How do you manufacture ic?

Answer 1

IC manufacturing processesA diverse range of integrated circuits provide invaluable support in every aspect of society. Let’s take a look at how they’re actually made. ICs are made of silicon, but what exactly IS silicon? The fact that integrated circuits are made of silicon is widely recognized, but most people cannot explain what silicon is. This makes for an ideal starting point for our discussion. Silicon is an element represented by the symbol "Si". The second most common element on Earth behind oxygen, silicon is the major component in most types of dirt and rocks. Silicon normally bonds rapidly with oxygen to form silicon oxide (SiO2), otherwise known as "silica". It truly is one of the building blocks of the world in which we live. One might think it would be easy to extract silicon from rocks and dirt, and convert it to the raw material used to make ICs, but it is in fact somewhat involved. The raw material normally employed in the creation of ICs is high-purity quartz from countries such as Norway and Brazil. Repeated reduction and rectification refines the quartz to approximately 99.999999999%, or "eleven nines" purity. Why is it necessary for the quartz to be refined to such an incredible degree of purity? The reason is the circuits to be formed on an IC are now so small and highly integrated, that line widths and intervals of 0.25µm and smaller are not uncommon. Furthermore, as circuit elements are produced within the IC in the following process, traces of chemical elements such as boron, phosphorous and arsenic are added to the oxidized silicon as required to form the characteristics of the intended semiconductor circuit. In order to maintain the precision of this reaction, the purest possible silicon is necessary. As we approach the molecular (nanometer) level of integration, it is ever more important to achieve the highest possible purity in the silicon to be used in IC manufacture. As shown in the portion of the Periodic Table displayed below, silicon is a Group IV element with an atomic number of 14 - meaning it has 14 electrons, in this case four of which are in the outermost shell. In crystallized silicon, adjacent atoms share electrons, which means that their outermost shells are united by a total of eight electrons. The most stable forms of silicon consist of either two or eight atoms, and permit virtually no electrical conductivity. This is neither a conductor nor an insulator... this is a pure semiconductor. Germanium, also a Group IV element with an atomic number of 32, was the first semiconducting material discovered and can also be used independently as a semiconductor. Silicon, as the world’s second most common element with characteristics strikingly similar to those of germanium, is extremely well-suited for microfabrication. It is the perfect choice for integrated circuits. Creating monocrystal silicon Even though we are dealing with silicon of "eleven nines" purity, it is not yet in a state in which it can be used in the production of ICs. The molecular structure consists of many crystals in disarray - the molecules must be uniformly arranged vertically, horizontally and diagonally to form a single crystal (monocrystal). This is due to the extremely high level of integration achieved in IC design. The following steps in the process entail the creation of a monocrystalline silicon ingot (lump) and then the cutting of silicon wafers measuring 200-300mm in width. One IC can consist of hundreds of individual parts. Within a single IC, there may be as many as one to ten million devices. If these steps are performed using silicon with an unstable molecular structure, it is not possible to achieve the same level of quality. In order to ensure uniform IC quality, the silicon base must be extremely homogeneous. This is why it is necessary to to convert the silicon to monocrystal form. The next step in the process is the creation of the monocrystalline silicon ingot. The most widely employed method, and the one we'll discuss here, is the Czochralski (CZ) method. First, the "eleven nines"-pure silicon is melted in a quartzware crucible. Minute quantities of conductive, impure elements such as boron and phosphorous are added, giving birth to p-type or n-type monocrystals*. Next, while rotating the crucible, a tiny seed crystal tied to a length of piano wire is lowered into the molten silicon. It is then stirred in the direction opposite the rotation of the crucible, creating monocrystal silicon identical to the seed crystal. Careful control of the molten silicon's temperature enables the creation of a silicon ingot 200 to 300mm in width, and as long as is required. Monocrystal atoms are arranged in a very orderly fashion. To illustrate... if we were using carbon instead of silicon, this would be a diamond ingot. "/* Over the past few years, compounds such as gallium-arsenide and gallium-phosphorous have become more in vogue as materials for use in IC manufacture, but problems still exist with these compounds when it comes to microfabrication and large-diameter wafer manufacture. Silicon remains the most practical material. The benefits of increased wafer size include the ability to manufacture ICs in larger quantities, which improves the cost performance for the manufacturing process and subsequently enables price reductions for electronic equipment. Simplified outline of IC manufacture Once the silicon monocrystal has been prepared, the actual IC manufacturing process can begin. The basic principles are as described below. 