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现代材料制备与技术

现代材料制备与技术. 主讲教师：王瑞林教授 教育部新世纪优秀人才人选 四川省学术带头人后备人选 博士生导师. Preparation Technologies of Materials. Lecturer ： Professor WANG RuiLin. T he N ew C entury E xcellent C andidate Awarded By the Ministry of Education. Chapter 7.3 Chemical Vapor Deposition. N P C V D. P E C V D. P C V

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现代材料制备与技术

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  1. 现代材料制备与技术 主讲教师：王瑞林教授 教育部新世纪优秀人才人选 四川省学术带头人后备人选 博士生导师

  2. Preparation Technologies of Materials Lecturer：Professor WANG RuiLin The New Century Excellent Candidate Awarded By the Ministry of Education

  3. Chapter 7.3 Chemical Vapor Deposition N P CVD P E C V D P C V D Set-up Methods The factors Advantages

  4. ? Chapter 7.3 Chemical Vapor Deposition Chemical Vapor Deposition • The most common thin film deposition method in advanced semiconductor manufacturing; • Deposited species are formed as a result of chemical reaction between gaseous reactants at elevated temperature in the vicinity of the substrate; • Solid product of the reaction is deposited on the surface of the substrate. There are so many kinds of CVD.

  5. They are: • Normal Pressure CVD (NPCVD)or Atmospheric Pressure CVD (APCVD) • Low Pressure CVD (LPCVD); ~a few hundred Pa • Photo CVD (PCVD); • Plasma Enhanced CVD (PECVD); • Metal-Organic CVD (MOCVD) and; • Others.

  6. I. NPCVD Method Main Tasks: Different deposition methods, and The growth impact factors 1. Principle According to the formation manner CVD can be classified as the decomposition under temperature and the chemical reactions A. Deposition by the Decomposition Heat up compounds and the compounds begin the decomposition to form the solid thin film on the substrates.

  7. For examples: SiH4 (g) 800℃～1200℃ Si(s)＋2H2 ↑ Ni(CO)4(g) 190～240℃ Ni(s)＋4 CO↑ CH4(g) 900~1000℃ C(s)＋2H2 ↑ TiI4(g) Heating up Ti(s)＋2I2 ↑ This technique is often used as the preparation of the thin films for Metals, semiconductors and insulators.

  8. The compounds or chemicals used for the decomposition • 1) Boron’s chlorides and hydrides;BH3 or BCl3 • 2) The chlorides and hydrides from GroupIV ; CH4, SiH4 • 3) The chlorides and hydrides from GroupsV and VI B ； • 4) Fe, Ni and Co’s carbony (CO) or the compounds • contained both chloride and carbony (CO); • 5) Metallic organic compounds contained Fe, Ni, Cr and Cu

  9. B. Deposition by the Chemical reactions Deposition due to the reaction occurred at the heating-up substrates by Two and more gaseous compounds. SiCl4(g)＋2H2(g) 1200℃ Si(s)＋4HCl↑ WF6(g) ＋3H2(g) 500～700℃ W(s)＋6HF↑ 2AlCl3(g)＋3CO2(g)＋3H2(g)  Al2O3(s)＋ 6HCl↑＋ 3CO(g)↑ (CH3)3Ga(g) ＋ AsH3(g) 630～675℃ GaAs(s)＋3CH4(g) ↑ 3SiH4(g) ＋ 4NH3(g) Si3N4(s) ＋ 12H2(g)↑

  10. C. The deposition conditions In order to obtain the high quality solid films the following conditions must be met: 1) There is a sufficient pressure under the deposition temperature； 2) Except the target object, other reactants and products must be gaseous ； 3) The deposited has to have a adequate vapor pressure to ensure the whole deposition reaction occurred at the surface of the heating substrates ； 4) The substrates should be stable and have lower vapor pressure.

  11. 2. The deposition set-up The system contains a reaction Chamber, Gas supplier and heating up system.

  12. 1). The CVD Reactor Types： Fig 7.3.2 CVD’s Reactor types

  13. 2). The deposition procedure: a. Within the main flow area，the reactants transport from the inlet of the reactor to the decomposition zone； b. The gaseous reaction takes place to form the precursorsand by-products； c. The precursors transport further into the growth surface； d. The precursors are absorbed by the growth surface； e. The precursors diffuse into the growth points； f. The film grows and the by-products get out； g. The by-products transport to the outlet to leave the reaction chamber.

  14. 3. Classification of CVD • The deposition temperature • a) High temperature CVD reaction chamber (>500oC) • widely used to deposit groupsIII-VA and II-VI A • compound semiconductors, and the chamber is hot; • b) Low temperature CVD reaction chamber(<500oC) • mainly used to form the films due to the limitations of • the substrates and the substrate holder. Such as plat Si • and MOS IC board.

