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					四:总结

超大规模集成电路发展到了亚微米时代,光靠技 术的改进已不能提高产品的成品率,环境净化已 日益显示出重要性。在集成电路成品率方面,70% 是由于污染造成器件失效。而最大的污染物来源 则是操作者本身。 超净车间使用; 操作者的净化; 无人化操作; 等等…

超净车间: 在硅片上附有异物,就会对器件制作带来不良影响。 一般说:当异物大小为加工尺寸的1/5-1/10时就会产生 不利影响。也就是说,对于目前的半导体硅平面技术 而言,0.1µm以上的异物就是有害物质了。 超净车间的标准早在20世纪70年代就由美国定下来 了。它对房间内的温度、湿度、照度、换气方式等均 有严格规定。而级别定义则与房间内尘埃粒子的大小 及数目有直接联系。 例如:Class10,000要求房内粒径大于0.5 µm的粒子数要 小 于 10000/ft3 , 而 粒 径 大 于 5 µm 的 粒 子 数 要 小 于 6.5/ft3。以前最高级别是Class100。

What is a Cleanroom?
A clean environment designed to reduce the contamination of processes and materials. This is accomplished by removing or reducing contamination sources.

Principles of the Clean Environment
♦ Air is highly (HEPA)

filtered (99.99% @ 0.3µ) ♦ Layout should minimize particle sources in filtered air stream ♦ Air flow should remove most particles generated by process

Types of Contamination
♦ Particulate

Dust, skin, hair, makeup… ♦ Chemical Oil, grease, metal ions, perfume… ♦ Biological Bacteria, fungi, rodents??? ♦ Radiation Ultraviolet light…

Particle Characteristics
♦ 50 micron particles are visible ♦ Average human hair is about 100 microns ♦ Time to fall 1 meter in still air – 33 seconds for 10 micron particle – 48 minutes for 1 micron particle ♦ Humans generate >1x105 particles per minute

when motionless (fully gowned) ♦ Humans can generate >1x106 particles when walking in the cleanroom

Contamination Sources
♦ People ~75% ♦ Ventilation ~15% ♦ Room Structure ~5% ♦ Equipment ~5%

Contamination Control
♦ Personnel Control – Dress code – Personal Hygiene – Gowning ♦ Environmental Control – Entrance and exit – Materials and supplies – Cleaning and maintenance – Atmospheric

Dress code
♦ No sleeveless shirts ♦ No shorts or skirts ♦ No slippers or sandals ♦ No jewelry that can puncture garments or

gloves ♦ Avoid clothing that sheds

Personal Hygiene
♦ Shower each day before entry ♦ Control Dermatitis & Dandruff ♦ Do not smoke before entry ♦ No chewing gum or tobacco ♦ No Cosmetics should be worn ♦ Facial hair will need to be covered

Gowning
♦ Proper gowning order – Hair cover – Hood – Shoe covers – Coverall – Gloves – Face mask – Safety Glasses

Entry & Exit
♦ Enter and exit quickly ♦ Only one person may enter at a time ♦ Each user must use their own access card ♦ Pass from the gowning area to the clean

area slowly to reduce migration of particles between areas

Materials and Supplies
♦ Do Not carry non-cleanroom items into the

cleanroom ♦ Do not carry cleanroom items out of the cleanroom ♦ Do not use pencils or erasers ♦ Paper should be kept in a plastic sleeve ♦ Do Not cut the cleanroom wipers ♦ Clean everything you carry into the cleanroom

Chemicals
♦ Do not take new chemicals into the cleanroom without ♦ ♦ ♦ ♦ ♦

permission Always read MSDS for every chemical you use Large quantities of chemicals must be stored outside the cleanroom Chemicals inside the cleanroom should be properly stored All chemical containers should be clearly labeled with their contents and Hazard Classification Unattended chemicals and experiments should be labeled with the owners name, immediate contact number, list of all chemicals involved, and estimated time of return or completion.

