Manufacturing of MicroprocessorFarooq Ahmad Shah diodes. etc. capacitors.Preliminary Discussion • Integrated circuit: An electronic circuit designed to perform some function. whereas a Pentium processor today contains over 800 million transistors! When an integrated circuit is extremely complex. in which the electronic components (transistors. it is usually known as a microprocessor. or "IC chips“ • The chip found inside of a "musical" birthday card contain only a few dozen components. resistors. More commonly referred to as "microchips".) are miniaturized. built into a small "chip" made of silicon and interconnected through tiny strands of aluminum. . ) • Microprocessors are manufactured in clean rooms. .Preliminary Discussion (contd. – The air in the clean room is air conditioned to a temperature of 21C (70F) and 45% relative humidity. the ambiance of which cleaner than a hospital operating room. – The air is passed through a high-efficiency particulate air (HEPA) filter to capture particle contaminants – workers must be covered from head to toe in specialized garments. designed to trap particles. called bunny suits. Outline of the processing steps Sequence of processing steps in the production of integrated circuits: (1) pure silicon is formed from the molten state into an ingot and then sliced into wafers. and (3) wafer is cut into chips and packaged. . (2) fabrication of integrated circuits on the wafer surface. the silicon must be almost totally pure and a perfect crystal. . and (b) during crystal pulling to form the boule. Ingot diameter 300mm(12 in) and up to 3m(10 ft) long The Czochralski process for growing single-crystal ingots of silicon: (a) initial setup prior to start of crystal pulling.Silicon Ingot • To provide uniform electrical properties throughout. and (b) a flat ground on the cylinder. .Silicon Ingot (contd.) Grinding operations used in shaping the silicon ingot: (a) a form of cylindrical grinding provides diameter and roundness control. .Silicon Wafers Wafer slicing using a diamond abrasive cutoff saw. Silicon Wafers (contd. .) Two of the steps in wafer preparation: (a) contour grinding to round the wafer rim. and (b) surface polishing. • Etching: Removes the material to give the desired pattern. conductors.IC Fabrication • Repeated sequential steps (200 times or more). • Photolithography: By exposing a light sensitive chemical (photoresist) through a mask. insulators. • Layering: Adding new material on top of or into the silicon like dopants. . the desired pattern is transferred onto the current top layer. ) AN EXAMPLE: How can you create a p-type region in a n-type doped silicon region? Ions of arsenic are bombarded using ion implantation to create a n-type doped region. • photoresist is an organic polymer sensitive to light radiation in a certain wavelength range. Layer of SiO2 is grown using oxidation. Layer of photoresist is applied. . the sensitivity causes either an increase or decrease in solubility of the polymer to certain chemicals.IC Fabrication (contd. contd. Implant boron Remove silicon dioxide . Etch photoresist and silicon dioxide.g. Develop the photoresist.) Expose photoresist using appropriate lithographic mask.IC Fabrication (E. .IC Fabrication (contd. for the insulator (C) Acceptor atoms (Boron) are diffused into the window in the Silicon Dioxide (D) Using another mask additional Silicon Dioxide is grown. Another mask is then used to implant evaporated Aluminum or Copper for the contacts. (E) Another mask is used to grow additional Silicon Dioxide. and donor atoms (elements like Arsenic with excess electrons) are implanted. This is a Bipolar Junction Transistor (BJT).) (A) A p-type wafer (silicon doped with Boron) has a epilayer of n-type (silicon doped with Phosphorous or Arsenic) (B) A mask is used to implant Silicon Dioxide. • Chip Separation: A thin diamond-impregnated saw blade is used to perform the cutting operation. • Die Bonding: Automated handling systems pick the separated chips and place them for on the die. Epoxy is applied to the base of the chip. • Video . the failed chips are marked with an ink dot.Packaging • Wafer Testing: a computer-controlled needle probes contacts the chip connection pads and a series of DC tests are carried out to indicate short circuits and other faults. • Wire Bonding After the die is bonded to the package. these defects are not packaged. The sawing machine is highly automatic and its alignment with the ‘‘streets’’ between circuits is very accurate. electrical connections are made between the contact pads on the chip surface and the package leads. Thank you. . The total dose of dopant depends upon how many ions are fired into the silicon. producing charged atoms. are screened out. the ions crash into the surface at high rates of speeds. Wafer must be annealed to allow the doper atoms and silicon atoms to position themselves in their proper places.Ion Implantation First a gas containing the desired dopant is ionized by bombarding it with electrons. In areas of silicon that are exposed. The dopant ions are then accelerated through a very strong electric field and fired at the wafer. . By carefully adjusting the field. A patterned layer of photoresist or other material is used to block the dopant atoms from areas where they are not needed. Ions that are heavier will curve too wide and ions that are lighter will curve too sharply to escape. This process will also produce ions of other types. the desired ions are given the correct arc to exit the mass spectrometer. Photolithography Photolithography. usually in the form of digital output from the CAD system used by the circuit designer. The mask consists of a flat plate of transparent glass on to which a thin film of an opaque substance has been deposited in certain areas to form the desired pattern. also known as optical lithography. whereas the deposited film is only a few mm thick—for some film materials. so that only the portions of the photoresist not blocked by the mask are exposed. less than 1 mm.The mask itself is fabricated by lithography. . a mask containing the required geometric pattern for each layer separates the light source from the wafer. the pattern being based on circuit design data.080 in). uses light radiation to expose a coating of photoresist on the surface of the silicon wafer. Thickness of the glass plate is around 2 mm (0. and using radio frequency (RF) electrical energy to ionize a portion of the gas. thus creating a plasma. Dry Plasma Etching uses an ionized gas to etch a target material. or it maybe a previously applied layer of material such as silicon dioxide. The high-energy plasma reacts with the target surface. usually an acid.Etching Etching is usually done selectively. by coating surface areas that are to be protected and leaving other areas exposed for etching. to etch away a target material. vaporizing the material to remove it. The ionized gas is created by introducing an appropriate gas mixture into a vacuum chamber. The etching solution is selected because it chemically attacks the specific material to be removed and not the protective layer used as a mask. Wet Chemical Etching involves the use of an aqueous solution. The coating maybe an etch-resistant photoresist. .