半导体工艺基础第三章 氧化

1、第 三 章,Oxidation 氧化,1,Oxidation氧化,简介 氧化膜的应用 氧化机理 氧化工艺 氧化设备 RTO快速热氧化,2,简介,硅与O2直接反应可得； SiO2性能稳定； 氧化工艺在半导体制造中广泛使用,Si + O2 SiO2,氧化层简介,3,Oxidation,氧化层简介,Silicon,4,氧化膜的应用,掺杂阻挡层 表面钝化(保护) Screen oxide, pad oxide, barrier oxide 隔离层 Field oxide and LOCOS 栅氧化层,氧化层应用,5,掺杂阻挡氧化层,Much lower B and P diffusion rates

2、in SiO2 than that in Si SiO2 can be used as diffusion mask,氧化层应用,6,表面钝化(保护)氧化层,Pad Oxide衬垫氧化层, Screen Oxide屏蔽氧化层 Sacrificial Oxide牺牲氧化层, Barrier Oxide阻挡氧化层,Normally thin oxide layer (150) to protect silicon defects from contamination and over-stress.,氧化层应用,7,Screen Oxide,氧化层应用,8,Pad and Barrier Oxid

3、es in STI Process,氧化层应用,USG: Undoped Silicate Glass未掺杂硅酸盐玻璃,9,Application, Pad Oxide,Relieve strong tensile stress of the nitride Prevent stress induced silicon defects,氧化层应用,10,牺牲氧化层 Sacrificial Oxide,Defects removal from silicon surface,氧化层应用,11,器件隔离氧化层,临近器件的绝缘隔离 Blanket field oxide Local oxidatio

4、n of silicon (LOCOS) Thick oxide, usually 3,000 to 10,000 ,氧化层应用,12,Blanket Field Oxide Isolation,氧化层应用,13,LOCOS Process,氧化层应用,14,LOCOS,Compare with blanket field oxide Better isolation更好的隔离 Lower step height更低台阶高度 Less steep sidewall侧墙不很陡峭 Disadvantage缺点 rough surface topography粗糙的表面形貌 Birds beak鸟嘴

5、 被浅的管沟(STI)所取代,氧化层应用,15,栅氧化层,Gate oxide: thinnest and most critical layer Capacitor dielectric,氧化层应用,16,氧化膜(层)应用,氧化层应用,17,Silicon Dioxide Grown on ImproperlyCleaned Silicon Surface,18,表面未清洗硅片的热氧化层,热氧化生长的SiO2层是无定形的 SiO2分子间趋于交联形成晶体 未清洗硅片表面的缺陷和微粒会成为SiO2的成核点 这种SiO2层的阻挡作用很差 氧化前需要清洗硅片表面,19,氧化前圆片清洗,颗粒 有机粘污

6、 无机粘污 本征氧化层,20,RCA清洗,Developed by Kern and Puotinen in 1960 at RCA Most commonly used clean processes in IC fabs (1号液)NH4OH:H2O2:H2O with 1:1:5 to 1:2:8 ratio at 70 to 80 to remove organic . (2号液)- HCl:H2O2:H2O with 1:1:6 to 1:2:8 ratio at 70 to 80 to remove inorganic contaminates ，DI water rinse HF

7、 dip or HF vapor etch to remove native oxide.,21,Pre-oxidation Wafer Clean Particulate Removal,High purity deionized (DI) water or H2SO4:H2O2 followed by DI H2O rinse. 高压清洗或者放在清洗液中加热漂洗，最后烘干High pressure scrub or immersion in heated dunk tank followed by rinse, spin dry and/or dry bake (100 to 125 C)

8、.,22,被氧化的硅片上有机物的清除,强氧化剂清除有机污垢 H2SO4:H2O2 or NH3OH:H2O2 followed by DI H2O rinse. High pressure scrub or immersion in heated dunk tank followed by rinse, spin dry and/or dry bake (100 to 125 C).,23,无机物的清洗,先用HCl:H2O液体浸泡 再在大的玻璃杯中浸泡清洗 Immersion in dunk tank followed by rinse, spin dry and/or dry bake (1