Equipment use
♦ All users must be trained before using any

equipment ♦ All equipment use should be scheduled ♦ If you are unable to use scheduled time please delete your reservation ♦ It is every users responsibility to report damaged or malfunctioning equipment ♦ It is every users responsibility to properly operate and clean each piece of equipment that they use

近来,由于集成度不断提高,要求也随之提高,美 国、日本相应地提出了自己的新标准。其最主要的是 将粒径在0.1-0.5 µm之间的微小粒子除去考虑在内。相 应 的 级 别 定 义 为 Class10,Class1 , 称 为 “ Super Clean Room”。
进气

PF

MF

FF

循环气 PF:Pre-Filter MF: Middle Filter FF: Final Filter 排气

Classification
Particle Diameter (um)

Class
1 10 100 1,000 10,000 100,000 35 350

0.1
3 30 300

0.3
1 10 100

0.5

5.0

1,000 10,000 100,000

7 70 700

Biotech Cleanrooms…@ Encelle

7/20/00

Technovation

19

硅片与半导体用器皿的清洗: 有机物(油、蜡、指纹等)
有机溶剂处理 活性剂处理(H2O2) 刷洗 酸处理 碱处理

干燥

氧化物
HF处理

水洗 金属杂质
酸处理 超音波、刷洗 酸处理

离子性杂质

不溶性杂质

CLEAN wafer: free from particles, organic contamination, metal ions contamination, low surface micro roughness and native oxide films.

Basic Concepts of Cleaning
♦ RCA Cleaning by Kern and Puotinen in 1970. ♦ SC-1 : NH4 OH:H2O2:H2O = 1:1:5 to 1:2:7 at 70-90oC. ♦ Remove organic contamination and particles by oxidation. ♦ SC-2 : HCL:H2O2:H2O =1:1:6 to 1:2:8 at 70-90oC. ♦ Remove metal contamination by forming a soluble complex.

Particles :
♦ General Guideline (smaller than 1/10 of feature size). ♦ Particle adhesion occurs during the process from the equipment,

ambient, gas, chemicals and DI water.

Method for removing Native Oxide
♦ Uncontrollable thin oxide growth, high contact resistance, and

inhibition of selective chemical vapor deposition or epitaxy. ♦ If this native oxide is not removed, it serves as the source of metallic impurities which diffuse into the silicon or precipitates at the interface of SiO2-Si , resulting in defects. ♦ Native oxide free surface is a key factor in obtaining high performance and reliability (after HF-dip: H-passivated surface).

Wet Cleaning Technology
Standard Method
1. H2SO4:H2O2 (2:1 to 4:1 at 120-130oC) : Remove greasy impurities which may be from the cassette or residues from the photoresist. 2. SC-1 : NH4OH:H2O2:H2O = 1:1:5, 70-80oC for 10 min : Remove organic films, desorption of trace metals.

Method for removing Native Oxide
♦ Uncontrollable thin oxide growth, high contact resistance, and

inhibition of selective chemical vapor deposition or epitaxy. ♦ If this native oxide is not removed, it serves as the source of metallic impurities which diffuse into the silicon or precipitates at the interface of SiO2-Si , resulting in defects. ♦ Native oxide free surface is a key factor in obtaining high performance and reliability (after HF-dip: H-passivated surface).

Wet Cleaning Technology
Standard Method
1. H2SO4:H2O2 (2:1 to 4:1 at 120-130oC) : Remove greasy impurities which may be from the cassette or residues from the photoresist. 2. SC-1 : NH4OH:H2O2:H2O = 1:1:5, 70-80oC for 10 min : Remove organic films, desorption of trace metals.

♦ 3. 1%HF-H2O, for 10-20 sec: remove oxide and trace metals in oxide. ♦ 4. SC-2 : HCl:H2O2:H2:O = 1:1:6, 70-80oC for 10 min: dissolve alkali

ions and hydroxides of Al+3, Fe+3, Mg+2. ♦ 5. DI water rinse (resistivity >17 Mohm-cm).

Equipment
♦ 1. Immersion technique: Quartz bath to prevent leaching of Al, B, and

alkalis which can results if Pyrex glass is used. ♦ 2. Megasonic cleaning: SC-1 solution at 35-42oC. ♦ 3. Megasonic cleaning: SC-1, SC-2, DI-water are fed directly onto the spinning wafer (Verteq, Semitool, SEZ).

