Glass substrates are used in a variety of applications including architectural applications, automotive applications, consumer appliances, etc. Oftentimes, the glass is coated with a functional coating(s) to provide the required properties. Examples of functional coatings include solar control coatings, conductive coatings, photocatalytic coatings, low emissivity coatings, etc.
Today, scientists and engineers are devising increasingly complex functional coatings. More specifically, functional coatings are being designed with more discrete coating layers. Generally, the more discrete layers of coating in a multi-layer coating stack, the easier it is to control properties of the coated substrate such as color and solar properties, e.g., emissivity.
Several techniques, such as chemical vapor deposition (“CVD”), spray pyrolysis, and magnetron sputtered vacuum deposition (“MSVD”) are known in the art for applying functional coatings on a substrate. MSVD processes are best suited for complex coatings containing one or more coating layers because they allow for a wider selection of coating materials to be deposited at thinner thicknesses on a broader variety of substrates.
MSVD processes are performed in coaters having one or more coating zones. A typical MSVD coater has between four and twenty zones. Each zone includes one or more targets, usually three, for depositing a specific type of material on a substrate. Each target is placed in a bay which has its own gas feeds by which gas comes into the zone. Although gas comes into a zone in different places, all of the gas that comes into the zone leaves at a certain place in the zone.
Each zone in a coater is run, i.e. operated to deposit a coating layer, in one of three modes—metal mode, transition mode, or oxide mode. Generally speaking, the amount of reactive gas, e.g. a gas like hydrogen or nitrogen that is capable of reacting with a target in the zone, determines the mode. In metal mode, the gaseous atmosphere in the zone consists of only non-reactive gas, e.g. argon, and the zone is run to deposit a layer of metal on a substrate. Of the three modes, metal mode generally has the fastest deposition rate, with the exception of a few target materials such as tungsten. In transition mode, the gaseous atmosphere in the zone consists of both non-reactive gas and a reactive gas, and the zone is run to deposit a layer of oxide on the substrate. The concentration of the reactive gas is constantly monitored and adjusted to ensure the oxide layer is being deposited at the maximum rate. The deposition rate in transition mode is slower than the deposition rate of metal mode but faster than the deposition rate of oxide mode. In oxide mode, the gaseous atmosphere in the zone consists of both non-reactive gas and reactive gas, and the zone is run to deposit a layer of oxide on the substrate. Of the three modes, oxide mode has the slowest deposition rate. The deposition rate in metal mode can be up to ten times faster than the deposition rate in oxide mode.
Conventionally, each bay in a single zone in an MSVD coater is run in the same mode; either metal mode, transition mode, or oxide mode. If different bays in a zone were run in different modes, oxide mode and metal mode, for example, reactive gas entering the bay being run in oxide mode could leak over (also referred to as “bleed through”) into the bay being run in metal mode and negatively impact the deposition process. The desired metal layer would not be deposited and/or the speed of the deposition would be reduced.
Because a single zone is always run in one mode, the types of coating compositions that can be deposited and the efficiency at which they can be deposited (the faster the rate of deposition, the faster the rate of production) are limited by the total number of zones in the coater. For example, a coating that has three silver layers sandwiched by four zinc oxide layers cannot be deposited via a continuous process in a coater having less than seven zones. Four zones are required to run in either oxide mode or transition mode to deposit the layers of zinc oxide and three zones are required to run in metal mode to deposit the silver layers. Although it may be possible to produce the described coating in a coater have less than seven zones by running the substrate through the coater more than once, such is undesirable for several reasons, chief among them, efficiency.
Coaters can be expanded to include more coating zones. Some multi-zone coaters are designed to accommodate an expansion to include more zones, but others are not. Regardless, it is expensive to add more zones to an existing coater. Typically, it will cost between $1 and $5 million to add one zone to an existing coater, depending on whether the coater was designed for expansion or not.
It would be extremely beneficial to have a method for coating substrates in a MSVD multi-zone coater that reduces the total number of zones required to deposit a coating. The present invention provides a method for coating a substrate that includes running a single zone of a MSVD multi-zone coater in at least two different modes, thereby reducing the total number of zones required to apply a given coating.