![]() The crucible is made up of fused silica (SiO 2) as this material is chemically unreactive with molten silicon. The furnace consists a crucible, crucible support, rotation mechanism and heating element housed in a chamber. The puller has four important subsystems namely furnace, crystal pulling mechanism, ambient control and control systems. The apparatus used for the crystal growth is called Czochralski crystal growth apparatus or puller. Czochralski method is used for silicon crystal growth from which ultimately silicon wafers are produced. ![]() In general, a phase change from solid, liquid or gas phases to crystalline solid phase is nothing but growing crystal. In practice all the silicon required for integrated circuits is prepared by using this method only. The primary method of the crystal growth is Czochralski (CZ) method. This process is advantageous because the costing of the process is low and the byproducts of the reactions are less harmful. This multistep process continues for many hours and finally results in polycrystalline structured EGS rods with 0.2 m diameter and several meter length. With the help of chemical reaction, hydrogen is reduced from trichlorosilane. After this purified trichlorosilane is applied with chemical vapour deposition process. Then by using fractional distillation, purification of trichlorosilane is carried out. After this reaction, the trichlorosilane obtained is liquid at room temperature. This Basic Planar Process in IC Fabrication is carried out with a catalyst in a fluidized bed at 350☌. Then it is added with unhydrous hydrogen chloride to form trichlorosilane (SiHC1 3). Then the silicon is pulverized mechanically. Using this step, MGS is solidified with a purity of about 98%. To obtain this purest form of silicon, first metallurgical grade silicon (MGS) is produced in a submerged electron arc furnace. The starting material for the crystal growth is highly purified polycrystalline silicon called as Electronic – Grade Silicon (EGS). The table 1.3 gives the comparison between the silicon and germanium material to be used as semiconductor material. But it was observed that it is advantageous to use silicon than germanium. ![]() As we have studied already that the bipolar junction transistor was invented in 1948 with germanium as a semiconductor material. It occurs naturally in the form of silica and silicates. ![]() In this Basic Planar Process in IC Fabrication following subprocesses, are involved –Īt present 95% of the semiconductor devices use silicon. Let us study each process in detail one by one. ![]()
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