第四章_微纳制造技术_光刻工艺

掩膜版工程
2. Phase shifting masks (PSM) （相移掩膜）
Introducing material which shifts the light by 180° for adjacent mask patterns barely resolved improved resolution
单项工艺： 光刻
1. Introduction
Photolithography
• Photo-litho-graphy: latin: light-stone-writing
• Photolithography is an optical means for transferring patterns onto a substrate. It is essentially the same process that is used in lithographic printing. • Patterns are first transferred to an imagable photoresist layer. • Photoresist is a liquid film that can be spread out onto a substrate, exposed with a desired pattern, and developed into a selectively placed layer for subsequent processing. • Photolithography is a binary pattern transfer: there is no grayscale, color, nor depth to the image.
UV
Carboxylic acid 羧酸 (dissolution enhancer)
正性光刻胶(I)
-Photoactive compound (DQ) is insoluble in base solution. -Carboxylic acid readily reacts with and dissolve in a base solution -resin/carboxylic acid mixture will rapidly takes up water (the nitrogen released in the reaction also foams the resist, further assisting the dissolution) -The chemical reaction during the dissolution is the breakdown of the carboxylic acid into water-soluble amines such aniline and slat of K (or Na depending on the developer). -Typical developer KOH or NaOH diluted with water
Removal of unexposed resist 去除非 曝光的胶
Next process (e.g. implantation, deposition)
掩模板设计软件L-Edit
掩模板制作
Starting material for reticle （刻线） manufacturing is ~800 Å thick
亮场和暗场
掩模板工程
1. Optical proximity correction (OPC)光学邻近校正
High-frequency components of the diffracted light is lost because of finite apertures, circular lenses etc Ends and bows of narrow lines are not ideal（端面和弯曲的地方不理想） OPC: Clever mask engineering based on software algoritms can compensate some of this error: （软件算法补偿）
- solvent added to adjust viscosity, however, most solvent
is evaporated from the PR before exposure and so plays little part in photochemistry • Diazoquinone(DQ) - 20-50 % weight - photosensitive - DQ
膜的晶圆片
Photoresist coating 旋涂 光刻胶
Prebake (softbake) 前烘
Mask alignment 对准
Removal of exposed photoresist去 除曝光的胶
Postbake 后烘
Development显 影
Exposure 曝光
Etching of mask film 腐蚀掩 膜
- 溶剂
• control the mechanical properties, such as the viscosity of the base, keeping it in liquid state.
正性光刻胶(I)
•Two-component DQN resists:
Currently the most popular positive resists are referred to as DQN, corresponding to the photo-active compound, diazoquinone (DQ) and resin, novolac (N), respectively. •Novolac 酚醛 (N): - a polymer whose monomer is an aromatic ring with two methyl groups and an OH group. - it dissolves源自文库in an aqueous solution easily.
正性光刻胶(II)
• PMMA (Ploymethyl methacrylate)
������ ������ ������ ������ short-wavelength lithography: deep UV, extreme UV, electron-beam lithography r resin itself is photosensitive (Slow) (pro’s) high resolution (con’s) ������ Plasma etch tolerance of the resist is very low. it needs to have thick PMMA to protect the thin film, otherwise the PMMA will disappear before the thin film doesdissociation of PMMA changes the chemistry of the plasma etch and often leads to polymeric deposits on the surface of the substrate. ������ Low sensitivity it needs to add PACs or to elevate exposure temperature to increase the speed ( the elevation of temperature can also increase the contrast)
Intensity ∝ (Electrical amplitude)2
Positive vs. Negative Photoresist 正性和负性光刻胶
传统光刻胶
Typically consist of 3 components: -树脂或基材 • a binder that provides mechanical properties (adhesion, chemical resistance, etc) - 光敏化合物(PAC)
• 1935- Louis Minsk of Eastman Kodak developed the first
synthetic photopolymer, poly(vinyl cinnamate), the basis of the first negative photoresists. • 1940- Otto Suess of Kalle Div. of Hoechst AG, developed the first diazoquinone-based positive photoresist. • 1954- Louis Plambeck, Jr., of Du Pont, develops the Dycryl polymeric letterpress plate.
Patterning by lithography and wet etching
掩模版
Cr patterned film
transparent glass
腐蚀Al film
光刻胶 Al film SiO2 film
Si 图形转移
Si UV曝光 显影
Si
Si
Si
完整的光刻工艺
Wafer with mask film (e.g. SiO2, Al)带有掩
Key Historical Events in Photolithography
• 1826- Joseph Nicephore Niepce, in Chalon, France, takes the first photograph using bitumen of Judea on a pewter plate, developed using oil of lavender and mineral spirits. • 1843- William Henry Fox Talbot, in England, develops dichromated gelatin, patented in Britain in 1852.
Advantages of DQN photoresists:
• the unexposed areas are essentially unchanged by the presence of the developer. Thus, line width and shape of a pattern is precisely retained.非曝光部分不变，维持线宽和形状 • novolac is a long-chain aromatic ring polymer that is fairly resistant chemical attack. The PR therefore is a good mask for the subsequent plasma etching. 酚醛是长链芳环聚合物 ， 耐化学腐蚀
film of chromium （铬）covered with resist and anti-reflective coating (ARC)
Chromium has very good adhesion and opaque properties （粘附力好，不透明） Substrate: quartz glass plate （石英玻璃板） Patterned by direct writing using e-beam or laser （电子束或激光直写） Usually wet etching of Cr after exposure 4 or 5x magnification is normal for projection litho （投影制版） Pellicle used for dust protection of reticle