专业英语2Chapter 3 Processing Technology (2).doc

Chapter 3 Processing Technology3.1 Crystal growth and epitaxy 晶体生长和外延As discussed previously in Chapter 1, the two most important semiconductors for discrete分离的 devices and integrated circuits are silicon and gallium镓 arsenate砷酸盐. 正如之前在第一章所讨论的，对于分立器件和集成电路而言, 两种最重要的半导体是硅和砷化镓。In this chapter we describe the common techniques for growing single crystals of these two semiconductors. 在本章, 我们描述生长这两种半导体单晶的常用技术。 The basic process flow is from starting materials to polished抛光 wafers. 基本流程是从原料到抛光片。The starting materials (e.g., silicon dioxide for a silicon wafer) are chemically processed to form a high-purity polycrystalline多晶 semiconductor from which single crystals are grown. 原材料(即，用于生长硅片的二氧化硅) 通过化学处理 形成高纯度的多晶半导体以生长单晶。 di-ox-ide 二-氧-化物 di-chlor-ide二-氯-化物 di-sulf-ide 二-硫-化物polycrystalline 多晶 前缀 poly-聚合、多, mulit-多 single- 单 singl-walled (layer)The single-crystal ingots锭 are shaped to define the diameter of material and sawed into wafers. 定形后的单晶锭决定了材料的直径，并且被切成晶元。These wafers are etched蚀刻 and polished to provide smooth, specular surfaces on which devices will be made.这些晶圆被蚀刻和抛光以得到光滑的镜面表面，器件将制造在其表面上。 A technology closely related to crystal growth involves the growth of single-crystal semiconductor layers upon a single-crystal semiconductor substrate基片，衬底. 晶体生长密切相关的一个技术包括在单晶半导体基板上生长单晶半导体层(的技术)。This is called epitaxy, from the Greek words epi (meaning “on”) and taxis (meaning “arrangement”). 这被称为外延，来源于希腊文字中的 epi（意为“on”）及 taxis（意为“安排”）。The epitaxial process offers an important means of controlling the doping profiles剖面，详细资料 so that device and circuit performances can be optimized优化. 外延工艺提供了控制掺杂分布，使设备和电路性能可以得到优化的重要手段。For example, a semiconductor layer with a relatively low doping concentration浓度 can be grown epitaxially upon a substrate which contains the same type of dopant掺杂剂in a much higher concentration(e.g.,n-type silicon on an n+ -silicon substrate). 例如，一个相对较低的掺杂浓度的半导体外延层可以外延生长在一个掺杂类型相同但浓度更高的的基片上（例如，n型硅生长在n+ - Si衬底硅）。In this way the series resistance 串联电阻associated with the substrate can be substantially reduced. 通过这种方式，与基板相关的串联电阻可以大幅地减少Many novel device structures, especially for microwave and photonic devices, can be made by epitaxial processes. 许多新的元件结构，特别是微波和光子器件，可以通过外延法加工。novel新颖的 n. 小说Later in this chapter we consider some important epitaxial growth techniques.在本章后面，我们会介绍一些重要的外延生长技术。3.2 Crystal Growth from the Melt从熔体生长晶体 There are basically two techniques for crystal growth from the melt (i.e., material in liquid form): the Czochralski techniques and the Bridgman technique. 有两种基本技术可以从熔体（即液态的材料）生长晶体：乔赫拉尔斯基法（也称为直拉法）和布里奇曼法(双温区生长法)。A substantial percentage (-90%) of the silicon crystals for the semiconductor industry are prepared by the Csochralski technique; virtually all the silicon used for fabrication integrated circuits is prepared by this technique. 一个相当大的比例（约90）的半导体工业用的硅晶体由CZ法制备，几乎所有用于制造集成电路的硅都采用这种技术制备。Most gallium arsenide, on the other hand, is grown by the Bridgman technique. However, the Czochralski technique is becoming more popular for the growth of large-diameter gallium arsenide.大多数砷化镓，反过来，是布里奇曼技术生长。然而，使用Czochralski技术来生长大直径的砷化镓也越来越多（流行）。gallium arsenide 砷化镓arsen-ide 砷化物arsenic 砷arsenate砷酸 3.2.1 Starting materials 原料The starting materials for silicon is a relatively pure form of sand (SiO2) called quartzite石英岩. 