To have a successful optical substrate surface, cleaning before the coating is an essential step.

This is because a contaminated substrate surface (whether particles emanating from the polishing abrasive or the substrate materials removed from optical paint) can affect the performance of the optical component, coating adhesion, and even cause defects, especially with laser components surfaces that have low particle densities.

However, the demands and specifications for optical precision coating may require a well-thought-out cleaning procedure as substrate cleaning in itself involves a multistage procedure.

Here are some of the processes involved in substrate cleaning.

Materials And Methods

Before we delve fully into some of the processes involved in substrate cleaning, it’ll be nice to mention the material used to carry out this cleaning experiment.

First off, you should know that several other chemical options can be used for substrate cleaning, and whichever you may decide to use is fine.  However, for this post, we’ll be using silica samples with a thickness of 2 mm and a diameter of 25 mm.

Silica was chosen because of its high quality and chemical resistance to prevent any impact of the substrate material on itself.

Processes involved in substrate cleaning are:

Cleaning Before Coating

The optics precision cleaning steps for all substrate surfaces are the same. There’s the:

  • 1st cleaning – rinsing stage
  • 2nd cleaning – rinsing stage
  • Another rinsing, then
  • Leave to dry stage

A substrate surface can be cleaned manually or automatically using either a standard semiconductor wet bench or an industrial ultrasonic cleaning machine. However, sometimes before cleaning, some substrate surfaces are often pre-cleaned.

This is done using just solvents (acetone at room temperature). The acetone solvent is often volatile and prepares the provision options for proper cleaning. During cleaning, the substrates get to dwell in a silica bath for a while before manual cleaning begins or probably get moved from bath to bath automatically after a while.

Anti-Reflective Coating

After the cleaning comes to the coating, this is the part where you get to deposit an anti-reflective coating onto the substrates. This is done through an ion beam faltering – the Veeco sector.

For effective results, you’ll have to ensure this process is done in a cleanroom environment. However, before coating, you’ll have to ensure that your coating basin was pre-heated to your desired temperature and that temperature is sustained during the deposition.

Surface Inspection

This is the third stage of the cleaning process. Once you are done cleaning, the samples will be inspected through transmission and reflection by a spot lamp. After which, laser damage testing is done on the substrate surface.

Once it’s damage-free, you know it was properly clean and can be used for what was planned.

Hydrogen Silsesquioxane

They are otherwise known as T-resins. Silsesquioxanes are a group of compounds with an empirical formula – RSiO1.5. The compounds get their name from either the one and a half (1.5) or from sesquistoichiometry of oxygen that’s bound to silicon.

Its substitute name T-resin is derived from 3 oxygen substituents on silicon. Silsesquioxane has several empirical formulas. However, the two most common representations are:

  • The ladder-type structure
  • The cubic structure

The cubit structure, also known as T8, is often drawn incorrectly as O-Si-O. But its actual structure is a Si-O cage framework and is quite easier to visualize.

The hydrogen silsesquioxane can be used to bridge the gap between two components (inorganic-organic) of materials. The silsesquioxane hybrid materials express an enhancement in properties. They are:

  • Thermal and thermomechanical stability
  • Solubility
  • Optical transparency
  • Gas permeability
  • Fire retardant and more

To further understand these chemical compositions mentioned above and how they function, you can visit us at Dischem chemicals. Here, we have qualified people who can give you chemical products you may need for your experiments.

Asides from that, we also offer many other chemical services such as:

  • Micro Lithography resist adhesion
  • E-beam lithography anti-charging agent
  • Electroforming and much more


Contact us today if you are looking to buy well-priced chemical commodities. We also have exciting new products that can be used for your chemical experiments. More so, if you need help using these products, we’re just one call away.