  15. 2) The deposition pressure a. Normal Pressure CVD(NPCVD)，～1 atm； b. Low pressure CVD(LPCVD)， a few hundred Pas； Merits of LPCVD The films are uniform, repeatable; The films are of small pinholes with excellent properties and high utility of the reactants; The method is widely used to form the outlayer of Si wafer and all kinds of amorphous passive films such as SiO2 Si3N4 and polycrystalline Si films. LPCVD is one of very promising techniques for thin film deposition.

  16. 4. The key factors to the film quality l）The deposition temperature, Td： Td is the most important factor to the film quality. T↗，depostion rate ↗，the deposits are more compact and the structure is more perfect; Td is decided by the temperature of the crystallinisation and the substrate resistance to the temperature。 For examples： AlCl3+CO2+H2 <1100℃，incomplete reactionAl2O3 > 1150℃ Al2O3(polycrystals) 1500～1550℃Al2O3(single crystal)

  17. 2）The ratio to the reactants In theory the stoichiometric ratio is ideal but in reality it isn’t. The ideal ratio must get from the experiments。 For example： BCl3(g)＋NH3(g)BN(s)＋3HCl(g) • In theory，The ratio of the flux of NH3 to BCl3 should be unity ； • In practice，under the deposition of 1200℃，when NH3／BCl3 issmaller than＜2，the deposition rate is very low；while NH3／BCl3＞4，the product (NH4Cl) appears as an intermediate；

  18. 3）The effects to the substrates In order to obtain high quality films the substrates first must meet the follows： a. Strong affinity between the substrate and the deposited； b. Certain similarity in the crystal structure between the substrate and the deposited； c. Close coefficients of thermal expansion between the substrate and the deposited.

  19. 5. Characteristic of CVD 1）Merits： a. The purity of the films are very high and the films are very compact with good orientation; For example：use sapphire as a substrate，the impurity of －Al2O3 made byCVD is about 30～34ppm，which is far less than sapphire itself； b. Immeltable materials can be obtained under low temperature WF6 ↘ W, Td 500～700℃<<TW=3377℃； c. Doping to form all kinds of the films of semiconductors, oxides and compounds .

  20. 2）Immerits a. The main shortcoming is to need high temperature. The higher the temperature of the substrates, the lower the deposition rate. b. Equipment for CVD is more complicated than that for electroplating; c. It is difficult to deposit the deposited in certain area; d. It is normally toxic. Its applications are less than vapor deposition or sputtering.

  21. II. PECVD Method Definition • process of chemical vapor deposition in which species deposited are generated in plasma; • as a result, deposition using the same source gases is taking place at lower wafer temperature then in conventional CVD which requires high temperature to break bonds and to release desired species from the input gases; • somewhat lower film quality than in the case of pure thermal Low Pressure Chemical Vapor Deposition (LPCVD).

  22. This technique combines the glow discharge with the chemical reactions, which partlysolves some problems in CVD above like the slow deposition rates due to high substrate temperatures. 1. Plasma 1）The 4th state Provide energy，that’s, T↗ S L  G  Plasma， ion +free electron，plasma. 2）How to form Natural world：ionosphere, the Sun’s surface Labs：Gas discharging with supply of energy.

  23. 3）Characteristics and applications a. High-extent ionization states； b.Electron Neutral :The same densities Characteristics of electron and positive ion but smaller than the atom density c. Good conductors for electricity and heat Applications:Sputtering；ion plating；PECVD etc. 2. Principle for PECVD PECVD uses the activiation of plasma to promote the reaction rates. Why?

  24. It is due to its properties: • High electron density, 109～ 1012cm-3; • Very high temperature for plasma it can reach as 10 -100 times higheras the normal gas temperature and it can excite those reacting gases to decompose and ionize under low temperatures, all above improve the activiation of the reactants； It is easily absorbed for these reactants with high activiation by the surfaces of the substrates at low temperature, and the reaction rate increases.

  25. 3. The PECVD Set-up NPCVD + High frequency power（produce Plasma) At a PECVD reactor，when T=650℃，P<1.3Pa，uniform and high quality films can be obtained。 At a NPCVD reactor, at the temperature range: 1050～1200℃，1atm or（5.3～13.3）×103Pa, the good quality films also can be obtained. Temperature: 350～400℃ Deposition rate: 50～100 nm/min

  26. 4. PECVD’s Characteristic （1） Key factor to influence the deposition rate is the power of high frequencies，Tsubstrate,P, gaseous components are the next. （2）The main advantage of thePECVD technique: reduction of the deposition temperature of the substrate, Tsubstrate, and moreover，fast deposition rate，good quality of the films, less pinholes and cracks etc. （3） The main disadvantages of thePECVD technique: more defects due to the plasma bombardment， more complication due to that more reactions produced and lower quality of the films obtained.

  27. III. Photo CVD（PCVD） To be present next week!

  28. Thank you and see you next time

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