硅的原料是相对纯净的砂子（SiO2），称为石英岩（或硅石）。This is placed in a furnace with various forms of carbon (coal, coke, and wood chips). While a number of reactions take place in the furnace, the overall reaction isSiC (solid) +SiO2(s) Si(s) + SiC(g) +CO(g)石英岩与各种形式的碳（煤，焦炭和木屑）一起放置在反应炉中。尽管反应炉中发生了很多反应，总反应是 SiC Silicon carbide 碳化硅 CO Carbon mono-x-ide 一氧化碳This process produces metallurgical冶金 grade silicon with a purity of about 98%. Next, the silicon is pulverized粉碎 and treated with hydrogen chloride (HCL) to form trichlorosilane (SiHCl3):Si(solid) + 2HCL(gas) SiHCl3(gas) +H2(gas)这一过程产生冶金级，纯度约98的硅。其次，硅被粉碎并和氯化氢（HCL）反应以形成三氯氢硅：Tri-chloro-silane 三-氯-硅烷HCL Hydrogen chlor-ide氯化氢The trichlorosilane is a liquid at room temperature (boiling point 32). 三氯氢硅在室温时是的液体（沸点为32）。boiling point 沸点melting point 熔点Fractional部分的distillation蒸馏of the liquid removes the unwanted impurities. 通过精馏液体除去不需要的杂质。distill v. 蒸馏 distillation n. 蒸馏The purified SiHCl3 is then used in hydrogen reduction reaction to prepare the electronic-grade silicon (EGS)： SiHCl3+ H2 Si + 3HCl纯化后的SiHCl3通过氢还原反应可以制备电子级硅（EGS）：This reaction takes place in a reactor containing a resistance-heated silicon rod, which serves as the nucleation核 point for deposition of silicon. 这种反应发生在一个含有电阻加热的硅棒的反应炉中，硅棒可作为硅沉积的成核点。The EGS, a polycrystalline material of high purity, is the raw material used to prepare device quality single-crystal silicon. 高纯度多晶硅材料，是用来制备器件级单晶硅的原始材料。Pure EGS generally has impurity concentrations in the part-per-billion range. 纯电子级硅的杂质浓度范围通常为亿分之一。 The starting materials for gallium arsenate are the elemental, chemically pure gallium and arsenic砷, which are used for the synthesis of polycrystalline gallium arsenide. 砷化镓的原材料是，化学纯镓和砷，用于合成多晶镓砷化物。arsenate【化】砷酸盐(或酯) arsenide【化】砷化物Because gallium arsenide is a combination化合物 of two materials, its behavior is quite different from that of a single materials such a silicon.由于砷化镓是两种材料的化合物，它的特性与例如硅这样的单一材料是完全不同的。The behavior of a combination can be described by a phase diagram图表. A phase is a state (e.g., solid, liquid, or gaseous) in which a material may exist. 化合物的表现可以用一个相图来描述。一个相是一种状态（如固态，液态或气态），一种物质可能存在于其中。A phase diagram shows the relationship between two components (e.g., gallium and arsenic) as a function of temperature. 相图显示了两个成份（例如，镓和砷）随温度的函数关系。 Unlike silicon, which has relatively low vapor pressure at its melting point (10-6 atm at 1240), both gallium and arsenic have much higher vapor pressure at the melting point of gallium arsenide (1238). 不同于硅，在其熔点具有相对较低的蒸汽压（1240时为10-6大气压），镓和砷在砷化镓的熔点（1238）具有更高的蒸气压力。In its vapor phase, arsenic has As2 and As4 as its major species. 在气相时，砷为主要以AS2和AS4分子的形式存在。The vapor pressure curves for gallium arsenide melt, and the solid curves are for gallium-rich melt, more arsenic (As2 and As4) will be vaporized from the arsenic-rich melt, thus resulting in a higher vapor pressure. 气体压力曲线对应于砷化镓熔体，固体曲线对应于富镓熔体。更多的砷（As2和As4）将从富砷的熔体中蒸发，从而造成更高的蒸汽压。A similar argument can explain the higher vapor pressure of gallium in a gallium-rich melt. Note that long before the melting point is reached, the surface layers of liquid gallium arsenide may decompose into gallium and arsenic. 类似的观点可以解释富镓熔体中镓的蒸气压较高。需要注意，在达到熔点之前，镓砷化液体的表面层可能分解成镓和砷。