Resistance heating evaporation source structure is simple, easy to use, easy to make, is the most widely used one kind of evaporation source. People are usually called heat generator or evaporation boat.
Heating the requirements of the resistance material used is: high temperature, resistivity, low vapor pressure at high temperatures, no chemical reaction with the membrane material, does not produce outgassing and pollution. Selected resistance heating materials mainly from refractory metals, such as W, Mo, Ta and other materials or selection of high-purity, high-strength graphite or boron nitride synthetic conductive ceramics and other materials. Sometimes, can also choose Fe, Ni, Ni-Cr alloy and Pt as evaporation source material.
Various resistance heating evaporation source of common materials (such as Ti, Mo, C, Ta, W, etc.) of the melting point and vapor pressure and temperature relationship curve is different. Among them, tungsten becomes brittle when heated to the evaporation temperature because of the heating junction product. Molybdenum, on the other hand, varies in purity, with some becoming brittle and others not. Tungsten reacts with water vapor to form the volatile oxygen compound WO3.
Therefore, when tungsten is heated in residual water vapor, the heated material is continuously depleted. When the residual gas pressure is low, there is not much material loss, but it is a serious contamination of the membrane.
The use of filamentary sources should pay attention to the wetting of the hot wire on the membrane material. For example, hot wire temperature rise too quickly, the membrane material is not easy to immediately melt all of the membrane material and hot wire wetting is not sufficient. As a result, the unmelted film may fall out of the wire basket. At the same time, the temperature rise is too fast will also cause the membrane material in the gas released quickly, resulting in bubbles or splashing, the result will make the formation of small droplets stick to the substrate. Therefore, filament sources should be used with temperature control.
The main disadvantage of wire baskets, conical coils or spiral coils is that the amount of supporting film material is too small, and this source will cause the temperature of the hot wire to rise as the amount of film material decreases after the film material is evaporated, thus causing the evaporation rate to rise. This is also a problem that should be noted for the film making process that requires strict control of the evaporation rate.
(2) The working principle and structure shape and use characteristic
Resistance heating evaporation source, in fact, is resistance heater it is the use of the heat generator or evaporation boat directly energized, so that the current through a large number of Joule heat and get high temperature to melt metal film material, so that its evaporation of a kind of evaporation source.
–This article is released by vacuum coating machine manufacturer Guangdong Zhenhua
Post time: Feb-23-2024