Electronic materials rely on all components working together seamlessly. There is no room for a mistake when it comes to the manufacture of electronics, with any step along the way.Barrier coatings, though a fairly invisible step in the process of semiconductor manufacture, are in fact an essential step.
Barrier coatings ensure that the photoresist remains free of impurities, air, or non uniform surface problems which can greatly depreciate the life of electronic materials. Barrier coatings are polymer films that are transparent and pressed directly over the photoresist surface after softbake in a spin coating process. They act to minimize interaction between two resist layers and allow resist layers to exist in much closer proximity.
Barrier Coats and CEM
Barrier coats are also usually necessary when using Contrast Enhancement Materials, or CEM. CEM is a photo-bleachable material, which is at first opaque to exposure wavelength, but becomes nearly transparent when exposed. CEM is used on top of the photoresist surface and then exposed. During exposure, the image from the mask hits the CEM layer and a conformal contact mask is formed. The result is a high contrast level of the aerial image used to expose the photoresist. The barrier coat is applied.
Some applications of CEM are in electro-optic or optoelectronic devices, analog devices, semiconductor lasers, wireless and telecom products, manufacturing GaAs microwave ICs, HBT, Metal 1/metal 2 – .08um metal lines and MESFET gate processing. CEM increases the process window, DOF, resolution and improves exposure. Barrier coats are an essential aspect of many of these photoresist processes and therefore the electronics materials that they are part of.
The Most Protection
How do we define efficiency when it comes to barrier coats for electronics? The thin polymer film that is the barrier coat is efficient in its ability to minimize interaction between the two photoresist layers during the lithography process. Protection against heat and moisture transfer is always a concern. Ideally, you have the most protection between the two layers to the least thickness possible.
There are also moisture and oxygen barrier films used in the LED industry. As 3D packaging becomes more and more widely used in response to the demand for smaller and smaller electronics materials in the semiconductor and electronics industry alike, so too do barrier coats that can meet the need to function with stacked die semiconductor manufacturing processes.