slight increase in power, the lithium begins to evaporate. This method is a good way to tell if the lithium pellets are significantly oxidized, as oxidized lithium will not melt at lower powers. Also, the coils are typically made of three tungsten wires twisted together which allows for a longer lifetime of the source before failure due to the lithium alloying with the tungsten. If using a KJLC^© system, we would recommend our EVF43025W. If a tungsten boat is preferred, we would recommend our EVS20A015W. Alumina coated evaporation sources are not recommended for lithium evaporation because they will oxidize the lithium.

In cases where thicker lithium films are required and more material needs to be loaded into the source, we've had limited success using a shielded, tantalum crucible heater with an alumina crucible and tantalum insert. We recommend our EVCH14 with EVC6AO and EVC6AOTA if using a KJLC^© system.

Since lithium has a relatively high vapor pressure one must carefully consider executing lithium evaporation in any deposition system. At 300°C, lithium has a significantly high enough vapor pressure to cause ppm level contamination in a vacuum system. Limiting exposure can be as simple as lining the system with vacuum-rated aluminum or copper foil. Great care must be taken not to bridge electrical circuits inside the system with the foil. It's possible that even when using aluminum or copper foil, trace lithium can remain. For this reason, some users prefer to use only dedicated vacuum chambers for lithium deposition.

E-beam Evaporation of Lithium (Li)

Lithium is rated 'good' for e-beam evaporation. We recommend using a tantalum crucible liner to e-beam evaporate lithium. It is important to note that thermal evaporation is the preferred method to deposit lithium films due to lithium's low melting point and high vapor pressure at low temperatures. Lithium has a vapor pressure of 10^-4 Torr at just 407°C. Controlling the rate at these low temperatures via e-beam evaporation can be difficult.

In order to successfully evaporate lithium, it is important that the material is not oxidized. Oxidized lithium will require more initial power to break through the oxide layer and then melt the metal. The power will then need to be brought down quickly as the oxide melts at a relatively high power and the remaining lithium metal would then evaporate quickly or even perhaps splash from the crucible at these higher powers. To avoid oxidation, lithium should be kept either in oil or an argon inert atmosphere.

A 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.

Crucible liners should be stored in a cool, dry place and always handled with gloves or forceps.

Since lithium has a relatively high vapor pressure one must carefully consider executing lithium evaporation in any deposition system. At 300°C, lithium has a significantly high enough vapor pressure to cause ppm level contamination in a vacuum system. Limiting exposure can be as simple as lining the system with vacuum-rated aluminum foil. Great care must be taken not to bridge electrical circuits inside the system with the foil. It's possible that even when using aluminum foil, trace lithium can remain. For this reason, some users prefer to use only dedicated vacuum chambers for lithium deposition.