Since the vapor pressure of gallium and arsenic are quite different, there is a preferential loss of the more volatile arsenic species, and the liquid becomes gallium rich.由于镓和砷的蒸汽压力是有很大差别，挥发性较强的砷将会优先损失，液体中镓变得丰富。 To synthesize gallium arsenide, an evacuated, sealed quartz tube system with a two-temperature furnace is commonly used. 通常用一个具有双温区的高温炉及抽真空的密封石英管系统来合成砷化镓。The high-purity arsenic is placed in a graphite boat and heated to 610 to 620 , while the high-purity gallium is placed in another graphite boat and heated to slightly above the gallium arsenide melting temperature (1240 to 1 260 ). 高纯度砷被放置在一个石墨舟中，加热到610至620，而高纯度镓是摆在另一石墨舟中，加热到略高于砷化镓的熔融温度（12401 260）Under these conditions, an overpressure of arsenic is established (1) to cause the transport of arsenic vapor to the gallium melt, converting it into gallium arsenic vapor to the gallium melt, converting it into gallium arsenide, and (2) to prevent decomposition of the gallium arsenide while it is being formed in the furnace. 在这种条件下，形成砷的过压（1）使砷气体输送到镓熔体，使之从砷化镓气体转化到镓熔体，使之转化为砷化镓，（2）防止砷化镓在（化应炉中）合成过程中分解。When the melt cools, a high-purity polycrystalline gallium arsenide results. This serves as the raw material to grow single-crystal gallium arsenide.当熔体冷却，可得到高纯度多晶硅砷化镓。这可作为生长单晶砷化镓的原料。3.2.2 The Czohcralski Technique The Czochralski technique for silicon crystal growth uses an apparatus called a puller拉单晶机, as shown in Figure 3-1. The puller has three main components: (1) a furnace, which includes a fused-silica (SiO2) crucible坩埚, a graphite susceptor基座, a rotation mechanism (clockwise as shown), a heating element, and a power supply;CZ法生长硅晶体生长使用的仪器称为拉单晶机，如图3-1所示。拉单晶机有三个主要部分组成：（1）反应炉，其中包括熔融石英（SiO2）的坩埚，石墨基座，旋转机械（顺时针方向如图所示），加热元件，以及电源;(2) a crystal-pulling mechanism, which includes a seed holder支架 and a rotation mechanism (counter-clockwise); and (3) an ambient气氛 control, which includes a gas source (such as argon), a flow control, and an exhaust排气 system. （2）拉单晶机，其中包括晶种支架和旋转装置（逆时针）和（3）气氛控制，其中包括气源（如氩气），流量控制，和排气系统。In addition, the puller has an overall microprocessor-based control system to control process parameters such as temperature, crystal diameter, pull rate, and rotation speeds, as well as to permit programmed steps. 此外，单晶机有一个基于微处理器的总控制系统来控制工艺参数，如温度，晶体直径，拉伸速度和旋转速度，并允许编程控制。Also, various sensors and feedback loops allow the control system to respond automatically, thereby reducing operator intervention干预.此外，各种传感器和反馈回路使控制系统自动响应，从而减少操作人员干预。 In the crystal-growing process, polycrystalline silicon is placed in the crucible and the furnace is heated above the melting temperature of silicon. 在晶体生长过程中，多晶硅是放置在坩埚中并且反应炉加热至硅的熔化温度以上。A suitably oriented seed crystal (e.g., ) is suspended over the crucible in a seed holder. The seed is inserted into the melt. Part of it melts but the tip of the remaining seed crystal still touches the liquid surface. It is then slowly withdrawn. 一个合适取向的晶种（如）装于支架中悬浮在坩埚上方。晶种被插入到融体中。如果部分融化，但剩余的晶体仍然接触液体表面。然后慢慢地撤回。Progressive freezing at the solid-liquid interface yields a large, single crystal. A typical pull rate is a few millimeters per minute.固液交界面逐步冷却后得到大块单晶。一个典型的拉单晶机的提拉速度是每分钟几毫米。 