In the fabrication of modern electronic devices, integrated circuits are manufactured on large, thin disks of semiconductor material called wafers. Before these circuits can be used, they must be separated into individual chips, a process known as dicing. Stealth dicing represents an advanced approach to this separation, utilizing laser technology to precisely divide wafers. This innovative method plays a part in the production of microprocessors, memory chips, and various electronic components that power today’s technology.
The Basics of Wafer Dicing
Wafer dicing is the process of cutting a semiconductor wafer, typically made of silicon, into many individual integrated circuits, also known as dies or chips. This step is a standard part of semiconductor manufacturing, allowing each functional circuit to be isolated for packaging and integration into electronic products.
Traditional dicing methods include mechanical saw dicing, which uses high-speed rotating blades coated with diamonds to cut through the wafer. Another method is conventional laser ablation, where a focused laser beam vaporizes material along the cut lines. These conventional techniques often face challenges such as material loss due to the width of the blade or laser kerf, the potential for micro-cracks and chipping on the chip edges, and the generation of debris and particles that can contaminate the wafer surface. Mechanical dicing can also induce mechanical stress and heat, requiring cooling agents like water during the process. These issues can reduce the overall yield and quality of the chips produced.
How Stealth Dicing Works
Stealth dicing operates on a distinct principle compared to traditional methods, focusing a laser beam inside the silicon wafer rather than on its surface. This process employs an infrared picosecond or femtosecond laser, whose wavelength allows it to pass through the silicon material without being absorbed until it reaches a specific focal point within the wafer. At this internal focal point, the high intensity of the laser light causes multiphoton absorption, where the silicon absorbs multiple photons simultaneously. This localized energy absorption creates a modified layer, sometimes referred to as a “stealth layer,” within the wafer’s bulk.
The modified layer is a region where the silicon’s crystalline structure is altered due to the highly localized thermal stress induced by the laser. This internal modification forms a weakened plane along the intended cut lines. After the laser irradiation process forms these internal layers, an external force is applied to the wafer. This force, often achieved by expanding the dicing tape on which the wafer is mounted, applies tensile stress to the modified internal layers. The stress then extends the cracks from the modified layer to the top and bottom surfaces of the wafer, causing it to separate cleanly into individual chips. This non-ablative, internal process means there is no material removal from the surface, distinguishing it from conventional laser cutting.
Key Advantages of Stealth Dicing
Stealth dicing offers several benefits over traditional wafer separation techniques.
Reduced Kerf Loss
One advantage is the reduction of kerf loss, the material wasted during cutting. Since stealth dicing creates an internal modification rather than removing surface material, the width of the separation line can be made much narrower, leading to more chips per wafer.
No Debris or Contamination
Another benefit is the absence of debris or contamination. As a dry process without material ablation or cooling water, stealth dicing generates no particles, chips, or slag. This eliminates post-dicing cleaning steps, reducing contamination risks and improving overall yield.
Minimized Damage and Thin Wafer Processing
The internal, non-contact nature of the process also minimizes micro-cracks and mechanical stress on the chip’s surface, contributing to higher quality chips with improved reliability. Stealth dicing is well-suited for processing thinner wafers, some even less than 50 micrometers thick, which are susceptible to breakage under conventional methods. It allows precise control over the depth of the modified layer, making it suitable for ultra-thin applications.
Increased Throughput
Stealth dicing can offer increased throughput due to its high-speed cutting capabilities, allowing more wafers to be processed in a shorter amount of time. This efficiency contributes to faster overall production cycles.
Industries Benefiting from Stealth Dicing
Stealth dicing technology finds widespread application across various sectors of the electronics industry due to its precision and minimal damage characteristics.
Semiconductor Manufacturing
In semiconductor manufacturing, it is used for producing microprocessors, memory chips, and other integrated circuits, where high quality and yield are paramount. The ability to create thinner, more robust chips is especially beneficial for advanced packaging solutions, including 3D chip stacking.
LED Manufacturing
The LED manufacturing industry also benefits from stealth dicing, as it enables the creation of individual LED chips with high brightness and efficiency.
Micro-Electro-Mechanical Systems (MEMS)
For Micro-Electro-Mechanical Systems (MEMS), such as sensors, accelerometers, and gyroscopes, stealth dicing is particularly advantageous because these delicate devices require precise separation without damage to their intricate structures. The dry process and reduced mechanical stress are highly compatible with MEMS devices that are sensitive to water and dicing loads.