The Silicon wafer dicing saw is an important instrument in the semiconductor wafer-cutting stage of manufacturing. The wafer dicing process can be accomplished through various means, each with its own pros and cons. Mechanical sawing through a wafer dicing saw has many things to consider before using and its own challenges to overcome. Let’s find out where in the semiconductor wafer manufacturing process the dicing saw comes into play, compare it to other wafer dicing methods, and how wafer dicing blades are chosen.
Why The Silicon Wafer Dicing Process Is Important
In semiconductor manufacturing, integrated circuits or chips are the results of multiple production processes before they are ready to be used for building everything from smartphones and kitchen appliances to advanced medical or industrial equipment. First, Silicon ingots are artificially grown and then sliced into thin disk-shaped layers called ‘wafers’.
These silicon wafers are then polished before any circuit paths are created on them. Next, the wafers go through a thorough inspection process to detect any manufacturing defects on their surface. Special imaging techniques are used by the semiconductor industry to inspect and qualify wafers before they are sent to the next step in manufacturing. To learn more, read Semiconductor Imaging Techniques Used for Wafer Inspection During Manufacturing.
Next, through a process called ‘Photolithography’, the circuit patterns are imprinted on the silicon wafer surface in many layers. Next, ion implantation alters specific regions of silicon wafers to alter their conductive properties, and transistors are formed using etching techniques. Temporary transistor gates are first formed using photoresists and then replaced with copper gates using metal deposition and electroplating processes. Interconnections between individual transistors are added before a final polishing to remove any unwanted material on the silicon wafer.
Individual integrated circuits are then tested to check for any functional defects by applying electrical signals using a wafer prober device. These automatic test equipment can check large volumes of wafers and sort them according to their performance. To learn more, read Semiconductor Chip Testing Using Automated Test Equipment.
Finally, the individual chips which are also called ‘die’ are separated from the silicon wafer through a wafer dicing process. After this wafer cutting, the chips are then packaged and made ready to be distributed to the equipment manufacturers who will use them to build more complex hardware devices like smart televisions, and voice assistants.
Silicon Wafer Dicing Methods
The silicon wafer dicing process can be done through various methods like wafer scribing and breaking, mechanical sawing, laser dicing, and plasma dicing. Each wafer dicing method requires sophisticated equipment to ensure accuracy.
Mechanical Sawing
In this semiconductor wafer dicing method, a mechanical saw is used which will cut entirely through the thickness of the wafer. Since it cuts completely through, this wafer dicing method is also called ‘Through Cutting’. The quality of the product that results from mechanical wafer sawing depends on factors like blade size, blade thickness, and wafer dicing speed.
Mechanical stresses will be applied to the semiconductor wafers during this process and the bottom side of the wafer may experience some chipping from the blade. However, wafer dicing with a saw is the most widely used method. It is a well-understood process that is easy for trainee technicians to grasp, has a smaller tool footprint, and is cheaper than other more exotic methods. While methods like laser dicing are taking over more and more duties, wafer dicing saws are still in high demand among semiconductor manufacturers as they scramble to supply the world’s growing hunger for more microchips.
Laser Dicing
There are two types of laser dicing. Laser ablation dicing involves focusing a laser beam onto a chosen spot on the wafer and using the beam’s energy to cut through the wafer according to a cut pattern. Depending on the required laser intensity, the beam could be a pulse or a continuous one. While there is no mechanical contact with the wafer-like when using a dicing saw, there is a risk of thermal damage due to the intense heating of the material. Cooling is water used in laser ablation to protect the wafer from heat and wash away any particles left over from the dicing process that might contaminate the product.
The second laser process is called ‘stealth dicing’. Here, the laser beam wavelength is semi transparent to the wafer substrate material. Therefore the beam can focus its energy on specific points inside the wafer instead of the surface. During this phase of the stealth dicing process, internal cracks are formed that so far do not extend to the surface of the wafer. Next, tensile stress is applied to these cracks by using the mounting tape attached to the bottom of the wafer. This causes the cracks to expand to the top and bottom which separates the wafer along the desired lines. There is no need for cooling water since there is no surface debris or no heat damage.
Plasma Dicing
The plasma dicing process also called ‘Deep Reactive Ion Etching’ (DRIE) uses Sulphur hexafluoride or Octafluorocyclobutane to etch narrow and deep trenches called ‘streets’ into the wafer. A wafer dicing saw can only be cut in rectangular shapes, a limitation that does not exist in the plasma wafer dicing process. It can also process the entire wafer in one go, and cut narrower trenches leaving more space for circuitry, which results in a better yield.
