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1、118 CHAPTER 3 The Semiconductor in Equilibrium 3.7.2 Impurity Atom Ion ImplantationIn a second method of doping,high-energy impurity ions are implanted into the semiconductor.A beam of impurity ions are accelerated to energies ranging from 1 keV to 1 MeV and impinges the surface of the semiconductor
2、.Such a process is referred to as ion implantation.Two primary advantages of ion implantation are the more precise control and reproducibility of impurity doping and the lower processing temperature compared to diffusion. Figure 3.23 shows a basic schematic of an ion implantation system.The depth of
3、 penetration or projected range is a function of the implanted ions since there is a certain randomness in the interaction of the implanted ions with the host semiconductor atoms.Figure 3.24 shows a typical impurity profile.By performing several implants at different energies,it is possible to creat
4、e a region that is almost uniformly doped. When energetic ions impinge on the semiconductor,they lose their energy by a series of collisions with the semiconductor atoms.As a result of this interaction,semiconductor atoms are displaced from their normal single-crystal positions.A damaged region is c
5、reated in the semiconductor and most of the implanted ions are not located in substitutional positions.To activate the implanted ion and repair the damaged area,the semiconductor must be annealed at an elevated temperature for a particular period of time.The conventional annealing temperature is on
6、the order of 600and the annealing time is on the order of 30min.Rapid thermal annealing process are also used.The anneal temperatures and times are considerably lower than those used in the diffusion process. The implant ions can be blocked from entering the semiconductor by metal,photoresist,or oxi
7、des.By defining specific patterns on the surface,only specific desired regions of the semiconductor will be doped.This technique is then used to create the many semiconductor devices in the integrated circuit.Figure 3.23 Schematic of an ion implanter.(Courtesy of Runyan and Bean) 3.8 Summary 119 Fig
8、ure 3.24 Typical implanted impurity profile.The peak of the implanted concentration can occur below the surface of the semiconductor.3.7 SUMMARY1.A. The concentration of electrons in the conduction band is found by integrating the product of the density of states function in the conduction band,and
9、the Ferm-Dirac probability function,over the energy range of the conduction band. B. The concentration of holes in the valence band is found by integrating the product of the density of states function in the valence band,and the probability of a state being empty,whish is,over the energy range of t
10、he valence band. C. Using the Boltzmann approximation, the thermal-equilibrium concentration of electrons in the conduction band is given by, whereis the effective density states in the conduction band.D. Using the Boltzmann approximation,the thermal-equilibrium concentration of electrons in the val
11、ence band is given by,whereis the effective density states in the valence band.E. The intrinsic carrier concentration can be found from the relation .F. The position of the intrinsic Fermi level was found to be very close to the midgap energy.2.A. The concept of doping the semiconductor with donor a
12、nd acceptor impurities to from n-type abd p-type extrinsic semiconductors was discussed. B.A group V element(phosphorus or arsenic)is a donor impurity in silicon and a group III element(boron)is an acceptor impurity in silicon.3.7.2 杂质原子离子注入 在第二个方法掺杂，高能的杂质离子被种入入半导体。杂质离子射线加速对范围从1 keV的能量到1个兆伏特并且冲击半导体的
13、表面。这样过程指离子注入。离子注入的二主要好处是掺杂杂质的更加精确的控制和的增殖率和更低的处理温度与扩散比较。 图3.23显示离子注入系统的一个基本的概要。因为有在被种入的离子的互作用的有些随机性与主人半导体原子的渗透或计划的范围的深度是被种入的离子的作用。图3.24显示典型的杂质外形。通过执行在不同的能量的几根植入管，创造几乎一致地被掺杂的区域是可能的。 当精力充沛的离子在半导体时冲击，他们由与半导体原子的一系列的碰撞丢失他们的能量。由于这互作用，半导体原子从他们的正常单晶体位置被偏移。一个损坏的区域在半导体被创造，并且大多被种入的离子没有位于代替位置。要激活被种入的离子和修理损坏的区域，必
14、须锻炼半导体在高温一个特殊时期。常规焖火温度是大约600，并且退火时间是大约30分钟。也使用迅速热量焖火过程。锻炼温度和时代低于用于扩散过程的那些相当地. 植入管离子可以从进入半导体被阻拦由金属、光致抗蚀剂或者氧化物。通过定义在表面的具体样式，半导体的仅具体期望地区将被掺杂。这个技术在集成电路然后被用于创造许多半导体装置。 图3.23示意的是一个离子注入机。图3.24典型的被种入的杂质外形。被种入的集中 的峰顶可能在半导体的表面之下发生。 3.8 总结 1. A. 集成密度的产品找到电子的集中在传导带的态函数，和Ferm-Dirac机率函数，在传导带的能量范围。 B. 集成密度的产品找到孔的集中在化学价带的在化学价带的态函数，并且状态的可能性空的，呼呼作声，在化学价带的能量范围。 C. 使用伯磁曼略计，给电子的热量平衡集中在传导带，其中在传导带的是有效的密度状态。 D. 使用伯磁曼略计，给电子的热量平衡集中在化学价带，其中在化学价带的是有效密度状态。 E. 本征载流子含量可以从联系被找到。 F. 发现内在费密水平的位置非常接近中间缺口能量。 2. A. 掺杂与捐款人和接受器杂质的半导体的概念对从n类型和p类型外半导体被谈论了。 B.A小组v元素(磷或砷)是在硅和小组的施主杂质元素的III (硼)是在硅的接受器杂质。
