Laser dicing is a non-contact wafer dicing process that uses a focused laser beam to separate chips from a semiconductor wafer. This method is more efficient and safer than traditional blade dicing. Results show that the front and backside breaking strength of fs laser-diced chips are higher than those of ns-laser and mechanically diced chips. This is the result of optimal fluence control. Which minimizes thermal side effects and periodic surface structures.
History of Laser Dicing
Laser dicing of brittle semiconductors like silicon (Si) and silicon carbide (SiC) wafers is becoming increasingly important for the industry. This method has a much higher cutting speed. Less damage to the wafer and smaller kerf width than traditional blade dicing. Traditionally these wafers are diced by pulverizing the wafer in the cutting path known as the “dicing street”. This can cause problems such as debris and damage to the wafer during the dicing process.
Laser dicing can solve these issues by cutting the wafer from the inside instead of the outside. The method called stealth dicing uses a laser beam to create a modified layer in the wafer that cracks it apart. This is followed by a tape expander to separate the individual chips. This process can result in high front-side and back-side breaking strength compared to mechanical or ns-laser dicing, respectively. This paper compares the performance of fs- and ns-laser dicing of SiC wafers to show the advantages of this technology.
How Laser Dicing Works
Laser dicing uses high concentrations of photon streams to heat the surface of a wafer. This produces a spot of high localized temperature that vaporizes or melts the area around it. Which is called the dicing lane. A tape expander is then used to separate the resulting die from the remainder of the wafer. This is called full-cut laser dicing. It enables the use of a narrower dicing street than blade dicing, which allows for more die per wafer.
This increases the number of die that can be made on a semiconductor wafer, and frees up space that would otherwise be taken by guard rings or other mechanical singulation steps. A variant of this technique, called stealth laser dicing, creates a modified layer in the workpiece by focusing the laser below the surface. This creates internal deformations and cracks that will expand when the piece is expanded, separating it into multiple die.
Applications of Laser Dicing
As a non-contact process, laser dicing is particularly well-suited to cutting fragile and stress-sensitive wafers. This can minimize the risk of chipping and cracking often caused by traditional blade dicing methods. Advanced dicing systems incorporate state-of-the-art inspection and metrology tools to provide real-time feedback on the quality of diced dies. Enabling manufacturers to quickly identify and adjust process parameters for consistent performance. This can help to improve dicing precision and accuracy while also reducing the time and cost of production.
Another important application for laser dicing is the singulation of ultrathin silicon wafers into individual microelectronic devices. A new method called stealth laser has been shown to be more effective than conventional ns-laser and blade dicing at separating low-k device chips. The technique focuses laser energy onto a very small area for a short time. Resulting in the material being blown away (ablated) or vaporized. This results in extremely clean cuts without the damaging thermal side effects associated with ns-laser and blade methods.
Advantages of Laser Dicing
Using lasers instead of blades for wafer dicing can reduce process damage and eliminate debris, saving time and money while ensuring high-quality dies. Laser dicing systems can be integrated with inspection and metrology tools to provide real-time feedback on the quality of the diced dies. Allowing manufacturers to quickly identify any deviations from the intended specifications and make the necessary adjustments. Conventional dicing methods can cause chipping and debris. Particularly for hard or brittle materials such as silicon and gallium arsenide.
Laser ablation and stealth dicing, on the other hand can be used to cut these devices with minimal stress. Stealth dicing uses the laser to create perforations underneath the surface of the wafer, leaving the front and back surfaces undamaged. This approach allows for a reduction in the dicing street width, which can increase the number of dies that can be produced from a single wafer. The process can also be performed in a dry, zero-waste process that does not require any cleaning.
Laser Dicing vs. Traditional Cutting Methods
Laser ablation is an alternative to traditional cutting methods, which are mostly mechanical. This processing method uses a laser beam to sublime (vaporize and evaporate) a workpiece by irradiating it with a burst of high energy for a short time, leaving a clean edge without chipping or cracking. The disadvantage of this type of dicing is that it can cause heat damage to the workpiece. It also creates a heat-affected zone (HAZ). Which leads to weaker fracture strength. Many technology have been developed to minimize HAZ. Such as upgrading machines. Parameter optimization and post-treatment.
However, it is difficult to improve the mechanical stability of cut chips when using a blade method, especially in the case of specialty wafers such as those with low-k material and MEMS devices. A recent study using ultrafast lasers showed that it is possible to improve the quality of the front side and backside of the chips by employing a stealth dicing process, which uses a step cut instead of a full cut.
Challenges and Limitations
As with other cutting methods, laser generates heat that can cause damage to the die or wafer. To reduce this risk, it’s important to regularly calibrate dicing equipment and optimize process parameters. This can help maintain consistent performance and improve overall die quality. For example adjusting the fluence or pulse duration of a laser can reduce the energy density and the amount of heat generated during cutting.
This can also help minimize mechanical stress and prevent cracking or chipping. Another way to improve laser dicing results is by applying protective films or coatings to the die surface before cutting. These materials can act as a barrier to absorb the heat and stress produced by the laser, reducing the risk of die damage.