Wafer Scribing And Breaking
In this dicing process, the semiconductor wafers are partially cut (scribed) using a tool like a dicing saw or laser. This creates a scribe line on the wafer surface. Force is then applied along the scribe lines to break the wafer as required. The wafer scribing and breaking methods were used by the industry up to the early 1980s and were replaced by wafer dicing saws. This is because dicing saws are not limited by wafer thickness, die size, crystal plane orientation, street structures, and wafer materials.
The Silicon Wafer Dicing Saw
Silicon wafer dicing saws come in a variety of models from manual to fully-automatic, single-blade, and multi-blade depending on the requirement of the manufacturer. The cutting mode is dependent on the complexity of the dicing and the volume of the wafer batch that needs to be processed.
For example, a fully-auto dicing saw can be loaded with up to 50 wafers at a time, and with pattern recognition enabled, can dice without any human technician present to guide it. This is great for large volumes. A semi-auto-dicing saw can handle low to medium complexity, although a technician is needed to monitor and intervene at various stages. A saw blade can go up to rotation speeds of 60,000 rpm depending on the requirement, and equipment may come with cooling water jets and multiple blades.
Silicon Wafer Dicing Blades
The dicing blade(s) of the saw is very important and is one of the most expensive components in wafer dicing equipment. A diamond blade is usually a disk made from a resin, nickel, or sintered metal matrix with diamond particles embedded on its cutting edge. Diamond is chosen due to its hardness and blade wear resistance.
A wafer blade is selected for a specific wafer dicing task based on its width, grit size, and exposure. The width of the blade is dependent on the width of the street that is required for dicing. The grit size is dependent on the diamond particles embedded in the cutting blade. If the street needs to be narrow, a thin blade with a small grit size will perform wafer dicing more smoothly.
The exposure is the height of the blade surface available for cutting the wafer. If the wafer that needs dicing is 10 mils in thickness, the blade needs to have an exposure of 20 to 25 mils to cut through it (01 mils = 0.0254 mm). If the street size is 4 mils, a blade with 01 mil thickness and 02 to 04 µm grit size can be used to dice it.
Mounting Tape
The wafer that undergoes dicing is securely mounted on a frame using the mounting tape. This tape has adhesive properties to hold each die in place during dicing until they are removed. The thickness of this tape is usually 80 to 95 µm which needs to be accounted for when choosing a blade of sufficient exposure.
Mounting tapes come in blue film and UV tape which have slightly different adhesive properties. The blue film is cheaper if the dicing process takes less than 72 hours. Leaving the die attached any long will cause the adhesive residue to stick to the bottom of the die. UV is more expensive but can be exposed to ultraviolet light after the dicing process to lower the adhesiveness during removal.
Using The Silicon Wafer Dicing Saw
Before wafer dicing can begin, the wafer is evaluated to check its thickness, required street width, and wafer material which can be pure Silicon, Silicon Germanium, Silicon on sapphire, or others. Based on these factors the blades are selected. Next, the wafer is placed face down on particle-free paper to protect its surface. The mounting adhesive tapes are stretched and placed over the back of the wafer. The tape is then evenly pressed and distributed to the wafer using rollers. Any excess tape is cut.
After the wafer is mounted and loaded securely onto the dicing equipment, a sample cut is made first for verification purposes. Based on the pattern that is programmed in, the wafer dicing begins with periodic checks performed to ensure proper alignment and quality of the dicing. Afterward, the wafer goes through cleaning to remove any silicon dust left over from the dicing process.
Challenges In The Wafer Dicing Process
Wafer dicing through a mechanical sawing process is not without its issues. The narrower the streets are, the thinner the blades need to be. This in combination with thick wafers can put stress on the blade which can cause it to break. This is bad for two reasons. First, if the blade breaks during dicing, this can damage the wafer. Secondly, diamond blades are the most expensive component in the dicing equipment.
While silicon wafer dicing is still done using sawing equipment, many manufacturers are shifting to stealth dicing with lasers and plasma dicing methods. Stealth dicing leaves no residual dust and requires no cleaning. It can also deliver narrower streets, allowing for more ICs on a wafer and higher yield. Plasma causes minimal damage to the wafer itself which results in better die strength. This can improve their reliability, increasing the lifetime of devices made from these ICs.
Even with more advanced dicing technology slowly replacing the trusted silicon wafer dicing saw, it’s still in heavy use by the semiconductor industry due to its reliability. For more on semiconductor manufacturing and industry news, check out Inquivix Technologies!
FAQs
Wafer sawing or dicing is the process where a semiconductor wafer is cut into individual die or integrated circuits (ICs).
Silicon wafers can be cut or diced using a mechanical saw with diamond blades, laser dicing, or plasma dicing methods.
