Sapphire Wafer Dicing - Why It Is Important In Led Production
Sapphire wafer dicing plays an important role in LED production most especially today
that there is an increasing demand of light emitting diode used for an array of applications like backlight displays for mobile devices, flat panel televisions, automotive headlamps, and other general lighting applications.
Why Sapphire is the most commonly used substrate
Sapphire is the most commonly used substrate material for a number of reasons. First, because it provides an excellent lattice match for the GaN, and, second it is transparent to LED output - a property that is really important since some of the light emitted by the LED partially passes through the edge of the sapphire substrate. And third, it helps in heat sinking the LEDs as it is a good thermal conductor.
What are the traditional methods used in Sapphire wafer dicing?
There are a number of traditional methods used for separating wafers with arrays of die into individual chips and these include dicing saw separation and scribe-and-break. However, such methods have some disadvantages including the following:
- they can waste valuable wafer area
- involve costly consumables
- long process time
Dicing saw separation, which uses blade with embedded diamonds to remove the material via brute force approach, is generally not employed for sapphire except for large die or wafers. This method needs wide streets (with a kerf width up to 250m) and wastes a lot of active area.
The scribe-and-break process mechanically weakens the substrate by employing a diamond scribe to provide a fracture line between die. A sharp straight edge then is used to break these rows, which results in a narrow kerf width. But the wafers must be thinned below 100m to achieve consistent yields above 80 percent. In addition, polishing may also be needed to reduce strain caused by the device layers on top of thinned sapphire.
Laser scribing - the advance method
Laser scribing a new and more advanced method - provides many advantages, addressing the challenges found in the traditional methods. Some of these are the following:
A more robust process flow at lower cost - this is brought by the combination of a narrow kerf width, high throughput, and wide process tolerance.
- In comparison with the other techniques, laser scribing has a 5 to 20 times faster throughput and this because the laser beam can be projected on the wafer surface as a long line or multiple lines, which are scribed simultaneously.
- Yield between 97 and 99% with a wafer thickness up to 700 m is achievable - this is because the cut depth can be adjusted easily while maintaining the same kerf width.
- And the most notable feature of laser scribing is that it has the capacity to scribe both front and back of a wafer before fracturing - this is useful for LEDs because of the requirement for uniform light emission.
by: Riza Deshpande
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