Adhesion Enhancements and Internal Stress in MgF2 Films Deposited with Ion Beam Assistance

摘要

Adhesion measurements were performed using a dynamically loaded scratch tester to evaluate Magnesium Fluoride deposited onto heated and unheated fused silica substrates. Resistance evaporation at 5 A/s with Ar(+)ion beam assistance improved the relative adhesive strength of films deposited onto unheated substrates by over an order of magnitude compared with the results for head substrates without ion beam assistance. Additional experiments were performed to measure internal stress in MgF2 films on specially masked BK-7 glass substrates using modulated transmission ellipsometry. We found that ion-assisted deposition can reduce internal stress to approximately 450 kgf sq. cm (tensile) in films 2300 A thick. The great potential for stress relaxation in MgF2 films deposited with ion assistance is suggested by these measurements, but additional work with films of higher purity may be required to identify the relative contributions of stress relief, substrate cleaning and chemical bonding to improved adhesion.