For Czochralski growth of gallium arsenide, the basic puller is identical to that for silicon. However, to prevent decomposition of the melt during crystal growth, a liquid encapsulation method is employed. The liquid encapsulate is a molten boron trioxide (B2O3) layer about 1 cm thick. Molten boron trioxide is inert to gallium arsenide at the growth temperature. 对于直拉砷化镓生长，拉单晶机和生长硅的基本一样。然而，为了防止晶体生长过程中融体分解，采用了液态密封法。密封的液体是用约1厘米厚的熔融三氧化二硼（B2O3的）。熔融三氧化二硼镓在砷化镓的生长温度时加入。The layer adheres to the gallium arsenide surface and serves as a cap to cover the melt. This cap prevents decomposition of the gallium arsenide as long as the pressure on its surface is higher than 1 atm (760 Torr). 该层粘附在砷化镓表面，向一个罩子一样覆盖在熔体上。覆盖在熔体上的罩子可以防止砷化镓在表面压力大于1大气压（760托）时发生分解。Since boron trioxide can dissolve silicon dioxide, the fused-silica crucible is replaced with a graphite crucible.由于三氧化二硼能溶解二氧化硅，采用石墨坩埚取代了熔融石英坩埚。3.3 Vapor-Phase Epitaxy In an epitaxial process, the substrate wafer acts as a seed crystal. Epitaxial processes are differentiated from the melt growth processes (described in section 3.1) in that the epitaxial layer can be grown at a temperature substantially below the melting point (typically 30% to 50% lower). Among various epitaxial processes, vapor phase epitaxy (VPE) is by far the most important for silicon devices. VPE is also important for gallium arsenide, but other epitaxial processes (e.g., molecular-beam epitaxy) can provide certain advantages not obtainable from VPE. Note that the geometric shape of the susceptor provides the name for the reactor: horizontal, pancake, and barrel susceprots-all made from graphite blocks. Susceptors in the epitaxial reactors are analogous to crucibles in the crystal growing furnaces. Not only do they mechanically support the wafer, but in induction-heated reactors they also serve as the source of thermal energy for the reaction. Four silicon sources have been used for vapor phase epitaxial growth. They are silicon tetrachloride (SiCl4), dichlorosiliane (SiH2Cl2), trichlorosilane (SiHCl3), and silane (SiH4). Silicon tetrachloride has been the most studied and has the widest industrial use. The typical reaction temperature is 1200. Other silicon sources are used because of lower reaction temperatures. The substitution of a hydrogen atom for each chlorine atom from silicon tetrachloride permits about a 50 reduction in the reaction temperature. The overall reaction of silicon tetrachloride that results in the growth of silicon layers is SiCl4(gas)+2H2(gas)Si(solid)+4HCl(gas) (3-4) An additional competing reaction is taking place along with that given in Eq.3-4: SiCl4(gas)+ Si(solid)2 SiCl2(solid) (3-5) As a result, if the silicon tetrachloride concentration is too high, etching rather than growth of silicon will take place. The effect of the concentration of silicon tetrachloride in the gas on the reaction is shown, where the mole fraction is defined as the ration of the number of molecules of a given species to the total number of molecules. Note that initially the growth rate increases linearly with increasing concentration of silicon tetrachloride. As the concentration of silicon tetrachloride is increased, a maximum growth rate is reaches. Beyond that, the growth rate starts to decrease, and eventually etching of the silicon will occur. Silicon is usually grown in the low concentration region. The reaction of Eq. 3-4 is reversible, that is, it can take place