1. Making silicon wafers from monocrystal silicon First, the monocrystalline silicon ingot is sliced into wafers using a diamond blade, to a thickness of approximately 0.5mm. The wafers are beveled and polished in order to minimize chipping and cracking, and then a portion of each wafer is cut off to create the "orientation flat" or "notch". Currently, the notch is most commonly cut in the shape of a "V". This is one of the standards of wafer formation and processing. (See fig. 1) 2. Oxide film coating The wafers are baked in a furnace at about 1000°C while being exposed to a combination of oxygen and silicon gas, creating an oxide film on the surface. After formation and processing, this oxide film will determine the shape of the circuit. (See fig. 2) 3. Photoresist coating The oxide film-coated wafers are rotated at high speed, allowing a very thin, uniform layer of photoresistant film (photosensitive agent) to form on the surface of the wafers. In the photolithography process that follows, the wafers are illuminated to locate areas coated in positive photoresist (likely to dissolve under illumination) and negative photoresist (less averse to illumination). This is one way in which photographic technology is contributing significantly to IC manufacturing. (See fig. 3) 4. Forming circuit patterns though photolithography The next step is to form the circuit patterns on the surface of the wafers. In scanner/steppers such as Nikon's NSR series, the electronic circuit pattern contained within the reticle (the photomask used to transfer the pattern to the wafer) is reduced to 20 or 25% in size as it is projected onto the wafer. Photolithography is performed one chip at a time, with exposure repeated hundreds of times for each wafer. The NSR-S207D, for example, can process 300mm wafers at a rate of up to 115 per hour. (See fig. 4) 5. Developing During the developing process, the positive photoresist on each wafer dissolves, leaving only the bare oxide film on those regions. The negative photoresist areas remain virtually intact, and the resist left on the surface is referred to as the "resist mask.". (See fig. 5) 6. Etching A gas or liquid is then used to dissolve the revealed oxide film layers, and to ensure all remaining photoresist is removed, a powerful developing agent is applied. This process is called "etching". (See fig. 6) 7. Doping Impurities - or "dopants" - including boron, phosphorous and arsenic are embedded into the wafer in a temperature-controlled furnace, creating transistors, diodes and other devices. A heat treatment known as "annealing" is then applied to the impurities to ensure the proper reaction. In order to form all of the necessary devices on the wafer, steps 3 through 6 above are performed repeatedly. The number of repetitions depends on the type of IC, but these steps must generally be performed anywhere from a dozen to several dozen times. (See figs. 7-1 & 7-2) 8. Interconnection Next, in order to connect the various devices created on the surface of the wafer, a technique called "vapor disposition" is used to cover the entire surface with aluminum. The aluminum is then stripped from places where it isn't required, leaving only the circuit traces (interconnection). In recent years, damascene processing using copper and other materials has become increasingly common. (See fig. 8) 9. Dicing Every wafer is checked to confirm that the circuits have been formed correctly on each chip. Then the undersurface is polished and a diamond cutter used to dice the wafer into individual chips by cutting a checkerboard pattern. (See fig. 9) 10. Bonding The diced chips are connected to leadframes (the frames used to connect the chip to the pins) using extremely fine gold wire. This process is called "wire bonding". (See fig. 10) 11. Molding After it is wire-bonded to the leadframe, each chip is inspected, and then encased in a synthetic resin or ceramic package in a procedure referred to as "encapsulation molding". At last, the process is nearly complete. (See fig. 11) 12. The final step The leadframe is trimmed off and the leads are formed into the shape required to mount the IC on a circuit board. Various packages are produced depending on the processing. (See figs. 12-1 & 12-2) IC manufacturing technology is constantly evolving. The materials technology and Nanotechnology of today will continue to advance, creating new techniques to meet tomorrow's production needs. Nikon stepper technology is also playing a central role in the manufacture of next-generation ICs, through the development of photoresists with increasingly intricate structures (down to the molecular level) and photolithography employing new light sources such as laser, electron beams and soft X-rays Sorry unbale to include pictures. ********************Crazy Nawab first answer by me ######### send feedback to get more on this topic