9、00 to 125),24,Pre-oxidation Wafer Clean Native Oxide Removal,HF:H2O Immersion in dunk tank or single wafer vapor etcher followed by rinse, spin dry and/or dry bake (100 to 125),25,Oxidation Mechanism,Si+O2SiO2 O来源于提供的氧气 Si来源于衬底硅圆片 O通过表面已有的氧化层向内扩散并与Si反应生长SiO2 氧化薄膜越厚，生长速率越低,干氧氧化（Dry Oxidation）,26,Oxid

10、e Growth Rate Regime,B/A为线性速率常数；B为抛物线速率常数,27, Silicon Dry Oxidation,28,水汽氧化(Steam Oxidation）,Si + 2H2O SiO2 + 2H2 At high temperature H2O is dissociated to H and H-O H-O diffuses faster in SiO2 than O2 Steam oxidation has higher growth rate than dry oxidation,29, Silicon Wet Oxidation Rate,30,湿氧氧化(W

11、et Oxidation),湿氧氧化法是将干燥纯净的氧气，在通入氧化炉之前，先经过一个水浴瓶，使氧气通过加热的高纯去离子水，携带一定量的水汽，湿氧氧化法的氧化剂是氧气和水的混合物。 Si+O2SiO2 Si + 2H2O SiO2 + 2H2,31,氧化速率,温度 湿氧或干氧 厚度 压力 圆片晶向(或) 硅中杂质,32,氧化速率与温度,氧化速率对温度很敏感，指数规律 温度升高会引起更大的氧化速率升高 物理机理：温度越高，O与Si的化学反应速率越高；温度越高，O在SiO2中的扩散速率越高。,33,氧化速率与圆片晶向,表面的氧化速率高于表面 表面的Si原子密度高,34,湿氧氧化速率,35,氧化速率

12、与杂质浓度,杂质元素和浓度 高掺磷的硅有更高的氧化层生长速率，更低密度的氧化层薄膜和更高的刻蚀速率 通常，掺杂浓度越高，氧化层生长速率越高；在氧化过程的线性区(氧化层较薄时)更为显著。,36,氧化：杂质堆积和耗尽效应,N型杂质(P、As、Sb)在Si中的溶解度高于在SiO2中的溶解度，当SiO2生长时，杂质向Si中移动，这引起杂质堆积或滚雪球效应 B倾向于向SiO2中运动，这引起杂质耗尽效应,37,Depletion and Pile-up Effects,38,氧化速率与HCl掺杂氧化,HCl is used to reduce mobile ion contamination Widely

13、 used for gate oxidation process Growth rate can increase from 1 to 5 percent,39,氧化速率与不均匀氧化,氧化层越厚，氧化速率越小 对于更厚的氧化层，O需要更多的时间扩散过氧化层与衬底硅发生反应,40,在干氧中的氧化速率,41,在合成水汽中的氧化速率,42,二氧化硅色谱,43,氧化工艺,干氧氧化，薄氧化层 栅氧化层 衬垫氧化层，屏蔽氧化层，牺牲氧化层，等等 湿氧氧化，厚氧化层 场氧化层 扩散掩膜氧化层,44,Dry Oxidation System,45,氧化装置系统,46,Dry Oxidation,Dry O2

14、as the main process gas HCl is used to remove mobile ions for gate oxidation High purity N2 as process purge gas Lower grade N2 as idle purge gas,47,Dangling Bonds and Interface Charge,48,Wet Oxidation Process,Faster, higher throughput Thick oxide, such as LOCOS Dry oxide has better quality,49,Water

15、 Vapor Sources,Boiler Bubbler Flush Pyrogenic,50,Boiler System,51,Bubbler System,52,Flush System,53,Pyrogenic Steam System,54,Pyrogenic System,Advantage All gas system Precisely control of flow rate Disadvantage Introducing of flammable, explosive hydrogen Typical H2:O2 ratio is between 1.8:1 to 1.9:1.,55,Rapid Thermal Oxidation,For gate oxidation of deep sub-micron device Very thin oxide film, 30 Need very good control of temperature uniformity RTO will be used to