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渗杂工艺是制造半导体器件必不可少的工序,目前广泛采用的是扩散法,这是一种在高温下利用分子扩散的原理向晶体中渗入杂质的方法。这种方法的缺点是不能严格地控制扩散深度和浓度,还会产生杂质的横向扩散。故无法得到平整的结面,也难以获得浅结和窄的基区,因而限制了器件工作频率和集成度的提高。用离子注入法渗杂,不仅克服了扩散法固有的缺陷,还可以得到特殊的杂质浓度分布和大面积的均匀准确注入。然而,离子注入渗杂也带来了新的问题,即高能量的杂质离子被注入到晶体内时,离子与晶格碰撞,造成品格损伤,单晶表面出现无序层和位错。把离子注入后的晶片进行热处理,可以消除晶格损伤,使被注入的杂质电激活。现行的办法是用退火炉退火,晶片在退火炉内被加热到很高的温度(通常为600—1000℃),经较长时间(半小时至一小时)的处理,方能退火。整个晶片被长时间高温加热,引起衬底性质发生变化,晶片还会受到周围有害杂质的污染,也会因高温造成热变形,被注入的杂质也会产生再分布。这种电炉退火的电激活率低,通常只有50%,位错也不能完全消除。这些问题若得不到解决,离子注入渗杂的优点也就难以完全得到发挥。
Diffusive process is indispensable for the manufacture of semiconductor devices processes, the current widely used diffusion method, which is a method of molecular diffusion into the crystal using impurities at high temperatures. The disadvantage of this method is that the diffusion depth and concentration can not be strictly controlled and the lateral diffusion of impurities also occurs. It can not get a smooth surface, it is difficult to obtain shallow junctions and narrow base area, thus limiting the device operating frequency and increase the integration. Impregnation by ion implantation not only overcomes the inherent defects of the diffusion method, but also provides a special impurity concentration distribution and a large area of uniform and accurate injection. However, ion implantation and entrapment also poses new problems. When high-energy impurity ions are implanted into the crystal, the ions collide with the crystal lattice, causing lattice damage and disordered layers and dislocations on the single crystal surface. Heat treatment of the ion-implanted wafer can eliminate lattice damage and electrically activate the implanted impurities. The current approach is to use an annealing furnace annealing, the wafer is heated to a very high temperature (usually 600-1000 ℃) in the annealing furnace, after a long time (half an hour to one hour) before annealing. The whole wafer is heated for a long time at a high temperature, causing the substrate properties to change. The wafer can also be contaminated by harmful impurities around it and also thermally distort due to the high temperature. The implanted impurities also have redistribution. The electrical activation of this furnace annealing is low, usually only 50%, dislocation can not be completely eliminated. If these problems can not be solved, the advantages of ion implantation will not be fully realized.