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# Ic fab

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### Ic fab

1. 1. Topic: Integrated Circuit Fabrication Researched By: Johnmar T. Diamante ECE5A What is an Integrated Circuit? An integrated circuit (IC), sometimes called a chip or microchip, is a semiconductor wafer on which thousands or millions of tiny resistors, capacitors, and transistors are fabricated. An IC can function as an amplifier, oscillator, timer, counter, computer memory, or microprocessor. A particular IC is categorized as either linear (analog) or digital, depending on its intended application. Linear ICs have continuously variable output (theoretically capable of attaining an infinite number of states) that depends on the input signal level. As the term implies, the output signal level is a linear function of the input signal level. Ideally, when the instantaneous output is graphed against the instantaneous input, the plot appears as a straight line. Linear ICs are used as audio-frequency (AF) and radio-frequency (RF) amplifiers. Digital ICs operate at only a few defined levels or states, rather than over a continuous range of signal amplitudes. These devices are used in computers, computer networks, modems, and frequency counters. The fundamental building blocks of digital ICs are logic gates, which work with binary data, that is, signals that have only two different states, called low (logic 0) and high (logic 1). Processes in IC Fabrication: Silicon Wafer Fabrication: 1. Converting sand to silicon Sand is composed of silica and is the starting point for making a silicon wafer. To extract the element silicon from the silica, it must be reduced. This is accomplished by heating a mixture of silica and carbon in an electric arc furnace to a temperature in excess of 2,000°C. Impurities such as
2. 2. iron, aluminum, boron and phosphorous also react to give their chlorides, which are then removed by fractional distillation. During the reaction, silicon is deposited on the surface of an electrically heated ultra-pure silicon rod to produce a silicon ingot. 2. Creating a cylindrical crystal To turn it into a usable material, the silicon must be turned into single crystals that have a regular atomic structure. This transformation is achieved through the Czochralski Process. Electronic-grade silicon is melted in a rotating quartz crucible and held at just above its melting point of 1,414°C. 3. Slicing the crystal into wafers Integrated circuits are approximately linear, which is to say that they're formed on the surface of the silicon. To maximize the surface area of silicon available for making chips, the silicon ingot is sliced up into discs called wafers. The wafers are just thick enough to allow them to be handled safely during semiconductor fabrication. 300mm wafers are typically 0.775mm thick. Sawing is carried out using a wire saw that cuts multiple slices simultaneously, in the same way that some kitchen gadgets cut an egg into several slices in a single operation. 4. Making a patterned oxide layer The wafer is heated to a high temperature in a furnace. The wafer is spun in a vacuum so that the photoresist spreads out evenly over the surface before being baked dry. The wafer is exposed to ultraviolet light through a photographic mask or film. The next stage is to develop the latent circuit image. The photoresist isn't sufficiently durable to withstand the hot gasses used in some steps, but it is able to withstand hydrofluoric acid, which is now used to dissolve those parts of the silicon oxide layer where the photoresist has been washed away. Finally, a solvent is used to remove the remaining photoresist, leaving a patterned oxide layer in the shape of the required circuit features. Wafer Testing: Wafer testing is a step performed during semiconductor device fabrication. During this step, performed before a wafer is sent to die preparation, all individual integrated circuits that are present on the wafer are tested for functional defects by applying special test patterns to them. The wafer testing is performed by a piece of test equipment called a wafer prober. Wafer Mounting: To facilitate the processing of the wafer at wafer saw, support is provided to the wafer by mounting the wafer on dicing tape. The dicing tape is a PVC sheet typically 3 mm in thickness with synthetic adhesive on one side to hold both the wafer frame and the wafer.