FABRICATION OF IC’S FABRICATION OF IC’S INTRODUCTION: The Manufacturing of IC’s (integrated circuit) is the process which need very accuracy and also need very precision instruments. It is the process which consists of many simple and sophisticated steps. Mainly it needs the very expensive labs and computer technology. Semiconductor device fabrication is the process used to create the integrated circuits (silicon chips) that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon is the most commonly used semiconductor material today, along with various compound semiconductors. The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs. SOME HISTORY: When feature widths were far greater than about 10 micrometres, purity was not the issue that it is today in device manufacturing. As devices became more integrated, cleanrooms became even cleaner. Today, the fabs are pressurized with filtered air to remove even the smallest particles, which could come to rest on the wafers and contribute to defects. The workers in a SYED AZEEM AHMED [email protected] 1 | P a g e FABRICATION OF IC’S semiconductor fabrication facility are required to wear cleanroom suits to protect the devices from human contamination. In an effort to increase profits, semiconductor device manufacturing has spread from Texas and California in the 1960s to the rest of the world, such as Europe, Israel, and Asia. It is a global business today. SOME SEMICONDUCTORS MANUFACTURERS: The leading semiconductor manufacturers typically have facilities all over the world. Intel, the world's largest manufacturer, has facilities in Europe and Asia as well as the U.S. Other top manufacturers include STMicroelectronics (Europe), Analog Devices (US), Integrated Device Technology (US), Atmel (US/Europe), Freescale Semiconductor (US), Samsung (Korea), Texas Instruments (US), GlobalFoundries (Germany, Singapore, future New York fab in construction), Toshiba (Japan), NEC Electronics (Japan), Infineon (Europe), Renesas (Japan), Taiwan Semiconductor Manufacturing Company (Taiwan), Fujitsu (Japan/US), NXP Semiconductors (Europe), Micron Technology (US), Hynix (Korea) and SMIC (China). The Detail Description of Semiconductor IC’s Fabrication consists of the following steps: 1-WAFER PREPERATION: A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices. The wafer serves as the substrate for microelectronic devices built in and over the wafer and undergoes many microfabrication process steps such as doping or ion implantation, etching, deposition of various materials, and photolithographic patterning. SYED AZEEM AHMED [email protected] 2 | P a g e FABRICATION OF IC’S Wafers are formed of highly pure (99.9999% purity),[1] nearly defect-free single crystalline material.[2] One process for forming crystalline wafers is known as Czochralski growth invented by the Polish chemist Jan Czochralski. In this process, a cylindrical ingot of high purity monocrystalline silicon is formed by pulling a seed crystal from a 'melt'.[3][4] Dopant impurity atoms such as boron or phosphorus can be added to the molten intrinsic silicon in precise amounts in order to dope the silicon, thus changing it into n-type or p-type extrinsic silicon. The ingot is then sliced with a wafer saw (wire saw) and polished to form wafers.[5] The size of wafers for photovoltaics is 100 – 200 mm square and the thickness is 200 - 300 μm. In the future, 160 μm will be the standard.[6] Electronics use wafer sizes from 100 - 300mm diameter. (The largest wafer made has a diameter of 450mm but isn't in production yet). SIX LAYERS OF INTERCONNECTION SYED AZEEM AHMED [email protected] 3 | P a g e FABRICATION OF IC’S FIGURE: Wafers are cleaned with weak acids to remove unwanted particles, or repair damage caused during the sawing process. When used for solar cells, the wafers are textured to create a rough surface to increase their efficiency. The generated PSG (phosphosilicate glass) is removed from the edge of the wafer in the etching. SYED AZEEM AHMED [email protected] 4 | P a g e FABRICATION OF IC’S Wafers are prepared using “Czochralski Process”. The “Czochralski Process” can be divided into following further steps: 1. Czochralski growth 2. Shaping 3. Slicing 4. Lapping and chemical etching 5. Polishing Crystal Growth: The two most important semiconductors for discrete devices and integrated circuits are silicon and gallium arsenide. Silicon Crystal Growth from the Melt. For Silicon Crystal growth the technique is called Czochralski technique. Process Flow • Starting Material: The staring material for silicon is a relative pure form of sand (SiO2) called quartzite. This is placed in a furnace with various forms of carbons (Coal, coke and wood chips) at 1200C. The overall reaction is SiC(solid) + SiO2 -> Si(Solid) + SiO(gas) + CO(gas) This process produces silicon with a purity of 98%. Now it react with HCl at 300C forming liquid cholride (SiHCl3) of Silicon. From this trichlorosilane (SiHCl3) is produced, it is liquid at room temperature. Fractional Distillation of this one removes the impurities. SYED AZEEM AHMED [email protected] 5 | P a g e FABRICATION OF IC’S Then from a reduction reaction a electronic-grade silicon (EGS) is produce, EGS a polycrystalline material of high purity, is the raw material used to prepare device quality, single crystal silicon.Pure EGS generally has impurity concentrations in the parts-per-billion range. Now after the preparation of the EGS, the pure polycrystalline Silicon is placed and heated above the melting temperature of the Silicon, then the suitable seed crystal is suspended on the polycrystalline solid then this seed is inserted in to the melt silicon. It is then slowly pull upward and the melting silicon is then converting in to the solid crystal. Two important parameters are Rotational speed and pull rate. Diameter of the ingot is a function of pull rate. 2- Wafer Shaping: In this step the ingot is grind to a uniform diameter using a lathe-type surface grinder.After the crystal grown, the first shaping operation is to remove the seed and the other end of the ingot, which is last to solidify. The next operation is to grind the surface so that the diameter of the material is defined. After that one or more flat regions are ground along the length of the ingot. These regions, or flats, mark the specific crystal orientation of the ingot and conductivity type of the material. Two types of flats are Primary Flats and Secondary Flats. SYED AZEEM AHMED [email protected] 6 | P a g e FABRICATION OF IC’S 3- Slicing: Ingot is sliced into wafers. The ingots are then ready to be sliced by diamond saw into wafers. 4- Chemical Etching & lapping: Is used to produce clean wafers of desired thickness..After slicing, both sides of the wafer are lapped to produce typical flatness uniformity within 2um. But it usually leaves the surface and edges of the wafer damaged and contaminated. This can be removed by chemical etching. 5- Polishing : Is used to provide a smooth surface to the wafers. In the last polishing is done to provide a smooth, specular surface where device feature can be defined by photolithographic processes. 6-Crystal Defects: A real crystal (such as silicon wafer) differs from the ideal crystal in important way, It is finite; thus surface atoms are incompletely bounded. Furthermore it has defects, which strongly influence the electrical, mechanical and optical properties of the semiconductor. There are four categories of defects * Point * Line * Area * Volume SYED AZEEM AHMED [email protected] 7 | P a g e FABRICATION OF IC’S 7- MASK Making: A glass plate with a pattern of transparent and opaque areas used to photo lithographically creates patterns on wafers. A mask is commonly used to refer to a plate that has a pattern large enough to pattern a whole wafer at one time. Purpose is to control adding and removal of material only at specified places. This pattern is transferred through the process of lithography. Types of mask are Full Wafer Mask and single Die mask. 8- PHOTOLITHOGRAPHY: Photolithography is the process of transferring patterns of geometric shapes on a mask to a thin layer of photosensitive material (called Photoresist) covering the surface of a semiconductor wafer. These patterns define the various regions in an IC, such as the implantation regions, the contact windows and the bonding pad areas. The resist patterns defined by the lithographic process are not permanent elements of the final device, but only replicas of circuit features. These patterns define the various regions in an IC, such as the implantation regions, the contact windows and the bonding pad areas. The resist patterns defined by the lithographic process are not permanent elements of the final device, but only replicas of circuit features. Optical Lithography: The vast majority of lithographic equipment for IC fabrication is optical equipment using ultraviolet light. SYED AZEEM AHMED [email protected] 8 | P a g e FABRICATION OF IC’S THE HOUSE WHERE IC’S ARE ABLE TO FABRICATE CLEAN ROOM: Lithography area in clean room The ultra-clean environment where microprocessors are made is called a clean room. Class one clean rooms are the cleanest of all, with no more than one speck SYED AZEEM AHMED [email protected] 9 | P a g e FABRICATION OF IC’S of dust per cubic foot. Imagine a boulder large enough to cause traffic jams all over a big city. If one fell on Times Square in New York, it could stop traffic on many streets around it, and eventually stop traffic on adjacent streets through a ripple effect.