Metallization

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1. Department of electronics & communication engineering Pondicherry university TOPIC PRESENTATION ON METALLIZATION PRESENTED BY GANESHKUMAR.P

2. OUTLINES Metallization Requirement of Metallization Schematic Representation Metallization Application in VLSI Methods of Metallization Problems in Metallization Vacuum Evaporation Different Part of the Apparatus Diagram of Local Evaporation Technique Sputter Deposition Apparatus Advantages Disadvantages

3. METALLIZATION Metallization is the process by which the components of the ICS are interconnected by aluminum conductor or metallization is the process that connects individual devices together by means of microscopic wires to form circuits. This process produces a thin film of metal layer that will serve as the required conductor pattern for the interconnection of the various components on the chips. With the help of metallization thousand of devices can be interconnected using fine line metal patterns. The metal films can be formed by various methods like Chemical Vapor Deposition (CVD) and Physical Vapor Deposition(PVD).

4. Requirements of metallization Low resistivity. Easy to form. Easy to etch for pattern generation. Should be Oxidizable. Mechanically stable. Smooth surface. Should be stable towards high temperature dry or wet oxidation etc. Should not contaminate wafers. Good life time. Low contact resistance to devices. Reliable long term operation. e

5. SCHEMATIC REPRESENTATION ADVENTAGE : Good Adherence. Easy ti Deposit. Good Mechanical Bonds . Good Resistance. DISADVENTAGE: Aluminum reacts with gold to form a metallic compound called purple plague. During packing operation, if temperature goes beyond 500 degree, Aluminum can get fused and can penetrate the oxide to cause short circuit.

6. METALLIZATION APPLICATION VLSI & METHODS OF METALLIZATION APPLICATION: Used to Gates for MOSFET. Used to make Ohmic Contacts. Interconnects. Used to connect thousand of MOSFET internally. Provides connection to the outside world . METHODES: Sputtering (SPUT). Evaporation(EVA). Physical vapour Deposition (PVD). Chemical Vapour Deposition (CVD).

7. Problems in metallization DEPOSITION: Impurities in the films, adhesion and thickness non uniformity are two various problems, related to deposition. Impurities in the films can be minimized by using pure evaporation and sputtering sources, high vacuum and clean surface. Cracks in the deposition are because of poor adhesion or surface unevenness. Controlling these effects will eliminate cracks. PROCESSING: Different stages of IC processing utilize metallization. Gate metal is deposited in early stages and the contact metal towards the end. Thus the gate metal in subjected to considerable processing while the contact metal experiences very little processing steps.

8. Problems in metallization METALLURGICAL AND CHEMICAL INTERACTION: Metallization can be completely destroyed by reaction induced by thermally activated process with the substrates or layer the top. ELECTRO MIGRATION: The corresponding current density becomes large. High current densities can cause devices failure due to Electromigration.

9. Vacuum evaporation: In this process the material to be evaporated is heated in a evacuated chamber so that it attains a gaseous state. Vapour of thin material transvers the space from the source to the substrate on which they eventually land. The pressure is maintained well below 10 torr.

10. Different parts of the apparatus ROUGHING PUMP: It is used to evacuate the chamber. HIGH VACUUM PUMP: Maintain high vacuum by reducing pressure with the help by nitrogen cooled trap. SPUTTER GAS: Is used to clean the surface of the wafer. The evaporation technique is of following two type: GLOBAL: Energy is supplied to the entire mass of the source present. The major problem with this scheme is that the boat containing the source material also gets evaporated and thus contaminates the deposition film. LOCAL: It employs laser beam and electron beam evaporation. In this systems a beam of focused electron is allowed to be incident on the sources contained in the crucible. The beam causes the source material to metal and vaporize locally at the point of incidence of the beam.

11. Diagram of local evaporation technique

12. Sputter deposition PRICIPAL: Sputtering is driven by momentum exchange between the ions and atoms in the material due to collision. The process can be thought of as atomic billiards, with the ion striking a large cluster of close-packed atoms.

13. apparatus The required breakdown voltage is given by the Pascal’s Law V α P*L log P* L+b P= Chamber Pressure L= Electrode Spacing b= is a Constant

14. apparatus

15. Advantages & disadvantages ADVANTAGES: The ability to deposit a wide variety of metal and insulation. The capability of cleaning the substrate prior to film deposition. DISADVANTAGES: This process damages the surface of the substrate.

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