Wafer Coring
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A 200mm silicon wafer that has been cut into two 100mm wafers with multiple wafer flats. The major wafer flats have been aligned to the original wafer’s notch.
Wafer Coring/Resizing
There are many discrete processes involved in the manufacturing of integrated circuits using semiconductor wafers, and each process has its own unique requirements for how a wafer is handled during processing. One of the most basic parameters is the size or diameter of the wafer.
Wafer coring involves reducing the diameter of the wafer so that it fits into the available processing equipment.
The process of wafer coring has many names that basically mean the same thing. It is sometimes referred to as wafer resizing, wafer downsizing and wafer cut down. It refers to the process of reducing the diameter of the wafer. Even so they all refer to the process of cutting a large wafer into smaller wafers.
WaferFab Services cores, or resizes, various types of wafers, including silicon wafers, up to 12″, or 300mm in diameter into smaller wafers. We core all standard sized wafers; 2″, 3″, 4″, 6″, 8″, and 12″. Patterned and blank wafers can be cut to any geometry or size; round, square, notched, flat on the bottom, multiple flats, etc.
Why Do We Need Wafer Resizing Services?
Over the years wafers have been getting larger and larger. Every time the industry increases the size of the wafer it creates a problem for the folks that have some very expensive process tooling designed for the old wafer size. There are a huge number of processes that are used to create integrated circuits. Each one of those processes have process tooling that is designed to handle the old wafers. In the short term it becomes much easier to have the wafer resized down to a smaller diameter than to go out and replace your multi-million dollar tooling. In the long term new tooling will have to be bought and installed to accommodate the larger wafer.
Why We Use a Mechanical Coring Process Instead of Lasers.
It comes down to the nature of our wafer processing services. We routinely handle a plethora of materials. One job could be silicon, the next could be glass, and the next could be sapphire or a composite. Because we use a mechanical cutting process we do not have to worry about the amount of laser energy a particular type of material will absorb. If it is hard and brittle then we know we can probably process it. Our mechanical sawing process and edge beveling is accomplished with a CNC machine. Using this type of process also means that we can be more cost effective than a laser.
Why We Use a Mechanical Coring Process Instead of Lasers.
- Unlike lasers, our processes can handle a large variety of materials, including composite materials.
- We can also process very thick materials.
- Anything that is a hard and brittle material is fair game for us. That being the case, we primarily do silicon wafer coring. Here is a short list of other materials we've worked with before: Silicon, Germanium, Gallium Arsenide, Silicon Carbide, Glass, Quartz, Sapphire, Ceramic Material and many others.
What's the Deal With Flats and Notches.
The wafer flat or notch on a silicon wafer serves two purposes.
- In either case they are used to provide a reference surface for automatic handling equipment. This allows precise alignment of the various lithographic processes that must occur to produce the finished integrated circuit.
- It also indicates the crystal orientation of the semiconductor wafer itself. This is important for certain applications.
On wafer sizes smaller than 200mm you will typically see flats and on wafers with a diameter of 200mm and larger you will see notches instead of flats. This change was probably done to minimize the amount of real estate that was lost due to the creation of the flat.
Sometimes a secondary flat is added to the smaller wafers to indicate which dopants have been added to it.
It is important to maintain the orientation of the flats and notches when the wafer is downsized. It is also important to round or bevel the wafer edge after coring.
We also have wafer dicing processes and can dice complete die from the remnants of the original wafer using standard dicing saws. If the wafers are ESD sensitive we will use all of the ESD protocols including wrist straps, foot straps, conductive work surfaces, etc.
WaferFab's Standard Coring Process Workflow:
- A layer of protection is added to the topside of the wafer to prevent damage to its surface
- The wafers are background to the required thickness if required
- A custom program is created based on customer requirements
- The wafers are cut to the customers requirements
- The resized wafers are edge rounded (beveled) to increase their mechanical stability
- A detailed inspection is performed
- The protective layer is removed from the surface of the processed wafers and they are sent through a cleaning process
- The wafers are packaged and shipped back to the customer