Advanced Wet Cleaning from Ohmi (Tohoku University)
1. H2O + O3 Organic Contamination 2. NH4OH:H2O2:H2O = 0.05:1:5 Particle, Organic and Metallic impurity. Effects on micro roughness.

♦ HF(0.5%) + H2O2(10%)

Native oxide, metallic impurity ♦ Ultra pure water Rinsing ♦ Omit RCA SC-2 if high purity HF solution is used.

Dry Cleaning Technology (25 years efforts)
♦ Problems of wet cleaning: particle generation, drying difficulty, cost,

chemical waste, incompatibility with advanced cluster process, inflexibility. ♦ The dry cleaning process can solve problems: so far not completely successful. ♦ The dry cleaning process: require excitation energy to enhance gasphase chemical reaction at low temperature such as plasma, particle beam, radiation, thermal heating. ♦ Additional energy enhance reaction but we have minimize damage on the wafer.

UV-Ozone Clean
♦ Effective way to remove hydrocarbon, although the surface is oxide ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦

passivated. Surface excitation process Absorbed impurity + hν (2000-3000 Ǻ UV) > Excited impurity Gas-phase excitation process O2 + hν (1849 Ǻ UV) > 2O O + O2 > O3 O3 + hν (2537 Ǻ UV) > O + O2 Excited impurity + (O + O3) > Volatile compound The subsequent HF/H2O vapor or Ar/H2 plasma cleaning can remove surface oxide.

HF/H2O vapor clean
♦ HF dip promotes a hydrogen-passivated surface ♦ HF/H2O vapor clean induces a fluorine-terminated surface

♦ Hydrophobic surface (high contact angle) vs. Hydrophilic surface (low

contact angle). ♦ With oxide layer on silicon: hydrophilic surface.

Ar/H2 Plasma Cleaning
♦ The gas molecules are excited or ionized by remote plasma to reduce

bombardment damage on silicon wafer. ♦ Excited Ar ions physically sputter the surface impurity away. ♦ Excited Hydrogen ions chemically etch the surface. ♦ By proper adjustment of two process, an optimum cleaning can be obtained.

Thermal Cleaning
1. The native oxide can be removed by heating the wafer to 800oC or above in UHV (10-10 Torr) to vaporize the oxide.

♦ ♦ ♦ ♦ ♦

2. High temperature cleaning should be carefully examined due to etching of Si surface: - Si + SiO2 = 2SiO at high temperature (>800oC) and low O2 partial pressure; - SiO is volatile at temperatures above 750oC and oxide film is removed; - 2Si + O2 = 2SiO Etching of the surface (micro roughness); At low temperatures and high oxygen partial pressure: smooth surface with thin oxide; At high temperatures and low oxygen partial pressure: clean surface with roughness.

新概念、新器件:
半导体工艺发展到今天,以存储器为例,单 个 芯 片 可 存 储 信 息 量 已 达 1Gbits , 即 109bits。预计到2010年64GbitsDRAM可被制 作在芯片上。但相对于人脑的容量,还相差 得很远。 人脑:140亿个脑细胞,其中约有4亿个起 存储作用, 人脑的容量~1020bits。

现有的VLSI技术,在将来会遇到以下问题的挑战: 光速的制约:当器件尺寸越来越小时,虽可以减 少器件动作时间,但信号传输过程中信号线、时钟 线会影响整个芯片动作时间的提高。更重要的是, 在传输过程中的损耗。 光刻技术的制约:光刻尺寸不可能永远减少,它 总要受到光源波长的限制。而新型光源包括X-ray, E-beam还存在曝光速度慢,掩膜材料难以寻找等问 题。 量子隧穿效应的制约:即绝缘膜不可能永远薄下 去,理论极限为3nm。与此同时,阈值电压也不可 能任意低下去,高的电场会导致热电子注入,绝缘 膜的击穿。

除上述制约之外,最终的制约因素只有一个:器件的 成本。VLSI技术的进一步提高需要有天文数字的投 入,这将成为最大的困难。

半导体技术和产业的发展需要有 新概念和新器件的出现。
半导体与纳米技术的结合:
纳米电子学 硅基光电子集成

半导体微加工技术与其他领域的结合:
微机械加工 生物芯片 显示技术


				
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