Semiconductor Production Support with Fiber Lasers
Lasers are used throughout the semiconductor industry, and they play a crucial role in many process stages. Here you will find an overview of their use in the industry, but our primary focus is on the application of fiber lasers in wafer dicing; separating the processed semiconductor wafer into individual chips. For reasons we explain, the process is known as “stealth dicing”.
Semiconductor production is a highly complex and sophisticated process involving many stages. The semiconductor, which may be silicon, gallium arsenide, silicon carbide or one of the more exotic specialist materials, must be purified to an exceptionally high standard and formed into an almost perfect crystal that is accurately sliced to produce thin wafers.
Next, in an ultra-clean environment, integrated circuits are produced within the wafers. Process steps include the formation of thin protective oxide layers, selective oxide removal using photoengraving, implantation and diffusion of dopants, deposition and patterning of metallic conducting layers, dicing the wafers into individual chips, and mounting the chips in packages.
The role of lasers
Lasers have various functions in many of these steps, ranging from the purification of the more exotic semiconductor materials through wafer processing to wafer dicing and lead frame manufacture. These are some examples:
- Semiconductor purification
- Laser deposition
- Laser annealing of deposited layers
- Dopant activation
- Laser patterning and lithography
- Wafer alignment
- Semiconductor wafer thinning
- Semiconductor wafer dicing and drilling
- Wire bonding and welding
- Debonding of components
- Marking and labelling
- Inspection and measurement
- Trimming of deposited resistors
- Solder bonding
- Debonding of flip chips
- Lead frame manufacture
Fiber lasers and wafer dicing
As an example of how fiber lasers really make a difference, we will look at their major role in wafer dicing, in other words machining silicon wafers, which might be 300mm diameter, to produce individual chips or die. Depending on the die size, several hundred to several thousand can be produced from a single wafer.
Previous scribing and dicing methods
Before laser dicing, diamond scribing and sawing were used. The first of these employed a diamond-tipped tool to scribe a channel between the chips which were subsequently separated mechanically. This technique was replaced by sawing using a high-speed diamond encrusted wheel. Neither of these was entirely satisfactory for various reasons and for the most part they have been replaced by laser dicing initially using laser ablation but more recently applying a process referred to as “stealth dicing.”
Advantages of fiber laser stealth dicing
A problem with most dicing methods is they produce excessive flaws in the semiconductor material that can impact on the performance of the chips. Fiber laser stealth dicing is a rapid process that avoids this problem. Unlike other methods, it doesn’t produce excessive heat, so it avoids the need for coolants; it produces very little debris; and, because the Kerf width is tiny, it allows more of the wafer real estate to be used for circuitry.
Fiber Lasers with a 1064nm wavelength are ideally suited. This wavelength is a close match to the silicon bandgap of 1117nm. Stealth dicing is a two-stage process. The laser is focussed within the body of the wafer to achieve maximum absorption, and the laser scans along the dicing lines between the active areas. This technique produces rapid melting and solidification forming lines of defects contained within a 30-micron wide track. Multiple scans are made with the focus adjusted at each scan to create defects at different depths within the silicon.
The next stage of the process is the mechanical separation of the individual die. Usually, before scanning, the wafer is mounted on an adhesive membrane, and this is expanded to fracture the wafer along the lines of internal defects producing the individual die.
Need to know more about semiconductor production support with fiber lasers?
Stealth laser dicing is just one field where pulsed fiber lasers are supporting semiconductor production, and we have mentioned many more areas too. They also have downline electronics applications in printed circuit board manufacture and component surface mounting. To find out more about the advantages pulsed and continuous wave (CW) fiber lasers offer the semiconductor and related industries; please contact SPI Lasers, there is so much more to discover.
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